Dear Sarah and Eric

Your paper has been assessed by two reviewers who are experts in the field. Both concluded that major revisions are required before your manuscript may be published. Both reviewers are concerned with the scientific and presentation quality of the present version of the manuscript and suggested various modifications and revisions.

The reviewers noted that you setup with fixed CO2 may influence your conclusions and the quantification of the disequilibrium term DICdis. I would have hoped that you would be able to provide conclusive, quantitative evidence in your reply that your approach is sound. It may not be sufficient to simply assert that “the effect on the disequilibrium fraction is expected to be small” even if this may be correct. A possibility would be to compare the components of DIC in two factorial simulations with an identical setup (away from the preindustrial equilibrium) except for atmospheric CO2. In one simulation, atmospheric CO2 is fixed (as already done) and in a new simulation atmospheric CO2 is allowed to vary. Such a comparison may permit the reader to judge to which extent DIC and it subcomponents are affected by your standard choice of a fixed CO2 concentration.

I also note the remark on ocean circulation by reviewer one. The current paper should not rely on submitted material which may or may not be accepted and a better presentation of the ocean circulation changes (perhaps using a figure?) is needed.

Both reviewers highlighted that the use of CO2 as a biogeochemical property versus as a way to vary radiative forcing must be clarified. It seems best to refer to temperature changes and radiative forcing in the latter case and not to the term “CO2”.

If you feel that you are able to address all the points raised by the two reviewers in a satisfactory manner, I kindly invite you to submit a revised version of your manuscript. I will then send out this version to further review.

Thank you very much for submitting your work to Biogeosciences.

With Season Greetings and all the best for 2018,

Fortunat

Dear Sarah and Eric

Your revised manuscript has been assessed by one of the original reviewer. I am happy to accept your contribution for publication in Biogeosciences based on the reviewer's recommendation and my own reading of the submitted documents.

Thank you for submitting your work to Biogeosciences.

With best wishes, Fortunat