Weakening Atlantic overturning circulation causes South Atlantic salinity pile-up

The slowdown in the Atlantic Meridional Overturning Circulation (AMOC) is remotely detected in an increasing South Atlantic salinity trend. This salinity pile-up is caused by reduced divergence of surface salinity transport under a weakened AMOC. The Atlantic Meridional Overturning Circulation (AMOC) is an active component of the Earth's climate system(1)and its response to global warming is of critical importance to society. Climate models have shown an AMOC slowdown under anthropogenic warming since the industrial revolution(2-4), but this slowdown has been difficult to detect in the short observational record(5-10)because of substantial interdecadal climate variability. This has led to the indirect detection of the slowdown from longer-term fingerprints(11-14)such as the subpolar North Atlantic 'warming hole'(11). However, these fingerprints, which exhibit some uncertainties(15), are all local indicators of AMOC slowdown around the subpolar North Atlantic. Here we show observational and modelling evidence of a remote indicator of AMOC slowdown outside the North Atlantic. Under global warming, the weakening AMOC reduces the salinity divergence and then leads to a 'salinity pile-up' remotely in the South Atlantic. This evidence is consistent with the AMOC slowdown under anthropogenic warming and, furthermore, suggests that this weakening has likely occurred all the way into the South Atlantic.