260 - Current state of Mercury Mass Balance in the Arctic

This presentation summarizes findings from the 2021 AMAP Mercury Assessment on present-day total mercury (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 transport in the atmosphere and ocean. Around two-thirds of this Hg is deposited in terrestrial ecosystems. Mercury deposited on land is stored predominantly in soils (~597,000 Mg, 0-3 m) followed by glaciers (~2,415 Mg) and seasonal snowpacks (~39 Mg). Rivers and coastal erosion transfer about ~80 Mg/y of terrestrial Hg to the Arctic Ocean, which is now in approximate balance with modeled net Hg deposition to land north of 60 degree N. It is likely that Arctic warming led to increased releases of terrestrial Hg by intensifying permafrost thaw, glacier melt, coastal erosion, wildfires, and river discharge. Melting glaciers releases ~0.4 Mg/y of Hg stored from atmospheric, which is dwarfed by ~40 Mg/y of geogenic particulate Hg exported by glacial rivers into adjacent seas. Mercury deposition to the Arctic Ocean (~65 Mg/y) exceeds evasion from the ocean waters (~32 Mg/y). The revised Arctic Ocean Hg budget (~1870 Mg) is lower than previous estimates (2847-7920 Mg), and implies higher sensitivity to changes in climate and emissions. The revised Arctic Ocean Hg mass balance suggests that Hg burial in inner-shelf sediments is currently underestimated (up to >100%), needing observations of sediment-ocean Hg exchange processes in all seasons. 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 can help improve the Arctic Hg mass balance and anticipate the impacts of climate change on downstream ecosystems.

Authors: Ashu Dastoor, Hélène Angot, Johannes Bieser, Jesper Christensen, Thomas Douglas, Lars-Eric Heimbuerger-Boavida, Martin Jiskra, Robert Mason, David McLagan, Daniel Obrist, Peter Outridge, Mariia Petrova ,Andrei Ryjkov, Kyra St. Pierre, Amina Schartup, Anne Soerensen, Kenjiro Toyota, Oleg Travnikov, Simon Wilson, Christian Zdanowicz