Decreasing marine biogenic calcification: A negative feedback on rising atmospheric p CO 2

In laboratory experiments with the coccolithophore species Emiliania huxleyi and Gephyrocapsa oceanica , the ratio of particulate inorganic carbon (PIC) to particulate organic carbon (POC) production decreased with increasing CO 2 concentration ([CO 2 ]). This was due to both reduced PIC and enhanced POC production at elevated [CO 2 ]. Carbon dioxide concentrations covered a range from a preindustrial level to a value predicted for 2100 according to a “business as usual” anthropogenic CO 2 emission scenario. The laboratory results were used to employ a model in which the immediate effect of a decrease in global marine calcification relative to POC production on the potential capacity for oceanic CO 2 uptake was simulated. Assuming that overall marine biogenic calcification shows a similar response as obtained for E. huxleyi or G. oceanica in the present study, the model reveals a negative feedback on increasing atmospheric CO 2 concentrations owing to a decrease in the PIC/POC ratio.