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[[File:Antarctica 1912 edit.jpg|460px|thumb|South-Polar-Map: a 1912 map by German publisher [[Justus Perthes]] showing an Antarktischer Ocean (Antarctic Ocean) encompassing Antarctica with surrounding islands.]]
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{{Five oceans}}
The '''Southern Ocean''' (also known as the '''Great Southern Ocean''', '''Antarctic Ocean''', '''South Polar Ocean''' and '''Austral Ocean''') comprises the southernmost waters of the [[World Ocean]], generally taken to be south of [[60th parallel south|60°S latitude]] and encircling [[Antarctica]].<ref name=CIAgeo>{{cite web |title=Geography - Southern Ocean|work=CIA Factbook |url=https://www.cia.gov/library/publications/the-world-factbook/geos/oo.html
|accessdate=2012-07-16|quote=... 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.}}</ref> As such, it is regarded as the fourth-largest of the five principal [[ocean]]ic divisions (after the [[Pacific Ocean|Pacific]], [[Atlantic Ocean|Atlantic]], and [[Indian Ocean]]s, but larger than the [[Arctic Ocean]]).<ref name=CIAintro>{{cite web |title=Introduction - Southern Ocean|work=CIA Factbook |url=https://www.cia.gov/library/publications/the-world-factbook/geos/oo.html
|accessdate=2012-07-16|quote=...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]]).}}</ref> This ocean zone is where cold, northward flowing waters from the [[Antarctic]] mix with warmer [[subantarctic]] waters.

Geographers disagree on the Southern Ocean's northern boundary, and some even its existence - considering the waters part of the [[Pacific Ocean|Pacific]], [[Atlantic Ocean|Atlantic]], and [[Indian Ocean]]s instead. Others regard the [[Antarctic Convergence]], an ocean zone which fluctuates seasonally, as separating the Southern Ocean from other oceans, rather than the 60th parallel.<ref>Pyne, Stephen J.; ''The Ice: A Journey to Antarctica''. University of Washington Press, 1986. (A study of Antarctica's exploration, earth-sciences, icescape, esthetics, literature, and geopolitics)</ref> [[Australia]]n authorities regard the Southern Ocean as lying immediately south of Australia.<ref>{{cite news|url=http://www.theage.com.au/articles/2003/12/21/1071941610556.html|title=Canberra all at sea over position of Southern Ocean|last=Darby|first=Andrew|date=22 December 2003|publisher=The Age|accessdate=13 January 2013}}</ref><ref>{{cite web|title=Indian Ocean|url=http://www.britannica.com/EBchecked/topic/285876/Indian-Ocean|publisher=Encyclopaedia Britannica|accessdate=13 January 2013}}</ref>

The [[International Hydrographic Organization]] (IHO) has not yet ratified its 2000 definition of the ocean as being south of [[60th parallel south|60°S]]. Its latest published definition of oceans dates from 1953; this does not include the Southern Ocean. However, the more recent definition is already in some use by the IHO and other organisations such as the [[National Geographic Society]], [[Merriam-Webster Dictionary|Merriam-Webster]] and the U.S. [[Central Intelligence Agency]].<ref name=CIAintro/><ref name=nationalgeographic/><ref name=merriamwebster>{{cite web |url=http://www.merriam-webster.com/dictionary/southern%20ocean |title=Southern Ocean |website=Merriam-Webster Online Dictionary |publisher= Merriam-Webster |accessdate=18 January 2014}}</ref>

== History of exploration==
{{Main|History of Antarctica}}

=== The unknown southern land ===
{{See also|Terra Australis}}
[[File:OrteliusWorldMap1570.jpg|thumb|right|250px|1564 ''Typus Orbis Terrarum'', a map by [[Abraham Ortelius]] showed the imagined link between the proposed continent of Antarctica and [[South America]].]]
Belief in the existence of a ''Terra Australis''—a vast continent in the far south of the globe to "balance" the northern lands of Europe, Asia and [[North Africa]]—had existed since the times of [[Ptolemy]]. The doubling of the [[Cape of Good Hope]] in 1487 by [[Bartolomeu Dias]] 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. [[Ferdinand Magellan]], who passed through the [[Straits of Magellan]] in 1520, assumed that the islands of [[Tierra del Fuego]] to the south were an extension of this unknown southern land. In 1564, [[Abraham Ortelius]] published his first map, ''Typus Orbis Terrarum'', an eight-leaved wall map of the world, on which he identified the ''[[Regio Patalis]]'' with ''[[Locach]]'' as a northward extension of the ''[[Terra Australis]]'', reaching as far as [[New Guinea]].<ref name=ODNB>Joost Depuydt, ‘[[Ortelius, Abraham]] (1527–1598)’, [[Oxford Dictionary of National Biography]], Oxford University Press, 2004</ref><ref>Peter Barber, "Ortelius' great world map", National Library of Australia, ''Mapping our World: Terra Incognita to Australia'', Canberra, National Library of Australia, 2013, p.95.</ref>

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 Ocean|Indian]] and [[Pacific Ocean|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 or Third World was a leading motive of explorers in the 16th and the early part of the 17th centuries.

The [[Spanish people|Spaniard]] [[Gabriel de Castilla]], who claimed having sighted "snow-covered mountains" beyond the [[64th parallel south|64° S]] in 1603, is recognized as the first explorer that discovered the continent of Antartica, although he was ignored in his time.

[[Pedro Fernández de Quirós|Quirós]] in 1606 took possession for the king of Spain all of the lands he had discovered in Australia del Espiritu Santo (the [[New Hebrides]]) and those he would discover "even to the Pole".

[[Francis Drake]] like Spanish explorers before him had speculated that there might be an open channel south of Tierra del Fuego. Indeed, when [[Willem Schouten|Schouten]] and [[Jacob Le Maire|Le Maire]] discovered the southern extremity of Tierra del Fuego and named it Cape Horn in 1615, they proved that the Tierra del Fuego archipelago was of small extent and not connected to the southern land. Subsequently, in 1642, [[Abel Tasman|Tasman]] showed that even [[New Holland (Australia)]] was separated by sea from any continuous southern continent.

[[File:Edmund Halley.gif|thumb|180px|right|Portrait of [[Edmund Halley]] by [[Thomas Murray (artist)|Thomas Murray]], c. 1687]]

=== South of the Antarctic Convergence===
{{See also|Anthony de la Roché}}

The visit to [[South Georgia and the South Sandwich Islands|South Georgia]] by [[Anthony de la Roché]] in 1675 was the first ever discovery of land south of the [[Antarctic Convergence]] i.e. in the [[Antarctic]].<ref>Dalrymple, Alexander. (1771). ''A Collection of Voyages Made to the Ocean Between Cape Horn and Cape of Good Hope''. Two volumes. London.</ref><ref>Headland, Robert K. (1984).  ''The Island of South Georgia'', Cambridge University Press. {{ISBN|0-521-25274-1}}</ref>  Soon after the voyage cartographers started to depict ‘[[Anthony de la Roché#Maps showing la Roché's discovery|Roché Island]]’, honouring the discoverer.  [[James Cook]] was aware of la Roché's discovery when surveying and mapping the island in 1775.<ref>Cook, James. (1777).  [http://www.gutenberg.org/files/15869/15869-8.txt ''A Voyage Towards the South Pole, and Round the World. Performed in His Majesty's Ships the Resolution and Adventure, In the Years 1772, 1773, 1774, and 1775.  In which is included, Captain Furneaux's Narrative of his Proceedings in the Adventure during the Separation of the Ships'']. Volume II. London: Printed for W. Strahan and T. Cadell. ([[:wikisource:James Cook and South Georgia in 1775|Relevant fragment]])</ref>

[[Edmond Halley]]'s voyage in [[HMS Paramour|HMS ''Paramour'']] for magnetic investigations in the South Atlantic met the pack ice in [[52nd parallel south|52°&nbsp;S]] in January 1700, but that latitude (he reached 140&nbsp;mi off the north coast of [[South Georgia]]) was his farthest south.  A determined effort on the part of the French naval officer [[Jean-Baptiste Charles Bouvet de Lozier]] to discover the "South Land" – described by a half legendary "sieur de Gonneyville" – resulted in the discovery of [[Bouvet Island]] in 54°10′&nbsp;S, and in the navigation of [[48th meridian west|48° of longitude]] of ice-cumbered sea nearly in [[55th parallel south|55°&nbsp;S]] in 1730  .

In 1771, [[Yves-Joseph de Kerguelen-Trémarec|Yves Joseph Kerguelen]] sailed from [[France]] with instructions to proceed south from [[Mauritius]] in search of "a very large continent."  He lighted upon a land in [[50th parallel south|50°&nbsp;S]] 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 [[Kerguelen Islands|was ultimately named after him]].<ref name=EB1911>{{EB1911|title=Polar Regions| inline=1}}</ref>

===South of the Antarctic Circle===
{{See also|James Cook}}
[[File:Geography world map.jpeg|thumb|right|250px|Map from 1771, showing "Terres Australes" (sic) label without any charted landmass.]]
[[File:James Weddell Expedition.jpg|thumb|250px|right|Painting of [[James Weddell]]'s second expedition in 1823, depicting the brig ''Jane'' and the cutter ''Beaufroy''.]]
The obsession of the undiscovered continent culminated in the brain of [[Alexander Dalrymple]], the brilliant and erratic [[hydrographer]] who was nominated by the [[Royal Society]] to command the [[Transit of Venus]] expedition to [[Tahiti]] in 1769.  The command of the expedition was given by the admiralty to Captain [[James Cook]]. Sailing in 1772 with the ''Resolution'', a vessel of 462 tons under his own command and the ''Adventure'' of 336 tons under Captain [[Tobias Furneaux]], Cook first searched in vain for [[Bouvet Island]], then sailed for 20 degrees of longitude to the westward in [[58th parallel south|latitude 58°&nbsp;S]], and then 30° eastward for the most part south of [[60th parallel south|60°&nbsp;S]], a lower southern latitude than had ever been voluntarily entered before by any vessel.  On 17 January 1773 the [[Antarctic Circle]] was crossed for the first time in history and the two ships reached {{nowrap|67° 15' S}} by {{nowrap|39° 35' E}}, where their course was stopped by ice.

Cook then turned northward to look for [[French Southern and Antarctic Lands]], of the discovery of which he had received news at [[Cape Town]], 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 {{nowrap|61° 52′ S}} by 95°&nbsp;E and continued eastward nearly on the parallel of [[60th parallel south|60°&nbsp;S]] to [[147th meridian east|147°&nbsp;E]]. 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 [[60th parallel south|60°&nbsp;S]] by [[177th meridian west|177°&nbsp;W]], 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 {{nowrap|67° 31′ S}} to stand north again in [[135th meridian west|135°&nbsp;W]].

A long detour to {{nowrap|47° 50′ S}} served to show that there was no land connection between New Zealand and [[Tierra del Fuego]]. Turning south again, Cook crossed the Antarctic Circle for the third time at {{nowrap|109° 30′ W}} before his progress was once again blocked by ice four days later at {{nowrap|71° 10′ S}} by {{nowrap|106° 54′ W}}.  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 [[53rd parallel south|53°]] and [[57th parallel south|57°&nbsp;S]] to Tierra del Fuego; then, passing Cape Horn on 29 December, he rediscovered [[Anthony de la Roché#Maps showing la Roché's discovery|Roché Island]] renaming it [[South Georgia and the South Sandwich Islands|Isle of Georgia]], and discovered the [[South Georgia and the South Sandwich Islands|South Sandwich Islands]] (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 [[55th parallel south|55°]] and [[60th parallel south|60°]]. 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 [[60th parallel south|60th parallel]], and he convinced himself that if land lay farther south it was practically inaccessible and of no economic value.<ref name="EB1911"/>

Voyagers rounding the 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, [[James Weddell]] commanded the the 160-ton [[brig]] ''Jane'', accompanied by his second ship ''Beaufoy'' captained by Matthew Brisbane. Together they sailed to the South Orkneys where [[sealing]] proved disappointing. They turned south in the hope of finding a better sealing ground. The season was unusually mild and tranquil, and on February 20, 1823 the two ships reached [[latitude]] 74°15'&nbsp;S and [[longitude]] 34°16'45"&nbsp;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 [[Coats Land|Coat's Land]] (to the east of the [[Weddell Sea]]) but Weddell decided to turn back.<ref>{{cite book
 | last = Weddel
 | first = James
 | authorlink = James Weddell
 | title = A voyage towards the South Pole: performed in the years 1822-24, containing an examination of the Antarctic Sea.
 | origyear = 1825
 | year = 1970
 | publisher = United States Naval Institute
 | pages = 44, map
 }}</ref>

=== First sighting of land ===
[[File:Admiral Faddey Faddeyevich Bellingshausen.jpg|thumb|180px|right|Admiral von Bellingshausen]]
{{See also|William Smith (mariner)|Fabian von Bellingshausen}}

The first land south of the [[60th parallel south|parallel 60° south latitude]] was discovered by the [[English people|Englishman]] [[William Smith (mariner)|William Smith]], who sighted [[Livingston Island]] on 19 February 1819.  A few months later Smith returned to explore the other islands of the [[South Shetland Islands|South Shetlands]] archipelago, landed on [[King George Island (Antarctica)|King George Island]], and claimed the new territories for [[United Kingdom of Great Britain and Ireland|Britain]].

In the meantime, the Spanish Navy ship [[San Telmo (ship)|San Telmo]] 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 [[Livingston Island]] ([[South Shetlands]]). It is unknown if some survivor managed to be the first setting 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,<ref>{{cite web |url=http://www.nsf.gov/pubs/1997/antpanel/antpan05.pdf |title=Antarctica —past and present |author=U.S. Antarctic Program External Panel |publisher=[[National Science Foundation|NSF]] |accessdate=2007-11-14}}</ref><ref>{{cite web |url=http://quest.arc.nasa.gov/antarctica/background/NSF/palmer.html |title=Nathaniel Brown Palmer |author=Guy G. Guthridge |publisher=[[NASA]] |accessdate=2007-11-14}}</ref><ref>[http://web.archive.org/web/20060828065910/http://arcane.ucsd.edu/pstat.html Palmer Station]. ucsd.edu</ref> three men all sighted the ice shelf or the continent within days or months of each other: von Bellingshausen, a captain in the Russian Imperial Navy; [[Edward Bransfield]], a captain in the British navy; and [[Nathaniel Palmer]], an American sealer out of Stonington, Connecticut. It is certain that the expedition, led by von Bellingshausen and Lazarev on the ships ''Vostok'' and ''Mirny'', reached a point within {{convert|32|km|mi|abbr=on|en=us}} from [[Princess Martha Coast]] and recorded the sight of an ice shelf at {{coord|69|21|28|S|2|14|50|W|}}<ref name=tammiksaar>{{cite news|author=Erki Tammiksaar|title=Punane Bellingshausen|newspaper=[[Postimees]]. Arvamus. Kultuur|date=14 December 2013|trans-title=Red Bellingshausen|language=Estonian}}</ref> that became known as the [[Fimbul Ice Shelf|Fimbul ice shelf]]. On 30 January 1820, Bransfield sighted [[Trinity Peninsula]], 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 [[Peter I Island]] and [[Alexander I Island]], the first islands to be discovered south of the circle.

{{Clear}}
{{Gallery
|title=Historical maps showing a southern ocean between Antarctica and the continents of South America, Africa and Australia
|width=330 | height=220 |align=center
|footer=
| File:Continent méridional austral ou Antarctique (Description de l'Univers, V, pl. 107).jpg|1683 map by French cartographer [[Alain Manesson Mallet]] from his publication ''Description de L'Univers''. Shows a sea below both the Atlantic and Pacific oceans at a time when [[Tierra del Fuego]] was believed joined to Antarctica. Sea is named ''Mer Magellanique'' after [[Ferdinand Magellan]].
| File:1794 Samuel Dunn Wall Map of the World in Hemispheres - Geographicus - World2-dunn-1794.jpg|[[1794 Samuel Dunn Map of the World in Hemispheres|Samuel Dunn's 1794 ''General Map of the World or Terraqeuous Globe'']] shows a ''Southern Ocean'' (but meaning what is today named the South Atlantic) and a ''Southern Icy Ocean''.
| File:1806 Cary Map of Asia, Polynesia, and Australia - Geographicus - Asia-cary-1806.jpg|''A New Map of Asia, from the Latest Authorities, by [[John Cary]], Engraver, 1806'', shows the ''Southern Ocean'' lying to the south of both the Indian Ocean and Australia.
| File:1811 Freycinet Map.jpg|[[Freycinet Map of 1811]] – resulted from the 1800-1803 French [[Baudin expedition to Australia]] and was the first full map of Australia ever to be published. The map named the ocean immediately below Australia the ''Grand Ocean''.
| File:Australia map 1863.jpg|1863 map of Australia shows the ''Southern Ocean'' lying immediately to the south of Australia.
| File:Antarctica map.jpg|1906 map by German publisher [[Justus Perthes]] showing an ''Antarktischer (Sudl. Eismeer) Ocean '' [''Antarctic (South Arctic) Ocean''] encompassing Antarctica.
}}

=== Antarctic expeditions ===
{{Main|List of Antarctic expeditions}}
[[File:Vincennes.jpg|right|thumb|250px|''USS Vincennes at Disappointment Bay, [[Antarctica]] in early 1840.'']]
[[File:Polar Regions exploration 1911.png|left|thumb|300px|1911 South Polar Regions exploration map]]
In December 1839, as part of the [[United States Exploring Expedition]] of 1838–42 conducted by the [[United States Navy]] (sometimes called the "the Wilkes Expedition"), an expedition sailed from Sydney, Australia, on the [[sloop-of-war|sloops-of-war]] {{USS |Vincennes |1826 | 6}} and {{USS |Peacock |1828 |6 }}, the [[brig]] {{USS |Porpoise |1836| 6}}, the [[full-rigged ship]] [[USS Relief (1836)|''Relief'']], and two [[schooner]]s [[USS Sea Gull (1838)|''Sea Gull'']] and {{USS |Flying Fish |1838 |6}}. They sailed into the Antarctic Ocean, as it was then known, and reported the discovery "of an Antarctic continent west of the [[Balleny Islands]]" on 25 January 1840. That part of Antarctica was later named "[[Wilkes Land]]", a name it maintains to this day.

Explorer [[James Clark Ross]] passed through what is now known as the [[Ross Sea]] and discovered [[Ross Island]] (both of which were named for him) in 1841. He sailed along a huge wall of ice that was later named the [[Ross Ice Shelf]]. [[Mount Erebus]] and [[Mount Terror (Antarctica)|Mount Terror]] are named after two ships from his expedition: [[HMS Erebus (1826)|HMS ''Erebus'']] and ''[[HMS Terror (1813)|Terror]]''.<ref>{{cite web|url=http://www.south-pole.com/p0000081.htm|title=South-Pole – Exploring Antarctica|work=South-Pole.com|accessdate=12 February 2006|archiveurl=http://web.archive.org/web/20060214042438/http://www.south-pole.com/p0000081.htm|archivedate=14 February 2006 |url-status=live}}</ref>

During the [[Nimrod Expedition]] led by [[Ernest Shackleton]] in 1907, parties led by [[Edgeworth David]] became the first to climb Mount Erebus and to reach the [[South Magnetic Pole]]. [[Douglas Mawson]], who assumed the leadership of the Magnetic Pole party on their perilous return, went on to lead several expeditions until retiring in 1931.<ref>{{cite web|url=http://www.antarctica.gov.au/about-antarctica/history/people-of-antarctic-history/tannatt-edgeworth-david|title=Tannatt William Edgeworth David|publisher=Australian Antarctic Division|accessdate=27 September 2010|archiveurl=http://web.archive.org/web/20100929041848/http://www.antarctica.gov.au/about-antarctica/history/people-of-antarctic-history/tannatt-edgeworth-david|archivedate=29 September 2010 |url-status=live}}</ref> In addition, Shackleton himself and three other members of his expedition made several firsts in December 1908 – February 1909: they were the first humans to traverse the [[Ross Ice Shelf]], the first to traverse the [[Transantarctic Mountains]] (via the [[Beardmore Glacier]]), and the first to set foot on the South Polar Plateau. An [[Amundsen's South Pole expedition|expedition led by Norwegian polar explorer Roald Amundsen]] from the ship ''[[Fram]]'' became the first to reach the geographic South Pole on 14 December 1911, using a route from the [[Bay of Whales]] and up the [[Axel Heiberg Glacier]].<ref>{{cite web|url=http://www.south-pole.com/p0000101.htm|title=Roald Amundsen|publisher=South-Pole.com|accessdate=9 February 2006|archiveurl=http://web.archive.org/web/20060205054029/http://www.south-pole.com/p0000101.htm|archivedate=5 February 2006 |url-status=live}}</ref> One month later, the doomed [[Terra Nova Expedition|Scott Expedition]] reached the pole.

[[File:Endurance trapped in pack ice.jpg|thumb|250px|Frank Hurley, ''As time wore on it became more and more evident that the ship was doomed'' (The [[Endurance (1912 ship)|Endurance]] trapped in pack ice), [[National Library of Australia]].]]
The [[Imperial Trans-Antarctic Expedition]] of 1914, led by Ernest Shackleton, set out to cross the continent via the pole, but their ship, the [[Endurance (1912 ship)|''Endurance'']], 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 [[Elephant Island]]. Then Shackleton and five others crossed the Southern Ocean, in an open boat called [[James Caird (boat)|''James Caird'']], and then trekked over [[South Georgia]] to raise the alarm at the whaling station [[Grytviken]].

US Navy Rear Admiral [[Richard Evelyn Byrd]] led five expeditions to Antarctica during the 1930s, 1940s, and 1950s. He overflew the South Pole with pilot [[Bernt Balchen]] on November 28 and 29, 1929, to match his overflight of the North Pole in 1926. Byrd's explorations had science as a major objective and pioneered the use of aircraft on the continent. Byrd is credited with doing more for Antarctic exploration than any other explorer. His expeditions set the scene for modern Antarctic exploration and research.

In 1946, Admiral Byrd and more than 4,700 military personnel returned to Antarctica in an expedition called [[Operation Highjump|Operation ''Highjump'']]. 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 [[Finn Ronne]], 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.<ref>{{cite magazine| url=http://www.time.com/time/magazine/article/0,9171,923941,00.html | magazine=Time | title=Milestones, Jan. 28, 1980 | date=28 January 1980 | accessdate=4 May 2010}}</ref>  The expedition explored and mapped large parts of Palmer Land and the Weddell Sea coastline, and identified the [[Ronne Ice Shelf]], named by Ronne after his wife [[Edith Ronne]].<ref>[http://traverse.npolar.no/historical-traverses/historic-names Historic Names — Norwegian-American Scientific Traverse of East Antarctica]. Traverse.npolar.no. Retrieved on 2012-01-29.</ref> Ronne covered 3,600 miles by ski and dog sled—more than any other explorer in history.<ref>[http://www.history.navy.mil/branches/teach/ends/ronne.htm Navy Military History]. History.navy.mil. Retrieved on 2012-01-29.</ref> The [[Ronne Antarctic Research Expedition]] discovered and mapped the last unknown coastline in the world and was the first Antarctic expedition to ever include women.<ref>[http://web.archive.org/web/20081003214538/http://www.encyclopedia.com/doc/1E1-Ronne-Fi.html Finn Ronne]. The Columbia Encyclopedia, Sixth Edition 2008</ref>

It was not until 31 October 1956 that anyone reached the South Pole again; on that day US Navy Rear Admiral [[George J. Dufek]]&nbsp;[http://www.history.navy.mil/wars/datesoct.htm] and others successfully landed a R4D Skytrain ([[Douglas DC-3]]) aircraft, as part of the expeditions mounted for the [[International Geophysical Year]] (IGY) of 1957. During the IGY, a large number of expeditions to the Antarctic were mounted, beginning with ''[[Operation Deep Freeze]] I''.

However, it was not until 31 October 1956 that anyone set foot on the South Pole again; on that day a U.S. Navy group led by Rear Admiral [[George J. Dufek]] successfully landed an aircraft there.<ref>{{cite web|url=http://www.history.navy.mil/wars/datesoct.htm|title=Dates in American Naval History: October|work=Naval History and Heritage Command|publisher=United States Navy|accessdate=12 February 2006|archiveurl=http://web.archive.org/web/20060130074910/http://www.history.navy.mil/wars/datesoct.htm|archivedate=30 January 2006 |url-status=live}}</ref>

=== Recent history ===
[[File:Glacier and Explorer.jpg|thumb|250px|right|MS ''Explorer'' in Antarctica in January 1999. She sank on 23 November 2007 after hitting an [[iceberg]].]]
The [[Antarctic Treaty]] was signed on 1 December 1959 and came into force on 23 June 1961. Among other provisions, this treaty limits [[military activity in the Antarctic]] to the support of scientific research.

The first person to sail single-handed to Antarctica was the New Zealander [[David Henry Lewis]], in 1972, in a 10-metre steel sloop ''Ice Bird''.

A baby, named [[Emilio Palma|Emilio Marcos de Palma]], was born near [[Hope Bay]] on 7 January 1978, becoming the first baby born on the continent. He also was born further south than anyone in history.<ref>[http://www.antarctica.org/old/UK/Envirn/pag/antar_history/pag/science1.htm#science antarctica.org]—Science: in force...</ref>

The '''[[Motor ship|MS]] ''Explorer''''' was a [[cruise ship]] operated by the [[Sweden|Swedish]] explorer [[Lars-Eric Lindblad]]. Observers point to the ''Explorer's'' 1969 expeditionary cruise to [[Antarctica]] as the frontrunner for today's sea-based tourism in that region.<ref>[http://www.antarctica.ac.uk/living_and_working/diaries/rrs_james_clark_ross/antarctic2003_2004/13_27/index.php Mar 28 – Hump Day], British Antarctic Survey.</ref><ref>[http://www.iaato.org/tourism_overview.html Scope of Antarctic Tourism — A Background Presentation], IAATO official website.</ref> The ''Explorer'' was the first cruise ship used specifically to sail the icy waters of the [[Antarctic Ocean]], and the first to sink there<ref>{{cite news|url=http://www.washingtonpost.com/wp-dyn/content/story/2007/11/24/ST2007112400367.html|title=Cruise Ship Sinks Off Antarctica|newspaper=The Washington Post|date= 24 November 2007 | first=Monte | last=Reel | accessdate=May 13, 2010}}</ref> when she struck an unidentified submerged object on 23 November 2007, reported to be ice, which caused a {{convert|10|by|4|in|cm}} gash in the hull.<ref name="CBS News">
{{cite news
 |url=http://www.cbsnews.com/stories/2007/11/23/world/main3534814.shtml
 |title=154 Rescued From Sinking Ship In Antarctic: Passengers, Crew Boarding Another Ship After Wait In Lifeboats; No Injuries Reported
 |date=23 November 2007
 |publisher=[[CBS News]]
 |accessdate=2007-11-23
}}</ref> The ''Explorer'' was abandoned in the early hours of 23 November 2007 after taking on water near the [[South Shetland Islands]] in the [[Southern Ocean]], an area which is usually stormy but was calm at the time.<ref>
{{cite news
 |url=http://news.aol.com/story/_a/doomed-ship-defies-antarctica-odds/20071123061209990001?ncid=NWS00010000000001
 |title=Doomed Ship Defies Antarctica Odds
 |date=25 November 2007
 |publisher=[[Reuters]]
 |accessdate=2007-11-28 
 |archiveurl = http://web.archive.org/web/20071127153727/http://news.aol.com/story/_a/doomed-ship-defies-antarctica-odds/20071123061209990001?ncid=NWS00010000000001 <!-- Bot retrieved archive --> 
 |archivedate = 2007-11-27
}}</ref> The ''Explorer'' was confirmed by the [[Chilean Navy]] to have sunk at approximately position: 62° 24′ South, 57° 16′ West,<ref>{{cite news|url=http://www.falklandnews.com/public/story.cfm?get=4760&source=3|title=MS Explorer — situation report|publisher=The Falkland Islands News|date=23 November 2007}}</ref> in roughly 600&nbsp;m of water.<ref>[http://www.shippingtimes.co.uk/item947_explorer_sinking.htm MV EXPLORER Cruise Ship Sinking In South Atlantic], The Shipping Times, 23 November 2007</ref> 
{{Clear}}<!--Clears up formatting issues experienced by users with high-resolution monitors. Please do not remove.-->

==The 'shrinking' Southern Ocean ==
By way of his 1770s voyages, Captain [[James Cook]] proved that waters encompassed the southern latitudes of the globe. Since then, the Southern Ocean has been variously known as the '''Great Southern Ocean''', '''Antarctic Ocean''', '''Southern Icy Ocean''', '''Grand Ocean''', '''South Polar Ocean''' and '''Austral Ocean'''.

It was not until the ''International Hydrographic Bureau'' (IHB), which later became the ''[[International Hydrographic Organization]]'' (IHO), convened the First International Conference on 24 July 1919 that borders and names for oceans and seas were internationally agreed. The IHO then published these in the publication ''Limits of Oceans and Seas'' - the first edition being 1928. Since the first edition, the limits of the Southern Ocean has moved progressively southwards, including a period between 1953 and 2002 when it was omitted from the publication and left to local hydrographic offices to determine their own limits.


[[File:The shrinking Southern Ocean.png|thumb|800px|center|The delineation of the ''Southern Ocean'' has moved steadily southwards since the original 1928 edition of the [[International Hydrographic Organization|International Hydrographic Bureau]]'s ''Limits of Oceans and Seas''. (Note: 1953 limits shown are those of Britain, as identified in third edition.)]]

[[File:Limit of Oceans and Seas - 1st Edition - 1928.jpg|thumb|220px|right|'''1928 First Edition''' of ''Limits of Oceans and Seas'' with original IHO delineation of Southern Ocean abutting land-masses.<ref name=NAOO1928/>]]

=== 1928 delineation ===

In the '''1928 first edition''' of ''Limits of Oceans and Seas'', the Southern Ocean was delineated by land-based limits - the continent of Antarctic to the south, and the continents of South America, Africa, and Australia plus [[Broughton Island, New Zealand]] in the north.

The detailed land-limits used were from [[Cape Horn]] in South America eastwards to [[Cape Agulhas]] in Africa, then further eastwards to the southern coast of mainland Australia to [[Cape Leeuwin]], [[Western Australia]]. From Cape Leeuwin, the limit then followed eastwards along the coast of mainland Australia to [[Cape Otway]], [[Victoria]], then southwards across [[Bass Strait]] to [[Cape Wickham]], [[King Island]], along the west coast of King Island, then the remainder of the way south across Bass Strait to [[Cape Grim]], [[Tasmania]].  The limit then followed the west coast of Tasmania southwards to the 
[[South East Cape]] and then went eastwards to Broughton Island, New Zealand, before returning to Cape Horn.<ref name=NAOO1928>{{cite web |url=http://www.photolib.noaa.gov/htmls/map00340.htm |title=Map accompanying first edition of IHO Publication Limits of Oceans and Seas, Special Publication 23 |website=NOAA Photo Library |publisher= [[National Oceanic and Atmospheric Administration]] (NOAA)|accessdate=19 January 2014}}</ref>


[[File:Limit of Oceans and Seas - 2nd Edition - 1st July 1937.jpg|thumb|220px|right|'''1937 Second Edition''' of ''Limits of Oceans and Seas'' showing IHO's pre-1953 delineation of Southern Ocean moved southwards.<ref name=NAOO1937/>]]

=== 1937 delineation ===

The 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 abutt land masses.

In the second edition, the Southern Ocean then extended from Antarctica northwards to latitude 40° south between [[Cape Agulhas]] in Africa (long. 20° east) and [[Cape Leeuwin]] in Western Australia (long. 115° east), and extended to latitude 55° south between [[Auckland Island]] of New Zealand (long. 165° or 166° east) and [[Cape Horn]] in South America (long. 67° west).<!-- delineators observed from 1937 map and not obtained from written IHO description with 1937 edition, which should be sought and checked too --><ref name=NAOO1937>{{cite web |url=http://www.photolib.noaa.gov/htmls/map00341.htm |title=Map accompanying second edition of IHO Publication Limits of Oceans and Seas, Special Publication 23 |website=NOAA Photo Library |publisher= [[National Oceanic and Atmospheric Administration]] (NOAA)|accessdate=18 January 2014}}</ref>

As is discussed in more detail below (see section on '2002 delineation'), prior to the 2002 (draft) edition the limits of oceans explicitly excluded the seas lying within each of them. The [[Great Australian Bight]] 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' and so the Bight would have still been within the Southern Ocean in 1937 if the 2002 convention was in place then. To perform direct comparisons of current and former limits of oceans (for example to compare surface areas) 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 delineation ===
The Southern Ocean did not appear in the '''1953 third edition''' and a note in the publication read:
<blockquote><poem>
''The Antarctic or Southern Ocean has been omitted from this publication as the majority of opinions received since the issue of the 2nd Edition in 1937 are to the effect that there exists no real justification for applying the term Ocean to this body of water, the northern limits of which are difficult to lay down owing to their seasonal change. The limits of the Atlantic, Pacific and Indian Oceans have therefore been extended South to the Antarctic Continent.''

''Hydrographic Offices who issue separate publications dealing with this area are therefore left to decide their own northern limits (Great Britain uses Latitude of 55 South.)''
</poem></blockquote>

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 [[South East Cape]], and the southern limits of the [[Great Australian Bight]] and the [[Tasman Sea]] were moved northwards.<ref name="IHO">{{cite web|url=http://www.iho.int/iho_pubs/standard/S-23/S-23_Ed3_1953_EN.pdf|title=Limits of Oceans and Seas, 3rd edition|year=1953|publisher=International Hydrographic Organization|accessdate=7 February 2010}}</ref>


[[File:Pacific Ocean - en IHO.png|thumb|right|250px|'''Pacific Ocean''' used as example to show terminology difference for 'seas'. Blue area = ''''seas included in Pacific Ocean'''' as per the [[CIA]] ''[[The World Factbook]]''.<ref>{{cite web |title= Pacific Ocean |work= [[The World Factbook]] |publisher= [[Central Intelligence Agency]] |url= https://www.cia.gov/library/publications/the-world-factbook/geos/zn.html |accessdate= 27 November 2010}}</ref>  Black outline = ''''seas excluded from Pacific Ocean'''' (ignoring marginal waterbodies) based on pre 2002 limits of Pacific Ocean.]]
[[File:Location Southern Ocean.svg|thumb|250px|right|'''Southern Ocean''' based on draft 2002 fourth edition of ''Limits of Oceans and Seas'']]

=== 2002 (draft) delineation ===

The 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 [[60th parallel south|60°S]] (with no land interruptions at this latitude), with the other 14 votes cast for other definitions, mostly [[50th parallel south|50°S]], but a few for as far north as [[35th parallel south|35°S]].

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).<ref name=IHO2002>{{cite web| url=http://www.iho.int/mtg_docs/com_wg/S-23WG/S-23WG_Misc/Draft_2002/Draft_2002.htm| title= IHO PUBLICATION S-23, ''Limits of Oceans and Seas, Draft 4th Edition'' |date=2002 |publisher=International Hydrographic Organisation|accessdate=22 January 2002}}</ref> It has yet to be published due to 'areas of concern' by several countries relating to various naming issues around the world - primarily the [[Sea of Japan naming dispute]] - and there have been various changes, 60 seas were given new names, and even the name of the publication was changed.<ref>{{cite news|url=http://eastsea.khoa.go.kr/eng/open_content/iho/magazine.asp|title=IHO Special Publication 23|publisher=Korean Hydrographic and Oceanographic Administration |accessdate=19 January 2014}}</ref> A reservation had also been lodged by Australia regarding the Southern Ocean limits.<ref>{{cite news|url=http://www.theage.com.au/articles/2003/12/21/1071941610556.html|title=Canberra all at sea over position of Southern Ocean|last=Darby|first=Andrew|date=22 December 2003|publisher=The Age|accessdate=21 December 2009}}</ref> Effectively, the 3rd edition (which did not delineate the Southern Ocean leaving delineation to local hydrographic offices) has yet to be superseded.

Despite this, the 4th edition definition has ''de facto'' usage by many organisations, scientists and nations - even by the IHO.<ref>{{cite conference|url=http://www.iho.int/mtg_docs/rhc/HCA/HCA3/HCA3-6.3B_Report_on_IBCSO.pdf|last=Schenke|first=Hans Werner|title=Proposal for the preparation of a new International Bathymetric Chart of the Southern Ocean| conference= Third HCA Meeting, 8–10 September 2003| book-title=IHO International Hydrographic Committee on Antarctica (HCA)|conference-url=http://www.iho.int/mtg_docs/rhc/HCA/HCA3/HCA3docs_list.htm |date=September 2003 |location=Monaco | publisher=[[International Hydrographic Organization]] (IHO)|accessdate=17 January 2014}}</ref> Some nations' hydrographic offices have defined their own boundaries; the United Kingdom used the [[55th parallel south|55°S parallel]] for example.<ref name="IHO"/>

Other sources, such as the [[National Geographic Society]], show the [[Atlantic Ocean|Atlantic]], [[Pacific Ocean|Pacific]] and [[Indian Ocean|Indian]] Oceans as extending to Antarctica, although articles on the National Geographic web site have begun to reference the Southern Ocean.<ref name=nationalgeographic>{{cite web| url=http://newswatch.nationalgeographic.com/tag/southern-ocean/| title= Southern Ocean - News Watch|publisher=National Geographic|accessdate=26 April 2013}}</ref>

In [[Australia]], [[Cartography|cartographical]] authorities defined the Southern Ocean as including the entire body of water between Antarctica and the south coasts of Australia and [[New Zealand]]. This delineation is basically the same as the original (first) edition of the IHO publication and effectively the same as the second edition. In the second edition, the [[Great Australian Bight]] was defined as the only geographical entity between the Australian coast and the Southern Ocean. Coastal maps of [[Tasmania]] and [[South Australia]] label the sea areas as ''Southern Ocean'',<ref>For example: {{citation |url=http://www.hydro.gov.au/webapps/jsp/charts/charts.jsp?chart=Aus343&subchart=0 |title=Chart Aus343: Australia South Coast - South Australia - Whidbey Isles to Cape Du Couedic |publisher=Australian Hydrographic Service |date=29 June 1990 |accessdate=11 October 2010}}, {{citation |url=http://www.hydro.gov.au/webapps/jsp/charts/charts.jsp?chart=Aus792&subchart=0 |title=Chart Aus792: Australia - Tasmania - Trial Harbour to Low Rocky Point |publisher=Australian Hydrographic Service |date=18 July 2008 |accessdate=11 October 2010}}</ref> while [[Cape Leeuwin]] in [[Western Australia]] is described as the point where the Indian and Southern Oceans meet.<ref>{{cite web |url=http://register.heritage.wa.gov.au/PDF_Files/00104%20Cape%20Leeuwin%28P-AD%29.PDF |title= - Assessment Documentation for Cape Leeuwin Lighthouse |page=11 |work=Register of Heritage Places |date=13 May 2005 |accessdate=13 October 2010}}</ref>

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 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 [[Tasman Sea]] between Australia and New Zealand was not regarded by the IHO as being part of the Pacific, but as of the 2002 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 [[Drake's Passage]] which includes all of the waters from South America to the Antarctic coast.  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.{{Clear}}

== Geography ==

The Southern Ocean, geologically the youngest of the oceans, 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.

With a northern limit at [[60th parallel south|60°S]], 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 [[Antarctic Circumpolar Current]] 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 4,000 and 5,000 m (13,000 to 16,000&nbsp;ft) over most of its extent with only limited areas of shallow water.  The Southern Ocean's greatest depth of {{convert|7,236|m|ft|abbr=on}} occurs at the southern end of the [[South Sandwich Trench]], at 60°00'S, 024°W. The [[Antarctic continental shelf]] appears generally narrow and unusually deep, its edge lying at depths up to {{convert|800|m|ft|abbr=on}}, compared to a global mean of {{convert|133|m|ft|0|abbr=on}}.

[[Equinox]] to equinox in line with the sun's seasonal influence, the Antarctic ice pack fluctuates from an average minimum of {{convert|2.6|e6km2|e6sqmi}} in March to about {{convert|18.8|e6km2|e6sqmi}} in September, more than a sevenfold increase in area.

=== Sub-divisions of the Southern Ocean ===

Sub-divisions of oceans are geographical features such as 'Seas', 'Straights', 'Bays', 'Channels' and 'Gulfs'. There are many recognized sub-divisions of the Southern Ocean defined in the draft 2002 fourth edition of the IHO publication ''Limits of Oceans and Seas''. In clockwise order these include (with IHO sub-division chartlet numbers in parenthesis) the [[Weddell Sea]] (10.1), the [[Lazarev Sea]] (10.2), the [[Riiser-Larsen Sea]] (10.3), the [[Cosmonauts Sea]] (10.4), the [[Cooperation Sea]] (10.5), the [[Davis Sea]] (10.6), [[Davis Sea|Tryoshinikova Gulf]] (10.6.1), the [[Mawson Sea]] (10.7), the [[D'Urville Sea|Dumont D'Urville Sea]] (10.8), the [[Somov Sea]] (10.9), the [[Ross Sea]] (10.10), [[McMurdo Sound]] (10.10.1), the [[Amundsen Sea]] (10.11), and the [[Bellingshausen Sea]] (10.12), part of the [[Drake Passage]] (10.13), [[Bransfield Strait]] (10.14) and part of the [[Scotia Sea]] (4.2).<ref name=IHO2002/>{{#tag:ref|Reservation by Norway" Norway recognizes the name [[King Haakon VII Sea|Kong Håkon VII Hav]] which covers the sea area adjacent to [[Dronning Maud Land]] and stretching from 20°W to 45°E.<ref name=IHO2002/>|group="note"}}{{#tag:ref|The [[Drake Passage]] is situated between the southern and eastern extremities of [[South America]] and the [[South Shetland Islands]], lying north of the [[Antarctic Peninsula]].
The [[Scotia Sea]] is an area defined by the southeastern extremity of South America and the [[South Shetland Islands]] on the west and by [[South Georgia]] and the [[South Sandwich Islands]] to the north and east. As they extend north of 60°S, Drake Passage and the Scotia Sea are also described as forming part of the [[Atlantic Ocean|South Atlantic Ocean]].<ref name=IHO2002/>|group="note"}}


[[Image:Manganknolle.jpg|thumb|250px|right|Manganese nodule]]
[[File:McMurdo Sound Glacier-iv.jpg|thumb|300px|left|An iceberg being pushed out of a shipping lane by three [[U.S. Navy]] ships in [[McMurdo Sound]], Southern Ocean]]

=== Natural resources ===

The Southern Ocean probably contains large, and possibly giant, [[Petroleum|oil]] and [[Natural gas|gas]] fields on the [[continental margin]]. [[Placer deposit]]s, accumulation of valuable minerals such as gold, formed by gravity separation during sedimentary processes are also expected to exist in the Southern Ocean.<ref name=CIAgeo/>

Manganese modules are expected to exist in the Southern Ocean. [[Manganese nodules]] are rock [[concretion]]s on the [[sea]] bottom formed of concentric layers of [[iron]] and [[manganese]] [[hydroxide]]s around a core.  The core may be microscopically small and is sometimes completely transformed into manganese minerals by [[crystallization]]. Interest in the potential exploitation of polymetallic nodules generated a great deal of activity among prospective mining consortia in the 1960s and 1970s.<ref name=CIAgeo/>

The [[iceberg]]s that form each year around in the Southern Ocean hold enough [[fresh water]] to meet the needs of every person on Earth for several months. For several decades there have been proposals, none feasible or successful, to tow Southern Ocean icebergs to more arid northern regions (such as Australia) where they can be harvested.

=== Natural hazards ===
[[Iceberg]]s 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 [[40th parallel south|40]] to [[70th parallel south|70 degrees south]] as the "[[Roaring Forties]]", "[[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, makes the area even more dangerous. The remoteness of the region makes sources of search and rescue scarce.

== Physical oceanography ==
[[File:Antarctica-Region.png|thumb|250px|left|Antarctic Convergence]]
[[File:Antarctic Circumpolar Current.jpg|right|thumb|250px|The Antarctic Circumpolar Current (ACC) is the strongest current system in the world oceans, linking the Atlantic, Indian and Pacific basins.]]

=== Antarctic Circumpolar Current and Antarctic Convergence===

The [[Antarctic Circumpolar Current]] moves perpetually eastward &mdash; chasing and joining itself, and at {{convert|21,000|km|mi|abbr=on}} in length &mdash; it comprises the world's longest ocean current, transporting {{convert|130|e6m3/s|e9cuft/s}} of water &ndash; 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 [[water mass]]es 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]].

Associated with the Circumpolar Current is the [[Antarctic Convergence]] encircling Antarctica, where cold northward-flowing Antarctic waters meet the relatively warmer waters of the [[subantarctic]], Antarctic waters predominantly sink beneath subantarctic waters, while associated zones of mixing and [[upwelling]] create a zone very high in nutrients. These nurture high levels of [[phytoplankton]] with associated copepods and [[Antarctic krill]], and resultant foodchains supporting fish, whales, seals, penguins, albatrosses and a wealth of other species.<ref>{{cite web |url=http://geonames.usgs.gov/apex/f?p=gnispq:5:0::NO::P5_ANTAR_ID:488|title=Antarctica Detail |accessdate=2014-01-18 |date=2000-10-18 |work=U.S. Department of the Interior, U.S. Geological Survey}}</ref>

The Antarctic Convergence is considered to be the best natural definition of the northern extent of the Southern Ocean.<ref name=CIAgeo/>

{{Clear}}
[[File:Antarctic bottom water hg.png|thumb|250px|left|{{center|Upwelling in the [[Southern Ocean]]}}]]

=== Upwelling ===

Large-scale [[upwelling]] is found in the Southern Ocean. Strong westerly (eastward) winds blow around [[Antarctica]], 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 [[South America]] and the tip of the [[Antarctic Peninsula]], 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 in off the west coasts of North and South America, northwest and southwest Africa, and southwest and [[Great South Australian Coastal Upwelling System|southeast Australia]], all associated with oceanic subtropical high pressure circulations (see coastal upwelling above).

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.

{{Clear}}
[[Image:Antarctic frontal-system hg.png|250px|thumb|Location of the Southern Ocean gyres.]]

=== Ross and Weddell Gyres ===

The [[Ross Gyre]] and [[Weddell Gyre]] are two [[Oceanic gyre|gyres]] that exist within the [[Southern Ocean]]. The gyres are is located in the [[Ross Sea]] and [[Weddell Sea]] respectively, and both rotate clockwise. The gyres are formed by interactions between the [[Antarctic Circumpolar Current]] and the [[Antarctic Continental Shelf]].

[[Sea ice]] has been noted to persist in the central area of the Ross Gyre.<ref>{{Cite book |last=Michael L. |first=Van Woert, et al. |authorlink= |editor-last=DiTullio |editor-first=Giacomo R. |editor2-last=Dunbar |editor2-first=Robert B. |contribution=The Ross Sea Circulation During the 1990s |title=Biogeochemistry of the Ross Sea |publisher=American Geophysical Union |year=2003 |location= |pages=4–34 |url=https://books.google.com/books?id=4o7i8yJeEPMC |isbn=0-87590-972-8}} p. 10.</ref> There is some evidence that [[global warming]] has resulted in some decrease of the [[salinity]] of the waters of the Ross Gyre since the 1950s.<ref>{{Cite book |last1=Florindo |first1=Fabio |authorlink= |last2=Siegert |first2=Martin J. |author2-link= |title=Antarctic Climate Evolution |publisher=Elsevier |year=2008 |location= |page=106 |url=https://books.google.com/books?id=yUu-x70CZEcC |isbn=978-0-444-52847-6}}</ref>

Due to the [[Coriolis force]] acting to the left in the [[Southern Hemisphere]] and the resulting [[Ekman transport]] away from the centres of the Weddell Gyre, these regions are very productive due to upwelling of cold, nutrient rich water.

{{Clear}}

== Climate ==
Sea temperatures vary from about &minus;2 to 10&nbsp;[[Celsius|°C]] (28 to 50 [[Fahrenheit|°F]]). Cyclonic storms travel eastward around the continent and frequently become intense because of the temperature contrast between ice and [[open ocean]]. The ocean-area from about [[40th parallel south|latitude 40 south]] to the Antarctic Circle has the strongest average winds found anywhere on Earth.<ref>{{cite web|url=https://www.cia.gov/library/publications/the-world-factbook/fields/2059.html |title=The World Fact Book: Climate |publisher=U.S. [[Central Intelligence Agency]] |date= |accessdate=2014-01-19}}</ref> In winter the ocean freezes outward to [[65th parallel south|65 degrees south latitude]] in the Pacific sector and [[55th parallel south|55 degrees south latitude]] 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.

{{clear}}

{{wide image|Southern Ocean-2.JPG|2000px|Clouds over Southern Ocean with Continent labels.}}

{{Clear}}

==Biodiversity==
{{See also|Antarctic ecozone|Antarctic microorganism|Wildlife of Antarctica}}

[[File:Antarctic krill (Euphausia superba).jpg|thumb|left|[[Antarctic krill]] (''Euphausia superba'') are a [[keystone species]], forming an important part of the Antarctic food web.]]

===Animals===

A variety of marine animals exist and rely, directly or indirectly, on the phytoplankton in the Southern Ocean. Antarctic sea life includes [[penguin]]s, [[blue whale]]s, [[orca]]s, [[colossal squid]]s and [[fur seal]]s. The [[emperor penguin]] is the only penguin that breeds during the winter in Antarctica, while the [[Adélie penguin]] breeds farther south than any other penguin. The [[rockhopper penguin]] has distinctive feathers around the eyes, giving the appearance of elaborate eyelashes. [[King penguin]]s, [[chinstrap penguin]]s, and [[gentoo penguin]]s also breed in the Antarctic.

The [[Antarctic fur seal]] was very heavily hunted in the 18th and 19th centuries for its pelt by sealers from the United States and the United Kingdom. The [[Weddell seal]], a "[[true seal]]", is named after [[James Weddell|Sir James Weddell]], commander of British sealing expeditions in the [[Weddell Sea]]. [[Antarctic krill]], which congregates in large [[Shoaling and schooling|schools]], is the [[keystone species]] of the [[ecosystem]] of the Southern Ocean, and is an important food organism for whales, seals, [[leopard seal]]s, fur seals, [[squid]], [[Notothenioidei|icefish]], penguins, [[albatross]]es and many other birds.<ref>{{cite web|url=http://www.knet.co.za/antarctica/fauna_and_flora.htm|title=Creatures of Antarctica|accessdate=6 February 2006|archiveurl=http://web.archive.org/web/20050214015049/http://www.knet.co.za/antarctica/fauna_and_flora.htm|archivedate=14 February 2005}}</ref>

The [[benthic]] communities of the seafloor are diverse and dense, with up to 155,000 animals found in {{convert|1|m2|sqft|1}}. 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. [[Deep-sea gigantism]] is common among these animals.<ref name="AADseabed">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seabed-benthic-communities |title=Seabed (benthic) communities |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20130319154433/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seabed-benthic-communities |archivedate=19 March 2013 |url-status=live}}</ref>

A census of sea life carried out during the [[International Polar Year]] and which involved some 500 researchers was released in 2010. The research is part of the global [[Census of Marine Life]] (CoML) and has disclosed some remarkable findings. More than 235 marine organisms live in both polar regions, having bridged the gap of {{convert|12000|km|0|abbr=on|en=us}}. Large animals such as some cetaceans and birds make the round trip annually. More surprising are small forms of life such as mudworms, [[sea cucumbers]] 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 5&nbsp;°C, and the major current systems or marine [[Thermohaline circulation|conveyor belt]] which transport egg and larva stages.<ref>{{Cite news|last=Kinver|first=Mark|date=15 February 2009|title=Ice oceans 'are not poles apart'|newspaper=BBC News|publisher=British Broadcasting Corporation|url=http://news.bbc.co.uk/2/hi/science/nature/7888558.stm|accessdate=22 October 2011}}</ref>

[[File:Wonder albat.jpg|thumb|A [[Wandering Albatross]] (''Diomedea exulans'') on [[South Georgia]]]]

===Birds===
{{See also|List of birds of Antarctica}}

The rocky shores of mainland Antarctica and its offshore islands provide nesting space for over 100 million birds every spring. These nesters include species of [[albatross]]es, [[petrel]]s, [[skua]]s, [[gull]]s and [[tern]]s.<ref name="AADbirds">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/flying-birds |title=Flying Birds |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=6 April 2013 |archiveurl=http://web.archive.org/web/20130319154403/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/flying-birds |archivedate=19 March 2013 |url-status=live}}</ref> The insectivorous [[South Georgia Pipit]] is [[endemic]] to [[South Georgia]] and some smaller surrounding islands. Freshwater ducks inhabit South Georgia and [[Kerguelen]].<ref name="BASanimals">{{cite web|url=http://www.antarctica.ac.uk/about_antarctica/wildlife/land_animals/index.php |title=Land Animals of Antarctica |author=British Antarctic Survey |publisher=Natural Environment Research Council |accessdate=18 March 2013 |archiveurl=http://web.archive.org/web/20121122145509/http://www.antarctica.ac.uk/about_antarctica/wildlife/land_animals/index.php |archivedate=22 November 2012 |url-status=live}}</ref>

The flightless [[penguin]]s are all located in the [[Southern Hemisphere]], with the greatest concentration located on and around Antartica. 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.<ref name="AADpenguins">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/penguins |title=Penguins |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=6 April 2013 |archiveurl=http://web.archive.org/web/20130319154517/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/penguins |archivedate=19 March 2013 |url-status=live}}</ref> [[Emperor penguins]] have four overlapping layers of feathers, keeping them warm. They are the only Antarctic animal to breed during the winter.<ref name="AADadapt">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/adapting-to-the-cold |title=Adapting to the cold |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=5 April 2013 |archiveurl=http://web.archive.org/web/20130118055107/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/adapting-to-the-cold |archivedate=18 January 2013 |url-status=live}}</ref>

[[File:Icefishuk.jpg|thumb|left|Fish of the [[Notothenioidei]] suborder, such as this young icefish, are mostly endemic to Antarctica.]]

===Fish===

There are very few species of fish in the Southern Ocean. The [[Channichthyidae]] family, also known as white-blooded fish, are only found in the Southern Ocean. They lack [[haemoglobin]] in their blood, resulting in their blood being colourless. One Channichthyidae species, the [[mackerel icefish]] (''Champsocephalus gunnari''), was once the most common fish in coastal waters less than {{convert|400|m|ft|0}} deep, but was [[overfishing|overfished]] in the 1970s and 1980s. Schools of icefish spend the day at the seafloor and the night higher in the [[water column]] eating plankton and smaller fish.<ref name="AADfish">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/fish |title=Fish |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=5 April 2013 |archiveurl=http://web.archive.org/web/20130319154530/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/fish |archivedate=19 March 2013 |url-status=live}}</ref>

There are two species from the ''[[Dissostichus]]'' genus, the [[Antarctic toothfish]] (''Dissostichus mawsoni'') and the [[Patagonian toothfish]] (''Dissostichus eleginoides''). These two species live on the seafloor {{convert|100|m|ft|0}} - {{convert|3000|m|ft|0}} deep, and can grow to around {{convert|2|m|ft|0}} long weighing up to {{convert|100|kg|lb|0}}, 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. Due to the low water temperatures around the mainland, the Antarctic toothfish has [[antifreeze protein]]s in its blood and tissues. Toothfish are commercially fished, and illegal overfishing has reduced toothfish populations.<ref name="AADfish"/>

Another abundant fish group is the ''[[Notothenia]]'' genus, which like the Antarctic toothfish have antifreeze in their bodies.<ref name="AADfish"/>

[[File:Phoque de Weddell - Weddell Seal.jpg|thumb|[[Weddell seal]]s (''Leptonychotes weddellii'') are the most southerly of Antarctic mammals.]]

===Mammals===
{{See also|List of mammals of Antarctica}}

Seven [[pinniped]] species inhabitat Antartica. The largest, the [[elephant seal]] (''Mirounga leonina''), can reach up to {{convert|4000|kg|lb|0}}, while females of the smallest, the [[Antarctic fur seal]] (''Arctocephalus gazella''), reach only {{convert|150|kg|lb|0}}. These two species live north of the sea ice, and breed in [[Harem (zoology)|harems]] on beaches. The other four species can live on the sea ice. [[Crabeater seal]]s (''Lobodon carcinophagus'') and [[Weddell seal]]s (''Leptonychotes weddellii'') form breeding colonies, whereas [[leopard seal]]s (''Hydrurga leptonyx'') and [[Ross seal]]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.<ref name="AADseals">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions |title=Seals and sea lions |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20130319154452/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions |archivedate=19 March 2013 |url-status=live}}</ref>

The four species that inhabit sea ice are thought to make up 50% of the total biomass of the world's seals.<ref name="AADicespecies">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/pack-ice-seals/pack-ice-seal-species |title=Pack-ice seal species |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20120826005443/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/pack-ice-seals/pack-ice-seal-species |archivedate=26 August 2012 |url-status=live}}</ref> Crabeater seals have a population of around 15 million, making them one of the most numerous large animals on the planet.<ref name="AADcrabeater">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/crabeater-seals |title=Salps |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20120819150020/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/crabeater-seals |archivedate=19 August 2012 |url-status=live}}</ref> The [[New Zealand sea lion]] (''Phocarctos hookeri''), one of the rarest and most localised pinnipeds, breeds almost exclusively on the subantarctic [[Auckland Islands]], although historically it had a wider range.<ref name="AADsealion">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/sea-lions |title=Sea lions |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20120803014932/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/sea-lions |archivedate=3 August 2012 |url-status=live}}</ref> Out of all permanent mammalian residents, the Weddell seals live the furthest south.<ref name="AADweddell">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/weddell-seals |title=Weddell seals |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20120804170832/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/seals-and-sea-lions/weddell-seals |archivedate=4 August 2012 |url-status=live}}</ref>

There are 10 [[cetacean]] species found in the Southern Ocean; six [[baleen whale]]s, and four [[toothed whale]]s. The largest of these, the [[blue whale]] (''Balaenoptera musculus''), grows to {{convert|24|m|ft|0}} long weighing 84 tonnes. Many of these species are [[Animal migration|migratory]], and travel to [[tropics|tropical]] waters during the Antarctic winter.<ref name="AADwhales">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/whales/what-is-a-whale |title=What is a whale? |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20120530194925/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/whales/what-is-a-whale |archivedate=30 May 2012 |url-status=live}}</ref>

===Arthropods===
Five species of [[krill]], small free-swimming [[crustaceans]], are found in the Southern Ocean.<ref name="AADmagic">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/krill/krill-magicians-of-the-southern-ocean |title=Krill: magicians of the Southern Ocean |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20120929115143/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/krill/krill-magicians-of-the-southern-ocean |archivedate=29 September 2012 |url-status=live}}</ref> The [[Antarctic krill]] (''Euphausia superba'') is one of the most abundant animal species on earth, with a [[biomass]] of around 500 million tonnes. Each individual is {{convert|6|cm|in|1}} long and weighs over {{convert|1|g|oz|3}}.<ref name="AADkrill">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/krill |title=Krill |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20130122123635/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/krill |archivedate=22 January 2013 |url-status=live}}</ref>  The swarms that form can stretch for kilometres, with up to 30,000 individuals per {{convert|1|m3|ft3}}, turning the water red.<ref name="AADmagic"/> Swarms usually remain in deep water during the day, ascending during the night to feed on [[plankton]]. Many larger animals depend on krill for their own survival.<ref name="AADkrill"/> During the winter when food is scarce, adult Antarctic krill can revert to a smaller juvenile stage, using their own body as nutrition.<ref name="AADmagic"/>

Many benthic crustaceans have a non-seasonal breeding cycle, and some raise their young in a [[Brood pouch (Peracarida)|brood pouch]]. ''[[Glyptonotus antarcticus]]'' is an unusually large benthic [[isopod]], reaching {{convert|20|cm|in|0}} in length weighing {{convert|70|g|oz|2}}. [[Amphipods]] are abundant in soft sediments, eating a range of items, from [[algae]] to other animals.<ref name="AADseabed"/>

Slow moving [[sea spider]]s are common, sometimes growing as large as a human hand. They feed on the [[coral]]s, [[sponge]]s, and [[bryozoa]]ns that litter the seabed.<ref name="AADseabed"/>

[[File:Onykia ingens 384 mm ML.jpg|thumb|A female [[Moroteuthis ingens|warty squid]] (''Moroteuthis ingens'')]]

===Invertebrates===

Many [[Aquatic animals|aquatic]] [[mollusc]]s are present in Antarctica. [[Bivalves]] such as ''[[Adamussium colbecki]]'' move around on the seafloor, while others such as ''[[Laternula elliptica]]'' live in burrows [[Filter feeder|filtering]] the water above.<ref name="AADseabed"/> There are around 70 [[cephalopod]] species in the Southern Ocean, the largest of which is the [[giant squid]] (''Architeuthis sp.''), which at {{convert|15|m|ft|0}} is the largest invertebrate in the world. [[Squid]] makes up the entire diet of some animals, such as [[grey-headed albatross]]es and [[sperm whale]]s, and the [[Moroteuthis ingens|warty squid]] (''Moroteuthis ingens'') is one of the subantarctic's most preyed upon species by vertebrates.<ref name="AADsquid">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/squid |title=Squid |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20130319154439/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/squid |archivedate=19 March 2013 |url-status=live}}</ref>

The [[sea urchin]] genus ''[[Abatus]]'' burrow through the sediment eating the nutrients they find in it.<ref name="AADseabed"/> Two species of [[salp]]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.<ref name="AADsalps">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/salps |title=Salps |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20130319154345/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/salps |archivedate=19 March 2013 |url-status=live}}</ref>

Antarctic [[sponge]]s are long lived, and sensitive to environmental changes due to the specificity of the [[symbiosis|symbiotic]] microbial communities within them. As a result, they function as indicators of environmental health.<ref name="AADsponges">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/wildlife/animals/sponges |title=Sponges |author=Australian Antarctic Division |publisher=Government of Australia |accessdate=8 April 2013 |archiveurl=http://web.archive.org/web/20130319154351/http://www.antarctica.gov.au/about-antarctica/wildlife/animals/sponges |archivedate=19 March 2013 |url-status=live}}</ref>

==Environment==

===Current issues===
Increased solar [[ultraviolet|ultraviolet radiation]] resulting from the Antarctic [[ozone hole]] has reduced marine primary productivity ([[phytoplankton]]) by as much as 15% and has started damaging the [[DNA]] of some fish.<ref>{{cite journal |author=Smith RC, Prézelin BB, Baker KS, Bidigare RR, Boucher NP, Coley T, Karentz D, MacIntyre S, Matlick HA, Menzies D, et al. |year=1992 |title=Ozone depletion: ultraviolet radiation and phytoplankton biology in antarctic waters. |url=http://www.ncbi.nlm.nih.gov/pubmed/1546292 |journal=Science (New York, N.Y.)|volume=255 |issue=5047 |pages=952–959 |doi=10.1126/science.1546292 |pmid=1546292 |issn=0036-8075 }}</ref> 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. Long-line fishing for toothfish causes a high incidence of seabird mortality.

===International agreements===
All international agreements regarding the world's oceans apply to the Southern Ocean. In addition, it is subject to these agreements specific to the region:

* [[International Whaling Commission]] (IWC), which prohibits commercial [[whaling]] south of [[40th parallel south|40 degrees south]] (south of [[60th parallel south|60 degrees south]] between [[50th meridian west|50 degrees]] and [[130th meridian west|130 degrees west]]). [[Japan]] 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 carries out an annual whale-hunt in the region. See [[Southern Ocean Whale Sanctuary]].
* [[Convention for the Conservation of Antarctic Seals]] is part of the [[Antarctic Treaty System]].  It was signed at the conclusion of a multilateral conference in London on February 11, 1972.<ref>''Antarctic Challenge: Conflicting Interests, Cooperation, Environmental Protection, Economic Development'' Proceedings of an Interdisciplinary Symposium, June 22nd-24th, 1983; 
Volume 88 of Veröffentlichungen des Instituts für Internationales Recht an der Universität Kiel (Rüdiger Wolfrum and Klaus Bockslaff, eds.), Duncker & Humblot, 1984, p99</ref>
* [[Convention on the Conservation of Antarctic Marine Living Resources]] (CCAMLR)  is part of the [[Antarctic Treaty System]]. The Convention was entered into force on 7 April 1982 and has its goal is to preserve [[marine life]] and environmental integrity in and near [[Antarctica]]. It was established in large part to concerns that an increase in [[krill]] catches in the [[Southern Ocean]] could have a serious impact on populations of other marine life which are dependent upon krill for food.<ref>{{cite web |url= http://www.ccamlr.org/ |title=Commission for the Conservation of Antarctic Marine Living Resources  |work=ccamlr.org |year=2011 |accessdate=11 October 2011}}</ref>

Many nations prohibit the exploration for and the exploitation of [[mineral]] resources south of the fluctuating [[Antarctic convergence]],<ref>{{cite web|url=https://www.cia.gov/library/publications/the-world-factbook/fields/2033.html |title=The World Fact Book: Environment - International Agreements |publisher=U.S. [[Central Intelligence Agency]] |date= |accessdate=2014-01-19}}</ref> 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 [[Antarctic Treaty]] covers the portion of the globe south of [[60th parallel south|sixty degrees south]],<ref>
[http://www.nsf.gov/od/opp/antarct/anttrty.jsp The Antarctic Treaty], article 6
</ref>
it prohibits new claims to Antarctica.<ref>
[http://www.nsf.gov/od/opp/antarct/anttrty.jsp The Antarctic Treaty], article 4, clause 2
</ref>

The Convention on 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.<ref>{{cite web |url= http://www.ccamlr.org/en/system/files/e-pt1.pdf |title=Text of the Convention on the Conservation of Antarctic Marine Living Resources|publisher=Convention on the Conservation of Antarctic Marine Living Resources |work=ccamlr.org |year=1972 |accessdate=23 January 2014}}</ref>

==Economy ==
Between 1 July 1998 and 30 June 1999, fisheries landed 119,898 [[tonne]]s, of which 85% consisted of [[krill]] and 14% of [[Patagonian toothfish]]. 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 harbors==
[[File:USNS Southern Cross at the ice pier in 1983.jpg|thumb|left|300px|Severe cracks in an [[ice pier]] in use for four seasons at [[McMurdo Station]] slowed cargo operations in 1983 and proved a safety hazard.]]

Major operational ports include: [[Rothera Research Station|Rothera Station]], [[Palmer Station]], [[Villa Las Estrellas]], [[Esperanza Base]], [[Mawson Station]], [[McMurdo Station]], 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 [[icebreaker]] 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 [[60th parallel south|60 degrees south]] are subject to inspection by Antarctic Treaty observers.

The Southern Ocean's southernmost port operates at McMurdo Station at {{coord|77|50|S|166|40|E|}}. [[Winter Quarters Bay]] forms a small harbor, on the southern tip of [[Ross Island]] where a floating [[Ice pier]] makes port operations possible in summer. [[Operation Deep Freeze]] personnel constructed the first ice pier at McMurdo in 1973.<ref name=Unique>
[http://antarcticsun.usap.gov/2005-2006/Documents/01-08-2006_antarcticsun.pdf#page=3 "Unique ice pier provides harbor for ships,"] Antarctic Sun. 8 January 2006; McMurdo Station, Antarctica.
</ref>

{{clear}}

== See also ==
{{Portal|Environment|Ecology|Geography|Weather}}
* [[Antarctic]]
* [[Ernest Shackleton]] (explorer)
* [[Extreme points of the Antarctic]]
* [[Roaring forties]]
* [[Seven seas]]
* [[Subantarctic]]
* [[Borders of the oceans]]

==Notes==
{{Reflist|group="note"}}

== References ==
{{Reflist|30em}}

===Further reading ===
* Gille, Sarah T. 2002. "Warming of the Southern Ocean since the 1950s": [http://www.sciencemag.org/cgi/content/abstract/295/5558/1275?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=%22global+ocean%22&searchid=1&FIRSTINDEX=10&resourcetype=HWCIT abstract], [http://www.sciencemag.org/cgi/content/full/295/5558/1275?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=%22global+ocean%22&searchid=1&FIRSTINDEX=10&resourcetype=HWCIT article]. ''[[Science (journal)|Science]]'': vol. 295 (no. 5558), pp.&nbsp;1275–1277.
* Descriptive Regional Oceanography, P. Tchernia, Pergamon Press, 1980.
* Matthias Tomczak and J. Stuart Godfrey. 2003. ''Regional Oceanography: an Introduction''. (see [http://www.es.flinders.edu.au/~mattom/regoc/ the site])

== External links==
{{Wiktionary}}
{{commons|Southern Ocean}}
* [http://www.whoi.edu/imageOfDay.do Oceanography Image of the Day], from the Woods Hole Oceanographic Institution
* [https://www.cia.gov/library/publications/the-world-factbook/geos/oo.html The CIA World Factbook's] entry on the Southern Ocean
* [http://geography.about.com/library/weekly/aa091500a.htm The Fifth Ocean] from Geography.About.com
* [http://purl.fdlp.gov/GPO/gpo45223 The International Bathymetric Chart of the Southern Ocean (IBCSO)] [[National Geophysical Data Center]]
* [http://www.photolib.noaa.gov/htmls/map00341.htm U.S. National Oceanic and Atmospheric Administration (NOAA): ''Limits of Oceans and Seas'' (2nd Edition), extant 1937 to 1953, with limits of ''Southern Ocean''.]
* [http://dapper.pmel.noaa.gov/dchart/ NOAA In-situ Ocean Data Viewer] Plot and download ocean observations
* [http://findanswers.noaa.gov/noaa.answers/consumer/kbdetail.asp?kbid=595&start=121 NOAA FAQ about the number of oceans]
* [http://www.ccamlr.org/ Commission for the Conservation of Antarctic Marine Living Resources]

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{{Marine realms}}
{{List of seas}}
{{Regions of the world}}
{{Antarctica}}
{{Polar exploration |state=collapsed}}

[[:Category:Southern Ocean|¤]]