Enhanced mercury deposition in Arctic Alaskan lake sediments coincides with early Holocene hydroclimate shift

Substantial amounts of mercury (Hg) are projected to be released into Arctic watersheds as permafrost thaws amid warmer and wetter conditions. This may have far-reaching consequences because the highly toxic methylated form of Hg biomagnifies rapidly in ecosystems. However, understanding how climate change affects Hg dynamics in permafrost regions is limited due to the lack of long-term Arctic Hg records. Using a 27-ka Hg sediment record from Burial Lake, northwestern Alaska, we examine how well-characterized temperature, precipitation, and vegetation shifts affected Hg mobilization in a catchment underlain by permafrost. During the Last Glacial Maximum (29.6-19.6 ka), Hg concentrations (63 ± 5 μg/kg) and Hg flux (8.6 ± 2.2 μg m^-2 yr^-1) remain relatively stable. Abrupt warming trends, starting at 17.6 ka, do not coincide with Hg levels. After 15 ka, the ecosystem transitions to shrub tundra, Hg concentrations (101.2 μg/kg) peak at 14.2 ka, while flux (5.3 ± 1.3 μg m^-2 yr^-1) declines and stabilizes. At ~11 ka, increased precipitation coincides with a 72 % rise in Hg concentrations and a 32 % increase in Hg flux compared to average Hg levels since 15 ka. These results suggest that summer rainfall was the primary driver of Hg mobilization from the catchment, while the vegetation shift influenced lake sediment Hg concentrations. At 1990 CE, peak Hg levels represent an 88 % increase in Hg concentrations (196.3 μg/kg) and a sixfold rise in Hg flux (38.1 μg m^-2 yr^-1) above background levels, underscoring the need for further research to understand Hg dynamics driven by anthropogenic Hg emissions and climate change.