oligotrophic seawater

The rates and concentration dependence of microbial dimethylsulfide (DMS) and dimethylsulfoniopro-pionate (DMSP) cycling were assessed in Vineyard Sound, Massachusetts, and the Sargasso Sea. Net rates of dissolved DMSP loss, DMS production from DMSP, and DMS consumption were measured at ambient and near-ambient substrate levels. Turnover times of dissolved DMSP, based on loss rates, were short, usually ranging from 1.5 d to several hours. However, the specific process of DMSP cleavage to form DMS accounted for only a portion of total DMSP turnover. Short-term variability obscured possible regional or seasonal trends in these data. Dissolved DMSP removal and cleavage exhibited saturable kinetics in spring in Vineyard Sound and in winter in the Sargasso Sea. In fall and spring in the Sargasso Sea, where dissolved DMSP levels ranged from 2 to 9 nM, DMSP cleavage did not saturate at DMSP levels as high as 1 PM. Kinetic parameters of DMSP uptake appeared to increase with proximity to summer, as did the proportion of DMSP uptake resulting in DMS production. The tertiary sulfonium compound dimethylsulfonio-propionate (DMSP), synthesized by marine algae, is a ubiquitous component of particulate matter in seawate