Discussions Interactive comment on “Algal constraints on the Cenozoic history of atmospheric CO2? ” by

• Main Authors: J. Henderiks, R. E. M. Rickaby, U. Riebesell
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Ocean acidification
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.521.651; http://www.cosis.net/copernicus/EGU/bgd/4/S22/bgd-4-S22_p.pdf?PHPSESSID=7eb3be07143bfd0d5c8ed9419845204e

The concept proposed by Henderiks and Rickaby- that the CO2 sensitivity of modern coccolithophore calcification reflects the CO2 concentration at the time of their origi-nation- is a very intriguing idea. It provides a new angle of looking at CO2/pH effects on coccolithophores, gives an evolutionary perspective to species-specific differences in calcification responses, and serves to stimulate the discussion on the potential for coccolithophores adaption to projected ocean acidification. The proposed concept rests upon three crucial assumptions: 1. Coccolithophore cal-cification is directly sensitive to CO2 (independent of an indirect effect of CO2 through its coupling with pH, carbonate ion concentration and carbonate saturation state). 2. Photosynthesis and calcification in coccolithophores are closely coupled. 3. "The cou-S22 pled photosynthetic and calcification potential of the various taxa is optimized for ocean carbonate chemistry at their time of origin and has been locked into genetic make-up since declined." As far as I can tell, there is no convincing evidence in the literature for either of these