The calcification process of planktic foraminifers and its implication for the incorporation of paleo-oceanographic signals to their shells

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The shells of planktic foraminifers found in ocean-sediments are frequently used for paleooceanographic reconstruction. The proposed project focuses on the ecology and shell geochemistry of planktic foraminifers. An accurate and reliable interpretation of foraminiferal isotopic signature in the sedimentary record requires a detailed knowledge of the modern behavior of living species with regard to their environment prior to proxy application. We aim to unravel and understand and quantify the depth dependent calcification of planktic foraminiferal shells by using a recently developed oxygen isotope mass balance model for planktic foraminiferal shell growth. The model will be tested using plankton tow and sediment trap collected foraminifers in the region off NW Africa. Stable isotope determination will be carried out using a new technique (Secondary Ion Mass Spectrometry) which allows analyses of successive chambers of foraminiferal calcite tests. Detailed quantification of species-specific depth habitat allows us further to investigate how the seawater carbonate chemistry ([CO3 2-]) controls the incorporation of carbon and oxygen isotopes into foraminiferal calcite during the depth-integrated shell growth process vertically throughout the water column in the region of NW Africa. After the calibration of the species-specific δ13Cshell/[CO3 2-] relationship, paleo-oceanographers will be able to estimate the δ13CDIC from the paleo-record by applying a species-specific correction factor. Additionally, the comparison of foraminiferal δ13C data from the water column and from core top sediments gives potentially information about invasion of anthropogenic CO2 into the surface ocean water. Quantifying an effect of [CO3 2-] on oxygen isotopes may improve estimation of paleo-temperatures.