Southern Ocean

The Southern Ocean, also known as the Antarctic Ocean or South Polar Ocean, is the ocean completely in Earth's southern hemisphere encircling Antarctica, comprising the southernmost waters of the World Ocean south of 60° S latitude. However, the Southern Ocean's northern boundary is not precise. Instead, the Antarctic Convergence, an ocean zone which fluctuates seasonally, separates the Southern Ocean from other oceans. ^[1] This dynamic, natural boundary is formed by the convergence of two circumpolar currents, one easterly flowing and one westerly.

The Southern Ocean is another name for what have traditionally been considered to be the southernmost portions of the Pacific, Atlantic and Indian Oceans. It is the world's fourth largest ocean and the latest to be 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.

Geography

The Southern Ocean is oceanographically defined as an ocean connected with the Antarctic Circumpolar Current, which circulates around Antarctica. The Southern Ocean includes the 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).

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 is that the water of the Southern Ocean is different than 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, the Indian Ocean, resembles the water in the Southern Ocean south of the Pacific and Atlantic Oceans more closely than it resembles the water in the 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.

The Southern Ocean is in many respects the opposite of the Arctic Ocean, located on the opposite end of the globe. While the Southern Ocean surrounds the Antarctic landmass, the Arctic Ocean is surrounded by the Eurasian and North American landmasses. 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 freshwater 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.

History

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 60 degrees south line of latitude (with no land interruptions at this 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.

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.^[2]

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.

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.

Latitudes from 50-70 degrees south are known to sailors as the "furious fifties" and the "screaming 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 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^{[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 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 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.

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.

Ports and harbors

File:Scross icepier.jpg

Severe cracks in an ice pier in use for four seasons at McMurdo Station slowed cargo operations in 1983 and proved to be a safety hazard.

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 / 77.833°S 166.667°E / -77.833; 166.667. 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.^[3] .

References

^ Pyne, Stephen J.; The Ice: A Journey to Antarctica. University of Washington Press, 1986. NOTE: Despite the title, Pyne's work is not a travel journal. Instead, Pyne presents a well-researched study of Antarctica's exploration, earth sciences, icescape, esthetics, literature, and geopolitics.
^ "Map showing Australian definition of the Southern Ocean" (PDF).
^ "Unique ice pier provides harbor for ships," Antarctic Sun. January 8, 2006; McMurdo Station, Antarctica.

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)

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

[1] Pyne, Stephen J.; The Ice: A Journey to Antarctica. University of Washington Press, 1986. NOTE: Despite the title, Pyne's work is not a travel journal. Instead, Pyne presents a well-researched study of Antarctica's exploration, earth sciences, icescape, esthetics, literature, and geopolitics.

[2] "Map showing Australian definition of the Southern Ocean" (PDF).

[Unique-3] "Unique ice pier provides harbor for ships," Antarctic Sun. January 8, 2006; McMurdo Station, Antarctica.

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