CO 2-driven and orbitally driven oxygen isotope variability in the Early Eocene

Campbell, Julia; Poulsen, Christopher J.; Zhu, Jiang; Tierney, Jessica E.; Keeler, Jeremy

Paleoclimate reconstructions of the Early Eocene provide important data constraints on the climate and hydrologic cycle under extreme warm conditions. Available terrestrial water isotope records have been primarily interpreted to signal an enhanced hydrologic cycle in the Early Eocene associated with large-scale warming induced by high atmospheric inline-formulaCO2. However, orbital-scale variations in these isotope records have been difficult to quantify and largely overlooked, even though orbitally driven changes in solar irradiance can impact temperature and the hydrologic cycle. In this study, we fill this gap using water isotope–climate simulations to investigate the orbital sensitivity of Earth's hydrologic cycle under different inline-formulaCO2 background states. We analyze the relative difference between climatic changes resulting from inline-formulaCO2 and orbital changes and find that the seasonal climate responses to orbital changes are larger than inline-formulaCO2-driven changes in several regions. Using terrestrial inline-formulaδ18O and inline-formulaδ2H records from the Paleocene–Eocene Thermal Maximum (PETM), we compare our modeled isotopic seasonal range to fossil evidence and find approximate agreement between empirical and simulated isotopic compositions. The limitations surrounding the equilibrated snapshot simulations of this transient event and empirical data include timing and time interval discrepancies between model and data, the preservation state of the proxy, analytical uncertainty, the relationship between inline-formulaδ18O or inline-formulaδ2H and environmental context, and vegetation uncertainties within the simulations. In spite of the limitations, this study illustrates the utility of fully coupled, isotope-enabled climate models when comparing climatic changes and interpreting proxy records in times of extreme warmth.



Campbell, Julia / Poulsen, Christopher J. / Zhu, Jiang / et al: CO2-driven and orbitally driven oxygen isotope variability in the Early Eocene. 2024. Copernicus Publications.


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