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:

1. Line 148-149: The role of the second oven is not sufficiently explained here.
2. Line 159-160: Strictly speaking, comparability across temperature windows requires that all experimental conditions are consistent, including carrier gas flow, heating rate, oxygen availability, and other operational parameters. If these differ between the applied techniques, then the same nominal temperature intervals may not correspond to equivalent processes or OM fractions. I therefore suggest that the authors explicitly clarify a bit here.
3. Line 187-190: Similar to Comment 2, the applied techniques rely on fundamentally different processes. Ts-Py-GCMS is a pyrolysis-based method, whereas ORO-AMS and SoliTOC are based on combustion. Therefore, signals within the same temperature range may not represent comparable OM fractions, which should be clarified.
4. Line 256-257: I saw higher ROC/TOC by ORO.
5. Line 286-287: HO2 also shows a rebound in carbon age.
6. Figure 4: The rationale for comparing 14C results from ORO with pyrolysis-based molecular fingerprints is not entirely clear.
7. Supplementary Material - Line 58: “green triangles”
8. Supplementary Material - Line 59: “with ORO–AMS reporting slightly higher ROC/TOC values"
9. Supplementary Material - Line 82: “yield lower TIC/TC values than SoliTOC"

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.