An explorative study of mercury export from a thawing palsa mire

Thawing of permafrost and a subsequent accelerated loss of mercury from the soil constitute a possible threat to the quality of high-latitude surface waters. In this paper we estimate the export of mercury generated by a thawing palsa mire in northern Sweden, by assessing net mercury storage changes along thermokarst erosion gradients. Lower mercury inventories in inundated hummocks covered by water (≤3.1 mg Hg m^-2) than in noneroding hummocks (between 5.5 and 8 mg Hg m^-2) suggests a release of ∼40-95% of the mercury pool from hummock peat experiencing subsidence and submerging. The documented expansion of submerged areas between 1970 and 2000 in the studied system indicates that permafrost thawing has initiated a mobilization of 34 to 50 g mercury. We stress the need of further assessing the fate of this mercury because the size of the mobilized mercury pool might be highly significant for subarctic surface waters.