Modelling the response of the marine microalgae Emiliania huxleyi to an elevation of pCO2

International audienceCoccolithophorids are marine microalgae producing micro calcite plates. Under certain circonstances these microorganisms can form massive blooms which can be detected by satellites. These phytoplanktonic organisms play an important role in atmospheric CO 2 trapping through large scale precipitations of calcium carbonate in the oceans. However, recent experiments revealed that the associated fluxes that represent a sink of carbon may be slow down by an increase in atmospheric CO 2 concentration. In this paper we design models to account for the decrease in calcification and photosynthesis rates observed after an increase of pCO 2 in Emiliania huxleyi continuous photobioreactors. Since the involved mechanisms are still not completely clear, we developed several models, each of them based on a different hypothesis. These models are kept at a very general level, by maintaining the growth and calcification functions in a generic form, i.e. independent on the shape of these functions and on parameters values. The analysis is thus performed using these generic functions were the only hypothesis is an increase of these rates with respect to the regulating carbon species. As a result, each model responds differently to a pCO 2 elevation. Surprisingly, the only model whose behaviour is in agreement with the experimental results corresponds to a coupling of photosynthesis and calcification with carbonate as the regulating species, whereas bicarbonate is the substrate of these processes