Investigating the influence of interannual wind forcing on the South Equatorial Current and spread of Indonesian Throughflow waters

The Indonesian Throughflow (ITF) transports relatively warm, and fresh waters into the Indian Ocean. These waters traverse the basin embedded within the westward-flowing South Equatorial Current (SEC), strongly influencing heat content, vertical stratification, and form a key link in the global exchange of water masses. Although the seasonal pathways of the SEC are well established, the interannual variability remains less understood. In this study, we use model sensitivity simulations to analyze the mechanisms driving variability in the SEC and subsequent spread of ITF waters within the South Indian Ocean. The analysis suggests that wind forcing over the South Indian Ocean basin is largely responsible for variability in the route of the SEC. The variability in these local winds appear to be translated through Rossby wave propagation leading to a basin scale adjustment; this is evidenced by anomalous routes of the SEC that either form large northwestward meanders or follow a zonal westward route further south. These anomalous routes appear to strongly impact salinity within thermocline depths across the region. This analysis provides insights into the variability of the SEC and spread of ITF waters that enhance our ability to anticipate potential downstream impacts related to stratification and connectivity in the South Indian Ocean.