Respiration rates in subsurface waters of the northern Indian Ocean: Evidence for low decomposition rates of organic matter within the water column in the Bay of Bengal

Depth profiles of activity of the respiratory electron transport system (ETS) have been generated at several locations in the northern Indian Ocean. The results reveal much lower ETS activities in subsurface waters of the Bay of Bengal than those measured in the Arabian Sea. Lower respiration rates in the Bay of Bengal are corroborated by the much weaker north-south gradients in oxygen and total carbon dioxide. These are, however, in conflict; with the higher sinking fluxes of organic carbon measured with sediment traps. The observations support the view that particulate organic matter may undergo a lesser degree of oxidation in the water column through its incorporation into rapidly sinking matter, perhaps as a result of the massive inputs of terrigenous matter in the Bay of Bengal. The differential respiration rates may cause changes in the distribution of suspended particulate matter and may also explain why the Bay of Bengal is not a site of water-column denitrification in spite of an apparently slower renewal of the intermediate waters as compared to the Arabian Sea.