Ocean currents off South Africa affect Gulf Stream

Marine researchers are discovering far-reaching effects in the ocean

Currents around South Africa (snapshot). The Agulhas Current (red ribbon) flows along the South African coast. Southwest of Cape Town, he makes an abrupt U-turn back to the Indian Ocean. He laces vertebrae that drift west into the Atlantic Ocean. (The colors indicate the strength of the flow.) © Leibniz Institute of Marine Sciences
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Fluctuations in the strength of the Gulf Stream - the "district heating" of Europe - are in part due to the flow of water off South Africa. This is the result of studies that have now appeared in "Nature" and the "Geophysical Research Letters". With the aid of a newly developed computer model, oceanographers succeeded in simulating the currents in unprecedented detail. Surprising realization: the effects of small-scale fluctuations of the Agulhas current south of Africa are noticeable into the North Atlantic.

Like the Gulf Stream, the Agulhas Current is one of the strongest currents in the world ocean, transporting water from the tropical Indian Ocean along the South African coast. Southwest of Cape Town, he makes an abrupt U-turn back to the Indian Ocean. Every three to four months, powerful vortices of several hundred kilometers in diameter are cut off from the Agulhas Stream, which transport warm and salt-rich water into the Atlantic Ocean

Make the sea area a key region for the Atlantic Ocean.

Distance effect so far unknown

"Even if it seems odd in the faraway Kiel to investigate the currents around South Africa, " explains the lead author, Arne Biastoch of IFM-GEOMAR, "their effects can be traced back to the North Atlantic. This surprising finding also has consequences for ongoing international measurement programs in the North Atlantic, with which the

feared long-term changes in the Gulf Stream system wants to get on the track. "Ad

The studies show that the natural fluctuations caused by the formation of agulhas rings within a few years influence the transport of warm water from the South Atlantic into the North Atlantic. This important long-distance effect was previously unknown.

Six months of computing time

"The investigation of such relationships requires highly complex computer models, which also have to represent fine details in the ocean currents, " explains Professor Claus Böning from IFM-GEOMAR. In close international cooperation with colleagues from France and South Africa, a new, high-resolution ocean model was developed and intensively tested.

It calculates the flow development on a very fine mesh network with a total of almost 40 million points. Supercomputers at the University of Kiel and the Supreme Computer Computing Center in Stuttgart required more than six months for the simulations. However, the Kiel researchers and their international colleagues will continue to work on the evaluation of the huge amounts of data so obtained for several years.

(Leibniz Institute for Marine Sciences Kiel, 27.11.2008 - NPO)