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Research Objectives:
Areas of the Southern Ocean have spectacular blooms of phytoplankton during the austral spring and early summer. One of the dominant species, the haptophyte Phaeocystis antarctica, is a prolific producer of the organic sulfur compound dimethylsulfoniopropionate (DMSP). Phaeocystis blooms are associated with some of the world's highest concentrations of DMSP and its volatile degradation product, dimethylsulfide (DMS). Sulfur in the form of DMS, is transferred from the oceans to the atmosphere and can affect the chemistry of precipitation and influence cloud properties and possibly climate. DMSP and DMS are also quantitatively significant components of the carbon, sulfur, and energy flows in many marine food webs, although very little information is available on these processes in high-latitude systems.
This project will investigate the biogeochemical cycling of DMSP and its degradation product, DMS, in the southern Ross Sea during the height of the seasonal phytoplankton bloom (Dec-Jan). The primary goals will to be quantify how light and nutrients influence the production and loss terms for DMS and to examine the role of DMSP in the carbon and sulfur cycles of the Ross Sea. Investigators will focus on the effects of solar radiation (including UV) on phytoplankton and bacterioplankton processes related to the DMSP/DMS cycles, as well as purely photochemical processes such as DMS photooxidation. Team members will sample from two to six hydrographic stations, carrying out extensive multi-day experiments involving deck-board incubations and in situ incubations with a free floating drifter array. Data collection will include concentration measurements of dimethyl sulfoxide (DMSO), DMSP and DMS using gas chromatography, and cycling rates using 35S-labeled radiotracers.
Project team members will join the R/V Nathaniel B. Palmer cruise NBP04-departing Lyttelton New Zealand and arriving at McMurdo Station. They will sample waters with different bloom stages and different mixing regimes using a CTC (conductivity temperature depth) rosette. Water samples will be incubated on deck, in the laboratory and over the side with a free-floating drifter for about 8 to 12 hours. Water samples will be processed onboard the vessel.
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