Award: OPP-1854454

Mercury (Hg) is a pervasive global pollutant known for its toxicity to humans, primarily in its most toxic and bioaccumulative form of methylmercury (MeHg). Its atmospheric concentration has been substantially enhanced by human-related emissions from coal burning and other industrial activities, and from the use of Hg in small-scale artisanal goldmining. Anthropogenic emissions have increased wet and dry Hg deposition to land and the surface ocean 5 to 10-fold, and especially for the Arctic Ocean. The increased MeHg in the Arctic foodweb has led to elevated levels of MeHg in fish and marine mammals, and heightened exposure of the people who consume these marine foods. While previous atmospheric Hg deposition studies and oceanic measurements in this region have investigated both (HgT) and methylated Hg cycling, the air-sea exchange and sediment-water exchange of these Hg forms has been less investigated and are not well constrained. Additionally, in the Arctic Ocean climate change has led to dramatic changes in seasonal ice cover and therefore to the relative amount of exchange of chemicals between the ocean and atmosphere. To examine this exchange further and quantify the controlling processes for Hg, we made both atmospheric Hg speciation measurements (gaseous, rain and aerosol) of total Hg (HgT) and methylmercury (MeHg) and conducted high-resolution surface seawater dimethylmercury (DMeHg) and elemental Hg (Hg0) measurements during an Arctic cruise (May/June 2021) from Dutch Harbor to the Chukchi Sea and back to Seward, AK. In addition to air and surface water measurements for Hg, ancillary variables were measured and rates of exchange of gases with the atmosphere quantified using radon, a radioactive inert gas, by our collaborators on the cruise. The primary focus was to examine the air-sea exchange of Hg species and the role of sea ice presence in influencing the exchange, but these objectives could not be achieved without also examining the concentrations and distributions of Hg forms in surface snow, sea ice and in the sediments. Studies onboard examined the rates of transformation of Hg species and also the rate of exchange of chemicals across the sediment-water interface. Water column samples were collected throughout the water column to understand the sources, cycling and transformations (e.g. methylation and demethylation) of Hg species, and how they were impacted by other variables, especially in the shallower dynamic regions and at the open water-sea ice interface. The underway sampling demonstrated that DMeHg is not ubiquitous in the surface waters of the region and is only present in high concentrations under very specific conditions. The Hg0 concentrations were not as high as expected under the ice suggesting that its rate of formation in the absence of light is less that previously expected. The atmospheric data demonstrated the formation of reactive gaseous Hg over the sea ice and this is the first concrete demonstration of this phenomenon, and also that the Hg associated with aerosols was mostly associated with large, likely sea salt, aerosols, as precited by models. The sediments are an important source of Hg and MeHg to the water column and have an impact on Hg dynamics in the region. Overall, our results provided a clearer understanding of Hg cycling in the region and the role of the ocean as a source of atmospheric Hg through gas evasion, and the impact of ice cover on Hg speciation in the upper waters of the Arctic Ocean. The project provided research experience for three graduate students who participated in the cruise and has led to the publication of several research manuscripts, as well as a MS and PhD thesis to date. Presentations have also been made at national and international meetings by the studys participants. While demonstrating the complexity of assessing the impact of this global pollutant on ecosystems and human well-being in the Arctic and elsewhere, this study has provided important information for managers and regulators and will assist modelers examining regional and global mercury cycling. Finally, the information collected will provide data for the current assessment of the effectiveness of the United Nations Environment Programmes Minamata Convention on Mercury, which is designed to reduce Hg emissions and releases globally, and the levels of Hg in the biosphere. The treaty came into force in 2013 so the evaluation is examining the impact of the first 10 years of the conventions activities. The project Principal Investigator and a former student are involved in this analysis of the Convention. Last Modified: 01/31/2024 Submitted by: RobertPMason