Biogeochemistry of the Bay of Bengal: physical, chemical and primary productivity characteristics of the central and western Bay of Bengal during summer monsoon 2001

Reliable data on biological characteristics from the Bay of Bengal are elusive. In this paper, we present results on physics, chemistry and biology simultaneously measured during the summer monsoon, 2001, from open-ocean and coastal areas of the region. It was characterised by cold-core eddies and thermocline oscillations. However, these were capped by prevalent a low-salinity upper regime that prevented surfacing of nutrients. The river plume effects were evident from the low salinity values observed in the surface layers of the upper bay, but this did not bring in significant amounts of nutrients. The chlorophyll a concentrations (10–20 mg m−2) and primary productivity values (40–502 mg C m−2 d−1) were low and not up to Arabian Sea values for the same season. Diatoms dominated the phytoplankton community and contained more genera compared to the Arabian Sea. Large colonies of the tunicate Pyrosoma, which occurred at the surface as well as mid-depths, could have consumed a part of the phytoplankton population. These results, albeit limited, have implications on the biogeochemistry of the region.