Cryoconite, a sediment found on the surface of glaciers, is known for its ability to accumulate radionuclides. New data on cryoconite from the Morteratsch glacier (Switzerland) are presented to shed light on the mechanisms that control the distribution of radioactivity in cryoconite. Among the radionuclides detected in our samples, we have identified Ag, an artificial species which has never been observed in terrestrial environments before. This finding supports that cryoconite has an extraordinary ability to accumulate radioactivity. Our results also show that the radioactivity of cryoconite from a single glacier is far from uniform. Both the absolute amount of radioactivity and the relative contribution of single radionuclides are highly variable in samples from the Morteratsch glacier. To investigate the processes responsible for such variability, we have explored the correlation between radionuclides, organic and inorganic carbon fractions and the morphological features of cryoconite deposits. We have found that the degree of connection between cryoconite and supraglacial hydrology is particularly important, since it strongly influences the accumulation of radionuclides in cryoconite. Cryoconite holes connected with supraglacial channels are rich in cosmogenic Be; in contrast, poorly connected deposits are rich in artificial fallout radionuclides and elemental carbon. The very different half-lives of Be and artificial radionuclides allowed us to discuss our findings in relation to the age and maturity of cryoconite deposits, highlighting the potential use of radionuclides to investigate hydrological supraglacial processes and material cycling at the surface of glaciers. 108m 7 7