Mercury in the Arctic tundra snowpack: temporal and spatial concentration patterns and trace gas exchanges

In the Arctic, the snowpack forms the major interface between atmospheric and terrestrial cycling of mercury (Hg), a global pollutant. We investigated Hg dynamics in an interior Arctic tundra snowpack in northern Alaska during two winter seasons. Using a snow tower system to monitor Hg trace gas exchange, we observed consistent concentration declines of gaseous elemental Hg (inline-formula $M1inlinescrollmathmlchem{\mathrm{normal\; Hg}}_{\mathrm{normal\; gas}}^{\mathrm{normal\; 0}}$ 29pt17ptsvg-formulamathimg9f004b3f39b1a9679b6cb048ad889d20 tc-12-1939-2018-ie00001.svg29pt17pttc-12-1939-2018-ie00001.png ) from the atmosphere to the snowpack to soils. The snowpack itself was unlikely a direct sink for atmospheric inline-formula $M2inlinescrollmathmlchem{\mathrm{normal\; Hg}}_{\mathrm{normal\; gas}}^{\mathrm{normal\; 0}}$ 29pt17ptsvg-formulamathimge37fdc46c52ee47ded1a1e120b546093 tc-12-1939-2018-ie00002.svg29pt17pttc-12-1939-2018-ie00002.png . In addition, there was no evidence of photochemical reduction of inline-formulaHg^II to inline-formula $M4inlinescrollmathmlchem{\mathrm{normal\; Hg}}_{\mathrm{normal\; gas}}^{\mathrm{normal\; 0}}$ 29pt17ptsvg-formulamathimgc284e9320edd3ffa12326016d932bb0e tc-12-1939-2018-ie00003.svg29pt17pttc-12-1939-2018-ie00003.png in the tundra snowpack, with the exception of short periods during late winter in the uppermost snow layer. The patterns in this interior Arctic snowpack thus differ substantially from observations in Arctic coastal and temperate snowpacks. We consistently measured low concentrations of both total and dissolved Hg in snowpack throughout the two seasons. Chemical tracers showed that Hg was mainly associated with local mineral dust and regional marine sea spray inputs. Mass balance calculations show that the snowpack represents a small reservoir of Hg, resulting in low inputs during snowmelt. Taken together, the results from this study suggest that interior Arctic snowpacks are negligible sources of Hg to the Arctic.