4.5 Environmental Impact and Preservation
4.5.1 Structure of the Arctic Ocean
The oceans, including the Arctic Ocean, play an important role in the diffusion and circulation of environmental pollutants. The Arctic Ocean is being critically examined for the feasibility of exploitation of their natural resources, and there is considerable evidence that global environmental problems will disproportionately impact the Arctic region. If we are to understand the influences of human activities in the Arctic and the response of the Arctic systems to human-induced perturbations, an appreciation of the role of the Arctic Ocean is required. A brief overview of the Arctic Ocean is therefore presented here.
A dominant characteristic of the Arctic Ocean is the year-round presence of a dynamic ice cover. The ice cover in the Arctic Ocean has a profound effect on the air-sea interaction, in particular, heat, mass and momentum transfers. The Arctic Ocean comprises deep central basins at the higher latitudes and several shallow marginal seas; the Chukchi Sea, East Siberian Sea, Laptev Sea, Kara Sea, Barents Sea and Beaufort Sea. As described in Section 3.1.1, the Arctic Ocean is almost a closed ocean, linked to the Pacific Ocean by the narrow Bering Strait and to the Atlantic Ocean by the Canadian Arctic Archipelago, the Fram Strait and the Barents Sea. The broad continental shelf off Siberia that constitutes the NSR, extending from 200km to as far as 800km into the ocean, is in most cases no more than 100m deep. Although these shallow seas account for 36% of the Arctic Ocean's total area, they contain only 2% of the total volume of water of the Arctic Ocean. This region has also freshwater inflow from numerous rivers, with the highest ones in the thawing season of snow.
Vertical circulation occurs in the Arctic by two counterbalancing processes.
* The inflow of fresh water from Arctic rivers creates density stratification, which blocks the vertical circulation. The freshwater inflow also generates currents that flow from the Arctic Ocean into the North Atlantic Ocean.
* As heat is lost from the water surface in the winter, sea ice forms. During sea ice formation, salt and impurities are discharged down into water, making the seawater below the sea ice heavier and causing it to sink.
The fundamental features of the currents in the Arctic Ocean vary little throughout the year. The salinity, on the other hand, varies considerably according to the formation and melting of ice. In the upper layer 25-50m, the salinity changes from 2.8% to 3.35%. The temperature is also controlled by the ice dynamics through considerable heat transfer. The latent heat of the sea ice as much as 80kcal/kg plays a major role in this transfer, which is equivalent to 80゜C change in water temperature.
The movements of water masses at different depths are illustrated in terms of pollution in Figure 4.5-1.