Southern Ocean

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Earth's oceans (World Ocean)
Arctic Ocean Atlantic Ocean Indian Ocean Pacific Ocean Southern Ocean

The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, is the International Hydrographic Organization's oceanic division encircling Antarctica, comprising the southernmost waters of the World Ocean south of 60° S latitude. Geographers disagree on the Southern Ocean's northern boundary or even its existence (see below), instead considering the waters part of the South Pacific, South Atlantic, and Indian Oceans. The Antarctic Convergence, an ocean zone which fluctuates seasonally, is considered by some to separate the Southern Ocean from other oceans, rather than 60° S.^[1] This ocean zone is formed by the convergence of two circumpolar currents, one easterly flowing and one westerly flowing.

The Southern Ocean is considered by the International Hydrographic Organization (IHO) to be the fourth largest of the five principal ocean divisions and the latest to be defined, having been promulgated by a decision of the IHO in 2000, though the term has long been traditional among some mariners. The Southern Ocean had been included in IHO's Limits of Oceans and Seas second edition (1937), dropped from the third edition (1957), and reinstated in the fourth edition (which has yet to be formally adopted due to a number of unresolved disputes). This change reflects the importance placed by oceanographers on ocean currents.

Contents 1 Geography 2 History 3 Features 4 Climate 5 Natural resources 6 Natural hazards 7 Environment 7.1 Current issues 7.2 International agreements 8 Economy 9 Ports and harbors 10 See also 11 References 12 Further reading 13 External links

[edit] 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, a small part of the Scotia Sea, and Weddell Sea. The total area is 20,327,000 square kilometers (7,848,000 mi²).

The Southern Ocean is different from the other oceans in that its largest boundary, the northern boundary, is not defined by any landmass, but merges into the Atlantic, Indian and Pacific Oceans. This calls into question why the Southern Ocean should be considered a separate ocean, as opposed to a southward extension of the other three oceans. One reason provided is that much of the water of the Southern Ocean is different from the water in the other oceans. Because of the Antarctic Circumpolar Current, that water is 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 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, water masses that are 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 is geologically the youngest of the oceans. It 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.

In many respects, the Southern Ocean is the opposite of the Arctic Ocean, located on the opposite end of the globe. While the Southern Ocean surrounds the Antarctic continent, the Arctic Ocean is surrounded by the Eurasian and North American continents. While the weather in the Southern Ocean is dominated by the frigid landmass at its center, the weather in the Arctic is dominated by the relatively warm Arctic Ocean surrounded by frigid landmasses. While rivers feed fresh water into the Arctic Ocean, the Antarctic continent feeds freshwater glaciers into the Southern Ocean. While sea ice forms at the center of the Arctic Ocean, sea ice forms at the margins of the Antarctic continent.

[edit] History

The second edition (1937) of the IHO's Limits of Oceans and Seas included the Southern Ocean; however, it was omitted from the third edition (1953) because of the fluctuation of its northern hydrographic limits with the seasons and because it was felt that an ocean should be defined as "water surrounded by land" not "water encircling land". Individual member states' hydrographic offices have defined their own boundaries; the United Kingdom used the 55°S parallel.^[2]

The IHO readdressed the question in a survey in 2000. Of the 68 member nations, 28 responded to 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 60 degrees south line of latitude (with no land interruptions at this latitude), with the other 14 votes cast for other definitions, mostly 50 degrees south, but a few for 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.

In Australia the Southern Ocean was defined also to include 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,^[3] while Cape Leeuwin in Western Australia is described as the point where the Indian and Southern Oceans meet.

[edit] Features

The Southern Ocean is located in the Southern Hemisphere possessing typical depths between 4,000—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), 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 is 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.

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.

[edit] 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.

[edit] 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

[edit] 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.

Latitudes from 50 to 70 degrees south are known to sailors as the "furious fifties" and the "shrieking sixties" due to high winds and large waves that form as winds blow around the entire globe unimpeded by any land mass. Ship ice, especially in May to October, makes the area even more dangerous. The remoteness of the region makes sources of search and rescue scarce.

[edit] Environment

[edit] 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^{[citation needed]}. 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 incidence of seabird mortality resulting from long-line fishing for toothfish.

[edit] 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 carries out an annual whale hunt in the region. See Southern Ocean Whale Sanctuary.
• 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^{[citation needed]}, 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.

[edit] 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 were expected during the 1999-2000 season.

[edit] 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.

Major ports that are operational include: Esperanza Base, Villa Las Estrellas, Chile, Mawson Station, McMurdo Station, Palmer Station, and offshore anchorages in Antarctica.

The Southern Ocean's southern-most port is located at McMurdo Station at 77°50′S, 166°40′E. The small harbor on the southern tip of Ross Island is formed by Winter Quarters Bay, where summer port operations are made possible by a floating Ice pier. Operation Deep Freeze personnel constructed the first ice pier at McMurdo in 1973.^[4]

[edit] See also

• Antarctica
• Antarctic Treaty System
• Ernest Shackleton--Explorer
• Extreme points of the Antarctic
• Roaring forties
• Sea Shepherd Conservation Society
• Southern Ocean Whale Sanctuary
• Whaling

[edit] References

[edit] Further reading

• Gille, Sarah T. 2002. "Warming of the Southern Ocean since the 1950s": abstract, article. Science: vol. 295 (no. 5558), pp. 1275-1277.
• Descriptive Regional Oceanography, P. Tchernia, Pergamon Press, 1980.
• Matthias Tomczak and J. Stuart Godfrey. 2003. Regional Oceanography: an Introduction. (see the site)

[edit] External links

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

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