| Summary: | High mercury (Hg) levels have been measured in fish in Kusawa Lake (KL), a subalpine, partly glacier-fed lake situated in the southwestern Yukon, Canada, but it is presently unknown where this Hg comes from. One possible source may be atmospheric deposition of Hg in snow and subsequent release by melt into the lake. In this study, the amounts of total Hg (THg) deposited in sampled alpine snow and glacial ice from the KL catchment area were measured in order to quantify this input. Samples of snow and glacial firn were also collected from another site (DIV) located on an icefield in the central St. Elias Mountains, to investigate possible spatial variations in Hg deposition as a function of altitude or distance from the Pacific Ocean. The samples were analysed for THg, major ions (incl. Ca2+, K+, Mg2+, Na+, NH4+, Cl-, and SO42-) and stable O/H isotopes. These analyses were performed to obtain clues on the sources/conditions of atmospheric Hg deposition in snow, and identify possible relationships between THg and other snow chemical properties. This is the first study to provide data on Hg deposition in snow from this vast mountain region. Measured THg concentrations ranged from 0.24 to 6.17 ng L-1 in snow and from 0.20 to 1.57 ng L-1 in glacial ice, which are comparable values to those measured at other sites in the North American subarctic and Arctic. The calculated net accumulation rates of THg varied from 0.57 to 0.71 µg m-2 a-1, which are relatively high compared to rates reported for the eastern Canadian Arctic. This could indicate that wet deposition in snowfall may be particularly important in promoting THg accumulation in mountains of the subarctic Yukon, when compared to the polar desert of the High Arctic. The stable O/H isotope data indicate that snowfall in the study area is primarily derived from moisture of marine origin, with only minor continental contributions, which points to the nearby Gulf of Alaska as the main source. The major ion analyses suggest a local dust source containing Ca2+ and ...
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