Wind-driven upwelling sustains weakened Atlantic overturning under climate extremes

Abstract The Atlantic Meridional Overturning Circulation (AMOC), vital for northward heat transport across the Atlantic Ocean, is projected to weaken due to global warming1, with significant global climate impacts2,3. However, the extent of AMOC weakening is uncertain with wide variation across climate models1,4,5, while some statistical indicators suggest an imminent collapse6. Here, we evaluate the AMOC’s resilience to extreme greenhouse gas and North Atlantic freshwater forcings in 34 climate models by analysing its upwelling pathways that return AMOC deep waters to the surface. We find that upwelling in the Southern Ocean (SO), driven by persistent SO winds, sustains a weakened AMOC in all cases, preventing its complete collapse. Since SO upwelling must be balanced by downwelling in the Atlantic or Pacific, the AMOC can only collapse if a compensating Pacific overturning (PMOC) develops. Remarkably, a PMOC does emerge in almost all models, but it is too weak to balance all of the SO upwelling, suggesting an AMOC collapse is unlikely this century. Our findings reveal novel AMOC stabilising mechanisms with implications for past and future AMOC changes, and hence for ecosystems and ocean biogeochemistry. They suggest that better understanding and estimates of the SO and Indo-Pacific circulations are urgently needed to accurately predict future AMOC change.