Abstract The Agulhas Return Current (ARC) transports warm, salty subtropical waters eastward into the South Indian Ocean, where it meets cold, fresh Southern Ocean waters to the south, creating strong meridional surface temperature and salinity gradients. Analysis of Argo data reveals coherent interannual variations in surface temperature (~ 1 °C) and salinity (~ 0.2 g/kg) downstream of the ARC from 2004 to 2023. Further analysis indicates that these variations are primarily driven by large-scale westerly wind fluctuations associated with the Southern Annular Mode (SAM). During positive SAM phases, the southward shift of westerlies weakens wind speed over the ARC region. This reduces northward Ekman advection of cold, fresh water, resulting in surface warming. Conversely, during negative SAM phases, the northward movement of westerlies enhances wind speed, enhancing Ekman advection and cooling the surface. These findings underscore the dominant role of meridional Ekman advection in driving hydrographic properties variability in the ARC region.
Hong et al. (Sat,) studied this question.