High fluxes of radium and barium from the mouth of the Ganges-Brahmaputra river during low river discharge suggest a large groundwater source

The annual flux of sediment from the Ganges-Brahmaputra River is among the highest in the world. The desorption of Ra-226 and Ba from this sediment produces a major point source of Ra-226 and Ba input to the ocean. Highest Ra-226 and Ba fluxes are expected to occur during high river flow (June-September) when most of the sediment is discharged. Surprisingly, during low discharge of the Ganges-Brahmaputra River, fluxes of Ra-226 and Ba to the northern Bay of Bengal are comparable to expected river-derived fluxes during peak river discharge. A large non-riverine source of Ra and Ba is required to explain the high fluxes during low river discharge. I suggest that this source is submarine discharge of groundwater containing high concentrations of Ra-226 and Ba. Total annual fluxes of Ra-226 and Ba to the ocean from this system an significantly greater than estimated previously. (C) 1997 Elsevier Science B.V.