This manuscript is an important contribution to the study of ice microstructure in mountain glaciers. Microstructural investigations in these environments remain relatively scarce compared with polar regions (Greenland and Antarctic ice sheets), despite their considerable potential to improve our understanding of glacier dynamics and regional environmental changes. These types of studies are particularly valuable given the rapid retreat and ongoing degradation affecting many mountain glaciers worldwide due to global warming. In addition, due to their remoteness and difficult accessibility, obtaining ice cores from mountain glaciers often requires significant logistical effort, which further highlights the value of datasets derived from these archives.

The geographic setting of this study also adds considerable relevance. High Mountain Asia represents one of the most important cryospheric regions on Earth, often referred to as the “Third Pole”, and plays a critical role in regional hydrology and water resources. Investigations focusing on glacier records from this region therefore have clear scientific importance. The authors present microstructural observations that have the potential to provide meaningful insights into the evolution of glacier ice. 

In order to further strengthen the manuscript and improve its clarity and scientific framing, I have several comments and suggestions that I hope the authors will find constructive. These mainly concern aspects of contextualization, methodological description, terminology, and the explanation of some interpretations presented in the text. I summarize these points briefly below before listing the specific comments in detail.

From a methodological perspective, several analytical procedures and aspects of the sampling strategy are not described in sufficient detail. In addition, some of the terminology and layer classifications used throughout the manuscript do not fully align with the more commonly adopted terminology in ice microstructure studies, which may create unnecessary ambiguity. Adopting more standard expressions could help enhance clarity. Finally, certain interpretations, particularly those linking microstructural patterns to temperature or climatic conditions, would benefit from clearer explanation and supporting information. 

Introduction

lines 18-22

The statement presented in this section is conceptually sound; however, the introduction feels somewhat abrupt and would benefit from clearer contextual framing supported by relevant references. A brief overview of ice-core research would help situate the study within the broader field. Ice cores have provided long environmental and climatic reconstructions in polar regions such as Antarctica and Greenland, where this type of research is well established. Introducing this broader context before transitioning to mountain glacier ice cores would provide a smoother narrative. Although mountain records are generally shorter and more discontinuous, they offer regionally specific and highly sensitive environmental archives. Including representative references to previous studies on mountain glaciers would help highlight the significance and distinctive value of such records.

Lines 20-22

The link between ice-crystal characteristics, glacier dynamics, and potential implications for climate change is reasonable and would be clear to readers specialized in microstructural studies. However, in the introduction this connection remains somewhat implicit. It would strengthen the manuscript to briefly provide a concrete example illustrating how changes in crystal size or fabric can be related to climate variability or change. 

Line 23

Change: “After decades of research, the polar ice core ‘three-stage model’ is widely adopted to characterize ice…” for “After decades of research, the polar ice core “three-stage model” has been widely adopted to describe ice…”.

Lines 28 and 29

The statement that ice crystal evolution is more complex in mid-latitude mountain glaciers effectively highlights the relevance of such studies. However, the explanation provided requires clarification. In particular, the reference to faster flow velocities and higher accumulation rates as inherent characteristics of warmer environments appears overly generalized. Warmer conditions alone do not necessarily imply faster glacier flow or higher accumulation, as these relationships depend on several other factors (e.g., impurities, slope, anisotropy, etc.) and may vary regionally. A brief clarification or justification of these links would improve the accuracy of the introduction.

Line 31

The term “typical mid-latitude glaciers” is used without a clear definition. It would be helpful to specify what is meant by mid-latitude in this context, at least by providing an approximate latitudinal range. In addition, including information on the typical elevation of these glaciers would strengthen the regional characterization. 

The Tibetan Plateau is introduced without sufficient regional context. Given that the broader geographical framework of this study is High Mountain Asia (HMA), it would be important to clearly situate the Tibetan Plateau within this setting. HMA (often referred to as the “Third Pole” due to the extent of its glacierized area) represents a climatically and hydrologically critical region. Therefore, briefly clarifying that the Tibetan Plateau forms part of the third pole, and outlining its relevance, would improve clarity and help emphasize the broader significance of the study.

Line 32

The statement referring to “regional climatic and topographic heterogeneities” remains too general. It would be helpful to briefly specify which climatic and topographic factors are being considered (e.g., precipitation gradients, temperature variability, monsoonal/westerlies influence, relief, slope, etc.)

Line 33

The term “divergent microstructural characteristics” is unclear in this context. It is not evident with respect to what these characteristics are considered divergent. If the authors intend to emphasize truly divergent behavior, this distinction should be clearly explained and supported. Otherwise, a more neutral term such as “different” may be more appropriate, as the current wording suggests a stronger contrast than what is clearly justified in the text.

Line 34

It is necessary a more complete review of previous work on mountain glacier ice cores. Several ice cores have been retrieved from glaciers on the Tibetan Plateau, and these studies should be acknowledged with appropriate references.

In addition, microstructural investigations have also been carried out in other mountain glacier regions, including the Alps, the Pyrenees, and other mountain ranges worldwide. Although such studies remain relatively limited, they do exist and should be considered when framing the present research. Including these references would provide a more balanced overview of the existing literature.

Line 36

The use of a Microstructure Mapping system should be accompanied by appropriate references to the original developers or key methodological studies establishing this approach.

Line 37

The manuscript states that longitudinal microstructure images span from the firn to the base of the ice cores. It would be useful to clarify how the firn section was accessed. Was the firn exposed at the glacier surface, or was it reached by excavating down to the firn–ice transition before drilling? If excavation was required, a brief description of the procedure would improve methodological clarity.

Samples and Methods 

Line 50

The drilling sites should be specified more clearly. It would be important to indicate whether the cores were retrieved from the accumulation or ablation zone, as the term “summit” does not necessarily imply a persistent accumulation area under current climatic conditions. The season of drilling should also be indicated to provide climatic context. If available, referencing previous studies on the glacier’s mass balance state (e.g., retreating, thinning, or stable) would further support the interpretation of the cores.

Line 51

Report the approximate snowline or equilibrium line altitude (ELA) for each glacier.

Line 53

Basic methodological details should be provided, including the type of drilling system used for core retrieval and the instruments used for temperature measurements. 

Line 56

The description of the sampling interval requires clarification. The statement that “560 slices were obtained from 22.30 m to the base of the BJGR core” is ambiguous. It should be specified whether sampling starts at 22.30 m and continues downward to the base, and if so, why the upper section of the core was not included in the microstructural analysis. In addition, the meaning of “sampling rate” expressed as a percentage is unclear. It would be helpful to explain how this value is calculated and what it represents.

Line 57

The manuscript states that the sample “was trimmed flat using a Leica…”. While the term trimmed is sometimes used, it is not entirely clear which preparation method is being referred to. Based on the overall methodological description, it seems possible that the surface was prepared using a microtome. If this is the case, it may be more precise to state that the sample was microtomed to obtain a flat surface. Please, clarify the preparation method to improve the methodological description.

Line 58

It would be helpful to indicate in which facilities this process was carried out, as this would clarify the environmental conditions under which the sample preparation was performed.

Results and discussion

Line 76

The expression “firn layer (<35 m)” is somewhat ambiguous. If the authors intend to refer to the firn interval extending from the surface down to approximately 35 m, it would be clearer to specify this as “0–35 m”.

Line 78

The manuscript states that both ice cores reached the critical density of 0.830 g cm⁻³. If density measurements were performed on the cores, the methodology used to obtain these measurements should be described in the Methods section.

Line 79

The description of the grain area as “small” appears somewhat redundant, since the manuscript already provides the quantitative range (ANMQ: 2–5 mm2; BJGR: 1–3 mm2). Given that the values are explicitly reported, the qualitative descriptor may be unnecessary and could be omitted.

Line 80

It should be clarified whether these grain-size proportions refer to both ice cores or to a single core. As currently written, it is not clear whether the reported distributions apply to ANMQ, BJGR, or both.

Line 81

The subdivision into “3.1.1 Firn layer (<35 m)” and “3.1.2 Growth layer (35–45 m)” may require reconsideration. Grain growth appears to occur within the firn layer as well, meaning that both sections are characterized by grain-growth processes. As a result, the term “growth layer” may be somewhat misleading, since growth is not exclusive to that interval. It may be worth exploring alternative terminology that more clearly reflects the processes or structural characteristics distinguishing these layers.

Line 87

The transition between the general description of polar studies and the discussion of the present results is not clearly marked. In this sentence, the text appears to shift to the specific case of the studied cores, but this change is not explicitly indicated. It would be helpful to clearly signal when the discussion moves from general observations (polar areas) to the results of the present study in order to avoid confusion for the reader.

Line 92

Please clarify whether any post-drilling borehole measurements were performed, such as temperature logging or other physical profiling along the boreholes. Such data could help contextualize the processes discussed here.

Line 95

The term “stable layer” is somewhat confusing in this context. The description of this interval indicates ongoing changes, including decreases in average grain area and large-grain proportions, as well as increases in small-grain proportions and total grain number. This suggests that microstructural evolution is still occurring rather than remaining stable. It may therefore be helpful to reconsider the terminology or clarify what is meant by “stable” in this context.

Line 103

Minor typographical and formatting inconsistencies are present throughout the manuscript (e.g., missing spaces between words and symbols). A careful review of the document is recommended, as attention to these stylistic details improves readability and overall presentation.

Line 105

The manuscript suggests that higher temperatures enhance grain growth and lead to a larger equilibrium grain area. It would be helpful to indicate whether there is supporting evidence in the literature for this interpretation. If such relationships have been previously documented, including appropriate references would provide better support for the argument.

Line 113

The manuscript states that SIBM typically occurs when ice temperatures exceed −10 °C and that the basal temperatures of the studied ice cores satisfy this condition. However, the basal temperatures of the cores are not reported in the manuscript. It would be helpful to specify the temperature values (measured or estimated).

Line 114

The term “oversized grains” is qualitative and would benefit from quantitative support. If possible, it would be helpful to indicate the approximate grain size or provide a representative value or range to better substantiate this description.

Line 114

The statement refers to a temperature transition at ~150 m depth, but the actual temperature values are not reported. 

Line 116

The terms “mutation layer” and “stable layer” are not standard in ice microstructure studies and is inappropriate in this context, as it may lead to confusion. More conventional terminology should be adopted. It may be clearer to define the sections based on depth intervals and dominant processes (e.g., polygonization, RRX, SIBM).

Line 123

Further explanation is needed. The manuscript states that the BJGR core reflects characteristics of Cold-type Ice Genesis, but the connection between the reported observations (lower temperature, lower firn density, smaller grain size) and this interpretation is not fully developed. It would strengthen the argument to more clearly explain how these observations support the classification as cold-type ice formation.

Line 134

The comparison presented here appears somewhat limited. It would be helpful to verify whether additional mountain glacier ice cores (particularly from High Mountain Asia) are available for comparison. If other records exist in the region, including them would strengthen the contextual interpretation.

In addition, comparisons with well-documented mountain glacier cores from other ranges (e.g., the Alps or other high-altitude regions) could also provide useful context. Expanding the set of reference sites would help place the reported firn temperatures in a broader framework.

Line 139

The description of cloudy band thickness requires clarification. It is unclear whether the statement means that the combined thickness of all cloudy bands within one meter of core is <20 cm, or whether it refers to an average thickness of ~20 cm per band. As currently written, the phrasing is ambiguous and should be explained more clearly.

Line 140

The description of the cloudy bands in this interval also requires clarification. It is not clear whether the reported total thickness of up to 90 cm refers to the combined thickness of all cloudy bands within the 120–140 m interval, or to the thickness of an individual band.

Line 146

The discussion linking impurities to grain-size variability is well supported by the cited polar ice-core studies and by the mountain glacier example already included (e.g., Eichler et al.) It may also be worth noting that similar relationships between impurities and ice microstructure have been reported in other mountain glacier settings. For instance, the study by González-Santacruz et al. (Annals of Glaciology) on the Monte Perdido Glacier in the Pyrenees documents comparable interactions between impurities and ice microstructure. Including these type reference could further broaden the contextual framework for interpreting impurity-related grain growth processes in mountain glaciers.

In addition, the manuscript would benefit from a brief overview of previous microstructural studies conducted on mountain glaciers. There is a long-standing body of work examining ice fabrics and microstructural characteristics in non-polar glacier settings that could help contextualize the present study. Early investigations include classic work on glaciers such as Aletsch (Perutz and Seligman, 1939) and Emmons Glacier (Rigsby, 1951), followed by comparative studies across several mountain and high-latitude glaciers (e.g., Rigsby, 1960; Kamb, 1959). More recent contributions have examined ice fabrics and microstructural properties in glaciers such as Tsanfleuron, Colle Gnifetti, Storglaciären, Rhône Glacier, sites in the Mont Blanc massif, and Jarvis Glacier, among others. While these studies often focus primarily on ice fabric, they nevertheless provide important background for understanding microstructural evolution in mountain glacier environments. Including a brief acknowledgment of this body of work would help place the present results within the broader historical development of mountain glacier microstructural research.

Line 149

“Ice temperature” instead of only “temperature”

Line 162

The interpretation that low d18O values in the cloudy-band zone reflect colder conditions is reasonable and consistent with the isotopic signal. However, the expression “cold periods” may benefit from further clarification. As currently written, it is not entirely clear whether the authors refer to large-scale climatic phases (e.g., glacial conditions) or to shorter-term colder intervals.

It is understandable that resolving the exact temporal scale may be difficult given the limitations of the chronology. Nevertheless, it may be useful to acknowledge the possible range of temporal scales involved. Previous studies have linked higher dust concentrations in ice cores to glacial conditions through mechanisms such as increased continental aridity and stronger atmospheric circulation. However, it is less clear whether the same mechanisms apply to shorter-term or seasonal cold intervals. Briefly recognizing these different possible scales would help refine the interpretation and avoid ambiguity.

REFERENCES 

Clavette, R. (2020) The Microstructural Heterogeneity of Ice in Jarvis Glacier, Alaska. Honors College. 589.

González-Santacruz, N., Muñoz-Marzagon, P., Bartolomé, M., Moreno, A., Huidobro, J., & Faria, S. H. (2023). Effects of impurities on the ice microstructure of Monte Perdido Glacier, Central Pyrenees, NE Spain. Annals of Glaciology, 64(91), 107-120. doi: 10.1017/aog.2023.66

Hellmann, S., Kerch, J., Weikusat, I., Bauder, A., Grab, M., Jouvet, G., Schwikowski, M., & Maurer, H. (2021) Crystallographic analysis of temperate ice on Rhonegletscher, Swiss Alps. The Cryosphere, 15(2), 677–694. doi: 10.5194/tc-15-677-2021)

Kerch, J. (2016) Crystal-orientation fabric variations on the cm-scale in cold Alpine ice: Interaction with paleoclimate proxies under deformation and implications for the interpretation of seismic velocities. PhD thesis, Universität Heidelberg. hdl: 10013/epic.49379.d001

Monz, M. E., Hudleston, P. J., Prior, D. J., Michels, Z., Fan, S., Negrini, M., Langhorne, P. J., & Qi, C. (2021) Full crystallographic orientation (c and a axes) of warm, coarse-grained ice in a shear-dominated setting: A case study, Storglaciären, Sweden. The Cryosphere, 15(1), 303–324. doi: 10.5194/tc-15-303-2021

Perutz, M. F. & Seligman, G. A. (1939) A crystallographic investigation of glacier structure and the mechanism of glacier flow. (1939). Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 172(950), 335–360. doi: 10.1098/rspa.1939.0108

Rigsby, G. P. (1951) Crystal Fabric Studies on Emmons Glacier Mount Rainier, Washington. The Journal of Geology, 59(6), 590–598. doi: 10.1086/625914

Rigsby, G. P. (1960) Crystal Orientation in Glacier and in Experimentally Deformed Ice. Journal of Glaciology, 3(27), 589–606. doi: 10.3189/S0022143000023716

Tison, J. L., & Hubbard, B. (2000) Ice crystallographic evolution at a temperate glacier: Glacier de Tsanfleuron, Switzerland. Geological Society, London, Special Publications, 176(1), 23–38. doi:10.1144/GSL.SP.2000.176.01.03

General Comments:

The work in this paper focuses on the temperature dependence of ice-crystal size through the investigation of recovered mountain ice cores from Tibet. This type of work is important as there is a general paucity of physical properties research on smaller, mountain-glacier cores (most fabric or micro-structure analyses are carried on on large ice-sheet cores). As such, it is important that these types of studies are carried out to help strengthen and broaden ice physical properties across different regions (particularly those more acutely sensitive to modern climate change) and show if crystal properties can indeed retain a temperature signal.

In addition to multiple minor formatting, spelling, and grammatical errors, this manuscript most notably lacks specificity across several areas. There are noteworthy method description deficiencies and exclusions, as well as a lack of site and context details. In several places qualitative descriptions are used when specific quantitative measurements are justified and more appropriate. It also seems that many conclusions and/or assertions are not fully developed and require more explanation or references. There are also many places where explicit comparisons with other mountain glacier studies would strengthen the manuscript.

Specific comments:

Abstract

line 8 should be "ice cores"

1. Intro

Very little context is given at the onset of the introduction. In general, this section would benefit from more "background" and previous research discussion, especially given that there is no dedicated background section that follows. There is a lot of important material to first introduce regarding deep ice-core work and the pioneering work on grain growth and temperature dependence from those in the 60s and 70s (such as Gow). Then a transition can be made to discussing a brief history of shallower mountain cores, and some important regional studies (and therefore the strong motivation for this work). Additionally, there needs to be a clear review of recovered cores from glaciers on the Tibetan plateau.

More clarification would be beneficial in the introduction as to complexity of mountain glaciers and what is known about ice crystal size and evolution. Also, it would help to be more specific as to what is included in the authors' use of "mid-latitude" in the context of mountain glaciers.

Line 32...rather than just citing Yao et al., perhaps consider writing out some examples of heterogeneities (or at least include additional references).

Line 33... "and" is printed twice

line 33... "divergent" to what exactly? It may be unclear to readers exactly what is meant by this without additional citations or examples.

Line 35...This would perhaps be the better place to reference the site map of figure 1 showing the locations.

Line 36...It is unclear what "Microstructure Mapping system" means exactly. There either needs to be a more detailed explanation of this system, or at the very least, first-level references that clearly detail the system.

Lines 37-40...In general there are some necessary details missing here. Where in the firn? How was the firn defined in each core? It is also unclear how any of these samples were obtained. What sort of recovery system or drill was used etc? I know this is discussed more in section 2, but there should at least be some details here or note if recovery was done following methods and practices from a previous study.

2. Samples and Methods 

Additional details are needed on the drilling itself. What drill was used, how was that drilling carried out and over what time frame, how was recovery handled, etc. 

Line 52...There are no details given for this passing remark of "borehole temperatures were measured." There are many studies that measure borehole temperatures...with several varied techniques and instrumentation. This needs to be clearly articulated for this study. What sensors were used (thermistors? platinum rtds?), what was the measurement technique? Were measurements punctuated with long waiting intervals to allow the air temperatures in the boreholes to re-equilibrate? etc. Also given the sites and their sensitivity to regional climate, carefully detailing the field and recovery timing of the drilling and borehole measurements is critical.

lines 55-60 - The sampling collection and interval is somewhat unclear. It's noted the samples are "longitudinal", and fig 2a shows a cut plan, however there's no mention of where and how those cuts were made and how the raw samples were prepped before creating the thin sections (were they traditional thin sections?). I would suggest also adding considerably more detail regarding the sample preparation. Clearly articulate the microtoming process (if indeed the "slicer" is a microtome), and then how the samples were mounted (if they were was it using glass plates and silicone or glue?) before imaging. As mentioned before, "Microstucture Mapping" should be clarified somewhat beyond just the citations. What sort of camera stage was used? etc. Also, it would be helpful to see an explanation and description of the lab where these measurements were carried out. 

line 65 - is the "Extraction" just a built in function of the MorphoLibJ plugin or is there more involved with that extraction process. Also, how are these data extracted...into a standard data file (e.g. CSV), or is additionaly manipulation/refinement needed before they are used for statistical analyses?

3. Results/Discussion

line 69 - A relevant citation here is warranted (perhaps Gow 1969?)

line 76 - Might be better to note "surface down" to 35 if that is indeed the density-derived firn/ice transition...or specify if the upper surface is not included in the "firn". With this all said, where did the density measurements come from? Was a field method used to determine density (i.e volumetric snow measurements or a borehole instrument), or was density measured later in a laboratory setting?

Line 79 - consider avoiding qualitative descriptors like "small" when explicit sizes are defined.

Lines 85-89 - This section seemed a bit out of place here. Consider rewording or moving up.

Line 100-104 - If indeed higher temperatures are enhancing grain growth, this is where additional discussion and citations would strengthen the paper.

Line 113-115 - When basal temperatures are noted here...is this in reference to borehole measurements, or direct temperature measurements of the ice upon recovery. Borehole temperatures are reported in Fig 1b, but it is unclear if that is where the "basal temperatures" noted here are from. To reiterate a comment noted above, there are no borehole temperature or direct temperature methods reported in the study. Is the "temperature transition" at 150 in reference to borehole temperatures?

line 117 - The authors might consider rewording/rearranging the section 3.2 title.

Line 133 - consider expanding on the statement "when comparing to other mountain glacier ice cores" - what cores and from what regions? etc.

line 139 - "cloudy bands" is not necessarily a standard and formally recognized term in the ice core sciences. It would help to define what is meant here. Is it assumed that these are faint tephra layers? dust layers? other impurities? or perhaps just a density contrast of some kind? It would also help to maybe add a sentence or two giving examples of other cores with similar cloudy bands and the conclusions those authors drew regarding formation origin.

Lines 146 - 159 - In general, this section lacks detail and more discussion (and a deeper dive into existing and/or supporting literature) 

lines 160-164 - In this section it is implied that cloudy bands are analogous to those seen in Greenland cores that time with long glacial (or perhaps shorter stadial) periods....but it isn't really clear the time interval context as written here in this study.