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

过去地表水pH的变化可以可靠地从浮游有孔虫硼同位素组成重建。为了从海洋表面pH值估计大气二氧化碳水平，除了pH值外，还需要第二个碳酸盐系统参数。然而，在早期的研究中，这样的参数（通常是碱度或碳酸盐离子浓度）受到现代海洋条件或碳酸盐补偿深度重建的间接限制。考虑到这些限制因素带来的相对较大的不确定性，开发除pH以外的碳酸盐体系参数的替代方法至关重要。本研究旨在系统地开发和应用除pH（浮游有孔虫B/Ca）以外的碳酸盐体系参数的新的潜在替代方法，以重建溶解的无机碳。浮游有孔虫和鞭毛虫的氧同位素差异用于重建碳酸盐离子浓度)。来自部分解耦的碳酸盐系统参数区域的地表沉积物样本将用于校准研究。随后，这些代用物将在更新世/全新世冰川期/间冰期上进行测试，使用来自少营养站点（大气二氧化碳与海水平衡）的沉积物岩心。结合对同一材料的有孔虫硼同位素分析得出的古ph值估计，可以检查更新世/全新世下岩芯记录是否与冰芯的二氧化碳记录相匹配。最后，将从ODP岩心重建中中新世二氧化碳水平，并与独立发表的替代记录（如烯酮碳同位素或气孔指数）进行比较。

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.