First Nansen-Tutu Center publication in Nature; Impact of intensified Indian Ocean winds on mesoscale variability in the Agulhas system

Dr. Björn C. Backeberg at the Nansen-Tutu Center in Cape Town, has published together with Pierrick Penven* and Mathieu Rouault at the MA-RE Institute, University of Cape Town, a paper on Impact of intensified Indian Ocean winds on mesoscale variability in the Agulhas system.

Satellite measurements from the last two decades reveal accelerated eddies moving around Southern Africa. Movement of eddies from the Indian to the Atlantic Ocean and their transport of warm, salty water plays a vital role maintaining present day climate.Satellite measurements from the last two decades reveal accelerated eddies moving around Southern Africa. Movement of eddies from the Indian to the Atlantic Ocean and their transport of warm, salty water plays a vital role maintaining present day climate.

The paper contributes new knowledge on the link between the Indian Ocean, the Agulhas system, and the leakage, which is known to play an important role in global climate and was published in the presigious Nature Climate Change journal on 8. July, 2012.

South of Africa, the Agulhas current retroflects and a portion of its waters flows into the South Atlantic Ocean, typically in the form of Agulhas rings. This flux of warm and salty water from the Indian to the Atlantic Ocean (the Agulhas leakage) is now recognized as a key element in global climate. An Agulhas leakage shutdown has been associated with extreme glacial periods, whereas a vigorous increase has preceded shifts towards interglacials. In the absence of a coherent observing system, studies of the Agulhas have relied heavily on ocean models, which have revealed a possible recent increase in Agulhas leakage. However, owing to the high levels of oceanic turbulence, model solutions of the region are highly sensitive to their numerical choices, stressing the need for observations to confirm these important model results. Here, using satellite altimetry observations from 1993 to 2009, we show that the mesoscale variability of the Agulhas system, in particular in the Mozambique Channel and south of Madagascar, has intensified. This seems to result from an increased south equatorial current driven by enhanced trade winds over the tropical Indian Ocean. Overall, the intensified mesoscale variability of the Agulhas system is reflected in accelerated eddy propagation, in source regions as well as the retroflection from which eddies propagate into the South Atlantic Ocean. This suggests that the Agulhas leakage may have increased from 1993 to 2009, confirming previous modelling studies that have further implied an increased Agulhas leakage may compensate a deceleration of meridional overturning circulation associated with a freshening of the North Atlantic Ocean.

The full paper is Impact of intensified Indian Ocean winds on mesoscale variability in the Agulhas system is available at Nature Climate Change journal.

 

* visitor at UCT and affiliated with; LMI ICEMASA, Laboratoire de Physique des Oceans, Plouzané, France.

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