Circulation thermohaline

The circulation thermohaline is permanent circulation with large scales of the water of the oceans generated by variations in temperature and Salinité of the water masses. Salinity and the temperature have an impact on the density of sea water. Water, cooled and salted plunges on the level of the high latitudes (Norway, Greenland,…) and go down towards the south to depths ranging between 1 and 3 km. They are heated in the Tropics, and go back then to surface, where they cool, and so on. It is estimated that a water molecule makes the whole circuit in approximately 1000 years. Circulation thermohaline has an impact badly measured today on the climate.

Engines of circulation thermohaline

As the name indicates it, there exist two engines at the origin of this circulation:

Of the differences in temperature: the sea water is all the more dense as its temperature is low.

Of the differences in salinity (concentration of salt water). A water more concentrated out of salt is denser than a less concentrated water.

These two engines act directly on the density of water.

A cool water having a strong salt concentration will be dense, whereas a warm water low in salt is not very dense.

In the polar regions (Arctic Ocean and Sea of Weddell), the sea water, cold thus dense, is transformed into ice. During solidification, salt is rejected (the ice does not contain any or little) and thus enriches liquid salt water. This makes it still denser, and it thus plunges towards sea-beds. In the absence of dense source of water in the Pacific basic water goes up gradually from a progressive reduction in its density.

See too

GULF-stream
Climatology

External bond

Oceanic circulation by the Ifremer

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