Definitions and useBorders and names for oceans and seas were internationally agreed when the , the precursor to the IHO, convened the First International Conference on 24 July 1919. The IHO then published these in its ''Limits of Oceans and Seas'', the first edition being 1928. Since the first edition, the limits of the Southern Ocean have moved progressively southwards; since 1953, it has been omitted from the official publication and left to local hydrographic offices to determine their own limits. The IHO included the ocean and its definition as the waters south of the in its 2000 revisions, but this has not been formally adopted, due to continuing impasses about some of the content, such as the over the . The 2000 IHO definition, however, was circulated in a draft edition in 2002, and is used by some within the IHO and by some other organizations such as the ' and . The Australian Government regards the Southern Ocean as lying immediately south of Australia (see ). The recognized the ocean officially in June 2021. Prior to this, it depicted it in a typeface different from the other world oceans; instead, it shows the Pacific, Atlantic, and Indian Oceans extending to Antarctica on both its print and online maps. Map publishers using the term Southern Ocean on their maps include Hema Maps and GeoNova.
Pre-20th century"Southern Ocean" is an obsolete name for the Pacific Ocean or South Pacific, coined by , the first European to discover it, who approached it from the north. The "South Seas" is a less archaic synonym. A 1745 British established a prize for discovering a to "the Western and Southern Ocean of ''America''". Authors using "Southern Ocean" to name the waters encircling the unknown southern polar regions used varying limits. 's account of implies borders it. Peacock's 1795 ''Geographical Dictionary'' said it lay "to the southward of America and Africa"; John Payne in 1796 used 40 degrees as the northern limit; the 1827 ''Edinburgh Gazetteer'' used 50 degrees. The ''Family Magazine'' in 1835 divided the "Great Southern Ocean" into the "Southern Ocean" and the "Antarctick 'sic''Ocean" along the Antarctic Circle, with the northern limit of the Southern Ocean being lines joining Cape Horn, the Cape of Good Hope, Van Diemen's Land and the south of New Zealand. The United Kingdom's ' described the waters forming the southern limit of the new province of as "the Southern Ocean". The 's ''Legislative Council Act 1881'' delimited part of the division of as "along the boundary to the Southern ocean".
1928 delineationIn the 1928 first edition of ''Limits of Oceans and Seas'', the Southern Ocean was delineated by land-based limits: Antarctica to the south, and South America, Africa, Australia, and to the north. The detailed land-limits used were from in Chile eastwards to in Africa, then further eastwards to the southern coast of mainland Australia to , . From Cape Leeuwin, the limit then followed eastwards along the coast of mainland Australia to , , then southwards across to , , along the west coast of King Island, then the remainder of the way south across Bass Strait to , . The limit then followed the west coast of Tasmania southwards to the and then went eastwards to Broughton Island, New Zealand, before returning to Cape Horn.
1937 delineationThe northern limits of the Southern Ocean were moved southwards in the IHO's 1937 second edition of the ''Limits of Oceans and Seas''. From this edition, much of the ocean's northern limit ceased to abut land masses. In the second edition, the Southern Ocean then extended from Antarctica northwards to latitude 40°S between in Africa (long. 20°E) and in Western Australia (long. 115°E), and extended to latitude 55°S between of New Zealand (165 or 166°E east) and in South America (67°W). As is discussed in more detail below, prior to the 2002 edition the limits of oceans explicitly excluded the seas lying within each of them. The was unnamed in the 1928 edition, and delineated as shown in the figure above in the 1937 edition. It therefore encompassed former Southern Ocean waters—as designated in 1928—but was technically not inside any of the three adjacent oceans by 1937. In the 2002 draft edition, the IHO have designated 'seas' as being subdivisions within 'oceans', so the Bight would have still been within the Southern Ocean in 1937 if the 2002 convention were in place then. To perform direct comparisons of current and former limits of oceans it is necessary to consider, or at least be aware of, how the 2002 change in IHO terminology for 'seas' can affect the comparison.
1953 delineationThe Southern Ocean did not appear in the 1953 third edition of ''Limits of Oceans and Seas'', a note in the publication read: Instead, in the IHO 1953 publication, the Atlantic, Indian and Pacific Oceans were extended southward, the Indian and Pacific Oceans (which had not previously touched pre 1953, as per the first and second editions) now abutted at the meridian of , and the southern limits of the and the were moved northwards.
2002 draft delineationThe IHO readdressed the question of the Southern Ocean in a survey in 2000. Of its 68 member nations, 28 responded, and all responding members except Argentina agreed to redefine the ocean, reflecting the importance placed by oceanographers on ocean currents. The proposal for the name ''Southern Ocean'' won 18 votes, beating the alternative ''Antarctic Ocean''. Half of the votes supported a definition of the ocean's northern limit at the —with no land interruptions at this latitude—with the other 14 votes cast for other definitions, mostly the , but a few for as far north as the . Notably the collates data from latitudes higher than 40 degrees south. A draft fourth edition of ''Limits of Oceans and Seas'' was circulated to IHO member states in August 2002 (sometimes referred to as the "2000 edition" as it summarized the progress to 2000). It has yet to be published due to 'areas of concern' by several countries relating to various naming issues around the world – primarily the – and there have been various changes, 60 seas were given new names, and even the name of the publication was changed. A reservation had also been lodged by Australia regarding the Southern Ocean limits. Effectively, the third edition—which did not delineate the Southern Ocean leaving delineation to local hydrographic offices—has yet to be superseded. Despite this, the fourth edition definition has partial ''de facto'' usage by many nations, scientists, and organisations such as the U.S. (the ' uses "Southern Ocean", but none of the other new sea names within the "Southern Ocean", such as the "") and , scientists and nations – and even by some within the IHO. Some nations' hydrographic offices have defined their own boundaries; the United Kingdom used the for example. Other organisations favour more northerly limits for the Southern Ocean. For example, ' describes the Southern Ocean as extending as far north as South America, and confers great significance on the , yet its description of the Indian Ocean contradicts this, describing the Indian Ocean as extending south to Antarctica. Other sources, such as the , show the , , and oceans as extending to Antarctica on its maps, although articles on the National Geographic web site have begun to reference the Southern Ocean. A radical shift from past IHO practices (1928–1953) was also seen in the 2002 draft edition when the IHO delineated 'seas' as being subdivisions that lay within the boundaries of 'oceans'. While the IHO are often considered the authority for such conventions, the shift brought them into line with the practices of other publications (e.g. the CIA ''World Fact Book'') which already adopted the principle that seas are contained within oceans. This difference in practice is markedly seen for the Pacific Ocean in the adjacent figure. Thus, for example, previously the between Australia and New Zealand was not regarded by the IHO as being part of the Pacific, but as of the 2002 draft edition it is. The new delineation of seas being subdivisions of oceans has avoided the need to interrupt the northern boundary of the Southern Ocean where intersected by which includes all of the waters from South America to the Antarctic coast, nor interrupt it for the , which also extends below the 60th parallel south. The new delineation of seas has also meant that the long-time named seas around Antarctica, excluded from the 1953 edition (the 1953 map did not even extend that far south), are 'automatically' part of the Southern Ocean.
Australian standpointIn Australia, authorities define the Southern Ocean as including the entire body of water between Antarctica and the south coasts of Australia and New Zealand, and up to 60°S elsewhere. Coastal maps of and label the sea areas as ''Southern Ocean'' and in is described as the point where the Indian and Southern Oceans meet.
History of exploration
Unknown southern landExploration of the Southern Ocean was inspired by a belief in the existence of a ''Terra Australis'' – a vast continent in the far south of the globe to "balance" the northern lands of Eurasia and North Africa – which had existed since the times of . The rounding of the in 1487 by first brought explorers within touch of the Antarctic cold, and proved that there was an ocean separating Africa from any Antarctic land that might exist. , who passed through the in 1520, assumed that the islands of to the south were an extension of this unknown southern land. In 1564, published his first map, ''Typus Orbis Terrarum'', an eight-leaved wall map of the world, on which he identified the ' with ' as a northward extension of the ', reaching as far as .Joost Depuydt, ‘ (1527–1598)’, , Oxford University Press, 2004 European geographers continued to connect the coast of Tierra del Fuego with the coast of New Guinea on their globes, and allowing their imaginations to run riot in the vast unknown spaces of the south Atlantic, south Indian and Pacific oceans they sketched the outlines of the ''Terra Australis Incognita'' ("Unknown Southern Land"), a vast continent stretching in parts into the tropics. The search for this great south land was a leading motive of explorers in the 16th and the early part of the 17th centuries. The , who claimed having sighted "snow-covered mountains" beyond the in 1603, is recognized as the first explorer that discovered the continent of Antarctica, although he was ignored in his time. In 1606, took possession for the king of Spain all of the lands he had discovered in Australia del Espiritu Santo (the ) and those he would discover "even to the Pole". , like Spanish explorers before him, had speculated that there might be an open channel south of Tierra del Fuego. When and discovered the southern extremity of Tierra del Fuego and named it in 1615, they proved that the Tierra del Fuego archipelago was of small extent and not connected to the southern land, as previously thought. Subsequently, in 1642, showed that even was separated by sea from any continuous southern continent.
South of the Antarctic ConvergenceThe visit to by in 1675 was the first ever discovery of land south of the i.e. in the Southern Ocean/Antarctic. Soon after the voyage cartographers started to depict "", honouring the discoverer. was aware of la Roché's discovery when surveying and mapping the island in 1775. 's voyage in for magnetic investigations in the South Atlantic met the pack ice in in January 1700, but that latitude (he reached 140 mi off the north coast of ) was his farthest south. A determined effort on the part of the French naval officer to discover the "South Land" – described by a half legendary "" – resulted in the discovery of in 54°10′ S, and in the navigation of of ice-cumbered sea nearly in in 1730. In 1771, sailed from with instructions to proceed south from in search of "a very large continent". He lighted upon a land in which he called South France, and believed to be the central mass of the southern continent. He was sent out again to complete the exploration of the new land, and found it to be only an inhospitable island which he renamed the Isle of Desolation, but which .
South of the Antarctic CircleThe obsession of the undiscovered continent culminated in the brain of , the brilliant and erratic who was nominated by the to command the expedition to in 1769. The command of the expedition was given by the admiralty to Captain . Sailing in 1772 with ''Resolution'', a vessel of 462 tons under his own command and ''Adventure'' of 336 tons under Captain , Cook first searched in vain for , then sailed for 20 degrees of longitude to the westward in , and then 30° eastward for the most part south of , a lower southern latitude than had ever been voluntarily entered before by any vessel. On 17 January 1773 the was crossed for the first time in history and the two ships reached by , where their course was stopped by ice. Cook then turned northward to look for , of the discovery of which he had received news at , but from the rough determination of his longitude by Kerguelen, Cook reached the assigned latitude 10° too far east and did not see it. He turned south again and was stopped by ice in by 95° E and continued eastward nearly on the parallel of to . On 16 March, the approaching winter drove him northward for rest to New Zealand and the tropical islands of the Pacific. In November 1773, Cook left New Zealand, having parted company with the ''Adventure'', and reached by , whence he sailed eastward keeping as far south as the floating ice allowed. The Antarctic Circle was crossed on 20 December and Cook remained south of it for three days, being compelled after reaching to stand north again in . A long detour to served to show that there was no land connection between New Zealand and . Turning south again, Cook crossed the Antarctic Circle for the third time at before his progress was once again blocked by ice four days later at by . This point, reached on 30 January 1774, was the farthest south attained in the 18th century. With a great detour to the east, almost to the coast of South America, the expedition regained Tahiti for refreshment. In November 1774, Cook started from New Zealand and crossed the South Pacific without sighting land between and to Tierra del Fuego; then, passing Cape Horn on 29 December, he rediscovered renaming it , and discovered the (named ''Sandwich Land'' by him), the only ice-clad land he had seen, before crossing the South Atlantic to the Cape of Good Hope between and . He thereby laid open the way for future Antarctic exploration by exploding the myth of a habitable southern continent. Cook's most southerly discovery of land lay on the temperate side of the , and he convinced himself that if land lay farther south it was practically inaccessible and without economic value. Voyagers rounding Cape Horn frequently met with contrary winds and were driven southward into snowy skies and ice-encumbered seas; but so far as can be ascertained none of them before 1770 reached the Antarctic Circle, or knew it, if they did. In a voyage from 1822 to 1824, commanded the 160-ton ''Jane'', accompanied by his second ship ''Beaufoy'' captained by Matthew Brisbane. Together they sailed to the South Orkneys where proved disappointing. They turned south in the hope of finding a better sealing ground. The season was unusually mild and tranquil, and on 20 February 1823 the two ships reached 74°15' S and 34°16'45″ W the southernmost position any ship had ever reached up to that time. A few icebergs were sighted but there was still no sight of land, leading Weddell to theorize that the sea continued as far as the South Pole. Another two days' sailing would have brought him to (to the east of the ) but Weddell decided to turn back.
First sighting of landThe first land south of the was discovered by the , who sighted on 19 February 1819. A few months later Smith returned to explore the other islands of the archipelago, landed on , and claimed the new territories for Britain. In the meantime, the Spanish Navy ship ' sank in September 1819 when trying to cross Cape Horn. Parts of her wreckage were found months later by sealers on the north coast of (). It is unknown if some survivor managed to be the first to set foot on these Antarctic islands. The first confirmed sighting of mainland Antarctica cannot be accurately attributed to one single person. It can, however, be narrowed down to three individuals. According to various sources, three men all sighted the ice shelf or the continent within days or months of each other: , a captain in the ; , a captain in the ; and , an American sealer out of . It is certain that the expedition, led by von Bellingshausen and Lazarev on the ships ''Vostok'' and ''Mirny'', reached a point within from and recorded the sight of an ice shelf at that became known as the . On 30 January 1820, Bransfield sighted , the northernmost point of the Antarctic mainland, while Palmer sighted the mainland in the area south of Trinity Peninsula in November 1820. Von Bellingshausen's expedition also discovered and , the first islands to be discovered south of the circle.
Antarctic expeditionsIn December 1839, as part of the of 1838–42 conducted by the (sometimes called "the Wilkes Expedition"), an expedition sailed from Sydney, Australia, on the sloops-of-war and , the brig , the full-rigged ship , and two schooners and . They sailed into the Antarctic Ocean, as it was then known, and reported the discovery "of an Antarctic continent west of the " on 25 January 1840. That part of Antarctica was later named "", a name it maintains to this day. Explorer passed through what is now known as the and discovered (both of which were named for him) in 1841. He sailed along a huge wall of ice that was later named the . and are named after two ships from his expedition: and . The of 1914, led by , set out to cross the continent via the pole, but their ship, , was trapped and crushed by pack ice before they even landed. The expedition members survived after an epic journey on sledges over pack ice to . Then Shackleton and five others crossed the Southern Ocean, in an open boat called , and then trekked over to raise the alarm at the whaling station . In 1946, US Navy Rear Admiral and more than 4,700 military personnel visited the Antarctic in an expedition called . Reported to the public as a scientific mission, the details were kept secret and it may have actually been a training or testing mission for the military. The expedition was, in both military or scientific planning terms, put together very quickly. The group contained an unusually high amount of military equipment, including an aircraft carrier, submarines, military support ships, assault troops and military vehicles. The expedition was planned to last for eight months but was unexpectedly terminated after only two months. With the exception of some eccentric entries in Admiral Byrd's diaries, no real explanation for the early termination has ever been officially given. Captain , Byrd's executive officer, returned to Antarctica with his own expedition in 1947–1948, with Navy support, three planes, and dogs. Ronne disproved the notion that the continent was divided in two and established that East and West Antarctica was one single continent, i.e. that the Weddell Sea and the Ross Sea are not connected. The expedition explored and mapped large parts of Palmer Land and the Weddell Sea coastline, and identified the , named by Ronne after his wife . Ronne covered by ski and dog sled – more than any other explorer in history. The discovered and mapped the last unknown coastline in the world and was the first Antarctic expedition to ever include women.
Recent historyThe was signed on 1 December 1959 and came into force on 23 June 1961. Among other provisions, this treaty limits to the support of scientific research. The first person to sail single-handed to Antarctica was the New Zealander , in 1972, in a steel sloop ''Ice Bird''. A baby, named , was born near on 7 January 1978, becoming the first baby born on the continent. He also was born further south than anyone in history. The was a operated by the explorer . Observers point to ''Explorers 1969 expeditionary cruise to as the frontrunner for today's sea-based tourism in that region. ''Explorer'' was the first cruise ship used specifically to sail the icy waters of the Antarctic Ocean and the first to sink there when she struck an unidentified submerged object on 23 November 2007, reported to be ice, which caused a gash in the hull. ''Explorer'' was abandoned in the early hours of 23 November 2007 after taking on water near the in the Southern Ocean, an area which is usually stormy but was calm at the time. ''Explorer'' was confirmed by the to have sunk at approximately position: 62° 24′ South, 57° 16′ West, in roughly 600 m of water. British engineer designed an called a "saildrone" that completed the first autonomous circumnavigation of the Southern Ocean on 3 August 2019 after 196 days at sea. The first completely expedition on the Southern Ocean was accomplished on 25 December 2019 by a team of rowers comprising captain (Iceland), first mate (US), (US), (South Africa), Jamie Douglas-Hamilton (UK) and John Petersen (US).
GeographyThe Southern Ocean, geologically the youngest of the oceans, was formed when Antarctica and moved apart, opening the , roughly 30 million years ago. The separation of the continents allowed the formation of the Antarctic Circumpolar Current. With a northern limit at , the Southern Ocean differs from the other oceans in that its largest boundary, the northern boundary, does not abut a landmass (as it did with the first edition of ''Limits of Oceans and Seas''). Instead, the northern limit is with the Atlantic, Indian and Pacific Oceans. One reason for considering it as a separate ocean stems from the fact that much of the water of the Southern Ocean differs from the water in the other oceans. Water gets transported around the Southern Ocean fairly rapidly because of the which circulates around Antarctica. Water in the Southern Ocean south of, for example, New Zealand, resembles the water in the Southern Ocean south of South America more closely than it resembles the water in the Pacific Ocean. The Southern Ocean has typical depths of between over most of its extent with only limited areas of shallow water. The Southern Ocean's greatest depth of occurs at the southern end of the , at 60°00'S, 024°W. The appears generally narrow and unusually deep, its edge lying at depths up to , compared to a global mean of . to equinox in line with the sun's seasonal influence, the Antarctic ice pack fluctuates from an average minimum of in March to about in September, more than a sevenfold increase in area.
Sub-divisions of the Southern OceanSub-divisions of oceans are geographical features such as "seas", "straits", "bays", "channels", and "gulfs". There are many sub-divisions of the Southern Ocean defined in the never-approved 2002 draft fourth edition of the IHO publication ''Limits of Oceans and Seas''. In clockwise order these include (with sector): * (57°18'W – 12°16'E) * (20°W – 45°E) * (0° – 14°E) * (14° – 30°E) * (30° – 50°E) * (59°34' – 85°E) * (82° – 96°E) * (95°45' – 113°E) * (140°E) * (150° – 170°E) * (166°E – 155°W) * (102°20′ – 126°W) * (57°18' – 102°20'W) * Part of the (54° – 68°W) * (54° – 62°W) * Part of the (26°30' – 65°W) A number of these such as the 2002 Russian-proposed "Cosmonauts Sea", "Cooperation Sea", and "Somov (mid-1950s Russian polar explorer) Sea" are not included in the 1953 IHO document which remains currently in force, because they received their names largely originated from 1962 onward. Leading geographic authorities and atlases do not use these latter three names, including the 2014 10th edition World Atlas from the United States' and the 2014 12th edition of the British , but Soviet and Russian-issued maps do.
Biggest seas in Southern OceanTop large seas: # – # – # – # – # – # – # – # – # – # – # – # – # #
Natural resourcesThe Southern Ocean probably contains large, and possibly giant, and fields on the . s, accumulation of valuable minerals such as gold, formed by gravity separation during sedimentary processes are also expected to exist in the Southern Ocean. are expected to exist in the Southern Ocean. Manganese nodules are rock s on the bottom formed of concentric layers of and s around a core. The core may be microscopically small and is sometimes completely transformed into manganese minerals by . Interest in the potential exploitation of polymetallic nodules generated a great deal of activity among prospective mining consortia in the 1960s and 1970s. The s that form each year around in the Southern Ocean hold enough to meet the needs of every person on Earth for several months. For several decades there have been proposals, none yet to be feasible or successful, to tow Southern Ocean icebergs to more arid northern regions (such as Australia) where they can be harvested.
Natural hazardss can occur 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 m thick) also pose problems for ships. The deep continental shelf has a floor of glacial deposits varying widely over short distances. Sailors know latitudes from to as the "", "Furious Fifties" and "Shrieking Sixties" due to high winds and large waves that form as winds blow around the entire globe unimpeded by any land-mass. Icebergs, especially in May to October, make the area even more dangerous. The remoteness of the region makes sources of search and rescue scarce.
Antarctic Circumpolar Current and Antarctic ConvergenceWhile the Southern is the second smallest ocean it contains the unique and highly energetic which moves perpetually eastward – chasing and joining itself, and at in length – it comprises the world's longest ocean current, transporting of water – 100 times the flow of all the world's rivers. Several processes operate along the coast of Antarctica to produce, in the Southern Ocean, types of es not produced elsewhere in the oceans of the . One of these is the , a very cold, highly saline, dense water that forms under . Another is , a mixture of Antarctic Bottom Water and . Associated with the Circumpolar Current is the encircling Antarctica, where cold northward-flowing Antarctic waters meet the relatively warmer waters of the , Antarctic waters predominantly sink beneath subantarctic waters, while associated zones of mixing and create a zone very high in nutrients. These nurture high levels of with associated copepods and , and resultant foodchains supporting fish, whales, seals, penguins, albatrosses and a wealth of other species. The Antarctic Convergence is considered to be the best natural definition of the northern extent of the Southern Ocean.
UpwellingLarge-scale is found in the Southern Ocean. Strong westerly (eastward) winds blow around , driving a significant flow of water northwards. This is actually a type of coastal upwelling. Since there are no continents in a band of open latitudes between and the tip of the , some of this water is drawn up from great depths. In many numerical models and observational syntheses, the Southern Ocean upwelling represents the primary means by which deep dense water is brought to the surface. Shallower, wind-driven upwelling is also found off the west coasts of North and South America, northwest and southwest Africa, and southwest and , all associated with oceanic subtropical high pressure circulations. Some models of the ocean circulation suggest that broad-scale upwelling occurs in the tropics, as pressure driven flows converge water toward the low latitudes where it is diffusively warmed from above. The required diffusion coefficients, however, appear to be larger than are observed in the real ocean. Nonetheless, some diffusive upwelling does probably occur.
Ross and Weddell GyresThe and are two that exist within the Southern Ocean. The gyres are located in the and respectively, and both rotate clockwise. The gyres are formed by interactions between the and the . has been noted to persist in the central area of the Ross Gyre. There is some evidence that has resulted in some decrease of the of the waters of the Ross Gyre since the 1950s. Due to the acting to the left in the and the resulting away from the centres of the Weddell Gyre, these regions are very productive due to upwelling of cold, nutrient rich water.
ObservationsObservation of the Southern Ocean is coordinated through the . This provides access to meta data for a significant proportion of the data collected in the regions over the past decades including hydrographic measurements and ocean currents. The data provision is setup to emphasize records that are related to for the ocean region south of 40°S.
ClimateSea temperatures vary from about −2 to 10 °C (28 to 50 °F). Cyclonic storms travel eastward around the continent and frequently become intense because of the temperature contrast between ice and . The ocean-area from about to the Antarctic Circle has the strongest average winds found anywhere on Earth. In winter the ocean freezes outward to in the Pacific sector and in the Atlantic sector, lowering surface temperatures well below 0 degrees Celsius. At some coastal points, however, persistent intense drainage winds from the interior keep the shoreline ice-free throughout the winter.
Climate changeThe Southern Ocean is one of the regions in which rapid climate change is the most visibly taking place. In this region, small perturbations in temperature lead to major environmental perturbation. The effects of climate change in the Southern Ocean are expected to manifest themselves in a regional and diverse manner. This will include changes in the climate and weather patterns across different time-scales with alterations to the long interdecadal background signals such as the (ENSO). Increasing ocean temperatures and changes in the extent and seasonality of sea ice affect the biological productivity and community of this ecosystem. The magnitude and exact manifestation of these changes could lead to different populations of the same species responding and adapting differently to climate change depending on the region of the Southern Ocean they inhabit.
AnimalsA variety of marine animals exist and rely, directly or indirectly, on the phytoplankton in the Southern Ocean. Antarctic sea life includes s, s, , s and s. The is the only penguin that breeds during the winter in Antarctica, while the breeds farther south than any other penguin. The has distinctive feathers around the eyes, giving the appearance of elaborate eyelashes. s, s, and s also breed in the Antarctic. The was very heavily hunted in the 18th and 19th centuries for its pelt by sealers from the United States and the United Kingdom. The , a "", is named after , commander of British sealing expeditions in the . , which congregates in large , is the of the of the Southern Ocean, and is an important food organism for whales, seals, s, fur seals, , , penguins, es and many other birds. The communities of the seafloor are diverse and dense, with up to 155,000 animals found in . As the seafloor environment is very similar all around the Antarctic, hundreds of species can be found all the way around the mainland, which is a uniquely wide distribution for such a large community. is common among these animals. A census of sea life carried out during the and which involved some 500 researchers was released in 2010. The research is part of the global (CoML) and has disclosed some remarkable findings. More than 235 marine organisms live in both polar regions, having bridged the gap of . Large animals such as some cetaceans and birds make the round trip annually. More surprising are small forms of life such as mudworms, s and free-swimming snails found in both polar oceans. Various factors may aid in their distribution – fairly uniform temperatures of the deep ocean at the poles and the equator which differ by no more than , and the major current systems or marine which transport egg and larva stages. However, among smaller marine animals generally assumed to be the same in the Antarctica and the Arctic, more detailed studies of each population have often—but not always—revealed differences, showing that they are closely related rather than a single bipolar species.
BirdsThe rocky shores of mainland Antarctica and its offshore islands provide nesting space for over 100 million birds every spring. These nesters include species of es, s, s, s and s. The insectivorous is to and some smaller surrounding islands. Freshwater ducks inhabit South Georgia and the . The flightless s are all located in the , with the greatest concentration located on and around Antarctica. Four of the 18 penguin species live and breed on the mainland and its close offshore islands. Another four species live on the subantarctic islands. have four overlapping layers of feathers, keeping them warm. They are the only Antarctic animal to breed during the winter.
FishThere are relatively few fish species in few in the Southern Ocean. The most species-rich family are the (Liparidae), followed by the (Nototheniidae) and (Zoarcidae). Together the snailfish, eelpouts and s (which includes cod icefish and several other families) account for almost of the more than 320 described fish species of the Southern Ocean (tens of also occur in the region, especially among the snailfish). Southern Ocean snailfish are generally found in deep waters, while the icefish also occur in shallower waters.
IcefishCod icefish (Nototheniidae), as well as several other families, are part of the suborder, collectively sometimes referred to as icefish. The suborder contains many species with s in their blood and tissue, allowing them to live in water that is around or slightly below . Antifreeze proteins are also known from Southern Ocean snailfish. The (family Channichthyidae), also known as white-blooded fish, are only found in the Southern Ocean. They lack in their blood, resulting in their blood being colourless. One Channichthyidae species, the (''Champsocephalus gunnari''), was once the most common fish in coastal waters less than deep, but was in the 1970s and 1980s. Schools of icefish spend the day at the seafloor and the night higher in the eating plankton and smaller fish. There are two species from the genus ', the (''Dissostichus mawsoni'') and the (''Dissostichus eleginoides''). These two species live on the seafloor deep, and can grow to around long weighing up to , living up to 45 years. The Antarctic toothfish lives close to the Antarctic mainland, whereas the Patagonian toothfish lives in the relatively warmer subantarctic waters. Toothfish are commercially fished, and overfishing has reduced toothfish populations. Another abundant fish group is the genus ', which like the Antarctic toothfish have antifreeze in their bodies. An unusual species of icefish is the (''Pleuragramma antarcticum''), which is the only truly fish in the waters near Antarctica.
MammalsSeven species inhabit Antarctica. The largest, the (''Mirounga leonina''), can reach up to , while females of the smallest, the (''Arctophoca gazella''), reach only . These two species live north of the sea ice, and breed in on beaches. The other four species can live on the sea ice. s (''Lobodon carcinophagus'') and s (''Leptonychotes weddellii'') form breeding colonies, whereas s (''Hydrurga leptonyx'') and s (''Ommatophoca rossii'') live solitary lives. Although these species hunt underwater, they breed on land or ice and spend a great deal of time there, as they have no terrestrial predators. The four species that inhabit sea ice are thought to make up 50% of the total biomass of the world's seals. Crabeater seals have a population of around 15 million, making them one of the most numerous large animals on the planet. The (''Phocarctos hookeri''), one of the rarest and most localised pinnipeds, breeds almost exclusively on the subantarctic , although historically it had a wider range. Out of all permanent mammalian residents, the Weddell seals live the furthest south. There are 10 n species found in the Southern Ocean; six s, and four s. The largest of these, the (''Balaenoptera musculus''), grows to long weighing 84 tonnes. Many of these species are , and travel to waters during the Antarctic winter.
ArthropodsFive species of , small free-swimming s, have been found in the Southern Ocean. The (''Euphausia superba'') is one of the most abundant animal species on earth, with a of around 500 million tonnes. Each individual is long and weighs over . The swarms that form can stretch for kilometres, with up to 30,000 individuals per , turning the water red. Swarms usually remain in deep water during the day, ascending during the night to feed on . Many larger animals depend on krill for their own survival. During the winter when food is scarce, adult Antarctic krill can revert to a smaller juvenile stage, using their own body as nutrition. Many benthic crustaceans have a non-seasonal breeding cycle, and some raise their young in a . ' is an unusually large benthic , reaching in length weighing . s are abundant in soft sediments, eating a range of items, from to other animals. The amphipods are highly diverse with more than 600 recognized species found south of the Antarctic Convergence and there are indications that many undescribed species remain. Among these are several "giants", such as the iconic that are up to long. Slow moving s are common, sometimes growing as large as a human hand. They feed on the s, s, and ns that litter the seabed.
OthersMany s are present in Antarctica. such as ' move around on the seafloor, while others such as ' live in burrows the water above. There are around 70 species in the Southern Ocean, the largest of which is the (''Mesonychoteuthis hamiltoni''), which at up to is among the largest invertebrate in the world. makes up most of the diet of some animals, such as es and s, and the (''Moroteuthis ingens'') is one of the subantarctic's most preyed upon species by vertebrates. The genus ''Abatus'' burrow through the sediment eating the nutrients they find in it. Two species of s are common in Antarctic waters, ''Salpa thompsoni'' and ''Ihlea racovitzai''. ''Salpa thompsoni'' is found in ice-free areas, whereas ''Ihlea racovitzai'' is found in the high latitude areas near ice. Due to their low nutritional value, they are normally only eaten by fish, with larger animals such as birds and marine mammals only eating them when other food is scarce. Antarctic s are long-lived, and sensitive to environmental changes due to the specificity of the microbial communities within them. As a result, they function as indicators of environmental health.
Current issuesIncreased solar radiation resulting from the Antarctic has reduced marine primary productivity () by as much as 15% and has started damaging the of some fish. , especially the landing of an estimated five to six times more than the regulated fishery, likely affects the sustainability of the stock. Long-line fishing for toothfish causes a high incidence of seabird mortality.
International agreementsAll international agreements regarding the world's oceans apply to the Southern Ocean. In addition, it is subject to these agreements specific to the region: * The ' of the (IWC) prohibits commercial south of (south of between and ). regularly does not recognize this provision, because the sanctuary violates IWC charter. Since the scope of the sanctuary is limited to commercial whaling, in regard to its whaling permit and whaling for scientific research, a Japanese fleet carried out an annual whale-hunt in the region. On 31 March 2014, the ruled that Japan's whaling program, which Japan has long claimed is for scientific purposes, was a cloak for commercial whaling, and no further permits would be granted. * ' is part of the '. It was signed at the conclusion of a multilateral conference in London on 11 February 1972. * ' (CCAMLR) is part of the '. The Convention was entered into force on 7 April 1982 and has its goal is to preserve and environmental integrity in and near . It was established in large part to concerns that an increase in catches in the Southern Ocean could have a serious impact on populations of other marine life which are dependent upon krill for food. Many nations prohibit the exploration for and the exploitation of resources south of the fluctuating , which lies 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. The covers the portion of the globe south of ; it prohibits new claims to Antarctica. The ''Convention for the Conservation of Antarctic Marine Living Resources'' applies to the area south of 60° South latitude as well as the areas further north up to the limit of the Antarctic Convergence.
EconomyBetween 1 July 1998 and 30 June 1999, fisheries landed 119,898 s, of which 85% consisted of and 14% of . International agreements came into force 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.
Ports and harborsMajor operational ports include: , , , , , , and offshore anchorages in Antarctica. Few ports or harbors exist on the southern (Antarctic) coast of the Southern Ocean, since ice conditions limit use of most shores to short periods in midsummer; even then some require escort for access. Most Antarctic ports are operated by government research stations and, except in an emergency, remain closed to commercial or private vessels; vessels in any port south of are subject to inspection by Antarctic Treaty observers. The Southern Ocean's southernmost port operates at McMurdo Station at . forms a small harbor, on the southern tip of where a floating makes port operations possible in summer. personnel constructed the first ice pier at McMurdo in 1973."Unique ice pier provides harbor for ships,"
See also* * * *
References* * * .
Further reading* Arndt, JE et al.: ''The International Bathymetric Chart of the Southern Ocean Version 1.0 – A new bathymetric compilation covering circum-Antarctic waters''. Geophysical Research Letters, 40(9), 1–7, 2013. * : ''Warming of the Southern Ocean since the 1950s''. ': Vol. 295 (no. 5558), 1275–1277, 2002. * Descriptive Regional Oceanography, P. Tchernia, Pergamon Press, 1980, . * Matthias Tomczak and J. Stuart Godfrey. 2003. ''Regional Oceanography: an Introduction''. (se