A multimillennial Alpine ice core chronology synchronized with an accurately dated Arctic Pb record

Gabrielli, Paolo; Jenk, Theo M.; Bertó, Michele; Dreossi, Giuliano; Festi, Daniela; Kofler, Werner; Winstrup, Mai; Oeggl, Klaus; Schwikowski, Margit; Stenni, Barbara; Barbante, Carlo

doi:10.5194/egusphere-2025-2174

Preprints

https://doi.org/10.5194/egusphere-2025-2174

Preprints

28 May 2025

| 28 May 2025

A multimillennial Alpine ice core chronology synchronized with an accurately dated Arctic Pb record

Paolo Gabrielli, Theo M. Jenk, Michele Bertó, Giuliano Dreossi, Daniela Festi, Werner Kofler, Mai Winstrup, Klaus Oeggl, Margit Schwikowski, Barbara Stenni, and Carlo Barbante

Abstract. A low latitude-high altitude Alpine ice core record was obtained in 2011 from the glacier Alto dell'Ortles (3859 m, Eastern Alps, Italy). A preliminary absolute timescale (TC2016) based on a peak in ³H activity, and ²¹⁰Pb and ¹⁴C dating of carbonaceous particles and organic remains provided evidence of one of the oldest Alpine ice core records spanning the last ~7000 years, back to the last Northern Hemisphere Climatic Optimum. Here we provide an additional number of time markers that corroborate the multimillennial nature of the Alto dell'Ortles ice cores while significantly decreasing the uncertainty of the chronology. First, ¹⁴C dating of an additional organic fragment (a charred spruce needle) discovered next to the basal ice provided an age (232 ± 126 BCE) which agrees with previous ¹⁴C dates in the oldest part of the record. Second, novel seasonally resolved pollen records from the upper firn/ice portion of the Alto dell'Ortles cores were combined with d¹⁸O and dust annual variations to refine the dating for the 20^th century by means of an automatic algorithm (Straticounter; between 1927 and 2011 CE) and visual counting (from 1900 to 1926 CE). The new and previous time markers were combined into a revised intermediate timescale (CP2025/1) by fitting using Markov chain Monte Carlo simulation (COPRA model). CP2025/1 was used for synchronizing a novel Pb concentration record obtained from the Alto dell'Ortles cores with a Pb record from an array of Arctic ice cores (AN), well-dated (±5 years) for the ~200 BCE to ~1900 CE period. The ties used for matching the two Pb records were within the uncertainty of CP2025/1 and of the selected tie-points (1- to 2-sigma, in the ancient part; 1-sigma, in the recent part). The correlation obtained after synchronization is 0.44 (Pearson's r, p < 0.001), demonstrating that these two distant atmospheric Pb records share a large portion of their variability back to 200 BCE. The synchronization of CP2025/1 with AN resulted in a, further refined, final timescale (CP2025/2). An investigation of CP2025/1 and CP2025/2 by means of a simple 1-D flow model suggests that non-steady-state conditions, in particular changes in past net accumulation rates, need to be considered to provide a full physical explanation of the age-depth relationship obtained. The new Alto dell'Ortles CP2025/2 chronology of improved accuracy will allow to constrain Holocene climatic and environmental histories emerging from this high-altitude glacial archive of Central Europe. The novel combination of methodologies used may also be adopted to build, or improve, the chronologies of other ice cores extracted from-low latitude/high-altitude glaciers that typically suffer from larger dating uncertainties compared with well dated polar records.

Received: 08 May 2025 – Discussion started: 28 May 2025

Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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Journal article(s) based on this preprint

22 May 2026

A multimillennial Alpine ice core chronology synchronized with an accurately dated Arctic Pb record

Paolo Gabrielli, Theo M. Jenk, Michele Bertó, Giuliano Dreossi, Daniela Festi, Werner Kofler, Mai Winstrup, Klaus Oeggl, Margit Schwikowski, Barbara Stenni, and Carlo Barbante

Clim. Past, 22, 1037–1055, https://doi.org/10.5194/cp-22-1037-2026,https://doi.org/10.5194/cp-22-1037-2026, 2026

Short summary

Paolo Gabrielli, Theo M. Jenk, Michele Bertó, Giuliano Dreossi, Daniela Festi, Werner Kofler, Mai Winstrup, Klaus Oeggl, Margit Schwikowski, Barbara Stenni, and Carlo Barbante

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2174', Anonymous Referee #1, 16 Jul 2025
Does the paper address relevant scientific questions within the scope of CP? Yes

Does the paper present novel concepts, ideas, tools, or data? Yes

Are substantial conclusions reached? Yes, however the primary goal of establishing a new chronology for the Alto dell’Ortles core, marks a more incremental change in knowledge. Interpretation of the Pb record is not described (instead it is saved for a future manuscript).

Are the scientific methods and assumptions valid and clearly outlined? Yes

Are the results sufficient to support the interpretations and conclusions? Yes

Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? Yes

Do the authors give proper credit to related work and clearly indicate their own new/original contribution? Yes

Does the title clearly reflect the contents of the paper? Yes

Does the abstract provide a concise and complete summary? Yes

Is the overall presentation well structured and clear? Yes, a few minor typos and grammatical errors throughout.

Is the language fluent and precise? Yes

Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? Yes

Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? Minor change to figure 1 described below.

Are the number and quality of references appropriate? Yes

Is the amount and quality of supplementary material appropriate? Yes

Overview:
Gabrielli et al. (2025) present an updated, age model (CP2025/2) for the Alto dell’Ortles ice cores (Eastern Alps), spanning ~7000 yr. They integrate a new basal ¹⁴C date, enhanced pollen-based annual-layer counts, and a quantitatively controlled Pb-wiggle-match to the Arctic Akademii Nauk (AN) record, within a two-stage COPRA Monte Carlo framework. A simple 1-D flow model is then used to explore non–steady-state accumulation effects.
Specific Comments:
Page 4 Line 22: Were any meltwater samples collected during CFA analysis of the core to test for Pb recovery following leaching to test the theory that different leaching times were the primary driver of the differences between core 1 and core 3?
Figure 1. The dotted blue lines across the cores are not described in the figure caption.
Page 15 Line 4: Using “remarkable” to describe the r value of 0.41 is an overstatement.
Citation: https://doi.org/10.5194/egusphere-2025-2174-RC1
- AC1: 'Reply on RC1', Paolo Gabrielli, 05 Sep 2025
  
  Review 1:
  
  • Does the paper address relevant scientific questions within the scope of CP? Yes
  
  • Does the paper present novel concepts, ideas, tools, or data? Yes
  
  • Are substantial conclusions reached? Yes, however the primary goal of establishing a new chronology for the Alto dell’Ortles core, marks a more incremental change in knowledge. Interpretation of the Pb record is not described (instead it is saved for a future manuscript).
  
  • Are the scientific methods and assumptions valid and clearly outlined? Yes
  
  • Are the results sufficient to support the interpretations and conclusions? Yes
  
  • Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? Yes
  
  • Do the authors give proper credit to related work and clearly indicate their own new/original contribution? Yes
  
  • Does the title clearly reflect the contents of the paper? Yes
  
  • Does the abstract provide a concise and complete summary? Yes
  
  • Is the overall presentation well structured and clear? Yes, a few minor typos and grammatical errors throughout.
  
  • Is the language fluent and precise? Yes
  
  • Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? Yes
  
  • Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? Minor change to figure 1 described below.
  
  • Are the number and quality of references appropriate? Yes
  
  • Is the amount and quality of supplementary material appropriate? Yes
  We thank Reviewer 1 for the positive evaluation of our manuscript and constructive suggestions.
  
  Specific Comments:
  
  Page 4 Line 22: Were any meltwater samples collected during CFA analysis of the core to test for Pb recovery following leaching to test the theory that different leaching times were the primary driver of the differences between core 1 and core 3?
  
  No additional leaching tests were performed for this specific study. Trace metal concentration differences due to acid leaching are related to method specific acidification of samples prior the analyses. It depends on acid concentration, acidification time (e.g., Uglietti et al., 2014; Rhodes et al., 2011) and, as we demonstrated in Uglietti et al. (2014), also on the chemical/mineralogical characteristics of the sample itself and the study site. According to a previous test with one single ice sample from the same Mt. Ortles ice core (Uglietti et al. 2014), Pb concentration would not seem to be affected by acid leaching time. However, in that study changes were investigated for acidification times between 24 h and 43 days, not covering the short acidification timescale typical of Continuous Flow Analysis (1-2 minutes; Core 3 analyses, this study) and Discrete Analysis (less than one day; Core 1 analyses, this study).
  
  A manuscript of one of our co-authors is currently under review in the Journal of Analytical Atomic Spectrometry (Münster et al., 2025 JAAS), in which these shorter timescales, from minutes to a few hours, were investigated (1.5-250 minutes) for alpine ice core samples. Those results show a 2-to-3-fold increases in the measured Pb concentration over that short time range, which may explain the observed difference in absolute Pb concentration between core 1 and 3, supporting our explanation of a leaching effect on a time scale of a few hours.
  
  In any event, a fundamental point is that acid leaching time does not affect the shape of the Pb records in cores 1 and 3 that are used in our paper for aligning the depths of these two cores. This point is already made in our manuscript where we state: “In any case, different acidification methods do not affect Pb trends and features (maxima, minima, Pb variations) used for wiggle matching.” In the revised manuscript, we will extend the information so far provided in a specific Supplementary Information section according to the text presented above.
  Figure 1. The dotted blue lines across the cores are not described in the figure caption.
  
  Thank you for the notification, the description will be added.
  Page 15 Line 4: Using “remarkable” to describe the r value of 0.41 is an overstatement.
  
  Agreed, this will be deleted.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2174-AC1
RC2:
'Comment on egusphere-2025-2174', Anonymous Referee #2, 18 Jul 2025

See pdf file in supplement

Citation: https://doi.org/10.5194/egusphere-2025-2174-RC2
- AC2: 'Reply on RC2', Paolo Gabrielli, 05 Sep 2025
  
  Please see our response in the attached pdf file.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2174-AC2
EC1: 'Comment on egusphere-2025-2174', Christo Buizert, 25 Jul 2025

Dear authors,
Your manuscript has now been seen by two reviewers. As per their reports, both reviewers are generally supportive of eventual publication. However, several major issues were raised (particularly by reviewer #2) that will need to be addressed. Please provide a detailed response to the reviewer comments. Given the nature of the recommendations, I will likely invite a revised manuscript. Therefore, you are welcome to provide your response in the form of proposed changes to the manuscript.
Please let me know if you have any questions.
All the best, Christo Buizert (CP editor)

Citation: https://doi.org/10.5194/egusphere-2025-2174-EC1

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2174', Anonymous Referee #1, 16 Jul 2025
Does the paper address relevant scientific questions within the scope of CP? Yes

Does the paper present novel concepts, ideas, tools, or data? Yes

Are substantial conclusions reached? Yes, however the primary goal of establishing a new chronology for the Alto dell’Ortles core, marks a more incremental change in knowledge. Interpretation of the Pb record is not described (instead it is saved for a future manuscript).

Are the scientific methods and assumptions valid and clearly outlined? Yes

Are the results sufficient to support the interpretations and conclusions? Yes

Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? Yes

Do the authors give proper credit to related work and clearly indicate their own new/original contribution? Yes

Does the title clearly reflect the contents of the paper? Yes

Does the abstract provide a concise and complete summary? Yes

Is the overall presentation well structured and clear? Yes, a few minor typos and grammatical errors throughout.

Is the language fluent and precise? Yes

Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? Yes

Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? Minor change to figure 1 described below.

Are the number and quality of references appropriate? Yes

Is the amount and quality of supplementary material appropriate? Yes

Overview:
Gabrielli et al. (2025) present an updated, age model (CP2025/2) for the Alto dell’Ortles ice cores (Eastern Alps), spanning ~7000 yr. They integrate a new basal ¹⁴C date, enhanced pollen-based annual-layer counts, and a quantitatively controlled Pb-wiggle-match to the Arctic Akademii Nauk (AN) record, within a two-stage COPRA Monte Carlo framework. A simple 1-D flow model is then used to explore non–steady-state accumulation effects.
Specific Comments:
Page 4 Line 22: Were any meltwater samples collected during CFA analysis of the core to test for Pb recovery following leaching to test the theory that different leaching times were the primary driver of the differences between core 1 and core 3?
Figure 1. The dotted blue lines across the cores are not described in the figure caption.
Page 15 Line 4: Using “remarkable” to describe the r value of 0.41 is an overstatement.
Citation: https://doi.org/10.5194/egusphere-2025-2174-RC1
- AC1: 'Reply on RC1', Paolo Gabrielli, 05 Sep 2025
  
  Review 1:
  
  • Does the paper address relevant scientific questions within the scope of CP? Yes
  
  • Does the paper present novel concepts, ideas, tools, or data? Yes
  
  • Are substantial conclusions reached? Yes, however the primary goal of establishing a new chronology for the Alto dell’Ortles core, marks a more incremental change in knowledge. Interpretation of the Pb record is not described (instead it is saved for a future manuscript).
  
  • Are the scientific methods and assumptions valid and clearly outlined? Yes
  
  • Are the results sufficient to support the interpretations and conclusions? Yes
  
  • Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? Yes
  
  • Do the authors give proper credit to related work and clearly indicate their own new/original contribution? Yes
  
  • Does the title clearly reflect the contents of the paper? Yes
  
  • Does the abstract provide a concise and complete summary? Yes
  
  • Is the overall presentation well structured and clear? Yes, a few minor typos and grammatical errors throughout.
  
  • Is the language fluent and precise? Yes
  
  • Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? Yes
  
  • Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? Minor change to figure 1 described below.
  
  • Are the number and quality of references appropriate? Yes
  
  • Is the amount and quality of supplementary material appropriate? Yes
  We thank Reviewer 1 for the positive evaluation of our manuscript and constructive suggestions.
  
  Specific Comments:
  
  Page 4 Line 22: Were any meltwater samples collected during CFA analysis of the core to test for Pb recovery following leaching to test the theory that different leaching times were the primary driver of the differences between core 1 and core 3?
  
  No additional leaching tests were performed for this specific study. Trace metal concentration differences due to acid leaching are related to method specific acidification of samples prior the analyses. It depends on acid concentration, acidification time (e.g., Uglietti et al., 2014; Rhodes et al., 2011) and, as we demonstrated in Uglietti et al. (2014), also on the chemical/mineralogical characteristics of the sample itself and the study site. According to a previous test with one single ice sample from the same Mt. Ortles ice core (Uglietti et al. 2014), Pb concentration would not seem to be affected by acid leaching time. However, in that study changes were investigated for acidification times between 24 h and 43 days, not covering the short acidification timescale typical of Continuous Flow Analysis (1-2 minutes; Core 3 analyses, this study) and Discrete Analysis (less than one day; Core 1 analyses, this study).
  
  A manuscript of one of our co-authors is currently under review in the Journal of Analytical Atomic Spectrometry (Münster et al., 2025 JAAS), in which these shorter timescales, from minutes to a few hours, were investigated (1.5-250 minutes) for alpine ice core samples. Those results show a 2-to-3-fold increases in the measured Pb concentration over that short time range, which may explain the observed difference in absolute Pb concentration between core 1 and 3, supporting our explanation of a leaching effect on a time scale of a few hours.
  
  In any event, a fundamental point is that acid leaching time does not affect the shape of the Pb records in cores 1 and 3 that are used in our paper for aligning the depths of these two cores. This point is already made in our manuscript where we state: “In any case, different acidification methods do not affect Pb trends and features (maxima, minima, Pb variations) used for wiggle matching.” In the revised manuscript, we will extend the information so far provided in a specific Supplementary Information section according to the text presented above.
  Figure 1. The dotted blue lines across the cores are not described in the figure caption.
  
  Thank you for the notification, the description will be added.
  Page 15 Line 4: Using “remarkable” to describe the r value of 0.41 is an overstatement.
  
  Agreed, this will be deleted.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2174-AC1
RC2:
'Comment on egusphere-2025-2174', Anonymous Referee #2, 18 Jul 2025

See pdf file in supplement

Citation: https://doi.org/10.5194/egusphere-2025-2174-RC2
- AC2: 'Reply on RC2', Paolo Gabrielli, 05 Sep 2025
  
  Please see our response in the attached pdf file.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2174-AC2
EC1: 'Comment on egusphere-2025-2174', Christo Buizert, 25 Jul 2025

Dear authors,
Your manuscript has now been seen by two reviewers. As per their reports, both reviewers are generally supportive of eventual publication. However, several major issues were raised (particularly by reviewer #2) that will need to be addressed. Please provide a detailed response to the reviewer comments. Given the nature of the recommendations, I will likely invite a revised manuscript. Therefore, you are welcome to provide your response in the form of proposed changes to the manuscript.
Please let me know if you have any questions.
All the best, Christo Buizert (CP editor)

Citation: https://doi.org/10.5194/egusphere-2025-2174-EC1

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (17 Sep 2025) by Christo Buizert

AR by Paolo Gabrielli on behalf of the Authors (17 Oct 2025) Author's response Author's tracked changes Manuscript

EF by Vitaly Muravyev (20 Oct 2025) Supplement

ED: Referee Nomination & Report Request started (20 Oct 2025) by Christo Buizert

RR by Anonymous Referee #1 (25 Nov 2025)

RR by Anonymous Referee #3 (07 Dec 2025)

ED: Reconsider after major revisions (08 Dec 2025) by Christo Buizert

AR by Paolo Gabrielli on behalf of the Authors (07 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (10 Mar 2026) by Christo Buizert

AR by Paolo Gabrielli on behalf of the Authors (29 Mar 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (09 Apr 2026) by Christo Buizert

AR by Paolo Gabrielli on behalf of the Authors (25 Apr 2026) Manuscript

Journal article(s) based on this preprint

22 May 2026

A multimillennial Alpine ice core chronology synchronized with an accurately dated Arctic Pb record

Paolo Gabrielli, Theo M. Jenk, Michele Bertó, Giuliano Dreossi, Daniela Festi, Werner Kofler, Mai Winstrup, Klaus Oeggl, Margit Schwikowski, Barbara Stenni, and Carlo Barbante

Clim. Past, 22, 1037–1055, https://doi.org/10.5194/cp-22-1037-2026,https://doi.org/10.5194/cp-22-1037-2026, 2026

Short summary

Paolo Gabrielli, Theo M. Jenk, Michele Bertó, Giuliano Dreossi, Daniela Festi, Werner Kofler, Mai Winstrup, Klaus Oeggl, Margit Schwikowski, Barbara Stenni, and Carlo Barbante

Supplement

https://doi.org/10.5194/egusphere-2025-2174-supplement

Paolo Gabrielli, Theo M. Jenk, Michele Bertó, Giuliano Dreossi, Daniela Festi, Werner Kofler, Mai Winstrup, Klaus Oeggl, Margit Schwikowski, Barbara Stenni, and Carlo Barbante

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Short summary

A low latitude-high altitude Alpine ice core record was obtained in 2011 from the glacier Alto dell’Ortles (Eastern Alps, Italy) and provided evidence of one of the oldest Alpine ice core records spanning the last ~7000 years, back to the last Northern Hemisphere Climatic Optimum. Here we provide a new Alto dell’Ortles chronology of improved accuracy that will allow to constrain Holocene climatic and environmental histories emerging from this high-altitude glacial archive of Central Europe.

A multimillennial Alpine ice core chronology synchronized with an accurately dated Arctic Pb record

Journal article(s) based on this preprint

Interactive discussion

Interactive discussion

Peer review completion

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Suggestions for revision or reasons for rejection

Journal article(s) based on this preprint

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