The Impacts of an AMOC Collapse on Southern Ocean Multidecadal Variability

The interaction between ocean eddies and the large-scale ocean circulation results in a pronounced multidecadal variability in the Southern Ocean, with a dominant periodicity of 40-50 years, referred to as the Southern Ocean Mode (SOM) (Le Bars et al., GRL, 2016). The SOM plays a critical role in modifying the ocean heat content, thereby influencing both sea-ice extent and basal melt around Antarctica. Additionally, this multidecadal variability propagates northward into the Atlantic Ocean, modulating the Atlantic Meridional Overturning Circulation (AMOC) strength. The AMOC is one of the most prominent climate tipping elements on Earth and can potentially collapse as a consequence of surface freshwater input in the North Atlantic. Here, we investigate the impacts of an AMOC collapse on multidecadal variability in the Southern Ocean using the results of the first modeled AMOC collapse in a high-resolution and strongly eddying (0.1° horizontal resolution) ocean-only model, the Parallel Ocean Program (POP). Our findings indicate that the magnitude of the SOM reduces significantly following an AMOC collapse. An analysis of the SOM variability before and after an AMOC collapse allows us to study the role of background stratification, baroclinic instability, and convection in shaping the SOM.