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Snow and ice re-emissions control Arctic atmospheric mercury concentrations during summer
Mercury is a toxic contaminant that impacts human, ecosystems and wildlife health globally and is a pressing concern in the Arctic due to the high concentrations found there.
However, there are very few mercury sources located in the Arctic and virtually all toxic mercury originates from outside the region. Elemental mercury (Hg0) is relatively inert (chemically inactive) and long lived and is found in air and the ocean that can be transported long distances, which can take days, months or even longer.
There is a well known summertime peak in the concentration of elemental mercury (Hg0), which has been suggested to come from mercury dissolved in rivers that is transported to the Arctic Ocean and then emitted when sea ice declines during summer. A new study co-authored by an international team (lead by French and Swiss researchers) shows clearly that this is not the case using isotopic analysis. Isotopic signatures are a fingerprint that allows researchers to trace the origin of mercury (Hg0) in air. This new study suggests that in summer, the peak in elemental mercury originates from mercury emission (Hg0) trapped in snow and sea ice and not from river inputs to the Arctic Ocean.
How does mercury end up trapped in snow and sea ice?
During Arctic spring, reactions in the atmosphere transform mercury (Hg0) that has arrived in the region from distant sources to another form of mercury (divalent mercury, mercury (II)) that sticks on snow, ice, and other surfaces.
Mercury (II) is a more alarming form of mercury that may eventually be integrated into the Arctic food web, effecting humans and ecosystems. While being trapped in snow and ice, this mercury (II) can be re-emitted to the atmosphere as mercury (Hg0) when there is sunlight available, especially during summer. These new findings have important implications for our understanding of how the Arctic Ocean, cryosphere (including snow and sea ice), and terrestrial systems control the lifecycle of mercury. Knowledge of the processes that control mercury in the Arctic are essential to understand now due to the fact that the cryosphere is rapidly melting and changing due to regional and global climate change.
Science understanding these processes and what controls toxic mercury is also important in order to deliver on commitments made as part of the Minamata Convention, which is global treaty to protect human health and the environment from the adverse effects of mercury. The Arctic region is particularly important for for this international treaty due to the high mercury concentrations that are found in human (especially native populations traditional hunting and fishing for food), beluga whales, polar bears, seals, fish, eagles and other birds within the region.
More info
Reference:
Araujo, B.F., Osterwalder, S., Szponar, N. et al. Mercury isotope evidence for Arctic summertime re-emission of mercury from the cryosphere. Nat Commun 13, 4956 (2022). https://doi.org/10.1038/s41467-022-32440-8
Scientific contact:
Jennie Thomas
Aurélien Dommergue