Mercury in permafrost landscapes in the Norwegian Subarctic – current status and potential for increased release and methylation by permafrost thaw

A vast amount of global mercury is believed to be stored in the Arctic, much of which is frozen in permafrost. Increasing temperatures in the Subarctic, leading to permafrost thaw, alter the global mercury cycle by mobilizing and releasing stored mercury. This is of concern since it allows mercury to spread though air- and waterways. Moreover, mobilized mercury in combination with increased microbial activity can increase the production of methyl mercury (MeHg), a highly potent neurotoxin which readily bioaccumulates throughout food webs. We report current levels of total mercury (HgT) and MeHg for permafrost cores, ambient surface waters, and active layer pore waters across a gradient of sporadic permafrost (peat plateaus) ranging from coastal-mild to inland-cold climate in the northernmost part of continental Europe (Finnmark, Norway). To investigate the effect of microbial activity on mercury methylation, permafrost samples were thawed and subjected to long-term incubation under oxic, and oxic/anoxic conditions, with and without additional native DOC and extraneous C, N, P, S, and Hg additions. Microbial activity was monitored by CO₂ and CH₄ production. Our field samples indicate that the %MeHg of HgT are higher in the outlet of the peat plateau than in the inlet and that streams have a significantly higher %MeHg of HgT than ponds. In contrast, thermokarst ponds (collapsed peat plateaus) have a significantly higher concentration of HgT than streams. In the incubation experiments, presence or absence of oxygen had the largest impact on DOC and dissolved HgT accumulation; soil slurries incubated under anoxic conditions yielded higher concentrations of both DOC and dissolved HgT compared to oxic conditions. Selected results from ongoing experiments will be presented.