|This paper describes ice on three distinct water bodies, in particular examining the methane within the ice and the physical properties associated with understanding the observed methane concentrations. The authors have taken considerable care to respond to the comments of the reviewers and (in my opinion) the revised version is much improved. The authors are much clearer about the aims of their study, and the description of the science and conclusions is clarified. The paper is now easy to read and almost without typographic error.|
As before I alert the editor to the fact that I am not expert on the suite of chemical techniques involved in the study.
I have a few remaining minor comments.
Comment 1: The title of the study (and I do prefer the new title) and the focus of the Introduction and Discussion is on winter ice. However the ice is sampled in spring. I would like some discussion regarding why the authors believe that the measurements are representative of winter. For example is the sampled ice thickness close to the maximum seasonal ice thickness? Is the ice still growing at the time of sampling? For those readers not familiar with the progress of the seasons in this geographic area, it would be useful to relate the seasons to the dates of the year. It would be very useful if the dates of sampling were given in Table 1.
Comment 2: I would still like more information about transport and storage of the cores (for example on p. 5, Sect 3.2). What was the approximate temperature during transport; how long between taking cores and performing the analyses? It is important for the reader to be convinced that there have not been irreversible changes during transport.
Comment 3: Could snow cover be added to Fig. 2 to help the reader understand the temperature measurements and the snow loading described in section 5.3?
p. 1: Abstract: Abstract is now much clearer.
p. 5, Table 1: In relation to statement that winter ice, please could you put dates of sampling in the Table.
p. 5, Sect 3.1: We are told the ice was sampled between Apr 5 and 12. But how is April related to winter ice?
p. 6, Line 32: “prior to freezing” or “during freezing”?
p. 7, Line 7: “2 months between sampling and measurement” Thank you – this is the sort of information that I consider important. But I was not sure whether “sampling” meant taking the core or filling the glass bottles.
p. 7, Line 9: replace “shaken” with “shaking”
p. 8, Line 4: Fig. 2 (rather than Fig. 3). Fig. 3 is cited before Fig. 2.
p. 8, Line 19-21: Paragraph break seems to have been placed part way through the description of BY ice. Please check.
p. 8, Line 20: Begin sentence “On the ice of Tiksi Bay, the snow thickness…”
p. 12, Lines 1-2: A rather strange sentence “While the …. (below 80-90 cm)” I think this sentence is unnecessary but I leave this as a decision of the authors.
p. 12, Line 7: “(Fig. 5)”
p. 14, Lines 7-9: This is a repetition of Lines 5-7.
p. 14, Lines 19-21: This could be written more concisely and without repetition.
p. 14, Lines 25-26: Please tell us which months and how these months relate to winter and spring (see Comment 1).
p. 16, Line 6: Please tell us when the onset of ice formation took place on BY.
p. 16, Line 7: Please mark Muostakh Island on Fig. 1.
p. 16, Line 21: delete “s” from “whens”
p. 16, Line 21-22: “The difference between both is within 1‰ for a large range of ice growth rates.” I don’t know what is meant by “both”. Please clarify.
p. 16, Line 35: I could not find a reference to Fig. 7 in the text. I think Fig. 8 is referred to before Fig. 7.
p. 18, Line 1-4: Why should there be mixing of saline water with additional water of meteoric origin when the ice was 90 cm thick? At what approximate time of year did this occur? Why would it take place if additional river outflow was unlikely at that time? Please speculate on a physical reason for your observations.
p. 18, Line 26: Formatting of Angelopoulos et al
p. 19, Line 20-23: “Ice has a high thermal conductivity and is susceptible to quick temperature changes. Since ice temperatures were also observed for windswept areas at LK, decreasing air temperatures from 8 April 2017 (final LK coring day) to 11 April 2017 (LG coring day) explain the generally colder ice temperature profiles at LG.”
I am not convinced by this explanation because the temperature of the ice at depths greater than 100 cm are higher for LK than LG and the air temperature takes some time to propagate to this depth. I suspect that the thickness of the snow cover is much more important since ice has a higher thermal conductivity than snow. More detail on dates of sampling (Comment 1) and a description of the snow cover (Comment 3) may help explain these observations.
p. 19, Line 31: “equilibrium”
p. 19, Line 31 & p. 20, Line 14-30: Snow loading discussion is very interesting. Please see Comment 3.
p. 23, Fig 9: I am surprised that the dashed line is the fit to the plus markers. This figure might be clearer and the fit more obvious if you plotted a linear fit of (13CCH4-(13CCH4)0) versus lnf