Southern Ocean

node · earth · Circumpolar, south of roughly 40°S

The band of water circling Antarctica, unbounded to the east and west, which is the reason the world ocean behaves as one system rather than three. Its westerly winds drive the Antarctic Circumpolar Current and pull deep water back to the surface; its shelves make the densest water on the planet. It is also the planet's main heat and carbon sink: the region south of about 30°S takes up roughly 40 per cent of the ocean's anthropogenic carbon dioxide, and estimates of its share of ocean heat uptake over the historical period run higher still, though with wide uncertainty. What happens here is not local — a change in Southern Ocean density propagates into the abyss of every other basin.