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3.2 Knowledge Status

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)
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.

3.2.1 Weathering of Oil Spilled in Ice

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

3.2.2 Oil in Ice Interactions

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)
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

Type of Ice FieldDescriptionConc1Characteristics

Fast Ice

Ice attached to or contiguous with the shore

 
  • Does not move with currents and wind
  • Most stable (extensive in areas with broad shallow shelf extending offshore)
  • Extends to 10 - 12m (water depth); potentially to 30m (but rougher terrain)

Open Drift Ice

Floats freely

1-5/10

  • Oil spreads similarly to open water conditions
  • Would not provide for stable operations; also little natural ‘containment’ properties
  • Relatively short term occurrences (e.g. 25 d/year)

Pack Ice

6/10

  • Unpredictable movement
  • Tends to corral oil

Close Pack Ice

7-8/10

Very Close Pack Ice

9-9+/10

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)
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).

3.2.3 Oil on Arctic Shorelines

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.

3.2.4 Oil-Sediment Interactions

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 (Kow) 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.