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Arctic Ocean

The north polar ocean lying between North Armerica and Asia, extending over about 386,000 mi2 (106 km2). It is nearly completely covered by 6–9 ft (2–3 m) of ice in winter, and in summer it becomes substantially open only at its peripheries. Its extent has been variably defined, but it is oceanogaphically appropriate to consider it bounded on the south by a line running from northern Greenland through Smith, Jones, and Lancaster sounds, along northwestern Baffin Island to the Canadian mainland, thence to the Alaskan coast, across Bering Strait, along the Siberian coast to Novaya Zemlya, across to Franz Josef Land and Spitsbergen, and over to northern Greenland. This definition omits the Barents, Norwegian, and Greenland seas and Baffin Bay, which have a pronounced North Atlantic character.

The central polar basin, somewhat triangular in shape, is surrounded by continental shelves which are interrupted only by the deep passage running through Fram Strait. The upper 650 ft (200 m) of the Arctic Ocean, referred to as Surface Water or Arctic Water, is characterized by a significant density stratification produced by the strong increase in salinity downward from the surface. This density stratification is of considerable importance, for it prevents a deep-reaching convection from developing within the Arctic Ocean and also prevents the heat of the underlying warm Atlantic Water from reaching the surface. The relatively low salinity at the surface is maintained against the upward diffusion of salt by the addition of fresh water, principally through river outflow. The upper 100–160 ft (30–50 m) of Surface Water tends to be relatively uniform vertically in temperature and salinity. Except for areas which become ice-free in summer, the water will be near the freezing point. Currents in the upper waters tend to be relatively slow (4 in./s or 10 cm/s or less), and they are similar in both speed and direction to the ice motion. The overall circulation in the upper waters has its ultimate cause in the prevailing wind pattern over the Arctic Ocean.

As in other oceans, the current at any instant can vary greatly from the mean condition. The most spectacular example observed in the Arctic Ocean occurs on an occasional basis in the Canadian Basin, consisting of a high-speed current core.Ocean circulation Seawater

Below the Surface Water, the temperature increases to a maximum, which over most of the region is about 33°F (0.5°C) and lies between 1000 and 1500 ft (300 and 500 m). The salinity is nearly uniform, and since at low temperatures the density of seawater depends almost solely on salinity, there is virtually no density stratification beneath the upper waters. Significant deviations from the stated temperature occur only in the southern Eurasian Basin closest to Spitsbergen, for it is there that the warm and saline water (called Atlantic Water) which maintains the temperature maximum throughout the Arctic Ocean first enters. This water has its origin in the North Atlantic. Once into the Arctic Ocean it sinks because of its high salinity and moves eastward along the Eurasian continental slope. Beneath the Atlantic Water lies cold, nearly uniform Bottom Water. These two water masses together constitute over 90% of the volume of the Arctic Ocean. The Bottom Water is formed in the Greenland Sea.

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From McGraw-Hill Concise Encyclopedia of Environmental Science. The Content is a copyrighted work of McGraw-Hill and McGraw-Hill reserves all rights in and to the Content. The Work is © 2008 by The McGraw-Hill Companies, Inc.
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