| Summary: | Agulhas leakage, the transport of warm and salty waters from the Indian Ocean into the South Atlantic, represents a choke point for the surface branch of the global overturning circulation. Previous studies suggest that Agulhas leakage has been increasing under anthropogenic climate change as a response to strengthening Southern Hemisphere westerly winds, and that the resulting enhanced salt transport into the South Atlantic may counteract the projected weakening of the Atlantic meridional overturning circulation (AMOC) through warming and ice melting. However, due to its turbulent and intermittent nature, estimates for the past and future evolution of Agulhas leakage are sparse and individual estimates are associated with considerable uncertainties. Here we present an analysis of already established as well as new observation- and model-based estimates for Agulhas leakage variability to robustly quantify it’s (sub-)decadal evolution since the 1960s. We find that Agulhas leakage very likely increased in the 1960s through the 1980s, in agreement with strengthening Southern Hemisphere winds, while it appears unlikely that Agulhas leakage substantially increased since the 1990s, despite continuously strengthening winds. Our models further suggest that the increase in leakage coincided with a strengthening of the AMOC in the South Atlantic, which propagated into the North Atlantic within one to two decades. Hence, the South Atlantic may not only be important for future AMOC changes but may already have modulated basin-wide AMOC variability over the past decades. This underlines the importance of sustained efforts to monitor the AMOC in the South Atlantic, e.g., across the SAMBA array.
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