Mechanisms driving the global tropical response to a weakened AMOC during Heinrich Stadial 1

Abstract

Heinrich Stadial 1 (HS1; $\sim$17.5-15 thousand years before present) was characterized by a weakening of the Atlantic Meridional Overturning Circulation (AMOC) that resulted in large hydroclimate changes across the global tropics. Here we investigate the mechanisms driving tropical rainfall changes by comparing an ensemble of numerical simulations against paleoclimate proxy records spanning the global tropics. Our multi-model ensemble and synthesis of 154 hydroclimate records both show drier conditions north of the equator and wetter conditions south of the equator - a pattern broadly consistent with a meridional mean shift in tropical rain belts. However, changes in rainfall outside of the Atlantic and in monsoonal regions require more complex mechanisms to explain the proxy-inferred patterns. Cooling of the tropical North Atlantic emerges as the key link connecting AMOC weakening and the tropical hydroclimate response. Mechanisms involving tropical North Atlantic cooling are essential for propagating the North Atlantic climate signals to remote regions such as West Africa, the Indian Ocean, and the Andes. Simulations and the proxy synthesis show globally consistent response patterns except for the Maritime Continent. Reconciling these differences will require the separation of different proxy types and improved proxy system modeling for this region.