Role of the Tropical Atlantic for the Interhemispheric Heat Transport During the Last Deglaciation

During the last deglaciation abrupt millennial‐scale perturbations of the Atlantic Meridional Overturning Circulation massively altered the interhemispheric heat distribution affecting, for example, continental ice volume and hydroclimate. If and how the related cross‐equatorial heat transport was controlled by the interplay between the southward‐flowing Brazil Current (BC) and northward‐flowing North Brazil Current (NBC) remains controversial. To assess the role of tropical heat transport during the last deglaciation, we obtained a high‐resolution foraminiferal Mg/Ca‐based sea surface temperature (SST) record from the BC domain at 21.5°S. The data reveal a yet undocumented warming of at least 4.6°C of the BC during Heinrich Stadial 1 at ∼16 ka indicating massive oceanic heat accumulation in the tropical South Atlantic. Simultaneously, a strongly diminished NBC prevented the release of this excess heat into the northern tropics. The observed magnitude of heat accumulation substantially exceeds numerical model simulations, stressing the need to further scrutinize atmospheric and oceanic heat transport during extreme climatic events.Plain Language Summary: The Atlantic overturning circulation underwent abrupt millennial‐scale perturbations. Such phases of sluggish oceanic circulation resulted in a substantial reduction of northward heat transport. As a consequence, substantial cooling occurred in the Northern Hemisphere and warming occurred in the Southern Hemisphere with severe effects on tropical precipitation. The distribution of heat within the western tropical Atlantic is accomplished by the southward‐flowing BC and the northward‐flowing NBC. By reconstructing SSTs for the interval between 20,000 and 10,000 yr before present, we assess the role of both currents in the interhemispheric heat transport during weak Atlantic overturning. We found that a sluggish overturning circulation resulted in anomalous southward heat transport by the BC in concert with a weak NBC, which lead to a yet undocumented warming of at least 4.6°C in the western tropical South Atlantic. This warming significantly exceeds reconstructions based on numerical simulations. This points to the need to further improve our understanding of changes in the cross‐equatorial oceanic and atmospheric heat transport in response to rapid changes in ocean circulation, in particular as a significant weakening of the Atlantic overturning circulation is predicted in the wake of anthropogenic climate change.Key Points: Brazil Current heat transport coupled to changes in strength of the Atlantic Meridional Overturning Circulation during the last deglacial. Antiphased heat transport by the Brazil and North Brazil Currents during Heinrich Event 1. Warming of western tropical South Atlantic sea surface based on foraminiferal Mg/Ca exceeds numerical model results for Heinrich Event 1.Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) http://dx.doi.org/10.13039/501100001807Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) http://dx.doi.org/10.13039/501100002322MCTI, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) http://dx.doi.org/10.13039/501100003593Focus Program of the Goethe University FrankfurtAlexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/10000515