Controls of dimethyl sulphide in the Bay of Bengal during BOBMEX-Pilot cruise 1998

The air-sea exchange is one of the main mechanisms maintaining the abundanc es of trace gases in the atmosphere. Some of these, such as carbon dioxide and dimethyl sulphide (DMS), will have a bearing on the atmospheric heat bu dget. While the former facilitates the trapping of radiation (greenhouse ef fect) the latter works in the opposite direction through reflectance of rad iation back into space by sulphate aerosols that form from oxidation of DMS in atmosphere. Here we report on the first measurements made on DMS in the Bay of Bengal and the factors regulating its abundance in seawater. Phytop lankton alone does not seem to control the extent of DMS concentrations. We find that changes in salinity could effectively regulate the extent of DMS P production by marine phytoplankton. In addition, we provide the first eve r evidence to the occurrence of DMS precursor, DMSP, in marine aerosols col lected in the boundary layer. This suggests that the marine aerosol transpo rt of DMSP will supplement DMS gaseous evasion in maintaining the atmospher ic non-sea salt sulphur budget.