the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Jun 2026
Speleothem sulphate and trace elements constrain Alpine glacial inception across the Marine Isotope Stage 11/10 transition
Abstract. Alpine glacier histories beyond the Last Glacial Maximum are poorly resolved, impeding our ability to test how mountain glaciers respond to dynamic forcings on orbital to sub‑orbital timescales. This gap may be addressed through proxy records from alpine caves, in which subglacial speleothem growth is facilitated by recharge beneath temperate glaciers through sulphide-bearing epikarst. However, the use of conventional stable isotopes of carbon (δ13C) and oxygen (δ18O) in speleothem calcite yields ambiguities when interpreting environmental transitions and ice cover during glacial inception and retreat. Herein, we present a multiproxy speleothem record from Betten Cave (Melchsee Frutt, central Swiss Alps) spanning 415–360 ka that integrates sulphate stable isotopes (δ34SSO4, δ18OSO4) and trace‑element geochemistry with calcite δ13C–δ18O to diagnose redox state, sulphide‑oxidation pathways, and hydrological reorganization across the Marine Isotope Stage 11/10 glacial inception. Three environmental phases are identified from this dataset, marking the transition from (1) a vegetated and soil-covered montane valley to (2) a soil-limited periglacial setting, hydrologically influenced by glacier advance through the adjacent valley (~2,000 m a.s.l.), to (3) subglacial speleothem growth, in which a temperature glacier covered the lowest elevation of the cave system (~1,700 m a.s.l.). After 402 ± 4 ka, a long-term decrease in the isotopic offset between water and aqueous sulphate (Δδ18OSO4−H2O) records progressive oxygen limitation concomitant with glacier thickening and advance over the cave site by 372 ± 3 ka. Coeval peaks in cations and redox‑sensitive transition metals reflect the enhanced delivery of glacially comminuted detritus and coupled Fe–Mn redox cycling within the subglacial karst system. These results directly link sulphate oxygen- and sulphur-isotope systematics and trace‑element fingerprints to glacier dynamics, providing geochronologically precise benchmarks and a transferable framework for reconstructing mountain glacier behaviour where geomorphic records are incomplete.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2840', Anonymous Referee #1, 22 Jul 2026
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RC2: 'Comment on egusphere-2026-2840', Anonymous Referee #2, 07 Aug 2026
Comments on egusphere-2026-2840:
“Speleothem sulphate and trace elements constrain Alpine glacial inception across the Marine Isotope Stage 11/10 transition” by Baker et al.
The authors present new records of sulphate stable isotopes (d34S and d18O) and trace element data from four stalagmites from Betten Cave (Melchsee-Frutt, central Swiss Alps) covering the period from 415-360 ka. Using a multi-proxy approach including previously published calcite d18O and d13C data from the same stalagmites (Honiat et al. 2026), the authors present a reconstruction of the timing and extent of progressive glaciation across the MIS 11/10 glacial inception depicted in Fig. 5.
General comment:
The multitude of proxies and their interrelations make this paper quite complex and demanding, and I had a hard time to get through and really understand it. I think there is potential to improve the manuscript in a way to make it easier for the reader to follow.
Comments on content:
In the following I will focus on a couple of specific aspects that I believe are substantial weak points related to data analysis and interpretation:
Line 247:
The authors write: “Stable-isotope records are largely reproducible between intervals of synchronous growth” and refer to Honiat et al. 2026. This statement is fair for the d18Occ records but looking at the d13C records in the original paper, it is evident that the d13C record of sample 60 is in antiphase with the corresponding records of samples 13 and 15D in the period between 381-372 ka. Is this an issue of age uncertainties only?
Line 268:
The authors write that they converted calcite d18Occ into drip water d18O values. How was this conversion accomplished? The reconstruction of drip water d18O from d18Occ requires knowledge of the cave temperature and an appropriate calibration of the water-calcite oxygen isotope fractionation. None of this is mentioned in the text.
Since drip water d18O is subsequently employed to calculate Δd18OSO4-H2O that is then used as environmental proxy, a proper description of the d18Occ conversion into drip water d18O is indispensable.
Alternatively, fluid inclusion d18O could be measured directly. Based on the stalagmite images shown in Fig. S2, I guess there should be enough water in the samples.
Line 371: Section 4.2
The discussion provided in section 4.2 is very interesting and informative, but in my opinion, it is based on a misinterpretation of the underlying data.
Looking at the data records in Fig. 2a and Fig. 3, d13C is the only proxy that seems to provide evidence for an environmental change from interglacial to periglacial conditions, indicated by a distinctive, continuous increase from about 0 to +3 ‰ between 406 and 402 ka in sample 61D. Other proxy records like d34S, UAR(i), Na+K+Al, U, and Ni, in contrast, show clear discontinuities at 402 ka that are obviously related to the change from sample 61D to stalagmite 13. As the two samples originate from distant parts of the cave with 300 m altitude difference, it appears more likely that the observed “abrupt changes” are caused by site-specific differences of the karst bedrock rather than to the proposed transition to periglacial conditions. Although it is unfortunate that the growth periods of stalagmites 61D and 13 do not overlap, site-specific differences of the records become also obvious when comparing the overlapping parts of stalagmite 15D and 60. Moreover, the distinctive darker colour of stalagmites 61D and 60 compared to samples 13 and 15D (see Fig. S2) supports this view.
In this context, I was very surprised to see that only the oldest part of sample 13 between 402 and 393 ka was analysed for the present study although it grew between ca. 402 and 373 ka (Honiat et al. 2026) and thus overlaps with samples 15D (and 60). As samples 13 and 15D come from the same part of the cave at ca. 2000 m a.s.l., this looks to me like a missed opportunity to check how well the sulphate d34S and d18O records and the various trace element records reproduce across stalagmites from the same cave location.
Finally, for the overlapping records of samples 15D and 60 I suggest indicating the sample from which the individual d34S and UAR(i) data points in Fig. 2 were obtained. The same applies to sulphate d18O and Δd18OSO4-H2O. By the way, the data tables are missing in the Supplement.
Line 401:
Here the authors argue that the geographic setting of Betten cave is conducive to the proposed scenario of the MIS11/10 glacial inception, thereby implying that the paleo-topography of the area 400 kyr ago was similar to present. Is this plausible? Considering a 200 m tectonic uplift of the area over the last 400 kyr (see Honiat et al. 2026 and references therein), and substantial erosion by four other glaciations in this period, one might speculate that the landscape in the Melchsee-Frutt area looked different than today. In connection with the tectonic uplift, one could also argue that the present-day passages of Betten Cave were not only at lower altitude, but also significantly deeper below the paleo-surface.
This could be of relevance for the interpretation of the Mg and Sr data. If 400 kyr ago, a different limestone strata or marls with higher Sr content than the MF1, MF2 and MF3 bedrock references were in contact with the glacier, it could potentially explain the inconsistency between the CaveCalc modelling experiments and the measured data shown in Fig. S3e,f. During subsequent glaciations these strata were eroded, and other limestone and limestone-marl strata are now exposed to the surface.
Line 482:
The authors report “a distinct negative trend following the statistical break point near 400 ka, after which Δd18OSO4-H2O declines from +22‰ to +15‰, possibly tracking long-term oxygen limitation (Fig. 2b)”. Indeed, there is a declining trend in the data, however, the beginning of this decrease is uncertain due to the low temporal resolution of the record between 380 and 400 ka and the scatter of the data. To me it looks like the Δd18OSO4-H2O decrease starts at around 390 ka, rather than 400 ka and in this case, it is not concurrent with the “400 ka break point” and d13C increase between 406 and 402 ka.
Minor comments:
- I suggest adding a subsection 2.1 “sample description” at the beginning of “Material and Methods”.
- Figure 3: For graphical reasons, it doesn’t make much sense to invert the Ni concentration axis to illustrate the opposing shifts of Ni and U concentrations.
- Figure 4b shows significant overlap between interglacial and periglacial samples. Is there a chronological trend within the periglacial data? E.g. the older the samples the closer they plot to the interglacial data points?
- Note, in Fig. S4c the Sr data are plotted for samples 13 and 15D only but not for 61D and 60.
- Fig. S4a and b need more explanation in the caption to help the reader understanding the meaning of the plots. Only referring to Sinclair (2011) and Wassenburg et al. (2024) is not sufficient.
- Figure S7: Add some text in the figure caption to explain the meaning and relevance of this figure. It is not self-explanatory.
Final recommendation:
Based on the above comments on the manuscript I conclude that the authors are mistaken with critical parts of their data interpretation. The point is that the data do not really show what the authors expected them to show. I don’t think their geochemical model for subglacial calcite dissolution is wrong. It’s much simpler - it’s an unfortunate selection of samples from different parts of the cave in combination with a missing temporal overlap between samples 61D and 13 that caused the misinterpretation of the data.
I therefore recommend rejection of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2026-2840-RC2
Data sets
Speleothem sulphate and trace elements constrain Alpine glacial inception across the Marine Isotope Stage 11/10 transition Baker, J., Honiat, A., Wynn, P. M., Fohlmeister, J., Trüssel, M., Hollowood, S., Ruan, J., Mertz-Kraus, R., Edwards, R. L., & Spötl, C. https://doi.org/10.5281/zenodo.20259664
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- 1
Review of “Speleothem sulphate and trace elements constrain Alpine glacial inception across the Marine Isotope Stage 11/10 transition” by Baker et al.
This manuscript presents a nice dataset obtained from the recently published stalagmites from Betten cave in the Swiss Alps (Honiat et al., 2026). The new proxies (isotopes in speleothem sulphate and trace elements) allow to interpret the environment associated with the speleothem formation in the studied time interval (transition MIS 11-MIS 10) and shed some light on the mechanisms related to subglacial speleothem precipitation. This is a very interesting study, well-written, original and that will help to further studies in this research line in other mountain ranges (eg. Pyrenees). I recommend publication, I just have some minor comments
Line 37: temperature glacier – is it correct or a typo? I think it has to be changed to: temperate or warm-based glacier
Line 64: in those depressions filled by lakes, is there any study on lake sediments that merits citation? It may be another type of continuous record to fill the gap!
Line 86: this paragraph about Paleoclimate records in alpine karst may be included in the following 1.3 about subglacial speleothems to simplify the introduction.
Line 107: change deposition by formation or by precipitation
Line 172: I wonder if any cosmogenic date or OSL date are available in the Alps for this MIS 10 glaciation. If so, it would be important to reflect it in the text and in the map of Figure 1.
Line 195: Since this methodology is quite novel (or at least it is not the usual one in speleothems) I suggest you to include a step by step procedure in the supplementary to help the readers in further studies.
Results: to me, Figure 3 should appear earlier in the manuscript when trace element profiles are described. As it is now, the reader gets lost in the Result section since the figures with the trace elements are in the supplementary; this fact makes the reading uncomfortable and unclear. I suggest to include at least one figure with trace element data in the main text or place Figure 3 earlier in the text.
I like Figure 5, with the explanation of the three phases on the landscape, well-illustrated and easy to understand the different signals in the different stalagmites from the same cave. I am just not totally sure if this figure will be clearer if removing the satellite image and using an elevation model. Just a suggestion to check. Regarding Figure 6, I suggest increasing the size (of the figure and, specially, of the text, it is really small).