the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Aug 2025
A continuous 6000 year age depth relationship for the remainder of the Weißseespitze summit glacier based on 39Ar and 14C dating
Abstract. Associated with ongoing global warming, prolonged periods of negative mass balance affect even Alpine glaciers in high summit regions, which are also prime candidates for paleoclimate-related ice core studies. This greatly complicates the already challenging task of establishing an age-depth relationship where now both, the age at depth and at the surface is an unknown. Radiometric ice dating methods are an important key to tackle this challenge. This study presents a comprehensive age-depth profile of the summit glacier of Weißseespitze (WSS, 3500 m a.s.l.) in the Austrian Alps, utilizing a novel combination of radiometric dating methods – 39Ar and 14C. Ice cores from drilling campaigns conducted in 2019, 2023, and 2024 were analyzed to overcome challenges posed by extensive ice loss and surface melting that limit traditional dating techniques. All 39Ar samples were measured using atom trap trace analysis (ATTA). Surface mass balance (SMB) data since 2019 were used to align core depths across years, and all samples were referenced to height above bedrock to standardize comparisons.
Age modeling using least squares fitting and Monte Carlo sampling was performed for three glaciological models: Nye, Raymond, and a two-parameter (2p) model to test their applicability. The 2p model provided the best fit (χ2red = 0.4), closely matching the data and providing a continuous age-depth scale. The model yielded a mean accumulation rate of 0.53 m w.e. a-1 (1σ range: 0.39–0.63 m w.e. a-1) and a thinning parameter p = 0.92 (1σ: 0.81–0.97), the former agreeing with current accumulation estimates.
The results show that the surface ice dates back approximately 400 a, emphasizing the extent of recent ice loss. Apart from this, the continuous age-depth relation shows no sign of prolonged periods of mass loss at WSS within the 6000 a glaciation history prior to today.
This work underscores the utility of 39Ar dating in alpine glaciology, enabling precise reconstruction of age-depth relationships even under advanced glacial retreat and enhancing our understanding of Holocene climate history in the Eastern Alps.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-3681', Wei Jiang, 27 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3681/egusphere-2025-3681-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2025-3681-RC1 -
RC2: 'Comment on egusphere-2025-3681', Anonymous Referee #2, 17 Sep 2025
Review of « A continuous 6000 year age depth relationship for the remainder of the Weißseespitze summit glacier based on 39Ar and 14C dating” by Wachs et al., submitted to CP, 2025.
This manuscript presents an innovative method of combining radiogenic dating methods using 14C (previously published) and 39Ar on a set of ice cores extracted between 2019 and 2024 from the Weißseespitze summit glacier. These dating points are then compiled and used to feed different dating models in order to evaluate them, obtain annual accumulation values and estimate the age of the surface ice.
I recommend this manuscript for publication, after some major revision.
General comments:
Although this combination of the two radiogenic methods has already been presented on other sites (Tibet, Dôme du Goûter), its use on an ablating glacier, having lost 80% of its thickness compared with its maximum extension, is particularly ambitious and interesting since these cases will unfortunately occur more and more often.
This study required the compilation of glaciological data and the use of statistical methods that went beyond the application of the dating methods mainly presented, and the rigorous presentation of the limits of these compilations, clearly highlighting the uncertainties in the data and methods used.
However, some aspects need corrections or adjustments:
1) The authors maintain that the data presented allow us to assert that there is no hiatus over the upper 2000 years of the profile. In Figure 4b, the zoom on the dated points, this conclusion is not obvious. In my opinion, between the 39Ar and 14C point series, it seems to me that these two series are not as well 'aligned', despite the uncertainty bars. This could possibly be due to a hiatus during this time interval, or as proposed that the 39Ar dates are inaccurate due to the half-life value not being updated.
2) The authors conclude that the combination of 39Ar and 14C has provided a significant advance in dating by allowing a better fit of the best dating model. For this conclusion, it would have been interesting to be able to judge this by presenting the best model fit using only the 14C and glaciological data, then a new version adding the 39Ar dating points, even if a short test (line 305-309) tries to convince us.
3) On these summit glacier sites, Weißseespitze, Colle Gnifetti or Dôme du Goûter, the net accumulations are not representative of precipitation because a major part of the winter and/or annual snow is blown away. This is one of the reasons why these sites are unique and have preserved fairly old ice, which is interesting for certain studies. On the other hand, this means that the annual record is not complete (often only wet summer snow is accumulated). Under these conditions, the comparison of chemical profiles, where the aim is to identify specific events and compare them with other sites, is questionable. The dust layers may have different sources, Saharan dust, or a longer period of local dust deposition following a period of ablation. In this manuscript, I propose to delete the paragraph concerning the Calcium profile and their comparison with Colle Gnifetti.
4) With regard to the accumulation values obtained by the models, it is clear that these have not been constant over this long 6000 years period. First of all, the values obtained with the 6 high points and then the 6 low points are quite different. Can you either expand on your conclusions, or use a model that allows accumulation to evolve over time?
Special remarks:
- Lines 24-25: "novel combination" is not correct, it has been used and published previously (Tibet, Dôme du Goûter).
- Line 45: add significant references to Alpine Holocene records.
- Lines 74-75: add information on temperatures, figures or data.
- Line 76: "is rapidly declining", add data
- Line 97-100: If the glacier is covered by a homogeneous layer of dust on the surface, this does not necessarily mean that it comes from a deep layer that appeared following the melting of the surface, but it may come from deposits of recent particles accumulated over the entire ablation period, just hidden during the winter but returning the following spring.
- Line 125: Illustrating the 3H profile in Figure 3 could complement the data presented.
- Line 179: Why has a 14C value been removed?
- Line 305-308: Do the 6 upper dots represent 39Ar, and the 6 lower dots 14C?
- Line 318-328: Should the new estimate of the half-life of 39Ar not be used, or at least compared with the current value, in this work?
- Line 339-364: The discussion of calcium profiles is not convincing.
Citation: https://doi.org/10.5194/egusphere-2025-3681-RC2 -
EC1: 'First editorial comment on egusphere-2025-3681', Eric Wolff, 22 Sep 2025
You will see that you have 2 reviews for your paper. There remain about 3 weeks before the discussion period closes but you are welcome to post replies to the reviews before that. At the end of the discussion period you will be asked to post a final reply and then I will be able (if your responses show that you will adequately address the issues raised in review) to invite you to submit a revised version. As you will see the comments of rev 1 are mainly of a technical nature about the methodology. The comments of rev 2 raise some fundamental questions about your interpretation so please do consider them carefully.
Citation: https://doi.org/10.5194/egusphere-2025-3681-EC1
Data sets
dataset Wachs et al., 2025 "A continuous 6000 year age depth relationship for the remainder of the Weißseespitze summit glacier based on 39Ar and 14C dating" David Wachs et al. https://zenodo.org/records/16528316
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