Dear Dr. Fletcher and co-authors,

Thank you for your substantial efforts in responding to the comments of the three reviewers. Two of the reviewers were critical of the approach taken to reconstruct CO2 from bryophytes at the Beaver Pond site, and all of the reviewers felt that statements regarding the role of fire as a mechanism for Arctic amplification of Pliocene warming should be toned down. Nevertheless, there was consensus that the manuscript presents valuable data from an important site.

I encourage you to formally submit the revised manuscript for consideration. When you do so, I also encourage you to carefully assess whether your revised manuscript adequately addresses the following points of criticism from the reviews, and make additional revisions along these lines as you see fit:

1. Unclear stratigraphic context, particularly with respect to interpreting the charcoal record (e.g. potential for charcoal reworking; assessing changes in charcoal concentration with respect to depositional environment)

2: Broad statements in the text (or even implied in the title) regarding the role of fire in amplification of Pliocene warming in the Arctic

Because of the technical suggestions and your changes regarding the bryophyte CO2 proxy, I will request one review to assess the revised manuscript. To do so requires that I indicate “reconsider after major revisions”.

Thank you again for submitting your work to Climate of the Past. I look forward to seeing the formally submitted revised manuscript soon.

Sincerely,
Alberto Reyes

Dear Dr. Fletcher and co-authors,

First of all let me thank you for your patience during this long review process, which has been interrupted by Christmas holidays and other delays. Two of the three original referees have now evaluated your revised submission; both have recommended major revisions. The reviewers continue to have substantial concerns with the CO2 reconstruction. Reviewer 2 also notes that some of the fire/climate/high-latitude-amplification concerns they identified in the first version of the manuscript are not yet resolved. My sense is that these concerns can still be addressed with revision. In particular, both reviewers recommend more details on the BRYOCARB model implementation and some consideration of uncertainties/challenges with the empirical CO2 model. If you would like to keep this manuscript in consideration for publication in Climate of the Past, I invite you to submit a revised manuscript that takes into account the comments of the reviewers.

Reviewer 1 has provided an annotated PDF with additional specific comments and suggestions. Please let me know if you are not able to access this PDF through the Copernicus manuscript handling system.

Again, please accept my apologies for the delays in the review process.

Sincerely,
Alberto Reyes

Dear Dr. Fletcher,

Thank you for the submission of a revised version of your manuscript on fire in the Pliocene forests of Ellesmere Island. Your decision to remove the CO2 reconstruction from the manuscript removes many of the contentious points that were raised in review, and at this point I’m keen to move forward with publishing your manuscript subject to some minor revision. I’m still concerned that Dana Royer’s earlier concerns about the feedback angle in the manuscript haven’t been fully dealt with, but I think this can be addressed with minor revision. I also have some other suggestions for minor revision, mostly for clarity, which are detailed below.

line 31: “much greater than present….”

Lines 65-67: Please check for more recent relevant literature on efforts to model warm intervals such as the Pliocene – a good starting point is the PlioMIP2 website. Depending on your assessment of newer literature, you might want to revise the next two sentences too.

Line 157: “charcoal counts” seems more appropriate?

Line 204: “it has been”… “it” could refer to several things in this context – please clarify.

Section 2.3: Please provide a brief explanation of how uncertainty is treated (both with reconstruction uncertainty and propagated analytical uncertainty). Ref. 1 picked up on this point too.

Line 433: “ 1 cm3”

Line 444: “…grid cells, was counted…”

Lines 650 and 651: I assume the quoted MAAT and MST are mean +/- stdev for n stratigraphic intervals? Please clarify, and provide the n.

Line 678: “definitively” not “definitely”

Line 711: “have” not “has”

Line 728: seems like a good spot to refer to Fig S3

Line 899: “….suggests mean reconstructed summer temperatures were…”

Lines 900-907: This section is pretty awkward. The caveat about comparing Pliocene-modern differences in MST vs MAT is a point well taken, the execution is clunky and needs careful wordsmithing. Similarly, the last sentence is a good point but needs some massaging.

Line 948: unclear what is meant by “causatively here”

Line 962: “…low concentration of charcoal in this stratigraphic interval…”

Line 967-970: use commas to separate clauses in this sentence

Line 997: do you mean Castor? Or the extinct taxon Dipoides?

Lines 1010-1012: minor editing to clarify what the many “it” occurrences refer to.
Lines 1027-1029: This is really just a snapshot in time, so I suggest being a little more equivocal: “Thus, while vegetation and fire regimes seemingly changed through time…..” and “…have no apparent trend, within analytical and reconstruction uncertainty.”

Line 1033: “…change in vegetation community”

Line 1034: what is a fine fuel load? Do you mean fire fuel load?

Line 1044-1050: This bit on fire and feedback comes as a bit of a surprise at this point in the manuscript. It’s also pretty underdeveloped. Is there not more literature to support the contention of a potential feedback to climate warming in a forested High Arctic?

Line 1053: Careful with the snapshot nature of this study when referring to “the Pliocene”

Line 1057: suggest omitting “as a feedback” here

Dear Dr. Fletcher and co-authors,

Thank you for submitting a revised version of your manuscript “Evidence for fire in the Pliocene Arctic in response to amplified temperature,” which addresses the few outstanding issues from my last review dated 29 April 2019. I’m pleased to confirm that the paper will be accepted for publication in Climate of the Past. Thank you for your patience and flexibility during the long review process.

Sincerely,
Alberto Reyes