Ocean salinity plays a crucial role in the upper ocean stratification and local marine ecosystem. This study reveals that the ocean salinity presents notable decadal variability in upper 200 meters over the southeast Indian Ocean (SEIO). Previous studies linked this salinity variability with precipitation anomalies over the Indo-Pacific region modulated by the tropical Pacific decadal variability. Here we conduct a quantitative salinity budget analysis and show that, in contrast, the oceanic advection, especially the anomalous meridional advection, plays a dominant role in modulating the decadal variation of the SEIO salinity. The anomalous meridional advection is mainly associated with a zonal dipole pattern of sea level anomaly (SLA) in the South Indian Ocean (SIO). Specifically, positive and negative SLAs in the east and west of the SIO correspond to anomalous southward oceanic current, which transports much fresher seawater from the warm pool into the SEIO and thereby decreases the local upper ocean salinity, and vice versa. Further investigation reveals that the local anomalous wind stress curl associated with tropical Pacific forcing is responsible for generating the sea level dipole pattern via oceanic Rossby wave adjustment on decadal timescale. This study highlights that the local ocean-atmosphere dynamical adjustment is critical for the decadal salinity variability in the SEIO.
 

Salinity,Indian Ocean,Ocean-Atmosphere Dynamics