Lifebuoys for the Gulf Stream?

Climate change is increasingly delivering high-salt water from the Indian Ocean

Temperatures and currents at 450 meters depth of the high-resolution Kiel computer model (instantaneous view). The Agulhas Current flows along the South African coast. Southwest of Cape Town, he makes an abrupt U-turn back to the Indian Ocean. In doing so, he laces vortices - "agulhas rings" - which transport warm and salty water into the Atlantic Ocean. © A. Biastoch / IFM-GEOMAR
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The Gulf Stream system is known for its contribution to the mild climate of Northern Europe. However, researchers have been worried for some time that climate change may gradually reduce their strength. Unexpected help may be provided by ocean currents south of Africa: scientists have discovered that the Agulhas Stream is transporting more saline water into the Atlantic Ocean.

This could contribute to stabilizing the Gulf Stream system, according to researchers from the Kiel Leibniz Institute for Marine Sciences (IFM-GEOMAR) and the University of Cape Town in the science journal "Nature".

Agulhas rings provide warm water

The Agulhas Current - like the Gulf Stream - one of the strongest currents in the world ocean, flows in the Indian Ocean along the South African coast. Southwest of Cape Town, he makes an abrupt U-turn back to the Indian Ocean. Here, every three to four months of powerful vortexes of several 100 kilometers in diameter, the Agulhas rings, come off the main stream. These bring warm and salty water from the Indian Ocean into the Atlantic Ocean.

"It sounds a bit adventurous that currents around South Africa should affect our latitudes, " admits the lead author of the study, Arne Biastoch of IFM-GEOMAR. "However, it has long been known that the Agulhas Stream is a key to replenishing salty water to the Atlantic Ocean, " continues Biastoch.

"By analyzing observational data and computational models, we have shown that this process has intensified as part of climate change in the Southern Ocean, " said co-author Professor Claus Böning of IFM-GEOMAR. display

Major changes in the Agulhas current

Why is that? Normally, the western winds in the southern ocean limit the exchange of water between the Indian Ocean and the Atlantic. However, shifting the westerly winds to the south has widened the inflow water corridor south of Africa in recent decades. According to the researchers, this trend could intensify in the future as a result of climate change.

The salt, which was also introduced into the Atlantic, finally finds its way into the far north with the prevailing currents and could thus stabilize the Gulf Stream system. According to the scientists in the northern North Atlantic, the constant supply of salt from the south counteracts the increasing precipitation and ice melt. However, whether the changes in the Agulhas Current have the potential to completely neutralize the feared strong "outpouring" in the North Atlantic remains open.

Soon new computer simulations?

More detailed explanations should be provided by further computer simulations. These require, according to the researchers even more detailed models that represent the fine structures of the ocean currents. However, even the latest generation of supercomputers at the University of Kiel and national supercomputing centers such as Berlin, Hamburg or Stuttgart require several months to simulate just a few decades with such models.

(idw - Leibniz Institute for Marine Sciences, 26.11.2009 - DLO)