Patagonian Ice Sheet discharge enhanced by AMOC slowdown through thermal bipolar seesaw

Significance: The Atlantic Meridional Overturning Circulation (AMOC), a major regulator of global climate, is weakening under ongoing warming, yet its far-field impacts remain uncertain. Past AMOC slowdown events during the last glacial period provide insights into how such changes propagate beyond the North Atlantic. By combining new marine sediment records from the South Pacific off Chile with long-term climate model simulations, we reveal that AMOC slowdowns enhanced precipitation along the Chilean margin by intensifying the Southern Hemisphere Westerly Winds and warming the South Pacific. These changes promoted sediment and meltwater discharge from the Patagonian Ice Sheet and may have strengthened Southern Ocean ventilation. Our findings demonstrate that AMOC weakening can trigger rapid, far-reaching hydroclimatic impacts extending into the Southern Hemisphere midlatitudes.

Resumen: The Atlantic Meridional Overturning Circulation (AMOC) transports heat globally, and its potential weakening would be crucial for future climate projections. Valuable insights into climatic impacts of AMOC slowdowns can be gained from the last glacial period, when millennial-scale AMOC reductions recurrently triggered large-scale reorganizations of the atmosphere-ocean system. However, hydroclimatic responses within the Southern Hemisphere Westerly Wind (SWW) belt—a key region for the global carbon cycle—remain poorly constrained. Here we present a marine sediment record from ~150 km offshore Chile in the eastern South Pacific that documents millennial-scale increases in detrital discharge from the western Patagonian Ice Sheet, temporally associated with AMOC slowdowns. These discharge events likely resulted from ice-sheet expansion and the associated marginal melt linked to gradually enhanced orographic precipitation under SWW and temperature rise. Our simulations with a coupled atmosphere-ocean general circulation model support enhanced precipitation along the Chilean margin south of 45°S and warming-induced melting due to millennial-scale AMOC slowdowns. The precipitation increase reflects the progressive southward intensification of the SWW and the enhanced sea-surface evaporation resulting from Southern Ocean warming through the thermal bipolar seesaw. Together, proxy and modeling results demonstrate that abrupt AMOC slowdowns drove coupled atmospheric-oceanic responses in the South Pacific that promoted Patagonian hydroclimate and ice-sheet changes and may have amplified wind-driven ventilation of the Southern Ocean. These findings highlight the tight coupling between interhemispheric atmospheric and oceanic circulation, cryosphere dynamics, and the global carbon cycle, and raise the possibility of future abrupt shifts in far-field hydroclimate and atmospheric CO₂.