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(geography) A circumpolar ocean belt including those portions of the Atlantic, Pacific, and Indian oceans which reach the Antarctic continent and are bounded on the north by the Subtropical Convergence; not recognized as a separate ocean.
The waters surrounding Antarctica, actually the southern extensions of the Atlantic, Pacific, and Indian oceans.
The Antarctic Ocean, sometimes called the Southern Ocean, is the watery belt surrounding Antarctica. It includes the great polar embayments of the Weddell Sea and Ross Sea, and the deep circumpolar belt of ocean between 50 and 60°S and the southern fringes of the warmer oceans to the north. Its northern boundary is often taken as 30°S (see illustration). The Antarctic is a cold ocean, covered by sea ice during the winter from Antarctica's coast northward to approximately 60°S.
Direction of the surface circulation and major surface boundaries of the Antarctic Ocean.
The remoteness of the Antarctic Ocean severely hampers the ability to observe its full character. The sparse data collected and the more recent addition of data obtained from satellite-borne sensors have led to an appreciation of the unique role that this ocean plays in the Earth's ocean and climate. Between 50 and 60°S there is the greatest of all ocean currents, the Antarctic Circumpolar Current sweeping seawater from west to east, blending waters of the Pacific, Atlantic, and Indian oceans. Observed within this current is the sinking of cool (approximately 4°C; 39.2°F), low-salinity waters to depths of near 1 km (0.6 mi), which then spreads along the base of the warm upper ocean waters or thermocline of more hospitable ocean environments. The cold polar atmosphere spreading northward from Antarctica removes great amount of heat from the ocean, heat which is carried to the sea surface from ocean depths, brought into the Antarctic Ocean from warmer parts of the ocean. At some sites along the margins of Antarctica, there is rapid descent of cold (near the freezing point of seawater, −1.9°C; 28.6°F) dense water, within thin convective plumes. This water reaches the sea floor, where it spreads northward, chilling the lower 2 km (1.2 mi) of the global ocean, even well north of the Equator.
The major flow is the Antarctic Circumpolar Current, or West Wind Drift (see illus). Along the Antarctic coast is the westward-flowing East Wind Drift. The strongest currents are in the vicinity of the polar front zone and restricted passages such as the Drake Passage, and over deep breaks in the meridionally oriented submarine ridge systems.
The extreme cold of the polar regions causes an extensive ice field to form over the southern regions of the Antarctic Ocean. The extent of the ice is seasonal in that during the October-to-March period the area decreases, and it increases during the remaining months. The seasonal difference in the volume of sea ice is estimated as 2.3 × 1019 grams (8.1 × 1017 oz). Satellite photographs reveal that the sea ice field is not uniform, but has many large polynyas (areas of water). The sea ice plays an important role in the heat balance since it reflects much more solar radiation (and therefore heat) into space than would be the case for a water surface. The polynyas would therefore be of special interest in radiation and heat-balance studies. In addition to the ice formed at sea, the ice calving at the coast of Antarctica introduces icebergs into the ocean at a rate of approximately 1 × 1018 g/year (3.5 × 1012 oz/year). See also Heat balance, terrestrial atmospheric; Iceberg; Sea ice.
Glacial (fresh-water) ice and the ocean meet along the shores of Antarctica. This occurs not only at the northern face of the ice sheet but also at hundreds of meters depth along the bases of floating ice shelves. Ocean-glacial ice interaction is believed to be a major factor in controlling Antarctica's glacial ice mass balance and stability.
Introduction
| Background: | A large body of recent oceanographic research has shown that the Antarctic Circumpolar Current (ACC), an ocean current that flows from west to east around Antarctica, plays a crucial role in global ocean circulation. The region where the cold waters of the ACC meet and mingle with the warmer waters of the north defines a distinct border - the Antarctic Convergence - which fluctuates with the seasons, but which encompasses a discrete body of water and a unique ecologic region. The Convergence concentrates nutrients, which promotes marine plant life, and which in turn allows for a greater abundance of animal life. In the spring of 2000, the International Hydrographic Organization decided to delimit the waters within the Convergence as a fifth world ocean - the Southern Ocean - by combining the southern portions of the Atlantic Ocean, Indian Ocean, and Pacific Ocean. The Southern Ocean extends from the coast of Antarctica north to 60 degrees south latitude, which coincides with the Antarctic Treaty Limit and which approximates the extent of the Antarctic Convergence. As such, the Southern Ocean is now the fourth largest of the world's five oceans (after the Pacific Ocean, Atlantic Ocean, and Indian Ocean, but larger than the Arctic Ocean). It should be noted that inclusion of the Southern Ocean does not imply recognition of this feature as one of the world's primary oceans by the US Government. |
Geography
| Location: | body of water between 60 degrees south latitude and Antarctica |
| Geographic coordinates: | 60 00 S, 90 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; this ring of water lies between 60 degrees south latitude and the coast of Antarctica and encompasses 360 degrees of longitude |
| Map references: | Antarctic Region |
| Area: | total: 20.327 million sq km note: includes Amundsen Sea, Bellingshausen Sea, part of the Drake Passage, Ross Sea, a small part of the Scotia Sea, Weddell Sea, and other tributary water bodies |
| Area - comparative: | slightly more than twice the size of the US |
| Coastline: | 17,968 km |
| Climate: | sea temperatures vary from about 10 degrees Celsius to -2 degrees Celsius; 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 |
| Terrain: | the Southern Ocean is deep, 4,000 to 5,000 m 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 m (the global mean is 133 m); the Antarctic icepack grows from an average minimum of 2.6 million sq km in March to about 18.8 million sq km in September, better than a sixfold 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 |
| Elevation extremes: | lowest point: -7,235 m at the southern end of the South Sandwich Trench highest point: sea level 0 m |
| 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, and seals - none exploited; krill, fish |
| Natural hazards: | huge icebergs with drafts up to several hundred meters; smaller bergs and iceberg fragments; sea ice (generally 0.5 to 1 m 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 region is remote from sources of search and rescue |
| Environment - current issues: | increased solar ultraviolet radiation resulting from the Antarctic ozone hole in recent years, reducing marine primary productivity (phytoplankton) by as much as 15% and damaging the DNA of some fish; illegal, unreported, and unregulated fishing in recent years, 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; large amount of incidental mortality of seabirds resulting from long-line fishing for toothfish note: the now-protected fur seal population is making a strong comeback after severe overexploitation in the 18th and 19th centuries |
| Environment - 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 Antarctic region: International Whaling Commission (prohibits commercial whaling south of 40 degrees south [south of 60 degrees south between 50 degrees and 130 degrees west]); Convention on the Conservation of Antarctic Seals (limits sealing); Convention on the Conservation of Antarctic Marine Living Resources (regulates fishing) note: many nations (including the US) prohibit mineral resource exploration and exploitation south of the fluctuating Polar Front (Antarctic Convergence), which is in the middle of the Antarctic Circumpolar Current and serves as the dividing line between the cold polar surface waters to the south and the warmer waters to the north |
| Geography - note: | the major chokepoint is the Drake Passage between South America and Antarctica; 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 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 |
Economy
| Economy - overview: | Fisheries in 2003-04 landed 136,262 metric tons, of which 87% (118,166 tons) was krill and 8% (11,182 tons) Patagonian toothfish, compared to 142,555 tons in 2002-03 of which 83% (117,728 tons) was krill and 12% (16,479 tons) Patagonian toothfish (estimated fishing from the area covered by the Convention of the Conservation of Antarctic Marine Living Resources (CCAMLR), which extends slightly beyond the Southern Ocean area). International agreements were adopted in late 1999 to reduce illegal, unreported, and unregulated fishing, which in the 2000-01 season landed, by one estimate, 8,376 metric tons of Patagonian and Antarctic toothfish. In the 2004-05 Antarctic summer, 28,202 tourists, most of them seaborne (approximately 97%), visited the Southern Ocean and Antarctica, compared to 14,762 in 1999-2000. |
Transportation
| Ports and terminals: | McMurdo, Palmer, and offshore anchorages in Antarctica note: few ports or harbors exist on southern side of Southern Ocean; ice conditions limit use of most 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 observers under Article 7 of the Antarctic Treaty; The Hydrographic Committee on Antarctica (HCA), a special hydrographic commission of International Hydrographic Organization (IHO), is responsible for hydrographic surveying and nautical charting matters in Antarctic Treaty area; it coordinates and facilitates provision of accurate and appropriate charts and other aids to navigation in support of safety of navigation in region; membership of HCA is open to any IHO Member State whose government has acceded to the Antarctic Treaty and which contributes resources and/or data to IHO Chart coverage of the area; members of HCA are Argentina, Australia, Chile, China, France, Germany, Greece, India, Italy, NZ, Norway, Russia, South Africa, Spain, and the UK (2005) |
| Transportation - note: | Drake Passage offers alternative to transit through the Panama Canal |
Transnational Issues
| Disputes - international: | Antarctic Treaty defers claims (see Antarctica entry), but Argentina, Australia, Chile, France, NZ, Norway, and UK assert claims (some overlapping), including the continental shelf in the Southern Ocean; several states have expressed an interest in extending those continental shelf claims under the United Nations Convention on the Law of the Sea (UNCLOS) to include undersea ridges; the US and most other states do not recognize the land or maritime claims of other states and have made no claims themselves (the US and Russia have reserved the right to do so); no formal claims exist in the waters in the sector between 90 degrees west and 150 degrees west |
| Earth's oceans (World Ocean) |
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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.
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 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.
The Second (1937) Edition of the IHO's Limits of Oceans and Seas included the Southern Ocean; however, it was omitted from the Third (1953) Edition, as it was felt its northern hydrographic limits fluctuated with the seasons and 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]
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.
Sea temperatures vary from about −2 to 10 °C (28 to 50
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 "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 May-October, make the area even more dangerous. The remoteness of the region makes sources of search and rescue scarce.
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.
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:
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.
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.
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 . 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]
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 | Sci-Tech Dictionary. McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/ Read more |
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| Statistics. The World Factbook 2005 is prepared by the Central Intelligence Agency. Read more |
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| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Southern Ocean". Read more |
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