Melting glaciers : a hidden mercury source in alpine ecosystems

To obtain these results, the scientists analysed sediment archives from two neighbouring Alpine lakes : one fed by precipitation, reflecting direct atmospheric deposition, and a proglacial lake fed by meltwater. Using radionuclide dating methods, they reconstructed mercury input trends over more than a century. Comparison of these records reveals contrasting trajectories : a decline consistent with reduced emissions in the first lake, and a continuous increase in the proglacial lake.

These results indicate that glacier melt releases mercury that has been previously trapped in ice, thereby masking the benefits of emission reduction policies. At the scale of the Alps, the expected loss of a significant fraction of glacier volume could lead to the release of substantial amounts of mercury into the environment, up to 1,000 kg by the end of the century. Once released, this mercury can be converted into methylmercury, a toxic form that accumulates in food webs. This temporal mismatch between emission reductions and ecosystem response highlights the need to incorporate the effects of climate change into the evaluation of environmental policies such as the Minamata Convention. More broadly, this study underscores the importance of environmental reservoirs such as glaciers in the global mercury cycle and opens new perspectives for better anticipating the combined impacts of climate change and pollution.