Variations in the strength of the Gulf Stream can in part attributed to currents off South Africa. Oceanographers at the Leibniz Institute of Marine Sciences (IFM-GEOMAR), Kiel and the University of Cape Town developed a computer model to study the currents systems in unsurpassed detail. To their surprise, they found the impact of small-scale fluctuations of the Agulhas Current south of Africa is detectable all the way into the North Atlantic Ocean.
The Agulhas Current is, like the Gulf Stream, one of the strongest currents in the world ocean. It carries warm and salty water from the tropical Indian Ocean along South Africa’s east coast. South-west of Cape Town it makes an abrupt turn back into the Indian Ocean. In this process huge rings of water with diameters of hundreds of kilometre are cut off at intervals of 3 to 4 months. These so-called “Agulhas Rings” carry extra heat and salt into the South Atlantic, making this a key region for the whole Atlantic Ocean.
"Even when it might seem strange for oceanographers in far-away from Germany to investigate currents near South Africa“ says Dr Arne Biastoch of the IFM-GEOMAR in Kiel, first author of the research papers. "Surprisingly, one can follow the influence of the Agulhas Current right up to the North Atlantic Ocean. This has important consequences for observational programmes in the North Atlantic that attempt to determine the much feared long-term, climatic changes in the Gulf Stream system.“
The new studies show that normal changes from year to year in the formation of Agulhas Rings lead within a few years to an increase in the flux of warm water across the equator from the South to the North Atlantic Ocean. This far-reaching influence was not known before.
"Studies of this kind can only be carried out using very large computer models, which have to simulate fine details in the ocean currents“, adds Prof. Claus Böning from IFM-GEOMAR.
In close international collaboration with colleagues of France and South Africa a new, high-resolution ocean model was developed and intensively tested. It calculates the evolution of the currents on a fine mesh of approximately 40 million grid points. For the simulation supercomputers at the University of Kiel and in Stuttgart were used for a period of over 6 months. The analysis of the enormous amounts of data will keep the scientists of Kiel and their international colleagues busy for years.
This research was recently published both in Nature and Geophysical Research Letters.
- A. Biastoch, C. W. Böning, J. R. E. Lutjeharms. Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation. Nature, 2008; 456 (7221): 489 DOI: 10.1038/nature07426
- A. Biastoch, J. R. E. Lutjeharms, C. W. Böning, M. Scheinert. Mesoscale perturbations control inter-ocean exchange south of Africa. Geophysical Research Letters, 2008; 35 (20) DOI: 10.1029/2008GL035132
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