Jeroen Sonke , Vladimir Shevchenko, Jonathan Prunier, Ruoyu Sun, Anatoly Prokushkin, Oleg Pokrovsky

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 and isotopic composition of epiphytic tree lichens and terricolous lichens and mosses from remote locations across the Eurasian Arctic and sub-Arctic (50 to 72o N, 30 to 180o E). 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, up to 300 km inland. The combined δ202Hg, Δ199Hg, and Δ200Hg signatures suggest that the elevated coastal Hg levels are delivered by marine air masses rich in gaseous and particulate oxidized HgII forms, such as HgBr2. Similar to other vegetation Hg isotope studies, inland terricolous lichen and moss Δ200Hg are near-zero, indicating a dominant (63%) atmospheric Hg0 origin, followed by HgII wet and dry deposition. Inland tree lichens carry more positive Δ200Hg of 0.15‰, similar to the atmospheric HgII end-member, suggesting they preferentially accumulate HgII wet and dry deposition compared to co-located terricolous lichens. Mosses from the European sub-Arctic show low δ202Hg of -3.1‰, which we speculate to result from regional soil Hg0 emissions that are re-captured by mosses. Overall, the Hg isotope variability of mosses and lichens reveal latitudinal gradients in Hg deposition pathways and identify preferential Hg0 or HgII uptake.