Biogeochemistry of dimethylsulfide in the South China Sea

The distribution of dimethylsulfide (DMS) was studied in surface seawater a nd vertical profiles at nineteen stations in the Nansha Islands sea area of the South China Sea. The concentrations of DMS in surface-layer (0-1 m) se awater vary from 64 to 140 ng S/L with high values found in the productive regions, in agreement with the horizontal distribution of chlorophyll a. Th e vertical profiles of DMS show a single peak shape with maximum concentrat ions occurring at depths between 30-75 m. The DMS concentrations are correl ated with chlorophyll a levels both in the upper 20 m of seawater as well a s in vertical profiles. A clear diel variation in DMS concentration is obse rved at the 50-m water layer at a fixed station with the highest DMS concen tration found in the late afternoon. The DMS concentrations are associated with environmental factors such as seawater temperature, dissolved O-2 and nutrient contents. Although DMS is correlated to chlorophyll a, the phytopl ankton species is a major factor responsible for the obviously higher DMS c oncentration than expected from the phytoplankton biomass in this sea area. The sea-to-air flux of DMS from this sea area is calculated to be 7.6 mu m ol m(-2) d(-1).