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The Arctic is an Ecosystem
by Bill Heal
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The Changing Arctic Ecosystem
  If you follow the system over decades or centuries you see periods of naturally warmer or cooler climates. Short periods of cooling may be caused by volcanic ash circulating in the stratosphere and reducing radiation for a few years as with eruption of Tambora in 1815, Krakatau in 1883 and Pinatubo in 1991. Longer periods of change result from shifts in the balance of two major circulation systems - the North Atlantic Oscillation which results from cold air from the North meeting warm air from the South, and the Global Conveyer Belt which brings warm water to the North where it is cooled by Arctic waters and returns South. Changes in these atmospheric and oceanic systems produce climatic shifts such as the Little Ice Age of the 16th and 17th centuries. Thus the Arctic experiences long-term fluctuations as well as the dramatic seasonal changes. Ice and snow extends and retreats, glaciers flow and carve U-shaped valleys in softer rocks, deposit moraines and change the shape of the land . Rivers surge, carving new channels and extending flood plains or the flow rate slows and sediment is deposited further downstream and the flood plains become drier with fewer pools.
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The land surface is repeatedly perturbed by freezing and thawing (cryoturbation), the permafrost and ice wedges slowly move up or down as climate changes, generating diverse patterns on flat and sloping ground (see figure 6).As glaciers and snowbeds retreat, plant growth increases, organic matter accumulates as soils mature and peat forms on wet ground. On land and in the sea the boundaries of plants and animals extend or retreat at both the northern and southern ends of their geographical range. On the islands and mountain tops, species which are at the edge of their ranges may become locally extinct - they have nowhere to go.
  Over millennia, even the surface of the Earth responds to climate change, rising and falling as the weight of the ice mass changes, creating new raised (or sunken) beaches and river terraces, and causing rivers to change direction. You notice this over millennia, but you can also measure the current rise of 2-3 mm per decades in some areas - one of many slow but continuous processes within the Arctic Ecosystem.
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Glacier ice and sea ice in Greenlandic fjord. Islands and valleys emerge when the ice retreats. Photo: Jónas Allansson, 2001
Climate variability has shaped the Arctic and been a way of life for millennia. Not only does it vary over time, it also varies in different parts of the region. Animals and plants which are best adapted to the conditions prevailing at the time are the ones which survive and thrive. But local habitats can be very varied and are particularly important on land where the climate is most severe and changeable. Warm sheltered south-facing pockets of land enable species which are less cold-tolerant to survive. Damp or wet depressions in a dry landscape are refuges for species during periods of low precipitation. Freeze-thaw perturbations allow species which are good colonisers but poor competitors to survive. Thus physical variety in the landscape and the past history of climate variability has selected animals and plants which may be 'pre-adapted' to resist the pressures of future changes in climate.
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The Arctic is an Ecosystem, by Bill Heal.
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