9530378 Kiene This three year study will increase our fundamental understanding of the role played by dissolved DMSP in the biogeochemistry of reduced sulfur in surface seawater. The specific objectives of the project are 1) to test whether the dissolved DMSP pool measured by conventional filtration techniques is truly dissolved; 2) to measure the kinetics of uptake for dissolved DMSP by natural microbial assemblages using 14C and 35S DMSP and to determine in situ turnover rates for DMSP (d); 3) to measure the sulfur products formed during DMSP degradation and to determine how the branching ratio between the lyase (DMS forming) and demethylation (methanethiol forming) pathways vary in different waters; 4) to determine mechanisms of methanethiol production in aerobic seawater and finally, to determine the loss kinetics of MeSH in seawater and the factors which affect these. The work will be carried out using primarily coastal and shelf water samples from the Northern Gulf of Mexico, but 2 oceanographic cruises are planned to provide complementary information from warm oligotrophic and cool mesotrophic ocean waters. The resulting data should greatly advance our knowledge of how DMSP is processed in the sea and how it impacts the chemistry of surface waters through production of important reduced sulfur compounds like DMS and methanethiol.
