This proposal seeks to reconstruct atmospheric pCO2 across the Pliocene/Pleistocene climate transition of the last 5 million years, which will provide a framework to test possible causes of the Plio-Pleistocene climatic transition. The primary objective of this proposal is to test the hypothesis that the pattern of warming during the early Pliocene warm period, as well as the subsequent cooling, was forced by a corresponding increase and decrease in pCO2. The PI's will evaluate pCO2 changes by reconstructing records of the total carbon isotopic fractionation that occurs during algal photosynthesis (Ep). The approach will be to extract and determine the carbon isotopic (d13C) values of haptophyte-derived long-chain ketone biomarkers (alkenones) obtained from a globally distributed set of DSDP and ODP cores. In addition, the carbon isotopic and Mg/Ca composition of one or more species of planktonic foraminifers will be analyzed from the same sample to constrain changes in the carbon isotopic composition of seawater and surface temperatures respectively. The difference between the d13C of alkenones and of the coeval near-surface dwelling planktonic foraminifera represents the approximate carbon isotopic fractionation that occurs during photosynthetic carbon fixation specific to alkenone-producing haptophyte algae. This technique has been used to reconstruct the magnitude of pCO2 change during the Cenozoic and is considered one of the most reliable paleo- pCO2 proxies presently available. Broader impacts include the bi-coastal collaboration between two major U.S. institutions, participation in the project by two undergraduates and a post-doc, and PI Pagani's participatetion in a middle and high school education program that will incorporate the results of this study into presentations to students and interns in the program.
