the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jul 2026
A 10 ka ice core from Tödi (Switzerland) reveals recent surface loss and revises Alpine age–altitude relationships
Abstract. Understanding whether the current decline of Alpine glaciers is unprecedented requires direct evidence of ice persistence through past warm periods. While maximum glacier extents are well constrained, for example through landmarks (moraines), minimum Holocene ice extents—particularly at high elevations—remain poorly documented. Cold, low-accumulation summit glaciers can preserve very old ice, yet these archives are increasingly threatened by recent atmospheric warming. Here we present the first ice core record from the summit glacier of Tödi at 3565 m a.s.l. (Swiss Alps). Two ice cores drilled to bedrock (~20 m) were absolute dated with multiple radionuclides (210Pb, 3H, 39Ar, 14C) complemented by glaciological observations and age–depth modelling. Based on evidence for recent surface ablation, we determined that the ice surface at the time of drilling (2023) dates to 1960 ± 1 CE. An exceptionally high-resolution radiocarbon dataset reveals stratigraphically consistent preservation of basal ice dating to ~10 ka cal BP, confirming the persistence of early Holocene ice. The Tödi basal age questions the previously suggested relationship in timing of Alpine ice-free conditions around 6 ka ago at altitudes of about 3500 m a.s.l.. Instead, our results indicate that long-term ice persistence is not controlled by elevation alone, but rather dependent on local glaciological factors. Further, our results imply that other cold-based high-altitude glaciers in the Alps may preserve older ice than currently recognized and underscore both the scientific value and increasing vulnerability of these disappearing climate archives.
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Status: open (until 16 Sep 2026)
- RC1: 'Comment on egusphere-2026-3356', Melaine Le Roy, 03 Sep 2026 reply
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RC2: 'Comment on egusphere-2026-3356', Anonymous Referee #2, 16 Sep 2026
reply
This manuscript presents results from the ice cores drilled on the Tödi’s glacier summit, combining absolute dating with glaciological observations, ice-flow modelling, age-scale reconstruction, and mass-balance estimates to investigate the persistence of high-altitude Alpine ice during the Holocene.
Overall, I find the manuscript scientifically sound, well structured, and clearly written. The study addresses relevant scientific questions within the scope of the journal and provides novel data and a robust chronological framework for the Tödi summit glacier. The methodological approach is appropriate and sufficiently described, and the results adequately support the interpretations and conclusions. A particular strength of the study is the combination of independent dating approaches. Overall, the manuscript represents a valuable contribution to understanding the behaviour of high-altitude Alpine glaciers throughout the Holocene and provides useful constraints for identifying other sites potentially preserving old ice.
However, the statement that the results “indicate that long-term ice persistence is not controlled by elevation alone, but rather dependent on local glaciological factors” seems overstated. Previous studies on Alpine cold-based summit glaciers have already highlighted the importance of local glaciological and topographic conditions for the preservation of old ice, including at comparatively low elevations (e.g., Bohleber et al., 2018). The novelty of the Tödi record appears instead to lie in its marked deviation from the existing empirical age–altitude relationship. I would therefore suggest reformulating this statement accordingly.
Besides of this, I have only a few minor comments that I believe would improve the clarity and completeness of the manuscript. I therefore recommend publication after minor revisions.
Minor comments
L62 – I would suggest citing Spagnesi et al. (2026), https://doi.org/10.3389/feart.2026.1680019, here, possibly in place of Wachs et al. (2026).
L93 – I assume that the description here refers to the lowermost 83 cm of TÖ23-BH1 (72 cm recovered in one drilling run + 11 cm in the subsequent run immediately before reaching bedrock). However, the text currently moves directly from stating that two continuous ~20 m cores were retrieved to bedrock to the description of these final 83 cm, without explicitly indicating that this passage concerns the bottom section of the core. I suggest adding a few words to make this transition clearer.
L125–135 – To make the cutting strategy and cutting ratios easier to understand and reproduce, I suggest adding a schematic representation of the core-cutting procedure to the SI.
L145 – I suggest explicitly reporting the approximate dating range or temporal applicability of 3H, similarly to what is already provided for 39Ar. This would help the reader understand the complementary chronological constraints provided by the different tracers.
L421 – Please report “CG” using the full glacier name, consistently with the other glaciers mentioned in the text.
Citation: https://doi.org/10.5194/egusphere-2026-3356-RC2
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- 1
Introduction
It is of foremost importance to quantify the glacier retreats during the Holocene to assess whether they fall within the bounds of current and projected scenarii for this century. Few methods actually exist for reconstructing the reduced extent or disappearance of glaciers located at very high altitudes in the Alps. The dating of basal layers of high elevation ice caps is the most promisisng, but it must be done with a certain sense of urgency, given the short lifespan of these objects in current climate.
The paper present novel valuable data on two high elevation 20 m-long ice cores drilled to bedrock at the small Tödi ice cap (3568 m asl). The age model is constrained by an unprecedentedly dense radiocarbon dataset that shows that basal ice is ca 10 ka old. These results challenge the previously established empirical relationship between ice basal age and elevation in the Alps, being older than one would expect at this altitude (~6 ka). The discrepancies with previous works are thought to be largely caused by methodological issues (e.g. loose age model, and/or whether or not bedrock was actually reached) and would imply that most of the published basal ages have been underestimated.
Main remark
My main concern is that the authors make no mention of the relationship between the basal age and what is known about the Holocene paleoclimate history (I can imagine that the paleoclimatic interpretation will be the subject of a companion paper ?). Previously, the interpretation of the WSS was that the summit was ice-free before 6 ka and that it gradually became glaciated from that period onward. What conclusions can be drawn from the Tödi dataset on this point? Given that the bedrock has been reached, and the precise dating of the lower layers, one might wonder whether the summit was ice free before 10 ka, and since when ?
Regarding the timing of the onset of ice accumulation during the early Holocene, we would encourage the authors to take note of our recent paper (Nicolussi et al., 2026) presenting the first evidence for the earliest Holocene glacier contraction in the Alps (i.e. smaller than 2025). The obtained tree ring dates for the glacier advance that ended the earliest paroxysmal retreat of the Holocene match the basal age of the Tödi ice cores. This would mean that the Preboreal glacier contraction – dated at Morteratsch Glacier (88 km SE of Tödi) between (at least) 10.8 and 10.3 ka – could have led to the complete disappearance of the ice on the summit of Tödi (and maybe on other peaks as well). If that is the case, it means that this melt event would never again be equalled later during the Holocene at this elevation ? (or maybe around 9 ka, if I remember well a talk about this work. In contrast, at the Morteratsch Glacier front, 1300 m lower than Tödi ice cap, evidence has been found that glacier retreats of similar magnitude occurred around 6.5 and 3.9 ka). Then, the Late Preboral advance, centred on 10.2 ka, would have been responsible for the re-icing of the summit, recorded by the ice cores dated here.
Overall, the paper is clear, well written and educational enough (the figures are very well designed) for someone like me, whose area of expertise is quite far from ice cores dating. I strongly recommend its publication after very few minor corrections.
Other points
Title : The title is informative but the wording of the last section is somewhat obscure to the uninitiated and to anyone who is not familiar with this relatively recent empirical relationship. Not sure the wording ‘revises Alpine age-altitude relationships’ evokes the age of ancient ice to a broad audience (by the way, I'm wondering if the plural is necessary here for relationship). Also, “revises” could mean that a new usable relationship has emerged. To put it provocatively, one could say that this new, more robust Tödi chronology “refutes/infirms/questions (or refines as used in the Conclusion) the previous relationship” because (i) most previous basal ages were not precise enough (no bedrock reached or dating issues) and (ii) elevation seems less significant than local conditions.
Line 21 : ‘Confirming the persistence of early Holocene ice’. Why ‘confirming’ is used here (and not ‘indicating’ or equivalent)? This would mean a prior evidence of the presence of such old ice, which does not seem to be the case. This part of the sentence is unclear and should be rewritten. The term “persistence” is also somewhat ambiguous and leaves room for doubt as to whether the ice melted down to the bedrock before 10 ka—which seems to be the case, but is never clearly stated. Was the summit ice-free before 10 ka?
Line 37 : What kind of geomorphological imprint can be left at high elevation (which appears to be above 3,000 metres in the paper) on the timescale considered here (the Holocene) and erased by subsequent advance? (please give an example, if any).
Cited reference :
Nicolussi, K., Le Roy, M., Hajdas, I., Pichler, T., Wacker, L., Schlüchter, C.,2026. Chasing the melting ice: evidence for the first Holocene glacier minimum in the Alps and precise dating of the subsequent advance at the end of the Preboreal. Quaternary Science Reviews 388, 10.1016/j.quascirev.2026.109962