Dear Authors,

Thank you very much for your point-by-point responses to the reviewer' comments. I believe that you are making a revised version of the manuscript following the comments and suggestions from the reviewers. So we would appreciate it very much if you could submit the revised manuscript to the website of BG. Once we get the manuscript, we will ask the reviewers to evaluate it soon.

Kind regards,

Koji Suzuki
Editor

Dear Authors,

Thank you very much for revising your manuscript. We have gotten two reviews on your revised manuscript from two experts of this research field. The reviewer Prof. Andrew McMinn kindly suggested us for its publication from our journal, but another referee still criticized your revised manuscript severely, especially in the lack of novelty and in-depth discussion – these issues were also pointed out by another reviewers in the first version of your manuscript. Please read the comments from the second reviewer carefully (see the attachment), and make a further revised manuscript if the authors consider that these issues can be conquered.

Again thank you for your nice effort to improve the manuscript.

Kind regards,

Koji Suzuki
Editor

Dear Dr. Hutchins,

We have received minor comments on your manuscript from a new reviewer (see below). So we would appreciate it very much if you could consider these issues carefully and make a further revised manuscript with point-by-point responses to the comments.

Thank you again for your nice effort to improve the paper.

Kind regards,

Koji Suzuki
Editor

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I commend the authors on their revised manuscript. The study is sound and the paper reads well. The inclusion of the points raised by the anonymous reviewer has certainly strengthened the manuscript. There are however a few minor points that need to be addressed before publication.

Firstly, the authors could consider citing two papers in the current special issue which support their findings. The first by Hancock et al, which shows a decline or loss of P. antarctica from population at high pCO2(line 424). The second is Deppler et al, who measured C:N ratios with pCO2 (lines 449-455).

The authors seem to have confused the discussion on silicification (Lines 460-470). As it reads now the authors contradict themselves. I believe the problem is a mistake in the sentence at 466, which reads "This suggests that future increases in diatom silicification at elevated pCO2 could partially or wholly offset the decreased silicification and higher dissolution rates of silica observed at warmer temperatures (above)..." Based on the literature arguments and their own data, I believe the authors have mixed up this sentence. Instead, it should be that the increase in silicification with temp could offset the decrease observed with high pCO2. However, please double check and revise accordingly.

Please note also, there is an error in the PDF, where the bottom two lines of each page is missing. Please ensure revised ms has all line numbers included when converted to pdf.

Minor edits:
Line 59: add 'the' before Ross Sea
Line 313: delete the 's' from responses, should read response.

We are delighted to inform you that your manuscript has just been accepted by the journal Biogeosciences. Thank you very much for taking all comments from the reviewers into account during the review process. I believe that your paper has been greatly improved.

Thank you again for choosing the journal Biogeosciences as an outlet of your nice work.

Kind regards,

Koji Suzuki
Editor