The Role of Tidal Mixing in Shaping Early Eocene Deep Ocean Circulation and Oxygenation

Diapycnal mixing in the ocean interior is largely fueled by internal tides. Mixing schemes thatrepresent the breaking of internal tides are now routinely included in ocean and earth system models applied tothe modern and future. However, this is more rarely the case in climate simulations of deep‐time intervals of theEarth, for which estimates of the energy dissipated by the tides are not always available. Here, we present andanalyze two IPSL‐CM5A2 earth system model simulations of the Early Eocene made under the framework ofDeepMIP. One simulation includes mixing by locally dissipating internal tides, while the other does not. Weshow how the inclusion of tidal mixing alters the shape of the deep ocean circulation, and thereby of large‐scalebiogeochemical patterns, in particular oxygen distributions. In our simulations, the absence of tidal mixing leadsto a relatively stagnant and poorly ventilated deep ocean in the North Atlantic, which promotes the developmentof a basin‐scale pool of oxygen‐deficient waters, at the limit of complete anoxia. The absence of large‐scaleanoxic records in the deep ocean after the Cretaceous anoxic events suggests that such an ocean state most likelydid not occur at any time across the Paleogene. This highlights how crucial it is for climate models applied to thedeep‐time to integrate the spatial variability of tidally driven mixing as well as the potential of usingbiogeochemical models to exclude aberrant dynamical model states