South Pole

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Lore & Background

By way of his voyages in the 1770s, James Cook proved that waters encompassed the southern latitudes of the globe. Yet, geographers have often disagreed on whether the Southern Ocean should be defined as a body of water bound by the seasonally fluctuating Antarctic Convergence — an oceanic zone where cold, northward flowing waters from the Antarctic mix with warmer Subantarctic waters — or not defined at all, with its waters instead treated as the southern limits of the Pacific, Atlantic, and Indian oceans. In 2000, the International Hydrographic Organization (IHO) finally settled the debate after the full importance of Southern Ocean overturning circulation had been ascertained, and the term Southern Ocean now defines the body of water which lies south of the northern limit of that circulation. The expedition leader and chief submersible pilot, Victor Vescovo, has proposed naming this deepest point the "Factorian Deep", based on the name of the crewed submersible DSV Limiting Factor, in which he successfully visited the bottom for the first time on February 3, 2019.

Reader's Guide

The Southern Ocean overturning circulation is important because it makes up the second half of the global thermohaline circulation, after the better known Atlantic meridional overturning circulation (AMOC). Much like AMOC, it has also been substantially affected by climate change, in ways that have increased ocean stratification, and which may also result in the circulation substantially slowing or even passing a tipping point and collapsing outright. The latter would have adverse impacts on global weather and the function of marine ecosystems here, unfolding over centuries. The ongoing warming is already changing marine ecosystems here. 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 was circulated as a draft edition in 2002, and is used by some within the IHO and other organizations, such as the CIA World Factbook and Merriam-Webster. The National Geographic Society recognized the ocean officially in June 2021.

Did You Know?

• The Southern Ocean is the second-smallest of the five principal oceanic divisions, larger than the Arctic Ocean but smaller than the Pacific, Atlantic, and Indian oceans.
• The deepest point of the Southern Ocean, at 7,434 metres (24,390 ft), was identified by the Five Deeps Expedition in early February 2019 at coordinates 60° 28' 46"S, 025° 32' 32"W.
• Victor Vescovo proposed naming the deepest point the 'Factorian Deep' after the submersible DSV Limiting Factor, which he piloted to the bottom on February 3, 2019.
• The IHO's 2000 definition of the Southern Ocean as waters south of the 60th parallel south has not been formally adopted due to disputes like the naming of the Sea of Japan.
• The National Geographic Society officially recognized the Southern Ocean in June 2021.

Physical Extent and the Quest for the Deepest Point

The Southern Ocean spans roughly 21.96 million square kilometers, making it the second-smallest of the five major oceanic divisions. Situated south of the 60th parallel south, it encircles Antarctica and is smaller than the Pacific, Atlantic, and Indian Oceans yet larger than the Arctic. In early February 2019, the Five Deeps Expedition deployed multibeam sonar to pinpoint the ocean's deepest location at 60° 28' 46"S, 025° 32' 32"W, reaching a depth of 7,434 meters. Expedition leader Victor Vescovo, piloting the crewed submersible DSV Limiting Factor, descended to the bottom on February 3, 2019, becoming the first person to visit this point. He proposed naming the site the "Factorian Deep" after his vessel. This achievement marked a milestone in understanding the physical extremes of a body of water that had long resisted precise characterization, and it underscored how much of the Southern Ocean's seafloor remained unexplored until very recently.

A Century of Shifting Boundaries

The question of where the Southern Ocean begins has generated more than a century of geographic disagreement. When the International Hydrographic Bureau convened its First International Conference in July 1919, it set the stage for defining ocean borders, and the first edition of Limits of Oceans and Seas followed in 1928. That initial delineation used land-based limits, tracing from Cape Horn in Chile around Antarctica to Broughton Island in New Zealand. By the 1937 second edition, northern limits had shifted southward, and much of the boundary no longer touched land masses. Since 1953, the ocean was omitted entirely from the official publication, leaving local hydrographic offices to draw their own lines. In 2000, the IHO revived the definition as waters south of the 60th parallel, but this has never been formally adopted due to unrelated naming disputes, such as the Sea of Japan controversy. The 2002 draft edition remains in use by organizations including the CIA World Factbook and Merriam-Webster, while the Australian Government simply regards the ocean as lying immediately south of its own coastline.

The Engine of Global Circulation

The Southern Ocean is not merely a body of water but a critical component of Earth's climate machinery. Its overturning circulation forms the second half of the global thermohaline system, complementing the better-known Atlantic meridional overturning circulation. The full importance of this role was only ascertained in the late twentieth century, which is partly why the IHO waited until 2000 to formally recognize the ocean as a distinct entity. However, climate change is already disrupting this system. Warming has increased ocean stratification, and scientists warn the circulation could slow substantially, pass a tipping point, or even collapse entirely. Such a collapse would unfold over centuries but would have severe consequences for global weather patterns and the marine ecosystems that depend on the ocean's mixing. Even now, ongoing warming is visibly altering the biological communities that inhabit these southern waters, making the health of this circulation a matter of planetary concern.

From Balboa's Naming to Modern Recognition

The name "Southern Ocean" carries a surprisingly layered history. The earliest known use of the term came from Spanish explorer Vasco Núñez de Balboa, who coined it to describe the Pacific Ocean after approaching it from Panama. A 1745 British Act of Parliament still referenced "the Western and Southern Ocean of America" in a prize for discovering a Northwest Passage. By the late eighteenth and early nineteenth centuries, various authors applied the name to waters encircling the unknown polar regions, but their proposed northern limits varied wildly, from 40 degrees south in John Payne's 1796 usage to 50 degrees in the 1827 Edinburgh Gazetteer. James Cook's 1770s voyages proved that open waters surrounded the southern latitudes, yet geographers continued to debate whether these waters constituted a separate ocean or simply the southern extensions of the Pacific, Atlantic, and Indian Oceans. It was not until June 2021 that the National Geographic Society officially recognized the Southern Ocean, ending a long period in which its maps showed the other three oceans extending all the way to Antarctica.