Strontium concentration and isotopic data for subsurface flowing groundwaters of the Ganges-Brahmaputra (G-B) delta in the Bengal Basin demonstrate that this is a potentially significant source of strontium to the oceans, equal in magnitude to the dissolved strontium concentration carried to the oceans by the G-B river waters. The strontium concentrations of groundwaters are higher by a factor of about 10 than typical G-B river waters and they have similar Sr-87/Sr-86 ratio to the river waters. These new data suggest that the present contribution of the G-B system to the rise in Sr-87/Sr-86 ratio in seawater is higher by at least a factor of 2 to 5 than the average over the past 40 million years.