Methylated mercury sources and cycling in the high latitude North Atlantic

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Determining inputs and outputs associated with ocean boundaries (atmosphere, rivers, ice and sediment) is crucial to understanding mercury (Hg) budgets in the ocean. Sediments are an important mercury reservoir, and a location where ionic mercury is converted to methylated mercury (TMeHg). This potential source of Hg to deep ocean waters is poorly constrained. Understanding the role of sediment-water exchange is especially important in the far North Atlantic, around Iceland, as this is a region of deep water formation and these waters are also a conduit for transport of chemicals between the North Atlantic and Arctic Oceans. The team proposes to use an opportunity to join the GEOTRACES Process Cruise (GApr16) in July/August 2021 to investigate Hg and TMeHg biogeochemical cycling in this region. This project will support training of a postdoctoral scholar and one graduate student, as well as undergraduates at UConn and all will gain research experience from this study. This research is formulated around the hypotheses that: H1) Benthic sediments are a net source of TMeHg to the deep water in this region and will dominate the TMeHg supply into the North Atlantic; H2) While sediment may release inorganic Hg due to various biochemical and physical processes, sediments will be a net sink for THg; and H3) Overall, the seas around Iceland are a net sink for total Hg but a source for TMeHg to the deep North Atlantic Ocean, with the sources being primarily from shelf- and sediment-derived TMeHg inputs. The GApr16 expedition provides a unique synergy and opportunity given the other measurements (radiochemical flux estimates and trace element distributions) that will be made on the cruise. This project will examine the distributions of total Hg (THg) and TMeHg throughout the water column as well as the sediment and porewaters to examine the role of ocean processes including water advection, sediment resuspension-redeposition, and dissolved exchange across the sediment-water interface on Hg cycling. With this holistic dataset and data from prior studies in subpolar regions, the team will develop a regional box model and construct a comprehensive Hg budget for the seas between the North Atlantic and Arctic Oceans, elucidating the role of sediments for the different Hg species.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.