Production and consumption of dimethylsulfide (DMS) in North Atlantic waters

Production and consumption of dimethylsulfide (DMS) were studied in surface waters of the northwest Atlantic between latitude 32° and 45° N during May 1998. The kinetics of DMS production by the whole planktonic community were studied in short-term (3 h) experiments using additions of dissolved dimethylsulfoniopropionate (DMSPd) (0 to 3000 nM). Measurements of DMS production and DMSPd consumption showed that the DMS production rate increased in direct proportion to the concentration of added DMSPd. This rate relationship did not saturate, suggesting acclimation of the microbial community to DMSPd concentrations much higher than the average for bulk seawater. Longer-term experiments were performed in which DMSPd consumption and DMS production were measured over 48 to 60 h. The DMSPd consumption rate decreased as the concentration of DMSPd decreased during the incubations. However, the DMS production rate was initially constant for the first 36 h. When DMSPd concentrations fell below 50 nM, DMS production stopped, even though DMSPd consumption continued. A possible explanation is that DMSP cleavage might dominate the total DMSP consumption at high DMSPd concentrations while DMSP demethylation and other processes dominate at low DMSPd concentrations. DMS consumption was measured both directly and by using the DMS consumption inhibitors dimethyl disulfide (DMDS) and methyl butyl ether (MBE). DMS consumption was generally undetectable except at 1 station dominated by a dense population of the DMSP-producing phytoplankton Chrysochromulina sp. and where ambient DMS concentrations were high. This suggests that the potential for DMS consumption is highest where ambient DMS levels are elevated. Pooling results from these experiments with earlier results from more northerly waters revealed an inverse exponential relationship (r2 = 0.75, p < 0.0001) between the potential rate constant and chlorophyll a standing stock across a wide area of the Northwest Atlantic. This finding is potentially useful for the development of DMS production models.