Characterizing near-surface salinity variability in the northern Bay of Bengal and its potential drivers during extreme freshening years of the 2011–2019 period

Northern Bay of Bengal (BoB) receives a significant amount of freshwater, from precipitation and river discharge, which makes it comparatively low saline, specifically during August/September. However, the factors that determine the dispersal of this freshwater within the BoB remain relatively less addressed. Analysis of the near-surface salinity data from a moored buoy located in the northern BoB during 2011–2019 supplemented with satellite and model data showed prominent interannual variability viz. time of occurrence, persistence and magnitude of freshening. The surface salinity exhibit significant lowering during 2011, 2015 and 2017 with unique prolonged freshening in 2017. The offshore advection of low salinity water is initiated with sustained low wind stress further favoured by existing surface circulation and mesoscale eddies contributing to the unique characteristics. In addition, the maximum freshening observed in 2011 coincides with positive Indian Ocean Dipole event, whereas that of the prolonged freshening in 2017 is favored with anomalously low wind stress.