Anthropogenic mercury (Hg) emissions have driven marked increases in Arctic Hg levels, which are now being impacted by regional warming, with uncertain ecological consequences. This Review presents a comprehensive assessment of the present-day total Hg mass balance in the Arctic. Over 98% of atmospheric Hg is emitted outside the region and is transported to the Arctic via long-range air and ocean transport. Around two thirds of this Hg is deposited in terrestrial ecosystems, where it predominantly accumulates in soils via vegetation uptake. Rivers and coastal erosion transfer about 80 Mg year−1 of terrestrial Hg to the Arctic Ocean, in approximate balance with modelled net terrestrial Hg deposition in the region. The revised Arctic Ocean Hg mass balance suggests net atmospheric Hg deposition to the ocean and that Hg burial in inner-shelf sediments is underestimated (up to >100%), needing seasonal observations of sediment-ocean Hg exchange. Terrestrial Hg mobilization pathways from soils and the cryosphere (permafrost, ice, snow and glaciers) remain uncertain. Improved soil, snowpack and glacial Hg inventories, transfer mechanisms of riverine Hg releases under accelerated glacier and soil thaw, coupled atmosphere–terrestrial modelling and monitoring of Hg in sensitive ecosystems such as fjords can help to anticipate impacts on downstream Arctic ecosystems.
Arctic terrestrial mercury (Hg) emissions from anthropogenic activities (14 Mg year−1), wildfires (8.8 ± 6.4 Mg year−1) and soil and vegetation re-volatilization (24 (7–59) Mg year−1) are low compared with deposition (118 ± 20 Mg year−1). Estimates suggest that atmospheric Hg input on land is balanced by riverine and erosional exports.
Large pools of Hg (~597,000 Mg, 0–3 m depth) have accumulated in permafrost soils. Permafrost thaw is ubiquitous, but impacts Hg mobilization variably across the Arctic, and its future impact is presently uncertain.
Melt releases ~0.4 Mg year−1 of deposited Hg stored in Arctic glaciers (2,415 Mg), which is dwarfed by ~40 Mg year−1 of geogenic particulate Hg exported by glacial rivers into adjacent seas. Coastal erosion mobilizes an estimated 39 (18–52) Mg year−1 of soil-bound Hg into the Arctic Ocean.
Pan-Arctic rivers export 41 ± 4 Mg year−1 of dissolved and particulate Hg (~50% each) to the Arctic Ocean, predominantly during the spring freshet, likely derived from seasonal snowpacks (≤50%) and active-layer surface soils (≥50%) of the watershed portion north of 60°N.
Arctic Ocean Hg deposition (65 ± 20 Mg year−1) exceeds evasion (32 (23–45) Mg year−1). The revised Arctic Ocean Hg budget (~1,870 Mg) is lower than previous estimates (2,847–7,920 Mg) and implies higher sensitivity to changes in climate and emissions.
Shelf-region particulate Hg settling (122 ± 55 Mg year−1) from surface waters is the largest Hg removal mechanism in the ocean. The revised Arctic Ocean Hg mass balance suggests that Hg burial in shelf sediments (42 ± 31 Mg year−1) is underestimated by up to 52.2 ± 43.5 Mg year−1.
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H.A. acknowledges N.E. Selin and the use of the Svante cluster provided by the Massachusetts Institute of Technology’s Joint Program on the Science and Policy of Global Change. M.J. acknowledges funding from the Swiss National Science Foundation grant PZ00P2_174101. R.P.M. acknowledges funding from the US National Science Foundation Office of Polar Programs grant 1854454. D.O. acknowledges funding from the US National Science Foundation (DEB no. 2027038 and AGS no. 1848212). A.T.S. acknowledges support from the US National Science Foundation (OCE no. 2023046). L.-E.H.-B. acknowledges funding from the Chantier Arctique Francais (Pollution in the Arctic System) and the AXA Research Fund. C.Z. acknowledges funding from the Swedish Research Council for Sustainable Development FORMAS (grant no. 2017-00660). The authors acknowledge the Arctic Monitoring and Assessment Programme (AMAP) for organizing the 2021 Arctic mercury assessment process that provided the basis for this Review. Finally, the authors acknowledge the Atmospheric Mercury Network (AMNet), the European Monitoring and Evaluation Programme (EMEP) and the Environment and Climate Change Canada-Atmospheric Mercury Measurement Network (ECCC-AMM) and their contributing scientists for the provision of mercury measurement data.
The authors declare no competing interests.
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Dastoor, A., Angot, H., Bieser, J. et al. Arctic mercury cycling. Nat Rev Earth Environ 3, 270–286 (2022). https://doi.org/10.1038/s43017-022-00269-w