Dissolved barium concentrations in water column of the Bay of Bengal along the 87¡ãE transect (~ 6¡ãN to ~ 21¡ãN) have been measured to track the dispersion of its large influx from the Ganga-Brahmaputra river system and the outflow to the equatorial Indian Ocean. A typical barium concentration-depth profile shows relatively higher Ba concentrations in surface waters (depth ¡Ü 5 m) followed by a minimum in the depth interval ~ 50-150 m and an increase at greater depth. The barium concentrations in surface waters (depth ¡Ü 5 m) of the Bay of Bengal vary from ~ 35 nmol/kg at the southernmost station 0806 to ~ 113 nmol/kg close to mouth of the Hooghly estuary (station 0816). The Ba data in upper layers (depth ¡Ü 100 m), excluding the very high Ba at station 0816, generally show a strong and significant inverse correlation with salinity (R
2 = 0.75; P < 0.0001). This indicates the southward flow of dissolved Ba from the Ganga-Brahmaputra river system that also includes its contributions by particle release and submarine groundwater discharge. The subsurface Ba minimum found in this study are ubiquitous and most probably a result of Ba uptake on settling particulates. On the other hand, the Ba concentrations in deep waters (depth > 500 m) is controlled dominantly by water mixing as suggested by a very strong and significant inverse correlation with salinity (R
2 > 0.95; P < 0.0001). Exceptions to this conservative behavior are the ¡°hot-spots¡± of dissolved Ba in bottom waters, which are probably resulted by the dissolution of sediments at and/or below the sediment-water interface.
Attempts were made to budget the Ba abundance in the Bay of Bengal using a two box model approach; surface (top ~ 100 m) and deep waters (below ~ 100 m). Under the steady state the annual Ba influx from the Ganga-Brahmaputra river system seems to be balanced through its removal via sinking particulates as a result there is no lateral outflow of dissolved Ba from the Ganga-Brahmaputra to the equatorial Indian Ocean through top ~ 100 m of the Bay of Bengal. Most of this sinking particulate Ba (~ 95 % ) is regenerated again in the lower box, preferentially in the intermediate waters ~ 100-500 m. Therefore, frequently ventilated intermediate waters of the Bay of Bengal, receiving a large input of dissolved Ba through particle remineralization can be a significant source of dissolved Ba to the Indian Ocean.
