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- Title
Insights from mercury stable isotopes on terrestrial – atmosphere exchange of Hg(0) in the Arctic tundra.
- Authors
Jiskra, Martin; Sonke, Jeroen E.; Agnan, Yannick; Helmig, Detlev; Obrist, Daniel
- Abstract
The tundra plays a pivotal role in the Arctic mercury (Hg) cycling by storing atmospheric Hg deposition and shuttling it to the Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg deposition to the tundra occurs by gaseous elemental mercury (GEM or Hg(0)) uptake by vegetation and soils. Processes controlling land – atmosphere exchange of Hg(0) in the Arctic tundra are therefore central, but remain understudied. Here, we combine Hg stable isotope analysis of Hg(0) in the atmosphere, interstitial snow and soil pore air, with Hg(0) flux measurements in a tundra ecosystem at Toolik field station in northern Alaska (USA). In dark winter months, planetary boundary layer (PBL) conditions and Hg(0) concentrations were generally stable throughout the day and small Hg(0) net deposition occurred. In spring, halogen-induced atmospheric mercury depletion events (AMDE's) occurred, with fast re-emission of Hg(0) after AMDE's resulting in net emission fluxes of Hg(0). During the short snow-free growing season in summer, vegetation uptake of atmospheric Hg(0) enhanced atmospheric Hg(0) net deposition to the Arctic tundra. At night, when PBL conditions were stable, ecosystem uptake of atmospheric Hg(0) led to a depletion of atmospheric Hg(0). The night time decline of atmospheric Hg(0) was concomitant with a depletion of lighter Hg(0) isotopes in the atmospheric Hg pool. The enrichment factor, ε202Hg = −4.2 ‰ ± 1.0 ‰ was consistent with the preferential uptake of light Hg(0) isotopes by vegetation. Hg(0) flux measurements indicated a partial re-emission of Hg(0) during daytime, when solar radiation was strongest. Hg(0) concentrations in soil pore air were depleted relative to atmospheric Hg(0) concentrations, concomitant with an enrichment of lighter Hg(0) isotopes in the soil pore air (ε202Hgsoilair-atmosphere = −1.00 ‰ (±0.25 ‰) and E199Hgsoilair-atmosphere = 0.07 ‰ (±0.04 ‰)). These first Hg stable isotope measurements of Hg(0) in soil pore air are consistent with the fractionation previously observed during Hg(0) oxidation by natural humic acids suggesting abiotic oxidation as a cause for observed soil Hg(0) uptake.
- Subjects
ALASKA; ATMOSPHERIC mercury; MERCURY isotopes; STABLE isotopes; ATMOSPHERIC boundary layer; STABLE isotope analysis; TUNDRAS
- Publication
Biogeosciences Discussions, 2019, p1
- ISSN
1810-6277
- Publication type
Article
- DOI
10.5194/bg-2019-225