Chapter 7 Monsoonal Impacts on the Biological Pump in the Northern Indian Ocean as Discerned from Sediment Trap Experiments

Abstract

Sediment trap data obtained from the western Arabian Sea have been used to characterize monsoon-induced environmental conditions driving the export of material from the surface ocean into the deep sea. The ratio between particulate organic carbon (POC) and particulate inorganic carbon (PIC) of exported material was taken as an indicator of the impact of the biological pump on the oceanic uptake of atmospheric CO 2 . The results indicate that the biological pump is most effective in nitrogen-limited systems in which the availability of dissolved silica allows diatoms to play an important but not necessarily a dominant role within the plankton community. Accordingly, the biological pump can even be more efficient in oligotrophic systems than in eutrophic upwelling areas. A comparison with results obtained from other sediment trap experiments in the northern Indian Ocean reveals the highest annual mean POC/PIC ratios in the northern Bay of Bengal. The high POC/PIC ratios have been attributed to the impact of river discharges on the plankton community structure. The climate anomaly El Niño Southern Oscillation (ENSO) seems to influence the efficiency of the biological pump in the northern Bay of Bengal via its impact on the precipitation rates and consequently on the river discharge.