Mercury Species Cycling and Fluxes in the Oceanic Water Column

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Mercury (Hg) in the marine environment is constantly moved through a complex biogeochemical cycle which includes the exchange of mercury across the sea-air interface, multiple mercury oxidation state changes, and the formation of numerous bioactive organometallic compounds. Many aspects of the mercury cycle are poorly understood, particularly the formation of mono- and di-methylmercury (MMHg and DMHg, respectively). Methylmercury is of significance in the marine environment, because of its toxicity and ability to bioaccumulate in aquatic food webs. In the proposed research, a scientist from the Woods Hole Oceanographic Institute would carry out speciation, flux, and process measurements to assess the cycling of mercury (Hg) and methylmercury (MMHg) in the water column. The data would be used to test the following hypotheses: (1) methylation occurs throughout the top 100 m of the water column; (2) particulate fluxes of MMHg throughout the water column exceed external inputs indicating net water column production; (3) sinking and suspended particles are sites of enhanced biological methylation; (4) significant photodemethylation occurs in the euphotic zone; (5) sulfate reduction cannot explain biological methylation; and (6) when integrated over the entire water column, pelagic methylation of Hg can provide more than enough MMHg to explain fish accumulation rates.In terms of the broader impacts, the scientist, in collaboration with the Woods Hole Oceanographic Institution Education and Media Relations staff, would publish a graphic presentation on results from the study (i.e., research images, figures, descriptive text, educational activities) in regional and national newspapers. One graduate student would be supported and trained in field and laboratory work as part of this project.