Ocean dynamical processes underlying sea-level change and variabilityin the Southern Ocean

The Southern Ocean (SO) plays a crucial role in the global climate system by absorbing heat and carbon dioxide from the atmosphere. Understanding sea level changes and associated physical processes in the SO can provide valuable insights into how the ocean contributes to regulating Earth’s climate. Ocean dynamical processes are crucial for redistributing ocean heat and mass, thereby significantly influencing sea level change in the SO and globally. Here we investigate the mechanisms of thermal and ocean mass (ocean bottom pressure, OBP) variations, which are two important components of sea level variability. Observations show that since the 1950s, the subsurface South Hemishphere has been rapidly warming in the south and cooling in the north. A theoretical analysis and ocean model perturbation experiments indicates that the subsurface cooling is mainly attributed to pure heaving caused by wind stress change. In the SO, OBP variations explain most of large-scale sea level variations at seasonal-to-decadal time scales. Regional OBP variations are mainly driven by surface wind and regulated by the bottom topography. Strong OBP signals are located in the deep basins where closed planetary vorticity isolines present. At interannual time scales, OBP patterns in the SO are closely associated with El Niño-Southern Oscillation and Southern Annular Mode, which can indicate interannual variability of Antarctic Circumpolar Current transport to a great extent.