Also known as the global thermohaline conveyor belt, the Atlantic thermohaline circulation begins when the Gulf Stream (and its extension, the North Atlantic Drift) bring warm, salty water to the north-east Atlantic, warming western Europe. The water cools, mixes with cold water coming from the Arctic Ocean, and becomes so dense that it sinks, both to the south and east of Greenland. This current is part of a larger system, connecting the Atlantic with the Indian and Pacific Oceans, and the Southern Ocean. Further sinking of dense water occurs near to Antarctica. Water from the two main sinking regions spreads out in the subsurface ocean affecting almost all the world’s oceans at depths from 1 000 m and below. The cold, dense water gradually warms and returns to the surface, throughout the world’s oceans. These surface and subsurface currents, the sinking regions, and the return of water to the surface form a closed loop.

Model simulations (for example, Srokozs (2003) Royal Society) suggest that a sudden shutdown of the thermohaline circulation will cause global climate changes. For an assessment of the risk of a collapse of the Atlantic thermohaline circulation, see Yin Yohe et al. (2005) Change 54.

Thermohaline circulation