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 pCO2. We corroborate these results with a suite of climate model simulations demonstrating that only simulations including a decline in pCO2 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.
|Number of pages||16|
|Early online date||2 Aug 2021|
|Publication status||Published - 1 Sep 2021|
Bibliographical noteFunding Information:
We thank NERC (reference: CC010) and NEIF (www.isotopesuk.org) for funding and maintenance of the instrumentation used for this work. We thank S. Blackbird at the University of Liverpool for technical assistance with the TOC analyses. This research was carried out with funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) and European Research Council Grant Agreement number 340923 “The greenhouse earth system” T-GRES (awarded to R.D.P.). Further funding was provided by the Royal Society as part of a Tata University Research Fellowship to B.D.A.N. and the associated enhancement award that funded V.L. Climate model simulations were carried out using the computational facilities of the Advanced Computing Research Centre, University of Bristol, and were supported by NERC (grant number NE/L002434/1).
© 2021, The Author(s), under exclusive licence to Springer Nature Limited.
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Sadaf R Alam (Manager), Steven A Chapman (Manager), Polly E Eccleston (Other), Simon H Atack (Other) & D A G Williams (Manager)