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Abstract

The southern hemisphere westerly winds are projected to increase in the future, altering local ocean hydrography and dynamics. While anomalies of southern hemisphere origin were shown to affect the Atlantic Meridional Overturning Circulation, many details of this connection remain unexplained. Most existing studies are limited by the application of forced ocean models that prevent an atmospheric response to the anomalies, coarse resolution ocean models not able to explicitly simulate mesoscale variability, or a short runtime of experiments. Here we apply a coupled, nested model configuration covering the entire Atlantic at an eddying resolution of 1/10°, to study the inter-hemispheric propagation of anomalies generated by a 30% increase in southern hemisphere wind stress. To obtain statistically more robust results, a 5-member ensemble experiment is conducted with a runtime of 120 years of each member. The South Atlantic response is dominated by a sustained increase of Agulhas Leakage by 3 Sv. Based on a combination of Lagrangian and Eulerian analysis, we show that the propagation of anomalies generated by an increased inflow of Indian Ocean water into the South Atlantic, is a complicated interplay of advection, mixing and local atmospheric responses and thus not simply follows the advective pathways of the leakage water. The North Atlantic overturning responds with a strengthening of 1.5 Sv after approximately 80 years. Anomalous water mass transformation associated with the increased AMOC mainly occurs at the entry into the Nordic Seas, while enhanced sinking is seen along the boundary of the subpolar gyre.