The Southern Ocean is the body of water encircling Antarctica, generally defined as lying south of 60° S latitude. With an area of 21,960,000 square kilometres, it is the second-smallest of the five principal oceanic divisions, larger only than the Arctic Ocean.
Its deepest point, the Factorian Deep, was surveyed by the Five Deeps Expedition in February 2019 at 7,434 metres. Expedition leader Victor Vescovo piloted the submersible DSV Limiting Factor to the bottom on 3 February 2019, the first crewed visit to that depth. Although James Cook’s voyages in the 1770s established that waters surrounded the southern latitudes, geographers long disagreed on whether to recognise a distinct Southern Ocean. In 2000 the International Hydrographic Organization formalised the definition, basing it on the oceanic circulation pattern rather than arbitrary latitude. The Southern Ocean overturning circulation forms the second half of the global thermohaline system and plays a critical role in regulating climate, though warming waters are now altering both the circulation and the marine ecosystems it sustains.
