The Southern Ocean is the body of water encircling the continent of Antarctica. It is the world's fourth largest ocean and the latest defined, having been accepted by a decision of the International Hydrographic Organization (IHO) in 2000, though the term has long been traditional among mariners. This change reflects the recent findings in oceanography of the importance of ocean currents. Twenty-eight among the 68 member nations responded to the IHO's survey in 2000, and all responding members except Argentina agreed to define a new ocean. Eighteen

voted for the Southern Ocean, beating the alternative name Antarctic Ocean. Fourteen votes were cast for ending the ocean at the imaginary 60 degrees south line of latitude, with the other 14 votes cast for other definitions as far north as 35 degrees south, the equivalent latitude south of the equator as that of the Mediterranean Sea in the northern hemisphere.

Other sources such as the National Geographic Society continue to show the Atlantic, Pacific and Indian Oceans as extending to Antarctica, which view is not preferred in oceanography however.

The Southern Ocean is oceanographically defined as an ocean connected with the Antarctic Circumpolar Current, which circulates around Antarctica. It includes Amundsen Sea, Bellingshausen Sea, part of the Drake Passage, Ross Sea, a small part of the Scotia Sea, and Weddell Sea. The total area is 20 327 000 km², and the coastline length is 17 968 km.

The geographic coordinates is 65°00'S 0°00'E nominally, but the Southern Ocean has the unique distinction of being a large circumpolar body of water totally encircling the continent of Antarctica as opposed to the normal definition of an ocean or sea, that of a water body mostly surrounded by land; this ring of water lies between 60 degrees south latitude and the coast of Antarctica, and encompasses 360 degrees of longitude.

This definition is, however, not universal. In Australia the Southern Ocean is defined in the same manner as the IHO but also includes the entire body of water between Antarctica and the south coasts of Australia and New Zealand, and is marked as such on maps.

The Southern Ocean was formed oceanographically when Antarctica and South America moved apart opening the Drake Passage and the Antarctic Circumpolar Current was formed roughly 30 million years ago, which makes the ocean much younger than other oceans.

The major chokepoint is the Drake Passage. The Polar Front (Antarctic Convergence) is the best natural definition of the northern extent of the Southern Ocean; it is a distinct region at the middle of the Antarctic Circumpolar Current that separates the very cold polar surface waters to the south from the warmer waters to the north; the Front and the Current extend entirely around Antarctica, reaching south of 60 degrees south near New Zealand and near 48 degrees south in the far South Atlantic coinciding with the path of the maximum westerly winds.

Sea temperatures vary from about -2 to 10 °C (28 to 50 °F). Cyclonic storms travel eastward around the continent and frequently are 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.

The Southern Ocean is deep, 4000 to 5000 meters over most of its extent with only limited areas of shallow water. The Antarctic continental shelf is generally narrow and unusually deep, its edge lying at depths of 400 to 800 meters (the global mean is 133 meters). The Antarctic ice pack fluctuates from an average minimum of 2.6 million square kilometers in March to about 18.8 million square kilometers in September, more than a sevenfold increase in area. The Antarctic Circumpolar Current (21 000 km in length) moves perpetually eastward; it is the world's largest ocean current, transporting 130 million cubic meters of water per second - 100 times the flow of all the world's rivers.

• lowest point: -7235 m at the southern end of the South Sandwich Trench, at 60°00'S, 024°W
• highest point: sea level 0 m.

Huge icebergs with drafts up to several hundred meters; smaller bergs and iceberg fragments; sea ice (generally 0.5 to 1 meter thick) with sometimes dynamic short-term variations and with large annual and interannual variations; deep continental shelf floored by glacial deposits varying widely over short distances; high winds and large waves much of the year; ship icing, especially May-October; most of the region is remote from sources of search and rescue.

Current Issues

• Increased solar ultraviolet radiation resulting from the Antarctic ozone hole, reducing marine primary productivity (phytoplankton) by as much as 15% and damaging the DNA of some fish.
• illegal, unreported, and unregulated fishing, especially the landing of an estimated five to six times more Patagonian toothfish than the regulated fishery, which is likely to affect the sustainability of the stock.
• high incidental mortality of seabirds resulting from long-line fishing for toothfish.

The Southern Ocean is subject to all international agreements regarding the world's oceans. In addition, it is subject to these agreements specific to the region: International Whaling Commission (prohibits commercial whaling south of 40 degrees south [south of 60 degrees south between 50 degrees and 130 degrees west]) NOTE: Japan regularly does not recognize this provision in regards to its whaling permit and whaling for scientific research and carries out whale hunts in the region.; Convention for the Conservation of Antarctic Seals (limits sealing); Convention on the Conservation of Antarctic Marine Living Resources (regulates fishing)