Dear Author,

Thank you for submitting a revised version of your manuscript submitted to Biogeosciences, which I am glad to accept for publication. Please address the minor comments and requests for change below.

I look forward to seeing this paper published and thank you for considering Biogeosciences to publish these very interesting results.


Best regards,
Jean-Pierre Gattuso
BG Editor

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- p1l20: "exponential growth from a low level". Either "Exponential growth" or "exponential growth from a low cell density"
-p1l20-21: "no artificial simulation" is cryptic if one has not read the paper. Why not "no nutrient enrichment?
- p1l24: 1000 uatm CO2
- p2l20 and elswhere: Omega_c should suffice. In any case, be consistent: "Calcite" or "calcite"?
- p2l23: also in E. huxleyi. See table 3 in Fiorini et al. (2011; Journal of Phycology)
- p8l27-29: it is a pity that you do not elaborate more on this result which seem important and very much relevant to the question asked in the title of the manuscript, with data collected during the same cruise as the other results discussed. It would be worrisome if this is part of a “salami” publication strategy.
- p9l8: "after 96 h."
- p9l29-30: "... environmental conditions... To investigate these possibilities, ..."
- I recommend that the size of Fig. 10 is increased, especially the font size.
- p10 l23-25, p11l24 (and possibly elsewhere): a referee commented that "calcification" was not consistently used. Here, it is still confusing. Calcification is usually used to indicated a rate (as you do when citing data from Poulton et al.). I disagree with this use in the case of morphometric measurements because there is no direct relationship between the calcite mass and the rate of calcification. I suggest that you use "degree of calcification" instead, as you do earlier in the manuscript (as well as at the end of this paragraph).
- 11l5: "low initial cell density/abundance"
- p12l22: "in situ" rather than "in-situ"
- p13l22: please provide the doi of the data set at BODC.
- Table 1, Fig. 8: salinity is the ratio of two conductivities and is therefore unit-less.
- Legend of table 3, fig. 5: always add a space between a number and its unit.
- All figures: use negative exponents in axes labels.
- Note that guideline for formatting references have not been followed.