Mercury isotope evidence for Arctic summertime re-emission of mercury from the cryosphere

During Arctic springtime, halogen radicals oxidize atmospheric elemental mercury (Hg-0), which deposits to the cryosphere. This is followed by a summertime atmospheric Hg-0 peak that is thought to result mostly from terrestrial Hg inputs to the Arctic Ocean, followed by photoreduction and emission to air. The large terrestrial Hg contribution to the Arctic Ocean and global atmosphere has raised concern over the potential release of permafrost Hg, via rivers and coastal erosion, with Arctic warming. Here we investigate Hg isotope variability of Arctic atmospheric, marine, and terrestrial Hg. We observe highly characteristic Hg isotope signatures during the summertime peak that reflect re-emission of Hg deposited to the cryosphere during spring. Air mass back trajectories support a cryospheric Hg emission source but no major terrestrial source. This implies that terrestrial Hg inputs to the Arctic Ocean remain in the marine ecosystem, without substantial loss to the global atmosphere, but with possible effects on food webs. Arctic warming thaws permafrost, leading to enhanced soil mercury transport to the Arctic Ocean. Mercury isotope signatures in arctic rivers, ocean and atmosphere suggest that permafrost mercury is buried in marine sediment and not emitted to the global atmosphere

Automated summary

During Arctic springtime, atmospheric elemental mercury is oxidized and deposited to the cryosphere by halogen radicals. This is followed by a summertime peak in atmospheric mercury, which is primarily attributed to terrestrial mercury inputs to the Arctic Ocean. The isotope signatures of mercury in the Arctic atmosphere, marine environment, and terrestrial sources reflect the re-emission of mercury deposited during spring. The study suggests that terrestrial mercury inputs remain in the marine ecosystem without substantial loss to the global atmosphere, but may have effects on food webs. The thawing of permafrost due to Arctic warming leads to increased transport of soil mercury to the Arctic Ocean, where it is buried in marine sediment rather than emitted to the global atmosphere.