The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons
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Published:2021-01-28
Issue:1
Volume:17
Page:269-315
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ISSN:1814-9332
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Container-title:Climate of the Past
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language:en
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Short-container-title:Clim. Past
Author:
Hutchinson David K.ORCID, Coxall Helen K.ORCID, Lunt Daniel J.ORCID, Steinthorsdottir MargretORCID, de Boer Agatha M., Baatsen Michiel, von der Heydt AnnaORCID, Huber MatthewORCID, Kennedy-Asser Alan T.ORCID, Kunzmann LutzORCID, Ladant Jean-BaptisteORCID, Lear Caroline H.ORCID, Moraweck Karolin, Pearson Paul N.ORCID, Piga EmanuelaORCID, Pound Matthew J.ORCID, Salzmann UlrichORCID, Scher Howie D., Sijp Willem P., Śliwińska Kasia K.ORCID, Wilson Paul A., Zhang ZhongshiORCID
Abstract
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.
Funder
Vetenskapsrådet Svenska Forskningsrådet Formas Natur og Univers, Det Frie Forskningsråd
Publisher
Copernicus GmbH
Subject
Paleontology,Stratigraphy,Global and Planetary Change
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