Pleistocene to Holocene and middle Miocene pCO2 reconstructions using new potential carbonate system proxies

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Past variations in surface water pH can be reliably reconstructed from the planktic foraminiferal boron isotopic composition. For estimating atmospheric carbon dioxide levels from surface ocean pH, a second carbonate system parameter apart from pH is required. However, in earlier studies such a parameter (usually alkalinity or carbonate ion concentration) was indirectly constrained from modern ocean conditions or carbonate compensation depth reconstructions. Considering the relatively large uncertainties afflicted with such constraints, it is of utmost importance to develop proxies for a carbonate system parameter other than pH. The proposed study aims to systematically develop and apply new potential proxies for carbonate system parameters other than pH (planktic foraminiferal B/Ca for reconstructing dissolved inorganic carbon, and oxygen isotope differential between planktic foraminifers and dinoflagellates for reconstructing carbonate ion concentration). Surface sediment samples from regions with partly decoupled carbonate system parameters will be used for calibration studies. Subsequently, these proxies will be tested on Pleistocene/Holocene glacials/interglacials using a sediment core from an oligotrophic site (where atmospheric carbon dioxide is in equilibrium with seawater). In combination with paleo-pH estimates from foraminiferal boron isotope analyses of the same material, the Pleistocene/Holocene downcore record can then be examined whether it matches the carbon dioxide record from ice-cores. Finally, middle Miocene carbon dioxide levels will be reconstructed from an ODP core and compared to independent published proxy records such as alkenone carbon isotopes or stomatal indices.