Oxygenated deep waters fed early Atlantic overturning circulation upon Antarctic glaciation

The Atlantic meridional overturning circulation (AMOC) exerts a major control on the global distribution of heat, dissolved oxygen and carbon in the ocean. Yet the timing and cause of the inception of this system and its evolution since the start of the Cenozoic Era 65 million years ago (Ma) remain highly uncertain. Here we present records of microbial source indicators based on glycerol dialkyl glycerol tetraether distributions from the Cenozoic Northwest Atlantic Ocean (~43‒18 Ma) and use them to infer changes in AMOC-driven deep-ocean oxygenation. At this location, oxygenation is strongly controlled by southwestward Deep Western Boundary Current transport of newly formed deep waters that feed AMOC. Our Eocene data show short-term high-amplitude variability and an overall decrease in oxygenation of AMOC-feed waters culminating in especially poor ventilation between ~36.5 and ~34 Ma. AMOC-feed waters became better oxygenated upon initiation of Antarctic glaciation at the Eocene/Oligocene transition, ~34 Ma, and were consistently well ventilated from ~30 Ma. Our findings indicate a close association between the inception of Antarctic glaciation and AMOC and suggest that both vertical mixing and wind-driven upwelling in the Southern Ocean were key to fully establishing AMOC as an agent of deep-ocean ventilation.