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Synchronous tropical and polar temperature evolution in the Eocene

Synchronous tropical and polar temperature evolution in the Eocene
Synchronous tropical and polar temperature evolution in the Eocene

Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO2 concentrations are crucial for developing better projections of future climate change. Deep-ocean 1,2 and high-latitude 3 palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data 4-6 to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing 7,8, rather than changes in ocean circulation 9,10, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO2 reconstructions 8 yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates 11 .

0028-0836
382-386
Cramwinckel, Margot J.
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Huber, Matthew
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Kocken, Ilja J.
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Agnini, Claudia
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Bijl, Peter K.
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Bohaty, Steven M.
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Frieling, Joost
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Goldner, Aaron
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Hilgen, Frederik J.
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Kip, Elizabeth L.
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Peterse, Francien
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Van Der Ploeg, Robin
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Röhl, Ursula
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Schouten, Stefan
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Sluijs, Appy
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Cramwinckel, Margot J.
e467976c-be0c-47a5-a7eb-ecfe93048373
Huber, Matthew
cac8c146-e2e3-4758-9fe9-46aa85e35ad2
Kocken, Ilja J.
9a15c736-f27f-4467-96e0-71fcf837ff29
Agnini, Claudia
accab295-8795-4af8-943a-22d2d2afda89
Bijl, Peter K.
fe283896-4066-490e-81b5-3212d00ef810
Bohaty, Steven M.
af9dbe78-8b9f-44f2-ba1d-20795837d2d1
Frieling, Joost
76c2d878-65e9-4945-bc6b-1ab1daf7cb4d
Goldner, Aaron
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Hilgen, Frederik J.
afa55c8c-67ff-47c9-b1c7-d1f50cc2e253
Kip, Elizabeth L.
fb409db5-2a44-4be8-9acf-24996b7dc860
Peterse, Francien
471cf1d7-57d4-4954-ae8d-14fa03f0278b
Van Der Ploeg, Robin
f17951c6-b5eb-479b-95a7-e04714635bb3
Röhl, Ursula
c28c498d-f0a1-4c25-bf94-4bf46641ceed
Schouten, Stefan
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Sluijs, Appy
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Cramwinckel, Margot J., Huber, Matthew, Kocken, Ilja J., Agnini, Claudia, Bijl, Peter K., Bohaty, Steven M., Frieling, Joost, Goldner, Aaron, Hilgen, Frederik J., Kip, Elizabeth L., Peterse, Francien, Van Der Ploeg, Robin, Röhl, Ursula, Schouten, Stefan and Sluijs, Appy (2018) Synchronous tropical and polar temperature evolution in the Eocene. Nature, 559 (7714), 382-386. (doi:10.1038/s41586-018-0272-2).

Record type: Article

Abstract

Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO2 concentrations are crucial for developing better projections of future climate change. Deep-ocean 1,2 and high-latitude 3 palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data 4-6 to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing 7,8, rather than changes in ocean circulation 9,10, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO2 reconstructions 8 yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates 11 .

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Cramwinckel_et_al_2018_final_accepted_version - Accepted Manuscript
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Accepted/In Press date: 13 April 2018
e-pub ahead of print date: 2 July 2018
Published date: 19 July 2018

Identifiers

Local EPrints ID: 422957
URI: http://eprints.soton.ac.uk/id/eprint/422957
ISSN: 0028-0836
PURE UUID: 788ac872-189d-496a-9a75-28893e317fad
ORCID for Margot J. Cramwinckel: ORCID iD orcid.org/0000-0002-6063-836X
ORCID for Steven M. Bohaty: ORCID iD orcid.org/0000-0002-1193-7398

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Date deposited: 08 Aug 2018 16:30
Last modified: 07 Oct 2020 06:36

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Contributors

Author: Matthew Huber
Author: Ilja J. Kocken
Author: Claudia Agnini
Author: Peter K. Bijl
Author: Joost Frieling
Author: Aaron Goldner
Author: Frederik J. Hilgen
Author: Elizabeth L. Kip
Author: Francien Peterse
Author: Robin Van Der Ploeg
Author: Ursula Röhl
Author: Stefan Schouten
Author: Appy Sluijs

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