Thermocline temperature and seawater δ18O reconstruction during Termination II and the Last Interglacial for the core GL-1090, in the western South Atlantic

Thermocline temperature and seawater d18O reconstruction during Termination II and the Last Interglacial for the core GL-1090, in the western South Atlantic.

The intensification of the Agulhas Leakage (AL) during glacial Terminations has long been proposed as a necessary mechanism to return the Atlantic Meridional Overturning Circulation (AMOC) to its interglacial mode. However, the lack of records showing the downstream evolution of the AL signal and the substantial temporal differences between AL intensification and resumption of deep-water convection cast doubt on the importance of this mechanism to the overturning. Here, we analyze a combination of new and previously published data related to Mg/Ca-derived temperatures and ice volume-corrected seawater δ18O records (δ18OIVC-SW as a proxy for ocean relative salinity changes) that demonstrate the propagation of the AL signal via surface and thermocline waters to the western South Atlantic (Santos Basin) during glacial Termination II and the early Last Interglacial. The saline AL waters were temporally stored in the upper subtropical South Atlantic until they were abruptly released in two steps into the North Atlantic via the surface and thermocline at ca. 129 and 123 ka BP, respectively. Within age uncertainties, these two steps are coeval with the resumption of convection in the Labrador and Nordic Seas during the Last Interglacial. We propose a mechanism whereby both an active AL and a favorable ocean-atmosphere configuration in the tropical Atlantic were required to allow the flux of AL waters into the North Atlantic, where they then contributed to enhancing the AMOC during the Last Interglacial period. Our results provide a framework that connects AL strengthening to the AMOC intensifications that follow glaciations.