Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
28 May 2009
Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.
Carbon fixation prediction during a bloom of Emiliania huxleyi is highly sensitive to the assumed regulation mechanism
O. Bernard1,2, A. Sciandra2, and S. Rabouille2 1COMORE-INRIA, BP 93, 06902 Sophia-Antipolis Cedex, France
2LOV, UMR 7093, Station Zoologique, BP 28, 06234, Villefranche-sur-mer, France
Abstract. Large scale precipitation of calcium carbonate in the oceans by coccolithophorids plays an important role in carbon sequestration. However, there is a controversy on the effect of an increase in atmospheric CO2 concentration on both calcification and photosynthesis of coccolithophorids. Indeed recent experiments, performed under nitrogen limitation, revealed that the associated fluxes may be slowed down, while other authors claim the reverse. We designed models to account for various scenarii of calcification and photosynthesis regulation in chemostat cultures of Emiliania huxleyi, based on different hypotheses on the regulation mechanism. These models consider that either carbon dioxide, bicarbonate, carbonate or calcite saturation state (Ω) is the regulating factor. All were calibrated to predict the same carbon fixation rate in nowadays pCO2, but they turn out to respond differently to an increase in CO2 concentration. Thus, using the four possible models, we simulated a large bloom of Emiliania huxleyi. It results that models assuming a regulation by CO32− or Ω predicted much higher carbon fluxes. The response when considering a doubled pCO2 was different and models controlled by CO2 or HCO3 led to increased carbon fluxes. In addition, the variability between the various scenarii proved to be in the same order of magnitude than the response to pCO2 increase. These sharp discrepancies reveal the consequences of model assumptions on the simulation outcome.
Citation: Bernard, O., Sciandra, A., and Rabouille, S.: Carbon fixation prediction during a bloom of Emiliania huxleyi is highly sensitive to the assumed regulation mechanism, Biogeosciences Discuss., 6, 5339-5372,, 2009.
O. Bernard et al.
O. Bernard et al.
O. Bernard et al.


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