Redox transformations of mercury in an Arctic snowpack at springtime

Abstract

We investigated the springtime temporal dynamics of both total mercury (Hg) and gaseous Hg in snowpacks from the High Arctic. In situ incubation experiments of snow samples indicated that the production of volatile mercury in snow (VMS) was photomediated and occurred in the first 3 cm of snow. The newly produced VMS (consisting mainly of elemental Hg) was partly oxidized back to Hg(II) when light intensity declined or in the absence of UV radiation, probably through a chain of reactions involving photo-induced radicals and organic compounds in the surface snow. During a 2 week monitoring of total Hg in surface snow, we observed a sharp increase in total Hg concentrations, reaching levels 11 times higher than background concentrations, likely as a result of an atmospheric mercury depletion event. Stratigraphic depth profiles indicated that this increase was restricted to the first 2 cm of the snowpack. Total Hg levels subsequently decreased by 92%, reaching background concentrations within 2 days after this event. The photoproduction rate of VMS calculated on the basis of this episode could account for subsequent daily loss of total Hg from the surface of the snowpack.

The fate of mercury in Arctic terrestrial and aquatic ecosystems, a review

“…Resolute, Canada (Poulain et al [293] ) Alert, Canada (St Louis et al [218] ) Barrow, Alaska (Johnson et al [248] ) to be particularly strong in the northernmost area. [258,259] This pattern is not due to higher wet deposition along the coast.…”

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

“…The lack of consistent statistically significant associations between major ions and Hg diss across the entire snowpack depth (Table 2a) further suggests that initial snowfall Hg content was maintained and largely unaltered after deposition, with no clear accumulation or depletion zones as found in other snowpacks (Ferrari et al, 2005;Poulain et al, 2004;Steffen et al, 2014). We found a small relative enrichment of alkaline earth elements in snowpack samples compared to surface snow, which indicates some additional contributions of local mineral dust, yet this did not result in a measurable increase in snowpack Hg levels.…”

“…This was a period when AMDEs occurred at this site, as evident by depletions of atmospheric Hg 0 gas with formation and deposition of oxidized atmospheric Hg II Van Dam et al, 2013). Surface snow Hg concentration enhancements during AMDEs are commonly reported in polar regions, with at times Hg concentration enhancements up to 100 times the base concentration in the Arctic (Lalonde et al, 2002;Lindberg et al, 1998;Poulain et al, 2004;Steffen et al, 2002). The presence of AMDEs generally results in increased deposition of Hg to snow and ice surfaces, yet such additional deposition often is short-lived due to the photochemical re-emission of Hg 0 gas (Kirk et al, 2006).…”

“…2). An alternative possibility may be that our sampling setup (between 5 and 7 cm below the surface during the three main AMDEs) may have limited our ability to detect and observe photo-reduction processes that may occur only in the upper few centimeters of the snowpack surface (King and Simpson, 2001;Poulain et al, 2004). However, using the same measurement system, Hg 0 gas concentration enhancements in temperate snowpacks were large (up to 8 ng m −3 ) and detectable up to a depth of > 90 cm from the snowpack surface (Fig.…”

“…To further visualize the relationships between analytes, we plotted a ternary diagram using three endmembers according to Garbarino et al (2002), Krnavek et al (2012), Poulain et al (2004), andBarrie (2002) (Fig. 8).…”