Anthropogenic impact on Agulhas leakage

Recent work suggests that changes of the Southern Hemisphere (SH) winds led to an increase in Agulhas leakage and a corresponding salinification of the Atlantic. Climate model projections for the 21st century predict a progressive southward migration and intensification of the SH westerlies. The potential effects on the ocean circulation of such an anthropogenic trend in wind stress are studied here with a high‐resolution ocean model forced by a step‐function change in SH wind stress that involves a 7% increase in westerlies strength and a 2° shift in the zero wind stress curl. The model simulation suggests a rapid dynamic adjustment of Agulhas leakage by 4.5 Sv, about a third of its original value, after a few years. The change in leakage is reflected in a concomitant change in the transport of the South Atlantic subtropical gyre, but leads only to a small increase in the Atlantic Meridional Overturning Circulation (AMOC) of O(1 Sv) after three decades. A main effect of the increasing inflow of Indian Ocean waters with potential long‐term ramifications for the AMOC is the salinification and densification of upper‐thermocline waters in the South Atlantic, which extends into the North Atlantic within the first three decades. Key Points Agulhas leakage increases under global warming The increase in Agulhas leakage increases the supergyre The increase in Agulhas leakage transports additional salt into the Atlantic