PONE-D-22-29357How do caves breath: the airflow patterns in karst undergroundPLOS ONE

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Reviewers' comments:

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Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: N/A

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The article describes the ventilation in caves with 2 entries, commonly called "chimney-effect", where the direction and velocity of the airflow is proportional to the internal/external temperature difference and to the altitude difference between both. This classical aspect is described in the first part. One would expect a perfect seasonal symmetry. Based on long measurements of these parameters in natural sites, the author shows on the contrary a clear seasonal asymmetry. This very interesting new observation is formalized in the second part by a conceptual model (whose physics I am not able to validate), on which a numerical model is then built to examine the role of the variations of vertical profile of passages, of width changes, etc. The results are discussed, showing in particular the orders of magnitude of the airflow variations according to the considered cases. The paper concludes by examining a V-shaped duct with two inlets at the same altitude, where the driving pressure is theoretically zero in summer, but where the winter instability is prolonged beyond the cold season due to the thermal inertia of the rock. These results confirm and extend those of Lismonde 2001 (https://doi.org/10.3406/karst.2001.2468). Again, the shape of the inlets, where the presence of a cold mass (snow or ice), significantly disrupts the theoretical scheme.

This paper presents considerable advances in the understanding of air flows previously described as "simple", advances made possible by numerical tools. Future implications are expected, on the conservation of now disappearing unground ice, subsurface condensation water, distribution of carbonate dissolution in the vadose part, etc. As such, it deserves to be published in this type of Journal.

I have no major substantive remarks, it is clearly written in both style and approach, and it can be published "as it is", considering the following very minor corrections:

- Paragraph "Driving pressure of the chimney effect..." (no line numbering here): Starting from the inlet E1 (not E2!) at the elevation z1 and pressure p1...

- 124 : author mentions "most of our observation sites...", whereas only 2 sites are documented before. Only at the final end of the paper, he discusses other sites. Be clearer, and make the difference between qualitative field observations and studied sites with quantitative records

- 293: In following scenarios the diameter in the vicinity...

- 384: The results are based on approximations and assumptions that are (in < remove) not always valid

Philippe Audra

Reviewer #2: More and more studies recognize the connection and joint control of air and water circulation on the processes of karstification that create and continuously modify karst systems. This study represents a significant step in the numerical modeling of air circulation by the chimney effect mechanism, which seems to be the most significant driver of air circulation, especially in the shallower parts of the karst subsurface. Modeling describes the features of seasonal air circulation for several typical morphological forms of caves. The presented results quantitatively show the features of the circulation, and are particularly useful for interpreting the results of the monitoring performed in-situ in the caves. Therefore, I highly recommend the manuscript for publication with a few minor suggestions.

Specific comments:

Lines 103-123: It seems to me that the described example is mostly based on the study published by Kukuljan et al. 2021, which is not noted in this section (otherwise monitoring setup should be described in more detail).

Fig. 13, Lines 313-322: According to the figure (and description within the text) it seems that in the case of colder outside air (-5°C), the air circulation in the cave is directed from the higher entrance (z+δz) to the lower one (downdraft). This is in contrast to the previous examples (updraft during the period of colder outside air), and also contrary to the described example of the "Kačna" Cave (Figure 15), where during the cold season the cold air enters through the lower (main) entrance of the cave. So, it looks that there is a mistake on the Figure 13 regarding airflow direction?

Line 323: Luetcher et al (2008) also noted cold trap behavior of u-shaped cave.

Figure 15: Short explanation for the varying colors of the arrows indicating airflow direction could be added.

Lines 368-380, Figure 16: Example of "Snežnik" Cave is interesting but slightly confusing: if the mentioned entrance is at the highest point of the massif, the formation of ice in it should indicate a downdraft during the cold season, which contradicts the previous considerations?

Also, the model shown in Figure 16 includes two inlets approximately at the same height, while the Snežnik example probably has a "snow covered" inlet significantly above the other one? Not sure if the model would show a similar results for a configuration more suitable for Snežnik example.

There is a recently published study of monitoring results from a very deep cave with extensive ice deposits (Velebit Mt., Dinaric Karst), which interprets the functioning of the cave as a cold-trap that causes a negative temperature anomaly within the karst massif (in accordance to your results and considerations).

Conclusion section: I propose to additionally include brief conclusions related to the influence of object morphology (L-shaped, V-shaped, varying diameter) on seasonal airflow patterns.

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Reviewer #1: Yes: Philippe AUDRA

Reviewer #2: No

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How do caves breathe: the airflow patterns in karst underground

PONE-D-22-29357R1

Dear Dr. Gabrovšek,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Yanping Yuan

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Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: (No Response)

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Reviewer #2: Yes: Andrej Stroj

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