Abstract
Abstract. The tundra plays a pivotal role in the Arctic mercury (Hg) cycle 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 through 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 central, but remain understudied. Here, we combine Hg stable isotope analysis of Hg(0) in the atmosphere, interstitial snow air, and soil pore air, with Hg(0) flux measurements in a tundra ecosystem at Toolik Field Station in northern Alaska (USA). In the 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 (AMDEs) occurred, with the fast re-emission of Hg(0) after AMDEs 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, ε202Hgvegetationuptake=-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. The combination of Hg stable isotope fingerprints with Hg(0) flux measurements and PBL stability assessment confirmed a dominant role of Hg(0) uptake by vegetation in the terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra.
Highlights
Mercury (Hg) is a high priority pollutant that causes neurodevelopmental deficits in children and cardiovascular disease in adults (Budtz-Jørgensen et al, 2000; Roman et al, 2011)
Arctic populations are exposed to high Hg levels, despite few local anthropogenic Hg emission sources, due to their traditional diet consisting of high trophic level seafood (Sheehan et al, 2014)
We explore the use of novel Hg stable isotope measurements of Hg(0) in interstitial snow air and soil pore air to identify the processes driving tundra Hg(0) deposition
Summary
Mercury (Hg) is a high priority pollutant that causes neurodevelopmental deficits in children and cardiovascular disease in adults (Budtz-Jørgensen et al, 2000; Roman et al, 2011). Jiskra et al.: Terrestrial–atmosphere exchange of Hg(0) in the Arctic tundra cury (GEM or Hg(0)) (Douglas et al, 2012) It has long bpeheontotchhoeumgihctaltlhyatprsopdriuncgetdimberoomxiindeatiroandicoaflsHBg(r0q)odnrisvuernfabcye snow, referred to as “atmospheric mercury depletion events” (AMDEs), leads to enhanced deposition of divalent mercury (Hg(II)) in Arctic regions (Steffen et al, 2008). Such Hg(II) deposition to the snowpack during AMDEs, can be subject to photoreduction and fast re-emission back into the atmosphere, minimising the net load of Hg by AMDEs to snow (Douglas et al, 2012; Johnson et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
