Role of Extreme Indian Ocean Dipole in Regulating Three-Dimensional Freshwater Content in the Southeast Indian Ocean

The tropical Southeast Indian Ocean (SEIO) is a key area linking the global freshwater and heat exchanges. The Indian Ocean Dipole (IOD) fundamentally modulates the Indian Ocean circulation and thus regulates the basin-wide freshwater balance. However, our knowledge of this effect remains limited. Using observational-based data sets, this study suggests that extreme positive IOD events have notable signatures on the three-dimensional freshwater content of the SEIO, leading to the vertically opposite salinity anomalies in the surface and subsurface layers. The wind changes led to the northwestward extension of the South Equatorial Current and intensified Sumatra-Java upwelling. The changing horizontal and vertical currents jointly result in the complicated salinity anomalies. The Equatorial Undercurrent serves as the conduit for water exchange between the equator and the SEIO. This work highlights a strong coupling between the equatorial circulation and the three-dimensional freshwater inventory of the SEIO within the framework of the IOD.