Koenig et al. submitted an interesting paper that describes the efforts to improve the information on permafrost thermal state in the Central Andes. In this alpine region, permafrost can be an important factor in planning and design of infrastructure and natural resource development. It is essential to have adequate information on ground properties including the presence of permafrost to make informed decisions. Long-term records of permafrost thermal state can also provide insights into the impact of climate change which is essential for adapting to future conditions. The paper addresses a critical lack of regional knowledge by compiling a large amount of information on permafrost thermal state acquired from measurements made by the private sector along a North-South transect in the Central Andes in an area having significant natural resource potential in various stages of development. Ground temperature measurements from 53 boreholes were compiled and used to characterize regional permafrost conditions. The study addresses a gap in permafrost knowledge in the southern hemisphere and complements the limited number of academic studies in the region. The paper would be of interest to both scientists and engineers and provides essential information for informed decision making and for climate change adaptation. Minor revisions, including many that are editorial, are required before acceptance for publication as described below.

The paper is generally well written and provides a good description of the approach, results and their interpretation and conclusions. However, some sections are probably longer than they need to be and could be more focussed. This is true of the abstract which should summarize the main conclusions of the paper with limited background information. The introduction could also be shortened to reduce the amount of background material and focus on the key things required to provide context for the study. The authors should read through the paper to ensure that unnecessary words are removed and there is no repetition of information. Some suggestions are provided in the detailed comments below.

Some figures and tables could be improved. The text in Table 1 should be enlarged. Symbols for some figures are difficult to see. See details below.

The authors correctly state that the record length (<9 yrs) is inadequate for characterizing trends in permafrost temperature. However, trends have been determined and presented for very short periods. In my view, one of the key outcomes of the study is a description of regional baseline conditions and better focus could be placed on this rather than discussion of long-term trends. Describing the variability in ground temperature on shorter time scales and their attribution with respect to climate variability etc. is a key part of the paper and should be highlighted with less emphasis on description of trends in relatively short records.

Other comments

L10-11 – Suggested revision “…under climate change with International collaborative efforts to collate standardized permafrost monitoring data.”    (the rest of the second sentence is not necessary).

L11-15 – Suggested revision “Compared to the Northern Hemisphere, there is a scarcity of ground temperature monitoring data in South America (Chile and Argentina). This has limited the understanding of thermal state and possible degradation of mountain permafrost.

L15-19 – Suggested revision “…..to compile and examine ground temperature trends for mountain (3,500 m to 5,500 m elev.) permafrost regions of the Central Andes. Ground temperature measurements from 53 boreholes along a north-south transect at the Chilean-Argentine border (27°S-34°S) reveals similarities in ground temperature characteristics with other mountain regions. This includes….”

L21-22 – Suggested revision “…observations support the hypothesis that the thermal regime of the Central…….other permafrost regions.” (end of sentence is no longer required)

L22-24 – Delete sentence starting with “With the longest record..” and revise the next sentence “The high temporal variability observed in the short records (<9 years) likely reflects short-term….”

L29-31 – The last two sentences may not be necessary or at least could be combined and shorter.

L33-123 – The paper is not a review of global permafrost monitoring but focuses on filling a key regional gap in South America. The information on global monitoring efforts including GCOS, GTN-P etc. should be reduced. All you need to really say is that permafrost thermal state is a key indicator of permafrost change. Highlight that compared to the Northern Hemisphere where there is considerable monitoring there is a gap in South America and explain reasons why it should be addressed. Towards the end of the introduction L110-115 you describe the need for baseline permafrost information. This should come earlier as it gets lost in the lengthy discussion about global monitoring etc. You define a few acronyms in this section (e.g. GCOS, EIA) which are not used again in the paper or defined again when the terms are used. These acronyms can be deleted.

L34- warming and thawing of permafrost has been documented

L45-50 – Be clear here that the active layer thickness refers to the thickness of the layer that freezes and thaws annually. This is not necessarily the same as the depth to the permafrost table particularly where permafrost is degrading and a talik has formed. The statement that the active layer is the distance from the ground surface to DZAA is incorrect as the DZAA is largely found well below the permafrost table. It is probably better to reduce this paragraph and just give the standard definition of active layer and indicate that the permafrost temperature at DZAA (and why – filter out high frequency variation etc) is commonly used for tracking long-term change. Mentioning that the ground thermal regime and ALT are influenced by climate is fine as is mentioning that the active layer responds more to short-term variations in climate compared to deeper ground temperatures. Other information in paragraph is probably not necessary.

L60-74 – See comments above. This section could be reduced substantially. Make the key point that there are many sites in North America, Russia/Siberia and Europe with less monitoring in central Asia, Antarctic and South America. You may want to highlight monitoring in mountain regions here (European Alps) as conditions are likely more comparable to your study.

L75 “– Revise to “The lack of ground temperature data…”

L79 – revise to “…make data collection challenging (Areson…)”

L80 – suggested revision “While limited ground temperatures have been collected and analysed in the Andes (e.g. Trombotto…..), most instruments…. “

L89 – suggested revision “This lack of measurements in deep boreholes…:

L91 – suggested revision “….of permafrost using boreholes…”

L93 – suggested revision “Some permafrost studies in…”

L96 – revise to “..with annual increases in ALT by up to 25 cm”  Note that layers have thickness rather than depth so you can refer to thickening of the active layer or deepening of the permafrost table.

L95-98 – Combine sentences and reduce text “Monnier and Kinnard (2013) installed two boreholes with thermistor strings reaching 18-25 m depth in the upper Choapa valley of northern Chile.”

L100 – replace “deep” with “thick”

L100-101 – Revision suggested to combine sentences and reduce text “Preliminary data from three boreholes (20-40 m deep) installed at the Goldfields Salres Norte mining project Chile, indicated favorable conditions for permafrost between 15 and 13 m depth at one borehole (Atacama Ambiente, 2017).

L104-105 – revision suggested “Although these other studies provide valuable….”

L110-115 – The importance of adequate baseline permafrost information for informed engineering design and environmental assessment of resource development projects should be mentioned earlier in the introduction as this is a key reason for addressing the regional permafrost knowledge gap.

L115 – suggested revision “Valuable data are generated that can…”

L119-120 – suggested revision “Temperature measurements were made available…”

L121 – revision suggested “…. site conditions to support…”

L121-122 – suggested revision “All instrumentation was installed …” (EIA) can also be deleted as it is not used elsewhere in paper (where it is used you define acronym again so better to delete)

Table 1 – enlarge text

L130 – Refer to Fig. 1 for location.

L137 – delete “also”

L141 – revision suggested “The eight project sites are situated at high….”

L142 – delete “also”

L156 – “remotely sensed imagery”

L157-158 – suggested revision “…and remains until spring…”

L176-195 – This section is probably too long and you could consider reducing. Given the relatively short records and the period covered by the records, you should consider what is necessary here and what might be more useful in your discussion and interpretation of results. This would reduce some of the repetition. Provide a short description of long-term change and indicate influence PDO and ENSO have in the region.

L197 – Change subheading to “3.1 Ground Temperature Data and Permafrost Presence” as this is a more correct description.

L203 – Accuracy and precision of measurement system should be provided. Were data loggers used to for data collection or were manual readings made?

L222-225 – If deep measurements below DZAA are available and temperature is below 0°C for most of the year, can you assume permafrost is present? Temperature changes are limited at these depths.

L256-263 – I don’t think you ever described the drilling methods used. Were fluids used which would cause significant disturbance compared to methods that don’t require drilling fluids.

L264-268 – Was the gully related to drilling disturbance or natural processes? If natural processes, the measurements were not necessarily compromised because they reflect the changes that occur at the surface, both changes in climate change and disturbance (natural or related to human activities). Knowledge of changes in surface conditions however are critical to interpretation of the ground temperature data. Assuming the casing hasn’t been affected yet, the temperature data would indicate that permafrost conditions are changing in the area.

L283-285 – Are these data spikes or noisy data for short periods? We have observed spikes in our data which could be electrical influences (lightning etc.). (no revision expected, just a question)

L325-338 – See earlier comment regarding discussion of trends. It is good you added this explanation given you are making comparison of trends determined over short periods to those in Swiss Alps where some records greater than 2 decades (same for Arctic and sub Arctic). However, is it even valid to determine trends when record is only 2-3 years long? It is important to note that for some Arctic/sub Arctic boreholes the surficial conditions are quite different from your sites. In Canada especially, there can be thick glacial sediments (including those that are fine-grained silts/clays) with high moisture/ice contents where latent heat effects are important. Also, in circumpolar region there are frozen peatlands so thermal response will also be different from your study sites. Comparisons to mountain permafrost regions is probably better to focus on or Arctic areas where finer grained material or peatlands are less likely. Here and in Fig. 6 reference is made to cold and warm permafrost. It might be useful to indicate how you are distinguishing between these.

L350 – Fig. 6 – It would be useful to give the number of sites considered in each region.

L354 – ALT was defined earlier so the sentence can be revised to “ALT in cryotic…”. You might want to consult Riseborough (2008, ICOP) regarding using interpolation/extrapolation to determine ALT and the best approach to use.

L369-370 – revision suggested “…overall increase in ALT over time…”

L369-372 – These results reflect short-term fluctuations in climate.

L373 – What is meant by deepening of permafrost? Referring to permafrost table or base? Be clear here.

L385 – Fig. 8. Is it possible to clearly delineate talik where it occurs so that it is clear to reader?

L421 – Delete “”in this dataset”

L436 Fig. 9 – some symbols are difficult to see

L439 – I think this section is good and makes use of the deeper temperatures that are available to give an indication of changes over several decades depending on depth.

L482 – suggested revision “..decrease as elevation increases (Figure….”

L487 – Be clear if permafrost depth refers to permafrost table rather than base.

L488 – suggested revision “..increase as altitude increases at…”

L510-519 – This repeats information provided in the introduction and isn’t necessary. You could start the section with line 520 and be clear that your study addresses a critical knowledge gap and then describe insights revealed etc.

L525-526 – revision suggested “..allows for characterization of average ground temperature below seasonal influences and thermal gradients….”

L534 – revision suggested “…without adequate ground temperature data…”

L562 – revision suggested “…of our sites in the Andes….”

L572-573 – Lewkowicz et al (2012) is also relevant here – uses ground surface temperature and ground temperature in the analysis to show the colder ground conditions in valley bottoms.

L628 – You can make a stronger statement here by replacing “illustrated” with “confirmed”

L632 – “from other boreholes” can be deleted (or replace with “from other sites”)

L687 – (EIA) can be deleted since you give the term

L693 – Delete “(GCOS)” since you give the term

References

Noetzli, J. et al. 2024. Permafrost (Global Climate) [in "State of the Climate in 2023"]. Bulletin of the American Meteorological Society (supplement), 105(8):S43-S44. https://doi.org/10.1175/BAMS-D-24-0116.1

Lewkowicz, A.G., Bonnaventure, P.P., Smith, S.L., and Kuntz, Z. 2012. Spatial and thermal characteristics of mountain permafrost, northwest Canada. Geografiska Annaler: Series A Physical Geography, 94: 195-215. doi:10.1111/j.1468-0459.2012.00462.x

Riseborough, D.W. 2008. Estimating active layer and talik thickness from temperature data: implications from modeling results. In Ninth International Conference on Permafrost. Edited by D.L. Kane and K.M. Hinkel. Fairbanks, Alaska. Institute of Northern Engineering, University of Alaska Fairbanks, Vol.2, pp. 1487-1492.

Smith, S.L., Romanovsky, V.E., Isaksen, K., Nyland, K., Shiklomanov, N.I., Streletskiy, D.A., and Christiansen, H.H. 2024. Permafrost (Arctic) [in "State of the Climate in 2023"]. Bulletin of the American Meteorological Society (supplement), 105(8): S314-S317. doi:10.1175/BAMS-D-24-0101.1

The submitted paper by Koenig et al. presents detailed ground temperature data recovered from 53 boreholes in the Central Andes of Chile and Argentina. These data highlight key thermal characteristics of permafrost and non-permafrost zones in the region. Additionally, the authors provide a discussion to understand the potential impacts of regional climatic phenomena (i.e., ENSO and PDO) on permafrost zones.

The Central Andes is a region with limited in-situ permafrost data, making the findings presented in this manuscript both novel and highly relevant to the research community. Furthermore, the proposed climate discussion represents a fresh and valuable perspective on the topic.

While the manuscript is generally well-written, there are several areas that require improvement before publication.

General comments:

Several sentences and phrases should be shortened or rewritten for conciseness and clarity. For instance, the introduction and methodology (see detailed comments).

The methodology and results sections include sentences better suited in other sections of the manuscript. Then, there are paragraphs that should be relocated (see detailed comments).

The discussion requires revision. ENSO reflects interannual variability in tropical sea surface temperatures, whereas PDO (or IPO) represents tropical sea surface temperatures in decadal trends. Then, if ENSO and PDO (or IPO) represent basically the same in distinct time scales, why present them as distinct processes interacting? In addition, if ENSO and PDO (or IPO) are relevant to the climate of the Central Andes (and potentially affecting permafrost), why was the Southern Annular Mode (SAM) not considered? several studies (e.g., DOI: 10.1038/NGEO1613, 10.1038/s41467-023-37643-1; 10.5194/tc-12-1027-2018) have demonstrated the influence of SAM in the Central Andes through the Southern Westerly Winds.

Reading section 4, I wondered whether it would be possible to organize the results by site or by “surface morphology”? I mean, for easier reading

Detailed comments:

• Line 16: change to “(i.e., 3600 m to 5250 m)”…following the methodology section
• Line 17-18: I didn’t see any borehole at 34° S. I suggest adjusting the latitude range to 27° - 33° S
• Line 69-72: could be just “Despite…. monitoring boreholes”. In a different paragraph, you may detail why the “challenges remain”
• Line 79: delete “Which make data extremely challenging to obtain”
• Line 84-86: you state two ideas in one paragraph “Consequently…below DZAA” and “limiting…is evident”. Rephrase
• Line 103-104: could be just “The preliminary…5 m and 13 m depth at one location”. The second part of your paragraph does not contribute at all
• Line 112-113: unnecessary details. The focus isn’t on mining. You could be more general
• Line 113: “Site investigation” or “Minning sites”. What is the focus of this paragraph?
• Line 117: “Semi-arid Central Andes”? to be consistent with the concepts. Is Central Andes or Semi-arid Central the central term?
• In Fig 1: I wonder if A and D are necessary for the legend
• In Fig 1: It would be great to know the year and authors who updated the Koppen-Geiger climate classification
• Line 136-137: 2,000 mm as average annual precipitation is extremely high for the latitudes of your study site. Please check
• Line 205: Then, how was the frequency of data collection expressed in the results? monthly average? Seasonal average?
• Line 148-152: could be simpler. For instance: “Seasonal average temperatures at 4000 m range from XXX XXx in July (reference). Nevertheless, some rock extend at 3500 m (reference)”
• Line 153-154: is contradictory with the previous sentence
• Line 162-164: It sounds as discussion. Why talk about other mountain regions in your study area section?
• Line 164-169: this could be just one phrase. Once you have presented all the topographic and climate background, you may state “topo-climate conditions in Central Andes favors a highly heterogeneous occurrence of permafrost in the region (Hilbich et al., 2022)”
• Line 173-176: Repeated. You already state that permafrost has heterogeneous occurrence
• Line 173: I suggest “the southern margin of our study area (32-33°S)…”
• Line 177-178: which several studies? Please, cite them
• Line 194-195: it is not necessary. I suggest deleting
• Line 198-200: Re-phrase to something like “Ground temperature was monitored between the years 2006 and 2017 at eight sites located distributed near the Chile and Argentinean border (Fig.1)”
• Line 211-214: Re-phrase to something like “The duration of monitoring varies from less than a month to nine years. Several monitories had interruptions that were attributed to climate/terrain factors (i.e., slope instability) and lack manutention”. After this phrase, you must explain how to solve the gaps
• Line 214-216: It is not necessary. Perhaps keep “A comprehensive discussion of data collection is included in section 3.2”
• Line 218-220: It is not necessary. I suggest deleting
• Line 227-228: Needs to be relocated after you describe the existence of “gaps” (i.e., line 211-214)
• Line 235: It is not necessary. I suggest deleting
• Line 238-241: must be shortened
• Line 242-251: must be shortened
• Line 255-259: It sounds like results. Relocate
• Line 259-262: re-write to something like “Boreholes affected by drilling disturbances had less weight in the analyses”. What do you mean with “weight”? clarify
• Line 265-266: It is not necessary. I suggest deleting
• Line 266-270: It is part of the discussion
• Line 275-286: It is part of results and/or discussion. You could erase these lines
• Line 301: replace “goodness” by another term or re-write
• Line 323-324: why does this reference to northern permafrost appear here? Move to discussion
• Line 330-342: Again, why do you refer to other permafrost regions in your results? Move to the discussion in a subsection called something like “thermal state of permafrost regions”
• In Fig 5 and 7: What do you mean with “Glacial Deposit”? moraines? are glacial deposits cryotic or non-cryotic features? Besides, please check the “@” in the label
• Fig 6: Move to discussion. It is valuable data. But not in your results
• Line 354-355: why is this line not in the section methodology?
• Line 367-369: It is not necessary. I suggest deleting
• Line 369-371: Move to discussion (“Similar…atmospheric warming”)
• Line 395-400: Move to discussion
• Line 402: I think section 4.3. starts here
• Line 412-419: Move to discussion
• Line 421-430: Move to discussion or present just as results
• Line 441: delete “may” and “some”
• Line 443-447: It sounds like methods. Move or delete

Line 468-472: Move to discussion or conclusion

• Line 476-478: Move to discussion
• Line 495: move to the discussion
• Line 532-534: re-write. I suggest something like this “This work provides temperature and depth permafrost data recovered from in situ measurements, evidencing XXX. Our findings contrast (or are coherent) with statistical methods…”
• Line 553: “medium”? Do you mean ground properties?
• Line 579: Please check the reference of Schultz et al., 2012. That paper refers to the Arid Coastal of Chile (18-30° S)
• Line 593: would be great to recall the latitude when you cite Site 3