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

David Hutchinson, Helen Katherine Coxall, Dan J Lunt, Margret Steinthorsdottir, Agatha M. De Boer, Michiel L.J. Baatsen, Anna S. Von Der Heydt, Matthew Huber, Alan T Kennedy-Asser, Lutz Kunzmann, Jean-Baptiste Ladant, Caroline Lear, Karolin Moraweck, Paul N Pearson, Emanuela Piga, Matthew J. Pound, Ulrich Salzmann, Howie Scher, Willem Sijp, Kasia ŚliwińskaPaul Wilson, Zhongshi Zhang

Research output: Contribution to journalReview article (Academic Journal)peer-review

Abstract

The Eocene–Oligocene transition (EOT) was a climate shift from a largely ice-free greenhouse world to an icehouse climate, involving the first major glaciation of Antarctica and global cooling occurring ∼34 million years ago (Ma) and lasting ∼790 kyr. The change is marked by a global shift in deep-sea δ18O representing a combination of deep-ocean cooling and growth in land ice volume. At the same time, multiple independent proxies for ocean temperature indicate sea surface cooling, and major changes in global fauna and flora record a shift toward more cold-climate-adapted species. The two principal suggested explanations of this transition are a decline in atmospheric CO2 and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. Here we review and synthesise proxy evidence of palaeogeography, temperature, ice sheets, ocean circulation and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of climate model simulations of temperature change across the EOT. The simulations compare three forcing mechanisms across the EOT: CO2 decrease, palaeogeographic changes and ice sheet growth. Our model ensemble results demonstrate the need for a global cooling mechanism beyond the imposition of an ice sheet or palaeogeographic changes. We find that CO2 forcing involving a large decrease in CO2 of ca. 40 % (∼325 ppm drop) provides the best fit to the available proxy evidence, with ice sheet and palaeogeographic changes playing a secondary role. While this large decrease is consistent with some CO2 proxy records (the extreme endmember of decrease), the positive feedback mechanisms on ice growth are so strong that a modest CO2 decrease beyond a critical threshold for ice sheet initiation is well capable of triggering rapid ice sheet growth. Thus, the amplitude of CO2 decrease signalled by our data–model comparison should be considered an upper estimate and perhaps artificially large, not least because the current generation of climate models do not include dynamic ice sheets and in some cases may be under-sensitive to CO2 forcing. The model ensemble also cannot exclude the possibility that palaeogeographic changes could have triggered a reduction in CO2.
Original languageEnglish
Pages (from-to)269-315
Number of pages47
JournalClimate of the Past
Volume17
Issue number1
DOIs
Publication statusPublished - 28 Jan 2021

Bibliographical note

Funding Information:
Acknowledgements. This work originated from a workshop on the Eocene–Oligocene transition in Stockholm in February 2017, funded by the Bolin Centre for Climate Research, Research Area 6.

Funding Information:
Financial support. This research has been supported by the Bolin Centre for Climate Research (Research Area 6), the Veten-skapsrådet (grant no. 2016-03912), the Svenska Forskningsrådet Formas (grant no. 2018-01621) and the Danish Council for Independent Research – Natural Sciences (DFF/FNU; grant no. 11-107497).

Publisher Copyright:
© 2021 Author(s).

Fingerprint

Dive into the research topics of 'The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons'. Together they form a unique fingerprint.

Cite this