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

过去地表水pH值的变化可以可靠地重建南极有孔虫硼同位素组成。为了从海洋表面pH值估算大气二氧化碳水平，除了pH值之外，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）间接地受到现代海洋条件或碳酸盐补偿深度重建的限制。考虑到这些约束条件带来的相对较大的不确定性，开发除pH值以外的碳酸盐系统参数的替代指标至关重要。拟议的研究旨在系统地开发和应用新的除pH值以外的碳酸盐系统参数的潜在替代指标（溶解无机碳重构的浮游有孔虫B/Ca，以及浮游有孔虫和甲藻之间的氧同位素差异，用于重建碳酸根离子浓度）。将使用碳酸盐系统参数部分分离的区域的表层沉积物样品进行校准研究。随后，将使用来自贫营养地点（大气二氧化碳与海水平衡）的沉积物岩心，在更新世/全新世冰川/间冰期上测试这些代用指标。结合对同一材料有孔虫硼同位素分析得出的古pH值估计值，就可以检查更新世/全新世岩芯记录是否与冰芯中的二氧化碳记录相匹配。最后，中中新世二氧化碳水平将重建ODP核心和独立出版的代理记录，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.