31 May 2023
 | 31 May 2023
Status: this preprint is currently under review for the journal CP.

CO2- and orbitally- driven oxygen isotope variability in the Early Eocene

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

Abstract. 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 CO2. 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 CO2 background states. We analyze the relative difference between climatic changes resulting from CO2 and orbital changes and find that the seasonal climate responses to orbital changes are larger than CO2-driven changes in several regions. Using terrestrial δ18O and δD records from the Paleocene-Eocene Thermal Maximum (PETM), we compare our modeled isotopic seasonal range to fossil evidence and find agreement between empirical and simulated isotopic compositions. Our conclusions consider systematic impacts on the proxy records, including the preservation state of the proxy, analytical uncertainty, and the relationship between δ18O or δD and environmental context, as well as illustrate the utility of fully coupled, isotope-enabled climate models when interpreting proxy records in times of extreme warmth.

Julia Campbell et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-37', Gordon Inglis, 11 Jul 2023
    • AC1: 'Reply on RC1', Julia Campbell, 03 Aug 2023
  • RC2: 'Comment on cp-2023-37', Anonymous Referee #2, 03 Aug 2023
    • AC2: 'Reply on RC2', Julia Campbell, 11 Aug 2023

Julia Campbell et al.

Data sets

CESM1.2 simulation data for "CO2 and orbitally driven oxygen isotope variability in the Early Eocene" Julia Campbell

Julia Campbell et al.


Total article views: 530 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
400 113 17 530 5 9
  • HTML: 400
  • PDF: 113
  • XML: 17
  • Total: 530
  • BibTeX: 5
  • EndNote: 9
Views and downloads (calculated since 31 May 2023)
Cumulative views and downloads (calculated since 31 May 2023)

Viewed (geographical distribution)

Total article views: 510 (including HTML, PDF, and XML) Thereof 510 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 04 Oct 2023
Short summary
In this study, we use climate modeling to investigate the relative impact of CO2 and orbit on Early Eocene (~55 million years ago) climate, as well as compare our modeled results to fossil records to determine the context for the Paleocene-Eocene Thermal Maximum, the most extreme hyperthermal in the Cenozoic. Our conclusions consider limitations and illustrate the importance of climate models when interpreting paleoclimate records in times of extreme warmth.