Calcification and photosynthesis of the coccolithophore Emiliania huxleyi cultured under a broad range of carbonate chemistry conditions

Two experiments have been conducted to study the effects of various carbonate system parameters on growth, particulate organic carbon-, particulate organic nitrogen-, particulate organic phosphate- (POC, PON, POP) and chlorophyll-production of the coccolithophore Emiliania huxleyi. In Experiment No.I, alkalinity was kept constant at -2350 µmol/kg whereas the fugacity of C02 was varied from -40 to -2320 µatm. In a second experiment, pHr was kept constant at -8.2 whereas fC02 was varied from -30 to -1690 µatm. Experiment No.2 was performed to distinguish pH-effects from C02-effects. POP-production is in both experiments independent of any carbonate system parameter. Instead it is correlating with the cell-density with lower POP-production at higher cell-densities. At constant alkalinity, POC-, PON-, chlorophyll-production and growth follow an optimum-curve along the fC02 range. Organic matter production of E.huxleyi profits from C02 fertilisation in non growth limiting conditions until a threshold of approximately 1000 µatm. Above that value it starts decreasing again. The optimum fC02 for growth is lower and situated at current atmospheric values. In contrast to the results of Experiment No. 1, no decrease of POC-production, chlorophyll-production and growth has been measured at high fC02 in pHr constant Experiment No.2, indicating that the low pHr at high fC02 in Experiment No. 1 is responsible for the measured decrease. In the very low fC02 range growth is decreasing at the approximately same C02 concentrations in both experiments albeit the DIC concentration is much higher in Experiment No. 1. Furthermore, there are strong indications that leakage of C02 out the cells is increasing from intermediate to low fC02 in Experiment No. 1. Due to these two observations, it is suggested that high leakage of C02 out of the cells might mainly be responsible for the measured decrease of growth and production at high pHr and low C02. Here, E. huxleyi cannot hold the carbon inside the cell which resembles an indirect carbon limitation. Due to technical difficulties, there is no quantitative data on calcite-production over the fC02 range available. However, images taken with the scanning electron microscope reveal serious malformations of the coccosphere at both, high and very low external fC02.