The Southern Ocean is a major component of Earth's ocean and climate. Its circulation is complex, with a zonal Antarctic Circumpolar Current (ACC) interacting with a meridional thermohaline circulation. The ACC is a highly variable, deep-reaching eastward flow driven mainly by the westerly winds. It is the longest (24,000km), largest (transport 137-147.106 m3 s-1) and only current to connect the major oceans. The Ekman component of the westerly winds also drives surface waters north. Near the ACC's northern limit, these waters sink to form Subantarctic Mode and Antarctic Intermediate waters, which continue north at depths < ~ 1,400 m. Interacting with the ACC is the density-forced thermohaline circulation. Super cooling and increased salinity of shelf waters off the Weddell, Wilkes Land and Ross coasts cause these waters to sink and flow equatorwards. The densest component, Antarctic Bottom Water, is captured in deep basins around Antarctica. Less dense water is entrained by the ACC and mixed with deep water moving south from the Atlantic, Indian and Pacific oceans. The resultant Lower Circumpolar Deep Water is tapped off by deep western boundary currents that enter the three oceans at depths > ~ 2,000 m. These northward inflows, with a total volume transport of ~ 55.106m3 s-1, disperse Antarctic and

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northern-sourced waters throughout the world ocean. Other circulation elements are the deep-reaching, cyclonic Weddell, Ross and unnamed gyres located south of the ACC. Further south again are the westward Antarctic Slope and Coastal currents that pass along the Antarctic continental margin under easterly polar winds.

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