The Eocene-Oligocene transition: a review of marine and terrestrial proxy data, models and model-data comparisons

• Main Authors: Hutchinson, David K., Coxall, Helen K., Lunt, Daniel J., Steinthorsdottir, Margret, Boer, Agatha M., Baatsen, Michiel, Heydt, Anna, Huber, Matthew, Kennedy-Asser, Alan T., Kunzmann, Lutz, Ladant, Jean-Baptiste, Lear, Caroline H., Moraweck, Karolin, Pearson, Paul N., Piga, Emanuela, Pound, Matthew J., Salzmann, Ulrich, Scher, Howie D., Sijp, Willem P., Śliwińska, Kasia K., Wilson, Paul A., Zhang, Zhongshi
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarc*; Antarctica; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-2020-68; https://cp.copernicus.org/preprints/cp-2020-68/

The Eocene-Oligocene transition (EOT) from a largely ice-free greenhouse world to an icehouse climate with the first major glaciation of Antarctica was a phase of major climate and environmental change occurring ~34 million years ago (Ma) and lasting ~500 kyr. The change is marked by a global shift in deep sea δ 18 O representing a combination of deep-ocean cooling and global ice sheet growth. At the same time, multiple independent proxies for sea surface temperature indicate a surface ocean cooling, and major changes in global fauna and flora record a shift toward more cold-climate adapted species. The major explanations of this transition that have been suggested are a decline in atmospheric CO 2 , and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. This work reviews and synthesises proxy evidence of paleogeography, temperature, ice sheets, ocean circulation, and CO 2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of model simulations of temperature change across the EOT. The model simulations compare three forcing mechanisms across the EOT: CO 2 decrease, paleogeographic changes, and ice sheet growth. We find that CO 2 forcing provides by far the best explanation of the combined proxy evidence, and based on our model ensemble, we estimate that a CO 2 decrease of about 1.6× across the EOT (e.g. from 910 to 560 ppmv) achieves the best fit to the temperature change recorded in the proxies. This model-derived CO 2 decrease is consistent with proxy estimates of CO 2 decline at the EOT.