Brief communication: Ice older than a century at Triglav Glacier and Skuta Glacier &ndash; isotopic characteristics of glacier remains in Southeastern Alps, Slovenia

Palcsu, László; Temovski, Marjan; Vargas, Danny; Nigro, Matteo; Henrich, Christoph; Vystavna, Yuliya; Zorn, Matija; Lipar, Matej; Pavšek, Miha; Tičar, Jure; Žagar, Klara; Vreča, Polona

doi:10.5194/egusphere-2026-3393

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https://doi.org/10.5194/egusphere-2026-3393

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11 Aug 2026

| 11 Aug 2026

Status: this preprint is open for discussion and under review for The Cryosphere (TC).

Brief communication: Ice older than a century at Triglav Glacier and Skuta Glacier – isotopic characteristics of glacier remains in Southeastern Alps, Slovenia

László Palcsu, Marjan Temovski, Danny Vargas, Matteo Nigro, Christoph Henrich, Yuliya Vystavna, Matija Zorn, Matej Lipar, Miha Pavšek, Jure Tičar, Klara Žagar, and Polona Vreča

Abstract. The Triglav Glacier and Skuta Glacier are the last remaining, although disappearing, surface ice masses in Slovenia. Based on environmental tracer profiles, the ice between 0–100 cm predates the 1960s at Triglav, suggesting negative net accumulation since the early 1960s. Ice below 1 m is older than 70 years. Skuta Glacier shows similar patterns, though deeper layers are affected by percolation water. Skuta Glacier shows relatively stable deposition (~5.5 cm/year) from the 1860s to 1960s, while Triglav Glacier had lower and declining rates (3.8 cm/year before 1900, dropping to 2.1 cm/year by the 1960s).

Received: 10 Jun 2026 – Discussion started: 11 Aug 2026

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László Palcsu, Marjan Temovski, Danny Vargas, Matteo Nigro, Christoph Henrich, Yuliya Vystavna, Matija Zorn, Matej Lipar, Miha Pavšek, Jure Tičar, Klara Žagar, and Polona Vreča

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'Comment on egusphere-2026-3393', Anonymous Referee #1, 20 Sep 2026 reply
The manuscript by Lazslo Palcsu and colleagues presents tritium, radiocarbon and water stable isotope data from Triglav and Skuta glaciers in Slovenia, with the aim of reconstructing the dynamics of these glaciers over the past century. The authors drilled several cores in the two glaciers, collected samples for tritium, oxygen and hydrogen stable isotope analyses, as well as one radiocarbon analysis on a sample from Triglav glacier. They combined the data to present a reconstruction of the ice dynamics for the two glaciers. While any study of quickly melting glaciers is worth pursuing, the one presented here suffers from several methodological failures, strongly questioning the results and their interpretation. Below is a presentation of the main issues.
Both glaciers are located at low elevations (Triglav at ~2500 m and Skuta at ~2000 m above sea level). At these altitudes and latitudes, precipitation in the Alps occurs in liquid form during the warm season. Realistically, it cannot be expected that none of this water will infiltrate inside the snow mass. Supplemental figure 1 show that both glaciers consist of snow and firn and the low density of these would promote infiltration of water. As a result, it is expected that the glaciers themselves do not consist of ice (firn/) formed from winter precipitation, only, but also of refrozen summer liquid rain. Positive air temperatures during the melt season would also promote melting of snow/ice and downward infiltration of water, a phenomenon observed by the authors, as well (page 3, line 8): “increased meltwater circulation along the whole ice sequence, as observed during coring”. Two consequences emerge: the glaciers are not formed from snow diagenesis, only – hence the various comparisons with winter air temperature and precipitation tritium concentration are wrong – and second, the same downwards percolating water would have drastically altered the original stratigraphy, the tritium content and the stable isotope composition of the ice. It these conditions, it is difficult to rule out that one organic samples was not also moved from its original depositional site. Next, it is surprising that the authors did not encounter (or did not described) summer melt layers, a common occurrence in the upper parts of glaciers with surface melt. Because of this issue of water freely moving inside the ice, it is very difficult to ignore the fact that all analytical results could be unreliable to a certain and varying degree.

The authors use d18O measured along the ice cores as a proxy of air temperature. Somehow, they seem to be oblivious to the clear potential alteration of the original signal in ice by the melt water that circulates through it. They do however exclude data from ice at the base of Triglav glacier which “was likely affected by the subglacial water fluxes”, but did not consider this to be a problem for Skuta Glacier. Water at the base of a glacier is a problem for stable isotope analyses if it mixes with the ice above, but then this would also happen when water circulate through the ice mass itself. The relatively homogenous d18O values in Skuta are a clear indicator of this process happening. Further, because of this mixing, it is not clear what the d180 signal would represent.

In order to reconstruct the age of the glacier, the authors combine tritium, radiocarbon and d18O data. They tune their d18O records to a reconstruction of air temperature at a nearby lake, Jezero v Ledvici. There are two problems here. First, the cited “reconstruction” is not a reconstruction, but an extrapolation of lowland gridded air temperatures from several sites across Europe to the location of the lake, using multiple regression analysis and subsequent corrections for latitude and latitude (Agusti-Panareda et al., 2002, Brancelj et al., 2002). The lake is located several hundreds of meters (almost 1000 m below Triglav) and the authors did not make any effort to further correct the data to account for these altitudinal differences. While instrumental times series similar in length to the data of Batarbee et al (2002) do no exist in Slovenia, reconstructions, do and these could have been better for comparisons. However, the fact that the stable isotope composition of ice was affected by downward percolation of water (and likely freezing) inside the ice, the measured d18O is not a meaningful indicator of air temperature (it is worth mentioning that the authors consider the ice as being formed from winter snow, only and yet they compare the d18O with an annual signal).

One additional problem related to the generation of the age depth model is the lack of consideration for the length of missing ice. The fact that no peak bomb was found indicate extensive melting, and yet this is not considered by the authors. The thickness of missing ice could be of any length (and hence age); hiatuses inside any sedimentary deposit are difficult to constrain in the absence of precise age determination below and above it. Considering the entire snow deposit as continuous for age modeling is thus difficult to understand.

Combining the issues above, it results that the reconstructed age depth models and inferred accumulations rates are problematic, to say the least. The circulating water through the ice makes any d18O signal problematic to interpret; presence of hiatuses of unknown age lead to a wide range of possible ages for the ice, the reconstructed air temperature used to tune the d18O record is not relevant for the study area. There are numerous minor issues with the manuscript, but considering the major ones above, it is not relevant to point them out here. One final comment, on the conclusions: these are not derived from the paper itself, e.g., lines 183 and 184 on the causes of the melt. The authors cite a change in the solar radiation between May and August in recent decades. It is not clear what they really understand by “solar radiation”. Solar radiation (or solar irradiance) changes on multi-decadal to multi-millennial time scales and it definitely did not change during the summer of the past decades. Also, the conclusions do not respond to the issues raised by the authors in the introduction on water availability and ecosystems. Bot these questions and the conclusions are just general statements.
Agustí-Panareda, A. & R. Thompson, 2002. Reconstructing air tem- perature at eleven remote alpine and arctic lakes in Europe from 1781 to 1997 AD. J. Paleolim. 28: 7–23.
Brancelj, A., M. Šiško, G. Muri, P. G. Appleby, A. Lami, E. Shilland, N. L. Rose, C. Kamenik, S. J. Brooks & J. A. Dearing, 2002. Lake Jezero v Ledvici (N.W. Slovenia) – changes in sediment records over the last two centuries. J. Paleolim. 28: 47–58.

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Citation: https://doi.org/10.5194/egusphere-2026-3393-RC1

László Palcsu, Marjan Temovski, Danny Vargas, Matteo Nigro, Christoph Henrich, Yuliya Vystavna, Matija Zorn, Matej Lipar, Miha Pavšek, Jure Tičar, Klara Žagar, and Polona Vreča

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https://doi.org/10.5194/egusphere-2026-3393-supplement

László Palcsu, Marjan Temovski, Danny Vargas, Matteo Nigro, Christoph Henrich, Yuliya Vystavna, Matija Zorn, Matej Lipar, Miha Pavšek, Jure Tičar, Klara Žagar, and Polona Vreča

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Short summary

The last two glaciers in Slovenia are just disappearing. In 2023, ice cores were taken from Triglav and Skuta Glacier to determine, as a first and maybe the last attempt, the age of ice. At Triglav, the net accumulation is negative since the early 1960s, while ice below 1 m is older than 70 years. Skuta Glacier shows similar patterns. Today, Triglav Glacier has nearly disappeared and Skuta Glacier continues to shrink despite its more sheltered location.


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