MERCURY AND MAJOR ELEMENT SNOW AND SNOWMELT CHEMISTRY AT AN ALASKAN ARCTIC COASTAL SITE

The net deposition of atmospheric Hg to the Arctic is the product of multiple processes that can be associated either with deposition or loss of Hg. Mercury is deposited to snow and ice in Polar Regions during the late winter and early spring. This deposition is driven by photochemical reactions that involve reactive halogens and snow and ice surfaces as part of so-called Atmospheric Mercury Depletion Events (“AMDEs”). Inputs include the total amount of Hg deposited onto snow and ice during springtime AMDEs plus Hg added by other atmospheric deposition processes to the snow pack, land, or fresh water (i.e. wet or dry deposition not associated with AMDEs). Outputs are gaseous Hg(0) re-emitted from snow and ice surfaces due to microbial or photochemical reduction of Hg(II) and the evasion of dissolved gaseous mercury from freshwater or seawater. Snow melt is a major aspect of the seasonal transition from winter to spring/summer since up to 75% of the yearly surface water discharge in Arctic watersheds is comprised of snow melt. Mercury and other atmospherically deposited metals in Arctic snow are likely mobilized during metamorphism, melt and surface runoff in the spring. This presentation will include an overview of AMDE physical and chemical processes in the Arctic and a summary of results from 6 years of trace metal, major ion, and stable isotope analyses of snow, sea ice, and melt waters near Barrow, Alaska. Our study results suggest there is an “ionic pulse” of major elements and mercury from the snow pack during the initial stages of snow melt. We believe much of this Hg is deposited in late winter as part of AMDEs.