Thauana Goncalves1,2*, Gabriel Pontes3, Laurie Menviel2, Himadri Saini4, Yanxuan Du4, Josephine Brown4, Luigi Jovane1: Sensitivity of Tropical Atlantic ITCZ migration to AMOC slowdown and shutdown in ACCESS-ESM1.5
1 Institute of Geoscience, University of São Paulo, Brazil
2 Climate Change Research Centre, University of New South Wales, Australia
3 School of Earth and Environment, University of Leeds, UK
4 School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Australia
The Intertropical Convergence Zone (ITCZ) is a narrow band of intense precipitation that modulates tropical hydroclimate. Its mean latitudinal position is driven by interhemispheric thermal gradients, making it sensitive to changes in the Atlantic Meridional Overturning Circulation (AMOC). Paleoclimate records show that periods of AMOC weakening during the last glacial period, such as Heinrich Stadials and Dansgaard-Oeschger (D-O) stadials, drove a southward migration of the ITCZ. However, how the magnitude of AMOC weakening translates into specific regional precipitation reorganizations remains poorly constrained. To address this, we integrate terrigenous proxy records from a marine sediment core in the western equatorial Atlantic with paleoclimate model simulations. Bulk-sediment major elemental ratios from this core reconstruct precipitation changes over the past 60,000 years, revealing enhanced precipitation over Northeastern Brazil associated with southward ITCZ shifts during all Heinrich Stadials and major D-O stadials. To investigate the physical mechanisms and sensitivity of this response, we analyze freshwater hosing experiments performed with the Australian Community Climate and Earth System Simulator version 1.5 (ACCESS-ESM1.5) across different background climate states. The simulations demonstrate distinct spatial signatures depending on the degree of AMOC disruption: an AMOC shutdown drives an intense, coastally focused precipitation enhancement, whereas an AMOC slowdown induces a more attenuated oceanic response accompanied by broader inland moisture propagation across South America. Together, this integrated proxy-model framework provides new constraints on tropical hydroclimate sensitivity to different regimes of AMOC weakening and offers a benchmark for evaluating tropical climate responses in ACCESS-ESM1.5 under changing circulation states.