1,2,3,5,- 1Department of Earth Science, University of Bergen, Bergen, Norway
- 2Bjerknes Center for Climate Research, Bergen, Norway
- 3School of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, UK
- 4School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, UK
- 5MARUM, University of Bremen, Germany
- 6Earth & Planetary Sciences Department, University of California, Santa Cruz, USA
- 7Earth & Planetary Sciences Department, University of California, Riverside, USA
Past greenhouse climates like the Early Eocene Climatic Optimum (~53-49 million years ago, Ma) provide an opportunity to assess the sensitivity of global temperature to greenhouse forcing, with proxy-based temperature reconstructions from such time intervals providing crucial benchmark data for evaluating Earth System Models. However, estimating global mean temperatures is complicated by sparse proxy evidence for surface temperatures and heterogenous warming patterns. For this reason, most depictions of global mean temperature evolution use temperature reconstructions from the deep ocean, a vast and (proposedly) relatively homogenous heat reservoir (e.g., Hansen et al., 2013; Westerhold et al., 2020). Deep ocean temperature reconstructions, however, are usually based on the oxygen isotopic composition (δ18O) of benthic foraminifera, which can additionally be influenced by the isotopic composition of seawater and other non-thermal factors.
Here we present new deep ocean temperature reconstructions for ~52–50 Ma from both the North Atlantic (IODP Site U1409) and the Pacific Ocean (ODP Site 1209) using clumped isotope thermometry, which is independent from seawater composition and less affected by non-thermal influences. We confirm previously reported deep North Atlantic temperatures exceeding δ18O-based estimates (Meckler et al., 2022). Crucially, our results show that deep ocean warmth is not a regional feature of the Atlantic Ocean, with similarly warm temperatures also found in the vast deep Pacific Ocean. The new data advocate for a revision of previous, δ18O-based estimates of global mean temperatures. Combined with new CO2 estimates, we derive an updated and more robust estimate of equilibrium climate sensitivity for the Early Eocene Climate Optimum, which is higher than most previous estimates, an important new constraint for Earth System Models.
References
Meckler, A.N., et al. (2022), Cenozoic evolution of deep ocean temperature from clumped isotope thermometry. Science 377, 86-90
Hansen, J., et al. (2013), Climate sensitivity, sea level and atmospheric carbon dioxide. Philos. Trans. A Math. Phys. Eng. Sci. 371, 20120294
Westerhold, T., et al. (2020), An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science 369, 1383–1387
How to cite: Meckler, N., Taylor, V., Marquardt, J., Lypiridou, I., Ring, S., Rae, J., Sexton, P., Westerhold, T., Zachos, J., and Kirtland-Turner, S.: Globally warm deep ocean during the Early Eocene Climatic Optimum indicates high climate sensitivity to greenhouse gases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19376, https://doi.org/10.5194/egusphere-egu26-19376, 2026.
