the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Evidence of radionuclide fractionation due to meltwater percolation in a temperate glacier
Elena Di Stefano
Giovanni Baccolo
Massimiliano Clemenza
Barbara Delmonte
Deborah Fiorini
Roberto Garzonio
Margit Schwikowski
Valter Maggi
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.
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Elena Di Stefano et al.
Status: open (until 12 Oct 2023)
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RC1: 'Comment on tc-2023-108', Anonymous Referee #1, 05 Sep 2023
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The authors compared the tritium and 137Cs profiles of a 46 m ice core drilled from a temperate glacier, and observed that the radioactive 3H peak occurs 1.5m above the 137Cs one. The authors suggest that the misalignment between 3H and 137 Cs peaks is caused by meltwater-induced postdepositional processes. Although there are many previous works on the meltwater-induced postdepositional processes altering the signal embedded in the ice, the particular merit of this current work might rely on the new observation of the misalignment between 3H and 137 Cs peaks.
The authors also observed that a layer rich in mineral dust (located in section 77-78) is approximately 1m deeper than the main 137Cs peak (section 74-75). It might be a puzzle for the meltwater to move downwards to form a 137Cs peak (i.e., the misalignment between 3H and 137 Cs peaks), and move approximately one more meter downwards to form a layer rich in mineral dust (i.e., the misalignment between 137Cs and dust peaks), especially taking account of the fact that 137Cs is mainly bound to particulate matter (Qin et al., 2012; Tanaka et al., 2013; Di Stefano et al., 2019).
The 137Cs profile (Fig. 4d) was taken from Di Stefano et al. (2019), which was from the measurements of the chips samples. From Fig. 4b, it’s easy to find that the main peaks were found at 29±0.6m from the low resolution chips dataset and at 30.530±0.025m from the high resolution ice core dataset (i.e., a gap of ~1.5m). Although it’s beyond my intention to apply the same observation for an alternative interpretation regarding the misalignment between 3H and 137 Cs peaks, the authors need to provide more pieces of evidence to eliminate such a kind of possibility.
Citation: https://doi.org/10.5194/tc-2023-108-RC1
Elena Di Stefano et al.
Elena Di Stefano et al.
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