Source: AMAP: Arctic pollution issues: A state of the Arctic environment report. Arctic Monitoring and Assessment Programme (AMAP), 1997.
Figure 4.5-2 Vertical section of the Arctic Ocean and the different water masses with their approximate residence time
Two main features characterize the surface currents of the Arctic Ocean. The first is the Transpolar Drift, in which the surface waters of the Eurasian basin move across the basin toward the North Pole and then toward the Fram Strait; the second is the anticyclonic flow around the Beaufort Gyre in the Canadian Basin. In the deep waters of the Arctic Ocean, water masses exhibit complex movements. Mean surface current speeds are slow, at about 1-4cm/sec (300-1,200km/year). Because the Arctic Ocean is about 4,000km wide, the surface layer is to be completely replaced in three to 10 years. An estimation based on drifting speeds of sea ice gives an average residence time of 5 years.
The vertical structure of the Arctic Ocean and the average residence time of water masses is illustrated in Figure 4.5-2. Below the Polar mixed layer of low salinity near the surface, haloclines exist, of which average residence time is about 10 years. The Atlantic layer below the haloclines is believed to have an average residence time around 30 years. Deeper still, the Arctic deep water below the Atlantic layer has an average residence time over 100 years.
4.5.2 Indigenous Peoples and the Ecosystem in the Arctic Ocean
To understand how pollution is spread and how it affects the ecosystem, it is important to look at the structure of the food chain. As in all other oceans, the primary producers of the food chain in the Arctic Ocean consists of small algae such as the pelagic unicellular algae, or phytoplankton. Together these species account for 97% of all the marine lives in the Arctic Ocean. The productivity of phytoplankton is controlled by light and the nutrient, which is closely connected with the retreat of the ice edge in spring. Forming the base of the food chain, phytoplankton is consumed by the next link in the chain above them, zooplankton such as small crustaceans. Cod and other fish live at the third trophic level being fed by the zooplankton. The fish provide the main source of sustenance for seabirds and marine mammals that are at the top of the food hierarchy. The fish therefore play a vital intermediary role, delivering the energy produced by the plankton to the vertebrates living on the ice. Figure 4.5-3 shows an overview of the food chain, illustrating how far various impact factors affect the elements of each ecosystem (for example, sea birds).
