Large mid- to late Holocene warming of equatorial Atlantic intermediate waters: The role of the southern branch of the Meridional Overturning Circulation

The ongoing intensification and southward shift of Southern Hemisphere westerly winds (SWWs) are dynamically involved in the downward deep-ocean transfer of excess heat arising from Earth’s radiative forcing imbalances. Yet, the process and extent of this heat transfer are poorly understood, in part due to insufficient data on analogous processes in the geologic record. I show, for the first time, an unprecedented and significant warming (5 ± 0.9 °C) of equatorial Atlantic upper intermediate waters (830 m) during the mid- to late Holocene, a period without significant increases in radiative forcing. I propose that this warming was dynamically linked to enhanced downwelling and advection of warm water equatorward of the wind stress maximum of intensified SWWs. My discovery highlights the important, yet underexplored, role of the wind-driven southern branch of the Meridional Overturning Circulation in redistributing heat to the tropical oceans. More broadly, my observations serve as an analogue, demonstrating the important role tropical upper intermediate waters may play in sequestering excess heat under ongoing global warming.