Tracing calcareous nannoplankton response to ocean acidification under extreme climatic and ecological conditions: comparing culture experiment and geological data

The project aims at providing a better understanding of the effects of extreme climatic conditions, in terms of high CO2, ocean acidification, temperature and surface water fertility variations, on coccolithophores biocalcification. Coccolithoporids are phytoplanktonic algae which produce a calcitic exoskeleton (coccosphere) and are therefore extremely important primary producers playing a direct role on the equilibrium of the carbon-cycle. At present day the burning of fossil fuels is causing ocean acidification which is having direct effects on calcifying organisms including the difficulty in doing biocalcification. Laboratory experiments on living coccolithophores focused on the effects of high CO2 on biocalcification but rarely investigated the effects of combined stressing factors (e.g. temperature, nutrients, trace metals) under high CO2. For this reasons, a complete and realistic picture of how biocalcification is affected under climatic ¿perturbed conditions¿ is not available. We intend to reproduce in laboratory different combination of ¿stressing¿ factors (e.g. different grade of temperature, high/low nutrient content, trace metals, different Mg/Ca, volcanic ashes having different chemical composition) and test the nannoplankton response, distinguishing the effects on different species. In particular we will examine coccolithophore species which differ taxonomically and for the grade of calcification. The results are intended to be compared with published and new data collected during the current project from the geological record. In fact, in order to predict future effects of OA and global warming on marine ecosystems, short-term current changes require integration with long-term variations, as those traced in the geological record. We intend to focus on geological case histories marked by extreme paleoenvironmental and ecological conditions, which will be considered as ¿natural experiments¿. We will trace coccolith size variations, presence/absence of malformation as well as changes in carbonate production through these critical intervals. The integration of the data from the geological record and from the laboratory experiments is expected to have an impact on (paleo)ecological and (palaeo)climatic reconstructions, since we expect to increase the applicability of calcareous nannofossils as proxies for temperature, surface water nutrient and pCO2. In particular, the modelling of nannoplankton species-specific reactions/adaptations to CO2 excess and ocean acidification during different geologic time slices is expected to open new scenarios on the characterization of other critical past events, and also on quantifying CO2 concentrations and temperature changes. Only the geological record contains the medium- to long-time perspective necessary to formulate projection for time intervals longer than a few decades.