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The Arctic Ecosystem |
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As you look down from outer space,
through the solar winds generated by the outpourings of the sun
gusting to 200 km per minute, through the -200° C ozone depleted
stratosphere, through the boundary layer at 3 km between the upper
and lower atmosphere, there you see the Arctic lying in winter darkness
dominated by the 15 million square miles of polar sea ice. In summer
this is reduced to about 8 million square kilometres. The sea ice
extends south to three exits of the Arctic Ocean - the narrow exit
west of Greenland into the North Atlantic; through the 500 km wide
strait between Greenland and Svalbard; and through the 70 kilometre
Bering Strait between Chukotka and Alaska into the Bering Sea and
onwards to the Pacific Ocean. The land surrounding the Arctic Ocean
is covered by many glaciers but is dominated by the Greenland Ice
Cap covering 1.7 million square kilometres and with a maximum thickness
of 3200 km - a massive volume of 2.8 million cubic kilometres. Glacial
fingers extend down the mountain ridges in Norway, the Urals, Kolyma,
Alaska, the Yukon and Baffin Island reaching well below the Arctic
Circle. |
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Deep snow blankets land near the oceans
but barely covers the polar deserts and semi-deserts of the continental
land masses. Here, on patterned ground, musk ox and reindeer scratch
for fodder while fox and wolf scavenge and female Polar Bears sleep
and give birth in their snow lairs. Below the frozen soil are solid
ice wedges and permafrost, deep and continuous in the high Arctic
but discontinuous in the sub-Arctic. The ice covering the surface
of deeper lakes, rivers and seas overlies water which is still above
freezing while the air temperature is -50oC or below. As you follow
the seasonal cycle, the sun rising above the horizon radiates the
Arctic, warming the air, causing the sea ice to thin and retreat.
The snow and ice melt on land, rivers flood with melt water, large
volumes flow into the coastal waters lowering both the temperature
and salinity. Migrating reindeer, geese, ducks and waders return
to feed on new plant growth and emerging insects. |
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The waters circulate within the Arctic
Ocean and force their way under the warmer surface waters, through
the narrow exits into the North Atlantic and Pacific Oceans (see
figure 1).Whales and seals move northwards providing food for
the polar bears. On land the sun's radiation warms the surface vegetation
and bare ground, raising temperatures above that of the air. The
land bursts into colour almost 'overnight' - partly because there
is no night. Migrating reindeer, geese, ducks and waders return
to feed on new plant growth and emerging insects. |
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Salmon run the rivers and the bears
gorge. Below the land surface temperatures rise more slowly and
the soil melts to form an 'active layer' where microorganisms and
insect larvae resume activity, and organic matter starts to decompose
above the permafrost (see figure 3). This
is the Arctic Ecosystem - the Cryosphere. It is relatively self-contained
(a Northern Mediterranean); the atmosphere, land, freshwater and
sea are highly interconnected (coupled) vertically and laterally.
There is circulation within the system from air to land to water
to sea and back again. There is circulation of ice and sea, of chemicals,
of animals and plants, and Humans within and around the Arctic Ocean.
If you 'push' one part of the system, the affects will be felt in
other parts of the system. Thus, if the climate changes - as it
has always done - increased melt water will circulate in the Arctic
Ocean; if the capelin population crashes in the sea the effects
are felt on land through the food web; if pollutants are released
into the atmosphere or the sea in one place they are transported
to other parts of the region. |
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This is a single, integrated, dynamic
ecosystem on a massive scale, driven by the sun.
But it is not isolated from the rest of the Globe - no ecosystem
is completely isolated. The Arctic Ecosystem grades into warmer
Southern regions of the World and interacts with them. The Arctic
air mass brings cold air to the South in the winter but the winds
from the South bring warmer air - and contaminants - northwards
(see figure 4). Mammals, birds and fish
migrate in summer to feed and breed at the rich sea ice margins,
coastal zones, estuaries and wetland, then return South for the
winter. Sea water cools as the currents bring it North and the cold
fresh water from melting snow and ice adds to the great ocean 'conveyer
belt' -the thermohaline circulation - which significantly affects
the climate on land as well sea conditions (see
figure 5). |
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