I found this a very stimulating and interesting manuscript, and beyond being encouraged by the apparent agreement with the sedimentary results published by Iglesias-Rodriguez and Halloran et al. (2008), feel that this is an ideal way to investigate the consequences of anthropogenic (and otherwise) change on marine ecosystems and carbon cycling.
I would like to make a couple of minor points regarding the description of the carbonate system, and suggest the possible addition of confidence intervals upon the linear regressions presented in figure 5. Although I don’t imagine that this statistical analysis would change the story, I feel it would be of interest for the reader.
Regarding the discussion of the calcification response to, and influence on, the carbonate system I would like to highlight the sentence starting on line 25 of page 4143, which in my reading implies that there is DIC production as a result of pH reduction in the culture medium. I understand and agree with the point that the authors are making, that manipulating cultures by adding CO2 increases [DIC], but to avoid confusion would suggest a slight change in the wording to make clear that, in contrast to manipulation by CO2 addition, by adding acid there is no change in total [DIC], only a change in the speciation of the individual components making up that total DIC concentration.
Additionally, regarding lines 16 to 19 on page 4144, I think it would be valuable to point out that rather than removing CO2 from the surface ocean, additional calcification (without a concomitant increase in organic carbon production) would actually increase the surface water CO2 concentration, if caused by ocean acidification, acting as a positive feedback on CO2. My reading of the manuscript gave the opposite impression.
Halloran P., 2008. Interactive comment on “Coccolithophore response to climate and surface hydrography in Santa Barbara Basin, California, AD 1917–2004” by M. Grelaud et al. Biogeosciences Discussions 5: S2181–S2182 Article source.
