Millennial- to centennial-scale Atlantic ITCZ swings during the penultimate deglaciation

Abstract

Growing concerns surround the future of the Atlantic Meridional Overturning Circulation (AMOC) and its impacts on tropical regions, particularly due to changes in the dynamics of the Intertropical Convergence Zone (ITCZ). Northeastern Brazil, a tropical region strongly influenced by ITCZ dynamics, exhibits significant biological and social vulnerability to climate change, making it timely to understand how its hydroclimate could be impacted by AMOC changes in the face of anthropogenic global warming. The penultimate deglaciation was marked by a millennial-scale weak AMOC event called Heinrich stadial 11 (HS11; ∼136-129 ka), providing an instructive target interval for improving our understanding of Northeastern Brazil hydroclimate responses to climate change. Here, we reconstruct paleoclimate changes during HS11 based on a multi-proxy approach applied to a high-resolution marine core from the western equatorial Atlantic. Our results suggest that HS11 was marked by a southward shift of the ITCZ, evidenced by paleoprecipitation records showing increased precipitation over Northeastern Brazil. These changes were concurrent with increased sea surface temperatures and reduced bottom water ventilation in the western equatorial Atlantic, interpreted as consequences of a weak AMOC. Importantly, we identified centennial-scale events within HS11, which are similar in nature but smaller in magnitude than HS11. These events align with North Atlantic climate changes, highlighting the crucial role that not only millennial- but also centennial-scale AMOC variability may play in low latitudes. Our findings raise concerns about the potential future impacts that an AMOC weakening may have on the hydroclimate of Northeastern Brazil and other tropical regions.