Collaborative Research: Soil-Snow-Atmosphere Exchanges of Mercury in the Interior Arctic Tundra

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The goal of this project is to characterize soil-snow-atmosphere dynamics of mercury (Hg) in the snow-dominated Arctic tundra. Chemical conversion of Hg in snowpack from non-volatile forms to gaseous elemental mercury (GEM) can lead to substantial degassing of Hg from snow, thereby reducing the impact of atmospheric deposition. Contrary to the GEM chemistry seen in the midlatitude snowpack, preliminary observations from Toolik Lake, on the north slope of the Brooks Range, Alaska, provide evidence that photochemical GEM formation and degassing are suppressed in tundra snow and that for much of the winter, interstitial GEM is actually converted into non-volatile Hg. These patterns result in extended periods when interstitial snowpack air is depleted in GEM. If confirmed, this chemistry would likely signify a net transfer of atmospheric GEM to snow or underlying soils, thereby increasing Hg deposition to tundra ecosystems. Proposed project objectives are to investigate (1) the frequency and underlying processes that determine GEM depletion and formation in arctic snowpack and tundra soils; (2) the degree to which GEM dynamics cause vertical Hg exchange between soils, snow, and the atmosphere; and (3) how these processes provide additional sources − or sinks − of Hg via atmosphere-surface transfer and snowmelt input. GEM concentrations in soils, snow, and air, as well as vertical exchanges, will be characterized at Toolik Field Station. Measurements will be made by means of a snow-sampling manifold system allowing for fully automated and continuous all-winter measurements of trace gases at multiple depths in the undisturbed snowpack and the atmosphere. These experiments will be supplemented by flux chamber measurements to assess the contribution of the underlying tundra soils. Other trace gas observations, and chemical characterization of soil, snow, melt water, and soil water will be incorporated to assess the environmental and biogeochemical controls on GEM dynamics and the Hg budget. This proposed research will leverage ongoing LTER and NEON projects at the Toolik Field station, providing linkages between in-snow processes, tundra soil and freshwater biogeochemical cycling, pollution import into the Arctic, and ecosystem processes. The project will directly involve high school, undergraduate, graduate students, and a postdoctoral scientist. It will expand an existing partnership with local high school chemistry classes through research presentations in classrooms, laboratory tours, and data analyses using study results. Dissemination to the scientific community will be accomplished through peer-reviewed publications and conference presentations, and by communication with U.S. and international regulatory agencies. The general public will be reached through news releases, institutional publications, open house events, and a web site. Data will be archived at the National Snow and Ice Data Center at the University of Colorado for distribution to the national and international polar research community.