| Arctic Ocean |
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Boundaries and Size 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 about 55 m (about 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 about 500 to 700 m (about 1640 to 2300 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, including its major subdivisions-the North Polar Sea (the main portion), the Norwegian Sea, the North Sea, and the Barents Sea-is about 14 million sq km (about 5.4 million sq mi). Structural Features 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 have only been discovered and explored since the late 1940s. The Lomonosov Ridge, the major ridge, cuts the North Polar Sea almost in half, extending as a submarine bridge 1700 km (1060 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 Mid-Ocean Ridge on the Eurasian side, defining the Nansen and Fram basins. The average depth of the Arctic Ocean is only about 1500 m (about 4900 ft) because of the vast shallow expanses on the continental shelves. The deepest point in the Arctic Ocean is 5450 m (17,880 ft). Islands 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 Archipelago extend north and east from the Canadian mainland to Greenland, the largest island of the Arctic Ocean. Ice 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 (33 ft) in depth. Resources Fish, in commercially exploitable quantities, are found only in the warmer marginal seas of the Arctic Ocean, notably in the North Sea (herring, cod, and flounder) and 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, and petroleum and natural gas are extracted north of Alaska and Canada and in the North Sea. |