Eocene to Oligocene terrestrial Southern Hemisphere cooling caused by declining 𝑝CO2

• Published in: Nature Geoscience
• Main Authors: Lauretano, Vittoria, Kennedy-asser, Alan T., Korasidis, Vera A., Wallace, Malcolm W., Valdes, Paul J., Lunt, Daniel J., Pancost, Richard D., Naafs, B. David A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Antarctic; Pacific; Antarc*
• Online Access: https://hdl.handle.net/1983/45dea1c1-704b-469d-9fce-7d760100a309; https://research-information.bris.ac.uk/en/publications/45dea1c1-704b-469d-9fce-7d760100a309; https://doi.org/10.1038/s41561-021-00788-z; https://research-information.bris.ac.uk/ws/files/334860632/Lauretanoetal_manuscript_fina.pdf

The greenhouse-to-icehouse climate transition from the Eocene into the Oligocene is well documented by sea surface temperature records from the southwest Pacific and Antarctic margin, which show evidence of pronounced long-term cooling. However, identification of a driving mechanism depends on a better understanding of whether this cooling was also present in terrestrial settings. Here, we present a semi-continuous terrestrial temperature record spanning from the middle Eocene to the early Oligocene (~41–33 million years ago), using bacterial molecular fossils (biomarkers) preserved in a sequence of southeast Australian lignites. Our results show that mean annual temperatures in southeast Australia gradually declined from ~27 °C (±4.7 °C) during the middle Eocene to ~22–24 °C (±4.7 °C) during the late Eocene, followed by a ~2.4 °C-step cooling across the Eocene/Oligocene boundary. This trend is comparable to other temperature records in the Southern Hemisphere, suggesting a common driving mechanism, likely p CO 2 . We corroborate these results with a suite of climate model simulations demonstrating that only simulations including a decline in p CO 2 lead to a cooling in southeast Australia consistent with our proxy record. Our data form an important benchmark for testing climate model performance, sea–land interaction and climatic forcings at the onset of a major Antarctic glaciation.