THE ROLE OF THE GANGES-BRAHMAPUTRA MIXING ZONE IN SUPPLYING BARIUM AND RA-226 TO THE BAY OF BENGAL

The Ganges-Brahmaputra river system is ranked fourth among world river s as a source of freshwater to the oceans and is believed to supply mo re sediment to the ocean than any other; 1.5 X 10(12) kg/yr (MILLIMAN and MEADE, 1983). Barium and Ra-226 are typically enriched in waters w here sediment-laden rivers enter the ocean. As such, the Ganges-Brahma putra is likely to produce globally significant barium and Ra-226 flux es to the ocean. Water samples for barium and Ra-226 were collected wi thin four major channels of the Ganges-Brahmaputra mixing zone during a period of low sediment and freshwater discharge. The data suggest th at, in addition to suspended sediments supplied directly from rivers, river sediments deposited during high discharge in mangroves and on is lands are desorbing barium and Ra-226 to seawater. The release of bari um and Ra-226 from these sediment deposits is out-of-phase with the di rect supply of sediments from the rivers. Estimates of the annual flux es of barium and Ra-226 from the Ganges-Brahmaputra mixing zone were a lso derived. The fluxes of barium and Ra-226 are 5.3 X 10(8) mol bariu m/yr and 9.5 X 10(14) dpm radium/yr. The first silicate and phosphate mixing profiles for this system are reported.