|This manuscript has significantly improved since the initial version. In particular, the Discussion and Conclusions are more suitably narrowed to the scope of what was studied, and the presentation of the expanded incubation results (up to 1 year) is interesting. The addition of site photos in Supp. Fig. 1 adds important context to the data presented in the paper. I also like the new Figure 4 much better than the old one—not only due to the better annotation of “not detected” and “below detection limit” data, but also the re-grouping of different field samples under the same incubation treatments, which makes it easier to compare different field sites.|
However, there are still a few minor revisions needed before publication, mainly related to correcting typos, but also a few minor content revisions. These are:
General comment: There is inconsistent use of “,” or “.” as a decimal separator.
Li 12-14: Sentence structures could use improvement. Suggested revision: “Here, we used an anaerobic incubation experiment to simulate permafrost thaw along a transect from upland Yedoma to floodplain in Kurungnakh Island. Potential CO2 and CH4 production were measured during incubation of active layer and permafrost soils at 4 and 20°C, first for 60 days (approximate length of growing season), and then continuing for one year.”
Li 18: Change “to trigger” to “triggering”
Li 21: Summary is missing opening sentence needed to understand “these gases” in li 22. Copied from tracked changes version: "Climate change is causing increasing temperatures and permafrost thaw, which might lead to increases in the release of greenhouse gases CO2 and CH4."
Li 39: Change “differ across Arctic” to “vary across the Arctic”
Li 41-43: Revise this sentence to: “Permafrost thaw is highly affected by landscape position: Low-lying ice-rich areas can become waterlogged following permafrost thaw, while higher areas can be drained by water run-off.”
Li 62: change “condition” to “conditions”
Li 63: change “increase of precipitations” to “increasing precipitation”
Li 64: Change “deepen active layer” to “deepening active layer”, and “hence” to “and hence”.
Li ~133-134 (Eq 1 and description): It would make more sense to put this equation above the previous paragraph (i.e. between lines 125 and 126), to be closer to the relevant method text.
Li 163: Change “used a linear regression between each measurement point to” to “a linear regression between each measurement point was used to”
Li 164-165, “calculated with the headspace and the volume of the dry content and normalized per gram soil C”: This wording is unclear. I’m guessing you meant that the headspace concentrations were converted to amounts using the headspace volume and the ideal gas law, and then the gas amounts were normalized to the weight of the dry sample?
Li 169-170: Going back to my question from the first manuscript version, it sounds like "cumulative" includes the entire time from day 0 to day 67? And what was the result of "calculat[ing] the glucose factor only after glucose addition and see if we have different values" (as mentioned in the Response to Reviews)?
Li 210: Typo in Table 2? It says the TOC of P17-F is 17.2% (old table version said 0.17).
Table 2: See comment above about the P17-F TOC. In addition, there is an extra decimal point in this sample’s C value, “2..3”. Also more generally, maybe it’s worth adding TN to the table as its own column separate from C/N, since there’s some discussion about it in the text?
Li 242-243: Specify which temperature this applies to, i.e. “With a cumulative 20°C CH4 production reaching…”
Li 247-248 “…and the permafrost layer of the same core at 4°C was the lowest”: For the P17-F sample, the CO2 production at 20°C actually looks slightly lower than at 4°C.
Li 250-251: Change to “At 4°C, the permafrost layers of the Yedoma core P16 and the floodplain core P17 had cumulative production…”
Li 254 & 256: Cite Supp. Fig. 4 here in addition to Fig. 2, since the changes in CO2 production are easier to see there.
Li 258-260: These values don't seem to match anything in Supplementary Table 2 (except for the 754 value for P17-F-4).
Li 260-261, “CO2 production plateaued for all the samples”: This doesn’t appear to be true for P17-A at 4°C (which shows an uptick at the end)?
Li 269 and 271: The “Table 2” references need to be corrected to “Table 3.”
Li 270: The “2.7 ± 2.6 and 2.6 ± 2.1” are slightly different from the values in Table 3.
Li 285-286: Change to “CO2:CH4 ratios represent means of total emission after 363 days of incubation.”
Li 287: Change “less CH4 production” to “less GHG production”
Li 296, “0.8 and 9.1”: I'm assuming these are absolute amounts (not the glucose factors themselves); what are the units?
Li 298, “glucose addition increased CO2 production at 20 °C by 46%”: For which sample? Or is this an average?
Li 302, “core P16-F”: Should this be "P17-A" (see upper left of Fig. 4)?
Li 318: Delete the extra parentheses around “P16”
Li 319: Either delete the “(d.)”, or add panel labels to the figure itself.
Li 338: Change “did not produce CH4” to “did not produce appreciable CH4” (because Fig. 3 still shows a small amount of CH4).
Li 339: Change “4°C and 20°C” to “4°C or 20°C”
Li 353: Correct the “Table 2” reference to “Table 3”
Li 359: Change “discrepancies” to “variability”
Li 363: The word "narrowness" applied to microbial communities needs more clarification. Therefore (and to correct other grammar), change “by the narrowness” to “due to the ecological and phylogenetic narrowness”.
Li 371: Change “microbial community growth” to “methanogen community growth”
Li 373: Change “were correlated” to “is correlated”
Li 374: Change to “For ecologically and phylogenetically narrow microbial communities, like methanogens, …” (same reasoning as above; plus other grammar correction)
Li 380: Correct missing period at the end of this sentence.
Li 382: What are these redox features? Also, change “On the first hand” to “On the one hand”.
Li 386: Remove the extraneous comma after “both”. Also change “that did not produce methane” to “which did not produce appreciable methane” (same reasoning as above).
Li 399-405: But the production per gram C would *always* be much higher than the production per gram DW, because the C is only a small percentage of the DW in mineral soils. Therefore, comparisons of production per gram C vs. per gram DW doesn't say anything about the lability of the C. To look at C lability, it only makes sense to compare the per-gram-C production across different samples, because most of the rest of the DW is just inert material. This might mean a re-write of this section; e.g. based on Supp. Fig. 3, you could say that the P17-A sample had the highest C lability because it has the highest production per gram C. But P17-F would still have a similar (or slightly lower) lability compared to the Yedoma soils, so its lability is not especially high.
Li 409: Change “as proved by” to “consistent with”
Li 417: Change “limited” to “limiting”
Li 433: Change to “under wet summer conditions, it is likely that there will be rapid C turnover”
Li 443: Delete the extraneous “in CH4”
Li 448: Change the last part of this line to “soil moisture might increase, and C in Yedoma”
Li 451-452: This sentence needs a few small corrections, as follows: “CH4 oxidation in overlying surfaces might have inhibited CH4 production in the active layers of the Yedoma samples (Figure 2; Figure 3), but our methanotroph results did not allow us to draw this conclusion.”
Li 453-457: But CH4 production in the Yedoma active layers was very low, and occurred only in these anaerobic incubations; whereas in the field the active layers are well-drained and the permafrost is frozen (and therefore not likely actively producing CH4). Therefore, it seems like in the field there wouldn't be much (if any) CH4 *to* transport or oxidize. So I'm puzzled by these assertions about CH4 oxidation and plant transport being important factors in the Yedoma sites, at least while the permafrost is still intact.
Li 465: Change “were” to “was”
Li 473: Change to “to better understand changes in redox conditions across the landscape to improve upscaling.”
Supp. Fig. 5: This figure is hard to read due to the line styles having no particular pattern, and some being very similar in appearance (e.g. the active layer 20C and frozen layer glucose 4C are both solid black). My suggestion would be to use the same set of colors as in Fig. 2 to represent the soil layers and incubation temperatures, and dashed / non-dashed lines to indicate presence or absence of glucose.
Supp. Table 2: In the third data column, “Max production rate CH4 (μg C-CO2.g C-1.d-1)”, it looks like “CH4” should be “CO2”.
Supp. Table 3, value “6539.022 ± 1299.21”: With these units (mg CH4-C / g C), this would mean that 6.5 times more CH4 was produced than there was C in the soil, which is impossible; and also this number is several orders of magnitude higher than the cumulative production in Supp. Fig. 3c. Maybe a misplaced decimal point? Or are the units for this row supposed to be μg instead of mg?