A revised pan-Arctic permafrost soil Hg pool based on Western Siberian peat Hg and carbon observations Academic Article uri icon

abstract

  • Natural and anthropogenic mercury (Hg) emissions are sequestered in terrestrial soils over short, annual to long, millennial timescales before Hg mobilization and run-off impact wetland and coastal ocean ecosystems. Recent studies have used Hg-to-carbon (C) ratios (R/HgC's) measured in Alaskan permafrost mineral and peat soils together with a northern circumpolar permafrost soil carbon inventory to estimate that these soils contain large amounts of Hg (between 184 and 755Gg) in the upper 1m. However, measurements of R/HgC on Siberian permafrost peatlands are largely missing, leaving the size of the estimated northern soil Hg budget and its fate under Arctic warming scenarios uncertain. Here we present Hg and carbon data for six peat cores down to mineral horizons at 1.5-4m depth, across a 1700km latitudinal (56 to 67g N) permafrost gradient in the Western Siberian Lowland (WSL). Mercury concentrations increase from south to north in all soil horizons, reflecting a higher stability of sequestered Hg with respect to re-emission. The R/HgC in the WSL peat horizons decreases with depth, from 0.38Gg Pg-1 in the active layer to 0.23Gg Pg-1 in continuously frozen peat of the WSL. We estimate the Hg pool (0-1m) in the permafrost-affected part of the WSL peatlands to be 9.3±2.7Gg. We review and estimate pan-Arctic organic and mineral soil R/HgC to be 0.19 and 0.63Gg Pg-1, respectively, and use a soil carbon budget to revise the pan-Arctic permafrost soil Hg pool to be 72Gg (39-91Gg; interquartile range, IQR) in the upper 30cm, 240Gg (110-336Gg) in the upper 1m, and 597Gg (384-750Gg) in the upper 3m. Using the same R/HgC approach, we revise the upper 30cm of the global soil Hg pool to contain 1086Gg of Hg (852-1265Gg, IQR), of which 7% (72Gg) resides in northern permafrost soils. Additional soil and river studies in eastern and northern Siberia are needed to lower the uncertainty on these estimates and assess the timing of Hg release to the atmosphere and rivers. © 2020 Copernicus GmbH. All rights reserved.

publication date

  • 2020-06-18