Forced changes in Atlantic overturning are distinctly fingerprinted by South Atlantic western boundary transports

Abstract As a major ocean circulation system, the Atlantic Meridional Overturning Circulation (AMOC) may approach a critical transition under anthropogenic forcing, yet how large-scale AMOC changes imprint on regional circulation pathways remains incompletely understood. While persistent changes in overturning are expected to be meridionally coherent, their horizontal expression may be highly non-uniform. Here, we use 22,000-year-long transient deglacial climate simulations to examine how latitudinally coherent AMOC variations are redistributed across the upper Atlantic circulation. By separating externally forced, long-term AMOC changes from internally generated, short-term variability, we show that the former are disproportionately reflected along the full meridional extent of the South Atlantic western boundary current system. In contrast, North Atlantic counterparts relate primarily to higher-frequency, unforced AMOC variability. Our findings highlight South Atlantic western boundary transports as outstanding fingerprints of past externally forced AMOC changes, thereby outlining their particular sensitivity to a predicted, anthropogenically forced weakening of the AMOC.