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)