Agulhas Leakage Predominantly Responds to the Southern Hemisphere Westerlies

• Published in: Journal of Physical Oceanography
• Main Authors: Durgadoo, Jonathan V., Loveday, Benjamin R., Reason, Chris J. C., Penven, Pierrick, Biastoch, Arne
• Other Authors: Helmholtz Centre for Ocean Research Kiel (GEOMAR), Department of Oceanography Cape Town, University of Cape Town, Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: Boundary currents; Meridional overturning circulation; Wind stress; Mesoscale models; Numerical analysis/modeling; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Antarctic; The Antarctic; Indian; Antarc*; South Atlantic Ocean
• Online Access: https://hal.science/hal-01153697; https://doi.org/10.1175/JPO-D-13-047.1

International audience The Agulhas Current plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic Ocean. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian–Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have little impact on the magnitude of Agulhas leakage. Here, employing three ocean models for robust analysis—a global coarse-resolution, a regional eddy-permitting, and a nested high-resolution eddy-resolving configuration—and systematically altering the position and intensity of the westerly wind belt in a series of sensitivity experiments, it is shown that the westerlies, in particular their intensity, control the leakage. Leakage responds proportionally to the intensity of westerlies up to a certain point. Beyond this, through the adjustment of the large-scale circulation, energetic interactions occur between the Agulhas Return Current and the Antarctic Circumpolar Current that result in a state where leakage no longer increases. This adjustment takes place within one or two decades. Contrary to previous assertions, these results further show that an equatorward (poleward) shift in westerlies increases (decreases) leakage. This occurs because of the redistribution of momentum input by the winds. It is concluded that the reported present-day leakage increase could therefore reflect an unadjusted oceanic response mainly to the strengthening westerlies over the last few decades.