Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Evans, David, Sagoo, Navjit, Renema, Willem, Cotton, Laura J., Müller, Wolfgang, Todd, Jonathan A., Saraswati, Pratul Kumar, Stassen, Peter, Ziegler, Martin, Pearson, Paul N., Valdes, Paul J., Affek, Hagit P.
• Other Authors: University of St Andrews.School of Earth & Environmental Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Clumped isotope; Eocene; Tropical sea-surface temperatures; Polar amplification; Seawater Mg/Ca; GE Environmental Sciences; QE Geology; DAS; SDG 13 - Climate Action; GE; QE; Planktonic foraminifera
• Online Access: https://hdl.handle.net/10023/15626; https://doi.org/10.1073/pnas.1714744115

D.E. and H.P.A. acknowledge support from Yale University and the Yale Analytical and Stable Isotope Center and from Grant 171/16 of the Israel Science Foundation. W.R. and L.J.C. were supported by NWO Grant ALW 822 01 009. The Tanzania Commission for Science and Technology (COSTECH) and the Tanzania Petroleum Development Corporation supported the Tanzania Drilling Project (TDP) which recovered the Tanzanian specimens. Laser-ablation ICPMS work at RHUL was partly funded by a 2014 Natural Environment Research Council (NERC) Capital Equipment Grant (Ref. CC073). The Research Foundation Flanders is acknowledged for financial support (to P.S.). M.Z. acknowledges support from the Netherlands Earth System Science Center and Horizon 2020 Grant MSCA-IF-2014 655073. Past greenhouse periods with elevated atmospheric CO2 were characterized by globally warmer sea-surface temperatures (SST). However, the extent to which the high latitudes warmed to a greater degree than the tropics (polar amplification) remains poorly constrained, in particular because there are only a few temperature reconstructions from the tropics. Consequently, the relationship between increased CO2, the degree of tropical warming, and the resulting latitudinal SST gradient is not well known. Here, we present coupled clumped isotope (Δ47)-Mg/Ca measurements of foraminifera from a set of globally distributed sites in the tropics and midlatitudes. Δ47 is insensitive to seawater chemistry and therefore provides a robust constraint on tropical SST. Crucially, coupling these data with Mg/Ca measurements allows the precise reconstruction of Mg/Casw throughout the Eocene, enabling the reinterpretation of all planktonic foraminifera Mg/Ca data. The combined dataset constrains the range in Eocene tropical SST to 30–36 °C (from sites in all basins). We compare these accurate tropical SST to deep-ocean temperatures, serving as a minimum constraint on high-latitude SST. This results in a robust conservative reconstruction of the early Eocene latitudinal gradient, ...