Collaborative Research: Mercury Biogeochemistry on the Continental Shelf and Slope

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Little is known about the sources and cycling of monomethylmercury (MMHg) in the marine environment. Continental shelf and slope sediments appear to be a potential source of MMHg. For this reason, investigators from the University of Connecticut and Wright State University, plan to further our understanding of the biogeochemical processes and reactions affecting MMHg production and mobilization from sediments on the continental shelf and slope of the northwestern Atlantic Ocean. To attain their goal, the scientists propose to carry out field and laboratory experiments during three cruises to this region, one in late summer when sedimentary mercury (Hg) methylation is optimal and the water column is stratified and two cruises in late winter/early spring when the water column in well mixed and MMHg production is reduced. Results would be used to test the following hypotheses: (1) MMHg production in sediments is dependent on the availability of Hg(II) substrate, which is a function of Hg loadings, organic matter, sulfur chemistry, and activity of methylating bacteria; (2) vertical and horizontal distributions of MMHg in the water column would be indicative of in situ sedimentary production in the summer, whereas limited vertical and horizontal segregation would occur in the winter; (3) sulfate reducing bacteria are the principal functional group of microorganisms producing MMHg in sediments on the continental shelf/slope; (4) water column methylation is not a major source of MMHg in continental shelf waters; and (5) MMHg bioaccumulates and biomagnifies in planktonic food webs on the shelf. As regards broader impacts, knowledge on the role of continental shelf/slope sediments in the production of methyl mercury fills an important gap in our current understanding of the biogeochemistry of mercury. One graduate and one undergraduate student from the University of Connecticut and one graduate and one undergraduate student from Wright State University would be supported and trained as part of this project.