Help to the Gulf Stream
Friday, December 4, 2009 4:13:00 PM
The Agulhas Current flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift, and one of the strongest ocean currents in the world. Southwest of Cape Town it abruptly turns back into the Indian Ocean. In this process huge rings of water with diameters of hundreds of kilometres are cut off at intervals of 3 to 4 months. These so-called "Agulhas Rings" carry warm and saline waters from the Indian Ocean into the Atlantic. It is known for quite some time that the Agulhas region is one of the key regions for the supply of salty waters into the Atlantic. By analyzing observational data and computers models it has been shown that this process is strengthening due to climate change in the Southern Ocean.
Westerlies in the Southern Ocean are blocking the water exchange between the Indian Ocean and the Atlantic. In the past decades, a southward shift of these westerlies has widened the corridor south of Africa for the inflow of water into the Atlantic. This trend could further intensify in the future as part of climate change.
In the Atlantic this extra amount of salty water is transported northward by the prevailing currents and could finally help to stabilize the Gulf Stream system in the northern North Atlantic. There it could act against the freshening process due to enhanced precipitation and the ice melting. Further studies are however required to prove the hypothesis.
Biastoch et al., 2009:
Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies.
Nature, 462 (7272), doi:10.1038/nature08519.
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