The early opening of the Equatorial Atlantic gateway and the evolution of Cretaceous peak warming

The Cretaceous opening of the Equatorial Atlantic gateway (EAG) is considered a driver of major changes in global oceanography, carbon cycling, and climate. However, the early stages of EAG opening are poorly understood. We present seawater Nd-isotope, bulk geochemical, and micropaleontological data from two South Atlantic drill cores that constrain the onset of shallow (<500 m) and intermediate (<~1000 m) water mass exchange across the EAG to 113 Ma and 107 Ma, respectively. Deep water mass exchange (>2000 m) was enabled by at least ca. 100 Ma, as much as 10 m.y. earlier than previously estimated. In response to EAG opening, deep-water ventilation in the South Atlantic, North Atlantic, and Tethys basins intensified, thereby triggering basin-scale reductions in organic carbon burial. We propose that the consequent drop in carbon sequestration in concert with increased atmospheric CO₂ fluxes from subduction zones acted as major amplifiers of global warming that culminated in peak greenhouse conditions during the mid-Cretaceous.