| Summary: | Mercury (Hg) concentrations in lichens and mosses can be used as surrogates for atmospheric Hg deposition to continental surfaces. In this study, we collected and analyzed Hg concentrations ( n = 334) and isotopic composition ( n = 67) of epiphytic tree lichens and terricolous lichens and mosses from remote locations across the Eurasian Arctic and sub-Arctic (50 to 72° N, 30 to 180° E). The total Hg (THg) concentrations ranged from 13 to 7700 ng g –1 . Epiphytic tree lichens had significantly higher median THg levels (243 ng g –1 ) than terricolous lichens (35 ng g –1 ) and mosses (74 ng g –1 ). THg is substantially higher in both tree lichens and terricolous lichens near the Arctic Ocean shore and up to 300 km inland. The combined δ 202 Hg, Δ 199 Hg, and Δ 200 Hg signatures suggest that the elevated coastal Hg levels are delivered by marine air masses rich in gaseous and particulate-oxidized Hg II forms, such as HgBr 2 . Similar to other vegetation Hg isotope studies, inland terricolous lichen and moss Δ 200 Hg are near zero, indicating a dominant (63%) atmospheric Hg 0 origin followed by Hg II wet and dry deposition. Inland tree lichens carry a more positive Δ 200 Hg of 0.15‰, similar to the atmospheric Hg II end-member, suggesting that they preferentially accumulate Hg II wet and dry deposition compared to colocated terricolous lichens. Mosses from the European sub-Arctic show a low δ 202 Hg of −3.1‰, which we speculate to result from regional soil Hg 0 emissions that are recaptured by mosses. Overall, the Hg isotope variability of mosses and lichens reveals latitudinal gradients in Hg deposition pathways and identifies preferential Hg 0 or Hg II uptake.
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