Arctic mercury cycling

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.

Automated summary

This article provides a comprehensive assessment of the present-day total mercury mass balance in the Arctic. The majority of mercury is transported to the Arctic via air and ocean transport, and the deposition mainly occurs in terrestrial ecosystems, particularly in soils. Rivers and coastal erosion transfer a significant amount of terrestrial mercury to the Arctic Ocean, in approximate balance with net terrestrial mercury deposition. The revised Arctic Ocean mercury mass balance suggests that the deposition to the ocean and mercury burial in inner-shelf sediments are underestimated, calling for the need for seasonal observations.