Impacts of Topography and Atmospheric Forcing on the Zonal SST Variation in the Southern Ocean

Abstract Sea surface temperature (SST) around Antarctica displays a distinct zonal variation, with high values in the Pacific sector and low values in the Atlantic and Indian sectors. This zonal variation of SST is an important index to characterize the thermal and dynamical differences between different ocean basins, and it has been weakened in recent decades, raising concerns about the controlling factors of the climatological mean SST. Previous studies have linked zonal SST variations to the topography-steered Antarctic Circumpolar Current (ACC) and analyzed the associated heat budget terms in sophisticated data-assimilative ocean models, but the respective roles of Antarctic topography and zonal variations in air–sea heat and momentum fluxes on the SST structure remain to be investigated. In this study, numerical experiments were conducted to separate the effects due to topographic control and zonal variations of heat and momentum fluxes. As demonstrated by these numerical experiments, although the topographic control is the dominant factor determining the zonal variations of the ACC and SST, the zonal variations of air–sea heat and momentum fluxes also have comparable effects to the topographic control in influencing the magnitude of zonal SST variations, with opposite effects. Specifically, the zonal variation in the net air–sea heat flux acts to inhibit the zonal SST variation, while the zonal variation in the wind stress acts to enhance the zonal SST variation. This suggests a possible link between changes in zonal SST variation and westerly winds in recent decades.