Collaborative Research: US GEOTRACES GP17-OCE and -ANT Sections: External sources, cycling and processes affecting mercury in the South Pacific and Southern Oceans

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This project will evaluate the concentrations of mercury (Hg) in its various forms in the ocean and atmosphere to examine the factors that control its concentration and chemistry in remote regions of the ocean. The proposed work will examine mercury sources, primarily from the atmosphere, and how mercury is finally removed from ocean waters. Specifically, this study is focused on the South Pacific and Southern Ocean around Antarctica, regions that are remote from human activity and their associated Hg inputs to the biosphere. Human activity has substantially enhanced the amount of Hg in the biosphere and its levels in seafood consumed by humans, and therefore their potential exposure, but its impact in these remote regions is poorly constrained. The measurements will be made during two ocean expeditions that form part of the international GEOTRACES program. GEOTRACES aims to examine the concentrations and distributions of trace elements and their isotopes in the atmosphere, surface and deep oceans of the world. Mercury is a primarily a concern because of its ability to bioaccumulate in marine food chains, primarily in its organic form, methylmercury (MeHg). Elevated levels of MeHg in fish and other marine organisms is a concern for human and wildlife health due to exposure through seafood consumption, and the factors controlling this exposure are not well understood. The proposed work will support three graduate and several undergraduate students across the three participating institutions.During the two expeditions, the research team will collect high resolution data on the concentrations of the primary Hg forms in the atmosphere, the water column, and the sediments, to examine the sources of Hg to these regions and the processes that lead to the conversion of Hg to its more toxic and bioaccumulative form, MeHg. Dissolved and particulate forms of the various Hg species (gaseous elemental Hg, ionic Hg, MeHg and dimethylmercury) will be determined in the atmosphere and throughout the water column using high resolution sampling and novel techniques. Additionally, measurements of Hg stable isotopes in atmospheric and water samples will be used to identify sources (e.g., geogenic or anthropogenic inputs) and delivery mechanisms (e.g., dry or wet deposition, glacial melt) of Hg to these regions. This comprehensive project will leverage Hg speciation and Hg source tracking capabilities to assess the importance of human activity and climate change in altering the amount of Hg and MeHg in these ocean waters, and the resultant levels in marine organisms consumed by humans.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.