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

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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RC1:
'Comment on egusphere-2026-3393', Anonymous Referee #1, 20 Sep 2026
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.
Citation: https://doi.org/10.5194/egusphere-2026-3393-RC1
- AC1: 'Reply on RC1', László Palcsu, 30 Oct 2026
  
  Dear Reviewer,
  
  thank you for your comments. Please find our responses in the attached pdf.
  Laszlo Palcsu, on behalf of the authors
  
  Citation: https://doi.org/10.5194/egusphere-2026-3393-AC1
RC2: 'Comment on egusphere-2026-3393', Anonymous Referee #2, 30 Oct 2026

General Comment
Palcsu et al. investigate the last two glaciers in Slovenia, Triglav Glacier and Skuta Glacier, and attempt to establish an age-depth relationship based on radiometric dating tracers as well as delta18O profiles. For the study, several ice cores were drilled in the remains of the two glaciers. The special location of the two glaciers (southeasternmost remaining glaciers of the Alps) and their expected complete disappearance in the near future qualify the authors’ attempt as a relevant and time-critical contribution to the reconstruction of past local climate conditions and glaciation history. However, the current state of the study suffers from major problems with the construction of the age-depth relationships for both glaciers, which I will elaborate on in the following comments.
Major Comments
The aim of the presented study is the reconstruction of age-depth relationships for the two glaciers that would allow deriving relevant parameters such as accumulation rates and the age of the oldest ice.
Triglav
For the Triglav Glacier the dataset used to establish the age-depth relationship consists of depth profiles of delta18O and 3H, provided by the combination of several cores, furthermore the 14C age of a plant stem found in a rocky layer at 0.9-1m depth, and activity depth profiles of 7Be, 137Cs, and 210Pb.

A general remark: the manuscript does not properly differentiate between ice and firn and does not give a depth for the firn-ice transition. In several instances the uppermost ~1 m at Triglav Glacier is either referred to as “firn” (e.g. l104), “firn ice” (e.g. l136) or “ice” (l124). While the photos in Fig. S3 A-C suggest actual firn and not ice to be present in the upper layers of the glacier this is never clearly stated and remains unclear to the reader. It does, however, play a crucial role due to the unclear origin and age of the firn (or ice) in the first 1 m of the profile. In the following, I will assume that the uppermost 1m consists of actual firn. Whether the glacier below the rocky layer at 1 m depth consists of ice is still unclear to me.
14C age from plant stem as tie-point for age scale

The 14C concentration from the plant stem points towards an origin around the year 1955 or 2018. The authors argue that an origin in 2018 seems unlikely given the 1m of firn above and negative mass balance during the time period of 2018 until today. From this finding the authors conclude that the rocky layer at depth 0.9-1m originates from 1955 and the entire following delta18O tie-point discussion is based on this conclusion. This is quite a problematic assumption as it ignores several possibilities as to why the plant stem could have an entirely different age than the rocky layers, let alone the ice layers directly underneath it: I) the stem could have melted through from some upper layer into the rocky layer due to its low albedo; II) the rocky layer could be an accumulated layer from a period of negative mass balance that would cause an age hiatus of unknown duration between the rocky layer, the ice layers below and the ice layers above; III) the stem could have an entirely different age from the surrounding layer, as it might have been originally deposited elsewhere and remobilized and deposited on the glacier at a much later point in time. This is all very speculative, but the authors need to provide a further discussion on why they think the age of the plant stem can be taken as the age of the rocky layer and why they do not assume an age hiatus across the rocky layer, especially as these assumptions are crucial for this key data point of the whole study.
3H profile

A further unclarity is the origin of the firn above the rocky layer (above 0.9-1m). If the rocky layer originates from 1955, then why is there no visible 3H bomb peak in the firn above the rocky layer? It is hard to imagine that ~1m of firn only originates from the few years between the 1955 tie-point and the bomb peak around 1963 with any firn and snow from later periods having melted already thus erasing the 3H bomb peak.

A general question that would be interesting to discuss is why there still is any firn on the glacier in the first place (if understood correctly, see discussion above). In “Site description” it is explained that the glacier has lost the major part of its original extent, supported by the extents indicated in Fig. 1. How do the authors explain the firn on the glacier? Did the glacier simply always consist mostly of firn while ice accounted only for the bottom few meters? Or could it have been added at a later stage due to e.g. avalanches? How would this make sense in the context of the dating efforts and the age-depth relationship presented here?
Tie-points of the delta18O profile

I am not an expert on stable water isotopes and I want to leave a more thorough critical analysis of this part of the study to colleagues with more expertise in this specific topic. Just a few comments:
Neglecting the questionable 14C tie-point of the delta18O record, as discussed above, does the tuning to the lake Jezero v Ledvicah temperature record still hold? The tie-points between the two records do not seem very obvious and convincing.
As Triglav Glacier is at fairly low elevation and has been suffering from prolonged mass loss (as also mentioned by the authors), how reliable is the delta18O record still despite meltwater percolation? Also, with the snow predominantly accumulating in the cold season, would this seasonal delta18O signal allow such close comparison to the (annually averaged?) temperature reconstruction from Jezero v Ledvicah?
Continuity of the age-depth relationship

A critical assumption at several points in the study is the assumption of a continuous age-depth relationship. Why do the authors believe that this is valid? We see no bomb peak in the upper layers – is this not a first sign of age hiatus? And there might be a hiatus in the age-depth relationship anywhere along the profile, e.g. at the rocky layer, as discussed above, but also in the deeper parts. This would call into question the linear age-depth model that the authors use between the three tie-points. The age-depth relationship and the depositional rate derived from it are the key findings of this study; unfortunately both suffer from being underdetermined and the scenario could be much different if the possibility of an age hiatus is included in the consideration. Also, generally, the values for the depositional rates are given without uncertainties, thus making comparison of different values pointless without adding a significance to the comparison. Furthermore, are the units of the depositional rate in cm/year snow equivalent, firn equivalent, ice equivalent or water equivalent?
Radiometric tracers 7Be, 137Cs, 210Pb

The authors argue that the elevated levels of 7Be in the recent snow layer originate from recent fall-out while the elevated levels of 137Cs originate from a dust layer at 0 cm (below the 10 cm of recent snow) depth that could be the layer containing the elevated levels either from the bomb peak or the 1986 Chernobyl signal. This would again indicate an age hiatus at least in the firn and it would mean that the firn between the rocky layer at 0.9-1.0 m depth and the top of the firn at 0 cm depth originates entirely either from the time period between 1955 and 1963 or 1955 and 1986. The former would be surprising due to the thickness of the layer (~1m of firn), the latter due to the absence of the 3H bomb peak.

Concerning the 210Pb data, why do the authors not attempt to use the 210Pb profile to verify their upper ice ages (see Gäggeler et al., 2020)? Please also check the units in Table S5. Is 210Pb really in Bq/kg?
Skuta
The age-depth relationship of Skuta Glacier closely follows the approach used for Triglav Glacier, with two major differences. First, no plant stems were found and therefore absolute age markers are missing entirely. Second, as indicated by the authors, the ice column at Skuta Glacier suffers from “meltwater circulation along the whole ice sequence, as observed during coring” (l107). This is very obvious in the 3H profile. With such strong signs of percolation, the delta18O profile is no longer suitable for a detailed signal tuning as done in this study, especially to a reconstructed temperature record from a lake 60 km away and located in a different mountain massif. In my opinion this age-depth scale is not constrained enough to draw any conclusion about the age of the oldest ice (compare l165) contained in the glacier or conclusions like “Skuta Glacier shows higher and more stable depositional rate from 1860s to 1960s (about 5.5 cm/year)” (repeated in l175 and 195).
Summary
In summary, in its current state the presented data do not allow the conclusions that are drawn in this study. The clear signs of meltwater percolation render a tuning of the delta18O record to external records questionable. Furthermore, the only absolute age from the plant stem is difficult to put into context and does not allow constraining a definite tie-point for the delta18O tuning.

With the complex setting of both glaciers, possibly involving periods of mass loss, a way forward could be to add more absolute age data, especially for the lower layers to support the assumptions made. 14C and, for the age range presented, 39Ar could help to add constraints to the age-depth scale (see Legrand et al., 2025; Ritterbusch et al., 2022; Wachs et al., 2026).

Minor comments:
Title: “Ice older than a century at…”: this is overclaiming the highly uncertain findings of the paper
L17 (and also l189): “suggesting negative net accumulation since the early 1960s”: sounds ambiguous, annually negative net accumulation could have started much later but then erasing the record back to the 1960s
L31+50+181: the authors evoke the impression that the two glaciers in question stem from the last glacial period, this would mean that they contain at least 12 ka old ice. As this study points to nothing close to this age, there is no reason to believe that these glaciers are remnants from the Pleistocene and not simply from the Little Ice Age and thus from the Holocene.
L32 and some others: consistency of citation style, add comma between author and year
L35: “The effects of climate change are also evident from the fact that all ten warmest melting seasons recorded have occurred in this century, with four out of the five warmest since 2012”: consider adding a reference
L36: “The other ice mass”: does not make sense as the text is not about Triglav before, please rephrase,
L44: “Our results on dating glacial remains in the Alps provides significant information for climate science, environmental studies, and understanding the Earth’s history and environment.”: consider rephrasing in a bit less overstated
L56 and others: consistency in writing hectares or ha
L57: “lost almost three times of its volume”: does not make sense, please specify
L62: “to the lower average snow depth in the last 30 years compared to the 130-year period before”: please provide reference
L63: “duration of solar radiation from May to August over the last decades”: what do the authors mean here? Less cloud cover? Please specify and provide a reference
L72: “in the first decade of April”: unusual wording, consider rephrasing
Materials and methods: generally very little information on the different ice cores, consider adding more information on the obtained cores, firn-ice transition etc. Also partly ambiguous which glacier is talked about, e.g. not clear here on which glacier the plant stem was found
L90: AnalysEs
L92+99: consider replacing “Supplementary” by “Supplementary Information”, “Supplement” or “SI”
L93: introduce abbreviation JSI
L130: “cannot be obviously seen” sounds awkward, consider rephrasing
L136+145: “firn ice”: firn or ice? Please specify
L141: what is meant by fall-out? This sentence is ambiguous. Do the authors mean recent deposition?
L152: consider replacing “The later” with a different more clear phrase

Gäggeler, H. W., Tobler, L., Schwikowski, M., and Jenk, T. M.: Application of the radionuclide 210Pb in glaciology – an overview, Journal of Glaciology, 66, 447–456, https://doi.org/10.1017/jog.2020.19, 2020.
Legrand, M., McConnell, J. R., Preunkert, S., Wachs, D., Chellman, N. J., Rehfeld, K., Bergametti, G., Wensman, S. M., Aeschbach, W., Oberthaler, M. K., and Friedrich, R.: Alpine ice core record of large changes in dust, sea-salt, and biogenic aerosol over Europe during deglaciation, PNAS Nexus, 4, pgaf186, https://doi.org/10.1093/pnasnexus/pgaf186, 2025.
Ritterbusch, F., Tian, L., Tong, A.-M., Gu, J.-Q., Jiang, W., Lu, Z.-T., Shao, L., Tang, M.-X., Yang, G.-M., Zhang, M.-J., and Zhao, L.: A Tibetan ice core covering the past 1,300 years radiometrically dated with 39Ar, Proceedings of the National Academy of Sciences, 119, e2200835119, https://doi.org/10.1073/pnas.2200835119, 2022.
Wachs, D., Spagnesi, A., Bohleber, P., Fischer, A., Stocker-Waldhuber, M., Junkermann, A., Kindermann, C., Langenbacher, L., Mandaric, N., Marks, J., Meienburg, F., Jenk, T. M., Oberthaler, M. K., and Aeschbach, W.: A continuous 6000 a age depth relationship for the remainder of the Weißseespitze summit glacier based on 39Ar and 14C dating, Climate of the Past, 22, 173–185, https://doi.org/10.5194/cp-22-173-2026, 2026.

Citation: https://doi.org/10.5194/egusphere-2026-3393-RC2

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

Supplement

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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