Internal cycling of dissolved barium in water column of the Bay of Bengal

Abstract

  • Dissolved barium concentrations in water column of the Bay of Bengal along the 87°E transect (~6°N to ~21°N) 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 ≤5m) followed by a minimum in the depth interval ~50-150m and an increase at greater depth. The barium concentrations in surface waters (depth≤5m) of the Bay of Bengal vary from ~35nmol/kg at the southernmost station 0806 to ~113nmol/kg close to mouth of the Hooghly estuary (station 0816). The Ba data in upper layers (depth ≤100m), excluding the very high Ba at station 0816, generally show a strong and significant inverse correlation with salinity (R2=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 >500m) is controlled dominantly by water mixing as suggested by a very strong and significant inverse correlation with salinity (R2>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. © 2013 Elsevier B.V.
  • Author List

  • Singh SP; Singh SK; Bhushan R
  • Start Page

  • 12
  • End Page

  • 23
  • Volume

  • 154