The Arctic at Risk:
A Circumpolar Atlas of Environmental Concerns
The Arctic at Risk:
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Sea Ice Sea ice forms when ocean water freezes. Because sea salt is largely excluded during the freezing process, the salinity of young sea ice is about 5[[perthousand]] in comparison with surface ocean waters, which typically have salinities greater than 34[[perthousand]].
Ice that does not melt during the first summer after it forms is called second-year ice. During the second winter, ice is added on to the underside of the floe. Ice that has survived more that two melt seasons is called multiyear ice. It is often thicker than 3 meters. As sea ice ages, it loses salt. Meltwater ponds forming on sea ice several years old may have water fresh enough to drink.
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First-year sea ice covers much of the Arctic and surrounding
seas in winter. In summer, this ice melts, thins, and moves offshore. Multiyear ice covers the
central Arctic and eastern Greenland areas. Winds and ocean currents keep most
of the ice in constant motion. As a result, the ice is broken up into floes,
with open water spaces, called leads, between the floes. The two main ice
circulation systems are the clockwise Beaufort Gyre in the Amerasian Arctic,
and the west-flowing Transpolar Drift Stream in the Eurasian Arctic.
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Much of the Arctic sea ice forms in winter in the
marginal seas, especially in the wide Siberian shelf seas, such as the Kara and Laptev. Along the coast
there is a band of fast ice--sea ice anchored to the sea floor and/or the
shore. A region of open water, called a polynya or a flaw lead, often exists
between the fast-ice zone and the drift ice. Typically areas of extensive ice
formation, polynyas may have elevated biological productivity. Both leads and
polynyas are also regions where the atmosphere is in direct contact with the
sea, so there can be direct deposition of atmospheric pollutants and air-sea
exchange of gases. (Ice Thickness in August)
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Growing concern about pollution of the Arctic air and water may have missed sea
ice as a key element in the transport of contaminants. Sea ice can incorporate
contaminants 1) if the water from which it freezes is contaminated, 2) if
contaminated sediments are frozen into the ice, 3) if it picks up pollutants
from the surface ocean microlayer during drift, and 4) if pollutants are
deposited on its surface from atmospheric deposition. Sea ice floes are
transported thousands of kilometers through the Arctic region over several
years. Accumulated contaminants are released into the ocean as the ice thaws,
refreezes, and thaws again. The pollutants can be taken up by algae attached
to the sea ice, as well as by phytoplankton in the surface waters along the
marginal ice zone (Muir et al., 1992; Pfirman et al., in press). The marginal
ice zone is the southernmost limit of the zone with concentrated ice floes. It
is a region with intense biologic productivity, providing the food source for
much of the Arctic marine food chain. (Sea Ice Flux)
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Glaciers Glaciers are large masses of ice that flow under their own weight. They form when enough snow accumulates to compress the lower layers and form ice. The largest glacier ice mass in the Arctic is on Greenland, where ice covers an area of 1,800,000 km2, which is nearly 85% of the land area (Encyclopedia Britannica, 1990). Some glaciers formed on land move downslope to where they meet the sea. Along the Greenland coast, outlet glaciers flow from the ice sheet to the sea. Glaciers terminating in the sea periodically break off, or calve, forming icebergs. Icebergs differ from sea ice because they are made up of ice that formed originally from snow, so they do not contain sea salt. Also, because they break off from glaciers, they are generally much thicker than sea ice, sometimes extending more than 100 meters below sea level. Icebergs from Greenland are frequently observed along its coast; from there they may drift into the North Atlantic Ocean, where they cause hazards to shipping. Although there are numerous glaciers in Canada, relatively few reach the sea and produce icebergs.
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Because glacier ice accumulates atmospheric pollutants deposited on the glacier surface, there are also concerns that icebergs may represent a source of contaminants to the surface waters.
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Permafrost Permafrost--permanently frozen ground--develops in regions where the temperature is constantly below 0deg.C. The depth of permafrost depends on such conditions as climate, vegetation, and whether or not it was covered recently by glaciers or sea ice. Some permafrost does occur in marine sediments. Very deep permafrost is often a relict feature formed in unglaciated areas during the last glacial maximum. Near the northern coasts of Siberia, permafrost regionally reaches depths of 240 to 600 m (Encyclopedia Britannica, 1990). As much as 80% of the soil volume may be comprised of ice in these areas.
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Typically, a shallow upper zone of permafrost thaws in summer. This zone is called the active layer. Because the frozen ground underneath inhibits groundwater drainage, pollutants deposited on the soil surface do not disperse as readily as in temperate regions. In hilly areas, thawing may cause the active layer to slide downslope, a process called solifluction. If global warming proceeds as predicted, the active layer may become thicker and some regions may lose permafrost altogether, causing prevalent ground failure.
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