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The thermohaline circulation

The term thermohalin ( compound from ancient Greek θερμός thermós , German 'warm' and ἅλς háls , German 'salt' ) describes the property of sea water to change its density due to temperature changes or changes in the salt content .

" Thermohaline circulation " describes part of the oceanic circulation : The global wind systems initially drive warm surface water northward in the Atlantic and then cool down significantly in the North Atlantic (see Gulf Stream , wind-driven circulation ). Through the thermohaline circulation, part of it is transported further north, where it replaces sinking water flowing towards the equator . Both cooling and an increase in salinity cause an increase in the density and thus the specific weight of the water, which leads to a decrease. In the North Atlantic Labrador Sea , this is only caused by heat emission, while in the Arctic Greenland Sea the salt from the freezing water gets into the surrounding water through ice formation, thus increasing the salt content. The cold deep water now flows back south as North Atlantic deep water and into the Indian and Pacific Oceans . On the way it mixes with other bodies of water and is slowly transported back to the surface. Molecular diffusion of heat and salt also plays a role here.

As in the earth's atmosphere, this circulation transports heat towards the poles and thus plays an important role in the global energy balance.

Due to the increasing ice melt on the polar ice caps associated with global warming , the salt content of the seawater changes with the additional fresh water input . This also changes the thermohaline dynamics there: the formation of Antarctic bottom water z. B. is one of the "engines" of thermohaline circulation.

Individual evidence

  1. a b Stefan Rahmstorf: Thermohaline Ocean Circulation . In: Encyclopedia of Quaternary Sciences . 2007, pp. 739-750. doi : 10.1016 / B0-44-452747-8 / 00014-4 .
  2. , Forschung aktuell , August 31, 2016, Dagmar Röhrlich : Antarctica: The drive for global ocean circulation is weak (September 3, 2016).