Diversity of isotopic composition of anthropogenic radioactivity on glaciers in the Alps

The dark sediment on the surface of glaciers, called cryoconite, plays an important role in accumulating various contaminants during glacier melting. One of the high-risk is anthropogenic fallout radioisotopes, which have been accumulating since 1945. The melting of alpine glaciers is accelerating, rapidly releasing stored pollutants, and becoming secondary sources of radioisotopes for nearby ecosystems. This study indicates the potential sources of radioisotopes based on their signatures with global and local signals using wide sampling covering eight glaciers in distinct regions of the Alps. For this purpose, the activity ratios of anthropogenic radionuclides (²³⁸Pu/^239+240Pu, ^239+240Pu/¹³⁷Cs, ²⁴¹Am/^239+240Pu) and mass ratios (²⁴⁰Pu/²³⁹Pu) were determined. The activity ratio of ²³⁸Pu/^239+240Pu in Alpine glaciers shows that plutonium-related radioactivity is mostly from global fallout, with an additional contribution from the atmospheric re-entry of the SNAP 9A satellite. ²⁴⁰Pu/²³⁹Pu atomic ratio suggests the heterogeneous contribution of low- and high-yielded nuclear detonations. The activity ratios of ²⁴¹Am/^239+240Pu are partly comparable to the reference isotopic ratio for global fallout, but the impact of unknown local radioactive contamination source(s) is also considered. The post-Chernobyl and global fallout account of ¹³⁷Cs in the examined glacial area of the Alps. The results confirm the ability of cryoconite to accumulate artificial radioisotopes while recording the influence of multiple regional and global sources. Cryoconite is confirmed as an extremely valuable environmental matrix for studying radioactive contamination in glacial environments.