Southern Ocean

The Antarctic Ocean, as delineated by the draft 4th edition of the International Hydrographic Organization's Limits of Oceans and Seas (2002).
A general delineation of the Antarctic Convergence, sometimes used by scientists as the demarcation of the Southern Ocean.

The Southern Ocean, also known as the Antarctic Ocean[1] or the Austral Ocean,[2][note 4] comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica.[6] As such, it is regarded as the fourth largest of the five principal oceanic divisions: smaller than the Pacific, Atlantic, and Indian Oceans but larger than the Arctic Ocean.[7] This oceanic zone is where cold, northward flowing waters from the Antarctic mix with warmer subantarctic waters.

By way of his voyages in the 1770s, Captain James Cook proved that waters encompassed the southern latitudes of the globe. Since then, geographers have disagreed on the Southern Ocean's northern boundary or even existence, considering the waters as various parts of the Pacific, Atlantic, and Indian Oceans, instead. However, according to Commodore John Leech of the International Hydrographic Organization (IHO), recent oceanographic research has discovered the importance of Southern Circulation, and the term Southern Ocean has been used to define the body of water which lies south of the northern limit of that circulation.[8] This remains the current official policy of the IHO, since a 2000 revision of its definitions including the Southern Ocean as the waters south of the 60th parallel has not yet been adopted. Others regard the seasonally-fluctuating Antarctic Convergence as the natural boundary.[9]

The maximum depth of the Southern Ocean, using the definition that it lies south of 60th parallel, was surveyed by the Five Deeps Expedition in early February 2019. The expedition's multibeam sonar team identified the deepest point at 60° 28' 46"S, 025° 32' 32"W, with a depth of 7,434 meters. The expedition leader and chief submersible pilot Victor Vescovo, has proposed naming this deepest point in the Southern Ocean the "Factorian Deep," based on the name of the manned submersible DSV Limiting Factor, in which he successfully visited the bottom for the first time on February 3, 2019.[10]

Definitions and use

The International Hydrographic Organization's delineation of the "Southern Ocean" has moved steadily southwards since the original 1928 edition of its Limits of Oceans and Seas.[6]

Borders and names for oceans and seas were internationally agreed when the International Hydrographic Bureau, 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 60th parallel south in its 2000 revisions, but this has not been formally adopted, due to continuing impasses about some of the content, such as the naming dispute over the Sea of Japan. 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 CIA World Factbook and Merriam-Webster.[7][11]

The Australian Government regards the Southern Ocean as lying immediately south of Australia (see § Australian standpoint).[12][13]

The National Geographic Society does not recognize the ocean,[2] depicting 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.[14] Map publishers using the term Southern Ocean on their maps include Hema Maps[15] and GeoNova.[16]

Pre-20th century

"Southern Ocean" as alternative to the Aethiopian Ocean, 18th century

"Southern Ocean" is an obsolete name for the Pacific Ocean or South Pacific, coined by Vasco Núñez de Balboa, the first European to discover it, who approached it from the north.[17] The "South Seas" is a less archaic synonym. A 1745 British Act of Parliament established a prize for discovering a Northwest Passage to "the Western and Southern Ocean of America".[18]

Authors using "Southern Ocean" to name the waters encircling the unknown southern polar regions used varying limits. James Cook's account of his second voyage implies New Caledonia borders it.[19] Peacock's 1795 Geographical Dictionary said it lay "to the southward of America and Africa";[20] John Payne in 1796 used 40 degrees as the northern limit;[21] the 1827 Edinburgh Gazetteer used 50 degrees.[22] 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.[23]

The United Kingdom's South Australia Act 1834 described the waters forming the southern limit of the new province of South Australia as "the Southern Ocean". The Colony of Victoria's Legislative Council Act 1881 delimited part of the division of Bairnsdale as "along the New South Wales boundary to the Southern ocean".[24]

1928 delineation

1928 delineation

In 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 Broughton Island, New Zealand to the north.

The detailed land-limits used were from Cape Horn in Chile 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.[25]

1937 delineation

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 abut land masses.

In the second edition, the Southern Ocean then extended from Antarctica northwards to latitude 40°S between Cape Agulhas in Africa (long. 20°E) and Cape Leeuwin in Western Australia (long. 115°E), and extended to latitude 55°S between Auckland Island of New Zealand (165 or 166°E east) and Cape Horn in South America (67°W).[26]

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 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', 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 delineation

The Southern Ocean did not appear in the 1953 third edition of Limits of Oceans and Seas a note in the publication read:

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.)
[citation needed][This quote needs a citation]

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.[27]

2002 draft delineation

Area inside the black line indicates the area constituting the Pacific Ocean prior to 2002; darker blue areas are its informal current borders following the recreation of the Southern Ocean and the reinclusion of marginal seas[28]

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 the 60th parallel south—with no land interruptions at this latitude—with the other 14 votes cast for other definitions, mostly the 50th parallel south, but a few for as far north as the 35th parallel 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).[29] 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.[30] A reservation had also been lodged by Australia regarding the Southern Ocean limits.[31] 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 CIA World Factbook uses "Southern Ocean" but none of the other new sea names within the "Southern Ocean" such as "Cosmonauts Sea") and Merriam-Webster,[7][11][14] scientists and nations – and even by some within the IHO.[32] Some nations' hydrographic offices have defined their own boundaries; the United Kingdom used the 55th parallel south for example.[27] Other organisations favour more northerly limits for the Southern Ocean. For example, Encyclopædia Britannica describes the Southern Ocean as extending as far north as South America, and confers great significance on the Antarctic Convergence, yet its description of the Indian Ocean contradicts this, describing the Indian Ocean as extending south to Antarctica.[33] [34]

Other sources, such as the National Geographic Society, show the Atlantic, Pacific and Indian Oceans as extending to Antarctica on its maps, although articles on the National Geographic web site have begun to reference the Southern Ocean.[14]

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 Tasman Sea 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 Drake Passage which includes all of the waters from South America to the Antarctic coast, nor interrupt it for the Scotia Sea, 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 standpoint

A map of Australia's official interpretation of the names and limits of oceans and seas around Australia

In Australia, cartographical 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.[35] Coastal maps of Tasmania and South Australia label the sea areas as Southern Ocean[36] and Cape Leeuwin in Western Australia is described as the point where the Indian and Southern Oceans meet.[37]

Other Languages
Адыгэбзэ: Ипшэ Хышхуэ
Afrikaans: Suidelike Oseaan
Alemannisch: Südlicher Ozean
azərbaycanca: Cənub okeanı
Bân-lâm-gú: Lâm-ke̍k-iûⁿ
башҡортса: Көньяҡ океан
беларуская: Паўднёвы акіян
беларуская (тарашкевіца)‎: Паўднёвы акіян
български: Южен океан
Boarisch: Sidlicha Ozean
bosanski: Južni okean
brezhoneg: Meurvor ar Su
буряад: Урда далай
Чӑвашла: Кăнтăр океан
čeština: Jižní oceán
Cymraeg: Cefnfor y De
Ελληνικά: Νότιος Ωκεανός
Esperanto: Suda Oceano
Fiji Hindi: Southern Ocean
français: Océan Austral
Gàidhlig: An Cuan a Deas
贛語: 南冰洋
客家語/Hak-kâ-ngî: 南冰洋
한국어: 남극해
hrvatski: Južni ocean
Bahasa Indonesia: Samudra Selatan
interlingua: Oceano Antarctic
íslenska: Suður-Íshaf
Kiswahili: Bahari ya Kusini
Kreyòl ayisyen: Antatik (oseyan)
Кыргызча: Түштүк океан
latviešu: Dienvidu okeāns
Lingua Franca Nova: Mar Antartica
la .lojban.: dzipo braxamsi
lumbaart: Ucean Antartich
македонски: Јужен Океан
მარგალური: ობჟათეშ ოკიანე
Bahasa Melayu: Lautan Selatan
Mìng-dĕ̤ng-ngṳ̄: Nàng-bĭng-iòng
монгол: Өмнөд далай
Nederlands: Zuidelijke Oceaan
नेपाल भाषा: दक्षिणी महासागर
日本語: 南極海
нохчийн: Къилба океан
Nordfriisk: Antarktisk Sia
norsk nynorsk: Sørishavet
oʻzbekcha/ўзбекча: Janubiy okean
Papiamentu: Oceano sur
Piemontèis: Océan Antàrtich
português: Oceano Antártico
rumantsch: Ocean Antarctic
русиньскый: Южный океан
русский: Южный океан
саха тыла: Соҕуруу далай
Sesotho sa Leboa: Southern Ocean
Simple English: Southern Ocean
slovenčina: Južný oceán
slovenščina: Južni ocean
српски / srpski: Јужни океан
srpskohrvatski / српскохрватски: Južni ocean
tarandíne: Mare antartece
татарча/tatarça: Көньяк океан
Türkçe: Güney Okyanusu
Türkmençe: Günorta okean
українська: Південний океан
ئۇيغۇرچە / Uyghurche: جەنۇبىي مۇز ئوكيان
Tiếng Việt: Nam Đại Dương
文言: 南冰洋
吴语: 南冰洋
ייִדיש: דרום אקעאן
粵語: 南大洋
žemaitėška: Pėitū ondėnīns
中文: 南冰洋