Impact of Mid‐Pliocene Boundary Conditions on the Atlantic Meridional Overturning Circulation (AMOC)

Abstract We use the coupled atmosphere‐ocean model MIROC4m to investigate the effect of mid‐Pliocene boundary conditions on the Atlantic Meridional Overturning Circulation (AMOC), studying the impact of increased CO 2 , reduced ice sheets and altered orography and vegetation. We find that a higher CO 2 concentration and smaller ice sheets both weaken the AMOC with respect to the pre‐industrial. The stronger mid‐Pliocene AMOC is therefore a consequence of mid‐Pliocene orography and vegetation, where the closed Arctic gateways are responsible for approximately 80% of the AMOC strengthening. The main mechanism for mid‐Pliocene AMOC strengthening is reduced transport of freshwater from the Arctic into the North Atlantic, enhanced by a decrease of surface freshwater flux into the high‐latitude North Atlantic.