Phosphate removal through adsorption on suspended matter in the Bay of Bengal: Possible implications to primary production

Abstract

Low primary production in the Bay of Bengal (BoB) could not be explained as this region receives nutrients from atmospheric deposition, rivers, eddies, and mixing due to depression/cyclones. In addition to nutrients, BoB also receives significant amount of suspended particulate matter (SPM) from the major rivers and their concentrations are in an order of magnitude higher than elsewhere in the open ocean region. Here we show that the removal of phosphorus (P) through adsorption on SPM may be a potential mechanism to decrease in primary production in the northern BoB. Significant fraction of P removal (5-50% of total dissolved inorganic phosphate) in association with SPM was observed in the BoB. The magnitude of removal of P through SPM is linearly related with dissolved inorganic phosphate (DIP), particulate organic carbon (POC) in the water column suggesting that P is removed in association with organic matter. The fraction of P removed from that of DIP showed inverse relation with salinity, and linear relation with SPM concentration suggesting that SPM brought by river discharge removed P from the water column. The P removed by SPM in the mixed layer showed inverse relation with mixed layer integrated primary production in the open sea region but its impact is negligible in the coastal waters. The laboratory experiment by measuring primary production in the presence of different quantities of SPM concentrations confirmed decrease in primary production due to removal of phosphate in the BoB.