Glacier Melt as a Source of Mercury: Implications for Ecosystem Recovery and Environmental Trends.

Mercury (Hg) atmospheric emissions in Europe peaked in the mid-20th century and have since declined due to environmental policies, reducing atmospheric deposition to ecosystems. However, regional disparities have emerged as climate change can remobilize Hg reservoirs, complicating efforts to assess environmental recovery. This study investigates Hg accumulation rates in lacustrine sediments from two neighboring high-altitude alpine lakes in the French Alps: Grand Lake (GDL), a rain-fed lake reflecting regional atmospheric deposition, and Eychauda Lake (EYC), a proglacial lake supplied by glacial meltwater and derived sediment. Sediment chronologies for both lakes were established using short-lived radionuclides, allowing for the reconstruction of Hg deposition over the past century. Comparison of the Hg records from both lakes revealed contrasting trends: GDL responds to regional anthropogenic emissions, while EYC shows a still increasing Hg accumulation rate over recent decades. This discrepancy and its correlation with erosion proxies suggest that glacier melting has released Hg stored in the ice, masking the expected trend of reduced regional emissions. These findings illustrate the importance of accounting for climate-mediated remobilization of Hg when evaluating the effectiveness of environmental policies as this process can impose a climate change-driven penalty that delays ecosystem recovery.