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, which was reduced by at least 32 ± 10% compared with present day, demonstrating greater polar amplification than captured by most climate models.
Evans, D., Department of Geology and Geophysics, Yale University, New Haven, CT 06511, United States, School of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL, United Kingdom; Sagoo, N., Department of Geology and Geophysics, Yale University, New Haven, CT 06511, United States; Renema, W., Naturalis Biodiversity Center, Leiden, 2300 RA, Netherlands; Cotton, L.J., Naturalis Biodiversity Center, Leiden, 2300 RA, Netherlands, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, United States, Department of Geosciences, University of Florida, Gainesville, FL 32611, United States; Müller, W., Institute of Geosciences, Goethe University Frankfurt, Frankfurt, 60438, Germany, Department of Earth Sciences, Royal Holloway University of London, Egham, TW20 0EX, United Kingdom; Todd, J.A., Department of Earth Sciences, Natural History Museum, London, SW7 5BD, United Kingdom; Saraswati, P.K., Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, 400076, India; Stassen, P., Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Leuven, B-3000, Belgium, Royal Belgian Institute of Natural Sciences, Brussels, B-1000, Belgium; Ziegler, M., Department of Earth Sciences, Utrecht University, Utrecht, 3584 CS, Netherlands; Pearson, P.N., School of Earth and Ocean Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom; Valdes, P.J., Cabot Institute, University of Bristol, Bristol, BS8 1UJ, United Kingdom, School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, United Kingdom; Affek, H.P., Department of Geology and Geophysics, Yale University, New Haven, CT 06511, United States, Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, 91904, Israel
Recommended Citation:
Evans D.,Sagoo N.,Renema W.,et al. Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry[J]. Proceedings of the National Academy of Sciences of the United States of America,2018-01-01,115(6)