Benthic foraminiferal Mg/Ca ratios and mixed planktic foraminiferal Nd isotopes of sediment cores recovered during METEOR cruise M78/1

Antarctic Intermediate Water (AAIW) is an important conduit for nutrients to reach the nutrient-poor low-latitude ocean areas. In the Atlantic, it forms part of the return path of the Atlantic Meridional Overturning Circulation (AMOC). Despite the importance of AAIW, little is known about variations in its composition and signature during the prominent AMOC and climate changes of the last deglaciation. Here, we reconstruct benthic foraminiferal Mg/Ca-based intermediate water temperatures (IWTMg/Ca) and intermediate water neodymium (Nd) isotope compositions at sub-millennial resolution from unique sediment cores located at the northern tip of modern AAIW extent in the tropical W-Atlantic (core M78/235-1, 850 water depth, and core M78/222-9, 1018 m water depth). Our data indicate a pronounced warming of AAIW in the tropical W-Atlantic during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). We argue that these warming events were induced by major AMOC perturbations resulting in the pronounced accumulation of heat in the surface Southern Ocean. Combined with published results, our data suggest the subsequent uptake of Southern Ocean heat by AAIW and its rapid northward transfer to the tropical W-Atlantic. Hence, the rapid deglacial northern climate perturbations directly controlled the AAIW heat budget in the tropical W-Atlantic after a detour via the Southern Ocean. We speculate that the ocean heat redistribution via AAIW effectively dampened Southern Hemisphere warming during the deglaciation and may therefore have been a crucial player in the climate seesaw mechanisms between the two hemispheres.