Interactions of Cobalt and Iron with in situ Cyanobacterial Physiology in the South Atlantic and the Benguela Upwelling Region

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ABSTRACTOCE-0452883The geochemistries of dissolved cobalt and iron in the oceanic water column share several characteristics such as extremely low concentrations, redox chemistry, low solubility, and utilization as micronutrients by marine microbes. Iron has been the subject of considerable research focus in recent years due to its role in limiting phytoplankton productivity in oceanic and coastal upwelling environments. Cobalt has been much less studied, but recent data shows it may be important in influencing primary productivity or phytoplankton community composition in certain geographical areas. In this project, researchers at the Woods Hole Oceanographic Institution will apply state-of-the-art geochemical and molecular biological techniques to study the biogeochemical cycling of these two trace metals in the South Atlantic. There will be 27-day 2007 cruise to the south Atlantic to study cobalt and iron biogeochemistry focusing on four major hypotheses: 1) Large fluxes of labile cobalt are associated with upwelling systems even in Aeolian dominated environments. 2) Cobalt and phosphate show correlations in (and only in) surface waters due to micronutrient utilization and rapid remineralization. The slope of the correlation is dependent on the chemical speciation of cobalt. 3) The absence of Trichodesmium populations in the subtropical and tropical South Atlantic is caused by iron limitation. 4) Based on work from the California and Peru Upwelling regimes, primary productivity in the Benguela upwelling regime off of South West Africa may be iron limited or iron-cobalt colimited. Broader Impacts - In addition to increasing our understanding of the biogeochemistry of two important trace metals (Fe and Co) in a region with little data coverage, this project will support the development of a Co stress assay that will be disseminated to the oceanographic community. This project will conclude the thesis work of one graduate student and initiate the work of another. These students will partake in analytical measurements and molecular studies. Three undergraduate research fellows will also work on molecular studies during summer internships. Priority will be given to students from underrepresented groups at small colleges that typically do not offer hands-on research opportunities.