Interaction of AMOC and Intrinsic Multi-decadal Southern Ocean Variability

Abstract. A strongly-eddying version (0.1° horizontal resolution) of the Parallel Ocean Program (POP) shows pronounced intrinsic multi-decadal variability in the Southern Ocean, the so-called Southern Ocean Mode (SOM). This Southern Ocean multi-decadal variability is induced by eddy-mean flow interaction and deep convection. The SOM variability propagates through the global ocean and influences the strength of the Atlantic Meridional Overturning Circulation (AMOC) by about 3 Sv. The opposite role on how the AMOC influences the SOM is unknown, as this requires long simulations and preferably with different AMOC background states. Here, using the results of a simulated AMOC collapse in the strongly-eddying ocean-only POP version, we find that the amplitude of the SOM is substantially reduced following an AMOC collapse. Associated changes in horizontal and vertical density variations lead to a weakening of the Antarctic Circumpolar Current transport and a shutdown of deep convection in the Weddell Sea. In contrast, these changes promote deep convection events and the emergence of multi-decadal variability in the Pacific sector of the Southern Ocean. A mechanical energy budget analysis shows both a reduction in the wind input and a disruption of the phase difference between wind work and the potential to kinetic energy conversion. The results highlight the strong connection between the AMOC and intrinsic multi-decadal variability in the Southern Ocean.