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The Southern Ocean


A spring 2000 decision by the International Hydrographic Organization defined a fifth World Ocean. The southern portions of the Atlantic, Indian, and Pacific Oceans south of 60 degree south latitude were put together to the new Southern Ocean. The new 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). On contrary to all other oceans, the Southern Ocean has the unique distinction of being a large body of water encompassing a continental landmass (Antarctica) by 360 degrees of longitude.


The iceberg B10 (red arrow, about 38 by 77 kilometers, about 90 meters above water and may reach as deep as 300 meters) broke off the end of the Thwaites glacier of Antarctica in 1992. In 1995 B10 split into two pieces, B10A and B10B. The larger piece B10A had moved out of the isolated waters around Antarctica and near the Drake Passage in 1999. (SeaWinds radar instrument, QuikScat satellite, NASA)

The Southern Ocean is mostly 4,000 to 5,000 meters deep. The Antarctic continental shelf is generally narrower and deeper than other global shelf seas.


In April, the Antarctic sea-ice starts to spread towards the North. During winter, the ocean freezes outward to 65 degrees south latitude in the Pacific Ocean sector and 55 degrees south latitude in the Atlantic sector. Sea ice generally has a thickness of 0.5 to 1 meter with dynamic short-term variations and with large annual and interannual changes. Strong offshore winds from the interior of Antarctica partly keep the shoreline ice-free throughout the winter (so-called polynyas: compare Arctic Ocean, particularly the Laptev Sea).


The Antarctic Circumpolar Current moves perpetually eastward. It is the World's largest ocean current, transporting 130 million cubic meters of water per second, which represents 100 times the annual discharge of all the World's rivers. The Polar Front is located 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. Huge icebergs with drafts up to several hundred meters drift around the Southern Ocean. Smaller icebergs and iceberg fragments frequently occur far North in warmer waters. During ice-free periods, strong winds cause high and long waves in the Southern Ocean.


Cyclonic storms travel eastward around the continent and frequently are intense because of the temperature contrast between ice and the open ocean. The ocean area from about 40 degree south latitude to the Antarctic Circle has the strongest average wind velocities found anywhere on Earth. Increased solar ultraviolet radiation resulting from the Antarctic ozone hole caused damages in marine life in recent years.


Some relatively small icebergs are "calving" off the edge of B10A. Since B10A is now in relatively warm water, it is breaking up more rapidly than before. (True color Landsat 7 image)

Many of the higher species of Antarctic flesh-eaters feed on krill (small crustaceas). This makes the Antarctic marine food web relatively simple, with krill as the key or central species. The top carnivores are the orca or killer whale and leopard seals who feed on penguins, squid and other seals. Krill is therefore very important to the marine ecology of Antarctica. It was first seriously fished in the late 1970s and illegal, unreported, and unregulated recent pirate-fishery affect the sustainability of the regional krill and fish stocks. Additionally, large amounts of incidental mortality of seabirds result from long-line fishing for toothfish.


The Drake Passage around the northernmost tip of South America offers alternative to transit through the Panama Canal. Few harbors exist along the coast of Antarctica. Severe ice conditions limit the use of most of them to short periods in midsummer; even then some ports cannot be entered without icebreaker support. Most Antarctic ports are operated by governmental research stations and, except in an emergency, are not open to commercial or private vessels.


The Southern Ocean is subject to all international agreements regarding the World's oceans. Furthermore, international commission agreements on whaling as well as on conservation of seals and marine living resources specific to the region were ratified. Many nations prohibited the exploration and exploitation of mineral resources south of the Polar Front.


In 1910, the Norwegian wooden research vessel „Fram“ started for its third large cruise. Under the command of Roald Amundsen, the vessel and its crew sailed to the Southern Ocean. On December 14, 1911, Amundsen reached the South Pole by feet and - as first man! More pioneer work was done by the "Meteor" in the South Atlantic in the 1920's, and comprehensive studies on the whole Southern Ocean were conducted by "Discovery II" during the 1930's resulting in a compilation of the first oceanographic maps for these waters.


No economic activity is conducted at present on Antarctica or in the surrounding waters, except for fishing and small-scale tourism. Nearly all tourists were passengers on commercial ships and private yachts. Most tourist trips in that region last approximately two weeks.


Giant oil and gas fields are assumed in the bedrocks on the continental margin of Antarctica. Furthermore, manganese nodules, sand and gravel, fresh water as icebergs, squid, whales, seals, krill and fishes are among the Antarctic natural resources. The now-protected fur seal population is making a strong comeback after severe over-exploitation in the 18th and 19th centuries.



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