Thermohaline circulation

The thermohaline circulation, also colloquially global conveyor belt (english ocean conveyor belt ), is an oceanographic term for a combination of ocean currents, which connect four of the five oceans together and unite it to a cycle of global proportions.

The drive for this extensive mass and heat exchange is thermohaline nature. This means: It is caused by temperature and salt concentration differences within the oceans, both of which are responsible for the different density of water. The temperature difference is caused in turn by the width function of the degree of sunlight.

History

In the early 1970s it was the first time possible to evaluate oceanographic data of the whole earth. This synopsis was the networking of wind and density driven currents and it has been postulated that the well-known Gulf Stream is only a partial flow of a global circulation. Based on a mechanical conveyor belt this globe for seamless flow was called the " large marine conveyor belt " or simply " global conveyor belt " or in scientific parlance as " global thermohaline circulation ."

Circulation patterns

The circulation currents occur either at the surface and in depth. The cold water moves in a depth of 1.5 bis 3.0 km mostly parallel to the continental slope on the western side of the ocean basins, caused by the Earth's rotation. Here are transported per second from 10 to 40 million cubic meters of water.

The global heat transfer tape is initiated mainly by the fall in the winter and cold salty sea water in the North Atlantic at 1-4 km depth, which is why these regions of the global circuit, they are suitable to consider the circulation pattern from here. The decrease is caused by cooling and an increase in the salt content due to evaporation. At or near the seabed, the Deep Water (North Atlantic Deep Water ) flows as cold deep flow to the exit of the South Atlantic and is then transported into the Indian Ocean and the Pacific Ocean to the Circumpolar Current. The Circumpolar Current of the Southern Ocean flows around the globe and mixed water masses of the three adjacent oceans and is probably the place where most of the cold water rises and is heated by wind-driven mixing. From there, the modified by mixing water masses move back to the surface ( surface water, Pacific) or in a few hundred feet below this ( intermediate water, the Indian Ocean ). The water heats up in the sequence, especially in the equatorial regions and is as warm surface flow initially to Indonesia over, hereinafter around the southern tip of Africa around the Gulf region of Central America, and finally as the Gulf Stream in the North Atlantic, where it drops again and the cycle closes it.

In addition to purely thermohaline effects play the distribution of the continents, the Coriolis force ( thus the flows occur mainly on the West Coast on ) and the wind-induced effect of the corkscrew flow is an issue. Together, these lead to a very complex regional training of different ocean currents, for example in the form of large eddies on the southeast coast of South America (see below). A small portion of this flow also water masses from the Arctic Ocean into the Atlantic, so this also requires the global conveyor belt has part. Since many of these factors on the local intensity of solar radiation depend on these ocean currents can learn over the year also different forms, such as in the Indian Ocean due to the monsoon. Significant effects are in this case upwelling and down- welling.

Due to the long-term effects of continental drift to the land-sea distribution and the main currents are variable with time. As a comparatively short-term factor, due to the melting of the polar ice caps, a more or less strong weakening of the North Atlantic Current is considered possible. For this purpose, it is also examples in the climate history find.

Deep boundary currents

A further contribution to global sea-water circulation represent the deep boundary currents dar. This refers to offshore deep-water eddy, as arise, for example, off the coast of Brazil in the Brazil Current ( the so-called Brazil Current rings). These vortices occur temporally and spatially periodic, ie, a situation called a vortex street. A detailed explanation of this discovered in 2004 phenomenon is still out, however, according to computer models of the Brazil current decays at the level of the Brazilian city of Recife because of there receding coast and thus reduces friction in a turbulent flow, compare eddy ( fluid mechanics ).