Seasonal variability of meridional heat and salt transport in the interior of South Indian Ocean

The absolute geostrophic currents in the South Indian Ocean were estimated using gridded Argo profiling float data from 2004 to 2023, and the P-vector method. These currents were subsequently used to investigate the spatial patterns and seasonal variability of meridional salt transport (MST) and meridional heat transport (MHT). On an annual basis, the geostrophic components of MST and MHT are directed southward north of 16°S, and reverse to a northward direction south of 16°S. The reversal is primarily attributed to variations in wind stress curl. In contrast, the Ekman components of MST and MHT remain southward throughout the basin. The total interior MST and MHT exhibit southward transport north of 20°S and northward transport south of 20°S, with pronounced maxima near 5°S, 13°S, and 24°S. These maxima are predominantly controlled by the geostrophic component. Meanwhile, the western boundary currents (WBCs), located near 14°S and 24°S. There are display extreme values opposite in sign to those of MST and MHT. This results from the Ekman suction effect and is consistent with Sverdrup balance theory. The seasonal variability of total interior MST and MHT is primarily driven by the Ekman component, exhibits strong agreement with variations in zonal wind stress.