the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Mar 2026
Distinct Phototrophic Community Structure on a Central Asian Glacier: Predominance of Filamentous Cyanobacteria and Absence of Glacier Algae (Ancylonema spp.)
Abstract. Cold-adapted algae and cyanobacteria are key drivers of snow and ice albedo reduction, yet their dynamics on dust-rich Central Asian glaciers remain poorly understood compared to the well-documented algal blooms in the Arctic. This study investigated the spatio-temporal distribution of phototrophic communities on Urumqi Glacier No.1, eastern Tien Shan, during a two-month melt season. Our findings reveal a distinct seasonal succession where snow-covered surfaces were dominated by snow algae Chloromonadinia species (Chlorophyceae), while the exposure of bare ice led to a sharp increase in biomass dominated by filamentous cyanobacteria (Oscillatoriaceae). Notably, glacier algae such as Ancylonema spp., which drive darkening on Arctic ice, were entirely absent, suggesting a fundamental ecological divergence. Statistical analyses indicated that cyanobacterial proliferation is closely linked to environmental factors, showing significant positive correlations with mineral-derived ions and negative correlations with inorganic nitrogen. These results, supported by recent evidence that specialized cyanobacterial taxa drive the initiation and structural development of cryoconite granules, suggest that high mineral dust deposition from surrounding arid regions facilitates a stable, nutrient-limited niche for cyanobacteria. This "cyanobacteria-mineral synergy" creates a more persistent biological darkening effect than the ephemeral algal blooms observed in polar regions. Our study highlights the necessity of integrating region-specific microbial dynamics, which is characterized by the absence of glacier algae and the dominance of mineral-buffered cyanobacterial communities, into glacier mass balance models to improve the accuracy of future projections for Central Asian water resources.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-1281', Anonymous Referee #1, 10 Apr 2026
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RC2: 'Comment on egusphere-2026-1281', Anonymous Referee #2, 04 May 2026
General comments
This preprint addresses an interesting and relevant topic and provides valuable data on glacier phototrophic communities from Central Asia, a region that remains underrepresented in the literature. The microscopy-based characterisation of surface communities is a clear strength, and the study has the potential to make a useful contribution to current discussions on glacier surface biota and darkening processes. The manuscript is generally well developed and contains several interesting observations, particularly regarding the predominance of filamentous cyanobacteria and the apparent absence of Ancylonema spp.
However, in its current form, the manuscript requires substantial revision before the main interpretations can be considered fully supported. The principal concerns relate to overinterpretation of the results, especially where the manuscript draws strong conclusions about biological darkening mechanisms and cryoconite-related processes without directly analysing cryoconite material or presenting albedo-based evidence. The manuscript would also benefit from clearer methodological justification, improved consistency in the presentation of quantitative results, a more focused and better integrated Discussion, and a careful revision of references and citation support. Overall, the study is promising and potentially publishable, but the interpretation needs to be better aligned with the actual scope of the data.
Specific comments
1. Interpretation and scope of conclusions
Several interpretations and conclusions are currently overstated relative to the data presented. Across the Abstract, Discussion, and Conclusion, the manuscript makes strong claims about mechanisms of glacier surface darkening, the ecological role of filamentous cyanobacteria, and the significance of cryoconite-related processes. However, the study did not directly analyse cryoconite holes or consolidated cryoconite granules, and it does not include albedo measurements or modelling approaches that would allow the authors to identify the primary biological mechanism driving persistent darkening with confidence. These interpretations should therefore be moderated and reframed more cautiously as hypotheses or possible explanations.
2. Methodological scope and study design
The methodological scope and study design need clearer justification, particularly regarding what was and was not sampled. The manuscript repeatedly refers to cryoconite holes, cryoconite granules, and previous findings from the glacier, but it remains unclear whether the absence of cryoconite holes was also confirmed during the 2013 field campaign and why cryoconite granules were not directly sampled despite their apparent relevance. The microscopy methods should be distinguished between light microscopy for taxonomic identification from epifluorescence microscopy for cell counting.
3. Quantitative results and internal consistency
The presentation and analysis of quantitative results require clarification and greater internal consistency. This includes inconsistent use of biomass units across the manuscript, limited explanation of how relative biovolume values shown in the figures relate to the underlying quantitative data, and insufficient presentation of cell counts and biomass estimates in a way that facilitates comparison across sites and sampling periods. Please provide cell count and detailed biomass by taxa results. Also, the comparison between ice and snow surfaces also appears potentially unbalanced, given the more limited representation of snow sites, and the statistical treatment of site and sampling period should therefore be clarified.
4. Discussion and integration of findings
The Discussion requires substantial restructuring to better integrate the main findings and remain aligned with the scope of the study. Several important observations are currently underdeveloped or insufficiently integrated, including the seasonal increase in biomass, the predominance of filamentous cyanobacteria, the potential ecological relevance of Chloromonadinia zygotes, and the contrast between previously reported metabarcoding diversity and the more limited set of taxa described microscopically here. At the same time, some parts of the Discussion extend too far beyond the dataset, particularly where cryoconite communities, albedo effects, or regional-scale implications are discussed.
5. Conclusion and citation support
The Conclusion is currently too long and includes material that would fit more appropriately in the Discussion. It should be streamlined to emphasise the principal take-home messages without repeating detailed results or extending beyond the evidence presented. More broadly, a careful revision of the references and citation support is needed throughout the manuscript. Several references appear to be inaccurate, misassigned, or used to support statements they do not directly address. This weakens parts of the Introduction and Discussion and should be corrected systematically.
Technical corrections
• Line 36: It is not clear what the reported 1029 microbial cells refer to. Please verify whether this value refers to a specific area, time period, or sampling unit.
• Line 52: The Yallop (2012) reference appears to concern the Greenland Ice Sheet rather than Midtre Lovénbreen, Svalbard. Please check and correct.
• Line 54: Consider including specific examples of Arctic glaciers together with their references.
• Line 58: The cited references appear to include both ice-sheet and glacier environments; this could be stated more explicitly.
• Line 60: Yallop (2012) and Musilova (2016) do not appear to address EPS production and cryoconite granule formation. Please revise the citation support.
• Line 63: “In cryoconite and cryoconite holes” appears incomplete; presumably this should read “In cryoconite granules and cryoconite holes”.
• Line 72: “Given their patchy” appears incomplete and may require revision to “patchy distribution” or similar.
• Line 81: The Segawa (2017) reference may be incorrect here; please verify whether Segawa (2010) is intended.
• Lines 112–118: If cryoconite was not directly analysed in this study, the level of detail provided here may be unnecessary unless it is more clearly tied to the study objectives.
• Figure 1: If available, photographs of the glacier surface features analysed in this study would strengthen the figure.
• Line 139: Please specify when microscopy and geochemical analyses were carried out after collection.
• Section 2.2.2: This section would benefit from additional references and a clearer explanation of the taxonomic classification criteria.
• Line 142: Please clarify the microscopy terminology and methodology.
• Line 149: The use of μL m⁻² as a proxy for biomass should be explicitly clarified as ‘biovolume-based biomass’ and used consistently throughout the manuscript, including in figures (like Figure 4).
• Line 168: Consider defining “surface status” here, for example as “ice vs snow”.
• Section 3.1: A table may help present this information more clearly and facilitate comparison across samples.
• Line 180: The sentence referring to previously detected OTUs may fit better in the Discussion than in the Results.
• Section 3.2: The seasonal narrative appears incomplete if it only extends to P3; further clarification would be helpful.
• Line 223: Please standardise biomass units across the manuscript.
• Line 226: Please clarify how site and sampling period were accounted for in the analysis comparing ice and snow surfaces.
• Figure 4: Please include P1–P5 labels for clarity.
• Section 3.3: The organisation of this section could be improved for consistency and readability.
• Line 240: Beginning this section with a clearer temporal marker such as “During P1” may improve readability.
• Line 265: The phrase “nearly absent” may not accurately describe the values shown for Oscillatoriales cyanobacteria 3 at P4S6 and P5S6.
• Figure 5: Please include P1–P5 labels for clarity.
• Line 285: The description of magnesium trends does not appear fully consistent with the figure and should be checked.
• Line 308: This statement requires either stronger support from the presented data or more cautious wording.
• Line 311: Please specify more clearly what is meant by “light-absorbing particles”.
• Line 319: The proposed synergistic mechanism should be framed more cautiously and supported with appropriate references.
• Line 328: Referring to “mature cryoconite communities” is potentially misleading, as cryoconite was not sampled directly in this study.
• Lines 356–360: The conclusion about consolidated cryoconite granules as the primary biological mechanism of persistent and cumulative darkening is too strong given the available evidence and should be revised.
• Line 363: This interpretation should be framed more cautiously to avoid implying direct causation.
• Line 373: It may be useful to mention the dominance of glacier algae in low-mineral environments in Svalbard, with appropriate reference support.
• Line 377: The contrast between Central Asian and Arctic systems would benefit from clearer consistency and stronger reference support.
• Line 393: Consider replacing “entirely” with a more accurate term.
• Line 402: A Svalbard reference appears to be missing.
• Lines 403–409: This passage could be made more concise, with greater emphasis on the point most relevant to the present study.
• Line 433: Please standardise the terminology used for the melt/ablation season throughout the manuscript.
• Line 443: Snowfall frequency was not measured in this study and should therefore not be discussed as though it were directly assessed.
Citation: https://doi.org/10.5194/egusphere-2026-1281-RC2
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- 1
General comments:
The manuscript presents a study of cyanobacteria on a central Asian Glacier. The authors present biomass values for six sample locations at five time points over the course of the summer on an alpine glacier. While the results are interesting, it is difficult to assess the value of the findings due to the methods lacking clarity, specifically around how the %biomass values were determined and what they represent. Additionally, since cell count data were not included in the manuscript it is difficult to fully interpret the results. The authors attempt to connect the results to both albedo and mineral dust, but neither albedo nor mineral dust were measured in the study. Thus, the related interpretations are overstated and are not supported by the data. Specifically, a “cyanobacteria-mineral synergy” has not been demonstrated by what is presented here. Additionally, there are several statements throughout the manuscript that incorrectly describe information from the literature that must be corrected.
Specific comments:
Line 28 and throughout the discussion: a “cyanobacteria-mineral synergy” has not been demonstrated. There has been no characterization of the mineral dust on the ice (either composition or quantity), nor has any meaningful evaluation of the relationship between the cyanobacteria and mineral dust been completed. Simply comparing against a few dissolved ions is insufficient. The authors should either provide data that supports this claim, or remove this phrase from the manuscript.
Line 36: this first sentence is misrepresenting the estimated 1029 cell count presented in the referenced article. That value is an upper estimate for the total global volume of glacial ice based on microbial counts from deep ice cores. It is not an estimate of cells on glacier and ice sheet surfaces, as is stated in the manuscript. Revise to correctly reflect the literature referenced.
Line 54: This is a broad statement, please identify where in the Arctic this cyanobacteria and cryoconite data is from.
Line 72: “Given their patchy and heterogeneity” is incomplete. Please revise for clarity. “Given their heterogeneity,” is probably sufficient.
Figure 1: what do the thin solid black lines indicate? They are not listed in the legend. I suggest using different colours to improve clarity. The S6 location label is a different font size than the others, and a space is needed between the elevation and units. Please increase the size of the date labels on the photographs.
Section 2.2.2 The manuscript describes cell counting to determine biomass, but it is not clear how the presented community composition was determined. Is it based on the light microscopy? That is what the first few sentences of the results suggest, but this is not clear in the methods and this information must be added to the manuscript. What literature references were used for the identification? Also, where is the cell count data?
Section 3.2 and Figure 4. The text uses units of mLm-2 for the biomass, but the figure is in µL m-2. Please use one unit consistently throughout the manuscript.
Section 3.3 It is not clear what presented % values represent. The terms: community composition, % biomass, % biovolume, and morphological community structure seem to be used interchangeably throughout. What is being presented here? How these numbers were determined and what these data represent must be clarified with consistent and accurate terminology.
Section 3.3 Where are the actual cell counts? Presenting only biovolumes makes it difficult to know how many cells are present at the study site, and therefore the impact of the data. For instance, are the presented ratios present in abundances of 101 cells/mL or 107 cells/mL? This drastically impacts the overall findings.
Section 3.4 It is unusual to see cryosphere geochemical data presented in µEq L-1 and will make it difficult for readers to compare these values to other datasets (typically presented in µg L-1 or mg L-1). Doing so also highlights that there is a strong charge imbalance in the presented data, with cations being disproportionately higher than the anions. Is this actually the case, or are there other dissolved ions present that are not included in the data?
Line 309: without any cell counts presented in the manuscript, the authors cannot claim that cyanobacteria are present in sufficient numbers to contribute to darkening. Please provide the cell count data that supports this statement. This will also require either presenting corresponding albedo measurements, or making comparisons to literature that demonstrates that cyanobacteria present in the reported cell abundances can in fact impact albedo.
Line 314 – 345: while some of the ideas presented in this discussion are interesting, there are no connections made to the literature. Appropriate references to the literature must be added throughout this section to support these points.
Line 346: this is an outdated interpretation. Arctic algal blooms on ice begin within a day or two of snow clearance. Therefore, is minimal difference in the timing of algae vs cryoconite impacting ice albedo.
Line 356-360: this is comparing very different environments. Additionally, this statement does not accurately reflect what is stated in either of the Cook and Hotaling articles referenced. The Hotaling article summarizes a range albedo measurements, which clearly show cryoconite and algae yielding a range of albedo reduction values, that very much overlap. The Cook article does not make any clear statements comparing algal and cryoconite impacts on albedo. Neither describe algal blooms as ‘transient’. Also, T=this interpretation does not account for the spatial extent of these two materials, as outlined in Cook et al. 2020 (https://doi.org/10.5194/tc-14-309-2020 ), while cryoconite on the surface has a greater impact on albedo, it occupies a far smaller surface area on ice sheets compared to ice algae, making the overall impact of cryoconite on albedo negligible. The discussion should be updated to correctly reflect the literature, and to also reflect these nuances of the topic.
Line 368: If assessing the relationship between cyanobacteria and mineral dust was an aim of the study, why was mineral dust not characterized? Simply measuring dissolved ions is insufficient to support the interpretations presented. Such data must be included to support these claims or they should be removed from the manuscript.
Line 381: This statement is incorrect. The McCutcheon 2021 article referenced here specifically characterizes algal biomass nutrient ratios in relation to mineral dust. It does not study cyanobacteria; correct the use of this reference.