Presenter: Yipeng He (University of Connecticut)

Description:
Air-sea exchange of mercury (Hg) is an important part of the global Hg cycle, as it affects the input and output of Hg from surface seawater, and prolongs the residence time of Hg in the biosphere. Previous studies, during 3 GEOTRACES expeditions, have provided new insights into the factors controlling the deposition and evasion of inorganic and methylated Hg across the air-sea interface, but the role of ice in modifying Hg cycling has not been adequately studied. In this study, we sampled in the Arctic, from May 20 to June 14, 2021, on the R/V Sikuliaq transiting from the Bering Sea (in open water, from 55°N) into the Chukchi Sea, entering the ice edge around 70°N. The research focus was aimed to improve the understanding of the distribution and air-sea gas exchange and deposition of ionic (Hg^II), elemental (Hg⁰) and methylated Hg (both methylmercury (CH₃Hg) and dimethylmercury ((CH₃)₂Hg)) in open water, within the marginal ice zone and under ice. We used Tekran 1130/1135 instruments for high-resolution measurements of atmospheric Hg speciation (Hg⁰, reactive gaseous Hg (RGHg) and particulate Hg (Hg^P)), which we also compared with a batch method, using the high-volume aerosol sampler with multistage filter packs with ion exchange membranes and glass fiber filters, to assess consistency and comparability between methods for RGHg and Hg^P. Also, wet deposition was collected for total Hg and CH₃Hg, and ice cores were analyzed for Hg species. An automated high resolution continuous equilibrium system was used for measuring dissolved Hg⁰ and (CH₃)₂Hg in surface water and the gas exchange rates were qualified using the radon-222 deficiency in the mixed layer with respect to its parent nuclide radium-226. Results of these measurements will be discussed in terms of the overall air-sea exchange of inorganic Hg and methylated Hg in the open water and marginal ice zone of the Arctic and the importance of gas exchange as a sink for Hg⁰ and methylated Hg.