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The Arctic is an Ecosystem
by Bill Heal
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Into The Seas And Oceans
Biological riches of the seas and ocean
  The combination and variation of physical factors (ice, rock, sand and mud substrate, temperature, salinity, water movement, nutrients, light) determine the biology of the system.
  The coasts. Estuaries and deltas with salt marshes and mudflats, sandy and rocky shores, bays, inlets and fjords, cliffs. These are the transition zones between land and sea - a foot in both camps. The narrow shores and wider deltas provide places to feed and breed. It is the birds that give the outward and visible signs of the productivity of the seas. They migrate North for the short summer, covering thousands of kilometers from temperate and tropical regions, even as far as the Antarctic in the case of the Arctic tern - an annual round trip of 32 thousand kilometers.
  On the mudflats and sandy shores, vast numbers of waders pick and probe for small crustaceans, molluscs, worms and small fish. Waders (dunlin, knot, sandpipers and stints) breed almost exclusively in the Arctic with total populations of individual species of up to 3.5 million birds, some of them also using the tundra wetlands. Terns breed in colonies and dive for small fish in coastal waters. Vast colonies, sometimes several hundred thousands, of guillemots (murres), auks, gannets, cormorants and puffins nest on high cliffs or burrows in the turf. They fish for capelin, sandeels, Polar cod and other fish. They are harassed by skuas and gulls. Their guano fertilises the vivid green patches of vegetation. The cliffs, filled with their cacophony in summer are silent in winter.
  Continental shelves, seas and oceans. The shallow coastal waters support considerable and diverse bottom fauna of crustacea, molluscs, sponges, worms, anemones and starfish with various small fish. They graze the algae or feed on detritus or plankton and provide a food source for larger fish, birds and mammals such as walrus and seals. The shallow waters are also the spawning ground for capelin, polar cod and other fish in March and April. Each school of capelin can contain many hundreds of tonnes of fish which then move out to deeper waters and the sea ice edge to feed on plankton - and to be preyed on by seabirds, larger fish such as cod, seals and whales. Ice plays an important role in the marine ecology. In winter the sea ice extends far South with maximum extent in March.
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Maximum and minimum sea-ice extent.
It retreats during summer, leaving the Arctic Ocean permanently covered by three meters or more of pack ice, with ridges both above and below surface (see figure 14). Yet even in the pack ice, there is open water (polynyas) even in winter, caused by wind and water movement and the upwelling of warmer water. In summer about 10% of the pack ice is open water. Nutrients transported from the rivers, from upwelling deeper waters or deposited from the atmosphere, provide the chemical base for the growth of algae. They grow on the surface, in and under the ice, and in the open water. They are adapted to grow at low temperatures, but also thrive where temperatures are enhanced by water from the Global Conveyer Belt. They can also grow in the minimal light that diffuses through the ice. These algae - the primary producers - are the key to the productive food chains of the Arctic seas and ocean.
  The ice edge, especially in shallower waters, is a very productive zone. A complex food web is developed that extends from the algal grazers, through various predators up to the polar bear and Arctic fox which move far out onto the ice to feed. In the open water the floating algae or phytoplankton are the food source for small and large crustacea (krill) which are the food for the herring, capelin and the various species of baleen whales - the filter feeders.
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The Arctic is an Ecosystem, by Bill Heal.
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