Southern Ocean

The Southern Ocean is the body of water encircling the continent of Antarctica according to some geographic and most hydrographic sources. 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.

Of the 68 member nations, 28 responded to the IHO's survey in 2000, and all responding members except Argentina agreed to define a new ocean. The name Southern Ocean was selected with 18 votes, beating the alternative Antarctic Ocean. Half of the 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.

Other sources such as the National Geographic Society continue to show the Atlantic, Pacific and Indian Oceans as extending to Antarctica.

Geography

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 square kilometers (7,848,000 mi²), and the coastline length is 17,968 kilometers (11,165 mi).

The geographic coordinates is 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—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. Coastal maps of Tasmania and South Australia label the sea areas as Southern Ocean.

Map showing Australian definition of the Southern Ocean (PDF)

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 passage offers an alternative to transit through the Panama Canal. 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.

Features

The Southern Ocean is located in the Southern Hemisphere at 4,000 to 5,000 meters (13,000 to 16,000 ft) deep 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 up to 800 meters (2,600 ft), with a global mean of 133 meters (436 ft). 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—at 21,000 kilometers (13,000 mi) in length—moves perpetually eastward; it is the world's largest 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.

Its greatest depth is 7,235 meters (23,737 ft) 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 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.

Natural resources

Probable large and possible giant oil and gas fields on the continental margin
Manganese nodules
Possible placer deposits
Sand and gravel
Fresh water as icebergs
Squid, whales, seals, krill and various fish

Natural hazards

Icebergs can be found at any time of year throughout the ocean. Some may have drafts up to several hundred meters; smaller icebergs, iceberg fragments and sea ice (generally 0.5 to 1 meter thick) are also a problem for ships. The deep continental shelf is floored by glacial deposits varying widely over short distances. High winds and large waves during much of the year, along with ship ice, especially May-October make the area even more dangerous. The remoteness of the region makes sources of search and rescue scarce.

Environment

Current issues

Increased solar ultraviolet radiation resulting from the Antarctic ozone hole has reduced marine primary productivity (phytoplankton) by as much as 15% and is 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, likely affects the sustainability of the stock. There is also a high incidental mortality of seabirds resulting from long-line fishing for toothfish.

International agreements

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:

The International Whaling Commission prohibits commercial whaling south of 40 degrees south (south of 60 degrees south between 50 degrees and 130 degrees west). Japan regularly does not recognize this provision in regards to its whaling permit and whaling for scientific research and occasionally carries out whale hunts in the region.
The Convention for the Conservation of Antarctic Seals has limited seal hunting.
The Convention on the Conservation of Antarctic Marine Living Resources regulates fishing in the region.

Many nations prohibit mineral resource exploration and exploitation south of the fluctuating Polar Front, which is in the middle of the Antarctic Circumpolar Current and serves as the dividing line between the very cold polar surface waters to the south and the warmer waters to the north.

Since the Antarctic Treaty covers the portion of the globe south of sixty degrees south, claims to Antarctica and all islands in the Southern Ocean are suspended.

Economy

Fisheries in 1998-99 between 1 July and 30 June landed 119,898 tonnes, of which 85% was krill and 14% Patagonian toothfish. International agreements were adopted in late 1999 to reduce illegal, unreported, and unregulated fishing, which in the 1998-99 season landed five to six times more Patagonian toothfish than the regulated fishery. In the 1998-99 Antarctic summer 10,013 tourists, most of them seaborne, visited the Southern Ocean and Antarctica, compared to 9,604 the previous year. Nearly 16,000 tourists are expected during the 1999-2000 season.

Ports and harbors

Few ports or harbors exist on the southern (Antarctic) coast of the Southern Ocean since ice conditions limit use of most of them to short periods in midsummer; even then some cannot be entered without icebreaker escort. Most Antarctic ports are operated by government research stations and, except in an emergency, are not open to commercial or private vessels; vessels in any port south of 60 degrees south are subject to inspection by Antarctic Treaty observers.

The major ones that are operational include: Esperanza Base, Mawson Station, McMurdo Station, Palmer Station, Scott Base, and offshore anchorages in Antarctica

References

Matthias Tomczak and J. Stuart Godfrey. 2003. Regional Oceanography: an Introduction. (see the site)

External links

Oceanography Image of the Day , from the Woods Hole Oceanographic Institution
The CIA World Factbook's article on the Southern Ocean
The Fifth Ocean from Geography.About.com
NOAA In-situ Ocean Data Viewer Plot and download ocean observations

Southern Ocean | Oceans | Antarctica

Gourt Home::Gourt :: Southern Ocean