Estimation of Fresh Water and Salt Transports in the Northern Indian Ocean Using Aquarius and Model Simulations

Abstract:

The Northern Indian Ocean presents a unique dipolar Sea Surface Salinity (SSS) structure with the salty Arabian Sea (AS) on the west and the fresher Bay of Bengal (BoB) on the east. By using a combination of observational data, reanalyses, and model studies, the salinity structure of this dichotomous yet interconnected region is quantified. At the surface, the largest driver of salinity interseasonal variability is caused by the monsoonal winds and their ability to transport volume between the two water masses. Time-depth profiles reveal a rich vertical salinity profile. The AS presents with a mild salinity inversion, with salty waters above fresher ones for the majority of each annual cycle. This vertical gradient is approximately 1 psu between the surface and 200m depth. In the BoB the opposite occurs, where larger volumes of precipitation and river runoff create a lens of freshwater from the surface to approximately 50m depth year around. Salt and freshwater fluxes at the surface show a strong zonal component between the two basins along Sri Lanka twice a year. Within the basins, meridional fluxes dominate especially along the coastal regions where the EICC and WICC flow. Meridional depth-integrated salt, freshwater, and volume transports along a slice of each basin at 6°N reveal the approximate time its takes for each basin to return to equilibrium after strong transports during each monsoonal seasons advect salt and/or freshwater into or out of each respective region.