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

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Evans, D, Sagoo, N, Renema, W, Cotton, LJ, Müller, W, Todd, JA, Kumar Saraswati, P, Stassen, P, Ziegler, M, Pearson, PN, Valdes, PJ, Affek, HP
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: PNAS 2019
• Subjects: clumped isotope; Eocene; tropical sea-surface temperatures; polar amplification; seawater Mg/Ca; Planktonic foraminifera
• Online Access: http://hdl.handle.net/10141/622509; https://doi.org/10.1073/pnas.1714744115

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. © 2018 Published under the PNAS license. The attached document is the authors’ final accepted/submitted version of the journal article. You are advised to consult the publisher’s version if you wish to cite from it. NHM Repository