Linking Ocean Forcing and Atmospheric Interactions to Atlantic Multidecadal Variability in MPI‐ESM1.2

We investigate how ocean‐driven multidecadal sea surface temperature (SST) variations force the atmosphere to jointly set the pace of Atlantic multidecadal variability (AMV). We generate periodic low‐frequency Atlantic Meridional Overturning Circulation oscillations by implementing time‐dependent deep‐ocean‐density restoring in MPI‐ESM1.2 to explicitly identify variations driven by Atlantic Meridional Overturning Circulation without any perturbation at the ocean‐atmosphere interface. We show in a coupled experiment that ocean heat convergence variations generate positive SST anomalies, turbulent heat release, and low sea level pressure in the subpolar North Atlantic (NA) and vice versa. The SST signal is communicated to the tropical NA by wind‐evaporative‐SST feedbacks and to the North‐East Atlantic by enhanced northward atmospheric heat transport. Such atmospheric feedbacks and the characteristic AMV‐SST pattern are synchronized to the multidecadal time scale of ocean circulation changes by air‐sea heat exchange. This coupled ocean‐atmosphere mechanism is consistent with observed features of AMV and thus supports a key role of ocean dynamics in driving the AMV. Plain Language Summary The Atlantic multidecadal variability is an observed fluctuation of North Atlantic ocean surface temperatures on multidecadal time scales. It strongly influences climatic conditions over the surrounding continents in the North Atlantic region as well as in remote areas. Therefore, it is essential to understand the underlying mechanisms, particularly in regard to predict the Atlantic multidecadal variability itself and its impacts. However, the respective contributions from fast atmospheric forcing and slow ocean variations to such long‐term climate variations have been controversially discussed. Here, by artificially increasing the variability of ocean dynamics in a climate model, we improve the mechanistic understanding of the role of ocean dynamics in driving the Atlantic Multidecadal Variability. We believe our results suggest a major role for ocean dynamics. A climate model reacts to an increase in ocean circulation by accumulating heat in the subpolar North Atlantic. Associated atmospheric responses to ocean forcing contribute to heat redistribution to form the basin‐wide sea surface temperature pattern of Atlantic Multidecadal Variability. None of these fundamental imprints of ocean dynamics can be reproduced by a model experiment that excludes ocean dynamics (slab‐ocea