Evidence of radionuclide fractionation due to meltwater percolation in a temperate glacier

Abstract. The article discusses the use of ³H and ¹³⁷Cs as temporal markers in ice cores extracted from temperate glaciers. We present a complete tritium (³H) profile for a 46 m ice core drilled from Adamello glacier, a temperate glacier in the Italian Alps, and compare it to ¹³⁷Cs profile from the same ice core. Our analysis reveals contamination of tritium between 19 and 32 m of depth, which can be attributed to the worldwide radioactive contamination caused by atmospheric nuclear bomb testing in the 1950s and 1960s. Results show that the radioactive peak associated with 1963 is not coincident for ³H and ¹³⁷Cs, but the ³H peak occurs 1.5 m above the ¹³⁷Cs one. This misalignment is caused by meltwater-induced postdepositional processes that affect ¹³⁷Cs, which is more sensitive to percolation than ³H. The total inventory of ¹³⁷Cs in this ice core is also among the lowest ever reported, providing additional evidence that meltwater disturbed its distribution into the ice. On the contrary, the total tritium inventory is comparable to what is reported in literature, making it a more reliable temporal marker for temperate glaciers.