SOUTHERN OCEAN

3 years ago by in Featured, Natural Science, Natural Science

arctic-ocean-mapThe Southern Ocean (also known as the Great Southern OceanAntarctic OceanSouth Polar Ocean and Austral Ocean) comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. As such, it is regarded as the fourth-largest of the five principal oceanic divisions (after the Pacific, Atlantic, and Indian Oceans, but larger than the Arctic Ocean). This ocean zone is where cold, northward flowing waters from the Antarctic mix with warmer subantarctic waters.

Geographers disagree on the Southern Ocean’s northern boundary or even its existence, with many considering the waters part of the Pacific, Atlantic, and Indian Oceans instead. Others regard the Antarctic Convergence, an ocean zone which fluctuates seasonally, as separating the Southern Ocean from other oceans, rather than the 60th parallel. Australian authorities regard the Southern Ocean as lying immediately south of Australia.

The International Hydrographic Organization (IHO) has not yet ratified its 2000 definition of the ocean as being south of 60°S. Its latest published definition of oceans dates from 1953; this does not include the Southern Ocean. However, the more recent definition is used by the IHO and others.

GEOGRAPHY

The Southern Ocean includes the Antarctic Circumpolar Current (which circulates around Antarctica) and parts of the Drake Passage, a part of the Scotia Sea, the Weddell Sea, theKing Haakon VII Sea, the Lazarev Sea, the Riiser-Larsen Sea, the Cosmonaut Sea, the Cooperation Sea, the Davis Sea, the Mawson Sea, the D’Urville Sea, the Somov Sea, the Ross Sea, the Amundsen Sea, and the Bellingshausen Sea (in clockwise order).

climateThe Southern Ocean differs from the other oceans in that its largest boundary, the northern boundary, does not abut a landmass, but merges into the Atlantic, Indian and Pacific Oceans. This calls into question why geographers should consider the Southern Ocean a separate ocean, as opposed to a southward extension of the other three oceans. One reason stems from the fact that much of the water of the Southern Ocean differs from the water in the other oceans. Because of the Antarctic Circumpolar Current, that water gets transported around the Southern Ocean fairly rapidly, so that the water in the Southern Ocean south of, for example, New Zealand, resembles the water in the Southern Ocean south of South America more closely than it resembles the water in the Pacific Ocean.

Several processes operate along the coast of Antarctica to produce, in the Southern Ocean, types of water masses not produced elsewhere in the oceans of the Southern Hemisphere. One of these is theAntarctic Bottom Water, a very cold, highly saline, dense water that forms under sea ice.

The Southern Ocean, geologically the youngest of the oceans, was formed when Antarctica and South America moved apart, opening the Drake Passage, roughly 30 million years ago. The separation of the continents allowed the formation of the Antarctic Circumpolar Current.

EXISTENCE AND DEFINITIONS

Different organizations and nations have differing points of view over the extents and existence of the Southern Ocean, though many mariners have long regarded the term as traditional.

The 1937 second edition of the International Hydrographic Organization’s (IHO) Limits of Oceans and Seas publication included a definition of an ocean around Antarctica. However, this ocean did not appear in the 1953 third edition because “the northern limits … are difficult to lay down owing to their seasonal change” – instead the Atlantic, Indian and Pacific Oceans were extended southward.

arctic-ocean-mapThe IHO readdressed the question of the ocean’s existence in a survey in 2000. Of its 68 member nations, 28 responded, and all responding members except Argentina agreed to define a new ocean, reflecting the importance placed by oceanographers on ocean currents. The proposal for the name Southern Ocean won 18 votes, beating the alternative Antarctic Ocean. Half of the votes supported a definition of the ocean’s northern limit at 60°S (with no land interruptions at this latitude), with the other 14 votes cast for other definitions, mostly 50°S, but a few for as far north as 35°S. However, the 4th edition ofLimits of Oceans and Seas was never ratified or published due to a reservation lodged by Australia, and so the 3rd edition (which does not delineate a separate Southern Ocean) has not been superseded. If and when the 4th edition is published, it will restore the Southern Ocean as originally outlined in the 2nd edition and subsequently omitted from the 3rd.

Despite this, the 4th edition definition has de facto usage by many organisations, scientists and nations – even by the IHO. Some nations’ hydrographic offices have defined their own boundaries; the United Kingdom used the 55°S parallel for example.

Other sources such as the National Geographic Society continue to show the Atlantic, Pacific and Indian Oceans as extending to Antarctica, although articles on the National Geographic web site have begun to reference the Southern Ocean. 

In Australia, cartographical authorities defined the Southern Ocean as including the entire body of water between Antarctica and the south coasts of Australia and New Zealand, although New Zealand authorities do not generally follow suit. Coastal maps of Tasmania and South Australia label the sea areas as Southern Ocean, while Cape Leeuwin in Western Australia is described as the point where the Indian and Southern Oceans meet.

beef ft) occurs at the southern end of the South Sandwich Trench, at 60°00’S, 024°W.

CLIMATE

Sea temperatures vary from about −2 to 10 °C (28 to 50 °F). Cyclonic storms travel eastward around the continent and frequently become intense because of the temperature contrast between ice and open ocean. The ocean-area from about latitude 40 south to the Antarctic Circle has the strongest average winds found anywhere on Earth. In winter the ocean freezes outward to 65 degrees south latitude in the Pacific sector and 55 degrees south latitude in the Atlantic sector, lowering surface temperatures well below 0 degrees Celsius. At some coastal points, however, persistent intense drainage winds from the interior keep the shoreline ice-free throughout the winter.

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