the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Feb 2026
In-depth characterisation of organic matter thermal lability and composition from Arctic Permafrost thaw slumps
Abstract. The rapid warming of the Arctic is accelerating permafrost thaw and mobilising large, previously frozen organic-carbon reservoirs. Retrogressive thaw slumps (RTS) are dynamic hotspots of abrupt permafrost disturbance that expose deep, millennial-aged material to erosion and transport. To assess the fate of slump-derived organic matter (OM), we analysed samples from (i) the seasonally thawed active layer, (ii) Holocene and Pleistocene permafrost, (iii) freshly thawed debris, and (iv) runoff across four RTS of contrasting sizes and ecological settings on the Peel Plateau, north-western Canada. We specifically quantified OM abundance, thermal stability, and radiocarbon content, complemented by thermally-sliced pyrolysis–gas chromatography–mass spectrometry (Ts-Py-GCMS) for molecular fingerprints. Our results show that OM age and stability primarily reflect geomorphic feature type. Permafrost, debris, and runoff contain radiocarbon-depleted, thermally stable carbon, whereas active-layer OM is younger and more labile, with minor contributions of stabilised, higher-energy fractions. Ts-Py-GCMS shows that low-temperature fractions are dominated by carbohydrate- and cellulose-derived pyrolysates, while higher-temperature fractions contain aromatic and long-chain aliphatic compounds consistent with more processed or mineral-associated OM. The close similarity between permafrost, debris, and runoff indicates that RTS predominantly export ancient, thermally stable OM with limited early-stage alteration. These findings highlight that a substantial portion of thaw-mobilised particulate carbon likely remains stable during initial transport, with important implications for Arctic carbon-climate feedbacks.
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RC1: 'Comment on egusphere-2026-845', Anonymous Referee #1, 28 Mar 2026
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AC1: 'Comment on egusphere-2026-845', Marco A. Bolandini, 13 Apr 2026
Dear Reviewer,
We sincerely thank you for the constructive and insightful comments. We appreciate the positive evaluation of our manuscript and the recognition of its technical innovation and relevance for permafrost carbon research.
In the revised version, we have implemented several modifications to improve clarity and address the reviewer’s concerns, including:
(1) We have clarified the use of harmonized temperature windows across SoliTOC, Ts-Py-GCMS, and ORO–AMS. We now explicitly state that these methods provide complementary constraints on organic matter thermal stability, and that the shared temperature framework is used as a conceptual and qualitative reference, rather than implying direct equivalence of organic matter fractions.
(2) We have revised the description and interpretation of cross-method comparisons, particularly in relation to Fig. 4, to better explain the rationale for combining molecular (Ts-Py-GCMS), thermal (SoliTOC), and radiocarbon (ORO–AMS) data. The text and figure captions now clearly state that the combined presentation is intended to relate molecular composition, thermal stability, and radiocarbon age.
(3) We have corrected inconsistencies in the reporting of ROC/TOC ratios between SoliTOC and ORO–AMS, and updated the corresponding text and Supplementary Material to ensure consistency with the data.
Detailed, point-by-point responses to all comments are provided below.
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AC1: 'Comment on egusphere-2026-845', Marco A. Bolandini, 13 Apr 2026
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AC1: 'Comment on egusphere-2026-845', Marco A. Bolandini, 13 Apr 2026
Dear Reviewer,
We sincerely thank you for the constructive and insightful comments. We appreciate the positive evaluation of our manuscript and the recognition of its technical innovation and relevance for permafrost carbon research.
In the revised version, we have implemented several modifications to improve clarity and address the reviewer’s concerns, including:
(1) We have clarified the use of harmonized temperature windows across SoliTOC, Ts-Py-GCMS, and ORO–AMS. We now explicitly state that these methods provide complementary constraints on organic matter thermal stability, and that the shared temperature framework is used as a conceptual and qualitative reference, rather than implying direct equivalence of organic matter fractions.
(2) We have revised the description and interpretation of cross-method comparisons, particularly in relation to Fig. 4, to better explain the rationale for combining molecular (Ts-Py-GCMS), thermal (SoliTOC), and radiocarbon (ORO–AMS) data. The text and figure captions now clearly state that the combined presentation is intended to relate molecular composition, thermal stability, and radiocarbon age.
(3) We have corrected inconsistencies in the reporting of ROC/TOC ratios between SoliTOC and ORO–AMS, and updated the corresponding text and Supplementary Material to ensure consistency with the data.
Detailed, point-by-point responses to all comments are provided below. -
RC2: 'Comment on egusphere-2026-845', Anonymous Referee #2, 03 May 2026
Review for Bolandini et al,
This is an interesting, innovative, and timely study. Understanding the fate of OM supply in terms of thermal stability from retrogressive Thaw Slumps across the fragile Arctic ecosystem is much needed, and as such, this study does make an important contribution to the field.
I do, however, believe that a few clarifications are much needed to aid the reader (and the community) :
1. Methodological clarification: The Ramped Oxidation technique is gaining traction in the community with ever-expanding applications. However, one thing that I am concerned about is the lack of homogeneity in step 1 of the process, i.e., the rate of heating and flow rate. This study uses 5 degree C/min. This is not the same across various other studies using this technique e.g., Garnett et al., or Stoner et al, (both of which haven't been cited here). A parallel can be drawn with something similar used to study e.g., atmospheric aerosol speciation (see Table 1 in Dasari et al., 2022 Front. Env. Sci. https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2022.907467/full).
I belive these set of authors are perhaps the most well placed to discuss /comment on this aspect in detail in this manuscript: 'How does decreasing or increasing this rate of heating (and flow rate) affect the thermograms and thereby the findings/implications ?' I suggest that the authors add a section or a paragraph regarding this in the methods or discussion, where they categorically discuss the lack of homogeneity (intentional or unintentional) of the heating /flow rates across the usage of RPO technique and its potential implications on the analysis (on this dataset) and in general. If possible, perhaps show in the Supp.info thermogram (s) using different heating /flow rates for such exotic samples if available, or for an equally interesting sample material.
A reader would want to know how and why this rate was chosen. Also, why didn't the authors consider heating ramp to 900 °C as in other studies using similar technique?
2. Charring issue: I believe any organic material can char after a certain temp range. How did the authors address this issue in this dataset? Please provide clarification in the manuscript.
3. Discussion: While the authors have touched a bit on the 'fate' of OM. I believe the run-off samples are super interesting and can be used to expand the discussion towards whether this thermally stable OM is expected to be a sink of C to the Arctic ocean or river sediment OR further in the river system, contribute to the release of 'aged' C as GHGs (see Dasari et al., 2024 PNAS Nexus) from the river system? I think it's important to at least comment on it in the discussion.
4. Minor issues: I have found in several places across the ms the statements are not followed by the Figure numbers. Please fix this to improve readability.
Citation: https://doi.org/10.5194/egusphere-2026-845-RC2 -
AC2: 'Reply on RC2', Marco A. Bolandini, 15 May 2026
Dear Reviewer,
We sincerely thank you for the constructive and insightful comments. We appreciate the positive evaluation of our manuscript and the recognition of its relevance for understanding the fate of thaw-mobilised organic matter in Arctic permafrost systems.
In the revised version, we have implemented several modifications to improve methodological clarity, strengthen the interpretation, and address the reviewer’s concerns, including:
(1) We have clarified the rationale for the selected ORO–AMS operational settings, including the heating rate and carrier-gas flow. We now state that these parameters were selected based on stable performance of the ORO–AMS configuration and previous optimisation, and we explicitly acknowledge that comparisons among RPO/ORO studies should consider differences in ramp rate, flow rate, gas composition, and system configuration. We also added relevant methodological references, including Dasari and Widory (2022), Garnett et al. (2023), and Stoner et al. (2023).
(2) We have clarified that samples were ramped to 900 °C, but thermograms are displayed only up to 800 °C because only minimal additional CO₂ was released above this temperature.
(3) We have addressed the potential issue of charring by clarifying that the oxygen-rich carrier gas in ORO–AMS was used to promote oxidative decomposition and minimise charring. For Ts-Py-GCMS, we now explicitly state that identified compounds are interpreted as operational pyrolysis products rather than direct molecular inventories of the original organic matter, and that high-temperature fractions are interpreted cautiously because they may include secondary pyrolysis or char-derived products.
(4) We have expanded the discussion of runoff samples as a transitional pool linking terrestrial mobilisation and downstream processing. The revised text now discusses both potential sedimentary storage of thermally stable particulate organic matter and possible delayed transformation into dissolved or gaseous carbon during riverine transport. We also added the suggested reference to Dasari et al. (2024) to support the discussion of aged carbon leakage from Arctic river systems.
(5) We have improved readability by adding missing figure references, correcting Table 1 for clarity, and implementing additional minor corrections to spacing, grammar, punctuation, and terminological consistency throughout the manuscript.
Detailed, point-by-point responses to all comments are provided below.
Citation: https://doi.org/10.5194/egusphere-2026-845
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AC2: 'Reply on RC2', Marco A. Bolandini, 15 May 2026
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This manuscript by Bolandini et al. investigates the thermal stability of OM from both bulk and molecular perspectives, combining multiple analytical approaches, including SoliTOC for OM composition, Ts-Py-GCMS for molecular fingerprinting, and ORO-AMS for radiocarbon characterization. Overall, the study is technically innovative and provides a valuable new perspective for permafrost carbon research, particularly in linking thermal reactivity with molecular composition and age.
However, one key concern relates to the harmonization of temperature windows across these three fundamentally different analytical techniques. While the use of consistent temperature intervals may suggest direct comparability, material released within the same nominal temperature range may not represent equivalent OM fractions across methods. This could potentially lead readers to overinterpret cross-method consistency. I therefore suggest that the authors explicitly clarify that these approaches provide complementary, rather than directly comparable, constraints on OM thermal stability, and that the shared temperature framework should be interpreted in a qualitative or conceptual sense rather than as a one-to-one correspondence.
Overall, I consider this to be a valuable contribution, the manuscript could be suitable for publication after addressing comments below.
Comments: