Thermohaline circulation

circulation of the oceans at a large scale. It is caused by the difference in salinity and temperature between masses of water. The cold salt-water sinks close to Norway and Greenland. It is reheated in the Tropics and then rises to the surface again where it cools and so on and so forth as a convector belt. It is estimated that it takes several thousand years for a single molecule of water to complete the circuit.