Southern Ocean

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The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of the World Ocean south of 60° S latitude. The International Hydrographic Organization has designated the Southern Ocean as an oceanic division encircling Antarctica. Geographers disagree on the Southern Ocean's northern boundary or even its existence (see below), sometimes considering the waters part of the South Pacific, South Atlantic, and Indian Oceans

instead.

Some scientists consider the Antarctic Convergence, an ocean zone which fluctuates seasonally, as separating the Southern Ocean from other oceans, rather than 60° S.^[1] This ocean zone is where cold, northward flowing waters from the Antarctic mix with warmer sub-Antarctic waters.

The International Hydrographic Organization (IHO) regards the Southern Ocean as the fourth-largest of the five principal oceanic divisions and the latest-defined one. The IHO promulgated the decision on its existence in 2000, though many mariners have long regarded the term as traditional. The Southern Ocean appeared in the IHO's Limits of Oceans and Seas second edition (1937), disappeared from the third edition (1957), and re-surfaced in the fourth edition (not yet^[update] formally adopted due to a number of unresolved disputes, including the lodgement of a reservation by Australia).^[2] This change reflects the importance placed by oceanographers on ocean currents.

Geography

The Southern Ocean includes the Antarctic Circumpolar Current (which circulates around Antarctica) the Amundsen Sea, Bellingshausen Sea, parts of the Drake Passage, Ross Sea, Cooperation Sea, the Cosmonaut Sea, a small part of the Scotia Sea, and Weddell Sea. Its total area comprises 20,327,000 square kilometers (7,848,000 mi²).

The Southern Ocean differs from the other oceans in that its largest boundary, the northern boundary, does not abut any 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, South America, resembles the water in the Southern Ocean south of New Zealand more closely than it resembles the water in the mid-Indian 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 the Antarctic Bottom Water, a very cold, highly saline, dense water that forms under sea ice.

The Southern Ocean, geologically the youngest of the oceans, 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.

In many respects, the Southern Ocean forms the opposite of the Arctic Ocean, located on the opposite end of the globe.

Arctic and Southern Oceans contrasted

Arctic Ocean	Southern Ocean
Surrounded by Eurasia and North America	Encircles the Antarctic continent
Warm ocean moderates frigid land	Icy landmass feeds cold ocean
Freshwater from rivers feeds the Arctic Ocean	The melting of glaciers feeds the Southern
Ice forms at very center of the Arctic	Ice forms along the Antarctic coastline

Features

The Southern Ocean lies in the Southern Hemisphere. It has typical depths of between 4,000 and 5,000 meters (13,000 to 16,000 ft) over most of its extent with only limited areas of shallow water. The Antarctic continental shelf appears generally narrow and unusually deep, its edge lying at depths up to 800 meters (2,600 ft), compared to a global mean of 133 meters (436 ft).

Equinox to equinox in line with the sun's seasonal influence, the Antarctic ice pack fluctuates from an average minimum of 2.6 million square kilometers (1.0 million mi²) in March to about 18.8 million square kilometers (7.2 million mi²) in September, more than a sevenfold increase in area.

The Antarctic Circumpolar Current moves perpetually eastward — chasing and joining itself, and at 21,000 kilometers (13,000 mi) in length — it comprises the world's longest ocean current, transporting 130 million cubic meters (4.6 billion ft³) of water per second — 100 times the flow of all the world's rivers.

The Southern Ocean's greatest depth of 7,235 meters (23,737 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 intense persistent drainage winds from the interior keep the shoreline ice-free throughout the winter.