Interaction of AMOC and intrinsic multidecadal Southern Ocean variability

Abstract

A strongly-eddying version (0.1° horizontal resolution) of the Parallel Ocean Program (POP) shows pronounced intrinsic multidecadal variability in the Southern Ocean, the so-called Southern Ocean Mode (SOM). This Southern Ocean multidecadal 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 multidecadal 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 multidecadal variability in the Southern Ocean.