Proposal Abstract:
Dimethylsulfide (DMS) is 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. Our proposed multi-investigator field and laboratory research will examine the biogeochemistry of water column and sedimentary DMS/DMSP (dimethylsulfoniopropionate), and the role of associated compounds (e.g. dimethylsulfoxide, dimethylated polysulfides) in Lake Bonney. Lake Bonney is a relatively simple (no turbulence, no grazers and little atmospheric exchange) aquatic system and therefore provides a highly tractable environment for investigating microbially mediated cycling of biogenic sulfur. Preliminary data suggest that maximum levels of DMS precursors occur in the deep-chlorophyll layer of the lake, a zone dominated by cryptophyte algae. In addition, DMS concentrations in the aphotic waters of Lake Bonney are among the highest recorded in a natural aquatic system. These observations indicate that precursors produced by trophogenic zone phytoplankton sink to the aphotic waters and sediments where they are microbially decomposed to DMS and other sulfur compounds. The proposed research will define the sources and sinks of DMS and associated compounds and relate them to overall ecosystem function. A model of biogeochemical transformations of organo-sulfur compounds in Lake Bonney will be developed.