Project A5

Development of a new paleo-pH/CO2 proxy and application in the late Cretaceous and Palaeogene

Douglas Coenen (PhD)

Principal Investigators: Wolfgang Müller, David Evans, Axel Gerdes, Horst Marschall (Goethe University Frankfurt), James Rae (University of St Andrews), Laura Cotton (Bristol University), Willem Renema (Naturalis)

Records of secular changes in ocean chemistry during past climate change events are fundamental to our understanding of the carbon cycle. The pH of the ocean is closely coupled to atmospheric pCO2, thus reconstructions of past changes in ocean pH are one of the principal means by which the climate of the past can be related to pCO2. In turn, this forms one method by which Earth System Sensitivity (ESS) can be derived, knowledge of which is critical to our ability to accurately predict future climate change and to test the accuracy of climate models. However, ocean pH reconstructions are lacking for many intervals in the geological past (see figure), and many existing CO2 proxies are associated with large uncertainties. We will calibrate and apply the well-established boron isotope pH proxy for the first time in large benthic foraminifera in order to produce a late-Cretaceous to Paleogene CO2 record at higher resolution than previous studies. These data will be used in conjunction with the new palaeotemperature data from project A1 to improve our understanding of the relationship between CO2 and temperature (i.e. ESS) in past warm periods, which in turn will be used to compare to the climate model output generated in Project C1.