Dimethylsulfide (DMS) has been shown to be the dominant volatile sulfur compound emitted from the ocean and may represent up to 90% of the sea to air biogenic sulfur flux. It has been hypothesized that cloud formation caused by condensation nuclei associated with products of DMS oxidation can directly counteract warming effects of anthropogenically produced CO2. Despite the global importance of DMS and related sulfonium compounds, and the significant role of aquatic systems in DMS production (particularly in south polar regions), the sources and sinks of DMS and associated sulfonium compounds remain equivocal.

During past research on the water column of Lake Bonney, a permanently ice covered lake in the McMurdo Dry Valleys, we have consistently detected the odor of DMS in the aphotic waters of the lake where temperature is about -5°C and salinity is about 4 times that of seawater. Quantitative measurements showed that DMS in these aphotic waters are among the highest recorded in a natural aquatic system (>450nM). Such water column levels typically occur in the ocean in association with intense algal blooms dominated by members of the certain phytoplankton genera. Unlike the typical situation, the DMS maximum we measured in Lake Bonney coincided with a region in the water column virtually devoid of phytoplankton biomass and activity. Maximum levels of particulate dimethylsulfoniopropionate (DMSPp), a known precurser of DMS, occurred in the deep-chlorophyll layer of the lake, a zone dominated by cryptophyte algae. These observations lead us to propose that DMSPp produced by trophogenic zone phytoplankton sinks to the deep, aphotic water and sediments where it is microbially decomposed to DMS and possible other sulfur compounds.

Our multi-investigator field and laboratory research will examine the biogeochemistry of water column and sedimentary DMS/DMSP, in addition to the role of associated compounds (e.g. dimethylsulfoxide, dimethylated polysulfides) in a relatively simple (e.g. no turbulence, no grazers, and little atmospheric exchange) system. The relative simplicity of the Lake Bonney environment provides a highly tractable situation for investigating the microbial mediated cycling of biogenic sulfur. Results from our study will help define the biogeochemistry of organo-sulfur compounds in nature and produce information that can be used to understand microbial processes in the sea. Our results will also be of direct relevance to the NSF funded LTER and LExEN projects now underway in the McMurdo Dry Valleys. Specifically, we will define sources and sinks of DMS and associated compounds, and relate them to overall ecosystem function. A final product of our research will be a systems model of the biogeochemical transformations of these organo-sulfur compounds in Lake Bonney.