Worldwide accumulation of atmospheric mercury in glacial cryoconite

This study presents the first comprehensive global analysis of the variation in mercury (Hg) concentrations in cryoconite, a heterogenous and often organic-rich material found on the surface of glaciers. Samples of cryoconite were collected from 39 glaciers across both hemispheres, comprising 130 samples in total. The highest Hg concentrations were measured in cryoconite from Norway and Alaska (up to 0.965 μg g^-1), followed by the European Alps (up to 0.498 μg g^-1), reflecting the levels of atmospheric deposition from heavily industrialized and inhabited areas in relatively close proximity to these glaciated regions. To better assess the environmental distribution of Hg in the glacial environment, in addition to cryoconite we also considered other environmental matrices found in glacial and proglacial areas, including algae, soils, and riverine sediments. This included a novel analysis of Hg in red snow algae from Qaanaaq Gletsjer (Greenland). Of all the environmental matrices considered in this study, cryoconite samples contained the highest Hg concentrations. The Pollution Load Index, Geoaccumulation Index, and Target Values for the Netherlands were used as pollution indices to identify hot spots of sediment contamination. According to these pollution indices, samples from the Northern Hemisphere were slightly and moderately polluted by Hg, while those from the Southern Hemisphere were unpolluted. Of the Northern Hemisphere samples, cryoconite from Sweden, Norway and Svalbard had the highest pollution status, while samples from Alaska and the European Alps were generally only slightly polluted. These results highlight the importance of improving our understanding of dynamic and rapidly changing glacial environments in the accumulation, transport, and re-emission of mercury.