Eric Webb, Biology Department WHOI
Funded by NSF Chemical Oceanography 2005-2008
The 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. This project applies state-of-the-art geochemical and molecular biological techniques to address trace metal biogeochemical questions in the South Atlantic. A 27-day 2007 cruise to the south Atlantic is currently being planned 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. A combination of geochemical and biological/molecular analyses will be made across an oligotrophic-upwelling transition to examine how changing metal regimes affect the physiology and growth of the important primary producers Trichodesmium and Synechococcus. Funding from NSF Chemical Oceanography.