Characterization and quantification of biosphere-climate interactions is critical to understanding and predicting climate change. The feedback between biosphere and climate is mediated to a significant degree by the dynamics of radiatively active, biogenic trace gases. Quantifying the dynamics and air-sea exchange of these gases is a major objective of the new I.G.B.P. (International Biosphere-Geosphere Program) program SOLAS, the Surface Ocean Lower Atmosphere Study. The biogenic production and subsequent ventilation of dimethyl sulfide (DMS) is climatically important as it has been postulated that DMS and its atmospheric oxidation products are part of a cloud albedo feedback mechanism which links global biosphere and climate. Progress in understanding biosphere-climate interactions is hampered largely because it is difficult to accurately constrain, parameterize, or validate models. There are simply not enough field observations collected in conjunction with the appropriate ancillary data to assess forcing factors in a mechanistic and predictive way. This project is designed to accomplish those goals. The study will reinitiate and expand a DMS time-series conducted in the early 1990's in the Sargasso Sea, part of the oligotrophic North Atlantic subtropical gyre. The previous time series (Dacey et al., 1998) is the only long-term time series for DMS in the deep ocean.

This new project will generate a robust new time-series data set of DMS dynamics that includes critical pool and rate measurements vital to assess not only the long-term variability of the DMS pool (and major associated compounds) but also the short-term dynamics of DMS and dimethylsulfoniopropionate (DMSP - the main precursor of DMS in ocean water) that underlie this long-term variability. By revisiting the same oceanic gyre, this new study will represent the first long term comparison of DMS and DMSP concentrations anywhere in deep ocean. The measurements made in the first study will be repeated now, more than a decade later, in addition to a broader suite of measurements to address new hypotheses measurements made in the first study to address new hypotheses about the factors controlling DMS dynamics. Monthly and process measurements will include key turnover dynamics of DMS and dissolved DMSP in surface waters using new 35S tracer methods, aqueous DMSO concentrations, and diel variations in atmospheric DMS during the BATS cruises. This comprehensive timeseries and process sampling scheme will allow us to mechanistically describe the controls on key DMS, DMSP, and DMSO turnover rates and will serve as a unique validation data set for past and future modeling efforts.