Water from the Indian Ocean does not reach the SouthAtlantic Ocean continuously, but in separate packages. These are calledAgulhas eddies, after the current along the east coast of SouthernAfrica where they originate from. Dutch researcher Astrid van Veldhovencharacterised the fate of these rapidly rotating, three hundredkilometre wide and five kilometres deep, warm eddies during theirjourney to the Atlantic Ocean.
Over the past four years, theRoyal Netherlands Institute for Sea Research (NIOZ) on Texel, inpartnership with Utrecht University and the University of Cape Town,has carried out a large NWO-funded project into the Agulhas eddies,which transport seawater from the Indian Ocean to the South AtlanticOcean. During this project the NIOZ research vessel 'Pelagia' and theUniversity of Cape Town's research vessel 'Agulhas' were remotelynavigated by the Utrecht researchers, who interpreted satellite imagesfrom behind their computers. Satellite images revealed that the warmAgulhas eddies rose up as small hills above the Atlantic Ocean with amaximum height of about one metre.
Moreover, Van Veldhovenvisited the eddies on three occasions onboard the research vessel. TheAgulhas eddies turned out to be large warm rings of water from theIndian Ocean with a diameter of about 300 kilometres within which thewater sometimes rotated at a speed of more than 3.6 kilometres per hourin an anticlockwise direction. To everyone's surprise the eddy wasfound to stretch from the ocean surface right down to the ocean floorat a depth of some five kilometres; it therefore has a volume of about350,000 cubic kilometres.
On the ocean surface, young eddies areat most 5 degrees Celsius warmer than the surrounding Atlantic Ocean.Due to their enormous volume, the eddies import considerable quantitiesof heat into the Atlantic Ocean.
Van Veldhoven carried out adetailed study of how these enormous eddies transformed, rotatedincreasingly slowly, and as a result of this gradually released theirheat and salt into the surrounding cold Atlantic Ocean and into theatmosphere. The eddies only completely subside when they are halfway toSouth America.
The knowledge acquired from this research will beused to improve computer models of the global ocean circulation. Suchmodels are necessary for improved predictions of climate change and thedegree of global warming due to the greenhouse effect.
Astrid van Veldhoven's research was funded by NWO.
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