Sunday, 12 January 2014

Arctic Ocean

Arctic Ocean, smallest of the five world oceans. The Arctic Ocean extends south from the North Pole to the shores of Europe, Asia, and North America. See also Arctic.
The surface waters of the Arctic Ocean mingle with those of the Pacific Ocean through the Bering Strait, by way of a narrow and shallow channel, which has a depth of 55 m (180 ft). More importantly, the Arctic waters mix with those of the Atlantic Ocean across a system of submarine sills (shallow ridges) that span the great distances from Scotland to Greenland and from Greenland to Baffin Island at depths of 500 to 700 m (1,600 to 2,300 ft). Emptying into the Arctic Ocean are the Ob’, Yenisey, and Lena rivers in Asia and the Mackenzie River in North America. The total surface area of the Arctic Ocean is 14.1 million sq km (5.4 million sq mi). The major subdivisions of the Arctic Ocean include the Norwegian, Barents, Kara, Laptev, and Beaufort seas.
Approximately one-third of the Arctic Ocean is underlain by continental shelf, which includes a broad shelf north of Eurasia and the narrower shelves of North America and Greenland. Seaward of the continental shelves lies the Arctic Basin proper, which is subdivided into a set of three parallel ridges and four basins (also known as deeps). These features were discovered and explored beginning in the late 1940s. The Lomonosov Ridge, the major ridge, cuts the Arctic Basin almost in half, extending as a submarine bridge 1,800 km (1,100 mi) from Siberia to the northwestern tip of Greenland. Parallel to it are two shorter ridges: the Alpha Ridge on the North American side, defining the Canada and Makarov basins, and the Arctic Mid-Ocean Ridge on the Eurasian side, defining the Nansen and Amundsen basins. The average depth of the Arctic Ocean is only 1,300 m (4,300 ft) because of the vast shallow expanses on the continental shelves. The deepest point in the Arctic Ocean is 5,450 m (17,880 ft).
The islands of the Arctic Ocean lie on the continental shelves. To the northeast of Norway lies the archipelago of Svalbard (formerly known as Spitsbergen); to the east are Franz Josef Land, Novaya Zemlya, Severnaya Zemlya, the New Siberian Islands, and Wrangel Island, all of which are located north of Russia. The numerous islands of the Canadian Arctic Archipelago extend north and east from the Canadian mainland to Greenland, the largest island of the Arctic Ocean.
Three forms of ice are found in the Arctic Ocean: land ice, river ice, and sea ice. Land ice enters the ocean in the form of icebergs, which are created when pieces of glaciers break off. In the Arctic Ocean, icebergs are created primarily along the coasts of Greenland. The freezing of fresh water, and its subsequent transport into the ocean by rivers, produces nearshore concentrations of river ice over small areas of the Siberian and North American shelves. Sea ice is formed by the freezing of seawater. It is the most extensive form of ice in the Arctic Ocean. In winter a permanent cap of sea ice covers all of the ocean surface, except for the area northeast of Iceland and north of Scandinavia. In summer the ice cover shrinks to expose narrow bands of relatively open water along the coasts of most of Siberia, Alaska, and Canada. The ice cap is composed of pack ice—that is, pieces of ice that pile up and are pressed in ridges or hummocks that may be more than 10 m (30 ft) in depth.
In 2005 scientists reported that the summer ice cover had shrunk for the fourth consecutive year to its smallest extent since 1978 and probably to its smallest extent in 100 years. The report by scientists from the National Snow and Ice Data Center and the National Aeronautics and Space Administration (NASA) warned that global warming had played a role in the decline. Using satellite data from NASA, scientists compared the Arctic sea ice cover in September 2005, when Arctic sea ice usually reaches its minimum, with the average extent of the sea ice cover since precise satellite measurements were first obtained in 1978. They found that the ice cover had declined by 1.3 million sq km (500,000 sq mi), an area about twice the size of Texas. Using other weather records, the scientists concluded that the total sea ice area of 5.3 million sq km (2 million sq mi) was probably the smallest in the last 100 years.
The scientists warned that the trend was not only likely to continue but also to accelerate due to factors that include a lack of winter recovery of sea ice, early onset of spring melting, warmer-than-average temperatures, and an increase in areas of open ocean water, which are dark and absorb solar radiation and therefore warm the area further. The melting of Arctic sea ice could affect global climate, the scientists said, because increased absorption of solar radiation warms the entire planet (see Albedo). At the current rate of sea ice shrinkage, the scientists calculated that the summer ice cover in the Arctic Ocean could disappear entirely by 2060. Some scientists said the Arctic Oscillation, a natural cycle in the polar atmosphere, could be a factor in the shrinkage of the ice cover, but there was a reported consensus that global warming due to greenhouse gas emissions was also involved.
In 2007 scientists announced that the melting of summer sea ice had reached its greatest extent ever, encompassing a third of the Arctic Ocean. Summer sea ice in September 2007 covered an area of 4.4 million sq km (1.7 million sq mi), down from 5.3 million sq km in September 2005. Some scientists said this meant that if the trend continued, the summer sea ice cover would disappear altogether by 2030, rather than 2060. They further predicted that winter ice recovery would probably not be complete during the winter of 2007-2008 when the Arctic is in total darkness, leaving areas of open ocean throughout the year.
Fish, in commercially exploitable quantities, are found only in the warmer marginal seas of the Arctic Ocean, notably in the Barents Sea (primarily cod). Sea mammals, including various species of seal and whale, were hunted to near extinction before being protected by quotas set during the 1900s. Tin is actively mined off the coast of eastern Siberia. Petroleum and natural gas are extracted north of Alaska and Canada. In 2007 the United States Geological Survey (USGS) estimated that the ocean basin off eastern Greenland may hold as much as 31.4 billion barrels of oil, natural gas, and natural gas liquids in an area of 500,000 sq km (193,000 sq mi). The USGS study of eastern Greenland is part of an effort to survey the entire Arctic for oil and natural gas deposits known as the Circum-Arctic Resource Appraisal.
Five nations—Canada, Denmark, Norway, Russia, and the United States—claim seabed rights in the Arctic Ocean. The claims include rights to exploit subsurface minerals, oil and gas deposits, and potentially useful bacteria. All five nations are signatories to the United Nations Convention on the Law of the Sea. The treaty gives each nation rights to exploit all natural resources within an area 370 km (200 nautical mi) off their coastline.
In addition the treaty allows each nation to claim an additional 278 km (150 nautical mi) of seabed if it can demonstrate that its continental shelf extends that far. Under the treaty a nation must make a formal claim to this additional area of seabed within ten years of ratifying the treaty. As of 2007 only Norway and Russia had made a formal claim. Russia maintains that the Lomonosov Ridge, a seabed feature that extends from Siberia to Greenland, is part of its continental shelf.
With the warming of the Arctic Ocean and the melting of sea ice, the competition for seabed rights has grown more acute as nations contemplate the ability to explore for and exploit seabed resources, especially oil and natural gas deposits. In 2007 Russia claimed sovereignty over the North Pole, and Canada claimed sovereignty over the Northwest Passage. In addition, Denmark sent a geological expedition to the Arctic to determine the extent of the continental shelf below Greenland, a self-governing part of Denmark. A successful claim to the North Pole would allow a country to set environmental standards and regulate maritime traffic.
The United States disputes Canada’s claim to the Northwest Passage sea route, which could be open to maritime traffic year-round by 2030. The route would considerably shorten the distance between Europe and Asia for ships that presently transit the Panama Canal.

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