In their study, Vignoni and colleagues present an interesting case study into the “Spatial variability of the modern radiocarbon reservoir effect in the high-altitude lake Laguna del Peinado (Southern Puna Plateau, Argentina)”. Whilst the phenomenon described is not in itself new, the dataset presented provides a useful example (that I shall no doubt cite myself in future!) of both spatial and temporal variability in the radiocarbon reservoir effect of a high altitude freshwater body, with fairly extreme effects (>>10,000 14C yrs) evident.

The manuscript is well written, and I recommend acceptance, pending very minor revisions, which I list below. N.B., not all suggestions/questions necessarily require revision of the text. I thank the authors (and editor!) for the opportunity to read this interesting submission, and wish them well for their future research.

L16-17: You obviously go on to talk about TEMPORAL variation in reservoir effects too, but I felt that this should also be mentioned right at the start here, along with your noting of “spatial variations”.

L24-25: You’re absolutely right about the implications of this study affecting both precision and accuracy of 14C-derived chronologies, and they’re obviously interwoven, but I wonder if these should be inverted to reflect the greater importance of accuracy over precision? (I.e., accuracy is fundamental – there’s no point having inaccurate chronology is there?! – and, after that, increased precision then makes the data increasingly useful, no?)

L31: You list “endorheic basins that host numerous saline lakes, playa-lakes and salars”; is there scope for these basins to episodically dry out completely, with consequent impacts (hiatuses!) upon age modelling/palaeoenvironmental reconstruction?

L48-49: “Sometimes, even assumptions on temporal variations of the reservoir effect are included in the construction of age-depth models”; please could you include one or two references to support this statement.

L119-124: In order to interpret any radiocarbon data, it is essential to specify what chemical pre-treatment procedures have been applied. (I take on trust that this has been performed robustly, but this needs to be fully clarified, and is probably the most significant of my comments.)

L123-124 (and also for Table 1): Why only calibrate the post-bomb 14C measurements, but not the pre-bomb?

L125-127: Again, what chemical pre-treatment procedures were applied to these samples prior to d13C analysis?

L129: Surely this is “precision” rather than “accuracy”?

L143: Your samples were collected in 2019… and so the latter age (2018-2019 cal CE) makes sense. But how do you explain the former age (1994-1996 cal CE)? A freshwater reservoir effect wouldn’t ENHANCE the 14C (112.39 pMC c.f. 101.61 pMC). Precisely what was the material sampled (for both of these samples)? Is the former sample more woody material (with an associated inbuilt “storage age”)? Please give more information around these samples, and suggest what has led to this.

L166-167: I would say that this wording is misleading; Yes, terrestrial plants are “expected to provide modern radiocarbon ages without any reservoir effect involved” (generally speaking! Although there could be rare examples where the expectation may differ…) BUT aquatic plants obviously take on their carbon from the water, and so they wouldn’t be “expected to” provide modern radiocarbon ages, surely? Isn’t that a fundamental premise of the present paper? I just find the wording of this sentence unnecessarily misleading, taken in isolation.

L168-169: This is really interesting. I am not a biologist – is the aged C being taken in by the grass from the air (localised atmospheric depletion from C release from the hydrothermal spring), or is the aged C being taken in through the roots (in the water taken up by the plant)?

L169: Clarify again that here you are referring to aquatic species(?).

L182-184: Give an approximate representation of the values given for the cited study.

L191-194: “The dissolution of carbonate-rich sediments or rocks in the catchment area is usually considered a main source of 14C-dead carbon influx into a lake (Macdonald et al., 1991; Ascough et al., 2010). However, the dissolution of catchment carbonates can only be a minor source of 14C-dead carbon into Laguna del Peinado because the lithology of the basin is dominated by volcanic rocks”. Does this contradict what was written earlier on (“Abundant carbonate precipitation takes place in the El Peinado basin…”, L81), or do I misunderstand? (Even if the latter, perhaps clarification is still needed?)

L213 and 216: Can you clarify what you mean by the terms “old” and “ancient” groundwater? (Is it the “100-10,000 years or longer” noted below, L219?)

L279: Is it possible to measure 14C on (the DIC/dissolved gasses of) the water itself? And would/could this, in combination with other isotope measures (including d13C and d3H, mentioned earlier) help to understand the “dominant process” question?

L287: I would actually say that “corrections of 14C chronologies based on a single reservoir age for an entire lake…” would result in INACCURATE results, rather than just “large uncertainties” (which, as I noted earlier would be a bigger problem). You would only end up with “large uncertainties” if these uncertainties were ACTUALLY accounted for and, the point that I think you’re making (which I totally agree with!) is that often these “large uncertainties” are NOT properly accounted for (…producing small uncertainties, but inaccurate chronologies).

Finally, a more general question relating to your Discussion: If the C assimilated by the species in the hydrothermal pool were solely sourced from magmatic C (rather than “old groundwater”), this would yield "infinitely old" 14C ages… And so, in that scenario, even the older 14C sample would still include some proportion of "modern" C input? (Is that reasonable to assume?) Why not perform a quick endmember "mixing model" to estimate the proportion of C (for each sample) that is from a modern (2019 CE atmospheric) source and what proportion from geologically old (14C dead) C? (N.B. this is a simple “back of an envelope” calculation, rather than requiring “proper” modelling!) I suggest that this will give a "better" impression of the differing contributions (of old vs modern C), which can be skewed by the exponential nature of the 14C decay curve, which can then carry through to all of your samples through the lake. (I.e., for each sample, what proportion of C is sourced from "modern" vs geologically "dead" sources?)

(Non-comprehensive) typo/wording suggestions:

L14: Insert comma after “This”.

L17: Change “constrain” to “constraint”.

L24: Here, do you mean the “centre of the lake” specifically?

L114: Missing word: “littoral [zone]”?

L115: Spell out “macrofossil”… Perhaps even “plant macrofossil”.

L127: “Mile” should read “mille”.

L143: “cal CE” is a suffix, and so should come after the date (e.g., “1994-1996 cal CE”).

L246: Even though I agree that your explanation is the overwhelmingly most likely one, is “proving” still too strong a word to use?

L278: I would say that “>26,000 14C years” is more than “up to several thousand years”?!

The reviewed manuscript focuses on the local variability of reservoir effects for radiocarbon dating on the Southern Puna Plateau (Argentina) comparing samples from different positions in and around Laguna del Peindado. The authors tackle reservoir effects, an important issue for the investigation of age-depth relationships for lake sediments and provide information about possible error sources.

Through the analysis of seven distinct samples, the authors demonstrate how and to which extent magmatic CO₂ and ancient groundwater effects the ¹⁴C composition and deliver a detailed and well-referenced investigation of possible error sources. In addition, these results are compared to a new sediment core from the lake providing four downcore radiocarbon samples and to a core from a previous study. The overall result of the manuscript is the spatial variability of the samples around but also within the lake, opening new questions about correcting the lake’s sediment chronology.

Strengths:

The aim of the manuscript is communicated clearly and the methodology of the study is well-suited to achieve it. The authors use a large number of relevant references and implement them nicely to their own results. Future studies especially at this location as well as from comparable areas will benefit from this manuscript in terms of dating. The manuscript provides all necessary information to comprehend the methods.

Weaknesses:

The overall weakness of the study is mentioned and discussed by the authors themselves: results would have benefitted from more samples, e.g. by having short cores from additional and especially more southern locations of the lake. Nevertheless, the study is well discussed and the arguments seem logic.

Contribution:

The contribution to the field seems significant, especially for studies of comparable locations. However, as the article provides no clear solution for the correction of reservoir effects for downcore samples from this lake, it only serves as a well-discussed summary and estimation about potential sources of error.

Conclusion:

Overall, this manuscript provides an interesting investigation of regional effects on radiocarbon dating and summarizes related information. It delivers a well-structured overview of previous studies from the study area and topics combined with new results. While the article has some limitations with regard to the sample size, it is a valuable addition to the literature of the studied location and to comparable areas providing insights into the interpretation of radiocarbon dates.

The manuscript follows the classical structure in an appropriate balance and is written in a clear and fluent language. I have only minor comments and questions to the manuscript:

Page 1

Line 22: Please check if it would make more sense to use here the term “younger” instead of “lower”.

Line 28: The introduction is very well written and the problem investigated and the aim of the study are clearly described. However, I think the manuscript might benefit from a few sentences about reservoir effects in general and/or definitions like the terms “C14-free”, “C14-depleted”,…. . Please consider adding some sentences.

Page 3

Line 80: I am not familiar with the study area, but as it is written “currently” I asked myself if information is available about the frequency of lake level changes and/or the history of earlier connections of both lake systems. In both cases the authors should add information here.

Lines 85 – 98: The climate patterns are well described, but to follow this paragraph even better, the manuscript would benefit from an addition of the climate patterns to Fig. 1.

Page 6:

Line 139: I have three questions/comments to Table 1:

• I count six questions marks in the table, e.g. “Hot spring 4?”. These uncertainties are not mentioned in the text or the Table caption. Question marks should be explained to avoid confusion.
• The first two samples result in two calibrated ages each. It should be explained why this is the case.
• Please explain why not all radiocarbon ages have been calibrated.

Page 9:

Line 172, 174, 180: The authors refer to Figure 4 only. Its orientation becomes clear only in comparison to Figure 1. However, I wish either an indication of e.g. “western hot spring”, a north arrow or maybe a numeration of the hot springs as indicated in Fig. 1 with sample names added to Fig. 4. Otherwise, this paragraph might not be understandable without comparison to Fig. 1. Moreover, Fig. 1 should be referred in addition to Fig. 4.

Page 12:

Line 257: How do the authors proceed with the sediment core and develop the chronology? I would suggest to implement this information here or somewhere later in the manuscript.

Line 263: Are there lithological indications that would support the hypothesis of a hiatus in the sediment core?

Page 16:

Line 380-381: Please check if the published year should be changed to 2022, as indicated on the journal’s homepage