the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Multi-annual temperature evolution and implications for cave ice development in a sag-type ice cave in the Austrian Alps
- 1Department of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, 6020, Austria
- 2Institute of Geology, University of Innsbruck, Innsbruck, 6020, Austria
- 1Department of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, 6020, Austria
- 2Institute of Geology, University of Innsbruck, Innsbruck, 6020, Austria
Abstract. Ice caves are, similar to mountain glaciers, threatened by the warming climate. To better understand the response of perennial ice in caves to a changing climate, we analysed the thermal characteristics of a sag-type ice cave in the Austrian Alps (Hundsalm ice cave), based on long-term temperature measurements for the period 2008–2021. Observations show a warming trend in all parts of the cave as well as a distinct seasonal pattern with two main regimes, i.e., an open (winter) and a closed (summer) period. During the closed period, a persistent stable stratification prevails that largely decouples the cave from the external atmosphere. The open period is characterised by unstable to neutral stratification and allows episodic penetrations of cold air from outside into the cave interior. Vertical temperature profiles also provide hints on corresponding circulation patterns and the spatial temperature variability in the cave. The positive air temperature trend is reflected in a decrease in perennial cave ice, derived from stake measurements. Besides surface melting, we find compelling evidence of basal melting of ice. The observed ablation rates can be well reproduced by applying a modified degree-day model, which, however, is less feasible regarding mass balance. Overall, we conclude that Hundsalm ice cave is highly impacted by regional warming which will lead to the disappearance of its perennial ice deposits within the next decades.
Maria Wind et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2022-67', Anonymous Referee #1, 29 Apr 2022
GENERAL COMMENTS
Dear Editor,
I’ve read the manuscript “Multi-annual temperature evolution and implications for cave ice development in a sag-type ice cave in the Austrian Alps” by Wind et al.
I found the manuscript an interesting submission describing fully and comprehensively the microclimate of a sag-type ice cave. The manuscript fits with the purpose of the journal TC.
The manuscript reports significant information generally poorly or not addressed in the existing literature and it is, therefore, a valuable work.
Although pointed out several times and accurately described, the only “weakness” of the work relates to the lack of data calculating the impact of visitors in the cave, which is indeed something hard to quantify. This is not something that affects the quality of the paper itself but makes the findings a bit less important than what could have been achieved in a non-touristic cave.
Besides such general comments and the specific comments below, I suggest the manuscript can be published after minor revision.
SPECIFIC COMMENTS
P 2 L 30-35: as I agree with the statement “it is crucial to assess and understand the microclimatic and glaciological conditions inside ice caves and their coupling to the outside atmosphere” I suggest the innovative CFD model approach proposed by Bertozzi et al., (2019) “On the interactions between airflow and ice melting in ice caves: A novel methodology based on computational fluid dynamics modelling” https://doi.org/10.1016/j.scitotenv.2019.03.074, 2019 is mentioned in this section.
Figure 1: for more clarity, I suggest adding the location of the stakes even in the elevation view (lower panel)
P 5 L 106 (also related to P20 L 416-419): I understood that, as you mentioned, it is really hard to quantify the effects of artificial snow input inside the cave, but can you be more specific about this process? I see that some information is retrievable from Fig. 8 and some are explained in the discussions but maybe you can add some more if known. For example: is the snow input affecting all the areas homogeneously or just near the entrances, how often does it happen usually, just in late winter? Has the artificial snow input ever been quantified at least in snow thickness at a stake to have a vague idea of its impact (maybe referring to some of the Figure 8 values)? Is the shovelling process documented every time or the listed markers are just some of them?
P21 L 430-437: I feel that having a range of values from other stakes and T sensors would enrich the discussions of this work and improve the eventual future comparisons with other studies using this methodology in different caves. I understand that stake B and T29 were used as references for deriving the DDF as they are more robust. Is there a chance that some other T sensors and stakes are used for calculation of shorter DDF periods and then compared with the reference values that you already mentioned? If stake B is affected by the artificial snow input, are there other stakes that can be less affected by snow shovelling and therefore can provide additional data in the discussion of DDF findings?
- AC1: 'Reply on RC1', Maria Wind, 20 Jun 2022
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RC2: 'Comment on tc-2022-67', Aurel Perşoiu, 07 Jun 2022
7-8: this sentence is quite uninformative
11:
26: “trap” would suffice
39-40: it is not clear how this sentence is linked to the case study. “Comprehensive” analysis for several caves or for this one only? It could be safely left out.
41: perhaps “ice level dynamics” (or similar) instead of “stake” records?
61: the diameters of the entrance shafts could be an important information for air circulation, please add them if available
76: please give the distance between the air measurement point and the nearest ice body. It is helpful to interpret air temperature variability and role of latent heat in shaping it.
96: what is the altitude of the precipitation sampling site?
104: does this shoveled snow reaches areas where air temperature ad/or ice dynamics are monitored?
105: somewhat strange, perhaps the climate is manipulated, not the entire cave?
122: how does this filtering influences the long-term averages calculated below?
131: this could be very useful for any subsequent studies. However, while deriving potential temperature from pressure data is quite straightforward in the free atmosphere, it might prove problematic in cave settings due to potential biases induced by pressure changes linked to movement of air inside cave passages. Did you consider these, and also potential differences between summer and winter?
147: normalized?
161-162: the warming trend is quite interesting, and puzzling, all the same. While it is tempting to see it as a sign of a warming climate, the fact that the logger located in the non-glaciated part of the cave does not register it (nor the external one) makes one wonder if the trend is related perhaps to changing distance from ice. melting of ice would necessarily act as a heat sink, thus keeping the temperature of air in the nearby atmosphere at 0 °C as long as ice is present. Any additional hat added to the air (by, e.g., warming outside) would be used to melt additional ice and thus removing any increase. So, how far from the ice are the loggers showing the warming trend placed? Did this distance increase? Did you detect any breakpoint in the time series linked to, e.g., drop in ice level?
179: how was this threshold chosen?
189-192 (and lines above): I find the discussion on the net external cooling required to induce a net cave cooling interesting and stimulating. Especially intriguing are the values of the net differences between outside and inside which are quite high (8.5 °C!). Perhaps daily means are masking the real difference, as minima tend to occur at different times in and out of the cave? Did you try a cross-correlation analysis that would indicate the time lag between external and internal variations and thus help sustain these very large differences? Perrier et al. (2005) for instances found very short times for cold air ”avalanches„ reaching lower parts of caves
202-203: this is an important observation, yet difficult to reconciliate with physics. Basically, the ms says that weak cooling in winter somehow results in warmer summers. Now, in any system where a heat sink is present (melting ice, in this case), temperature will be controlled by latent heat. Further, the rock surrounding the cave has an oversized fingerprint on the overall thermal balance of the cave air+cave ice system. In the absence of the meting ice, one could imagine that weaker cooling in winter leads to warmer summer air temperatures, but the melting of ice would obliterate any such influence. Basically, you should provide a mechanistic explanation for the processes that lead from weak winter cooling to warmer summers – this would be a major point for future similar studies.
Chapter 3.3. This is a long chapter with very detailed discussion of the data that seems to result in a loss of focus. Perhaps the data description should be shortened and the discussion focus on the interaction between cold air intrusion, distance of air measurements points from ice and the role of internal air circulation. These are all linked and the presence of ice acts as a strong modifier of air circulation/temperature. This could/should perhaps merged with the subsequent chapter 3.4 (which I will not discuss further down).
Chapter 3.5. The discussion of rock/ice temperatures could be used to support/reject the inferences made on lines 202-203 (see above).
Chapter 3.6. I miss a discussion of the links between PDD outside the cave and ice dynamics – this would help understand the role of external air temperature variations on ice dynamics – see also the opening line of the discussions (L343)
312 – well, this lack of correlation is somehow normal. Dripping water, direct snowfall and snow shoveling by cave managers result in a complex and possibly impossible to understand link between snow accumulation and precipitation amount.
315-319: I am not sure a model that excludes outside temperature would help understand the ice dynamics, this should be included.
335 – this density refers to ice at maximum density. Is this the case here? I would expect lower density, based on how ice forms.
338 – these are extremely high values. What are the errors associated to the measurements?
344-346 – this is extremely interesting, but perhaps it should be moved after the discussion of the data.
351-358 – this section somehow does not fit well in here, especially given the strong opening statement of the section (344-346)
372 and subsequent: again, apart from correlation, which can be the result of artifacts in statistical analyses, an explanation is required. Basically here, the results are presented again but no discussion follows.
412-415: again, see my comments above. Melting in summer has to be the result of warm temperatures and/or the sum of low winter accumulation and (high) summer melting, rather than warm winters only. Also, the unquantified snow shoveling must play an (oversized) role.
General observation for the “discussions” section: this study can be broken down on a climate analysis and links between ice dynamics and climate. The first part is nicely done, however, the links with ice dynamics are somehow weakly supported by the observations and hampered by the anthropic influence. I suggest reducing the entire discussion to the discussion of 1) cave climate and 2) links with ice, but with the later stating from the beginning the fact that snow shoveling inside the cave strongly masks the natural processes.
Perrier, F., Le Mouel, J.L., Kossobokov, V., Crouzeix, C., Morat, P. & P. Richon, 2005: Properties of turbulent air avalanches in a vertical pit.- European Physical Journal B, 46, 4, 563–579.
- AC2: 'Reply on RC2', Maria Wind, 20 Jun 2022
Maria Wind et al.
Maria Wind et al.
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