Spatial variations of DMS, DMSP and phytoplankton in the Bay of Bengal during the summer monsoon 2001

Abstract

Data on the distribution of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in relation to phytoplankton abundance in different oceanic environments is important to understand the biogeochemistry of DMS, which plays an important role in the radiation balance of the earth. During the summer monsoon of 2001 measurements were made for DMS and DMSP_t (total DMSP) together with related biological parameters in the Bay of Bengal. Both DMS and DMSP_t were restricted to the upper 40 m of the water column. Diatoms accounted for more than 95% of the phytoplankton and were the major contributors to the DMS and DMSP_t pool. The mean concentration of DMS in the upper 40 m was observed to be around 1.8 ± 1.9 nM in the study area, while DMSP_t concentrations varied between 0.7 nM and 40.2 nM with a mean of 10.4 ± 8.2 nM. The observed lower DMSP_t in the northern Bay in spite of higher mean primary productivity, chlorophyll a and phytoplankton cell counts seemed to result from grazing. Though salinity divides the Bay into different biogeochemical provinces there is no relation between salinity and DMS or DMSPt. On the other hand DMS was linearly related to chlorophyll a:phaeopigments ratio. The results suggest the need for deeper insight into the role of diatoms in the biogeochemical cycling of DMS.