Photo E-1. Summer storm in the Arctic

The International Association of Oil and Gas Producers (OGP) in support of the Arctic Oil Spill Response Technology – Joint Industry Programme (JIP) funded this review of available information on the environmental impacts from oil spills in the Arctic and impacts that may be associated with the application of specific treatment technologies that may be applied during an oil spill response.  The objective of the review was to compile significant findings of prior investigations and suggest priority areas of work needed to improve assessment of the consequences of the various treatment strategies prior to application under Arctic conditions. The primary outcome is development of a process to integrate ecological consequence assessments within net environmental benefit analyses (NEBA) to better evaluate the environmental effects to valuable ecosystem components (VECs) within key environmental compartments (ECs) c that would result from using different response actions in the Arctic.  Specifically, development of Arctic response consequence analysis table matrices (ARCAT) and a semi-quantitative analytical tool will optimize decision-making and lessen environmental impact related to arctic oil spills in the Arctic.  The process is proactive rather than responsive to a spill event improving the ability to reduce environmental damage by chosing mitigating measures with the minimized effect on the environment.  As a result of this proactive approach there will also be broader consensus and acceptance of decisions among regulators and stakeholders.

To increase confidence in evaluations and environmental impact statement (EIS) of oil spills and oil spill response (OSR) technologies proposed for the Arctic, a comprehensive review of the existing literature was conducted to identify priority areas for future research efforts.  Because of the breadth of topic areas supporting consequence analysis approaches, this effort called for a multidisciplinary team with an understanding of food webs throughout the Arctic; behavior of oil in surface waters, at depth, and in ice; the effectiveness of OSR countermeasures in cold-water surface and subsurface environments; the toxicity of petroleum treatment residues on Arctic species; and models used to predict individual and population effects in Arctic ecosystems based on the concept of resilience.  This literature review followed a pan-arctic approach that recognizes regional similarities and differences based on peer-reviewed literature and technical reports from government and research institutions representing circumpolar interests.  The review is based on more than 650 literature citations and the personal experience of the work group participants.  To best utilize the expertise assembled on this team, representatives from different regions and disciplines worked in subgroups and all were able to review the entire document since many of the investigators have multi-disciplinary research backgrounds. The team was divided into nine technical working groups, each with a focused assessment goal and each with the assignment to identify areas of priority research:

• The Physical Environment – Summarize available literature to describe the different environmental compartments present in the Arctic and the physical characteristics of those compartments that could potentially affect the fate and effects of oil, as well as defining what response measures are an option for those environment compartments.  Seasonality in Arctic eco-regions is addressed (ice or ice-free conditions) as well as unique habitats and use of those compartments by VECs (e.g. areas with significant riverine input).  
• Arctic Ecosystems and Valuable Resources – Identify environmental compartments, food web connections within those environmental compartments, key Valuable Ecosystem Components (VEC species/taxa) within each compartment that connects those food webs and variations among VEC species/taxa between sub-regions within the Arctic.
• Transport and Fate of Oil in the Arctic – The various treatment strategies may enhance or reduce the amount of oil that is transported away from sites of surface or subsea released oil.  This section discusses the mechanisms behind short and long term transport of spilled oil in the Arctic.
• Oil Spill Response and Related Effects – Identify the implications of various response actions to increase or decrease the exposure to various treatment residuals within environmental compartments. Identify alternative response options for surface and subsurface spills of oil under Arctic seasonal conditions and describe the environmental effects of those response actions.
• Biodegradation – Identify the measurement tools that can quantify the use of oil by Arctic microbes including direct uptake and use of carbon containing petroleum compounds, mineralization of petroleum hydrocarbons to CO₂ and chemical changes of parent petroleum compounds to other compounds under different treatment options and how those changes are modified in different ECs
• Ecotoxicology of Oil and Treated Oil in the Arctic – The four lines of ecotoxicity research include acute and chronic response assessments and biomarker and body burden assessments of exposure.  Evaluate the literature to establish the environmental relevance of these four lines of evidence.  Identify gaps in experimental programs to address the ecotoxicology of oil in separate environmental compartments.
• Population Effects Modeling – Petroleum treatment residuals are environmental stressors that have the potential to produce adverse impacts on individuals or populations of VECs.  Determine which parameters are necessary components of a population impact model for VECs; identify models useful in predicting the effects of treatment options on these species/taxa.  Parameters of interest include changes in the toxicity of biodegraded oil, transfer of impact related effects to other trophic level VECs, or consideration of the resiliency of populations to recover from a stress.
• Ecosystem Recovery – The ecotoxicology and biodegradation of oil spill residuals is better understood than the ability of a compartment or VEC to recover from the impacts of a spill.  Environmental compartments have different abilities to recover from oil impacts.  Application of treatment methods need to account for and minimize the movement of oil to locations or species that have a low resiliency to respond to oil.  This section examines the duration of continued impact of an oil release and expected recovery of different environmental compartments and VECs. Response actions need to minimize encroachment on less resilient ECs and VECs.
• Net Environmental Benefit Analyses for Oil Spill Response Options in the Arctic – The environmental consequences of an oil spill response strategy will influence the overall impact of an oil spill (surface or subsurface).  In typical applications of net environmental benefit analysis (NEBA) framework, the consequences of a treatment option are generally associated with the near-term impacts and less so with consideration of the longer term consequences to recovery resulting from impacts to less resilient environmental compartments or VECs.  As an example, far-field impacts can result from not selecting a dispersant option which result in stranding of untreated oil on cobble shorelines where the effects can be observed decades after a spill.  Alternatively, selection of the dispersant option will result in greater impacts to the more resilient zooplankton community while reducing the effects on less resilient seabird and marine mammals that might contact oil on the sea surface.  The goal of this workgroup was to develop a preliminary consequence analysis of treatment decisions and demonstrate through an adaptive NEBA process the interrelationships between treatment decisions and shortening or lengthening of recovery from all forms of environmental effects, not restricted to the immediate near-field impacts.

Recent literature was reviewed for each topic area, and the information was compiled into a Microsoft Access® database.  Approximately 650 documents have been cited within the body of this report, and at this time there are over 1300 documents represented in the Access database that has been produced for recent JIP programs.  The database is searchable and can generate a list of references related to Arctic ecology, food webs, deep water food webs, petroleum-related fate and effects, biodegradation, and ecosystem-level case studies; aquatic toxicity and chemistry data can be queried via pivot graphs to dynamically represent the data compiled to date.   Based on results of these summary investigations, recommended new environmental studies are identified and prioritized. The recommended research will help reduce uncertainties related to each topic area and strengthen the NEBA approach in the Arctic.  The organizations and team members participating in this synergistic effort are presented in Figure E-1.

Figure E-1. Organizational matrix (Workgroup chairmen and co-chairmen are noted in bold text)

Currently five of the eight countries bordering the polar region are pursuing exploration and/or development of oil and gas resources in the Arctic [Canada, Greenland (Denmark), Norway, Russia, and the United States]. The changing environmental conditions in the Arctic may provide increased opportunity for development of these resources that were less accessible due to presence of ice in past decades and the improved technological advances for extracting petroleum resources. Activities of the petroleum industry are based on promulgated regulations set by each sovereign nation but there has been a move toward international cooperation and sharing of knowledge related to the technological development required to ensure safe drilling operations as well as spill response preparedness. International, federal, and local agencies from North America, Northern Europe, and Russia are in the process of developing baseline ecosystem and biodiversity assessments and research programs in order to better understand and protect the Arctic marine ecosystem and the communities that rely on these resources. For example, the Arctic Monitoring and Assessment Program (AMAP) has completed a significant effort in publishing comprehensive baseline information on Arctic geo-political activities and regulations, available drilling technologies, spill response initiatives, and potential environmental impacts (AMAP 2010). Additional cooperative research sponsored by joint industry programs (JIP) have augmented the knowledge base associated with the oil and gas industry activities (Sørstrøm et al. 2010; NewFields 2012). These efforts and convened workshops have integrated contributions from the scientific community, governmental agencies, public interest groups, and indigenous people of the Arctic.

Additionally, extensive field and laboratory studies have been conducted to examine the behavior and fate of oil and its potential effects on Arctic resources under the disparate seasonal conditions. Many recent studies have concentrated on understanding the influence of these harsh environmental conditions on the relative sensitivity of Arctic species to additional stressors, the success and rates of microbial degradation of oil compounds, and more recently the resilience of Arctic populations to recover from responses to those stressors. Similar to other parts of the world these investigations have increased our understanding of the basic behavior and movement of oil, its potential effects on VECs and the ultimate fate of released oil in various environmental compartments. The Arctic environment has added complexities resulting from seasonal patterns of ice and light that need to be considered to provide the foundation for development of strategic spill response strategies and evaluation of the environmental consequences of released oil that are very relevant today. Excellent comprehensive reviews have been published in recent years (Potter et al. 2012, Lee et al. 2012, SL Ross et al. 2010; USGS 2011).

The fundamental role of comparing the adverse biological effects of different response options in NEBA requires an information base that identifies VECs within multiple environmental compartments. The potential adverse effects and resiliency of these VEC organisms within each of these various compartments are then compared as a consequence of the OSR actions. These comparisons should examine the acute and long-term effects of spilled oil resulting from the impacts of various response options such as natural attenuation, surface-applied or subsea-injected dispersants, in-situ burning, and mechanical or naturally occurring containment methods followed up by recovery of spilled petroleum in Arctic ecosystems. Review and tabulation of published data, such as toxicity effect concentrations and population recovery times, is a key component of this review. However, the overall objective related to exploration and production projects in the Arctic is not only to tabulate this information or determine the most sensitive end-points that might be considered but to demonstrate the relative differences in the magnitude and duration of effects that might be observed at various ecosystem compartments associated with various response actions. As has been attempted for other regions where new exploration and production activities have been implemented, demonstrating these relative differences will require additional effort aimed at bridging the gap between relatively straightforward measurements of toxicity to arctic species and more complex investigations to assess ecosystem-level or population level impacts and recovery dynamics. This report considers the similarities and differences in species sensitivity between arctic and non-arctic species. To effectively monitor habitat recovery and identify ecologically relevant endpoints for remediation operations in Arctic regions there is a need to increase our knowledge on natural variability among populations and how that variability relates to vulnerability to petroleum exposure.

Prior to the granting of approvals for exploration and production activities, the public seeks increased assurances that industry and the various governmental entities have the capability to ensure safe exploration and extraction of oil as well as the capability to respond to oil spills. To meet these challenges a number of current and emerging oil spill countermeasure technologies have been identified for use in the Arctic. While use of different OSR methods can potentially reduce the impact of spills within the Arctic under various environmental conditions, not all options have been readily accepted by the public and regulators. Lack of endorsement of some OSR options is related to the perceived change in impacts and biodegradation rates that the use of these options in the Arctic marine ecosystem may bring. Several studies have been undertaken to address such concerns for different response measures; however, conflicting interpretations and conclusions impact stakeholders’ confidence. For example, the assumptions that dispersant treated oils are more toxic than undispersed oil, dispersants are more toxic than oil, dispersants reduce the ability of microbes to degrade oil, and Arctic species are more sensitive to oil than non-arctic species are incorrect although all of these assumptions may be proposed as facts by multiple stakeholders.

The purpose of the following section is to describe those key areas that the workgroup recommended for further evaluation based on their critical review of available information. The subjects for further consideration are grouped into major subject headings for this executive summary. Details of the recommendations will be found in each of the sections of the reports.

Arctic conditions influence the behavior and fate of untreated surface oil due to the low temperatures and the presence of different types of ice. Petroleum is generally immiscible in seawater and more so under colder temperatures. Surface oils with lower specific gravity accumulate on the sea surface and spread horizontally with the more volatile or soluble components quickly released into the air or into the water, respectively (NRC 1989; EPPR 2011). The surface oil also encounters disturbance by wind and wave action increasing the exposed surface area of the oil to the vertical transport processes of volatilization and solubilization. The wind and waves also adds water to oil creating oil/water emulsions that become more stable with time. The presence of broken ice with wind and waves enhances the disruption of the surface oil. These physical processes produce small globules of oil that may undergo further physical, chemical and biological weathering, creating aggregations of the heavier residual compounds that remain, eventually producing tar balls. In general, slicks formed in cold water are thicker with less exposed surface areas with reduced spatial coverage than the same oil released under temperate conditions. Laboratory trials have provided Information on key parameters that influence oil spreading under solid ice such as under-ice currents and ice roughness (Potter et al. 2012). In situations that the pour point of oil is above ambient temperature, the physical characteristics of the oil change dramatically with the wax components of the oil precipitating and forming a gel-like semi solid that is resistant to flow and spreading and which also restricts diffusion of volatiles through the slick, effectively reducing evaporation.

Untreated surface oils form slicks that are transported laterally by winds and currents and largely remain on the water surface and in the upper water column. The oil continues to spread on the surface of the ocean forming ribbons of slicks that rapidly spread to approximately 1 mm in thickness and are patchily distributed. Wind and waves break up and drive some of this surface oil into the water column in relatively large globules (>100 µm). The oil slick contains all of the chemical components of the spilled oil less those components that volatilize into the atmosphere or solubilize into the water column under the slick. The maximum concentration of oil is therefore contained in the immediate slick area, potentially exposing organisms that use the water near the air-water interface to the highest petroleum hydrocarbon concentrations that immediately follow a spill event.

The behavior and fate of released petroleum is an important consideration in understanding the potential effects of released petroleum and in evaluating the potential OSR options in the arctic. The spreading and weathering of petroleum in the arctic is complex, influenced by factors such as water temperature, local currents and wind conditions, the presence and absence of seasonal and multi-year ice, effects of pressure in deep water environments and seasonal changes in salinity during the Arctic spring. The presence of ice has been shown to slow the rate of spreading and weathering of surface oil, as well as affecting predictions of spill locations and trajectories. Migration of petroleum into brine channels or fissures in the ice can not only alter fate, but also the species that are potentially exposed and the exposure point concentration. At depth, petroleum is affected by increased pressures and decreased temperatures, resulting in phase shifts and changes in solubility as well as the dynamics of deep water currents and bathymetry. Key considerations included in the review were as follows:

• Cold water temperatures and the presence of ice can dramatically affect the weathering and natural attenuation of oil in the Arctic, but the ice can also trap oil so that OSR options and time available to implement the necessary response can be extended.
• Changes in behavior and fate of petroleum in deep sea environments associated with seeps and well blow-outs or leakage alter the bioavailability of oil components by allowing more volatile components to diffuse into the water where they may form clathrates altering the biodegradation potential and toxicity of those structures.
• Adhesion of oil to particulate matter and how this may affect the potential for uptake into tissues;
• The change in globule size and bioavailability of physically and chemically/OMA dispersed oil under Arctic conditions and,
• The behavior of oil in the absence and presence of ice and how it influences the selection of OSR options.

The microbial degradation potential of oil in the Arctic has been demonstrated and is as effective as this process occurring in lower latitudes when natural communities of Arctic microbes respond to the presence of oil. Microbial response to oil in the Arctic and deep, cold and dark waters are emerging areas of research. While microbial degradation in temperate waters has long been recognized, recent laboratory and field studies have documented microbial degradation of petroleum and dispersed petroleum in these extreme environments. Current research is using analytical chemistry, respirometry, genomics, transcriptomics, and proteomics assays to not only show the presence of oil-degrading species, but measure the response and results of microbial activity upon being exposed to oil. Key considerations included in the review are as follows:

• The presence and effectiveness of microbial communities to degrade oil in the Arctic (in open waters, in the presence of ice, along shorelines and in subtidal sediments);
• The characterization of the microbial community responses and gene expression associated with exposure to oil and aerobic and anaerobic biodegradation and use of hydrocarbons and organosulfur compounds associated with the unresolved complex mixture; and,
• The effects of biodegradation on the toxicity and availability of metabolites created during biological use of oil compounds and the changes that occur in toxicity and further biodegradation resulting from the more recalcitrant residual compounds of oil

There has been substantial research regarding the fate and effects of oil in the Arctic over the past 40 years; studies have been published in a number of different forums including peer-reviewed literature, technical reports, government studies and professional symposia. Additional data exists in a number of different languages, since research has been conducted throughout the North American, European, and Russian Arctic. Finally, important sources of data include emerging datasets from current research and older datasets that may not be as readily found in electronic search engines but nonetheless contain valuable information on environmental conditions and ecological resources. Consideration must also be given to the quality of data available for use. However, the most important aspect of making environmental consequence comparisons for OSR options is the appropriate framing of questions so that the consequences of response actions can be compared appropriately among all environmental compartments.

The physiological, morphological, and behavioral adaptations of Arctic species may alter their sensitivity to petroleum and treated petroleum. To address this concern there have been a number of recent efforts to characterize the sensitivity of Arctic species to treated and untreated petroleum. Evaluations have included pelagic and benthic species, as well as those in close association with the ice. Endpoints that have been evaluated include survival, growth, reproduction, and behavioral effects, as well as molecular, cellular, physiological responses. Custom experimental facilities have been developed for working with chemically and mechanically dispersed oil and water soluble fractions (WSF) of differently weathered oil. Methodologies have been developed by project team members to capture and maintain Arctic species of interest for controlled laboratory studies. The VEC species that have been evaluated to this point have been found to have sensitivities similar to non-Arctic species for oil exposure. Both field and laboratory data have also been integrated with population models to provide estimates of population-level effects from oil exposures (e.g. SYMBIOSES and fishery population analysis). Key considerations included in the review are as follows:

• Recent, historic and ongoing field and laboratory studies evaluating toxicity of petroleum and treated petroleum provided in Species Sensitivity Distributions to compare sensitivity of tested species.
• Different exposure scenarios facilitate different types of evaluations and can dramatically affect comparability of data. Spiked exposures followed by reducing concentrations of oil represent the exposures of stationary species or those present in the water column when oil is undergoing the initial spreading and dilution following the spill event or after application of dispersants or OMA. Exposures to constant concentrations of oil represent zones of concentrated oil observed with neuston associated species and life stages and marine mammals and seabirds that move in and out of the air/water interface. These more constant higher exposure concentrations can also occur when oil is concentrated at edges such as shorelines, convergence zones, and water/ice edges.    
• Endpoints found in the literature review range from body burden assessment to biomarker responses as well as mortality, growth, reproductive, developmental and behavioral responses. The diversity of potential end point assessments range from exposure assessment to end points that have a direct influence on estimating population level response to the oil components. For the purpose of this review, those responses that are better predictors of effects at the individual and population levels are the central focus. Mortality, growth and reproductive endpoints are those most closely associated with population level effects. Reviews on exposure markers will concentrate on demonstrating the relationship of the exposure marker to mortality, growth or reproductive endpoints.
• All toxicity assessments are surrogate measures used to predict the potential effects of oil spills on living resources. As such, data obtained using sub-arctic and temperate species representing different groups of organisms or different environmental compartments may also be useful in augmenting datasets with Arctic species. Recent comparisons of the relative sensitivity of Arctic and non-arctic species suggest that non-arctic species have similar sensitivities warranting a broader evaluation of much larger data sets.
• Additional testing of species that are long-lived, unique to selected habitat types and low in reproductive capacity that have not been evaluated in other regions have been identified during the reviews.

The toxicity of a mixture is characterized based on the analytical approach used to characterize the exposure. Variable conclusions regarding the relative toxicity of oil and water often can be tracked to the test waters being produced by different processes. The water accommodated fraction (WAF) is designed to only introduce the more soluble components into the water column while retaining the less soluble components on the surface of the water. The breaking wave water accommodated fraction (BWWAF) introduces additional physical disturbance, introducing more oil into the water as droplets with increased surface area exposure than occurs with the WAF allowing more of the soluble components to diffuse into the water from the oil droplets. The chemically enhanced water accommodated fraction (CEWAF) reduces the surface tension of the oil and produces much smaller droplets with much larger available surface area for diffusion of the soluble components of the oil. One of the objectives of the ecotoxicology section was to evaluate alternative methods of characterizing exposure.

A NEBA evaluation of OSR strategies for use in the Arctic must consider ecosystem-level consequences of the selected response. First, the effectiveness of the proposed solution(s) under the appropriate conditions to determine how much of the oil can be treated by the proposed action. Second, the consequences to various compartment VECs resulting from exposure to the untreated oil and the treated oil. Such comparisons must be made for resources in environmental compartments to determine the relative environmental benefits or risks of different response options. Third, the resilience of the populations of organisms that are being exposed as a result of no action or a response treatment needs to be addressed in order to determine the long term consequences of the decision.

Due to both logistical and environmental constraints, responses to oil spills rely on combinations of remote sensing and monitoring. The OSR options include 1) natural attenuation, 2) containment followed by recovery, 3) in-situ burning, and 4) dispersion using chemicals or oil mineral aggregates. With the exception of lower temperatures, oil spill response (OSR) options during the ice-free season are generally similar to other parts of the world. The presence of ice results in additional challenges as well as opportunities not encountered in regions without ice. The manner in which ice affects OSR effectiveness is determined in part by the ice characteristics which can differ regionally and seasonally. Recent field and laboratory studies that have evaluated the behavior, fate and effects of chemically dispersed oil, in-situ burning, OMA, and natural attenuation. Team members have evaluated spill response options in the presence and absence of ice and in both surface and deeper water environments. Both COOGER and SINTEF have led field releases of oil and studied field applications of OSRs on arctic shoreline/intertidal environments and in cold water and harsh environments including ice.

The objective of consequence analysis applied to oil spills is to provide spill responders a choice of response option(s) in terms of the lowest overall negative impact on the environment. It is likely that multiple response options will be selected and utilized for various stages of the response to reduce the exposure of VEC species. This process recognizes that once oil is spilled, some level of environmental impacts will occur, independent of the spill response options chosen. The goal of an effective response is to apply the combination of response techniques that will be effective in minimizing overall short and long term impacts. For the Arctic and other environments, this approach helps to focus technical discussions on the potential for short term and long term impacts on key ecosystem components and those resources of greatest cultural value to indigenous peoples. Assessments include comprehensive discussions of acute and chronic toxicity, food web bioaccumulation issues and reproductive and developmental impacts to exposed species. However, the discussions should focus on overall assessments at the population and community level of ecological organization, and ultimately promote a response strategy that allows for the fastest recovery of important ecosystem components. This approach has been used by governments and industry around the world to establish environmental protection priorities and spill response preparedness that will provide the greatest degree of overall environmental protection. IPIECA, International Maritime Organization (IMO), and OGP have long-supported this approach fostering development of a rational basis for setting oil spill response guidance and regulations (www.world-petroleum.org; www.imo.org; www.ogp.org).

These consequence evaluations have recently been incorporated into consensus building exercises that include all stakeholders. The process guides technical discussions and social prioritization among response planners, environmental agencies and local citizens as they compare ecological consequences of specific response options. The communication process is complex with many different opinions and levels of understanding of the effects of various response actions. The NEBA process has been particularly useful when considering use or non-use of dispersants, in-situ burning, containment and recovery of oil, as all of these present challenges with regard to potential environmental impacts. The process recognizes there will be damage during a spill but focuses on ecological consequences of different responses and compares “trade-offs” or cross-resource comparisons. Through a facilitated and structured analytical approach, participants find “common ground” for evaluating impacts and to develop defensible logic to support their conclusions. Discussion often can get stalled when there is a focus on localized and transient impacts of spills and response actions, without stepping back and trying to incorporate a longer term view of population and community recovery. Technical advisors and facilitators help guide the group to reaching their consensus among the diverse stakeholders by using a series of analytical tools specifically developed for use in a group environment. Knowledge regarding oil spill response capabilities and strategies gained by participants in the consensus-building process facilitates real-time decision-making in the event of actual spill incidences.

Resiliency of VEC communities is a critical component to evaluating the consequences of OSR that needs to be further addressed in non-Arctic as well as Arctic environments. The direct, toxic effects of oil on individuals among the VECs are better understood than the resiliency of the populations and communities of these valuable ecosystem resources within various environmental compartments. Each environmental compartment is at a different level of risk resulting from response actions. Their resiliency is related to biological, physical and chemical attributes of the compartment and the species living in that compartment. The arctic environment is variable and harsh, featuring water temperatures that can range from -2 °C to greater than 5 °C, a light regime ranging from total darkness to total light, and regions that are covered in ice year-round and areas that cycle from being ice-covered to being ice-free. These widely varying conditions require behavioral, physiological, and morphological adaptations that may affect the sensitivity of some species to released petroleum as well as the dynamics of the population during recovery. The Arctic is considered to have relatively short food webs, with the higher trophic levels dominated by mammals and birds. Many of these species are dependent on rich populations of plankton that bloom heavily in spring in close association with ice break-up or upwelling zones. Key considerations included in the review were based on the following observations:

• The projected damages to VEC populations are based on application of each OSR option. Use of OSRs changes the fate of oil; whatever OSR (including no response) is selected will alter the communities of organisms exposed to the oil at concentrations that can result in adverse effects. Damages include acute and chronic toxicity responses to oil. Additionally, the potential for recovery from oil contamination is also influenced by physical/chemical attributes that control the distribution and availability of the oil in each of the compartment as well as the availability of the oil to microbial degradation. Environmental compartment attributes that influence oil availability and ongoing biodegradation vary and need to be well quantified when establishing the long term consequences of OSR options.
• The focus of the section on recovery potential is to document the available knowledge and identify uncertainties in our understanding for VECs in different environmental compartments. Species found in arctic waters have a number of unique physiological and morphological adaptations to allow them to tolerate the cold water temperatures and the extensive periods of ice cover and absence of sunlight and associated food resources. The data reviews in the ecotoxicology section shows that these factors may influence the time period for demonstration of effects after exposure. However, the responses of Arctic VECs are similar to non-Arctic test species.
• The reproductive potential of Arctic VEC species is the key factor in assessing the ability of their populations to recover from stress/damage. In terms of recovery times, this resilience will vary from very short periods of hours in the case of microbial populations to many decades in the case of marine mammals and seabirds. This resilience and recovery potential for VECs in the Arctic is similar to what has been characterized in other regions of the world.
• Communities and food webs change dramatically during periods of open water or iced over water resulting in seasonal modifications of the available environmental compartments. During the winter the annual ice environmental compartments increase while during the spring and summer the melting ice adds more open water pelagic compartments. Seasonal OSR evaluations need to consider the change in the availability of these compartments, as well as the associated seasonal changes in effectiveness of the response options.
• There are specialized and unique species that live under and within ice, including larval forms of important water-column species. While the communities under the multi-year ice are becoming better known the ecological importance of the annual undersea ice is less understood.
• There are also deep-water Arctic communities that feature unique species and communities, including deep water corals and sponges. The extent of these communities under multi-year ice is not well characterized but the presence of ridge topography determined by geophysical means indicate there is a potential for these species to be more broadly distributed than is known at the present time.
• There are also regional and seasonal differences across the arctic which is principally associated with some of the higher trophic level species. The rationale for selection of VEC species is to emphasize those which are pan-arctic species that support these higher trophic levels. Unique species are also examined to determine associations with specific environmental compartments.
• In general, there is less knowledge of ecological processes occurring during the Arctic winter season.

Current oil spill contingency and response models representing transport, fate, and limited effect-based components have been used to support ecosystem evaluations. A key area of additional research recommended by the work groups is to augment Arctic NEBA assessments with an environmental compartment approach in order to evaluate the short and long term consequences of oil potentially impacting the resources in those compartments (Figure ES-2). Resiliency of the inhabitants using different environmental compartments will govern the recovery from oiling and is the key focus for the recommended new work.

The review of Arctic literature found many high quality assessments at the laboratory, mesocosm, and field scales on the efficacy of the treatment options (natural recovery; containment and product recovery; use of chemical dispersants or OMA; and in-situ burning). These studies provide information for efficacy estimates and for application to transport models providing good estimates of the movement of residuals from one EC to another within the Arctic. There are also high quality toxicological effect and biodegradation studies conducted under Arctic conditions that indicate the relative acute sensitivity of Arctic species are equivalent to sub-Arctic, temperate and tropical species and that biodegradation of oil by indigenous Arctic microbes is efficient and more rapid than anticipated based on the cold inclement conditions in the Arctic. The priority recommendations of each workgroup are included at the end of each section. A list of the high priority work elements within each section is appended to the summary of recommendations. Several of the recommendations apply to local operations and should be incorporated in baseline monitoring programs, Environmental Impact Assessments and operational oil spill response plans. These recommendations have not been prioritized here, but should be considered by the individual operators.

Four overarching areas of research were identified and were considered by the scientific panel of experts to be of the highest priority to advancing NEBA applications in the Arctic:

1. Increase availability of the vast amount of data on the impacts of oil spill response techniques and on the resilience of VECs reviewed in the current study by developing and populating matrices, or Arctic Response Consequence Analysis Tables (ARCATs), in support of Arctic NEBA processes.
2. Determine influence of oil on unique Arctic communities within EC interface habitats as well as corresponding response consequences (resiliency, sensitivity, and exposure potential)
3. Further investigate in-situ biodegradation of oil and oil residues
4. Further explore consequences of acute and chronic toxicity from oil exposure through use of population modeling

All response actions, including natural recovery, result in adverse effects on some portion of the environment and to some species. The consequences of those actions need to be compared holistically among all ECs and VECs. Direct ecotoxicological responses to the oil spill residuals is an important aspect of these considerations but the long term recovery potential of the ECs and VECs is even more important. The relationships between EC resilience and the sensitivity and resilience of VECs within those ECs is an important area that needs to be addressed in OSR consequence analysis. A way to consistently summarize and present available data on the impacts of oil spill response techniques on selected VECs within ECs would be through the development of information matrices that collate the relevant available data to support Arctic NEBA processes. These ARCATs (Arctic response consequence analysis tables) summarize the relevant information from literature to focus on the initial and long term consequences of oil spill response actions so that impacts to ECs and VECs that are less resilient and which take the longest time to recover are avoided. To accomplish that goal a number of tasks are suggested.

1. Develop a format for ARCAT matrices that will address the potential effects of oil spill response treatment residuals on ECs and VECs
2. Describe the OSR actions, ECs and VECs that will be used to develop the ARCAT matrices.
3. Map the EC locations that are relatively permanent and indicate the areas for seasonal positions of other ECs.
4. Document the use of ECs by VECs on a seasonal basis with the assumption that EC usage by VECs occurs during those seasons whether they are observed or not during a spill event.
5. Provide biological attributes that influence exposure potential (e.g. skim feeding, haul-out locations), reproductive capacity (e.g. time to adult, progeny production rates that may be influenced by age, daily natural mortality rates of populations), and immigration potential that augment recovery potential.
6. Document physiological and behavioral characteristics of VECs that increase or decrease exposure potential especially for mobile species (e.g. large fish marine mammals and seabirds).
7. Document assumptions of the population sizes and age classes of VEC components.
8. Document those characteristics that will be used to compare the resiliency of EC and VEC response to oil spill residuals.
9. Summarize the responses of species to OSR that are less studied (e.g. ISB, OMA, and chemical herding).
10. Demonstrate food web complexity in the Arctic using stable isotope ratios to demonstrate structure or unstructured aspects of key food webs

Figure E-2. Arctic ecosystem (surface microlayer, ice, nearshore continental shelf, pelagic and deep water communities) [Most literature is representative of the pelagic community, outlined in red]

An understanding of the transport, fate, and exposure potential of oil spill treatment residuals is an ongoing need for convergence zone communities. Convergence zones include shorelines, air/water, sediment/water, ice/water, and water/water interfaces. The VECs that occupy these convergence zones or that move in and out of these zones undergo exposures that are not similar to the better understood open pelagic water exposures. The areas of additional work suggested by the work group include a better understanding of toxicology and biodegradation for two convergence zones air/water and ice/water:

1. Describe the ecological relevance of interface zones, specifically the surface of the ocean and the ice water interface edges.
2. Describe the seasonal use of these two interface zones by VECs.
3. Develop testing protocol for exposure evaluations at these two interfaces. Consider Early Life History of fish, Arctic algal/kelp, sediment, deep water hard substrate, and fouling exposures, bioaccumulation and lipid characterization.
4. Develop or provide analytical chemistry methods for OSR residuals and degradation products in water, sediment and tissues.
5. Describe the differences in exposure of VECs to OSR residuals and the modes of toxic action encountered in the surface microlayer (neuston) and water/ice interface environments.
6. Initial responses by pelagic organisms to oil spills are relatively well understood and predictable. However, the long term consequences of an oil spill and subsequent effects on the recovery potential of sites, species or communities is less well developed. A better understanding of the factors that control the physical, chemical and biological attributes that control VEC and EC resiliency, which ultimately controls the amount of time for recovery needs to be developed.
   1. Define and establish measurements of resilience and develop methods to combine resiliency metrics into compartment specific short and long term recovery assessments.
   2. Compare EC population sizes for VEC in EC so that the relative importance of the air/water and ice/water interface environments can be assessed.
   3. Toxicity responses to exposure from accommodated fractions of fresh oil and chemically dispersed oil have predictable results based on the measured concentrations of oil in the liquid phase of these preparations. The responses are relatively consistent from experiments performed on tropical, temperate and Arctic species. Less is known about the toxicity of other OSR residuals (ISB, OMA, chemical herders) and weathered OSR residuals.

Biodegradation of fresh and chemically dispersed oil using indigenous organisms from pelagic Arctic environments has been demonstrated to occur at rates similar to those observed in deep and surface waters throughout the marine environment. Biodegradation of oil and OSR residuals when they are concentrated at interfaces (e.g. air/water and ice/water) is less well understood but assumed to be slower based on the reduction in surface area of the oil when it is re-concentrated in these convergence zones. The recommended areas of research for these areas are:

1. Establish a method to evaluate biodegradation occurring at interface environments (air/water and ice/water).
2. Compare biodegradation success for OSR residuals using this method.
3. Evaluate –omics procedures for application to OSR residual assessments.
4. Consider the implications of the storage of OSR residuals within convergence zones. This should not only include the air/water and ice/water but also shoreline stranding and the influence of shoreline sediment type on short and long term storage of OSR residuals.
5. Produce a GIS or EC database that addresses recovery potential of those ECs impacted by OSR residuals.
6. Evaluate food web structure within areas of oil/gas seeps and demonstrate the presence or absence of food webs that are oil/gas based and whether those food webs are supplementary to detrital based food webs in the same area.
7. Demonstrate whether these oil/gas based food webs provide communities that are pre-adapted and more resilient to exposure of OSR residuals.

Key attributes to determining the importance of acute and chronic responses of organisms to OSR residuals are measures of the natural resiliency of individuals, populations of species, and structure of food webs. Modeling of the transport, fate and effects of oil spills is relatively well known and predictable. Toxicity at interface environments is much higher due to the concentration of contaminants at these locations but the population influence of that concentrated contaminant exposure is less well understood. The areas of research suggested to provide improvement in the understanding of population impacts to VEC from exposure to OSR, especially at these interface habitats is provide in the following:

1. Establish the natural structural, functional and population dynamics measures for VECs within key ECs, including comparing the interface environments of air/water and ice/water interfaces.
   1. Determine whether the ‘sustainable’ reduction of 20% used in resiliency assessments for fishery harvests is applicable and whether that level of effect can be determined within the natural population fluctuations of VECs.
   2. Evaluate whether a 20% reduction of a VEC population would influence success of food web structure.
2. Obtain population dynamics, age-related characteristics of populations of key components leading to VECs (daily mortality rates, age/size population structure, variation in population size/standing crop, seasonal sequestration of significant portions of populations, emigration/immigration potential of individuals, etc.).
   1. Refine those characteristics for populations of these species living in different ECs.
3. Establish food web connections based on literature and alternative measures (e.g., stable isotope ratios).
4. Provide a predictive modeling diagram that incorporates knowledge of spilled materials, transport and fate of OSR residuals, influence of biological transport of contaminants within the water column, toxicity assessment and consequence analysis of the application of alternative OSR actions.
5. Develop factors to address transport and fate of OSR residuals along ice edges, under ice and near sea-surface.
6. Modify models based on new input parameters obtained from these research areas.

Each review team arrived at similar overall conclusions. They observed that there were high quality assessments on the efficacy of various response options. Those assessments were conducted under different physical conditions representing the Arctic at laboratory, mesocosm, and field scales. It was also generally recognized that strong transport models exist and are applicable to some Arctic conditions, including broken ice but some necessary adjustments to include information on currents, and transport under multi-year and annual ice conditions may be required. However, past estimations of the effects of various response actions have been generally isolated to a single environmental compartment or species based on acute toxicity responses using pelagic species or age classes. These response data have been used to predict ecosystem level effects in different habitats by modeling the concentrations of oil as it moves through the environment and interacts with new species or age classes. Although the research on the acute effects is generally well done, the long term consequences to different environmental compartments and species has not been well developed. This includes chronic toxicity responses but more importantly the overarching physical and chemical resiliency of environmental compartments and the biological recovery potential for species or age classes living in those compartments that are exposed to weathered and treated or untreated oil. Resiliency of environmental compartments and population to oil exposure is less well known not only in the Arctic but also non-Arctic environments. These longer term factors in recovery are key components needed to provide a better balance to evaluations of the consequences of oil spills and use of alternative treatment options.

In contrast to Antarctica, the physical environment in the Arctic is a consequence of recent glaciation and the relatively short time span for ecosystem and faunal diversification.  Polar ecosystems are characterized by extreme environmental conditions induced by cold temperatures, extensive snow and ice cover with abbreviated periods of solar radiation and primary productivity.  In general the productivity in Arctic freshwater and marine systems is concentrated over short periods of time centered around ice breakup when nutrients become available and light becomes more prevalent and water temperatures warm as the ice cover is reduced.  These environmental constraints concentrate recolonization during a few months of the year resulting in low species diversity due to extremely fast population growth of key zooplankton species responding to the release of nutrients which then contribute food to slower growing and longer-lived species. The objective of this chapter is to present an overview of the physical environment of the Arctic and indicate important characteristics that determine presence of Arctic ecosystem components.

The Arctic Ocean and associated waters comprise one of the most unique marine ecosystems in the world.  Two sources of productivity are instrumental in actively replenishing nutrients over short time periods:  ice algae, and riverine input.  It has been estimated that ice algae contributes 10-70% of annual productivity (AMAP 1998).  River discharges to the Arctic shelf regions augment nutrients, organic materials, and sedimentation on a seasonal basis.  The marginal seas are either influenced by the Atlantic or Pacific Oceans (Nordic, Barents, Northern Labrador Sea and Bering, Chukchi Seas, respectively), or are relatively isolated and border the Asian or North American continents (Kara, Laprev, East Siberian, and Beaufort, respectively).  The Chukchi, Bering and Barents Seas are among the most seasonally productive ecosystems.  The seas bordering the continental landmasses are influenced by freshwater runoff from the river systems and prior to the onset of recent increased warming trends had landfast ice associated with the shorelines for most of the year.  Freshwater discharge from rivers leads to earlier open water in the nearshore zone.  Maximum productivity is limited to open coastal waters during spring/summer months or to polynyas between landfast ice and the polar pack ice (occurring near the continental shelf edges).  Organic material not cycled through organisms or advected to the central Arctic basin is incorporated into sediments, producing localized areas of high organic enrichment near the mouths of major rivers and to locally deposited sections of tundra breaking off from shore locations.  Nearshore river systems are characterized by estuarine conditions, i.e. higher water temperatures, lower salinity, increased turbidity, as well as increased productivity due to the organic enrichment.  In most other areas the benthic standing crop decreases with increasing depth; ridges such as the Lomonosov Ridge have higher benthic standing crops than adjacent basins (Kröncke 1994; Kröncke et al. 1994).  The age of the organisms creating these standing crops on ridge environments may be quite old and reflect development over many decades but this has been a difficult environment to investigate so little is well known.

The two main deep basins, the Eurasian and the Canadian are separated by the transpolar Lomonosov Ridge (Figures 1-2 and 1-3).  The Canadian Basin which is < 3500 m in depth is transected by the Alpha Cordillera ridge into the Makarov and Canada Basins.  The Eurasian Basin is deeper, reaching depths of 4000m, and is divided by the Nansen Cordillera into Amundsen and Nansen basins.  While the continental shelf generally extends 50 to 100 km offshore, the shelf is broad north of Siberia, extending up to 900 km offshore. 

Figure 1-2.   Basins and ridges of the Arctic Basin  (Mike Norton)

Figure 1-3.  Main water bodies of the Arctic (Source: AMAP 1998)

Most oil and gas development activities, shipping routes, as well as major fishing grounds occur along the margins of the Arctic Ocean at the interface of land and sea edges.  Figure 1-4 highlights the main shipping routes transiting Arctic waters and areas of active oil and gas exploration.  Increased periods of ice-free conditions along shipping routes will result in increased vessel and fishing activities.   It should be noted that increased commercial fishery pressure itself may lead to changes in fishery stocks and biodiversity in the Arctic.

Continental runoff is a major source of freshwater, terrigenous materials and nutrient loads to the Arctic Ocean.  Information gathered from the Regional Arctic Hydrographic Network data set (R-ArcticNET) indicates that the overall annual discharge is ~3,300 km³ y^-1.  This buoyant freshwater contributes to a low saline layer (upper 200 m) of the Arctic Ocean which is isolated from the warmer, saltier Atlantic layer by a strong halocline (Fichot et al. 2013).  Rivers account for 2% of the influx of water to the Arctic region resulting in highly productive areas, particularly during the peak flow occurring from April to July (~60%).  The rivers in Siberia (Ob, Yenisey, Lena, and Kolyma) and in North America (Yukon, and Mackenzie) provide the majority of continental fresh water to the Arctic Ocean.  The Arctic Great Rivers Observatory (Arctic-GRO) monitors the discharge of these six river systems.

River systems generally increase productivity due to the availability of increased organic nutrients in the areas of riverine discharges.  Figure 1-5 shows the locations of the major rivers in the Arctic.   The regions along the continental shelf may be the most likely to encounter oil spill incidents, either due to oil and gas production activities or vessel mishaps. In determining environmental impacts of released oil, areas of special importance are the interfaces where oil components may re-concentrate (e.g. current convergence zones, pycnoclines, upwelling or downwelling of water masses, shoreline stranding or concentration at air-water, ice-water, or sediment-water interfaces).

Figure 1-4. Circumpolar regions of activities (AMAP)

Figure 1-5. Major river systems in the Arctic

Ocean temperatures vary widely depending on latitude and proximity to warm Atlantic or Pacific Ocean waters.  For the Arctic Ocean, temperature variation between winter and summer is small (remains close to freezing year round) and salinities vary between 30 and 33.  In the coastal shelf areas, surface water temperatures range from -1 °C to 4-5 °C, winter to summer, respectively while salinities may be <30, especially in areas receiving freshwater from rivers and ice melt.  In areas where oceanic mixing occurs, the temperature remains higher than 0 °C throughout the year.  In the Kara Sea and Siberian shelf, salinity is <20 throughout the year, and may drop to 10 during the summer (Figure 1-5; AMAP 1998).  Arctic seas are primarily ‘beta oceans’, i.e. a salinity profile is the most important permanent stratification feature (Carmack and Wassmann 2006).

Figure 1-6. Temperature, salinity, and density profiles (AMAP 1998)

Warm ocean currents flow northward from the Atlantic and Pacific Oceans and cold Arctic countercurrents flow southward (Figure 1-6).  Arctic Ocean water mainly flows from the Atlantic Ocean (79%), while inflow from the Bering Strait accounts for only 19%.  Concern with thinning of Arctic ice cover over recent decades has generated numerous investigations of the ocean-ice heat flux and changes in the Arctic Ocean surface layer (ASL).  The ASL is generally insulated from the warmer and higher salinity bottom water (Atlantic water layer; AWL) by a well-developed halocline (cold halocline layer, CHL).  The halocline establishes as a strong barrier to upward mixing by turbulence, and consequently most of the ocean heat flux in the central basins of the Arctic is generated by solar heating through open leads and thin ice during the summer months.

Figure 1-7. Arctic currents (AMAP 1998)

Researchers have found that although changes in surface velocity and surface stress in the open ocean reflects large scale atmospheric pressure fields (the Arctic oscillation, AO), the properties of sea-ice concentrate energy into relatively narrow zones of intense shear which can raise the pycnocline.  Such events may greatly enhance ocean-to-ice heat transfer (McPhee et al. 2005).  Examination of hydrographic records indicated that the CHL dissipated during a low pressure system from 1988 to 1997 in the Nansen and Amundsen Basins, resulting in an increased rate of melting sea-ice (15-25 cm/y).  The lateral Ekman currents moved in a counter-clockwise direction, resulting in upwelling of warmer, saltier water from the AWL and raising a weakened halocline layer about 50 m.  Average seasonal changes in sea-ice conditions (concentration and movement), sea level pressure, Ekman transport vectors, and upwelling patterns are presented in Figure 1-7 (Yang 2008).  

Figure 1-8. Seasonal sea-ice and ocean movement averaged over a 28 year period (Yang 2008)

Closer to shore, the seasonal cycle of Ekman transport is highly influenced by high sea level pressure in fall and winter.  For example, strong offshore transport along the Beaufort, Chukchi and East Siberian coasts intensifies coastal upwelling and downwelling in the interior Canadian Basin.  The offshore transport also pushes low-salinity warm shelf water toward the deeper basins, reducing salinity and increasing temperature.  

The continental shelf zones comprise about 50% of the Arctic Ocean surface and there are marked regional differences.  Narrow shelves are characteristic of the North American continent, and wide shelves with very steep slopes are typical of Eurasian continents (Table 1-1). Carmack and Wassmann (2006) group shelf areas according to function:  1) Inflow shelves (Bering Strait/Chukchi Sea, Barents Sea); 2) 2) Interior shelves (Beaufort and Kara/Laptev/East Siberian Seas); and 3) Outflow shelves (Canadian Archipelago and East-Greenland shelf).   The pan-Arctic shelves are estuarine in nature in that waters originating from the Atlantic and/or the Pacific Oceans mix with inflowing river waters.  Although there are regional differences in source water characteristics, all shelf areas are generally associated with the nutrient enrichment, productivity, and biodiversity.  Figure 1-8 is an excellent illustration of the dynamic physical, chemical, and biological interactions occurring in the Arctic shelf regions in the vicinity of receiving waters of major river systems.  In general, the nearshore ecosystems are characterized by relatively few trophic links and low biodiversity, and would be more sensitive to increased climatic warming than temperate regions (Carmack and Wassmann 2006).

Table 1-3. Characteristics of Arctic shelves (after Carmack and Wassmann 2006)

Figure 1-9. Dynamic shelf processes augmented by nutrient loading from riverine discharge (Source: AMAP 1998)

Sea ice forms when the temperature of the ocean falls below the freezing point, effectively converting the seawater to ice (-1.8 °C at 33 ‰ salinity).  Ice is characterized by where it is located:  landfast ice lines the shoreline and first year ice is intermediate between the multi-year ice and open water.  The annual changes in pack ice are determined by temperature, winds, and ocean currents (such as the Alaska, Labrador, East Greenland currents and the warm West Spitsbergen and North Cape currents).  Multi-year ice averages 2.5 to 4 m in thickness and may be intersected by leads such as shown in the photo above (~1% open in winter to 10-20% open in summer; Gow and Tucker 1990).  The two main ice circulation systems in the Arctic are the clockwise Beaufort Gyre in the Amerasian Arctic and the Transpolar Drift in the Eurasian Arctic (migrating east to west, exiting via the Fram Strait).  The North Cap current keeps the southern Barents Sea ice-free during the winter.

Photo 1-2. Ice lead (Lionel Camus)

Photo 1-3.  Polynya

Ice leads and open-water lenses (polynyas) form in nearshore or ocean areas and are characterized by cold, highly saline water (Photos 1-2 and 1-3).  The processes of ice production, salt flux, and heat transfer from leads and polynyas are important contributors to the larger scale climate events in the Arctic.  Polynyas occur for the most part during winter and harsh weather conditions and may be formed by two processes: 1) Mechanically forced (wind-driven; strong winds force ice cover away from the coast; 2) Convectively forced (ice subsidence; subsurface heat is transferred to the surface water by the upwelling of warmer, deeper water); refer to Figure 1-10.   Improved satellite technologies (e.g. synthetic aperture radar, SAR) and mathematical algorithms (e.g. polynya signature simulation method, PSSM) have made it possible to define the size and shape of polynyas as well as differentiate open water, new ice, and young ice (Dokken et al. 2002).  The heat exchange from the ocean to the atmosphere can be orders of magnitude larger in polynyas compared to the surrounding ice pack, and polynyas can contribute ~50% of the seasonal mean of annual ice production in some areas (Winsor and Bork 2000).  Winsor and Bjork (2000) estimated the mean ice production and corresponding salt flux from Arctic polynyas and found that the salt flux represents about 30% of that necessary to maintain the CHL.    The marginal seas contributing the most to the CHL are the Barents, Kara, Chukchi, and Bering; the Chukchi Sea is the only sea contributing actively to deep water formation.  The North Water Polynya is located between Greenland and Canada in northern Baffin Bay.  It is 85,000 sq. km in area and creates a warm microclimate that is one of the most biologically productive marine areas in the Arctic Ocean.  Polynyas are of critical importance to significant populations of marine birds, mammals, and fish.

Figure 1-10. Polynyas and Sensible-Heat Exchange [Based on image modified from Ocean Circulation, 2nd Edition by Open University, Butterworth-Heinemann Publishers, page 219; Source: National Sea Ice Data Center (NSIDC)]

The term seasonal ice zone (SIZ) describes the presence of transitional ice (i.e. freezes and melts annually) whereas marginal ice zone (MIZ) is used to describe the areas where open water meets ice cover during any season.  About half of the Arctic sea-ice freezes and melts annually.  During summer months, narrow MIZ and wide SIZ bands circumscribe the polar region.  It is along this band of expanding and shrinking open water linkages that most of the Arctic Ocean productivity takes place and where climatic changes would be most evident (Carmack and Wassmann 2006).  In recent years, the ice-free season in the Arctic increased at a steady rate of 1.1 days/year.  A record low in sea ice was recorded in 2007, with 168 ice-free days (Rodrigues 2009).  Increasing seasonal open water periods is coincident with anticipated increases in shipping traffic via the polar routes (Northwest Passage and Northern Sea Route).

Biological productivity hinges upon solar irradiance and nutrient availability.  These two resources are regulated by salinity stratification of the Arctic waters.  In general stratification is expressed as buoyancy frequency relating vertical temperature and salinity gradients with consideration of gravity, thermal expansion, and haline contraction coefficients (Carmack and Wassmann 2006).

The annual productivity/carbon cycle in the Arctic is illustrated in Figure 1-10.  The sun appears over the horizon in April, supplying light to support the growth of ice algae and phytoplankton. Production peaks in June when the sun is at its highest; zooplankton thrive on this superabundance of food. The production gradually declines during the season as the phytoplankton use up the nutrients in the water and as the sun sinks below the horizon, the plankton hibernate until the next growing season (http://www.arcticsystem.no). For areas in the Canadian high Arctic, Welch et al. (1992) estimated the relative importance of contributors to primary productivity as: phytoplankton (90%) > ice algae (10%) > benthic algae (1%).  This relationship likely varies in different locations.

Figure 1-11. Productivity/carbon cycle in the Arctic [Original illustration: Alexander Keck & Paul Wassmann (1993), modified by Frøydis Strand, NFH, University of Tromso; with adaptation from Forest et al. 2013)]

Physical processes inherent in ice field characteristics, water column stratification, vertical mixing, light and nutrients in combination with phytoplankton determine the balance of productivity and biomass build-up in the euphotic zone and its transfer to the aphotic zone.  The fate of suspended and sinking biogenic matter is based on the magnitude of export production and biological activities such as grazing in the upper water column.  The transfer of carbon from the surface layer to the deep ocean is accomplished via the passive sinking (exported) or the active transport of organic material (harvested, fecal production).   The greatest congregation of zooplankton often occurs just below the euphotic zone (Olli et al. 2006); excess detrital matter ultimately sinks into the aphotic zone.  In some regions such as the Barents Sea, the pelagic food web is positively correlated with benthic standing stocks (Carmack and Wassmann 2008).   There is considerable variability in sediment community structures and biomass, depending on carbon development in the upper layers.   Ice cover and other physical factors have been observed to limit primary production and benthic biomass (Grebmeier et al. 1995). 

The highly seasonal attributes of the Arctic influence species abundance and distribution patterns.  The lack of sunlight during the Arctic winter in combination with ice-covered waters limits primary and secondary production when solar irradiance is unavailable.  The periods of low production are punctuated by extremely high production during breakup and seasonal open water.  The combination of open water, long days, and high nutrient concentrations during break up and early summer creates intense periods of primary production, grazing by primary consumers, and predation by the higher trophic levels.  Whereas the aquatic communities are limited during the winter, the diversity and abundance of species increases dramatically in the summer. Key Arctic species have adapted their life cycles to take advantage of this period of high production, and larval or juvenile life stages are adapted to capitalize on the short period of enriched food resources.

The initiation and duration of summer production follows a latitudinal gradient from the southern Barents Sea in March – April to August – September in the Fram Strait and Arctic Ocean (Figure 2-5; Falk-Peterson et al. 2007) with substantially shorter periods of high production in the higher latitudes.  This suggests not only a strong temporal component, but a strong regional component. The largest seasonal effects are seen in the surface and nearshore waters, however there are seasonal patterns in the deeper waters as well, with Arctic cod (adults, YOY and larval cod) and copepods moving to deeper waters during the winter months. 

Seasonal migrations and changes in abundance, particularly of the younger life stages are an important consideration for environmental consequence analysis (ECA) and the relative vulnerability of different VECs.  Based on information provided in this review, there are some general pan-Arctic patterns of seasonal sensitivity.  However, for the purposes of assessing the spill response options, a regional approach is recommended.  Surface waters along ice-edges and in leads, particularly during the breakup and early ice-free period are important concentration points for copepods and juvenile cod, as well as migratory birds and mammals.  During the ice-free period, the ice edge continues to be an important feeding ground for large marine mammals as well as ice-seal pups.  Nearshore waters, are also a concentration point for water column resources, particularly juvenile forms and migratory species (e.g. toothed whales, sea birds).  As in more temperate waters, estuarine lagoons and rocky intertidal habitat during the ice-free season are important nursery grounds and act as a convergence point for aquatic, avian, and terrestrial species (Dunton et al. 2006).  During the open water season, nearshore waters and shallow shelf waters are also important feeding and breeding grounds for walrus.  Portions of the nearshore and shallow shelf are staging and feeding grounds for nesting sea birds and their chicks (Robertson 2013).  The midwater pelagic region is a concentration point for shoals of arctic cod and feeding migratory whales.  In the winter months, Arctic cod and Calanoid copepods move to deeper waters.  Leads and polynyas are concentration points for VEC species during the winter, in particular toothed whales.

For further detailed information on Arctic species, communities, and trophic linkages, please refer to Section 2.

The review of the physical environment described by the authors in this section led to suggestions of further research which can reduce remaining uncertainties; these recommendations are summarized below while recommendations that are particularly important for improving Arctic NEBA are listed separately. 

1. Seasonal and interannual fluctuations. The prevailing environmental characteristics such as extreme cold temperatures, variable solar irradiation and ice coverage affect the marine ecosystem and its populations. Seasonal productivity ties in with the degree of solar irradiation and ice coverage and directly affects species population recruitment and migration patterns.
   1. A better understanding of ice, and the corresponding variance of faunal distributions and life-history patterns on a spatial (regionally and throughout the pan-artic region) and temporal (annual and interannual) scale would be especially useful to protecting areas of densely populated VECs. 
2. Interface habitats. The physical structure of the Arctic provides additional interface as well as open water environments that are occupied by VECs.
   1. Interface environments that are stable (e.g. shorelines, sediment/water interface, edges of multi-year ice, convergence of water masses near subsurface topographic features) have generally been mapped throughout most of the Arctic. Where they have not been mapped they need to be. Seasonal use patterns by VECs need to be summarized by these interface ECs (see Section 2). 
   2. Interface environments that are variable (annual ice edges including polynyas and under-ice brine channels, fresh water releases and their transport, barrier island beaches/shorelines should be characterized by indicating most likely locations in the Arctic for these less permanent features. Understanding of patterns of use by VECs will be strengthened under work proposed in Section 2. 
3. Alterations in chemical processes. We need to better understand how cold temperatures and extreme weather interacts with broken and more permanent ice to affect the chemical processes associated with the fate of oil compounds and natural biodegradation rates (Sections 3 and 5). 

The recommendations presented below indicate where increased knowledge of physical environment would result in reducing existing uncertainties in NEBA assessments. No prioritization has been made to the list; for some of the recommendations, surrogate data may be already available. 

1. Arctic ecosystem consequence analyses need to include impact assessments of open pelagic waters as well as shorelines, river discharges, sediment/water interfaces, ice/water interfaces, convergence zones and surface layers near the air/water interface. These ECs may receive concentrated oil exposure depending on the type of OSR actions employed, and should receive further study.
   1. The location of primary ECs used by VECs could be added to regional sensitivity maps already available. 
   2. The locations where less permanent ECs can be prevalent are also important to VEC distribution and need to be located generally so that site specific assessments of their presence can be added to environmental sensitivity maps for reference during response actions. The environmental features that control the locations of these less permanent features and means to determine their presence during a response action are an area of additional study.

Authors Jack Q. Word and Lucinda S. Word (ENVIRON) 

The objective of this section is to compile existing information on the dominant organisms that comprise the communities associated with the Arctic marine waters and to identify the valuable ecosystem components (VECs).  For the purposes of this review, a valuable ecosystem component (VEC) is a species of the marine ecosystem that is identified as having scientific, social, cultural, or economic importance. VECs may be determined on the basis of any or all of these important concerns.  The VECs defined here are based on five qualities that include their importance in supporting the Arctic marine food webs, as well as ecosystem services.  In addition, consideration is given to those species that may act as indicators of potential effects of oil spill response measures on the different ecosystem compartments. 

• Taxa that are important to the function of Arctic food webs: Certain taxa play a critical role in maintaining and supporting the ecosystems and other trophic levels, as well as supporting the ecosystem resources and function.   For example, many species in each of the ECs of the Arctic rely on copepods and Arctic cod as a primary food source.  The removal or reduction of populations of copepods, krill or cod would have a significant impact on ecosystem function in the Arctic, as well as impacting upper trophic levels that may represent the ecosystem services for that realm (e.g. traditional fisheries for Bowhead whales are supported by copepod and krill food resources).
• Taxa that are representative of pelagic, benthic, deep-sea, and sea-ice realms: Taxa and age classes important to marine food webs in each of the primary ecosystem compartments were included as potential VECs. 
• Taxa that are relatively abundant: While abundance is not a core characteristic of keystone species, the removal or significant reduction in population levels of species that are relatively abundant or have a greater number of food-web linkages are more likely to impact ecosystem function than species that are less common or form fewer food web linkages.
• Taxa that may have cultural or commercial importance: Ecosystem services are incorporated in VEC determinations.  This can include both economic values (e.g. commercial fisheries) and social values.  Arctic communities are tightly linked to ecosystem services with goods and services extending beyond typical economic values of natural resources.  Most of the goods and services for Arctic communities have cultural and social values and are dependent on other food web components.  While some of the traditional ecosystem services are captured here, often they are locally defined and may include species not listed here.
• Taxa that are well suited to impacts analysis:    Species that are well suited to experimental approaches for evaluating the effects of OSR alternatives were included in this list of VECs.  This includes species for which there are toxicity testing methods that can or have been used to evaluate effects at the individual or population level.   Species characteristics for toxicity evaluations include sensitivity, availability, and the ability to withstand laboratory handling and stress.  Copepods and Arctic cod are common test models for the Arctic.

Recently, there have been several notable international efforts to consolidate data to provide a more pan-Arctic understanding of the biological communities of the Arctic.  As part of the International Polar Year (IPY; 2007-2008), specimen collections and data sets from numerous research institutes and government agencies were collated, reviewed and entered into a centralized database.  As part of the CENSUS, the Arctic Organism Database (ArcOD) has allowed for pan-Arctic reviews of species distributions throughout the Arctic.  The IPY was also the incentive for a number of research programs to address data gaps.  The RUSALCA program is an international effort to better understand the environment of the Beaufort, Chukchi, Bering Strait, and Siberian system.  This has included studies on circulation, benthic substrates, benthic and demersal communities, fish, zooplankton and birds and mammals.  Similar efforts have been conducted in the Atlantic Sector, in the High Canadian Arctic and the Eurasian Arctic.  The current review includes the findings of recent pan-Arctic studies and reviews, recent research programs, and peer-reviewed literature. 

The Arctic marine waters generally include those waters above the Arctic Circle; however, the southern boundaries of the Arctic are variously defined by physical, biological, and political boundaries.  For the purposes of this review, the Arctic will be defined in a manner consistent with the Arctic Ocean Diversity program and the Arctic Register of Marine Species (ARMS) which is based on biologically relevant physical criteria (areas within the seasonally average 2 °C surface isotherm or the median maximum sea-ice extent; Sirenko et al. 2011).  Based on this definition, the Arctic includes the Arctic Ocean and associated coastal seas and bays bounded by the North American and Eurasian continental landmasses, including the northern portions of the Bering Sea, the Bering Strait, the Norwegian Sea, the Labrador Sea, Disko Bay, the Lincoln Sea, and Hudson Bay (Figure 2-1).  The Atlantic portion of the Arctic is sometimes referred to as the Atlantic sector and includes the waters surrounding Greenland and Iceland, as well as the Norwegian Sea and into the Barents Sea, those areas most heavily affected by the advancement of Atlantic waters.

Figure 2-1. The Arctic Region and Major Water Bodies 9 (Map created by Brad Cole http://geology.com/world/arctic-ocean-map.shtml)

Figure 2-2. Bathymetric Features of the Arctic Ocean (Base map is from IBCAO http://www.ngdc.noaa.gov/mgg/bathymetry/arctic/)

The Arctic Ocean is a central deep ocean divided into four abyssal plains by prominent ridges surrounded by shallower continental shelves.  The only deep water connection to the world’s oceans is through Fram Strait to the Norwegian Deep and Atlantic Ocean (Figure 2-2).  A secondary connection to the Atlantic is through the Baffin Bay and the Labrador Sea and the Bering Strait, linking the Arctic Ocean to the Pacific.  The shelves comprise nearly 50% of the area in the Arctic and are a dominant feature of the East Siberian, Laptev, Kara, and Barents Seas; the shelves are relatively narrow in the Beaufort and Chukchi Seas.  Sandy and soft-bottom substrate dominates the Arctic, with finer silts and clays found in the outer shelves and deep basins.  Coarser sand and gravel are predominant substrate on the inner shelf and nearshore areas.  Although less common, there are notable and important harder substrate boulder fields and rocky intertidal areas, particularly in the vicinity of northern Greenland, Svalbard, and other island groups in eastern Canada.

Figure 2-3. Sea Ice Extent (National Snow and Ice Data Center, Boulder, CO)

The predominant environmental influences on aquatic food webs in the Arctic are sea ice and light.  A substantial portion of the Arctic Ocean is covered in ice throughout the year, while the adjoining waters are seasonally covered in ice with varying open-water periods coinciding with periods of 24h bright daylight.  Approximately 14 to 15 million km² of the Arctic region are covered in ice during the winter months (Figure 2-3).  In the summer, the northernmost portions of the Arctic remain ice-covered (approximately 4 to 7 million km²).  The lack of sunlight during the Arctic winter in combination with ice-covered waters limits primary production in Arctic waters, resulting in a period of low secondary productivity.  The periods of low production are punctuated by periods of extremely high production during breakup and periods of open water in spring and summer.  The combination of open water and long, bright days creates intense periods of primary production, grazing by primary consumers, and predation in the higher trophic levels.  Whereas the aquatic communities are limited during the winter, the diversity and abundance of species increases dramatically in the summer.  Thus the nearshore and open water communities vary considerably during these seasonal periods.

A secondary effect of the breakup and snow melt periods is a shift in temperature and salinity, particularly in the nearshore areas.  The Arctic waters are stratified throughout the year; however, the freshwater input from extensive river systems in the Russian and Canadian Arctic result in coastal corridors of estuarine to freshwater conditions during breakup.   Nearshore species assemblages change throughout the open water season in response to the transition in salinity and water temperature.

In many respects the Arctic seas are shared waters and as such have similar components in their aquatic food webs.  However, regional differences and geographic isolation have also created some notable differences in the food web components. As in other oceanic basins, the Arctic region includes nearshore, pelagic, and deep-sea food webs.  In addition, the Arctic includes communities associated with the annual and multi-year ice.  An understanding of food webs and the key species (valuable ecosystem components) within those food webs allows is an important component of the environmental consequences analysis.

Marine communities of the Arctic can be divided into three compartments or realms:  the pelagic, benthic and sea-ice.  While each of these compartments have a closely associated assemblage of organisms, they are linked to each other with many overlapping species.

Our understanding of food webs and trophic linkages within the food web are built upon several different types of data.  Direct observations of feeding behavior and stomach contents analysis are the most common types of information used to determine prey items and linkages.  However, the ability to collect this type of data in certain habitats is difficult, particularly in Arctic and deep water environments.  More recent methods have been developed that evaluate stable isotope ratios in tissues and in lipids.  In the Arctic, the ratio of N13 and N15 has been an effective method for evaluating trophic levels.  The presence of long-chained C20:1(n-9) and C22:1(n-11) fatty acids and alcohols has also been used as an indication of whether Calanoid copepods are a component of the diet.

In this section we briefly summarize the food webs for each of these different realms and identify VECs for the Arctic marine ecosystems (Figure 2-4).  Following this section, the components of each of these different food webs is discussed in more detail.

The pelagic food web is controlled by light and ice cover, altering the growth conditions for phytoplankton and the ability of surface-oriented predators to access prey.  In early spring, increasing light and ice melt result in the release of ice algae into the water column and a dramatic increase in phytoplankton growth (Falk-Peterson et al. 2005).  Some of the highest rates of primary production occur in these marginal ice zones (MIZ).  While phytoplankton blooms are initiated by an increase in light, the magnitude and duration of the blooms are controlled by the nutrient concentrations (Tremblay et al. 2012). Nutrients increase in surface waters during the low production of the polar night and allow for the high production (approximately 50% of the total annual production) in the MIZ.  The duration of the phytoplankton blooms is limited by nutrient availability and the decrease in light availability during the fall results in only one significant bloom event in the Arctic Ocean.  The increase in open water and phytoplankton blooms begins in the boreal waters and progresses northwards towards higher latitudes over the spring and summer (Falk-Peterson et al. 2005). The predominant groups of phytoplankton include prasinophytes, diatoms, haptophytes, green flagellates, dinoflagellates, and chrysophytes, with blue-green algae (cyanobacteria) in the southern regions (Hsiao 1978, Sakshaug 2004; Li et al. 2009, Fujiwara et al. 2014).

The zooplankton community in the Arctic is dominated by copepods, particularly the Calanoid copepods Calanus glacialis and C. hyperboreus.  Both species are endemic to Arctic waters, with all life stages found in the Arctic (Sakshaug 2004). Calanus finmarchicus is a subarctic species that is found in the Atlantic domain, but does not reproduce in Arctic waters (Falk-Petersen et al. 2007).  The diatom –Calanus food chain is considered to be critical to the overall production in the Arctic.  Calanus spp. take advantage of early ice-algae blooms, continue feeding through the planktonic diatom blooms, converting low energy sugars into a high energy lipid reserves (Niehoff 2007).  They create lipid stores that are rich in longer-chained fatty acids and alcohols; a characteristic that allows them to over-winter in a non-feeding state.  The combination of rich lipid reserves and their large size make C. glacialis and C. hyperboreus a key prey item for higher level consumers throughout the Arctic.  While less lipid rich and smaller in size, C. finmarchicus is a valuable food resource in the Atlantic sector, particularly the Barents Sea.  Other pan-Arctic copepods include Oithona similis and Metridia longa.  The subarctic species Neocalanus spp., Eucalanus bungii, Pseudocalanus spp. and M. pacifica are found in the Pacific domain (Sakshaug 2004; Griffiths and Thomson 2002).

Figure 2-4. Arctic Food Webs

Euphausiids (krill) are a subarctic herbivorous species that is abundant in portions of the Atlantic domain (Thysanoessa inermis) and in the Bering Strait-Chukchi-Beaufort region (T. longicauda and T. raschii; Suydam and Moore 2004; Letessier et al. 2009).  While not as common as in the Antarctic, euphausiids are a key prey resource for higher-level consumers, in particularly the Bowhead whale (Brinton 1962).  Other pelagic invertebrates that act as secondary consumers include amphipods, squid, and jellyfish.  Hyperiid amphipods are large, free-swimming amphipods that feed on both smaller zooplankton and Calanoid copepods (Auel et al. 2002).  The species Themisto libellula is a pan-arctic species found associated with sea-ice and shelf waters, whereas the species T. abyssorum and Cyclocaris guilelmi are more closely associated with outer shelf and deep waters of the Arctic (Auel et al. 2002; Kraft 2012).  Second to copepods, hyperiid amphipods are a common food item for fish, seals, and birds.  The squid,Gonatus fabricii is abundant in the Arctic and subarctic waters of the North Atlantic, with the squid Berryteuthis magister more commonly found in the Pacific Siberian-Chukchi waters (Gardiner and Dick 2010; Roper and Young 1975).  Squid are agressive predators and can move easily from the surface to deeper waters of the Arctic, being an important vertical integrator of marine food webs (Navarro et al.2013).  Arctic squid are an important prey item for narwhals (Monodon monoceros), White whales (Delphinapterus leucas), porpoise, and some seals.  Jellyfish are common in Arctic waters and can occur in abundance, representing a important consumer of zooplankton (Gardiner and Dick 2010).

Throughout the Arctic, Arctic cod (Boreogadus saida) and Polar cod (Arctogadus glacialis) represent a critical link between the zooplankton community and higher trophic levels (e.g. seals, toothed whales).  Both species are truly pan-Arctic occurring in all marine waters of the Arctic and are widely distributed throughout the Arctic, occupying nearshore, pelagic, and sea-ice habitats, residing both at depth and near the surface waters, depending upon age and season (Breines et al. 2008; Madsen et al. 2009).  Both B. saida and A. glacialis can be found in small numbers or in large, densely packed schools.  The primary prey for the Arctic gadids is Calanoid copepods and hyperiid amphipods (Sufke et al. 1998; Lonne and Gulleksen 1989; Bradstreet and Cross 1982; Frost and Lowry 1984).  Capelin (Mallotus villosus) are also an important secondary consumer throughout the Arctic, particularly in the Barents Sea where they are the primary link between C. finmarchicus and Atlantic cod (Gadus morhua; Blanchard et al. 2002; Hamre 1994; Mehl and Yaragina 1992; Titov et al. 2006).  Capelin are energy dense fish that move throughout the more estuarine nearshore waters and the Arctic waters.  Arctic and polar cod, capelin, and herring are important food resources for higher trophic levels including larger fish (e.g. Atlantic cod), marine mammals, and birds.

Anadromous fish are primarily found in the sub-adult and adult stages in the nearshore brackish waters of the Arctic.  Arctic char are circumpolar and can be numerous in waters of the Russian Arctic, where lower salinity waters extend across much of the shelf (Craig 1984; Mecklenburg et al. 2011; Sherman and Hempel 2008).  Cisco (Coregonus spp.) and salmonids will also use the nearshore zone during periods of high river flow and ice melt.  Anadromous fish feed on a variety of nearshore resources including benthic copepods and amphipods, herring and capelin (Dunton et al. 2012).  They represent an important prey resource for marine mammals and humans while in their freshwater habitats.

Pelagic fishes of the Arctic deep water regions are not as well understood as nearshore and shelf species.  Studies that have focused on deep waters have found that Arctic cod are numerically important throughout the year, with some stratification by water properties and by age group (Geoffrey et al. 2013; Parker-Stettner et al. 2011). Other midwater and deep water fishes common in other oceanic basins have been observed in the Arctic, including Myctophids and Gonostomidae (Reist and Majewski 2013; Dolgov et al. 2009; Jorgensen et al. 2005).  The diel vertical migration patterns observed in other systems may not occur throughout the year in the Arctic due to the polar day and night.

Benthic communities in the Arctic are influenced by substrate type, presence and interaction with seasonal or permanent ice, salinity and temperature.  Intertidal and nearshore subtidal communities are often limited by direct contact with ice, seasonal freezing of soft substrates, and scouring and scraping behavior of melting ice.  Additional limitations in community diversity and abundance in the nearshore environments are highly variable salinities in areas influenced by large river systems in the Beaufort, Barents, Kara, and Laptev seas.  Soft substrates dominate the Arctic seas, with silts and clays occupying the deep water basins and the outer shelf; fine sands and silts are common across the shelf, while coarser sands and cobbles limited to isolated portions of the shelf and the nearshore zone.

Benthic macrofauna in the Arctic, like most oceanic basins, are dominated by polychaetes, bivalve mollusks, crustaceans (e.g. amphipods and isopods), and echinoderms.  In the nearshore and inner shelf communities, Arctic mollusks often define the benthic communities and are a key prey item for higher trophic levels (e.g. walrus, bearded seals).  The salinity tolerant bivalve clam Portlandia arctica is a dominant species in nearshore zones and is able to rapidly repopulate areas of disturbance.  The Greenland cockle, Serripes groenlandicus, is a common circumpolar bivalve found up to 100 m depth on a variety of substrates and is a main component of the diet for walrus and bearded seals.  Macoma calcarea is also a common component in Siberian-Chukchi-Beaufort and Barents-Kara-Laptev shelf communities, as well as in the fjords of northern Canada and Baffin Island (Grebmeier and Cooper 2012; Denisenko 2007; Filatova and Zenevich 1957).  Other dominant clams in the shelf include Astarte sp.,Mya truncata, Tellina sp. and Yoldiella solidula.  In deep water benthic habitats, bivalves are smaller and less common, with species that are common to other oceanic regions (Axinopsida, Nucula, andNuculana.

As with clams, amphipods play an amplified role in the benthic communities of the Arctic, relative to other oceanic regions.  Arctic amphipods include both infaunal and epifaunal species.  The most widely distributed species across the Arctic are Ampelisca eschrichti, Anonyx nugax, Arrhis phyllonyx, Gammarus setosus, and Byblis gaimardi (Piepenburg et al. 2011; Dunton et al. 2012).  Of particular interest are the Lysianassid amphipods; a species rich group of epibenthic omnivorous amphipods that are key scavengers in the Arctic and deep sea waters.  Many are especially adapted to scavenging with specialized mouthparts and extendable guts for food storage.  In shallower waters, Lysianassid amphipods may have a more diverse diet.  Lysianassid amphipods are domenate invetebrate macrofauna in certain environments.  On tidal flats, Onisimus litoralis constitutes up to 95% of the macrofaunal density (Weslawski et al. 2000).

Polychaetes are among the most abundant infaunal species of the shelf and deep water benthos throughout much of the Arctic (Bluhm et al. 2011).  Species that represent the Arctic shelf are species observed in temperate habitats and include Maldane sarsi, Spiochaetopterus sp., Chone sp., Lumbrineris sp., Capitella capitata, and Eteona longa (MacDonald et al. 2010; Renaud et al. 2007).  Echinoderms in the Arctic are the dominant epibenthic megafauna, with ophiuroid brittle stars occurring throughout the shelf.  Dense aggregations of brittle stars can be found in areas of organic enrichment, such as polynyas (Piepenburg et al. 1997).  The sea urchin, Strongylocentrotus droebachiensis is also found in Arctic waters and is an epibenthic omnivore, often grazing along the bottom of rocky or soft substrates.  Decapod crustaceans are less common in the Arctic and are primarily represented by the shrimp Pandalus borealis and Pandalopsis dispar and the crab Chionoecetes spp. and the Red king crab (Paralithodes camtschaticus; Bluhm et al. 2009; Iken et al. 2010; Orlov and Ivanovo 1978).

Epibenthic or demersal fish communities in the Arctic are dominated by sculpins (Cottids) and eelpouts (Zoarcids); taxa that are speciose, eurybathic, and pan-arctic (Mecklenberg et al. 2011).  Arctic cod are also an important demersal fish found associated with the benthic zone at all depth ranges (Majewski and Riest 2013).  The genera Myoxocephalus and Lycodes are genera that well represented in the Arctic (Mecklenburg et al. 2011).  The Arctic flounder (Pleuronectes glacialis) and the Greenland halibut (Reinhardtius hippoglossoides) are also important epibenthic predators.  Demersal fish generally feed on benthic infauna, as well as small or juvenile fish.  Common predators include seals, birds, and some larger fish.  As such demersal fish act as a link between benthic infauna and epifauna and higher trophic levels (Dunton et al. 2012).

Sympagic communities include those organisms that live in close association with sea-ice.  In some cases, species are obligate to the sea ice, but many are representatives of the pelagic or benthic community that have a portion or all of their life cycle in the ice (Melnikov 1997).  There appear to be differences between the seasonal ice communities and those that inhabit the permanent ice.  However, to a great extent the species assemblage appears to be similar with differences in abundance and biomass.  Brine channels that form in the ice-water interface create a protected environment for an algal community dominated by pennate diatoms (Melnikov 1997; Sakshaug et al. 2009).  Harpacticoid and cyclopoid copepods are the primary consumers of the ice-algae moving within the brine channels as well as along the ice bottom (Kramer 2010).  The sympagic amphipods (Gammarus wilkitzkii, Onismus spp. and Apherusa glacialis) represent a critical link between the sympagic algal and copepod communities and higher trophic levels (Hop et al. 2000; Melnikov 1997; Arndt and Swadling 2006).  The herbivorous amphipod, A. glacialis, is a primary food source for the Little auk, Alle alle.  Both G. wilkitzkii and Onismus spp. are motile predators that feed on the sympagic copepods and are important prey items for fish (e.g. cod) and sea birds.  The amphipod G. wilkitzkii has a life span of up to six years and generally prefers multi-year ice (Arndt and Swadling 2006). 

Sea ice provides a productive substrate and protective shelter.  As such there are a number of pelagic or benthic species that spend a portion of their life in close association with sea ice.  Pelagic copepods will perform diel migrations to feed at the ice-water interface, particularly during the ice melt when the ice algae and early season phytoplankton blooms can account for more than 50% of the copepods lipid reserves (Melnikov 1997; Arndt and Swadling 2006).  One and two-year-old Arctic and polar cod find shelter in the shelves and fissures of the sea-ice, feeding on sympagic amphipods and pelagic copepods (Lonne and Guilliksen 1989; Gradinger and Bluhm 2005).  Adult fish are seldom observed in close association with the sea ice (Hop et al. 2000).  Ice amphipods and cod are subject to strong predation by top carnivores including seals and sea birds.

Arctic mammals include species associated with the sea ice and pelagic species.  Ice seals include Ringed seals (Phoca hispeda) that feed primarily on cod and hyperiid and sea-ice amphipods when young, Bearded seals (Erignatus barbatus) that feed on clams, and Hooded (Cystophora cristata) and Harp (P. groenlandica) seals that feed on cod, capelin, squid and pelagic amphipods (Bradstreet and Cross 1982; NAMMCO 2005a).  Walrus are found in the Bering-Chukchi, the Laptev Sea, and in the Barents-Greenland-High Canadian Seas (NAMMCO 2005b).  Walrus feed primarily on clams of the inner continental shelves (Outrides et al. 2003; Bluhm and Gradinger 2008).  Whales of the Arctic include both baleen and toothed whales.  Bowhead whales (Balaena mysticetus) feed on copepods and euphausiids in the open Pacific and Atlantic waters (Rice 1998; NAMMCO 2005c).  The White, narwhal, and Orca (Orcinas orca) whales are the dominant toothed whales of the Arctic.  White whales and narwhals feed primarily on cod and capelin.

Arctic seabirds are dependent on Arctic marine resources for all or most of their energy requirements while they are in the region.  Most seabirds are migratory arriving as spring blooms and breakup begins. Arctic birds that forage in the open pelagic are mostly alcids, gulls, skuas, and terns (Huettmann et al. 2011).  Other taxa tied to marine food webs are sea ducks, most notably eider ducks. 

Polynyas, estuarine lagoons, and rocky substrate habitats represent important but less common habitats in the Arctic.  The species that occur in these areas are not necessarily unique in Arctic or boreal waters, but they are found either in great abundance or in an assemblage of species that are well adapted to that habitat.

Polynyas are openings or leads in the sea-ice that form due to currents or water temperatures generally in nearshore areas.  They are a seasonal feature that allows light to penetrate into the water column and allows for direct access of the water surface in the absence of ice.  Narwhals remain in close association with pack ice and congregate in great abundance in polynyas using this time for most of their annual feeding.  Pelagic copepods and fish also congregate in these areas.  Sediments associated with polynyas are highly organically enriched during the polar winter, and the abundance and biomass of the more motile components of the benthic community respond with increased abundance and biomass; strong evidence for pelagic-benthic coupling.

Estuarine lagoons also represent another productive ecosystem, receiving organic input from terrigenous sources (e.g. riverine systems).  Estuarine benthos (including amphipods, polychaetes, benthic copepods, clams, and snails) in lagoons are protected from ice or ice scour, enabling them to take advantage of organically enriched sediments.  In response to the protected habitat and enriched benthic communities, epibenthic fish use the lagoons as feeding and nursery grounds.  Anadromous fish, particularly char, cisco, and salmonids will move along the brackish nearshore zone as young adult and adult fish, taking advantage of the availability of food resources.  As salinities increase in the lagoons, pelagic invertebrates and small fish will move into the protection and production of the lagoons.  Finally, the productive lagoons are an important feeding ground for sea birds, in particular Eider ducks.

Rocky substrate is less common in the Arctic, predominantly occurring in the Atlantic region of the Arctic.  The communities associated with rocky intertidal and subtidal habitats are generally similar to those that occur in the northern Atlantic, with brown macroalgae (e.g. Fucus and Laminariales), barnacles, serpulid worms, mussels, and motile scavengers such as amphipods.  Hard substrate in the deep sea occurs along the ridges, however, there is currently little data associated with the fauna on the Arctic ridges.

The pelagic environment includes those waters associated with the nearshore zone, the continental shelf and the deep water basins of the Arctic.  The distribution of pelagic fish and invertebrates is defined largely by salinity, temperature, and light.  In the extensive shelf waters of North America and the Russian Arctic there are two distinctly different bodies of water, the nearshore brackish waters and the Arctic Surface Water (ASW) or Atlantic Water (AW; Craig 1984).  The occurrence of a shore-parallel band of turbid, warmer (5-10°C) brackish (10 - 25‰) water is a characteristic feature of the Arctic coastlines (Craig 1984).  The ASW includes all open waters, extending a depth of approximately 100 m.  The ASW is typically colder (-1° to 10° C) and more saline (28‰ – 34‰) than the nearshore waters.  Underlying the ASW is the Arctic Intermediate Water (AIW), layers of denser and colder waters that extend from approximately 75 to 450 m (lower).  The shallower portions of the AIW tend to have temperatures <2°C and salinities ranging from 34.7 to 34.9‰.  The deeper portions of AIW have temperatures that are 0-3°C and salinities greater than 34.9‰.  During certain portions of the year, the deeper water may be slightly warmer than the shallower waters, with pelagic species using the deeper water as refuge from colder waters.  AW on the other hand, pushes northward into the Arctic during the spring and summer months.  Temperatures in the Eurasian Arctic increase as AW pushes northward in the spring and summer months.  This push of AW is an important transport mechanism for larval dispersal and for boreal species to enter the Arctic.  The Arctic Deep Water (ADW) occupy the abyssal basins of the Arctic, with stable environmental conditions with temperatures ranging from -2°C to -10°C and a salinity of 34.9‰.

The phytoplankton population and primary production in Arctic waters are controlled primarily by light and nutrient availability.  Ice cover limits light availability in the water column throughout the winter season. Phytoplankton blooms develop as the ice opens, with propagation of the algal bloom following along a latitudinal gradient from the southern Barents Sea in March – April to August – September in the Fram Strait and Arctic Ocean (Figure 2-5).  Once the ice recedes, there is a gradual increase in phytoplankton abundance (Falk-Peterson et al. 2007). 

Figure 2-5. Timing of Plankton Blooms in the Arctic Oceans. From Falk-Petersen et al. 2005

While light controls the timing and seasonality of primary production in the Arctic, the bloom duration and seasonal production are controlled by nutrient availability (Tremblay et al. 2012).  Nutrient limitations in the Arctic are exacerbated by a persistent stratified water column, caused by salinity and temperature differences resulting from riverine input and melting pack ice.  The nearly permanent stratification limits replenishment of nutrients from deeper, nutrient rich waters (Hsiao 1978). Chlorophyll-aestimates indicate that phytoplankton abundance is highest in the nearshore band, gradually decreasing with distance from shore.  Unlike population cycles in more temperate waters, conditions in the Arctic do not allow for a second phytoplankton bloom during the late summer.  Although nutrients in the water column slowly recover with periodic upwelling events, solar radiation begins to decline rapidly following the equinox.  With the combination of short periods of light and nutrient limitations, primary production in the high Arctic is among the lowest in the world.  The highest primary production is found in areas with energetic mixing with deep waters (Figure 2-6; Bering Strait, Fram Strait and the Atlantic sector).  Nearshore and shelf areas having variable production depending upon the extent of stratification and import of nutrients from terrestrial sources (Tremblay et al. 2012; Carmack et al. 2006). 

Phytoplankton in the Arctic includes prasinophytes, diatoms, haptophytes, green flagellates, dinoflagellates, and chrysophytes, with blue-green algae (cyanobacteria) in the southern regions (Hsiao 1978, Sakshaug 2004; Li et al. 2009, Fujiwara et al. 2014).  Recent field investigations have documented the distribution and potentially changing functional roles of picoplankton (<2µm) and nanoplankton (2-20 µm) due to changes in sea ice coverage in the Arctic Ocean (e.g. Coupel et al. 2012).  The Sea of Okhotsk and western Barents Sea are the most speciose regions, with the deep Arctic Ocean having the fewest species (Melnikov 1997; Sakshaug 2006).  Diatoms and flagellates are most abundant, followed by lower densities of dinoflagellates and chrysophytes.  Centric diatoms are the most common planktonic diatoms, withChaetoceros spp. and Thalassiosira spp. associated with spring blooms.  Pennate diatoms are less common in the phytoplankton, but are dominant in the ice-algal community.  The microplankton Phaeocystis is also common throughout the sub-Arctic coastal basins and can form blooms of several billion cells per m³ (Sakshaug 2006)  Flagellates were more predominant at offshore stations in colder, less turbid water and lower nutrient concentrations (Hsiao 1978).  Horner (1984) found that in the western Beaufort both diatoms and flagellates were found in the open waters, with distribution controlled on a vertical rather than horizontal scale.  Li et al. (2009) found that the nearshore phytoplankton community shifted from larger nanoplankton towards picoplankton and bacterioplankton with salinity and distance.  The picoplankton community was dominated by the unique pan-Arctic, cold-adapted Micromonas.

Figure 2-6. Annual Primary Production in Arctic (gC/m²/year) [Source: Carmack et al. 2006]

Sea-ice algae represent an important component of primary production, particularly in regions with permanent ice.  The ice algae community is discussed more fully in later sections.  However, it is important to understand that the spring blooms of ice algae precede the phytoplankton community and provide a critical food source for zooplankton.

Copepods and euphausiids represent the most important zooplankton group in terms of energy transfer to upper trophic levels (i.e. Arctic cod, birds, baleen whales).  Among the large copepods (1-5 mm adult size), the Calanus species Calanus hyperboreus and C. glacialis are dominant throughout the Arctic region.  The subarctic species Calanus finmarchicus and Oithona atlantica are also common in Atlantic Water and adjacent coastal waters (Sakshaug 2004).  While not considered to be an Arctic species, C. finmarchicus, it is widely distributed across the Arctic by the northern Atlantic current that moves northward along the Norwegian coast through Fram Strait and into the Barents Sea and onto the Arctic Ocean (Falk-Petersen et al. 2007).  Other pan-arctic copepods include O. similis and Metridia longa.  In Pacific waters Neocalanus spp., Eucalanus bungii, Pseudocalanus spp. and M. pacifica are also common in the Pacific Water (Sakshaug 2004; Griffiths and Thomson 2002).  Smaller copepods dominate the brackish shelf waters Russian Arctic including Limnocalanus macrurus and Drepanopus bungei (Peters et al. 2004).

Herbivorous krill are also an important component of the pelagic food web throughout the Arctic.  The euphausiids Thysanoessa raschii and T. inermis are common in the Pacific and Atlantic arctic, with T. rachii also numerically important in the middle and Coastal Bering shelf.  In the subarctic Atlantic, T. longicauda can be common; whereas T. longipes and Euphausia pacifica are more common in the Pacific Waters.  Both T. longipes and E. pacifica are important prey items associated with bowhead whales in the western Beaufort Sea (Brinton 1962).

The diatom – Calanus food chain is considered to be critical to the overall production in the Arctic (Falk-Petersen et al. 2007).  Calanoid copepods comprise 50% to 80% of the mesozooplankton biomass in the Arctic.  Calanus spp. take advantage of early ice-algae blooms and feed through planktonic diatom blooms, converting low energy sugars into a high energy lipid reserves.  Calanoid copepods create lipids that are rich in longer-chained fatty acids and alcohols; a characteristic not shared by other smaller copepod species (Peters et al. 2004).  The combination of rich lipid reserves and their large size makeCalanus spp. a key prey item for a number of higher level consumers, in particular Arctic cod. 

While the three dominant calanoid copepods co-occur, they differ in their life histories.  Calanus hyperboreus is the most polar species and is most common in the deep sea areas of the Arctic, including the Arctic Ocean, Fram Strait, and the Greenland Sea.  It is a large copepod (4.5-7 mm) that can overwinter at depths of 500 m to 2000 m (Falk-Peterson et al. 2007).  C. hyperboreus has a 2-yr life span during periods of high productivity which can extend to 3 to 5 years during periods of extensive ice cover.  Calanus hyperboreus reproduce in deep waters in the winter/spring prior to the phytoplankton blooms (Niehoff 2007) with the naupliar forms developing just under the ice surface, feeding on sympagic (ice-associated) algae.  Egg releases in early March appear to provide a lipid-rich food source prior to significant primary production (Darnis et al. 2012).

Calanus glacialis is a smaller copepod (3-4.6 mm) that is found primarily on shelf waters of the Arctic.  C. glacialis has a life span of 1-3 years, spawning throughout the Arctic prior to the yearly spring bloom.  Most larvae reach the C1 copepod stage (early adult form) by ice break up allowing the nauplii to feed on ice algae in the relative protection of the pack ice (Falk-Petersen et al. 2007; Niehoff 2007).  The C1 copepods are then able to take advantage of the phytoplankton blooms in early summer.  It descends to deep areas on the shelf (200-300 m) to enter diapause and over winter (Falk-Petersen et al. 2007).

Calanus finmarchicus is the smallest of the three Calanus species (2-3.2 mm) and has less lipid-rich reserves.   While nauplii and copepodites may be advected into the Arctic Ocean and other northerly waters, C. finmarchicus does not appear to reproduce in Arctic waters (Niehoff 2007) but relies more heavily on reliable ice-algal blooms for reproduction.  As with other calanoid copepods, C. finmarchicusrelease eggs prior to the phytoplankton blooms, which develop during the Arctic summer prior to over wintering at depths of 500 to 2,000 m (Falk-Petersen et al. 2007).

In late-spring/early summer, reproduction rates for other copepods and euphausiids increase following blooms of phytoplankton, microzooplankton, and small copepods (Pseudocalanus spp.).  Omnivorous zooplankton, such as Metridia longa feed on both living plankton, as well as the organic carbon spikes following blooms.  Reproduction in such species appears to be more independent of the plankton blooms.

Neuston refers to a community of microbial, plant (phytoneuston) and animal (zooneuston) species that live at the water’s surface.  Surface communities include obligate species that are in the surface layer throughout their life cycle, as well as facultative species that occupy the surface only during larval stages.  Arctic neuston have a number of adaptations that allow them to live in the harsh surface environment, including oil droplets to shield them from ultra violet (UV) exposure and keep them at the surface, and diel migrations that help them compensate for the temperature extremes (Zaitsev 1971).

While large temperature fluctuations and extreme UV exposure limit species diversity, marine phytoneuston abundance per unit volume may be a thousand times higher than the underlying bulk water populations (Zaitsev 1971; Word et al. 1986).  Marine phytoneustonic communities are dominated by small diatoms and flagellates.  As with abundance, the production per unit volume can be many times that of the underlying water.  The zooneustonic community in Arctic waters include chaetognathans, copepods, euphausiids, hyperiids, and in smaller numbers of rotifers, pontellids, cladocerans, decapods, and fish larvae and eggs (Zaitsev 1971).  Microbial populations, including bacterioneuston, may be 10,000 times denser than bacterioplankton populations (Hardy 1982; Sieberth 1971).

The neuston community is somewhat self-contained, with zooneuston feeding on phytoneuston.  Neuston is an important component of the pelagic food web, with zooplankton, fish, birds, and marine mammals feeding at the surface, particularly along convergence zones where the surface populations are highest (Zaitsev 1971).  Bowhead whales, as well as other baleen whales, have been observed skim-feeding at the surface (Koski and Miller 2002).

The pelagic invertebrate community includes a wide variety of other species, including amphipods, mysids, shrimp, squid, jellyfish, pteropods, chaetognaths, and ichthyoplankton.  There are only two Arctic species of pelagic shrimp and they do not appear to be a common component of the nekton (Hopcroft et al. 2008).  This section will focus on certain elements of the pelagic invertebrate community that are important food web components.

Krill

Unlike the Antarctic, euphausiids are not abundant in Arctic waters.  However they can be difficult to accurately assess in ice-covered waters as they seek shelter in the pockets and fissures in the ice (Percy and Fife 1985).  Euphausiids are not considered to be a truly Arctic species, rather they are advected from the Bering Sea Water inflow (Suydam and Moore 2004) or from the Atlantic (Letessier et al. 2009).    The euphausiids Thysanoessa raschii and T. inermis were important prey items associated with bowhead whales in the western Beaufort Sea (Brinton 1962).  Euphausiids are found from the surface to the deep midwater pelagic areas, in depths greater than 500 m. 

Amphipods

Free-swimming amphipods are a key component of the Arctic food web, representing a link between zooplankton and higher level consumers such as fish, marine mammals, and birds.  Hyperiid and Lysianassid amphipods are among the common taxa found in Arctic waters and are a dominant component of the zooplankton abundance and biomass (Auel et al. 2002).  The hyperiid amphipod, Themisto libellula is a pan-Arctic species that can occur in high numbers in the ice free waters of the Arctic.  Based on the high amounts of C20:1 (n-9) and C22:1 (n-11) fatty acids and alcohols found in T. libellulatissues, their diet was domianted by Calanoid copepods.  Further analysis indicated a close association with ice-algal production.  This confirms field sampling data showing Themisto sp. associated wtih sympagic communities.

Themisto abyssorum is more closely associated with deepwater communties.  Themisto abyssorum is  considered to be a boreal species and is found in close association with the Atlantic Water that moves northward through Fram Strait.  Abundance generally decreases from east to west, dropping from >200 ind/m² over the contiental slope north of Spitsbergen to <40 ind/m² in the central Arctic (Auel et al. 2002).  It does not show a similar lipid signature seen in T. libellula, indicating that copepods are not a dominnant component of the diet.  Rather, the deepwater species is more likely an omnivore and scavenger.

Cyclocaris guilelmi, is also an epipelagic species, occurring in the deep-waters of the Arctic.  As wtih T. abyssorum, C. guilelmi appears to be Atlantic in origin but is found throughout the Arctic ocean.  Kraft (2012) found C. guilelmi to be a dominant component found in deepwater traps in Fram Strait.  The population appeared to be stable with peaks from August to February.

Cephalopods

Cephalopods are a predator of and a key prey item for many of the VECs in the Arctic.  Squid move vertically through the water column, integrating marine resources throughout the pelagic environment.  The squid Gonatus fabricii is the most commonly reported species in the Arctic, with numerous records in the Atlantic sector, the Barents Sea and the high Canadian Arctic (Gardiner and Dick 2010). Berrytheuthis magister is the predominant squid species found in the Pacific domain.  Squid exhibit all manners of vertical distribution: near-surface dwellers (to 50 m), vertical migrators that either move into the surface waters at night or just move higher in the water column, and near-bottom dwellers.  In addition, some species exhibit ontogenetic descent moving progressively deeper as they age (Roper and Young 1975).  Cephalopods are voracious predators feeding on crustaceans, fish, other squids, and zooplankton.  Based on isotope analysis, squid are occupying different trophic levels in different regions (Navarro et al. 2013) indicating that squid are able to shift their diet based on availability.  The isotope ratios for Arctic squid indicated a trophic level of 3 to 5.  Squid are an important component of marine mammal and sea bird diets, including narwhals, White whales, walrus, murres and fulmars (Gardiner and Dick 2010).

Jellyfish

Gelatinous zooplankton are poorly understood in the Arctic, largely due to the difficulty of capturing them with traditional sampling methods.  However, they are considered to be a substantial sink for primary and secondary production (Purcell et al. 2009).  In the Beaufort Sea, the scyphomedusa, Chrysaora melanaster is among the most common gelatinous zooplankton in shelf waters 25 to 75 m in depth (Purcell et al. 2009).  In shallower waters, there was a more diverse community dominated by the delicate medusa Bolinopsis infundibulum, other small cnidarians, and ctenophore species occurred immediately underneath the sea ice (Purcell et al. 2009; Raskoff et al. 2010b).  Other common species include Sminthea arctica in the midwater depths, and Atolla tenella which was found in high abundance in the deep Canadian Basin (Raskoff et al. 2010b). 

Large populations of gelatinous zooplankton have been observed throughout the Arctic, particularly in at convergences, fronts, and polynyas (Ashjian et al. 1997).  In such areas, medusa and ctenophores can have a substantial grazing impact.  In the eastern Canadian high Arctic, the ctenophore Mertensia ovum was estimated to consume up to 9% per day of the C. hyperboreus population and 3-4% of the C. glacialis population.   Other prey items included hyperiid amphipods, pteropods, and smaller copepods.  Other food resources for gelatinous zooplankton include detritus and algal cells and in some cases small or juvenile fish (e.g. larval capelin and herring; Raskoff et al. 2010b).

Unlike the Antarctic, euphausiids are not abundant in Arctic waters.  However they can be difficult to accurately assess in ice-covered waters as they seek shelter in the pockets and fissures in the ice (Percy and Fife 1985).  Euphausiids are not considered to be a truly Arctic species, rather they are advected from the Bering Sea Water inflow (Suydam and Moore 2004) or from the Atlantic (Letessier et al. 2009).    The euphausiids Thysanoessa raschii and T. inermis were important prey items associated with bowhead whales in the western Beaufort Sea (Brinton 1962).  Euphausiids are found from the surface to the deep midwater pelagic areas, in depths greater than 500 m. 

Free-swimming amphipods are a key component of the Arctic food web, representing a link between zooplankton and higher level consumers such as fish, marine mammals, and birds.  Hyperiid and Lysianassid amphipods are among the common taxa found in Arctic waters and are a dominant component of the zooplankton abundance and biomass (Auel et al. 2002).  The hyperiid amphipod, Themisto libellula is a pan-Arctic species that can occur in high numbers in the ice free waters of the Arctic.  Based on the high amounts of C20:1 (n-9) and C22:1 (n-11) fatty acids and alcohols found in T. libellulatissues, their diet was domianted by Calanoid copepods.  Further analysis indicated a close association with ice-algal production.  This confirms field sampling data showing Themisto sp. associated wtih sympagic communities.

Themisto abyssorum is more closely associated with deepwater communties.  Themisto abyssorum is  considered to be a boreal species and is found in close association with the Atlantic Water that moves northward through Fram Strait.  Abundance generally decreases from east to west, dropping from >200 ind/m² over the contiental slope north of Spitsbergen to <40 ind/m² in the central Arctic (Auel et al. 2002).  It does not show a similar lipid signature seen in T. libellula, indicating that copepods are not a dominnant component of the diet.  Rather, the deepwater species is more likely an omnivore and scavenger.

Cyclocaris guilelmi, is also an epipelagic species, occurring in the deep-waters of the Arctic.  As wtih T. abyssorum, C. guilelmi appears to be Atlantic in origin but is found throughout the Arctic ocean.  Kraft (2012) found C. guilelmi to be a dominant component found in deepwater traps in Fram Strait.  The population appeared to be stable with peaks from August to February.

Cephalopods are a predator of and a key prey item for many of the VECs in the Arctic.  Squid move vertically through the water column, integrating marine resources throughout the pelagic environment.  The squid Gonatus fabricii is the most commonly reported species in the Arctic, with numerous records in the Atlantic sector, the Barents Sea and the high Canadian Arctic (Gardiner and Dick 2010). Berrytheuthis magister is the predominant squid species found in the Pacific domain.  Squid exhibit all manners of vertical distribution: near-surface dwellers (to 50 m), vertical migrators that either move into the surface waters at night or just move higher in the water column, and near-bottom dwellers.  In addition, some species exhibit ontogenetic descent moving progressively deeper as they age (Roper and Young 1975).  Cephalopods are voracious predators feeding on crustaceans, fish, other squids, and zooplankton.  Based on isotope analysis, squid are occupying different trophic levels in different regions (Navarro et al. 2013) indicating that squid are able to shift their diet based on availability.  The isotope ratios for Arctic squid indicated a trophic level of 3 to 5.  Squid are an important component of marine mammal and sea bird diets, including narwhals, White whales, walrus, murres and fulmars (Gardiner and Dick 2010).

Gelatinous zooplankton are poorly understood in the Arctic, largely due to the difficulty of capturing them with traditional sampling methods.  However, they are considered to be a substantial sink for primary and secondary production (Purcell et al. 2009).  In the Beaufort Sea, the scyphomedusa, Chrysaora melanaster is among the most common gelatinous zooplankton in shelf waters 25 to 75 m in depth (Purcell et al. 2009).  In shallower waters, there was a more diverse community dominated by the delicate medusa Bolinopsis infundibulum, other small cnidarians, and ctenophore species occurred immediately underneath the sea ice (Purcell et al. 2009; Raskoff et al. 2010b).  Other common species include Sminthea arctica in the midwater depths, and Atolla tenella which was found in high abundance in the deep Canadian Basin (Raskoff et al. 2010b). 

Large populations of gelatinous zooplankton have been observed throughout the Arctic, particularly in at convergences, fronts, and polynyas (Ashjian et al. 1997).  In such areas, medusa and ctenophores can have a substantial grazing impact.  In the eastern Canadian high Arctic, the ctenophore Mertensia ovum was estimated to consume up to 9% per day of the C. hyperboreus population and 3-4% of the C. glacialis population.   Other prey items included hyperiid amphipods, pteropods, and smaller copepods.  Other food resources for gelatinous zooplankton include detritus and algal cells and in some cases small or juvenile fish (e.g. larval capelin and herring; Raskoff et al. 2010b).

For the purposes of this review, fish in the Arctic can be divided into four general groups, the pelagic shallow and midwater species, anadromous species, and demersal fishes.  The bottom fish include nearshore, shelf, and deep water species.  Pelagic fish are the least diverse group representing 13% of the 242 recorded Arctic species (Bluhm et al. 2011; Mecklenberg et al. 2011).   There are 31 species considered to be anadromous.  The remaining species are marine demersal fish.

Throughout the Arctic, gadoids (cod) represent a critical link between the zooplankton community and higher trophic levels (e.g. seals, White whales).  Arctic cod (Boreogadus saida) and Polar cod (Arctogadus glacialis) are truly pan-arctic species occurring in all marine waters of the Arctic.  Cod are widely distributed throughout the Arctic, occupying nearshore, pelagic, and sea-ice habitats, residing both at depth and near the surface waters, depending upon age and season.  Both B. saida and A. glacialis can be found in small numbers or in large, densely packed schools.  In the scientific literature there is confusion on the common names “Arctic cod” and “Polar cod” at times referring to either B. saida or A. glacialis.  While these species are similar in appearance and life history, gene sequencing has shown that they are genetically distinct (Breines et al. 2008; Madsen et al. 2009). 

Both B. saida and A. glacialis have a diet dominated by pelagic or sympagic components (Sufke et al. 1998; Lonne and Gulleksen 1989; Bradstreet and Cross 1982).  Stomach contents of B. saida cod sampled in the pelagic ranges of the Beaufort Sea, northern Canadian waters, and the Barents Sea were dominated by calanoid copepods and gammarid amphipods.  Other prey items included hyperiid amphipods, mysids, and shrimps (Frost and Lowry 1984; Lonne and Gulliksen 1989).  A similar pelagic diet was observed for A. glacialis in the Northeast Water Polynya near Greenland (Sufke et al. 1998).  In the nearshore zone, the diet is dominated by copepods, gammarid amphipods, and young-of-the-year Arctic cod. 

Both B. saida and A. glacialis spawn under the ice in the winter months; however recent observations indicate that there are regional differences in the hatching season of B. saida (Figure 2-7).  Bouchard and Fortier (2011) noted that cod hatching started as early as January and extended to July in areas with significant freshwater input (Laptev/East Siberian Seas, Hudson Bay, and Beaufort Sea).  In contrast, hatching was restricted to April-July in regions with little freshwater input (Canadian Archipelago, North Baffin Bay, and Northeast Water).  The authors found that the different hatching periods resulted with different length and weight classes co-occurring throughout the Arctic.  Cod larvae generally occupy a depth of 10 – 30 m, settling to the bottom in September (Craig 1984; Graham and Hop 1995). 

As noted above, the distribution of B. saida and A. glacialis includes nearly all marine waters of the Arctic depending upon the age class and the season.  Arctic cod have been found to be a dominant component of both the pelagic and demersal communities at all depths; cod have been collected from the mixed water mass (<200 m), at the sharp halocline (200-300 m), and in the deeper Atlantic water mass (>300 to 1000 m; Majewski and Riest 2013; Norcross et al. 2012). One and two year old fish also occupy fissures and gaps in the ice pack, feeding on the sympagic fauna.  In the summer months, adult cod are dispersed in habitats ranging from coastal brackish waters to the demersal and pelagic zones of the shallow shelves, including the ice-water interface (Craig et al. 1982; Lonne and Gulliksen 1989; Gradinger and Bluhm 2004).  In autumn, as nearshore salinities increase, large shoals of cod are observed in shallow (<10 m) waters (Hop et al. 1997; Welch et al. 1993), presumably following shoreward fronts of plankton.

Acoustic surveys conducted as part of the BREA program as well as others conducted in the US Beaufort have found large shoals of Arctic cod in the water column and near the bottom along the entire shelf of the Beaufort Sea (Geoffrey et al. 2013; Parker-Stettner 2011).  There was a clear segregation between the young-of-the-year (YOY) and age 1+ fish in the summer months.  Age 1+ fish were found to aggregate in the deeper waters of the shelf  and slope at depths ranging from 200 to >1000 m while large shoals of YOY Arctic cod were found nearer to the surface (20 to 100 m) in nearshore waters extending into waters over the outer shelf and slope (Figure 2-8). The near bottom aggregations of Arctic cod at depths of 200 to 400 m appear to span the Canadian Beaufort shelf into the fall and winter months (Geoffrey et al. 2013; Benoit et al. 2008). Acoustic surveys during the winter months have found massive aggregations of adult cod at depths of 140 to 230 m under the pack ice in the Canadian Beaufort waters (Benoit et al. 2008) and at depths of 300 to 1,300 m near the North Pole (Geoffrey 2013). In winter months, adult cod appear to remain in schools at the deep inverse thermocline (160-230 m, -1 to 0°C) throughout the Polar night to avoid seal predation; whereas smaller cod (<25 g) periodically migrate into the isothermal cold intermediate layer (90-150 m) to feed on Calanoid copepods and then return to the deeper layer (Benoit et al. 2010).

An exception to the Arctic cod dominated pelagic food web is in the Barents Sea and White Sea.  The Barents Sea is located between the Arctic and boreal oceanic systems and is influenced by the variations in the Atlantic current and the Polar front.  In the southern portions of the Barents Sea, where the Atlantic water is more predominant, capelin (Mallotus villosus) is the primary link between pelagic crustaceans (e.g. copepods and amphipods) and higher trophic levels (Blanchard et al. 2002; Hamre 1994; Mehl and Yaragina 1992; Titov et al. 2006).  The importance of capelin to the Barents Sea ecosystem was demonstrated when capelin stocks decreased markedly in the 1980s, resulting in decreases in stocks of the commercially important Atlantic cod (Gadus morhua) and ringed seals.  Subsequent studies have demonstrated linkages between the location of the polar front, the population of capelin and subsequent changes in the population of Atlantic cod (Titov et al. 2006).  Capelin are also an important forage fish in the northern boreal waters of Greenland, the Sea of Okhotsk and the Bering Strait.  Unlike Arctic cod, Atlantic cod are more demersal in nature, generally feeding near the bottom.  The diet of Atlantic cod is remarkably varied, with Mehl and Yaragina (1992) reporting with over 180 prey species.  While capable of feeding on a variety of invertebrate and vertebrate prey, capelins appear to be the primary energy source.

Figure 2-8. Arctic cod (Boreogadus saida) vertical distribution during the ice-free season along the Mackenzie Slope 2012 (from Geoffrey et al. 2013).

Pacific herring (Clupea harengus pallasi) are another nearshore forage fish that represents an important link between zooplankton and higher level consumers, particularly anadromous fishes of the Bering-Chukchi-Laptev and Lofoten-Barents Sea systems (Mehl and Yaragina 1992; Hamre 1994).  Herring feed primarily in the water column on copepods, euphausiids, and mysids.  Herring spawn en masse and their eggs and larvae are a vital food source for nearshore migrating anadromous fish in the Arctic such as salmonids, cisco, and char. In the Arctic they are generally found in the nearshore waters and avoid the colder, Arctic water (Craig 1984).  While numerically less important than the Arctic cod, capelin and herring are important forage species for upper trophic level consumers.

Anadromous fish include those species with a life history that includes both freshwater and marine habitats.  In the Arctic, utilization of marine waters is typically limited to the brackish waters found in nearshore corridor immediately following breakup.  Anadromous fishes in the Arctic include Arctic char (Salvelinus alpinus), least and Arctic cisco (Coregonus sardinella and C. autumnalis), broad and humpback whitefish (C. pidschian and C. nasus), Inconnu (Stenodus leucichthys), and several species of salmonids (Craig 1984; Mecklenburg et al. 2011).  These species spawn in fresh water and typically do not enter coastal waters until months, or often years, after hatch.  Thus, the most sensitive life stages for anadromous fish are spent in the Arctic rivers and lakes.  Use of marine waters is limited to feeding and migration.  Coregonids are the most common anadromous fish in the Laptev-Kara-East Siberian waters, with Arctic cisco more commonly found in the marine waters than Least cisco (Sherman and Hempel 2008; Craig 1984).  Arctic char range widely from their stream of origin and might be found in more open water during high flow years (Jarvela and Thorsteinson 1999; Johnson 1980).  When occupying the nearshore brackish water, anadromous fish feed nearly exclusively on epibenthic fauna (e.g. polychaetes, mysids, and amphipods; Dunton et al. 2012).  In turn, anadromous fish become an important food source for seals as well as subsistence fishers.

A number of salmonid species are found in river systems throughout the Arctic; however, their use of marine waters is limited.  Atlantic salmon are the most common form found in the Lapotov-Barents Sea and Hudson Bay river systems (Sherman and Hempel 2008).  Pink and chum salmon (O. gorbuscha) are the most abundant species of Pacific salmon documented in the Arctic, with populations in Russian (Yana and Lena Rivers), Canadian (Mackenzie River), Alaskan, and Norwegian waters (Sherman and Hempel 2008; Mecklenburg et al. 2002).  With the exception of some juvenile use of the brackish nearshore waters, adults are the most common life stage found in marine waters.

Demersal fishes are those that are found in close association with the bottom.  Sculpins (Cottidae) and eelpouts (Zoarcidae) are the most speciose fish taxa in the Arctic, comprising over 50% of the species in polar waters (Mecklenberg et al. 2011).  Both taxa are well adapted to living in the dominant substrates found in the Arctic (sand, silt, and mud), as well as rocky bottoms, with most species spending the majority of their life cycle in close association with the bottoms.  Adults often deposit eggs directly on benthic substrates or on bottom oriented vegetation.  Larval and early juvenile forms may remain on the bottom near the adults or move into the water column or into vegetation before descending to the bottom as young fish.  Common and pan-Arctic sculpin species include the Arctic Staghorn sculpin (Gymnocanthus tricuspis), the large Short-horned sculpin (Myoxocephalus scorpius: 90 cm length), and Spatulate sculpin (Icelus spatula; Mecklenberg et al. 2011).  Two genera account for most Arctic eelpouts, Gymnelus and Lycodes.  Sculpin and eelpout diets vary, but many sculpin and eelpouts feed on benthic infauna and epifauna, including polychaetes, benthic amphipods, small mollusks, and epibenthic crustaceans, with larger species feeding on fish, including cods, flounders, and smelts (Dunton et al. 2012).  Anti-freeze proteins have been found in several species of Myoxocephalus sculpins, showing their adaptation to Arctic waters (Fletcher et al. 1982).

Flatfishes or flounders live on the bottom, usually in shallow marine waters, and burrow into the surface sediment to rest and wait for prey. They eat worms, mollusks, echinoderms, crustaceans, other benthic invertebrates, and fishes. Arctic flounder (Pleuronectes glacialis) are a pan-Arctic species that prefer coastal and nearshore waters (Mecklenberg et al. 2011).

The deep-sea fishes are perhaps the poorest known group in the Arctic.  Recently there have been several targeted efforts to sample the deep basins in the Arctic (Reist and Majewski 2013; Dolgov et al. 2009; Jorgensen et al. 2005). In the deep Canadian Beaufort, Arctic cod were the dominant species in the water column and associated with the demersal community (Reist and Majewski 2013). Other species found in midwater trawls included species found in other deep ocean basins, including Myctophids (lanternfish) and Gonostomids (bristlemouths).  The myctophids, Benthosoma glaciale and Protomyctophium arcticum, spawn above the Polar front (Dolgov et al. 2009) and were found in deep water trawls (Riest and Majewski 2013).  Other species have been recently collected from the Kara Sea, includingMyctophum punctulum (Dolgov et al. 2009; Weinrroither et al. 2010).  The wide-spread gonostomid, Cyclothone microdon, has been observed in trawls in Baffin Bay (Riest and Majewski 2013; Mecklenburg et al. 2011).  Based on observations of myctophids and bristlemouths throughout the world, their diet is dominated by pelagic crustacean, migrating to the surface from depth to feed.  It is not known if the diel vertical migrations occur in the Arctic.

Deepwater demersal fish taxa are generally similar to those found in other oceanic basins and include Zoarcids (eelpouts) and Macrourids (grenadiers).   The globally distributed macrourids, Coryphaenoides rupestris and Macrourus berglax have been found in the Baffin Bay (Jorgensen et al. 2005).  The Glacial eelpout (Lycodes glacialis) is one of the most dominant demersal fishes in the Arctic basins.  This large eelpout (~70 cm) moves along the bottom stirring up the bottom sediments to feed on small benthic crustaceans and mollusks; L. glacialis also feeds on other fishes and cephalopods (Mecklenberg and Mecklenburg 2011).  This is a truly deep water species, spending its entire life cycle at depths >1,000m.  The Greenland halibut (Reinhardtius hippoglossoides) is a right-eyed flounder typically associated with deep waters of the Arctic (200 – 1600 m), as well as deep waters of the Atlantic and Pacific Oceans.  The Greenland halibut is epibenthic, and feeds on epibenthic crustaceans, demersal fish, and other invertebrates.  Deepwater rays found in the southern Arctic waters in Alaska and Baffin Bay include Rajella spp. and Amblyraja radiata (Dolgov et al. 2009; Mecklenburg et al. 2002).

Marine mammals are both permanent and seasonal members of the Arctic and include baleen and toothed whales, seals, walrus, and Polar bear.  The following section focuses on those mammals closely linked to the marine food webs.

Bowhead whales are circumpolar, residing in the high latitudes from late April to October.  In the spring months, bowheads migrate northward as the sea ice breaks up.  Five stocks have been identified, including the Spitsbergen, Baffin Bay-Davis Strait, Hudson Bay-Fox Basin, Sea of Okhotsk, and Bering-Chukchi-Beaufort stocks (Rugh et al. 2003).  The latter stock overwinters in the Bering Sea.  In the spring, the Bowheads move north and east, past Point Barrow into the western Beaufort Sea (Lowry et al. 2004).  The majority of whales move into the Canadian Beaufort Sea for the summer months; however, some Bowhead whales will either remain in the eastern Alaskan Beaufort or move into the Arctic Ocean.  While Bowhead whales appear to favor continental slope waters in the spring and summer, they appear to favor the inner shelf waters (<200 m depth) of the western Beaufort in September and October (Moore et al. 2000).  As the ice cover increases in late fall, the whales migrate into the Bering Sea for the winter months. 

Bowhead whales are considered to be second order consumers (Hoekstra et al. 2002), with a diet dominated by euphausiids and calanoid copepods (Bluhm and Gradinger 2008).  Stomach content analyses indicate that, while benthic crustaceans and fish occur, their consumption is either occasional or incidental (Frost and Lowry 1984; Lowry et al. 2004).  In the Bering-Chukchi-Beaufort system, there appears to be some seasonality in the diet which is dominated by euphausiids in spring and by copepods in the summer and autumn months.  This distribution of diet is likely to be a result of opportunity, rather than selection.  Dominant species in stomach contents included the euphausiids Thysanoessa raschii and the copepods C. hyperboreus and C. glacialis (Frost and Lowry 1984; Lowry et al. 2004).

The White whale, or Beluga, is a circumpolar species inhabiting cold waters of the Arctic and subarctic waters (Rice 1998; NAMMCO 2005a).  During the winter months, White whales retreat to subarctic regions with loose pack ice and winter polynyas (Barber et al. 2001).  During the summer months, White whales live in coastal waters, estuaries, shelf breaks and deep basins.  In the Alaskan Arctic, White whales move into the Beaufort Sea in May, moving east into the Canadian Beaufort or north to the Arctic Ocean for much of the summer (Loseto et al. 2006).  In the fall as the Arctic cod congregate in the nearshore waters, White whales cross along the Alaskan mid-shelf in late August and September (Suydam and Moore 2004).  The  Eastern Chukchi White whale typically remains in the more open waters (>200 m depth) throughout the year, whereas the Eastern Beaufort Sea White whales move closer to shore when in the eastern Beaufort Sea (Suydam et al. 2001).

White whales are considered to be third order consumers (Hoekstra et al. 2002), with a diet dominated by Arctic cod (B. saida and A. glacialis), and to a lesser extent whitefish (Coregonidae) in the Russian and Greenland Arctic.  A variety of other prey items have been observed in stomach contents, including capelin, herring, smelt, sculpins, cephalopods and benthic invertebrates (Bluhm and Gradinger 2008).  Nitrogen and carbon isotope signatures indicate that they also feed on copepods and euphausiids, particularly in the spring and fall (Hoekstra et al. 2002; Frost and Lowry 1984).  Known predators of White whales include Orca whales, Polar bears, and humans (NAMMCO 2005a).

Narwhal occur in the deep and offshore waters of the Canadian High Arctic, the Barents and Kara Seas, eastern Laptev Sea and the waters surrounding Greenland (Sherman and Hempel 2008).  Narwhal appear to have high site fidelity, remaining in close association with the ice in winter.  Winter feeding grounds appear to be more important than summer feeding areas, with remarkable aggregations of narwhals found in polynyas.  In winter, a large number of whales can share the limited open water areas; near Greenland, between 17,000 and 19,000 narwhals were found to occupy 2% of the surveyed area (approximately 73 whales per km² of open water (Laidre, personal communication).  Narwhals feed mostly in deep water and possibly at or near the bottom. Dives of up to nearly 1,500 m and 25 minutes are documented (Laidre et al. 2003), and there are some seasonal differences in the depth and intensity of diving (Laidre et al. 2002, Laidre et al. 2003).  Arctic cod (B. saida and A. glacialis) and the squidGonatus fabricii dominate the narwhal diet, with lesser amounts of Greenland halibut and other deep-sea fish (Laidre and Heide-Jørgensen 2005a; Bluhm and Gradinger 2008). Predators include Orca, Polar bears and humans (Hay and Mansfield 1989). 

Ice seals of the Arctic include Ringed seals, Ribbon Seals, Spotted Seal, and Bearded Arctic seals.   Ringed seals (Phoca hispida) are the most common and widely distributed ice seal in the Arctic (Reeves 1998).  Ringed seals are relatively small seals (1.5 m) that are generally found on permanent ice or large floes, maintaining breathing holes allowing it to use ice habitats when other seals cannot (NAMMCO 2005b).  Major foods eaten are Arctic cod, nektonic crustaceans (hyperiid amphipods and euphausiids), capelin, sculpin, and sea-ice and benthic crustaceans (Bluhm and Gradinger 2008).  The balance of the diet varies seasonally.  Ringed seals are a primary prey item for Polar bear, Arctic fox and Glaucous gulls (NAMMCO 2005b).

The Bearded seal (Erignathus barbatus) is a solitary seal with a circumpolar distribution.  It is most abundant where it can reach the sea bottom to feed.  The bearded seal is generally found in the pack ice where openings are common since it cannot maintain a breathing hole.  In the Beaufort and Chukchi system, E. barbatus consumed crab, shrimp, and clams (Lowry et al. 1980).  In the Kara and Barents Seas, and Sea of Okhotsk bearded seals fed primarily on Arctic cod (B. saida) as well as shrimp (Sclerocrangon boreas) and mollusks (Finley and Evans 1983).  In the areas of NW Greenland and the Canadian High Arctic, bearded seals had a varied diet including fish, crustaceans, gastropods, cephalopods and polychaetes (Finley and Evans 1983).

Other seals that are found in the Arctic include Ribbon seals (Phoca fasciata), Harp seals (P. groenlandica), and Spotted seals (P. largha).  Both the Ribbon and Spotted seals feed primarily on Arctic cod, capelin, as well as demersal fish and large benthic crustaceans.  Harp seals feed primarily on Arctic cod and shoaling fishes, such as herring and capelin (Bluhm and Gradinger 2008).

Three subspecies of walrus occur in the Arctic: the Pacific walrus (O. rosmarus divergins) in the Bering-Chukchi), the Laptev walrus (O. rosmarus laptevi) in the Laptev Sea, and the Atlantic walrus (O. rosmarus rosmarus) in the Barents-Kara, Greenland, and High Canadian Arctic waters (NAMMCO 2005c).  Walrus are extremely gregarious, often hauled out on land or ice floes, with several thousand individuals in a herd. 

Walrus feed in shallow waters (10-50 m), foraging through bottom sediments with their stiff beard bristles. Their primary diet appears to be dominated by bivalve clams, however, stomach contents analysis also indicates that other benthos are also important, including snails, echinoderms, and crabs (Outridge et al. 2003; Bluhm and Gradinger 2008).  Dominant clam species found in stomachs included Mya truncata, Serripes groenlandica, and Macoma sp.  Due to their size, tusks, and their gregarious behavior walrus predators are limited to Polar bear, Orca, and humans (NAMMCO 2005c).

Orcas occur in the Arctic during open water periods.  Orcas move northward from the Bering Sea or the North Atlantic.  Distribution likely varies, with movements tracking those of favored prey species or pulses in prey abundance of availability (such as seal pups or fish runs).  In the Arctic, Orcas rarely move close along or into the pack ice (Reeves et al. 2002).  The frequency and abundance of Orcas in the Arctic appears to increase during years with decreased ice coverage.  Orcas are a top predator and feed on a variety of large vertebrate prey including anadromous and pelagic fish, ringed seals, and whales.  Orcas are considered a significant threat to Bowhead whales (COSEWIC 2009).

Polar bears are linked to the marine habitat through diet and daily or seasonal migration.  Although they reside on the ice during the winter, polar bears are accomplished swimmers and inhabit the open waters along the ice edge; they migrate toward land once the ice melts.  Polar bears are linked to the marine pelagic food web, feeding primarily on ringed seals, although they will also feed opportunistically on other marine mammals (Thiemann et al. 2007). 

Arctic seabirds are dependent on marine resources from the Arctic for all or most of their energy requirements while they are in the region.  Most seabirds are migratory arriving as spring blooms and breakup begins. Arctic birds that forage in the open pelagic are mostly alcids, gulls, skuas, and terns (Huettmann et al. 2011).  Other taxa tied to marine food webs are sea ducks, most notably eider ducks.

Black-legged kittiwakes are one of the most numerous seabirds with a circumpolar distribution.  Arriving in southern portions of the Arctic in February and moving northerly through April.  Kittiwakes feed in ice floes as well as in open water, skimming the water surface or feeding from the surface.  Based on stomach contents analysis from kittiwakes in Lancaster Sound, the summer diet is dominated by Arctic cod (93% to 98%; Bradstreet 1976).  Dahl et al. (2003) indicate that kittiwakes in the vicinity of Svalbard feed primarily on capelin, Arctic cod, and hyperiid amphipods.  A similar diet was observed in Barents Sea.  Isotope analysis in the High Canadian Arctic indicated that amphipods may play an important role to fish over the course of the year (Hobson 1993).

Black guillemots are a common bird in open water and amongst the ice floes.  Black guillemots are generalists.  Stomach contents analysis in Lancaster Sound showed that amphipods, copepods, and Arctic cod were all important components in guillemot diets.  Amphipods and copepods appeared to be a more dominant component of the diet when the guillemots fed along the ice edge in later spring to early summer (Bradstreet 1980), with fish being an important component of the diet throughout the year (Hobson 1993).

Thick-billed murres or Brunnichs guillemots are members of the auk family (Alcids).  Thick-billed murres over-winter in boreal regions where there are open waters.  In summer, U. lomvia congregate and breed in the Chukchi Sea, the Siberian coast, eastern Canadian Arctic, Greenland and northern Norway.  Murres are agile diving birds that consume both fish and crustaceans, with Arctic cod comprising the majority of the diet in both coastal and offshore ice edges (Bradstreet 1980; Hobson 1993).  Summer diet was more variable feeding on pelagic amphipods when cod are unavailable.  Murre chicks’ diet is dominated by Arctic cod and sculpin.

Northern fulmars are long-lived (32 years) migratory birds, moving northwards to the Arctic between May and July.  Fulmars are pelagic birds, preferring shelf habitats, particularly shelf breaks or over the continental slope, though they are seldom further than 100 km from shore (Dewey 2009).  As with many other sea birds, the fulmar diet is dominated by Arctic cod, copepods and pelagic amphipods.  Fulmars also prey on the squid, Gonatus fabricii.  Seasonal analysis showed that amphipods and copepods were dominant in the diet of adult and nesting fulmars.  Arctic cod are the primary diet once chicks have hatched and during rearing.  After that time, amphipods (Hyperia sp., Gammarus sp, Themsto sp.) and copepods once again dominated the diet.

The Common eider is a large diving duck common in the Arctic, particularly in the High Canadian and Atlantic sectors.  Common eiders feed primarily on benthic prey including mollusks (Buccinum glacialis, Hiatella arctica), barnacles (Balanus balanus), decapods (e.g. Hyas araneus), and amphipods (Gamarellus homari; Dahl et al. 2003).  Eiders are an upper level consumer in kelp forest (Fredriksen 2003) and estuarine lagoons (Dunton et al. 2012).  Isotope analysis confirms that eiders feed at the lower trophic levels (Hobson 1993).  Unlike other Arctic species, lipids analysis and stomach contents analysis show that copepods are not an important prey item for eiders.

Dovekies are a small marine diving bird that is circumpolar in distribution (Day et al. 1988).  This small auk overwinters in boreal waters, such as the North Sea and Norwegian Sea.  In early spring they migrate northwards to feed on the sympagic copepods and amphipods (Dahl et al. 2003).  The Little auk feeds on the herbivorous sea-ice amphipod, Apherusa glacialis (Kramer 2010).  Dovekies also rely heavily on Calanus copepods, relying on the lipid rich C. glacialis and C. hyperborealis to successfully raise their chicks (Falk-Petersen 2007).   Breeding colonies can be quite large with 30 million birds observed in northwestern Greenland. 

Glaucous gulls are pan-Arctic and are a primary avian predator in the Arctic that feed on a wide variety of fish, mollusks, crustaceans, eggs, chicks, and adult seabirds, as well as carrion.  They will often prey on young and adult birds, as well as the catch from other birds.  Arctic fox are important predators of gulls and skua, as well as other nesting birds, preying on eggs and chicks.

Arctic jaegers are a top avian predator during the summer months, migrating annually to overwinter in the Antarctic.  Jaeger primarily on fish, though they will also feed on insects and berries.  While they can catch their own food, they will often steal fish from other birds.  They will also prey on the nests of waterfowl, eating the eggs and young, as well as small mammals (e.g. lemmings).

Benthic communities are strongly influenced by the substrate-type and sediment grain size.  Benthic substrates in the Arctic are dominated by fine-grained sands, silts, and clays on the shelves and fine clays and silts in the oceanic basins (Bluhm et al. 2010).  Sediment in the expansive shelves of the Barents, Kara, and Laptev Seas are typically dominated by fine grained sediments (Stein et al. 2004, Semiletov et al. 2011; Cochrane et al. 2009), with areas of sandy substrate occurring in the nearshore areas.  Similarly the narrowing shelves of the Bering and Chukchi seas are fine in nature, with some sandy areas occurring in the Bering Strait.  In the central reaches of Russian, Greenlandic, and Baffin Island fjords, sediments are dominated by very fine, unconsolidated clays and silts (Aitken and Fournier 1993, Stein et al. 2004).  Sands and gravelly substrate is more common in the nearshore zone and in erosional areas.  Hard substrate is localized and includes subtidal boulder fields as well as nearshore rocky outcrops.  Notable examples are the boulder fields in the Beaufort Sea, portions of the Barents Sea, and the rocky shoreline in northern Greenland and Svalbard.

Intertidal benthic communities in the Arctic are generally thought to be less diverse than those found in lower latitudes due to ice scour and UV exposure.  The disturbance from ice comes from direct contact of foot or anchor ice and scouring during breakup.  Such disturbance results in a continually changing benthic community dominated by fast-settling, opportunistic meiofauna (Barnes 1999).  Estimates suggest that Arctic intertidal macrofaunal communities typically have no more than 100 species, with some areas nearly devoid of intertidal macrofauna (animals larger than 0.5 mm).  In contrast intertidal boreal communities in Alaska and Norway may have over 200 to over 300 species (Weslawski et al. 2011).  Most intertidal species are circumpolar; however, their regional distribution can be highly variable.  For example, areas of the Beaufort and Siberian coasts are devoid of intertidal macro-organisms as beaches are predominately gravelly with little stability and fast ice in the winter months (Weslawski et al. 2011).  Conversely, estuarine lagoons along the Beaufort are relative benthic hotspots, with well-developed benthic infaunal communities that are protected from fast ice and coastal erosion (Dunton et al. 2012).

Rocky intertidal and shallow subtidal communities are an important component in certain portions of the Arctic, particularly the Atlantic sector (Figure 2-9).  Benthic communities in these areas are more akin to those of north Atlantic rocky intertidal and shallow subtidal habitats.  For example, in the steep rocky substrate in Svalbard (Kuklinski and Barnes 2008) the most common species include the macroalgaeFucus spp., sessile (i.e., non-mobile) barnacles (Balanus balanoides), and motile gastropods (Littorina saxatilis) and amphipods (Gammarus setosus and G. oceanicus).  Associated subtidal communities are dominated by the barnacle Balanus balanus, brittle stars (Ophiopholis sp.), motile amphipods (Calliopidae sp.), isopods (Munna sp. and Janira maculosa), sipunculid polychaete worms, and snails (Alvaniasp.).

Figure 2-9. Locations with Shoreline Dominated by Hard Substrate (Red outline, from Lantuit et al. 2012)

In the western Arctic, hard-substrate communities are uncommon in intertidal and subtidal waters.  However, there are isolated communities associated with patches of boulders and cobble.  Dunton et al. (1982) characterized an Arctic kelp community associated with subtidal (<10m) boulder patches in the Alaskan Beaufort Sea.  Exposed boulders and cobble provided an attachment point for Laminarian kelp (Saccharina latissima, L. solidungula, Alaria esculenta).  The community associated with the kelp beds were characterized as being similar to those found in northern Atlantic waters.  Large sponges and cnidarians were common, as were the chitons and mussels; barnacles (B. balanus), snails, and sipunculid polychaete worms were also common.  The crab Hyas coarctatus was the dominant crustacean, along with mysids, amphipods, and hermit crabs (Pagurus trigonocheirus).

The benthic communities of the coastal nearshore zone (<50 m) can be variable depending upon the salinity regime and substrate.  Infaunal biomass is variable across the Arctic, ranging from 41 gC/m² in the Beaufort Sea to over 250 gC/m² in the Baffin Island, Lancaster Sound area (Thompson 1982).  The nearshore zone in the Beaufort Sea has relatively low biomass and highly dynamic communities due to the gravelly nature of the shallow subtidal substrate.  In gravelly or cobble substrate meiofauna and barnacles dominate.  In sand and sandy silts, the sediment fauna is dominated by small polychaetes (Scoloplos armiger, Spio filicornis, and Chaetozone setosa) and oligochaetes.  Feder and Schamel (1976) found that species diversity, abundance and biomass increased with distance from shore, which was attributed to ice and wave action affecting stability.  Nearshore coastal areas of Lancaster Sound, the high Canadian Arctic, and Greenland, infaunal communities have higher biomass, with bivalve dominated communities including Astarte borealis, A. motagui, Serripes groenlandicus, Mya truncata, Cistenides granulata, and Macoma calcarea (Thompson et al. 1986).  Similar species complexes that also included the bivalvesPortlandia arctica, and Nuculana sp. are found along the Russian Arctic (Gebruk 2004).

Estuarine flats and lagoons can have abundant and well developed benthic communities.  Lagoon areas are often protected from fast ice and wave action, are enriched by terrestrial sources of organic matter, and have warmer water temperatures.  However they may also have highly variable salinities that can limit species diversity.  In lagoons along the Beaufort Sea and in the Kara Sea, infaunal diversity was noticeably lower in estuarine lagoons than the neighboring marine waters.  However, abundance and biomass were equivalent or greater.  As in temperate waters, the lagoons act as a rich habitat for phytoplankton, harpacticoid copepods, calanoid copepods, polychaetes (Nephtys sp., Prionospio sp., Spio sp., Terebellides sp., and Travisia sp.), Pandalus shrimp, mysids, clams (Astarte sp., Yoldia sp.,Macoma sp., Portlandia sp.), a variety of amphipods (Anonyx sp., Gammarus spp.), and isopods, anadromous fishes (Arctic and Least cisco, Arctic char, salmonids) and birds (Dunton et al. 2012; Gebruk 2004).  Many of the species found in the lagoon communities are similar to those found in boreal and temperate waters.

As indicated above, the majority of the benthic habitat in the Arctic basins is fine grained sand, silt, and clay.  In general, soft bottom infaunal and epifaunal communities in the Arctic are similar to those of other oceanic basin, being dominated by polychaetes, amphipods, mollusks, and echinoderms.  Abundance, biomass, and species diversity in Arctic shelf communities is considered to be similar to the lower range for boreal and temperate basins.  Community abundance, biomass, and diversity are variable throughout the Arctic, and are controlled by factors such as substrate type and availability of organic carbon appear to be the primary drivers for abundance and biomass (Thompson 1982; Grebmeier and Cooper 2012; Piepenburg et al. 2011).   In the Barents Sea, Cochrane et al. (2009) found that ice cover was inversely proportional to organic carbon and abundance.  A number of studies have noted the importance of pelagic-benthic coupling in determining the benthic assemblage (Grebmeier and Cooper 2012; Carmack et al. 2006; Carmack and Wassmann 2006).  Pelagic sources of organic carbon in the Arctic includes both water-column and sea-ice production.  In the high Arctic, the ice algae are the primary source of carbon for the benthic communities.  However, productivity in these regions is limited due to the reduced daylight and ice cover and this appears to limit abundance and biomass in the associated benthic communities.  Species assemblages have also been shown to vary across the shelf from east to west, with the southern Greenland, Norwegian, and Barents Seas affected by the species in the North Atlantic.  Similarly, the Siberian-Chukchi-Beaufort system is affected by Pacific species associated with the Bering Sea and Strait (Grebmeier 2012).

Beyond the shelf, species diversity, abundance and biomass decreases markedly with depth.  Unlike other oceanic basins, there was no increase in diversity and biomass at the mid-depths, rather all three benthic measures decrease steadily with depth (Table 2-2; Bluhm et al. 2011).  Many of the species that comprise the deep water communities are eurybenthic and are found on the outer continental shelves.  Similarly, many of the dominant deep water species are similar to those of the boreal and temperate deep water communities.  When considering deep water benthos, it is important to bear in mind that data at depth in the Arctic is limited.  Sampling methods commonly deployed in other ocean basins cannot be deployed in the Arctic.

Table 2-1.  Abundance and Biomass for Arctic Deep-Sea Benthos (Bluhm et al. 2011).

The general taxa groups that dominate the benthic macro- and megafauna in the Arctic are similar to those of other oceanic basins, namely polychaetes, amphipods, isopods, mollusks, and echinoderms.  Other epibenthic crustaceans such as crab and shrimp are also found in the Arctic but are not as common throughout the region.  While polychaetes are the most abundant of the major taxa throughout the shelf, Arctic clams are perhaps a more important component in the Arctic food webs, relative to other regions, with a number of larger and important predators (e.g. walrus, bearded seal).  The following section discusses each of these taxa groups.

Bivalve mollusks are an important component of Arctic shelf communities, serving as a primary prey item for walrus and bearded seals, among other higher vertebrates.  Benthic communities of the inner shelf are often defined by the dominant bivalve species.  Bivalves (clams and mussels) can comprise up to 15% of the infauna in slope and plain sediments, but often dominate the biomass.  In substantial portions of the East Siberian Sea-Chukchi-Beaufort and Barents-Kara-Laptev shelves, bivalves were the dominant taxa (Grebmeier and Cooper 2012; Denisenko 2007; Filatova and Zenevich 1957).

The Greenland cockle, Serripes groenlandicus, is a common circumpolar bivalve found up to 100 m depth on a variety of substrates.  A fairly large (up to 112 m) and long-lived clam (up to 39 years) it is a main component of the diet for walrus and Bearded seals.  Macoma calcarea are also a common component in the shallower portions of the Siberian-Chukchi- Beaufort and Barents-Kara-Laptev seas (<50 m depth), as well as the fjords of northern Canada and Baffin Island.  Areas with organic enrichment had higher Macoma abundance (Grebmeier and Cooper 2012; Filatova 1957).  Other dominant clams in the shelf include Astarte sp., Portlandia, Mya truncata, Telina sp. and Yoldialla solidula. 

Deep-sea species are generally smaller and less abundant.  Common deep sea species include the taxa Axinopsidae, Nucula, and Nuculanacia while other species are unique to the deep sea (e.g. Bathymodiolus spp. and Abra spp.; Gage and Tyler 1991). Clams are generally suspension or deposit feeders that are well adapted to processing particulate organic matter (POM) in the deep sea.  The digestive tract in many deep-sea species is elongated with intra and extracellular digestive enzymes that allows for efficient digestion of recalcitrant forms of carbon.  In addition, deep-sea clams have modified palps that sort particles before sending them to the mouth (Allen 1979).  Some deep-sea species are carnivorous, with modified siphons that allow for predation on copepods and ostracods. 

Polychaetes dominate the infaunal community on the slope, rise and abyssal plain.  MacDonald et al. (2010) found dominant families in the Arctic including Cirratulidae and Paraonidae (Aricidea sp).  Other species considered to have pan-oceanic distributions based are Capitella capitata, Lumbrineris minuta, Maldanid, Oweniid, and Chaetozone complexes.  There are a number of different feeding strategies used by polychaetes, including filter feeders, surface deposit feeders, subsurface-burrowing feeders, and carnivores.  On the shelf and in fjords, the species assemblages change with feeding strategies.  Renaud et al. (2007) found that the inner fjords and nearshore areas were typically dominated by few species and species that were highly motile or surface deposit feeders (e.g. Lumbrineris sp., Chaetozonesp.). In the mid- to outer fjords, the polychaete community was more diverse with an increase in subsurface deposit feeders.  There is a strong indication for pelagic-benthic coupling in the Arctic with the distribution of benthic fauna strongly associated with patterns in the associated water column, particularly near polynyas where regionally high production in the water column is reflected in the benthic community (Piepenburg et al. 2005).

Amphipods are common members of the benthic community, including both infaunal and epibenthic species.  Amphipods are broadly distributed throughout the world’s shelf and deep sea basins.  The most widely distributed species across the Arctic are Ampelisca eschrichti, Anonyx nugax, Arrhis phyllonyx, Pontoporeia femorata, Gammarus setosus, and Byblis gaimardi (Piepenburg et al. 2011; Dunton et al. 2012).  Petrova and Dzhurinskiy (2012) found that Ampeliscidae were more common in the inner shelf areas, while Pontoporeiidae were more common in Bering Strait.  In the Gulf of Finland, a similar trend was observed with Pontoporeiidae more abundant at the mouth of the Gulf and Ampelisca more common near the head of the Gulf.  Amphipods are primarily deposit feeders or active scavengers, either free-burrowing or living in tubes.  Infaunal amphipods are commonly used in toxicological evaluations of whole sediment, with established methods for testing whole sediments or spiked water samples.

Lysianassid amphipods are a species rich group of epibenthic omnivorous amphipods that are key scavengers in the Arctic and deep sea waters.  Many are especially adapted to scavenging with specialized mouthparts, extendable guts for food storage, and a highly motile foraging behavior.  Premke (2003) has reported on food-fall scavenging activities of the Lysianassid amphipod Eurythenes gryllus  in deep Arctic waters of the Norwegian Deep.  However, in shallower waters, Lysianassid amphipods may have a more diverse diet.  Lysianassid amphipods  dominate invertebrate macrofauna in certain environments.  On tidal flats, Onismus litoralis constitutes up to 95% of the macrofaunal density (Weslawski et al. 2000). 

Many species of Lysianassid amphipods are barotolerant. E. gryllus may be easily retrieved and decompressed from deep water with no apparent deleterious effects, as long as temperature is kept below 4 °C (Sainte-Marie 1992).  Their geographic distribution and depth range is also considered to be extensive, being found throughout the world to depths up to 2,500 m above the bottom (Krapp et al. 2008, Sainte-Marie 1992, Premke 2003).  Anonyx nugax is also a common benthic amphipod in the Arctic found associated with the sea ice and with abyssal communties as deep as 1700 m.

In general, decapod crustaceans are less common in the Arctic.  There are however, several notable exceptions, particularly in the boreal-Arctic waters of the Bering Sea-Chukchi and the Barents-Greenland Seas.  Crab and shrimp are the primary decapods in the Arctic. These include the shrimp, Pandalus borealis and the deep water prawns Pandalopsis dispar.  In the eastern Arctic, the densest concentrations are found in the central region of the Barents Sea, Hopen Deep, Thor Iversen Bank and near the western Murman coast at depths from 200 to 350 meters.  The caridean shrimp, Nematocarcinus ensifer is found from the North Sea into the Arctic.  Epibenthic shrimp are primarily detritivores; however the diet is augmented with slow-moving prey such as gastropods, ostracods, and hydrozoan polyps (Cartes 1993).  In general, larval and juvenile demersal shrimp appear to occur deeper than adults, migrating to the shallower end of their distribution as they grow older.  Demersal shrimp are an important food source for demersal fish, in particular Alepocepalus and Macrouridae.  There is a substantial fishery for P. borealis in the Russian Arctic.

The crab, Chionoecetes spp., is native to waters in Alaska, the east coast of Canada and west of Greenland, and is an invasive species in the Barents Sea.  Main items in the Chionoecetes spp. diet in the southeastern Barents Sea are polychaetes, mollusks, crustaceans and echinoderms.  Chionoecetes spp.in the Barents Sea were recorded in waters from 39 to 387 m depth, predominantly on muddy or sandy and muddy grounds, at temperatures from –1.6° C to 5.9° C and salinity from 34.5 to 35.1 ‰ in the near-bottom layer.  In the Bering Strait and Chukchi Sea, Chionoecetes spp. has shown increased abundance (Bluhm et al. 2009; Iken et al. 2010). 

The Red king crab (Paralithodes camtschaticus) occurs in portions of the Barents Sea and was deliberately introduced to the Barents Sea at several locations during the 1960s and 1970s from the northern part of the Pacific (Orlov and Ivanovo 1978). It has continuously spread to new areas and is now distributed from the Kluge Island to east, the Goose Bank to north, and west to Lofoten and Kvænangen to west along the Norwegian coast. The expansion of the area inhabited by red-king crabs occurred during years when water temperature in Atlantic currents was higher than normal (Pinchukov and Karsakov, in press). Several studies have revealed that the crab besides being an important fishing resource, also significantly impact the bottom ecosystem in areas of high densities of crabs (Sundet and Berenboim 2008).

In the Russian waters of the Barents Sea, red-king crabs occur in areas from shallow waters to the depths below 335 m. In spring, April-May, they form spawning aggregations of individuals of both sexes, whereas in August-September, red-king crabs form separate aggregations where males aggregate in concentrations within the temperature range 4-6° С and females within 5-7° С.  Red-king crabs are benthic predators (Gerasimova and Kachanov 1997; Manushin 2008), but in areas with intensive fishing, they predominantly feed on fish offal (Pinchukov and Pavlov 2002; Anisimova and Manushin 2003). The main red-king crab predators in the Barents Sea are cod and skates (Matyshkin 2003).

Galatheid crabs (Munida spp) are widely distributed on bathyal bottoms in most deep ocean regions (Cartes et al. 2004).  Munida tenuimana is common in the north Atlantic along the middle and lower slope from depths of 300 to 1900 m (Cartes 1993).  The diet of the galatheid crabs includes polychaetes, crustaceans, and fish remains.  Galatheid crabs are also found in the hydrothermal vent communities, living within the large tube worms (Martin and Haney 2005).

As in other oceanic basins, Ophiuroid brittle stars are among the most common megafauna occurring in Arctic shelf habitats.  Dominant species include Ophiocten sericeum, Ophiura sarsi, Ophiura robusta,Ophiopleura borealis, and Ophiacantha bidentata (Piepenburg et al. 1997; Gebruk 2004; Thomson 1982 Anisimova 1989).  In the Laptev Sea, populations of O. sericeum and O. sarsi were abundant (as high as 36 ind/m²) but highly variable with nearby areas devoid of brittle stars (Piepenburg et al. 1997; Sirenko et al. 2010).  Similar trends were observed in shelf habitats in Greenland and Barents Sea and the outer shelf in the Siberian Sea (Bluhm et al.2009). 

Photo 2-4. Dense aggregations of Brittle Stars

Most ophiuroids are motile epifaunal grazers using their flexible arms to feed on detritus, suspended organic material, small epifauna, and infaunal organisms.  Ophiuroids have the ability to aggregate in areas of organic carbon deposition and have been associated in the Arctic with polynyas and marginal ice zones, where ice algae and associated detritus are deposited at higher rates (Photo 2-4).  Predators of ophiuroids include shrimp, crabs, and epibenthic feeding fish such as Zoarcidae and small Macrouridae.

At deeper sites, holothoroids become a dominant component of the demersal invertebrate community.  Holothoroids, or sea cucumbers, are ubiquitous on the abyssal plain and relatively abundant.  Sea cucumbers are detritivores, ingesting sediment and digesting the incorporated organic material.

The sea-ice realm is defined by a complex of permanent or multi-year ice that can reach thicknesses in excess of 5 m and seasonal, first-year ice that is generally <1 to 2 m in thickness (Melnikov 1997).  The structure of sea-ice varies with the depth and age of the pack ice.  At the ice-water interface, the sea-ice surface is uneven and porous, with brine channels that extend upwards nearly 1 m into the ice pack.  Brine channels are created as the water freezes and salts are excluded from the structure of the ice.  In first-year ice, brine channel density can be 50 to 300 channels per m² and average 0.4 cm diameter (Arndt et al. 2009).  The ice temperature and interstitial water salinity increases with increasing distance from the ice-water interface.  Temperatures in the bottom meter of ice are relatively stable, remaining between 0 and -2°C and salinities ranging from brackish to marine (4 to 40‰; Petrich and Eiken 2010).  In the middle depths of the ice pack, ice density increases, brine channels become smaller, and interstitial water salinity increases (>100 ppt).  Temperatures in the mid to upper ice pack are more variable and can range from -35°C to >5°C.  In older multi-year ice, the upper layers of ice are comprised of fresh water ice, with more fully developed structure and no brine channels.   With the exception of some microbial and bacterial species, the majority of the flora and fauna associated with the sea ice are found on or in the bottom ~20 cm of ice.

Sympagic organisms are those species that live in and on sea ice and include autochthonous species (those that spend their entire life history in the ice) and allochthonous species (those that migrate to the sea ice from the benthic or pelagic realm to spend a portion of their life cycle associated with the sea ice.  The sympagic community includes ice algae, ciliates, nematodes, rotatorians, acoel turbellarians, cyclopoid and harpactacoid copepods, amphipods, and polychaetes (Melnikov 1997).  These species in turn support larger pelagic and avian predators that are closely associated with the ice (e.g. Arctic and polar cod).  The species composition and distribution of sympagic fauna can exhibit large spatial and inter annual variations due to the origin and history of the ice, the water depth, the physical and biological characteristics of the underlying water.  Despite variation, the dominant components of the sea-ice community are similar throughout the Arctic, and include the ice algae, cyclopoid and harpacticoid copepods, sea-ice amphipods, and polar or Arctic cod.  The following section will focus on these species, with reference to the associated upper trophic levels. 

ce algae form the base of the sea-ice food web.  Although primary production by sea ice algae is generally low compared to phytoplankton, they comprise the primary source of fixed carbon to higher trophic levels in ice covered waters (Arndt and Swadling 2006).  Gradinger (2010) noted that in portions of the Arctic Ocean, sea ice primary production accounts for 50% of the total annual production.  In addition, the sea-ice blooms in the spring coincide with the ice melt, representing an important early source of nutrition for zooplankton (Bluhm et al. 2011).  Ice algae primary production is controlled by available light and nutrients.  During the Polar night, production is limited by light availability.  However, increases in light during April and May initiates algal blooms.  As with phytoplankton production, nutrient limitation becomes a controlling force during these blooms.

The sea algal ice communities are diverse and variable throughout the Arctic, with hundreds of reported sympagic species (Sakshaug et al. 2009).  While centric diatoms are a dominant form in the phytoplankton community, ice algae are dominated by pennate diatoms (Melnikov 1997; Sakshaug et al. 2009).  Of 21 species observed in sea ice near Barrow, Alaska, only one centric diatom (Thalassiosirasp) was found in the sea ice.  Common diatoms found in sea ice include Nitzchia spp, Navicula spp, Pinnularia, Pleurosigma, Gomphonema, and Surirella.  Sea ice algae often exists as single cells within brine channels, with pennate diatoms being well suited to living in the limited space of brine channels.  Along the bottom of the ice, sea ice algae may also form dense mats or long strand communities (Melosira arctica).  Melnikov (1997) found long strands of the diatom Melosira arctica under multiyear ice that supports faunal communities.

Ice algae also form communities in melt-ponds of the pack-ice surface.  The melt-pond communities occur in the summer and autumn in brackish to marine waters that are created by melting snow and ice and marine water that penetrate upwards through channels in the ice.  Melt pond communities are dominated by unicellular green algae and flagellates that are commonly found in Arctic freshwater basins at altitudes from sea level to 3000 m (Melnikov 1997).  The communities shift to diatom-dominated communities as salinity in the melt ponds increases (von Quillfelt et al. 2009).

The sympagic mesofaunal community is dominated by harpacticoid and cyclopoid copepods (Kramer 2010).  These smaller copepods are generally considered to be epibenthic in nature, with feeding habits and morphology that makes them well suited to living in and under the sea-ice.  Harpacticoid and cyclopoid copepods can occur in populations as high as tens of thousands per m² in pack ice and are several orders of magnitude greater in abundance than the surrounding water column (Kramer 2010).  The highest population densities generally coincide with the highest algal densities and the more moderate temperatures and salinities, within the bottom 20 cm of the ice pack (Gradinger et al. 1999; Bluhm et al. 2010).  As with ice algae, sympagic copepods biomass and abundance is highly variable depending upon the ice age and location.  The copepod genera Harpacticus, Halectinosoma, Tisebe and Cyclopina appear to have a circumpolar distribution (Arndt and Swadling 2006).  However, the relative proportion of the dominant taxa varies with the type of ice, the region, and with season.  For example, the copepod H. superfluxus and other Harpacticus species appear the be nearly absent from the interstices of perennial ice in the Arctic ocean and the northern Barents and Greenland Seas (Melnikov 1997) and are scarce underneath old ice.  In contrast, in the seasonal fast ice of Frobisher Bay Canada, H. superfluxuspopulations can reach >380 individuals per sq. m.  Another harpacticoid species, Halectinosoma sp. is typically found in multi-year ice in particular near Svalbard and northern Greenland.  Both species can be found in areas where young ice and multi-year ice mix (Kern and Carey 1983). 

In Frobisher Bay, Grainger (1991) found two dominant copepods, Tisbe furcata and Cyclospina schneideri move to the ice in the winter months at a time when the algal production in the ice exceeds that of the sea bottom or water column.  The timing of the ice-ward migration for the two species differed, with Tisbe migrating gradually from February to April at which time, a new generation was produced.  The migration of Cyclopina consisted of only young copepods moving to the ice in early winter and remaining there until April, emerging as mature adults. Despite phytoplankton blooms in the water column in early June, the two ice copepods descend to the bottom to take advantage of the organic material dropping from the melting ice and the water column (Grainger 1991).

The feeding habits of harpacticoid copepods is considered to be herbivorous with little selective feeding (Grainger and Hsiao 1990; Kramer 2011), though many species will supplement their diatom-based diet with detritus during periods of low productivity (Arndt and Swadling 2006).  Tisbe spp. has also been found with fish larvae and copepod eggs and copepodites (Grainger et al. 1985).  Cyclopoids appear to be more omnivorous, with gut contents and lipid biomarkers showing a diet of diatoms, copepod eggs, and detritus.

Cyclopoid copepods are known to use sea ice for reproduction and development.  A large portion of the Cyclopina population is comprised of ovigerous females and up to three cohorts (Arndt and Swadling, Kern and Carey 1983) with a generation cycle of 31 days.  While the full life history of harpacticoid copepods is less well known, Arndt and Swadling (2006) infer that the ice is used for reproduction and growth, given that the eggs, nauplii and copepodite stages, as well as gravid females are found in the ice.  Furthermore, harpacticoid copepods can have >10 broods per year and a generation cycle of 20 days (Tisbe furcata).

The sympagic macroinvertebrate community is dominated by ice amphipods, in particular the pan-Arctic species Gammarus wilkitzkii, Apherusa glacialis, Onismus nanseni and O. glacialis (Hop et al. 2000; Melnikov 1997; Arndt and Swadling 2006).  These autochthonous amphipods reside primarily in sea ice, occupying the three dimensional structure under the ice, as well as somewhat limited use of the brine channels and structure created by the algal mats and strands.  Amphipod abundance is highly variable across the Arctic.  While all five of the dominant species are found in areas impacted with the perennial Arctic ice, Onismus spp. is more commonly associated with young, seasonal ice (Arndt and Swadling 2006).  The amphipod G. wilkitzkii is more abundant in multiyear ice, but will move from drifting multi-year ice to first year ice.

Allochthonous amphipods that are pelagic or benthic in origin are also found under the pack ice, generally taking advantage of the high spring production associated with the sympagic communities (Melnikov 1997).  Planktonic amphipods may include Parathemisto spp. which can be common at the ice-water interface and may occur in swarms of several hundred individuals per m² (Dalpadao et al. 2001).  However, most allochthonous species are benthic in origin, occurring in the land fast ice, or seasonal ice forming over shallow coastal areas.  Species may include Anonyx nugax, Anonyx sarsi, and G. setosuswhich may occur in abundance of tens per m² (Arndt and Swadling 2006)

Apherusa glacialis is an herbivorous amphipod and an important grazer of ice algae (Arndt et al. 2005).  This species concentrates along ice edges and beneath more translucent new ice, where the onset of primary production takes place (Hop et al. 2000).  The diet may shift towards detritus when algae become less abundant in winter.  In areas with high amphipod abundance, the ice algae biomass may decrease at a rate of 30% to 60% of the standing stock per day (Arndt and Swadling 2006).  Phytodetritus is a major food item for Onismus spp.; however, O nanseni is a species repeatedly collected by baited traps, scavenging on carcasses and live prey including sympagic harpacticoid and cyclopoid copepods.  Gammarus wilkitzkii is primarily a predator, catching copepods, chaetognaths and other live prey, as well as amorphous organic debris, diatoms and microflagellates.  Other Lysianassid amphipods that move from pelagic or benthic communities to the pack ice are typically generalists feeding on ice algae, detritus, copepods, and fish eggs. (Arndt and Swadling 2006)  These species can occur in large swarms and in turn become an important food source for Arctic and Polar cod. 

Sympagic amphipods have perennial life cycles and are thought to spawn once a year. Apherusa glacialis can reach 2 years in age but has a high fecundity (>500 eggs develop for 6 months in a female’s brood pouch).  Offspring are released between March and August, presumably to take advantage of the spring growth of ice algae (Arndt and Swadling 2006).  The life span for Onisimus spp. is 2.5 to 3.5 years (Hop et al. 2000).  The reproductive cycles for the two species are offset, with O. glacialis spawning a few months earlier than O. nanseni.  Both species have one brood per year and produce approximately 100 eggs over the female’s life span. G. wilkitzkii is the longest lived ice amphipod, having a 5 to 6 year life span.  This species matures after two years and has one brood per year, releasing 90 to 250 eggs per year.   Eggs are deposited into the females marsupium during winter and release them in April and May when primary production peaks in ice-filled waters.  However, they can be flexible as the amphipods (such as G. wilkitzkii) are generalists and can release young April to September.

The pelagic calanoid copepods common in the Arctic are commonly found under the pack ice, particularly during the spring bloom (Melnikov 1997; Arndt and Swadling 2006).  While they do not appear to colonize the ice, the eggs and nauplii may be advected to the ice sheet.  Calanus glacialis, C. hyperboreus, Pseudocalanus acuspes, Metridia longa, and Oithona similis perform diel vertical migrations to the ice surface at dusk (Fortier et al. 2001) to feed at the ice-water boundary.  Biomass estimates for pelagic copepods are highly variable and are typically highest during the spring bloom, particularly during the ice melt (Arndt and Swadling 2006).  There are some indications that during this time of both ice algae and phytoplankton blooms, calanoid copepod build up a significant portion of their lipid reserves.  The ice-water interface can be an important nursery ground for Calanoid eggs and nauplii, providing food and shelter.  Other omnivorous copepods, such as M. longa come to the sea-ice to feed on Calanus eggs and the small ice crustacean, as well as sympagic diatoms.

Both B. saida and A. glacialis spend a portion of their life history in close association with the sea-ice, utilizing cavities and ledges on the underside of the pack ice, as well as the edges of melting ice floes (Lonne and Guilliksen 1983; Gradinger and Bluhm 2005).  The larval and juvenile life stages are commonly found individually or in small groups, with adults are seldom found in close association with the ice.  In multiyear and first year ice, Lonne and Guilliksen (1983) found both one and two-year old fish living in and under the pack ice.  No fish older than 2-year-olds were observed. 

The diet of Arctic cod in multiyear ice is comprised of a mixture of sympagic amphipods as well as pelagic copepods (Lonne and Gulliksen 1989; Melnikov 1997).  In first-year ice, Lonne and Gulliksen (1989) found the Arctic cod diet dominated by calanoid copepods, however, this was likely due to the distribution and abundance of food items.  Arctic cod have been observed feeding on sympagic amphipods in first year ice in other regions of the Arctic.  Younger cod tended to favor harpacticoid and cyclopoid copepods, shifting to the larger prey with age (Bradstreet 1979).  The amphipod, G. wilkitzkii, was seldom found in Arctic cod stomach contents.  This is likely due to the large size and spiny morphology of the G. wilkitzkii.

Ice amphipods and the more energy rich polar cod are subject to strong predation by top carnivores.  The sympagic macrofauna is a major link in the transfer of energy from sympagic primary producers to the ice-associated sea birds and marine mammals. 

Ice seals are perennial predators under the ice.  The seal diet is variable and is based on food availability.  Based on stomach contents and fecal analysis from seals in the high Canadian Arctic, Arctic cod comprised the majority of the adult ringed seal (P. hispeda) diet, with small proportions (approximately 8%) of amphipods and larger pelagic copepods (Bradstreet and Cross 1982).  Immature seals had a diet that was numerically dominated by ice amphipods, with approximately 3% cod.  However, the cod comprised 62% of the biomass in the stomach contents.  Both A. glacialis and B. saida were present in the stomach contents of young seals.  When Arctic cod are less common, a variety of crustacean species dominate the stomach contents, including ice-amphipods, mysids and other under-ice fauna (Melnikov 1997).

Other seals living amongst the ice include the leporine or bearded seal (E. barbatus), the harp seal (P. groenlandica), and hooded seal (C. cristata).  Erignatus barbatus is primarily a benthic feeder primarily on mollusks, crustaceans, and demersal fish including B. saida and A. glacialis (Melnikov 1997; Finley and Evans 1983).  Four taxa dominate the hooded and harp seal diets in Greenland: Arctic cod, capelin, the squid Gonatus fabricii and the pelagic amphipod, Parathemisto sp. (Haug et al. 2004).  Based on the stomach contents and satellite tracking data, the feeding habits of these two species is more pelagic in nature and not necessarily associated with the communities under the ice.

Sea birds are a primary consumer of sympagic fauna while their access is limited to areas with open water along ice edges.  Important avian predators include northern fulmars, black legged kittiwakes (Rissa tridactyla), guillemots (Uria lombia and Ceppus grille), murres, thick-billed murres, Little auks (Alle alle), and gulls.

Kittiwakes, Black guillemots (C. grille) and Brunnichs guillemots (U. lombia) and murres feed mainly on polar cod.  Other guillemots feed on fammasur in the Canadian Arctic and Themisto spp when the water is ice free.  In the Barents Sea, Little auks forage in multiyear ice mainly on A. glacialis (makes up 80% of their diet).  In the Canadian and Norwegian Arctic, the diet of Little auks is primarily C. glacialis (Falk-Petersen et al. 2007). 

The key VECS for four Arctic realms are presented in Table 2-1.  In many cases, the species overlap between different realms.  For example Calanoid copepods, Arctic cod, and amphipods play a key role throughout Arctic food webs.  Additionally, interface habitats that contribute to the functioning and diversity of the Arctic should be further studied. These habitats include: surface microlayer, ice edges and ice margins, under-ice flora and fauna, water mass convergence zones, demersal communities and shorelines.

Determining areas of seasonal population aggregations of VECs is important to inform NEBA decision making. However, these efforts require information on life-history and presence/absence data for each VEC.  Such analyses have been done for certain portions of the Arctic including the US and Canadian Beaufort.    An example of such an effort is the Beaufort Regional Environmental Assessment (BREA) program in the eastern Beaufort.  Seasonal movements of VEC species have been overlain with traditional hunting grounds and other data to create VEC vulnerability profiles that indicate specific locations and time periods where the population may be sensitive to certain OSRs (Trudel 2013).  As an example, data has been summarized for White whales (D. leucas) as they enter the eastern Beaufort in early June, with adults and young congregating at the mouth of the Mackenzie River delta (Figure 2-10).  During July, population densities are highest close to the mouth of the river, in areas used by indigenous fisheries.  In September and October, all whales leave the area.  Based on the vulnerability analysis, the White whales would be most vulnerable close to the mouth of the river during July. This approach has been used in different portions of the Arctic; a pan-Arctic compilation of such data would be useful to OSR strategizing.

Table 2-2.  Valuable Ecosystem Components of Arctic Communities

There has been a dramatic increase in data available on various aspects of marine Arctic communities over the last decade, particularly on the pan-Arctic distribution of species and trophic interactions.  New studies include investigations of the trophic links within different systems (e.g. the central role of Arctic and Polar cod and Calanoid copepods in the pelagic food webs).  The review of Arctic ecosystems and VECs described by the authors in this section led to suggestions of further research which can reduce remaining uncertainties.  The more generic recommendations for further research compiled from this review are summarized below while recommendations that are important for improving Arctic NEBA are listed separately.

1. Continue studies on Arctic faunal groups.  Some Arctic populations are now well understood in terms of natural history and toxicological profiles; however, groups of species require further examination regarding trophic roles, distributions, abundances, and ecotoxicological profiles based on annual and Interannual patterns.
   1. Knowledge of the interrelationships of Arctic species in areas of high productivity could benefit from further attention, especially with respect to migration and emigration through river systems, lagoons, and polynyas.
   2. The distributions and abundances of benthic and bathypelagic communities of the Arctic are not well known.  Boulder patch and other isolated areas of hard substrate as well as lagoon systems have proven to be important areas of increased production in the Arctic, but have received little attention.  While there have been some studies evaluating the deep sea communities particularly in the Norwegian Deep, eastern Beaufort, and parts of Baffin Bay, there are substantial portions of the Arctic deep water that have not been assessed.  This is a difficult area to characterize; however, recent studies in the High Canadian Arctic (Geoffroy et al. 2011, 2013; Reist and Majewski 2013) indicate that during certain portions of the year, Arctic cod can be found in large numbers in deeper waters of the Arctic.  There are indications that VECs known to occupy the deep sea habitats in other oceanic basins are present in the Arctic (e.g. myctophids, deep-sea corals), however, these communities are not likely to be disrupted by near-term oil and gas activities.  Deep water assessments would become important if there were a deep water release from a drilling platform.
2. Continue pan-Arctic data collation.  Data from holistic efforts, such as BREA and RUSALCA could be collated and put into a GIS platform.  VEC species or regions for which there is not sufficient data may require additional data collection efforts.  These types of efforts generally occur as new areas are open for exploration or development.
3. Evaluate ecosystem services.  Ecosystem services are the conditions and processes through which natural ecosystems and the species that comprise them sustain and fulfill human needs (Daily 1997).   Marine ecosystem services include functions that support human life, such as the production of ecosystem goods (e.g. seafood) and cleansing and sequestering wastes (e.g. uptake of excess nutrients by phytoplankton).  The marine ecosystem confers intangible aesthetic and cultural benefits (Kaufman and Dayton 1997; Peterson and Lubchenco 1997) to residents of the Arctic.

There are only a handful of studies useful to understanding the trophic interactions of emerging habitats of concern (e.g. interface habitats and deep-sea basins of the Arctic).  The recommendations presented below indicate where increased knowledge of Arctic ECs and VECs would result in reducing existing uncertainties in NEBA assessments. No prioritization has been made to the list; for some of the recommendations, surrogate data may be already available.

1. Expand knowledge of Arctic ECs.  Assessment of Arctic ECs should be expanded to include the communities populating interface habitats. These habitats include: sea surface microlayer, ice edges and margins, under-ice flora and fauna, water mass convergence zones, demersal communities, and shorelines.  These specialized habitats and resident or transient species may contribute significantly to the overall functioning, diversity, and resilience of the Arctic.  While the effects caused by individual OSR actions to key VECs living in the open water pelagic environment has been examined, repercussions of oil exposure to aggregating communities within convergent interface habitats is less well understood. 
   1. The surface microlayer (SML).  The surface microlayer refers to the uppermost surface layer(s) of the ocean.  The depth of the layer(s) is defined differently by physical oceanographers, chemists and biologists based on their conceptual model developed to address their different fields of interest.  Physical oceanographers and atmospheric scientists view the layer as the interface between the air and water while chemical oceanographers describe the layer based on the behavior of hydrophilic and hydrophobic moieties of chemical compounds.  Biological oceanographers define these layers based on where organisms and life stages reside or interact with the sea surface.  Certain communities of plants, invertebrates and vertebrates spend all of their life history at the sea surface and these are typically referred to as neuston.  The SML also acts as a nursery ground for many larval fish and invertebrate species, including larval species settling onto intertidal surfaces.  This group of surface oriented species represents a community of organisms that is most closely associated with surfaced oil as the oil sheen spreads over the water’s surface.  Whether the oil sheen is only a few microns or centimeters thick the organisms that contact this layer are exposed to the highest oil concentrations with the potential of activating multiple modes of toxic action.  In some cases larger marine organisms can skim feed on the concentrated masses of food and contaminants (certain fish, birds, and mammals) while others swim through the layer(s) to breath.  An understanding of the role of the neuston in the pelagic and intertidal food webs is needed to better characterize the impacts of surfaced, untreated oil and potential recovery rate of this vital micro-compartment.  Exposure to oil at the upper sea surface layer may result in additional toxic stress via different modes of toxic action, including fouling and respiratory stress from evaporating volatile compounds.
   2. Ice edges and margins, polynyas and other interface communities.  Polynyas have been identified as areas of enriched abundance and production during the Arctic winter.  Pelagic-benthic coupling is also showing that the increased pelagic activity is mirrored in the benthic community.  These different communities are typically an aggregation of species already known to be important in other portions of the Arctic.  Identifying and further studying the importance of these areas is of importance for the selection of OSR alternatives.
2. Emphasize functional role of faunal groups.  The list of VEC species to be included in NEBA analyses is not static for all areas of the Arctic.  Emphasis will be placed on functional roles while addressing regional differences. New information regarding trophic food webs, population abundances and distribution patterns as well as toxicological profiles of VECs should be continuously expanded and updated (e.g. for ophiuroids, hard corals, jellyfish and neuston).  Population size estimates of VECs that occupy interface habitats compared to bulk pelagic waters is needed to determine the relative impact of the various OSR options.
3. Increase understanding of resiliency and potential for recovery of Arctic species and populations.  An evaluation of the resiliency of potentially impacted populations of VEC species within Arctic ECs is critical in determining the ultimate biological consequences of each oil spill response considered during emergency oil spill response planning. Generic metrics for resilience should be developed and scored for keystone VECs. Refer to Sections 7, 8 and 9 for further concept development (Population Effects Modeling, Ecosystem Recovery, and NEBA for Oil Spill Response Options in the Arctic, respectively).

Authors William Gardiner and Dr. Jack Q Word (ENVIRON), Ida Breathe Øverjordet (SINTEF), Dr. Oleg Titov and Andrei Zhilin (PINRO), Dr. Thierry Baussant (IRIS) 

The type of oil designates the relative spectrum of chemical components present in the oil, e.g. fuel oil versus heavy crude oil.  Table 3-1 summarizes the various chemical components that may be present in oil.  The properties of the oil itself will define the physico-chemical interactions that will ensue following release to the marine environment, and will influence the important processes represented in Figure 3-1 (e.g. spreading, dissolution, evaporation).

When oil is spilled at sea, a number of natural processes change the physical and chemical properties of the oil and influence interactions with seawater and ice. These natural processes are spreading, drifting, evaporation, dissolution, photolysis, biodegradation and formation of oil-in-water (dispersion) and water-in-oil (w/o) emulsions. The relative contribution of these processes varies during a spill under cold conditions.  Figure 3-1 illustrates how the different weathering processes vary with time. Evaporation is, for example, most important the first days after the spill, while biodegradation is a significant process one to two weeks after the spill (see Section 5). The behavior of spilled crude oils and petroleum products depends on the oils physical and chemical properties, the release conditions, and the environmental conditions (e.g. temperature, waves, wind, currents, presence of ice).  Factors that increase the spread of an oil slick are gravity and net interfacial tension whereas inertia and viscosity retard its motion (Hollebone 1997).

Table3-1.  Oil constituents based on carbon composition

¹Organic carbon/water  partition coefficient

Figure 3-1. Weathering processes relative importance with time (Adapted from Mackay et al. 1983)

A key determinant of oil weathering is based on the viscosity of the oil mixture.  This property largely affects the tendency of the specific oil to spread out on surfaces under cold conditions.  Oils have a range of viscosities; less viscous oils cover larger surface areas than the more viscous oil types which also tend to spread more slowly.  As the oil spreads and the thickness of the oil slick becomes thinner, the release of soluble and volatile compounds is increased.  The cold temperatures in the Arctic increase the viscosity of the oil and thus reduce the rate of spreading on surfaces.  The reduced spreading and increased thickness of the oil decreases the loss of volatile and soluble components to the air or water, respectively.  The cold temperature also slows the rate of volatility and solubility of the chemical compounds. 

These changes in viscosity and the impact that has on volatile and soluble compound releases is one factor that extends the time scales portrayed in Figure 3-1, allowing an extended time period for OSR actions to be implemented.  Since the Arctic is significantly influenced by seasonally prevailing climate conditions, oil behavior changes according to summer, winter, and transitional seasonal conditions.  During the summer periods surface oil may encounter shorelines, lagoons, estuaries, and convergence zones in open waters.  Although the fate of oils during this season is generally similar to non-Arctic environments, factors such as lower temperatures and decreased viscosity of the oil reduce the speed of volatilization and the occurrence of 24-h light periods increasing the potential for UV activation on constituents such as PAHs that can impact organisms, especially those living near surface waters.  The influence of these factors on biodegradation and exposure to organisms is similar to other high latitude non-Arctic environments. The influence of cold water on shoreline stranding to various substrates during ice-free periods is an area of ongoing study. Oil may become entrained within or under the ice during winter conditions as seawater becomes covered in ice.  In ice-covered waters, several studies have indicated that the time-dependent weathering processes can be slower as a result of less energy input, increased oil film thickness, and lower temperatures.  Pack ice consists of a variety of ice types depending on the season.  In the fall, pack ice may contain a mix of older ice from the previous winter, vast floes of thin new ice known as “nilas”, and patches of newly forming ice.  In the spring, pack ice consists of deteriorating first year floes.  Frazil or slush ices are typically associated with freeze-up whereas brash ice is typical of spring melt (Buist et al. 2003). 

The bioavailability of oil components in the water column is governed by processes both generating and depleting bioavailable oil fractions.  While the process of generating oil droplets and dissolution of water soluble components are reasonably well understood, the potential importance and kinetics of the depletion processes determining the fate of oil in ice and oil droplets in the water column are not well understood.  Chemical dispersion, which increases the fraction of dispersed oil, is now more frequently included as one of the response actions after an oil spill, but not in all countries.

This section focuses on the physical fate of oil, relevant for Arctic conditions, with emphasis on identification of literature and studies of operative importance. An extensive body of research performed both in the field and in the laboratory over the last 30 years has aimed at understanding the fate, behavior and weathering processes for oil spilled under Arctic conditions.  Most of this research has been performed in USA, Canada, and Norway.   Numerous field investigations including spills of opportunity, laboratory and tank tests, and theoretical modeling of the fate and behavior of oil under Arctic conditions have been summarized by Dickins and Fleet (1992), Hollebone (1997), Fingas and Hollebone (2003), Brandvik (2007), Sørstrøm et al. (2010), SL Ross et al. (2010), and Dickins (2011).  These compilations of salient technical elements from this broad range of historical studies contributes to the current knowledge base of information on the physico-chemical interactions of oil and sea ice. 

Experimental oil releases under solid ice (up to 6 tons per spill) were performed in the 1970s and early 1980s (reviewed by Hume et al. 1983).  The first experimental oil spill in broken ice was carried out in 1986 on the Canadian East Coast (SL Ross and Dickins 1987).  This project was followed by the first large-scale experimental oil spill (26 m³ oil) in April 1993 in the Barents Sea marginal ice zone (Vefsnmo and Johannesen 1994; Singsaas et al. 1994). These field experiments proved invaluable in understanding the weathering processes of oil in a variety of spill scenarios and environmental conditions (including wind, waves, ice conditions, drift and spreading in the marginal ice zone).  The studies clearly showed that marine oil spills have different weathering properties under Arctic conditions compared to spills under more moderate temperatures (Brandvik et al. 2004).

The different aspects of oil weathering in Arctic environments have been summarized by Payne et al. (1991a) and field observations regarding weathering at low temperatures and in broken ice were also studied in small- and meso-scale lab facilities (Singsaas et al. 1994).  The findings from an experimental oil spill of 3400 liters of Statfjord crude under first-year sea ice on Svalbard in March 2006 are described in Dickins et al. (2007).  The experiment demonstrated the ability of ground penetration radar to detect and map oil under natural sea ice from the surface.  It also documented oil weathering beneath relatively warm ice sheets under spring conditions.

Several reports provide good overviews of the state of knowledge, e.g. the final report from the Norwegian program “Oil spill contingency in cold and Arctic areas” – ONA I and ONA II (Løset et al. 1994) and “Oil spill response in ice infested waters” (Vefsnmo et al. 1996). The ONA research program included information on physical environment, behavior and properties of oil and oil spill response (biological, burning, dispersing, emulsion breaking, and mechanical oil recovery).  Later work evaluating the status and research needs for future oil in ice research was presented in Dickins (2004), Owens (2004), and Brandvik et al. (2005 and 2006).

Photo 3-2. Oil-in-Ice JIP field investigation (SINTEF, Liv-Guri Faksness)

Fingas (1992) summarized accidental spills and the experiments conducted from the 1970s up to 1990 to gain knowledge and understanding of the interactions occurring when oil is discharged in water where ice is present.  A more recent review (Fingas and Hollebone 2003) summarized the studies of oil behavior in ice infested environments related to the specific ice situation or behavioral mechanism.  The authors concluded that the knowledge basis of the complex behavior and fate processes associated with oil spills in ice infested water should be improved in order to better predict oil behavior and fate in an ice infested environment.

The latest large-scale field experiment took place in the marginal ice zone in the Barents Sea in May 2009 as a part of the Joint Industry Program (JIP) to develop and advance the knowledge, methods and technology for oil spill response in Arctic and ice-covered waters (Oil-in-Ice JIP; Brandvik et al. 2010).  Fresh oil (7000 liters) was released uncontained between the ice floes to study oil weathering and spreading in ice and surface water throughout the six-day experiment. In addition, meteorological and oceanographic data that were monitored included wind speed and direction, air temperature, currents and ice floe movements.  The monitoring showed low concentrations of dissolved hydrocarbons; the predicted acute toxicity associated with that level of exposure indicated that the potential for acute toxicity was low. The ice field drifted nearly 80 km during the experimental period, and the oil drifted with the ice and remained contained between the ice floes (Faksness et al. 2011a).  The JIP summary report gives an overview of the total program, main findings, and the technical reports (Sørstrøm et al. 2010). Findings from the program show that the presence of cold water and ice can enhance response effectiveness by limiting oil spreading and slowing down the weathering processes, resulting in an increased window of opportunity for in-situ burning or use of dispersants compared to ice-free conditions.

After release to the Arctic marine environment, oil will gradually weather due to natural physical and chemical processes including spreading, evaporation, dispersion, emulsification, dissolution, and chemical modification by oxidative processes (refer to Figure 3-1). From earlier studies it is known that this weathering is influenced by the oil composition, release conditions, temperature, water quality, and solar radiation (Duursma and Dawson 1981, Sydnes et al. 1985, and Sydnes 1991).

Environmental conditions will influence an oil spill in the Arctic differently compared to temperate regions, particularly under conditions of lower temperatures, the presence of ice, and different light conditions. Low temperatures and lack of waves in ice act to reduce oil spreading, evaporation, emulsification and dispersion (e.g. Brandvik et al. 2010).  Wax and asphaltene content of oils that act in combination with reduced spreading due to temperature-dependent oil viscosity differences combined with reduced weathering that occurs within the more stable ice fields are important aspects of the fate of oil in the Arctic.  These factors extend the period of time when various response actions can be deployed.   

Different locations of spilled oil associated with ice are: oil between broken ice, oil under the ice, submerged oil, and oil on the surface of the ice including oil in melt ponds as shown in Figure 3-2. . The oil can be entrapped in ice and become difficult to track particularly during the winter darkness. The sequestering of oil also results in a secondary discharge situation during the spring season, where the oil released from the ice appears relatively un-weathered (Payne et al. 1991a and 1991b).  In the spring and summer season chemical photo-oxidation of oil may become an important hydrocarbon degradation process.  The water-soluble components released from the encapsulated oil may be transported through the brine channels, thereby contacting sea-ice microbes in the brine and the underlying water.  Ice fauna do not avoid the exposure by moving to non-oiled ice locations and may be exposed to toxic water-soluble components for a prolonged period of time while the oil is present within the brine channels, crack and crevices of the ice.

In the summer, local melting enhanced by changes in albedo due to the presence of oil causes the ice to break up weeks earlier than normal seasonal break-up.  Once the oil reaches the surface of the ice or within leads or polynyas, evaporation and other weathering processes commence.  However, low temperatures and increasing film thickness due to confinement in ice reduce the rate and degree of evaporation (e.g. Brandvik and Faksness 2009, and Brandvik et al. 2010).  As the ice cover dwindles, the oil slick begins to act similarly to open water conditions.  Since biological activity is high in early spring, and the amount of open water available for birds and mammals is small, the release of oil into leads and polynyas at this time would be expected to be damaging to resident and migratory species (AMAP 1998).

The presence of ice reduces the wave activity (breaking waves), and emulsification usually decreases with increasing ice coverage.  The water uptake rate decreases with increasing ice coverage due to the wave damping effects, and will be slower in dense sea ice.  The viscosity increases with increasing water uptake and evaporation as in open sea, but the increase will be slower due to reduced evaporation and water uptake. The rate of natural dispersion decreases with increasing ice coverage and could be very low due to reduced energy conditions in the ice (Singsaas et al. 1994, and Brandvik et al. 2010).  Spreading of oil in ice is dependent on ice type and ice coverage with oil film thickness increasing with increasing ice coverage (Vefsnmo and Johannesen 1994, Fingas and Hollebone 2003, and Brandvik and Faksness 2009).

Figure 3-2. Weathering of oil spilled in ice infested environment (AMAP 1998).

Spill response strategies in open waters versus the ice seasons (spring breakup, fall freeze, and winter) are expected to be fundamentally the same.  Table 3-2 presents general characteristics of oil movement with associated ice conditions.  Oil drifting in ice-covered waters is very dependent on the amount of surface area covered by ice.  The knowledge about oil drift in ice and oil-ice interactions is limited, but the current assumption is that at ice coverage less than 30%, the drifting of oil will be independent of the ice.  At ice coverage greater than 60-70%, the oil will mainly drift with the ice (Vefsnmo and Johannesen 1994).  Under pack ice conditions, oil will move with the ice.  The rate of drift of pack ice influences film thickness and areal distribution of spilled oil.  Ultimately, the rate of pack ice drift determines the magnitude of offshore logistics required to recover released oil since the ice can travel hundreds of km in a few months.  Open drift ice presents a challenge for spill containment and recovery.  The ice itself can contain oil as a natural boom and encapsulate oil as the ice begins to freeze resulting in transporting the oil away from the active response areas.

Photo 3-3. Field experiment during Oil-in-Ice JIP program (SINTEF)

During a six-day experimental field trial in the Barents Sea in May 2009 the ice concentration in the area varied from 70 to 90% (Faksness et al. 2011a).  During this experiment a storm occurred which resulted in transport of the oil and ice over a long distance. However, the key observation is that even under storm conditions the oil slick was still contained within the ice field, thus the monitoring during the experiment verified that in high ice concentrations oil drifts with the ice.

Prevalence of ice is indicative of environmental conditions that do not facilitate weathering of oil:  low air and water temperatures as well as a relative lack of waves significantly reduce the rate of evaporation, natural dispersion and emulsification.  Additionally, oil spilled in the Arctic marine environment can be rapidly frozen into the ice as the ice grows downwards and encapsulates oil beneath or within the ice during freezing.  Once the oil becomes fixed within ice, it moves only as the ice moves. The oil will in this way be preserved, in the sense that evaporation, dissolution, and degradation are expected to be reduced (Hollebone 1997).

Table 3-2.  Sea ice and behavior of oil

¹Ratio of pack ice to visible open water; adapted from Dickins 2011

This implies that the oil will retain much of its potential toxicity upon release from the ice, either via transport in brine channels, and/or eventual breakup and melting of the ice.  Work to date has led to a good general understanding of the key processes controlling the behavior of fresh and emulsified crude oil in a variety of ice conditions, including landfast and broken pack ice.    The encapsulated oil will be released in the spring as the ice sheet deteriorates.  Oil escapes from the ice sheet by a combination of two general processes: Vertical rise of the oil through the brine channels and ablation of the ice surface down to the oil lens in the ice (Fingas and Hollebone 2003).  Oil, initially trapped under or in the ice, may appear on the upper ice surface due to density-mediated migration up through the open brine channel pathways.  Migration rates of oil in brine channels during the spring thaw may vary as a function of oil chemistry and viscosity, as controlled by water contents due to previous emulsification and temperature gradients within the ice, as well as depth in the ice canopy (Martin 1979, and Payne et al. 1991a).

When oil is released or drifts into an area with ice, spill responders will face a complex interaction between oil, water and ice.  A review by Fingas and Hollebone (2003) summarized the studies of oil behavior in ice environments under the topics of specific ice situations or behavioral mechanisms.  The oil will be absorbed by snow on the ice edges, it may be trapped in the ice in brine channels (Faksness and Brandvik, 2008b) or it may be moved underneath the ice.  The ice field will also be under a constant transformation driven by wind, currents and temperature.  The result over time is that the individual ice floes may change their relative position and melt or freeze.  Some ice floes may be transported relatively far from both their original position and their original neighbors, which may be a strong driving force for the drift and spread of oil after oil has been released in an ice field.

Until recently, most of the research conducted on migration of oil through ice has focused on bulk oil (e.g. NORCOR 1975, Martin 1979, Payne et al. 1991a Reed et al. 1999, Fingas and Hollebone 2003, and Brandvik et al. 2004).  Existing conceptual models for oil-in-ice mainly discuss upward migration of oil through brine channels during melting, due to density differences, solar radiation and heat capacity of the oil.  Very few studies have actually attempted to determine the transport and fate of individual compounds, such as PAHs or changes in oil compositions in ice scenarios.  The field and tank studies of Payne et al. (1991a and 1991b) show that dissolved aromatic hydrocarbons in brine waters are effectively transported downward with the dense brine water.  The knowledge of the migration process of the water soluble components from oil encapsulation in ice has been very limited. However, recent work from three field seasons with oil encapsulated in first-year Arctic sea ice on Svalbard has shown that the more soluble oil components are transported downwards through brine channels (Faksness and Brandvik, 2005, 2008a, 2008b, and Faksness et al. 2011b).  Furthermore, the results from this research suggests that the presence and dynamics of brine channels transports the bioavailable oil components downward from an “encapsulated slick” through diffusion and advection. These observations are in accordance with the findings in laboratory experiments with sea ice columns, which have shown that there is a downwards migration of water soluble oil components from oil encapsulated in the ice, and that the migration starts after spring thawing has increased the porosity of the ice (Faksness et al. 2011b).  However, Faksness and Brandvik (2008b) observed an upward migration of oil during their field experiments on Svalbard, but no upward transport was observed during the melting process in these laboratory experiments, indicating that the tide movement, sunlight, and albedo effect are important factors that should be taken into account.  The differences in the oil’s migration rates as a function of oil properties and chemical composition are illustrated in Photos 3-4 through 3-7.  As can be seen in the upper photos in this figure, the major part of the encapsulated oils of Heidrun Åre (naphthenic oil) and Goliath had migrated through the brine channels to the surface.  For Kyrtael (bottom left photo), which has high wax contents and a pour point of 8 °C, there had been some vertical rise through the ice, but mainly only melting of the ice over the oil.  The major part of the oil was still encapsulated in the ice. The heavy fuel oil, IFO 180 (bottom right photo), was still encapsulated in the ice, and no upward migration had occurred.  IFO 180 was the oil with the highest viscosity in these experiments. The transport and fate of oil components within different oil types need to be performed in order to determine the controlling aspects of what portions of the oil move within an ice column.

Photos 3-4—3-7. Details from sampling of ice cores with encapsulated oil in June, 2004. Melt ponds with Heidrun Åre and Goliat in the upper photos, and Kyrtael and IFO 180 in the bottom photos (From Faksness 2008c).

The short and long term fate of stranded oil in the Arctic has not been extensively studied.  What is known from other environments is that the slope and sediment characteristics of the intertidal environment has a strong influence on the retention of stranded oil.  Additionally, those studies in non-Arctic environments also indicate that oil stranded in deep sediments, especially within cobble intertidal environments can retain oil that continues to impact the environment for decades (Etkin et al. 2007; Peterson et al. 2003).  In contrast, stranded oil on sandy intertidal environments with ice is subject to large physical disturbances when the ice begins to break up and is remobilized during that period (Potter et al. 2012; see also Section 4).  Therefore, the preferred OSR option should protect cobble beach environments from oiling because of the extended residence time of oil that does not undergoing significant weathering.  In most instances, the presence of ice-covered water or ice in the shore zone prevents surface oil from making contact with the shoreline substrate.  Owens (2004) summarized the following relevant scenarios for oil on icy shorelines:

• Where oil comes in contact with exposed ice surfaces, the oil is unlikely to adhere except in cold temperatures when the air, water, and oil surface temperatures are below 0 °C.
• During freeze-up, oil present on the shore or stranded on the shore-zone ice during a period of freezing temperatures can become covered and encapsulated within the ice.
• During a thaw cycle, or if the surface of the ice is melting and wet, oil is unlikely to adhere to the ice surface and would remain on the water surface or in shore leads.
• In broken ice, without a landfast ice cover, oil may reach the shore and be stranded on the substrate in between the ice floes.
• If continuous shore-fast ice (an ice foot) is present, the ice may protect the shore zone, but in the few instances when near shore ice is present adjacent to the shore zone as a solid floating ice layer, oil can migrate through ice cracks and accumulate under the ice.
• Ice in beach sediments (frozen groundwater) can prevent the penetration of stranded oil.

The fate of oil that becomes associated with intertidal and subtidal sediment has been extensively studied in many areas throughout the world and there are good predictive models that describe the uptake of toxic components from sediment based on the concentrations of organic carbon and the octanol-water partition coefficient (K_ow) of the compounds.   There are also excellent studies on the reduction in bioavailability of the toxic compounds based on the decreased desorption that occurs with time.  These studies are not a part of the current review but demonstrate that oil associated with sediment becomes less bioavailable to processes of toxicity and presumably biodegradation.

The first association of oil with sediment occurs within the water column where it comes in contact with suspended sediment grains or solids.  If the specific gravity of the suspended sediment is sufficient to counteract the buoyancy of oil droplets then the combined materials will settle to the substrate at rate that is based on Stoke’s Law.  The current literature review identified a number of studies on oil-mineral-aggregation (OMA) with focus on use of fine, clay-sized particles.  Some studies have included systematic variation of oil type, salinity, presence of dispersants and mineral type, thereby increasing our understanding of the importance of these variables in OMA.  Many of the studies have focused on the potential use of fine mineral aggregation as a combat technique for free floating and beached oil spills, but there is a lack of systematic studies on the adsorption and trapping of oil in bottom sediments under turbulent conditions in shallow waters. The size and density of these mineral particles and their association with oil droplets counteract part of the buoyancy of the oil droplets, suspending the mixtures in the water but the buoyancy is not sufficiently impacted to have them settle rapidly.   

Etkin et al. (2007) has prepared a literature review on state-of-the-art on modelling interactions between spilled oil and shorelines.  They state, in general, that OMA does not play a significant role in the fate of oil in the early stages after oil deposition on the shoreline, and, as such, is of relatively minimal importance in shoreline-oil interaction modelling efforts; however, OMA may play a role in longer-term shoreline processes.  Oil/sediment interactions may be very important in areas where there are higher concentrations of fines or in areas with coarse gravel and cobble with sub-surface open spaces that can trap oil.  A number of studies focused on OMA as a pathway for transport of oil from shorelines, sea-surface and the water columns to the seafloor.  These studies emphasize the modification to the settling rates that occur with well mixed oil and OMA and tend to over predict the amount of oil that would settle to the bottom.  Lee (2002) has also given an overview of OMA formation, including the formation of OMA as a method to mobilize and remove stranded oil from low-energy, intertidal environments.  Increasing knowledge of this process has fostered the development and evaluation of oil spill countermeasure strategies based on the promotion of oil-particle interactions.  Muschenheim and Lee (2002) provide a comprehensive literature review of the role of oil-particle interactions in removal of petroleum hydrocarbons from the sea surface and provide estimates of the small degree to which presence of particulate matter augments the deposition of oil. They discuss the interaction between oil weathering, placement methods of the OMA on the oil, sinking, adsorption, microbial processes, flocculation and ingestion by zooplankton, which all contribute to packaging oil and suspended particulate matter (SPM) into settling aggregates.  Findings from the literature covering many of these processes are described in the following.  The majority of published literature on characterization of adhesion of oil to particulate matter has focused on OMA, where much of the work has been directed towards investigation of OMA as a response action.  Delvigne (2002) investigated the physical appearance of oil in three types of oil-contaminated sediment.  Microscopic observations showed possible presence of three oil phases in the sediment as distinct oil droplets, oil coating on sediment particles and as 'oil patches'.  It was concluded that the division of oil in the different phases affects the oil-sediment interaction processes.  A number of studies have focused on adhesion properties in general, uncoupled to a mechanistic understanding of the process (Sterling et al. 2004, Ajijolaiya et al. 2006, Ma et al. 2008, Devadoss et al. 2009, Lee et al. 2008, Lee et al. 1996, and Weise et al. 1999).  These studies show that OMA can be an important process for determining the fate of oil in scenarios where the properties of oil are favorable, and mineral fines are present in necessary quantities.

Studies on the effect of viscosity of oil on OMA (Kepkay et al. 2002, Danchuk and Wilson 2011, Omotoso et al. 2002, Payne et al. 2003, and Stoffyn-Egli and Lee 2002) have shown that oils with low density have a higher propensity to form OMA than oils with higher density.  Other studies have focused on the effect of salinity on OMA (Danchuk and Wilson 2011, Guyomarch et al. 2002, Le Floch et al. 2002, Khelifa et al. 2005, Lebedeva and Fogden 2010, and Sterling et al. 2004), where the major findings are that the effect of salinity on droplet size distribution is strongly influenced by clay type, and that there is a minimum salinity threshold for obtaining significant OMA.

The effect of mineral type and surface properties has been investigated in a few studies (Danchuk and Wilson 2011, Omotoso et al. 2002, Stoffyn-Egli and Lee 2002, Zhang et al. 2010, and Wang et al. 2011). These studies show an effect of mineral type and mineral grain size on the adhesion strength, where better adhesion properties are found for the smallest particles.  The surface energy seems important for understanding the adhesion strength, and hydrophobic minerals will give rise to better adhesion, compared to hydrophilic minerals.  The strength of adhesion is also a function of ion strength (salinity), oil type (viscosity and content of natural surface active components), pH, and presence of chemical dispersants.

The effect of mixing energy has been investigated and discussed in some studies (Devadoss et al. 2009, Sterling et al. 2004, Cloutier and Doyon 2008, and Stoffyn-Egli and Lee 2002), where they find a strong positive correlation between mixing energy (i.e. breaking waves, strong flood currents) and OMA formation.

Effort has been made to develop models that include the process of OMA, and use these for oil mass balance calculations, and as a decision support tool for oil spills (Khelifa et al. 2002, Hill et al. 2002, Bandara et al. 2011, Lee et al. 2002, Sterling et al. 2005, and Niu et al. 2010 and 2011).  A number of papers describe field observations of OMA formation, both after accidental oil spills and controlled field experiments (Owens et al. 1994, Owens 1999, Lee and Lunel 1997, Lee et al. 2002, Lee et al. 2003, Owens and Lee 2003, and Wood et al. 1997). These field studies all show the potential for OMA formation to occur, and to be an important factor for fate of spilled oil in the Arctic.

The use of OMA as a OSR technique has been investigated and discussed in several studies (Ajijolaiya et al. 2007, Lee and Lunel 1997, Owens 1999, Owens and Lee 2003, and Sun and Zheng 2009), and these studies clearly conclude that enhancing OMA formation in certain cases might serve as a sound response option for oiled shorelines, with references to field studies at two spill events the Tampa Bay response in Florida and the Sea Empress operation in Wales and at a controlled oil spill experiment in the field [the 1997 In Situ Treatment of Sediment Shorelines (ITOSS) Program (Guenette et al. 2003)].

Investigations of oil-particle interaction after the Deepwater Horizon accident in the Gulf of Mexico are described by Passow et al. (2012). They proposed a mechanism for understanding the formation of marine snow on the basis of the complex processes involved in bacterial decomposition of oil and subsequent interaction with organic matter and phytoplankton.  The findings related to oil-particle interactions from the Deepwater Horizon spill demonstrate that oil-particle interactions are important also for deep water and water column processes affecting dispersed oil, and that knowledge gaps related to these processes remain.

The review of the transport and fate of oil in the Arctic described by the authors in this section led to suggestions of further research which can reduce remaining uncertainties.  The more generic suggestions compiled from this review are summarized below while recommendations that are important for improving Arctic NEBA are listed separately.

Behavior of Oil in the Arctic. Develop a better understanding of the key environmental variables that alter the dissolution, mineralization and biodegradation of oil.  As an example, it has been well demonstrated that small droplets of oil are able to more rapidly undergo degradation than larger oil droplets and that this is based on the surface area exposed to microbes.  Using this basic understanding it is reasonable to conclude that concentrated oil masses (at the air/water or ice/water interfaces, convergence zones, shorelines, and within shoreline beaches) will be less bioavailable and decrease the ability of microbes to effectively degrade the oil.  Habitats that accumulate oil are more likely to experience longer term impacts on resident biota at the concentration zone or in adjacent areas as a result of oil remobilization.   The ability for these environments to recover is therefore based not only on the resilience of the organisms at these locations but on the duration of contact with concentrated oil.

1. Impact of seasons:  Develop a better understanding of the seasonal physical and chemical weathering processes on oil that occur in brine channels under ice and in polynyas to provide better exposure estimates and increase the accuracy of impact assessments of these specialized ECs. 
2. Shoreline stranding:  The seasonal difference in stranding processes for oil on shorelines is beginning to be well understood.  Ice can act as a protective barrier, minimizing contact and stranding of oil in the presence of ice.  During open water periods the stranding process is different and the effects on shorelines need to be characterized to provide an assessment of the potential for stranded oil to reside for extended periods of time with little to no additional weathering.
   1. As part of an input to tactical OSR plans mapping of shorelines with a propensity to recover rapidly and those that are projected to retain unweathered oil should take place preferably using GIS.  GIS is recommended because the seasonal use of the various types of environments by valuable ecosystem component (VEC) species could be added as an information layer.  One example of a shoreline is a sandy beach that may be able to recover rapidly from stranded oil but it may also be located in areas of marine mammal (e.g. walrus) haul-outs.  Knowing the location of this type of EC combined with seasonal patterns of haul out use would provide needed information to protect VECs from this type of exposure.  Similarly, a cobble shoreline may have an extended time for recovery with a release of oil on a regular basis that could influence the spawning habitat for VEC species that use the area.  The regional identification of shoreline ECs and the spatial and temporal use of local intertidal environments will provide a specialized component for regionally adapted NEBA assessments. 
   2. Experimental studies examining OMA suggest that OMA may play a useful role in longer-term shoreline processes. The use of OMA on stranded oil to remobilize the oil is an intriguing response option that needs to be characterized more completely at mesocosm and field scales. 
3. Oil-particle interactions:  Interactions between dispersed oil and other types of particles, e.g. marine snow, microorganisms, phytoplankton, and zooplankton have not been well characterized. These interactions need to be investigated in order to produce new data to improve fate modeling tools.
   1. Similarly, whether OMA are predominantly consumed as food and/or transferred as contaminants into the Arctic food webs is unknown.  Establishing the rate of biodegradation and fate of oil contained in OMA are fundamental steps for evaluating the potential positive and negative effects of OMA to pelagic, demersal and intertidal communities.

The recommendations presented below indicate where increased knowledge of oil transport and fate processes would result in reducing existing uncertainties in NEBA assessments.  No prioritization has been made to the list; for some of the recommendations, surrogate data may be already available.

1. Attributes of ECs that impact fate of oil.  Develop a better understanding of environmental compartment attributes that affect the dissolution, mineralization and biodegradation of oil.  Two primary compartments for study include the sea surface and ice/water interfaces.
2. Attributes of ECs that affect resiliency and recovery.  Habitats that accumulate oil are more likely to experience longer term impacts on resident biota including additional effects of oil remobilization.   The ability for these environments to recover is therefore based on the resilience of the compartment and removal of oil.  Define environmental compartment attributes the decrease or increase resiliency and ultimately recover.
3. Remobilization of oil.  Information on the chromatographic separation of oil components as they become sequestered into ice and brine channels and the extent of biodegradation and physical/chemical changes that occur during ice encapsulation would provide information needed to assess remobilization of oil during ice break-up and provide justification for extending response action periods.
4. Fate of oil associated with ice communities.  The fate and effects of oil under ice where ice algae and species living in that compartment become exposed need further characterization.
5. Fate of OSR residues.  Each OSR action produces residual materials that behave differently.   Modeled transport processes should include settling of particles derived from OMA, residues from in-situ burning (e.g. increased volatilization and ash formation), natural or enhance dispersion of oil, transport of surface oils, retention of stranded oil on or in shorelines, and convergence of water masses to adequately predict the fate of all oil components.
6. Role of biological processes on degradation of OSR residues.  The physical and microbial processes that control the fate of OSR residues also need to be incorporated in transport and fate models.

Authors Drs. Alf Melbye and Liv-Guri Faksness (SINTEF), Dr. Janne Fritt-Rasmussen (ARTEK), Dr. Torgeir Bakke (NIVA), Dr. Oleg Titov (PINRO) 

The Arctic region is characterized by the presence or absence of ice at different times of the year which generates a seasonal regime of ice coverage and ice thickness (AMAP 2007, SL Ross 2012b, Wang et al. 1999).  When spilled, the oil fate and behavior will depend on a combination of the ice growth stage and coverage area which together can reduce or stop the weathering processes and limit the spreading.  In some cases, the oil can be trapped by the ice and remain fresh and unweathered until the melting season. 

The extent and nature of ice coverage also greatly affects the OSR options that might be considered and their operational effectiveness (SL Ross 2011).  While shorelines and lagoons are not unique to the Arctic these are critical environmental compartments that have seasonal congregations of valuable ecosystem components that create significant risks to populations (refer to Sections 2, 7 and 8).  The importance of these seasonally used compartments and the logistical challenges of positioning manpower and equipment at remote locations that ultimately limit response feasibility and/or timing suggest that response options need to be selected to avoid contact with these environmental compartments during those seasonal uses (refer to Sections 7, 8 and 9).  Surface or subsurface oil releases will be influenced by the presence of ice (refer to Section 3) and will impact both environmental compartments and key species groups differently depending on location and density of the ice cover and seasonal use of those environmental compartments by VECs (refer to Section 2).   Depending on the season of the year and the site of released oil, an incident may result in different types or magnitudes of environmental impacts.  Generally speaking, “Arctic habitats are characterized by extreme seasonal change, which drives extensive migrations on land and at sea. The seasonal patterns of movement to, from, and within the Arctic determine to a large extent the vulnerability of Arctic ecosystems to oil spills. These patterns of seasonal activity and movement must be taken into account in selecting response strategies designed to reduce or avoid environmental impacts from oil and gas activities” (AMAP 2007). 

Arctic species are subject to potentially dense concentrations (e.g. for birds, mammals, and fish) according to migrations patterns and corresponding ice regime.  Ice edges are important locations for concentrating marine mammals and birds as a result of high biological activity. In addition, possibly due to the low ambient temperature, there is a low turnover for many species and consequently population recovery can be slow.  As an example, some Arctic fish spawn under ice in winter; their eggs incubate under ice and hatch when ice begins to melt and plankton blooms occur.  An oil spill in such spawning areas and during early life stages could severely reduce that year’s recruitment (AMAP 2007).  The presence and the movements of the different species in both localized and regional areas is generally not  known to the extent needed to make some of the important tradeoff decisions when selecting spill response options.  Baseline studies are often conducted as part of the Environmental Impact Assessment (EIA) process that is undertaken in areas where oil and gas production is envisaged or in the process of being developed. Mapping (spatial and temporal) the ecological vulnerability of Arctic habitats in these areas will contribute significantly to regional oil spill response planning. 

Several field tests with experimentally released oil have been completed in the Arctic (see SL Ross, 2012 for an overview).  However, except for the Baffin Island Oil Spill (BIOS) experiment these tests were devoted to studying the behavior and environmental fate of the oil in icy conditions and not the environmental impact at the spill location or other ECs.  Nonetheless, this information helps frame the physical and chemical factors that affect the nature of oil released in an Arctic environment and help to identify the challenges to be encountered in implementation of any type of OSR activity.  In fact, this sets the basic expectations for what might occur if natural attenuation were the only response option implemented. 

The specific challenge encountered in the Arctic during OSR is the presence of permanent or seasonal ice, which has many consequences (Potter et al. 2012).   Ice reduces the sea surface agitation which coupled with the low prevailing temperature, slows down the spreading of the oil slick reducing physical weathering and emulsification that occurs with more active surface water disruption.  Ice also limits oil spreading when it is between ice blocks, or when beneath or on top of the ice.  This helps keep the oil relatively concentrated reducing the rate of oil weathering.  Large quantities of oil can be trapped either in snow, or on or under the ice within spaces found in the unevenness of the ice surface.  When ice is forming, oil can be encapsulated in the new ice and thus kept unaltered during the winter season.  Oil trapped in ice can then be released to surrounding waters when the ice melts, possibly reappearing as fresh, unweathered oil.  Oil has been observed to migrate through the ice, at a rate that is dependent on oil viscosity.  Experimental studies have determined that oil components separate within the ice and undergo degradation during the winter in the ice brine channels, as discussed below and in Section 5.

If spilled oil is not recovered or treated, heavier oils may persist on the surface of water or surface of ice and can affect biological communities that are utilizing these interfaces, especially birds or mammals with fur (due to the potential loss of thermal insulation) whereas lighter oils may naturally disperse into the water column.  A reduced rate of oil weathering may occur if oil is encapsulated by ice and the oil may not be biologically available until the spring thaw.    Another unique attribute of the Arctic is that oil can strand on the shore during the ice-free season, whereas at other times the shoreline may be protected by landfast ice, which prevents oil from coming ashore.  Oil stranding on shoreline substrates during the ice free period is subjected to the strong erosional forces of the ice on shoreline substrates during the next ice build-up and ice break-up seasons.  Only deeply buried oil that might occur in intertidal cobble fields would be sequestered for extended periods of time (e.g., decades).  Therefore in many cases the persistence of oil onshore will be governed by the physical erosional forces that occur in many shorelines which minimize its retention.  However, the weathering and recovery processes may be longer (e.g. occupy those area for more than one year) in cases where oil is sequestered in spaces among cobble or boulder fields or where oil may be trapped in isolated nearshore water bodies.  The practicalities of staging recovery operations in remote locations are also a consideration.

The effect of oil that is left to natural attenuation on the shoreline depends upon:

• The environmental resources of concern that are present when the oiling occurs and during subsequent seasons when extended oil exposures could be possible.
• The duration certain ECs of shoreline contamination, which may not persist for more than one year in while in others it may be extended for longer periods.
• The resiliency of the populations of various species that were impacted as a result of the spill and treatment methods that were used.  The resiliency of these populations and communities of organisms is controlled by fecundity, immigration from unaffected areas, and the diversity of organisms present within the affected habitats.

McAuliffe et al. 1980 reported on the effects of oil on under-ice meiofauna as a part of the BIOS project (McAuliffe et al. 1980).  Effects of this experimental spill on ice algae are summarized in a report by SL Ross (2010).  In that study, the bottom 10 cm of ice had decreased density of meiofauna, no adverse effects were observed on the ice algal community, and under-ice invertebrates showed no mortality but did drift away from the oil impacted area for days following the spill.  All the findings of the BIOS Project are summarized in Li et al. (1992).

A separate study conducted on first-year sea ice off Svalbard showed that there is a migration of bioavailable water soluble components (WSC) from encapsulated oil through the ice to the underlying water (Dickins et al. 2006, Faksness et al. 2012).  The estimated toxicity of these dissolved oil components in the ice was calculated using toxic units and the findings indicated that the concentration of WSC in the brine channels might be acutely toxic to the ice fauna.   Results from another field study of an experimental release of 7000 L crude oil in the Barents Sea showed low concentrations of dissolved hydrocarbons (maximum concentrations were 4 ppb dissolved hydrocarbons and 32 ppb total hydrocarbons) in subsurface water.  Predicted toxicity to the exposed community in the upper layers of the water, expressed as toxic units, was 0.11 or less, indicating that the potential for acute toxicity was low in subsurface bulk water (Faksness et al. 2012).  However, the effects of surface oil on organisms using the surface layer, polynyas, ice-edges or adjacent shorelines where oil compounds can be re-concentrated was not assessed.

These studies indicate that there could be effects on the local ice biota if the oil is encapsulated in the ice or trapped underneath the ice. The organisms associated directly with the ice could be exposed to potentially toxic dissolved hydrocarbons over the course of several months, causing potentially toxic oil components to enter the Arctic marine food web. On the other hand, the measured concentrations of dissolved hydrocarbons in the water column, or underneath an untreated oil slick, have been lower than potentially toxic concentrations, perhaps indicating that severe effects to organisms residing in the water column would be negligible.  However, this does not take into account the reconcentration processes that occur at interfaces such as the surface of the water, at ice water interfaces, convergence zones and shorelines (refer to Sections 2 and 3).

Oil remaining in Arctic habitats without treatment will behave similarly to non-Arctic situations, although chemical processes such as dissolution, volatilization, and biodegradation may occur at a slower rate resulting in increased persistence.  In non-ice periods oil spills on the sea surface will remain at the sea surface and be transported in slicks by winds and currents to shorelines, convergence zones, and offshore surface waters.  During that process some of the oil will dissolve into the water column or be physically dispersed into the water column as droplets, some will volatilize into the atmosphere, while the majority of the oil may remain on the surface where it will weather, biodegrade, emulsify and accumulate in zones of reconcentration.  Subsurface releases of untreated oil will generally rise towards the sea surface but during that transport it may also be rapidly biodegraded based on the increased surface area of oil droplets created by the turbulence of the release.  Oil that remains on the sea surface can be stranded on shorelines or concentrate in convergence zones but the oil may also be encapsulated by ice as it forms.  In order to facilitate the forecasting of the seasonal dynamics of oil in these compartments, it is important that data are available for NEBA evaluations. This will facilitate the decision making process regarding the most appropriate response option under various conditions. 

Such a NEBA process would evaluate the trade-offs of untreated oil containment by ice and treatment efficiency with decreased impact on pelagic environments by dispersant treated oil in non-ice environments.  In addition the increased effects of surfaced oil as it is captured and released by formation and melting of ice on seabirds, marine mammals, annual ice fauna and flora should be evaluated. Also the biological significance of overwintered oil and ice must be determined.

Many data that serves as a basis for such evaluations is already available, but improvement of the information base would result in further reduction of uncertainties. Suggested topics for such studies are: 

1. Biodegradation
   • Measure the biodegradation of oil in ice and trapped within leads or under ice over a winter season.  Compare to biodegradation of oil in pelagic waters and surface layers during non-ice periods.
   • Does frazzle ice increase biodegradation of oil released from ice by physical grinding and disturbance of oil, creating larger surface area for microbes to degrade the oil?
2. 2. Presence of VECs
   • Determine avoidance behavior for fish and invertebrate VEC’s associated with oil trapped with ice.  Indications are that they will move away from oil.
   • Evaluate the use of polynyas or leads by VEC fish, invertebrates, sea birds, and marine mammals and the potential for oil effects in these critical habitats. Compare oil within broken ice fields and open waters as an attraction to seabirds, marine mammals, fish and invertebrates.
   • Summarize the same types of information for seabirds, shorebirds, marine mammals. 
3. Considering the uniqueness of Arctic shorelines influenced by landfast ice, it will be important to understand the dynamic processes controlling the fate and persistence of oil on such shorelines.  This will require an assessment of the potential for lingering oil releases and the assessment of the natural decontamination rate resulting from different responses

When oil is spilled on the surface of the water or rises from a deep water discharge and then accumulates on the surface it is possible to concentrate the oil by placement of booms in the pathway of the oil transport.  As the oil accumulates next to the booms it can be recovered by pumping the captured oil into collection containers.  Oil can also be collected e.g. using boats and surface water booms that accumulate the oil as the vessels travel through oil slicks.  The success of these processes depends on the encounter rate and efficacy of the mechanical collection techniques and the success of containment or accumulation.  Ice can act as a natural boom that allows oil to collect along its edges, within leads, under the ice in pockets, and within polynyas.  Ice can also hold the oil for extended periods of time, allowing mechanical recovery to occur over more extended periods of time from its formation to when it begins to melt.  Many of the tools used for mechanical recovery are not unique to application in the Arctic but for some adaptations have been made to collect oil mixed with ice (Broje and Keller 2007).   The tools used to mechanically recover oil after it is concentrated are described in more detail in the Artic response technology report by SL Ross (2012). 

Moving ice, either as ice floes or frazzle ice can interfere with containment and recovery equipment deployment and operations (Potter et al. 2012, EPPR 1998).  On the other hand, ice can also slow the spreading of oil on water, keeping a slick thicker during recovery, which increases the efficiency of this type of response activity.  Environmental impacts of mechanical recovery are usually considered in terms of emissions of response equipment, noise, and the impacts of the presence of large numbers of personnel.  However, it is important to consider that mechanical containment and recovery is a slow, tedious, and challenging response method. Mobilizing and supporting such activities in remote areas adds further inefficiencies and time constraints.  Impacts from a containment and recovery response effort are:  the impact from oil that is left behind (oil that escapes containment), and impacts from the activities necessary to reclaim or dispose of the recovered oil and associated oily debris.

The impacts considered with natural attenuation are also associated with the residual oil left behind from mechanical recovery.  Historically, mechanical recovery in open water spills is often reported as less than 15% of the spill volume and in most cases less than 5%, although specific performance can vary widely from incident to incident (EPPR 1998). Thus, for this report, impacts considered under MNR will also be a large part of any mechanical containment response scenario.  Our consideration of the ISB, dispersants and OMA and herder technologies will therefore compare tradeoffs using either mechanical response or naturally attenuation as their baselines.

Mechanical recovery in an Arctic spill situation may have marginal improvements in effectiveness due to the presences of some types of ice conditions, or may have additional inefficiencies brought on by different types of ice.  Impacts of residual oil left in the environment due to the low effectiveness of mechanical recovery can also serve as the baseline assessments for evaluating tradeoffs for ISB (with or without herders), chemical and physical dispersants. The areas of proposed work are the same as those included in the natural attenuation section of this report. 

The in-situ burning (ISB), also referred to as controlled burning, has been the subject of extensive research, development, and testing over the past 30 years in temperate and sub-arctic water (Potter et al. 2012).  The basic premise for effective and efficient burns is to collect and/or concentrate the oil slick to a thickness greater than 2 mm and provide an ignition source that can start the burning of surfaced oil.  The oil must not be weathered or emulsified to such an extent that there are not enough lower molecular weight compounds (LMW) and available oil to sustain combustion (Fingas and Punt 2000).

Photo 4-6. In-situ Burning (Liv-Guri Faksness)

ISB can be effective in rapidly removing large quantities of oil from the marine environment. Ideally, about 85 to 95% of the burned oil becomes carbon dioxide and water. The rest, 5 to 15% which is not burned efficiently is converted into particulates (soot) and a few percent is converted into organic compounds and combustion products that remain in the marine environment (Potter et al. 2012). The burn residue from a typical efficient ISB operation is in the order of less than 15% (SL Ross 2010).  ISB seems well suited to Arctic conditions and the presence of ice (Photo 4-5). The presence of significant ice formations can keep  oil from reaching water (burning of oil on ice) or limit the spreading of the oil on water (burning thick patches of oil on water contained among ice formations).

In-situ burning is an efficient process that removes ~80% of the oil (SL Ross, 2010).  However, the residuals of these burns include unburned volatile materials that are released into the air, soot particles that are also mobilized and transported into the air, and the modification of oil compounds into new products or the addition of agents (e.g., herders) and their burn products for release into the air or water.  These residues of the burning process (smoke, volatiles, soot particles, additives and unburnt oil) are the potential materials that can pose environmental and human health effects.  In addition there is a small risk of causing secondary fires that could threaten human life, property and natural resources; this risk is, however, easily manageable.  

Chemical herding agents are products used for thickening an oil slick and concentrating oil on the water surface in order to reverse the effects of spreading.  The increase in thickness may facilitate oil combustion during an in-situ burning operation.  Several herding agents are listed on the National Contingency Plan registry as approved for use during oil spills, including Thickslick 6535 and Siltech OP-40.  A third herder employed by the US Navy (USN herder) has been tested under arctic conditions.  The USN herders (65% Span-20 and 35% 2-ethyl 1-butanol) and silicon based herders have been used under Arctic conditions and have been shown to work in cold open water environments as well as in broken ice (Buist and Nedwed 2011). 

Generally an efficient burn leaves 5 to 15% of the initial oil as residual or unburnt oil (SL Ross 2010).  The residual is mainly composed of high molecular weight (HMW) oil compounds which are similar to those in highly weathered heavy fuel oil.  The physical properties of burn residues depend on burn efficiency and type of oil.  Factors that determine whether residues float or will sink are:  water density, oil chemical properties, thickness of slick, and efficiency of the burn (Buist and Trudel 1995).  The residual ash may also settle on the surface of the surrounding ice or sea where it may come into contact with surface dwelling organisms. 

Tests have been carried out on the burn residue of Alberta Sweet Mixed Blend which had been used in the Newfoundland Offshore Burn Experiment (NOBE).  The water accommodated fraction (WAF) was prepared from the unburnt residue and tested on rainbow trout to assess the 96 h LC₅₀ and on sea urchin for inhibition of fertilization (20 min contact). The maximum total petroleum hydrocarbon (TPH) concentration measured in the test solutions (WAF) was 1.1 mg/L.  All samples were not toxic to the tested species (Blenkinsopp et al. 1997).  In another study, Daykin et al. (1994) concluded the toxicity of the residue should be lower than that of the initial oil.  Other studies showed that the residue had very little or no acute toxicity to key indicator species in salt water and freshwater because an effective burn removes the lightest, most toxic components of crude oil (Blenkinsopp et al. 1997).

In a recent study by Faksness et al. (2010), the semi-volatile organic compounds (SVOCs) in a crude oil prior to and after ISB were analyzed.  No volatile analyses were performed, but a removal of approximately 60% of the SVOCs, mainly the decalines and naphthalenes, had occurred during the ISB. Acute toxicity tests with the marine copepod Calanus finmarchicus exposed to the underlying water after ISB indicated no increase in toxicity when compared to WAF generated with unburned weathered oil. These findings were in accordance with the results presented by Daykin et al. (1994) as a part of NOBE.  Concerning potential for exposures to the PAHs in burned oil residue, several studies have demonstrated that the concentrations of PAHs in the residue were lower than that in the initial oil.

While the toxicity from uptake of chemical components of the residue does not appear to be a concern to water column organisms, there is possible impact on surface dwelling species (by ingestion and/or direct smothering) and benthic species if the residues were to be stranded onshore or sink onto the sea bed. These risks are however considerably lower than when fresh oil remains on the surface or strands.  Concern for such an impact arose during oil spill incidents involving ISB, e.g. the Honan Jade spill in South Korea (1983) and the Haven spill in Italy (1991) where the NRC (2005) reported that the burn residue was typically a semisolid, tar-like layer.  The surface oils were burnt, removing the impacts in the surface waters but the burnt residues would sink where they affected the benthos.  Such sinking residues consisted of scattered chunks rather than as a continuous mat covering a broad area.   While this type of impact on the benthos is very hard to assess it must be considered as part of an overall assessment of potential benefits and impacts of ISB.

Oil combustion produces gas, smoke and soot into the atmosphere.  Typically the smoke plume is composed of CO₂, steam, soot, CO, SO₂, NO₂ and VOCs including PAH and BTEX, dioxins and dibenzofuran (Tennyson 1994, Fingas et al. 1993).  Despite the fact that VOC concentrations in the plume are usually lower than the accepted threshold value for human health concerns (Buist et al. 1999), responders put an exclusion zone in place to ensure there is limited exposure of downwind communities or wildlife populations to these compounds.  Responders are also excluded from the immediate area of the fire and at more lengthy distances downwind of the fire. 

In one assessment of the NOBE study Ross et al. (1996) found that burning of 1 Kg of oil produced 40 µg of PAH in the soot/particles while the original oil had 9.5 g/kg of oil.  Therefore multiple authors have concluded the ISB residue would have a lower toxicity than the initial oil (Buist et al. 1999, Fraser et al. 1993, Garrett et al. 2000, Li et al. 1992, Lin et al. 2005).  The potential effects that would occur with species living at the air/water interface or that break through the surface (e.g. seabirds and marine mammals) were unaddressed by these studies. 

The production of smoke during an ISB, and the concentrations of smoke particles at ground or sea levels are usually of most concern to the public as they are highly visible from significant distances and can persist for several miles downwind of a burn.  Concerns include human health and wildlife inhalation risks from particulates carried in the smoke plume.  Particulate concentrations in the plume are greatest at the burn site, but they decline with increasing distance from the site, primarily through dilution, dispersion, and fallout, but also through washing out by rain and snow (API 2004). The species of greatest concern to atmospheric pollution or fallout of soot and particles will be downstream of the burn and include marine mammals that must breathe at the surface of the sea or species and life stages that live within the very surface of the water.

The literature dealing with herders is rather old as these products have not been considered or promoted until very recently.  Available data shows that most chemical herding agents are not soluble either in water or in oil (less than 1%; Hayward et al. 1995, MSRC 1993) and are used at low application rates; therefore, acute toxicity of these products to pelagic organisms is generally not considered to be an issue.  Additional considerations may be required under special use conditions such as very shallow waters with low flushing rates and organisms abundant in early life stages, but exposures are still likely to be at very low concentrations (Walker et al. 1999, MSRC 1993). The more recent documents deal with the efficiency or operations related to herder use (SL Ross 2010).  As with dispersants, the toxicity information is limited to water column organisms and there is little information available on the toxicity of these materials to surface dwelling organisms.

Most of the available information on ISB deals with the efficiency of the technique and operational guidance.  While there is some information regarding monitoring activities to ensure air pollution is not a human health or wildlife exposure issue, information on the environmental impact is more limited.  Information on fate and effects studies could be compiled, taking into account the specificity of Arctic environment (species with the possibility of large concentrations of juvenile life stages, especially within the surface microlayer) and additional studies could be conducted to evaluate the persistence of these products and their residues where necessary.

Chemical dispersants are most effective when applied during or quickly after a spill or sub-sea release event, before dilution, weathering and emulsification of the oil reduces the effectiveness of the dispersants.  Modern dispersants are mixtures of solvents consisting of organic carbon chains that are oleophilic and surfactants that are hydrophilic.  The combination of oleophilic and hydrophilic components change the surface viscosity of the oils and create small droplets of oil that are released from the surface water and move into the water column or from deep water releases into adjacent deep pelagic environments.  These small oil droplets have greatly increased surface area that increases the rate of microbial degradation compared to the oil prior to dispersant application.  Dispersant mixtures have been evaluated by numerous organizations to determine their toxicity and efficiency of dispersion under many different environmental conditions.  By breaking up the oil and creating micron-sized droplets, chemical dispersion reduces the persistence of a surface slick or the potential for sub-sea discharges to reach the surface and thereby minimizes potential encounters by marine mammals and offshore bird populations. Application of chemical dispersant to sub-surface and to surface oil slicks reduces the amount of oil that becomes stranded on the shoreline and prevents oil from transforming into weathered oil-in-water emulsions that are resistant to further biodegradation (Lewis and Daling 2001). 

However, dispersing oil into the water column from surface slicks or deep water releases is most effective when the oil is fresh and unweathered.  Mitigating damage to the shoreline and to organisms that may encounter surface slicks means exposing the near surface and shallow or deep pelagic communities to elevated concentrations of dispersed oil for short periods of time. 

The literature reviewed focused on dispersant applied at the sea surface and it contains information on the toxicity of oil chemically dispersed into the water column and effects on those marine organisms from laboratory studies.  Information on the behavior of dispersants applied below the upper surface layer during blow-out scenarios were sparse during this review period.  However, it is expected that post-spill studies of the recent Macondo well blow-out and explosion that occurred in 2010 in the Gulf of Mexico will contribute greatly to our knowledge of subsea application of dispersants as well as natural dissolution and biodegradation processes that can occur in the deep ocean environment and at very cold temperatures that are similar to arctic temperatures.

There are limited holistic assessments that combine the toxicity of chemically dispersed oil data with information on specific assessments on toxic impacts associated with Arctic communities or the comparative damage resulting if oil persists on the surface or comes ashore.  Therefore, the rationale for application of chemical dispersants should be based on the comparison of the possible extent and duration of impacts to the organisms living in the water column (e.g. fish, shellfish, plankton, etc.) resulting from the use of dispersants, and the extent and duration of potential damage which would result if dispersants were not used, i.e. from a persistent surface slick (e.g. effects to birds, mammals, and fish and invertebrates that live in the very surface of the water) and from the stranding of the weathered oil on the shoreline (e.g. effects to coastal shoreline species and benthic organisms).  This type of information must be factored into the tradeoffs associated with Arctic dispersant use, and is considered in the section “Monitoring Natural Recovery (no active response)”.

Most toxicity studies evaluate the impact of increasing the exposure of pelagic organisms to oil as a result of dispersing the material into the water column.  Considering the toxicity toward water column organisms, it is recognized that the observed toxicity effects from chemically dispersed oil is due to the effects of the increased quantity of dispersed oil into the water and are not caused by­­­­ the dispersant itself, as modern dispersant formulations are much less toxic than oils (Hemmer et al. 2011).

In assessing dispersed oil toxicity, determinants of adverse effects for a given species are exposure concentration and duration of exposure (see also a more detailed review of peer-reviewed literature presented in Section 6, Ecotoxicology of Oil and Treated Oil).  A review of field studies found that small-scale field tests have demonstrated that the concentration of dispersant in water falls to less than 1 mg/L within hours (NRC 2005).  The available data suggest that in general, maximum dispersed oil concentrations after a spill are less than 50 mg/L immediately after dispersion into the upper water column (top 3 m) and that dispersed oil concentrations dilute rapidly, dropping to 1 to 2 mg/L in less than 2 h throughout the water column (Cormack and Nichols 1977, Daling and Indrebo 1996, McAuliffe et al.1980).  These low concentrations are generally below estimated toxicity threshold concentrations derived from exposure experiments for most common water column organisms (McFarlin et al. 2011, Gardiner et al. 2013). 

The BIOS experiment conducted in sub-Arctic nearshore areas in the 1970s studied oil dispersion impact on nearshore environments and concluded that the results offer no compelling ecological reasons to prohibit the use of chemical dispersants on oil slicks in nearshore areas (Potter et al. 2012).  Secondly, the results provide no strong ecological reasons to undertake an intrusive effort to cleanup stranded oil (on certain shoreline types).

During an experimental oil spill in the Barents Sea in 2009, 2000 L of crude oil were dispersed six hours after release (Potter et al. 2012). Two hours later, measurements of oil in water were performed at depths of 1, 2 and 3 m. The maximum concentration of oil in water was measured to 5.5 ppm (at 2 m depth) with an oil droplet size smaller than 10 µm, 30 minutes after mixing energy was added by the ship thrusters.  The monitoring indicated background concentrations were restored shortly after these measurements, as the plume had most likely drifted and diluted with the currents (Merlin and Le Floch 2012).  After the Sea Empress incident, a major spill in nearshore waters at the port of Milford Haven, UK, dispersed oil concentrations were monitored and quantified in the field.  Results showed 10 ppm dispersed oil immediately after the dispersant application, decreasing to 1 ppm 2 days after, 0.5 ppm 1 week after and 2 ppb 1 month after (SEEEC 1998). 

Such a decrease can be modeled with the following relationship:

                                   C = C₀ e^-1.35                                                                                                 Equation 1

Where C equals oil concentration at time (t in hours);

C₀ is the initial concentration;

e^-1.35 represents an exponential decline in oil concentration 

Application of the equation yields a half-life of 12 h for the dispersed oil concentrations [every 12 hours the concentration is divided by 2 (Merlin and Le Floch 2012)]. This reflects a dilution rate for a sustained spill response implemented over several days in a deep, but nearshore environment.  In more recent toxicology studies carried out in several laboratories in North America (Aurand and Coelho 2005), the exposure duration was modeled after a single dispersant application to offshore, open water habitats establishing a half-life of 4 hours. These representations of ‘spiked’ exposures are more environmentally realistic (closer to real field conditions) than standard laboratory ‘constant’ exposures, and result in a reduced level of effects (Gardiner et al. 2013). 

The effect and toxicity of a water soluble fraction (WSF) versus chemically dispersed oil was studied by using realistic exposure concentrations based on the WSF concentrations  monitored during an offshore field experiment (i.e. initial TPAH concentration of less than 7 ppb; NRC 2005).  The Arctic amphipod Gammarus setosus was used as test species in a continuous flow experiment. Body burden measurements showed higher level of PAHs in the gammarids exposed to oil and dispersant for 12 days than in those exposed to oil alone, consistent with the higher concentrations of oil that would be present when dispersant are used.  Several biomarkers were monitored, and gammarids exposed to oil and dispersant also showed moderate signals of exposure after recovery in clean seawater.

In a recent study on adult and juvenile fish and bivalve species conducted at elevated concentrations (up to 70 mg/L), the observed effects were sublethal and temporary.   After 2 weeks, sublethal bioindicators did not show any differences between animals exposed to the chemically dispersed oil and mechanically dispersed oil (Merlin and LeFloch 2012).  This demonstrates that exposure to chemically dispersed oil is not more toxic than the physically dispersed oil.  However, the same research team reported that fish kept in a natural environment after exposure did show residual responses (persistent) in terms of growth (Merlin and LeFloch 2012).  In conjunction with the previous study, experiments conducted with herring embryos in a wave tank showed abnormalities after constant exposure to elevated concentrations (to 10 ppm), but no effect when a more realistic and rapid dilution exposure regime was generated (McIntosh et al. 2010). 

Dispersant toxicity research has been conducted recently on specific Arctic species of concern as part of a laboratory toxicity testing program conducted in Barrow, Alaska.  It was found that Arctic species that were tested have similar or greater tolerance to representative concentrations of dispersed oil compared to the numerous temperate species that have been tested (Word and Gardiner in prep.).  Also, the acute toxicity of exposures to dispersant alone only occurs at concentrations that are greater than concentrations proposed for application of dispersant products in OSR (McFarlin et al. 2011; Gardiner et al. 2013).  For most species that have been tested, dispersed-oil acute toxicity thresholds are on the order of 1 mg/L based on laboratory tests that expose test organisms for periods of 2 to 4 days.  Water column concentrations above toxicity thresholds in an actual spill are limited to the top few meters and exposures at potentially toxic concentrations are limited in duration due to rapid dilution kinetics. 

The available body of laboratory data, experimental field studies and monitoring following actual spills shows that dispersed oil may potentially cause environmental impacts but these will be limited to the organisms in the immediate vicinity of dispersed oil plume and in cases when the rate of dilution of the dispersed oil plume is slow.  This would be the case for sensitive areas with limited water exchange,e.g. close to the shore.  Even in such cases, these impacts would generally be limited to non-mobile organisms.  For example, monitoring following dispersant use at major oil spill incidents over the past 40 years has never reported significant losses of mature fish populations at sea following dispersant applications. 

Laboratory and field research as well as monitoring following actual incidents assessing the impact of use of dispersants in OSR, demonstrate that:

• The toxicity of oil/dispersant mixtures is related to the oil in the mixture and not the dispersant.
• The toxicity of the oil is directly related to the amount of oil that organisms are exposed to.  That is, when dispersants are applied to oil the increase in response of pelagic organisms is directly related to the exposure concentration and duration of exposure to the oil.
• The toxicity of dispersed oil is relatively low and often not observable in real environment as long as there is no restriction to the rapid dilution process of the plume of dispersed oil (e.g. open-ocean).
• There is no evidence that Arctic species are more or less sensitive than other temperate climate species that have been tested with dispersed oil.

The use of fine mineral particle (such as clay minerals) is an alternative response method to dispersant used to break up an oil slick into small droplets and stabilize the oil dispersion in the water column.  When applied to physically dispersed oil, oil droplets aggregate readily with suspended particulate matter (SPM) such as clay minerals and organic matter to form [oil-SPM] aggregates called oil mineral aggregates (OMA; Le Floch et al. 2002).  It is important to distinguish the use of OMA from sinking agents.  Rather than bind to bulk oil as dense sediment and cause the oil droplets to sink, OMA will cause the oil to be suspended in the water as micron-sized droplets associated with a complex of mineral material in much the same result as chemical dispersants generate micron sized droplets (Khelifa 2005, Khelifa et al. 2005).  The simplest form of OMA consists of an oil droplet coated with micrometer-sized solid mineral particles that prevent the droplets from sticking to each other and reforming a slick.  When OMA forms, the dense mineral fines (small but 2.5 to 3.5 times denser than most oils) adhering to the oil droplets will reduce the overall buoyancy of the droplets, retarding their rise to the surface but keeping them somewhat buoyant so they do not sink.  This promotes oil droplet dispersion throughout the water column to low concentrations, and ultimately enhancing their biodegradation by natural bacteria (Lee et al. 2011).

Positive lab and basin tests of the concept led to a field test in 2008 (Lee et al. 2011).  The field test was designed to evaluate the concept of using an icebreaker’s propeller and application of mineral chalk fines with seawater to create OMA. Visual observations confirmed that the oil stayed physically dispersed in the upper water column and did not resurface (Potter et al. 2012).   Attempts were made to combine chemical dispersant use with fine mineral application.  The dispersant was added to promote the dispersion of micron-sized droplets into the water column while the addition of fines attempted to stabilize this dispersion.  The result was not especially convincing, as dispersant presence seemed to inhibit the formation of OMA complex with the oil droplets.

Preventing the re-surfacing of the droplets under the adjacent ice in the Arctic would be a significant environmental benefit since OMA also enhances natural biodegradation of spilled oil.  The application of fine minerals seems well adapted to ice infested conditions as the presence of ice reduces the sea surface agitation; chemically dispersed oil may tend to resurface over prolonged time periods if not stabilized by OMA formation.  It is also beneficial that the types of fine minerals needed for OMA dispersion are those that are commonly stockpiled in oil exploration facilities as drilling mud components; consequently, a source would be readily available in the event of a spill.

Most of the studies on this topic were devoted to the mechanism and efficiency of the technique to optimize the application conditions; very few considered the environmental impact of the use of OMA.  A lab study dealing with the use of dispersant in estuaries assessed the toxicity of dispersed oil with presence of Montmorillonite clay (Merlin and Le Floch 2012).  It was shown that the presence of this fine grained material reduced the observed impact on biota exposed to the dispersed oil plume to the level of impact commonly seen from oil that is mechanically dispersed (without chemical dispersant addition).  To date, sparse information has been identified on the environmental impacts and relative toxicity of OMA in the Arctic.

Laboratory and field research as well as monitoring following actual incidents assessing the impact of use of OMA in OSR, demonstrate whether:

• The toxicity of oil/OMA mixtures is altered or if the oil in the mixture is the predominant cause of any toxicity observed with OMA use.
• The association of oil and OMA may alter the toxicity of the oil by decreasing bioavailability due to the adsorptive process that occurs to the OMA.

The environmental advantages of using OMA to stabilize oil dispersion in the upper water column are similar to those expected from the use of chemical dispersant.   Mineral fines are nontoxic to marine life.  The main impact expected from addition of the mineral fines could be a temporary increase of the sea turbidity which should be similar to the level of turbidity promoted by chemical dispersion.  Other mechanisms of impact would be similar to the environmental/biological impacts discussed with chemically dispersed oil.  The description of the flocculation of fines to the outer surface of small oil droplets leads to the following questions prior to its acceptance as an OSR option for the Arctic.

• What is the optimum rate of OMA application to oil to maximize its benefits (OMA may need a 1:1 ratio with oil to provide its benefits.
• Does OMA surface coating of oil droplets reduce potential microbial degradation or use of the oil droplets?
• Does OMA surface coating of oil droplets reduce the potential toxicity of the droplets or decrease the solubility and exposure of the more soluble/toxic components of the oil?
• Are OMA coated oil droplets available to suspension feeding organisms in an unweathered, potentially more toxic form?
• The remaining questions regarding the long term environmental fate of the OMA aggregates are: do they tend to sink progressively with time? What is the impact of settled OMA to the exposed area of bottom resources that could be large but at very diffuse concentrations?  Does the mineral separate from the oil droplet?   What is the impact of OMA or separated mineral exposures to dilute inorganic particulate matter and would it be any different than that endured from settling of ocean particulate matter? 

The review of the main oil spill response strategies to be used in the Arctic described by the authors in this section led to suggestions of further research which can reduce remaining uncertainties.  The more generic suggestions compiled from this review are summarized below while recommendations that are important for improving Arctic NEBA are listed separately.  Recommendations for further study captured previously within each response option section are summarized below.

1. Expand effect data for non-water column species.  Data are available on impacts of OSR technologies on species living in the upper pelagic environment.  Additional studies on species living in other ECs (e.g., deep sea, surface layers, ice/water interfaces, hard substrates) should be performed.  Noteworthy limitations of the available data are:
   1. Most of the toxicological information provided for different response strategies is in terms of sensitivity to organisms that are exposed in the water column (generally the upper 10 m) and do not include species that are using deep water, surface layer, ice/water and shoreline interfaces.
   2. Models have been developed to predict the toxicity of a constant concentration of oil and dispersed oil components to these species based on a narcosis model associated with uptake into lipids.  Other modes of action (fouling, epithelial damage, developmental abnormalities, and others) and exposure types (declining dose) need to be considered.
   3. Assimilated information on recent subsea processes is appearing in the peer-reviewed literature; these studies need to be reviewed and important trends summarized.
2. Expand Assessment to Population-Level Effects, Resilience, and Recovery Potential.   Toxicity evaluations have been generally limited to studies on the acute impact on individuals of a single species and do not evaluate recovery times for the suite of species, at the population-level.  The resiliency of a population to a stressor is built around the population’s ability to recover from the stress, i.e. it is dependent on how widely the species or population is distributed, its reproductive potential, its mobility, and ability to avoid exposure to the stressor.  Knowledge of the length of recovery time for populations living in each environmental compartment is needed prior to evaluating the consequences of each response decision.  Critical summaries of the biological attributes that extend or shorten recovery times need to be developed for populations residing in the different EC that would be affected by response actions.
3. Examine persistent effects.  Investigations have been conducted on oil and chemical toxicity, generally focusing only on the acute and short term toxicity.  In NEBA decision-making chronic sublethal effects are often treated as acute mortality levels.  An analysis should be performed to better understand the role of chronic sublethal effects in NEBA decision making. This includes the change in bioavailability, toxicity and biodegradation potential of oil and its components as physical weathering and biodegradation occurs after treatment by OSR actions. 
4. Explore additional modes of toxic action.  There is little information on other types of effects of oil exposure other than toxicity due to water borne exposure and uptake into tissues; additional study of fouling and epithelial tissue disruption by oil or oil residues on organisms that reside or move through the air/water, ice/water or shoreline interfaces or breathe contaminated air above an oil slick is warranted.  Smothering/fouling related toxicity, atmospheric contamination and interference with air breathing mammals and birds has not been well investigated. 
5. Evaluate potential for impact on the basis of habitat function.  The available information is often concentrated on individual species or groups of species rather than on habitat function.  However, it is the effects on population or habitat which are important in the overall assessments of the consequences of selecting alternative response actions.

The recommendations presented below indicate where increased knowledge of OSR processes and consequences would result in reducing existing uncertainties in NEBA assessments.  No prioritization has been made to the list; for some of the recommendations, surrogate data may be already available.

1. Identify VECs and ECs that can be impacted by each OSR.  Develop structured overviews of all VECs that can potentially be impacted by each OSR technology with special focus on VECs at interfaces and on seasonality.
   1. Improve knowledge on the spatial distribution of the living resources and seasonal evolution in the Arctic because large movements of populations occur.
   2. The resources should be ranked in terms of vulnerability to the oil in its different forms:  surfaced oil (fresh, weathered and burnt), dispersed oil, and smoke and soot (in case of burning), oil on the shore.
2. Collate available data.  Identify data needs for all potentially impacted VECs to score exposure potential, sensitivity, resilience, recovery preferably on a population level basis, using ARCAT approach.
   1. The oiling mechanism on Arctic shoreline and related impact on living resources taking into account the uniqueness of Arctic shoreline which are subject to strong icing periods.
   2. Short and long term effects of dispersed oil on Arctic living resources, especially those which are the most vulnerable and which are identified to congregate locally at certain times of the year.
   3. Data on air emissions should be included as well as residues for ISB (fate, exposure potential, effects, biodegradation).
3. Highlight uncertainties in data.  Identify data uncertainties and evaluate needs for additional studies such as:
   1. Effects caused by surfaced oil (ingestion, fouling, smothering) to the different living resources of concern (birds, mammals, etc.)
   2. Increased knowledge of the effects produced by-products (smoke, soot and un-burnt residue) of ISB towards the Arctic living resources subject to direct or indirect ISB contact
   3. Effects of herding chemicals and OMA have not been fully evaluated to date.  Investigation of the intrinsic toxicity of chemical herding agents towards Arctic species especially related to the possible exposure to early life stages.

Authors François Merlin and Dr. Stephane Le Floch (CEDRE), Dr. Jack Q Word (ENVIRON), 

Dr. James Clark (HDR/EM&A), Dr. Janne Fritt-Rasmussen (DCE/Department of Bioscience), Dr. Liv-Guri Faksness (SINTEF) 

The cold waters and harsh environmental conditions in the Arctic have led some investigators to conclude that spilled oil will be more recalcitrant and remain in the environment for longer periods of time than oil spilled in less harsh environments. Other investigators have concluded that the microorganisms in the Arctic are adapted to those conditions and rapidly respond to spilled oil. The objective of this document is to examine experimental evidence from peer-reviewed literature that addresses these conclusions and identify areas of additional research. 

This chapter focuses on biodegradation of oil spilled into the marine Arctic environment. The state-of-knowledge will be summarized, and main uncertainties that need further addressing will be highlighted. In this summary we also describe some of the specific conditions that organisms involved in biodegradation processes encounter in the Arctic environment but not at lower latitudes. These differentiating conditions, which may affect biodegradation rates and capabilities in the Arctic, include generally low near-surface temperatures, ice coverage and (in open water) extreme fluctuations in the photoperiod during the Arctic summer and winter. 

The risk of oil pollution in the Arctic is relevant to both marine and terrestrial environments. The Arctic marine environment may be influenced by recently discovered oil and gas deposits, together with the potential for increased traffic attributable to shipping lanes made possible by historically low summer ice cover. The terrestrial environments may be exposed to pollution risk, for instance, from oil transport pipeline systems and other land-based activities. In this review we will focus on the marine environments, although references will also be made to terrestrial studies, when relevant. 

Oil compounds can be degraded by a variety of prokaryotic and eukaryotic organisms. After uptake in eukaryotic macro-organisms, provided they are at sub-lethal or sub-inhibitory concentrations, the compounds may be transformed by the metabolic apparatus, bio-accumulated, or removed through fecal excretion. Despite the range of organism types that can act on oil, however, the microbial communities are regarded as the main source for biological degradation of marine contamination. This perspective is based on the large concentrations of microorganisms, large surface-to-volume ratios and their rapid responses to the situation. This section will therefore focus on the microbial populations and their responses to possible oil discharges in the Arctic marine environment. 

Based on sequencing studies of the 16S rRNA gene, in the mid-1970s Carl Woese and colleagues separated living organisms into the domains Eukarya, Archaea and Bacteria (Woese et al. 1990). Microorganisms are present in all three domains. The bacteria and archaea are all microorganisms, though some (e.g. cyanobacteria) sometimes aggregate into visible mats or filaments. Among the eukaryotes are unicellular microorganisms often referred to as protists, which include the photosynthetic phytoplankton as well as some heterotrophic organisms (e.g. amoebae). Within this diverse collective of microorganisms, biodegradation of oil compounds is primarily associated with bacterial processes. In the marine environment the archaeal responses to oil pollution have mainly been considered low when compared to bacterial responses (e.g. Röling et al. 2004). However, archaea are important members of communities in petroleum reservoirs and are involved in the mineralization of petroleum hydrocarbons, for instance by methanogenesis under anoxic conditions. Recent studies have also implied the contribution of halophilic archaea to the biodegradation of hydrocarbons in the marine environment (Al-Mailem et al. 2010; Liu et al. 2009). Specific to the Arctic marine environment, essentially nothing is known of the archaeal contributions to oil degradation. 

Among eukaryotes, degradation of oil is mainly associated with fungi (Prince 2005). Only a few studies have been conducted to characterize fungal communities in Arctic marine environments (e.g. Gunde-Cimerman et al. 2003; Butinar et al. 2011). Among the microorganisms, our understanding of the protist contribution to oil biodegradation is also limited. Heterotrophic protists may affect petroleum biodegradation indirectly through their role as bacterial predators. Efficient grazing by protists can maintain the bacterial community in the log-growth phase, resulting in increased metabolic rates and thus increased biodegradation rates (Ballestero and Magdol 2011). 

In summary, most evidence for microbial degradation in the Arctic is connected to bacteria and bacterial communities. Our focus in this section will be on bacterial communities and the bacterial processes involved in oil biodegradation in the Arctic environment. However, the need for greater knowledge related to the contribution of archaeal and protistan organisms to oil biodegradation is an incentive to develop a better understanding of their contribution to oil biodegradation and microbial ecology in the Arctic. 

The cold waters and harsh environmental conditions in the Arctic have led some investigators to conclude that spilled oil will be more recalcitrant and remain in the environment for longer periods of time than oil spilled in less harsh environments. Other investigators have concluded that the microorganisms in the Arctic are adapted to those conditions and rapidly respond to spilled oil. The objective of this document is to examine experimental evidence from peer-reviewed literature that addresses these conclusions and identify areas of additional research. 

This chapter focuses on biodegradation of oil spilled into the marine Arctic environment. The state-of-knowledge will be summarized, and main uncertainties that need further addressing will be highlighted. In this summary we also describe some of the specific conditions that organisms involved in biodegradation processes encounter in the Arctic environment but not at lower latitudes. These differentiating conditions, which may affect biodegradation rates and capabilities in the Arctic, include generally low near-surface temperatures, ice coverage and (in open water) extreme fluctuations in the photoperiod during the Arctic summer and winter. 

The risk of oil pollution in the Arctic is relevant to both marine and terrestrial environments. The Arctic marine environment may be influenced by recently discovered oil and gas deposits, together with the potential for increased traffic attributable to shipping lanes made possible by historically low summer ice cover. The terrestrial environments may be exposed to pollution risk, for instance, from oil transport pipeline systems and other land-based activities. In this review we will focus on the marine environments, although references will also be made to terrestrial studies, when relevant. 

Oil compounds can be degraded by a variety of prokaryotic and eukaryotic organisms. After uptake in eukaryotic macro-organisms, provided they are at sub-lethal or sub-inhibitory concentrations, the compounds may be transformed by the metabolic apparatus, bio-accumulated, or removed through fecal excretion. Despite the range of organism types that can act on oil, however, the microbial communities are regarded as the main source for biological degradation of marine contamination. This perspective is based on the large concentrations of microorganisms, large surface-to-volume ratios and their rapid responses to the situation. This section will therefore focus on the microbial populations and their responses to possible oil discharges in the Arctic marine environment. 

Based on sequencing studies of the 16S rRNA gene, in the mid-1970s Carl Woese and colleagues separated living organisms into the domains Eukarya, Archaea and Bacteria (Woese et al. 1990). Microorganisms are present in all three domains. The bacteria and archaea are all microorganisms, though some (e.g. cyanobacteria) sometimes aggregate into visible mats or filaments. Among the eukaryotes are unicellular microorganisms often referred to as protists, which include the photosynthetic phytoplankton as well as some heterotrophic organisms (e.g. amoebae). Within this diverse collective of microorganisms, biodegradation of oil compounds is primarily associated with bacterial processes. In the marine environment the archaeal responses to oil pollution have mainly been considered low when compared to bacterial responses (e.g. Röling et al. 2004). However, archaea are important members of communities in petroleum reservoirs and are involved in the mineralization of petroleum hydrocarbons, for instance by methanogenesis under anoxic conditions. Recent studies have also implied the contribution of halophilic archaea to the biodegradation of hydrocarbons in the marine environment (Al-Mailem et al. 2010; Liu et al. 2009). Specific to the Arctic marine environment, essentially nothing is known of the archaeal contributions to oil degradation. 

Among eukaryotes, degradation of oil is mainly associated with fungi (Prince 2005). Only a few studies have been conducted to characterize fungal communities in Arctic marine environments (e.g. Gunde-Cimerman et al. 2003; Butinar et al. 2011). Among the microorganisms, our understanding of the protist contribution to oil biodegradation is also limited. Heterotrophic protists may affect petroleum biodegradation indirectly through their role as bacterial predators. Efficient grazing by protists can maintain the bacterial community in the log-growth phase, resulting in increased metabolic rates and thus increased biodegradation rates (Ballestero and Magdol 2011). 

In summary, most evidence for microbial degradation in the Arctic is connected to bacteria and bacterial communities. Our focus in this section will be on bacterial communities and the bacterial processes involved in oil biodegradation in the Arctic environment. However, the need for greater knowledge related to the contribution of archaeal and protistan organisms to oil biodegradation is an incentive to develop a better understanding of their contribution to oil biodegradation and microbial ecology in the Arctic. 

The Arctic Ocean represents a complex system of currents with influx and efflux of water (see Figure 5-1).  Cold and relatively less saline water enters the Arctic Ocean through the narrow Bering Strait between Alaska and Siberia, while warmer, more saline surface waters from the Atlantic penetrate the Arctic Ocean and are cooled as they move through the Greenland Sea and the Norwegian Sea. Water reaching the Arctic Ocean basin is swept into a huge circular current — driven by strong winds — the Beaufort Gyre. Siberian and Canadian rivers drain into the circular marine current to create a captured internal reservoir of relatively fresh water. Periodically, the circular current weakens, allowing large volumes of fresh water to leak out and cross the Arctic in the Transpolar Current. The water exits the Arctic Ocean via several “gateways.” It can flow through the Fram Strait, between northeast Greenland and Svalbard Island, and then branch around either side of Iceland. It can flow around the west side of Greenland through Baffin Bay and out Davis Strait. It can also flow through a maze of Canadian islands and out Hudson Strait. These mixes of salty and fresh water also generate Arctic haloclines, a vertical effect in which the cold fresh water lies atop warmer saltier water.

Figure 5-1. Prevailing currents in the Arctic Ocean (Source: Woods Hole Oceanographic Institution; http://www.divediscover.whoi.edu

The transport routes carry microorganisms into the Arctic from a complex mixture of seawater and river sources, with the North-Atlantic current (number 6 in Figure 5-1) as the single most important influx transport route. This results in cosmopolitanism of microorganisms in the Arctic Ocean and the presence of sometimes unexpected microorganisms in this cold marine environment (Hubert et al. 2009).

Significant to the discussion of currents, water masses, and effects on microbial population structures, a considerable part of the Arctic consists of one- or multi-year ice coverage. Since marine ice is frozen seawater the microbes frozen into the ice are transported with ice movement. This movement essentially follows two routes; the Beaufort Gyre circulating clockwise around the North Pole and the Transpolar Drift Stream, where ice moves from the Siberian coast of Russia across the Arctic basin, exiting into the North Atlantic off the east coast of Greenland (number 5 in Figure 1).  During ice growth, brine pockets are generated in the ice, since ice crystal generation is almost devoid of impurities (Petrich and Eicken 2010).  Brine accumulations are first generated as pockets, and later as chimney-like tubes termed brine channels. Microbes require a fluid environment for active metabolism, and these brine channels represent a fluid microenvironment within the ice mass. These channels therefore become important ecological niches for microbes which are able to survive in the high salinity and subzero temperatures in these systems. Eventually, contact with seawater will result in nutrient transport and reduced salinity in the channels. If channels are wide enough (approximately 2 mm in diameter), they are able to support counter-flow, i.e. simultaneous upward and downward movement inside the same channel (Lake and Lewis 1970).  Despite the potential for flow and mixing with bulk marine water, brine salinity tends to increase with distance to the seawater.   These salinity gradients in brine channels may result in gradients of microbial population density.  In winter, the apparent effect is higher bacterial and algal concentrations in the lower than the upper parts of the ice (Gradinger and Zhang 1997). However, in late spring and summer with rising air temperatures, the opposite situation is observed. The ice is warmed up from the top, becoming more porous, and melt water penetrates the porous ice and generates a linear bulk salinity profile that is commonly observed in the upper 20 to 50 cm of the ice during melt. The organisms in the brine channels are therefore exposed to fluctuating and physiologically challenging salinity conditions during the periods of ice freezing and melting (Faksness et al. 2011). Since much of the brines are drained off the ice during the first year after freezing, multi-year ice tends to have lower salinity and density than first-year ice (Tang et al. 2007), resulting in fewer brine pockets and also fewer possibilities for active microbial metabolism in the ice.

The population structures of bacteria in Arctic seawater are comparable to those in seawater from temperate regions, with the predominance of Alphaproteobacteria, Flavobacteria/Bacteroidetes,Gammaproteobacteria and Verrucomicrobia constituting more than 90% of the communities (Comeau et al. 2011; Teske et al. 2011; Ghiglione et al. 2012). It is also relevant to compare the microbial communities in the Arctic and Southern Oceans, since the two geographical areas have similar climatic conditions. Although some comparative studies of the microbial communities in Arctic and Antarctic marine environments indicated a high degree of resemblance (e.g. Bano et al. 2004; Brinkmeyer et al. 2003), a recent pole-to-pole study of surface and deep marine bacterial communities revealed significant differences, with 78% of operational taxonomic units (OTUs) unique to the Southern Ocean and 70% unique to the Arctic Ocean. Despite these dissimilarities, polar ocean bacterial communities were more similar to each other than to lower latitude pelagic communities (Ghiglione et al. 2012).

At a more localized scale, sea ice microbial communities may differ from those in the surrounding seawater. A study of first-year Arctic ice showed differences between ice and source seawater populations that were characterized by an increased abundance of Gammaproteobacteria and a lower abundance of Bacteroidetes in sea ice relative to seawater.  Winter sea ice communities were more similar to autumn water communities; species-specific die off processes were not observed in sea ice.  The implication was that winter sea ice communities are stable, whereas seawater communities undergo seasonal succession. The Alphaproteobacteria dominated in both environments (Collins et al. 2010). A study of multi-year ice revealed overall dominance of Gammaproteobacteria, as well as an increase ofBacteroidetes in the sea ice when compared to source seawater; the abundance of Alphaproteobacteria was greatly reduced in sea ice relative to the abundance in surrounding seawater (Bowman et al. 2012). A number of studies have also investigated the microbial communities in Arctic sediments, which may be regarded as pristine environments compared to most other sediments investigated. Studies from an Arctic fjord (Svalbard) showed that the Alphaproteobacteria predominated in the overlying seawater, while Gammaproteobacteria were more abundant in surface sediments. Deeper anoxic sediment layers were dominated by Deltaproteobacteria, which include common genera of strictly anaerobic bacteria associated with marine sediments (Ravenschlag et al. 2001; Teske et al. 2011).

The primary climatic condition associated with the Arctic is low temperature, and therefore most reviews and fundamental studies of Arctic microbiology focus on low temperature and psychrophilic (cold-loving) microbes. However, other conditions are also specific for this environment, including extreme light/dark conditions in the Arctic summer and winter, respectively. The Arctic area also includes coverage, with 9-12 million km² of pack ice with average ice thicknesses of 3-4 m, with ridges up to 20 m thick. As described above the microbes in this ice are not only challenged by the subzero temperature, but also by high salt concentrations in the brine channels.

The temperature of the Arctic Ocean normally does not exceed 4-5°C, with cold (close to 0°C) low-salinity surface water and warmer high-salinity water (up to 5°C) below 50 m depth. The marine organisms in the Arctic are therefore consistently exposed to low temperatures. Numerous studies of microbial adaptions to low temperature have been published (e.g.  Brakstad et al. 2008; Helmke and Weyland, 2004; Knoblauch et al. 1999; Robador et al. 2009). As the temperature decreases with concomitant decrease in the thermal energy of a system (enthalpy), increased stability and rigidity of biomolecules occur. Proteins become less flexible, while the secondary structures of DNA and RNA become more stable, and the processes of DNA replication, transcription of RNA and translation of proteins are inhibited (Bakermans 2012). However, psychrophilic microorganisms have adapted to these low-temperature conditions in a number of ways:

• Enzymes in bacteria isolated from sea ice may be activated by the cold, with detectable catalytic activity well below the freezing point of seawater (Groudieva et al. 2004). The enzymes of psychrophilic microbes are characterized by increased flexibility of active sites resulting from structural modifications to address freezing temperatures.  These modifications may include less enzyme core hydrophobicity, increased surface polarity and fewer interactions between amino acids (hydrogen bonds, salt and disulphide bridges). These characteristics facilitate retention of enzymatic activities at low temperature (Bakersman 2012).
• Nucleic acids show adaption to low temperature at the sequence level in psychrophiles, as exemplified by increased uracil content in ribosomal RNA and dihydrouridine content in transfer RNA as a result of decreased temperature (Khachane et al. 2005; Dalluge et al. 1997).
• Microbial membrane structures may crystallize at low temperatures, impairing function. However, in psychrophiles, membrane fluidity is retained by increasing the proportion of unsaturated fatty acids and by desaturation of membrane lipids, resulting in unsaturated fatty acyl chains and less tightly packed lipid chains (Russel 2008).
• Microorganisms can be challenged in ice by reduced water availability due to the formation of ice crystals. However, psychrophiles can combat the effects of reduced water activity by the synthesis of compatible solutes such as sugars, amino acids, alcohols or cryoprotective proteins. Ice crystal formation can also be prevented by production of anti-nucleating materials (Bakersman 2012).
• Psychrophilic bacteria in brine channels are challenged by both low temperature and high salinity.  These may produce extracellular polymeric substances (exopolysaccharides), which have a cryoprotective role in the sea ice brine channels, as well as binding essential cationic trace metals to enhance halotolerance (Nichols et al. 2005).
• Microbes exposed to large drops in temperature may produce cold shock and cold acclimation proteins (Berger et al. 1996). Cold shock proteins are supposed to be involved in protein translation regulation, while cold acclimation proteins show high catalytic activity at low temperatures and rapid inactivation at moderate temperatures (Fukunaga et al. 1999).

In Arctic regions, with a long polar summer and a correspondingly long polar winter and associated widespread ice coverage, phototrophic organisms must tackle a number of challenges.  For example, phytoplankton communities responded rapidly and increased in numbers by an order of magnitude in the Beaufort Sea with the increased solar irradiation in May, despite the presence of sea ice. However, eukaryotic phototrophs somehow also persisted throughout the winter darkness (Terrado et al. 2008). Among phototrophic bacteria isolated from the Arctic Ocean were photoheterotrophic microbes, which are capable of both utilizing dissolved organic materials and harvesting light energy.  Photoheterotrophic taxa included coccoid cyanobacteria (Synechococcus and Prochlorococcus), aerobic anoxygenic phototrophic (AAP) bacteria, and proteorhodopsin (PR)-containing bacteria. In a study of photoheterotrophic microbes in the Arctic Ocean in the summer and winter it was observed that some of these bacteria (AAP and PR containing bacteria) decreased from summer to winter, in parallel with a threefold decrease in the total prokaryotic community, while the abundance of Synechococcus did not decrease in winter (Cottrell and Kirchman 2009). These data demonstrated the ability of phototrophs to switch from photosynthesis to heterotrophic activities during the winter.  Characterization of green light-absorbing PR from bacterial isolates from the Arctic Ocean showed a slower photocycle, relatively larger change in activation energy of the transition between the oxygen intermediate and the ground state compared to PR from bacterial phototrophs isolated from temperate seawater (Jung et al. 2008).

Photosynthesizing microbes have also been observed within sea ice. Marine algae seem to be more sensitive to brine salinity than bacteria and therefore are detected mainly in the lower parts of sea ice (lower salinity in winter associated with contact with seawater; Gradinger and Zhang 1997). Recent studies have also identified marine autotrophic bacteria in marine ice indicating the potential ability for ongoing use of dissolved organic materials (Díez et al. 2012).

Conditions in marine ice vary considerably from those in seawater. The temperature is lower in the ice relative to fluid water, and may drop as low as the air temperature during the polar winter. Transmission of light through the ice is severely reduced compared to seawater, and light may be entirely absent when the ice is covered by a snow cap. In first-year ice, brine inclusion networks are generated by salting-out processes, as described in previous sections. The brine channels of the ice provide liquid saline niches at subzero temperatures which enable microbial motility and metabolic activity (Junge et al. 2002; 2003; 2004; 2006). The brine channels also act as a matrix for transport of soluble organic matter and other nutrients.  In the brine channels the ice temperatures can be as low as -20°C and salinity conditions can be as high as 200 Practical Salinity Units (Salinity in normal seawater is 35 PSU). Though challenging to microbial life, laboratory experiments have shown that bacteria (Colwellia psychroerythraea) were able to incorporate amino acids into proteins at temperatures as low as -20°C in brines (Junge et al. 2006). This metabolic activity was associated with particles or with the surfaces of the brine channels (Junge et al. 2003; 2004). In addition, the ability to grow at subzero temperatures has been demonstrated in the bacterium Psychromonas ingrahamii, which was cultured at temperatures as low as ‑12°C (Breezee et al. 2004). The brine channels may become depleted in oxygen, for instance if microbial processes occur without oxygen renewal (seawater or photosynthesis), and anaerobic denitrification processes have been measured in marine ice (Rysgaard and Glud 2004). These studies therefore demonstrate that bacterial activity can take place in marine ice, both with respect to motility within the ice and active metabolism. Recently, Mykytzuk et al. (2013) presented a detailed characterization of the physiological adaptations that enable a halotolerant psychrophilic permafrost bacterium to grow and metabolize at temperatures as low as -15°C.  The implication is that halotolerant psychrophilic species may also exist in the ice.

Since Arctic environments are increasingly exposed to petroleum exploration, production and transport, the studies of microbes and processes involved in cold-environment biodegradation is essential both for the industries operating in these areas and the governmental bodies responsible for environmental stewardship.  As described, microbes can function within most Arctic environments, including ice at sub-zero temperatures.

Numerous studies have shown that populations of known oil-degrading bacteria are present in Arctic environments (Zinger et al. 2011, Ghiglione et al. 2012; Sul et al. 2013).  However, few studies have directly assessed microbial community composition with the ability to clearly distinguish all of those taxa that can be defined as oil-degrading bacteria (e.g. heterotrophic and other non-designated microbes that respond positively to oil). 

The physico-chemical characteristics and weathering conditions of different oils at low temperatures and which are treated chemically may vary, having impacts on biodegradation efficiencies and should be an issue for further research, for instance, in the relationship between biodegradation and oil appearance (e.g. viscosity, dispersibility, resurfacing) after a spill.  A variety of processes in the Arctic are season-variable (e.g. photooxidation, different ice-conditions).

Marine ice poses a particular challenge to the indigenous microbes, which require the ability to survive and be metabolically active at sub-zero temperatures and at high salinity.  Microbial metabolism has been demonstrated in marine ice, and populations have been stimulated by oil in the ice.  However, the extent of hydrocarbon biodegradation in Arctic ice is likely to be low but requires more attention.

Few studies have attempted to use modeling approaches to predict oil biodegradation in cold marine environments.  Modeling tools are used today by oil companies and authorities to predict the fate of oil spills, but these models are often less well calibrated for the Arctic environment.    In that respect temperature-related biodegradation data, which often are based on Q₁₀-approaches may show erroneous results at very low temperatures, probably due to physical changes in the oil.  Therefore, more detailed temperature-related biodegradation studies will be required to improve fate models, which often rely on incomplete data sets for cold climate spills. 

Typical oil discharge scenarios include process losses or accidental releases from exploration, production, processing or transport related activities. However, the risk of accidental oil discharges will always be present in an environment with oil-related activities. In addition, the diminishing Arctic ice zones will likely increase ship activity through the Northwest and Northeast passages, activities which may contribute to an increased risk of oil discharges in Arctic marine environments. Biodegradation of oil compounds is regarded as the most complete process, as it is able to completely remove oil compounds, through the mineralization to carbon dioxide and water. In particular, two large oil spills in marine water have drawn public attention to oil biodegradation issues in general, the Exxon Valdez grounding in Prince William Sound in 1989 and the recent Deepwater Horizon blowout in 2010, both recently reviewed by Atlas and Hazen (2011). Media attention on the deep water plume from the Deepwater Horizonblowout has resulted in increased focus on the potential effects of oil spills in cold water environments. 

Physico-chemical properties of the spilled oil will affect biodegradation. Crude oils may be separated into 4 main types; paraffinic, asphalthenic, naphthenic and wax-rich (Moldestad et al. 2003). For instance, paraffinic oils will have a distinct chromatographic n-alkane pattern and a high content of light compounds like BTEX and naphthalenes. These oils therefore contain a high degree of easily biodegradable compounds. However, naphthenic oils are often biodegraded in-reservoir (Head et al. 2003), and in these oils most of the easily biodegradable compounds may have been consumed before oil production.  Asphalthenic oils are rich in poorly biodegradable asphaltenes and resins, while wax-rich oils will often have a high pour point and may be solidified in cold water, a physical factor that will affect their availability for biodegradation.  Marine fuel oils may also be spilled.

When oil is discharged to the marine environment a number of weathering processes occur:

Volatile compounds with low boiling points (e.g. saturates up to nC₁₁, mono- and some diaromatic hydrocarbons) are rapidly evaporated after surface spills. These are compounds that are normally rapidly biodegradable in the water column, but evaporation is normally more rapid than biodegradation after a surface spill. Evaporation is slower in cold than in temperate seawater (Brandvik et al. 2005), and this may result in temporarily higher concentrations of volatile toxic compounds (e.g. BTEX) in the seawater. At high concentrations these compounds may prolong microbial lag-phases and delay the onset of biodegradation (Atlas and Bartha 1972; Hokstad et al. 1999), although it is not known if this will have an impact on biodegradation under field conditions. In subsurface releases these volatiles are rapidly dissolved from dispersed oil and we suspect may be biodegraded rather than evaporated. Evaporation also results in increased viscosity of the residual oil (Faksness 2008), which will negatively affect the ability of oil to disperse, thereby slowing biodegradation.

Components dissolved from the oil phase are available for biodegrading microbes in the water column. In cold seawater the dissolution of oil compounds is decreased compared to temperate water (Faksness, 2008). The typical oil compounds in a water-soluble fraction (WSF) from fresh oils include phenols, naphthalenes and 2-3 ring PAHs. In addition, the WSF contains considerable amounts of highly polar compounds with nitrogen, sulphur, and oxygen atoms in their structures (so-called NSO compounds), often present as a chromatographic "hump", termed the "unresolved complex mixture" (UCM). In a study of WSF from an in-reservoir biodegraded oil (Troll) approximately 70 % of the WSF was separated by preparative high-pressure liquid chromatography, into a polar fraction (Melbye et al. 2009).  The non-polar compounds of the WSF are often considered to be rapidly biodegraded in the marine environment (Brakstad and Faksness 2000), and biodegradation of these compounds may result in a significant increase in the UCM  concentration relative to other crude oil components (e.g. Meredith et al. 2000), highlighting their persistence (Han et al. 2008).

Photooxidation is an important process in degrading and transforming crude oil compounds after release to the environment. The polar region exhibits vast seasonal differences in light conditions, and as a result photooxidation varies significantly between the polar summer and winter. UV-irradiation of crude oils has shown that aliphatic compounds are mainly resistant to photodegradation, while aromatic compounds appear particularly sensitive to this process (Maki et al. 2001). In contrast to biodegradation, increased size and alkyl substitution result in increased sensitivity of aromatic hydrocarbons to photochemical oxidation. As photooxidation leads to the inclusion of oxygen atoms in the structures of these compounds, photooxidized products appear mainly in the polar resin fraction of the oil (Maki et al. 2001; Garrett et al. 1998; Prince et al. 2003). Additionally, the average molecular weight of oil compounds is reduced and the oxygen content increased.  Studies have also shown that the photooxidized compounds subsequently exhibit increased susceptibility to biodegradation (Dutta and Harayama 2000; Maki et al. 2001; Ni'matuzahroh et al. 1999). Consistent with the physico-chemical properties of the photooxidized compounds, both the dissolved organic carbon concentration and acute toxicity of the water-soluble fraction of oil increased during the irradiation period (Maki et al. 2001). Thus, photooxidation results in a greater proportion of oxidized compounds that exhibit increased water-solubility and subsequently more significant impacts on toxicity and biodegradation. However, investigation of the relationship between photooxidation, biodegradation and toxicity would be of interest as part of the fate-determination of different oil compounds during the Arctic summer.

In shallow seawater and at higher levels of suspended sediments (e.g. after a storm), sediment particles may adhere to the oil and sink to the subtidal seabed sediments. Oil spills may also drift to shore and be mixed into the intertidal sediments. Oils mixed into the sediments will be subject to microbial processes in the sediment (Refer to Section 3). If seawater replenishment is poor, aerobic processes may consume most of the oxygen, resulting in anoxic conditions. Anaerobic biodegradation of hydrocarbons, by several alternative mechanisms, will occur in the absence of oxygen, as reviewed by Heider (2007).  Genes associated with anaerobic hydrocarbon degradation (e.g. benzyl- and alkylsuccinate synthase genes) have been detected in hydrocarbon-contaminated sediments (Callaghan et al. 2010).  

Water uptake into the spilled oil may cause the formation of viscous and often stable water-in-oil emulsions. Emulsions have been shown to be poorly biodegradable (Brakstad et al. 2011; Cook et al., 2011). Water taken up in the emulsions may contain oil-degrading microbes, but if water is trapped in the emulsions this will not promote biodegradation on the bulk oil as the emulsions may be depleted in essential nutrients. 

With sufficient energy from wave action the oil may break up into droplets in the water column. If oils are easily dispersed, small droplets are generated. The rising or settling rate of the droplets is related to the size and specific gravity of particles. As an example droplets 100 µm in diameter and a lower specific gravity that the surrounding seawater have been observed to rise with a velocity of approximately 1.5 m/h. Thus, larger droplets will resurface rapidly and thin oil films (sheens) may be formed. Oil dispersion is important for biodegradation. Dispersible oils will generate relatively small droplets, resulting in large surface areas for bacterial attachment. For instance, fresh Louisiana Sweet Crude oil can be made to generate dispersions with a median droplet size of 50-150 µm under continuous breaking wave conditions in an oil-on-seawater flume experiment (Brakstad et al. 2011). Several biodegradation studies of dispersed oil in cold seawater (5-8°C) have shown bacterial colonization of oil-droplets and biodegradation of dispersible oils (e.g. Lindstrom and Braddock 2002; MacNaughton et al. 2003; Venosa and Holder 2007; Prince et al. 2012). This colonization may tend to generate flocs of oil and biomass (MacNaughton et al. 2003; Bælum et al. 2012). However, for waxy oils with high pour points, evaporation, dilution and dispersion may be reduced in cold seawater, since precipitated wax may form a matrix which limits internal mixing and acts as a diffusion barrier between the oil and the water (Faksness 2008).

As described above, surface and resurfaced oil may generate thin films on the sea surface. In a series of studies with thin oil films immobilized on hydrophobic adsorbents, n-alkanes in these films were rapidly biodegraded in temperate and cold seawater (0-13°C), while aromatic compounds were subject to mixed dissolution and biodegradation (e.g. Brakstad and Bonaunet 2006; Brakstad et al. 2004). In experiments over a period of 112 days with different oil thicknesses of a wax-rich oil it was apparent that a thickness limit for measurable biodegradation (nC₁₇/Pristane and nC₁₈/Phytane) was between 0.1 and 1.0 mm in cold (6-10°C) seawater (Brandvik et al. 2006). 

In the aftermath of the Deepwater Horizon incident, a large body of new information has been collected and integrated with our already existing understanding of the microbial response to oil spilled in the marine environment (Hazen et al. 2010; Mason et al. 2012; Valentine et al. 2012). In general, in situ sampling and analysis revealed unexpectedly rapid disappearance of released oil in the Gulf of Mexico environment, which is characterized by a temperate climate (Hazen et al. 2010). This rapid disappearance was affected by the prevalence of water-soluble constituents in the crude oil (Reddy et al. 2012), injection of subsea dispersant into the erupting oil flow (Kujawinski et al. 2011), and presence of indigenous oil-degrading microorganisms in this area that is well known for natural seeps of crude oil from reservoirs (Lu et al. 2012). Such indigenous oil-degrading microorganisms are the topic of this section.

Following the Deepwater Horizon incident, extensive analysis of microbial responses was done both in situ and in laboratory microcosms. These analyses support, in general, a paradigm of successive blooms of taxonomically distinct indigenous microbial populations as the oil weathers and labile components are sequentially degraded leaving less-readily degraded components to feed subsequent blooms (Hazen et al. 2010; Valentine et al. 2010; Kostka et al. 2011; Baelum et al. 2012; Beazley et al. 2012; Lu et al. 2012; Mason et al. 2012; Valentine et al. 2012).

Conditions are very different in high latitude marine environments.  As described in previous sections, the Arctic and Antarctic marine environments are characterized by seasonal extremes of photoperiod, spatial variability in salinity and temperature, as well as generally colder surface temperatures compared to the temperate latitudes. These differences may result in different expectations about the rate of oil degradation, as described in previous sections.  They also result in different expectations about the indigenous populations of oil degrading microorganisms.

As mentioned in previous sections, microbial responses to oil in marine environments generally are dominated by bacteria rather than archaea (Roling et al. 2004). Although fungi are known to degrade petroleum compounds in some marine settings (Zinjarde and Pant 2002), few surveys of fungal abundance in high latitude marine environments have been done (Butinar et al. 2011) and thus far none have addressed oil degradation by fungi in high latitude environments. For these reasons, this section focuses on the bacterial component of the marine microbiological community. 

Among the bacterial taxa catalogued in high latitude marine environments, many appear to be specific to that environment (Ghiglione et al. 2012; Sul et al. 2013).  This apparent specificity may be due to truly unique populations, or it may be a function of the limit of detection.  Community members that thrive in the high latitude marine environment grow to relatively high cell densities and are therefore more easily detected.  Various investigations have found that microbial species richness curves are not saturated with typical levels of effort.  This finding has led to the hypothesis that there is an under sampled “rare biosphere” of organisms with low population density (Sogin et al. 2006) that, despite low population levels, can respond to changes in environment and energy source.  This phenomenon may be typified by the explosion of Oceanospiralles and Colwellia populations in the presence of different partitions of spilled oil during the Deepwater Horizon incident (Hazen et al. 2010; Bælum et al. 2012).

Marine ice represents an extreme biosphere with below-zero-centigrade temperatures and high salt concentrations. It has been demonstrated by field studies that bacterial populations in Arctic marine ice are affected by oil pollution, stimulating species of a few genera like Colwellia, Marinomonas and Glaciecola (Brakstad et al. 2008). 

Not all of the microorganisms found in the Arctic oceans are adapted to that environment.  The various currents carry viable microorganisms from diverse locations to the Arctic (Rosnes et al. 1991; Hubert et al. 2009; Hubert et al. 2010); thus, there is an expectation of cosmopolitanism among the free-living microorganisms.  This is not to say that the population structure is homogenous as if the Arctic were a giant mixing bowl.  In fact, there is documented variability in population structures, with different communities associated with water masses of different origins (Galand et al. 2010; Sul et al. 2013).   The presence of non-adapted microorganisms such as thermophiles does, however, indicate that microbial populations adapted to the consumption of natural or human-induced oil releases might be transported to and be present in areas that are not commonly exposed to oil.

Crude mineral oil is degradable by indigenous microorganism populations in the Arctic marine environment, even at near-freezing temperatures (Brakstad and Bonaunet 2006), although at slower rates compared to higher temperatures (Margesin et al. 2003; Michaud et al. 2004).  Nevertheless, over a time course on the order of weeks substantial biodegradation can be observed in nutrient-enriched cold Arctic seawater (Brakstad and Bonaunet 2006). Community analysis of oil-degrading Arctic microbial consortia indicated that several taxa of bacteria are involved in biodegradation in this environment, including genera related to Pseudoalteromonas, Pseudomonas, Shewanella, Marinobacter, Psychrobacter, and Agreia (Deppe et al. 2005).  Of interest, these are different organisms from those directly associated with degradation in the Deepwater Horizon spill in the Gulf of Mexico, specifically bacteria of the orders Oceanospiralles (Hazen et al. 2010; Kostka et al. 2011) and Alteromonadales (Bælum et al. 2012), among others.

Linear alkanes often are characterized as an easily accessible carbon source, either through degradation or direct incorporation into microbial biomass, in the marine environment (Harayama et al. 1999).  The metabolic pathways for linear, branched, and cyclic alkanes have been studied and described since the 1960s (Jobson et al. 1972, Coates et al. 1997, Feng et al. 2007, Rojo 2009, Gray et al. 2011).  Preferential degradation of short-chain alkanes (represented by C₁₅) over long-chain alkanes (represented by C₂₆) was observed in situ in a deep plume (circa 1,400 m) in the Gulf of Mexico under aerobic conditions (Hazen et al. 2010).  Furthermore, during weathering in subsurface petroleum reservoirs, alkyl chains on substituted soluble PAHs such as alkane-substituted naphthalenes may be transformed even more rapidly than linear alkanes (Jones et al. 2008).  Whether this phenomenon, observed in anaerobic subsurface reservoirs, would occur in the presence of petroleum hydrocarbons released into the deep sea, remains unknown. 

The specific bacteria known to accomplish alkane degradation are numerous (Whyte et al. 1997; Rabus et al. 1999, Hara et al. 2003, van Beilen et al. 2004, Throne-Holst et al. 2006, Feng et al. 2007, Throne-Holst et al. 2007, Wentzel et al. 2007, Rojo 2009, Teramoto et al. 2009, Wasmund et al. 2009, Tapilatu et al. 2010, Alonso-Gutierrez et al. 2011, Teramoto et al. 2011).  Among these, many were characterized from high-latitude marine environments.  Specifically, the Pseudomonas strains isolated by Whyte et al. (1997) from Arctic soils may be transported to the marine environment via runoff.  Alcanivorax species are known to be widespread in marine environments exposed to oil (Hara et al. 2003, van Beilen et al. 2004) and, if not prevalent in the Arctic environment, might be expected to be present because of currents.  Thus, bacteria capable of alkane degradation are expected to be present in the Arctic oceans.

The ability to degrade aromatic hydrocarbons and, in particular, polynuclear aromatic hydrocarbons typically is considered to be less widespread than the ability to degrade alkanes.  For example, some organisms have diverse pathways that confer the ability to degrade polynuclear aromatic hydrocarbons, e.g., Mycobacterium vanbaalenii (Kweon et al. 2011) and various Pseudomonas spp. (Whyte et al.1997). The distribution of these genes among bacteria in Arctic marine environments remains unknown.