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Palaeogeographic controls on climate and proxy interpretation

Palaeogeographic controls on climate and proxy interpretation
Palaeogeographic controls on climate and proxy interpretation
During the period from approximately 150 to 35?million years ago, the Cretaceous–Paleocene–Eocene (CPE), the Earth was in a “greenhouse” state with little or no ice at either pole. It was also a period of considerable global change, from the warmest periods of the mid-Cretaceous, to the threshold of icehouse conditions at the end of the Eocene. However, the relative contribution of palaeogeographic change, solar change, and carbon cycle change to these climatic variations is unknown. Here, making use of recent advances in computing power, and a set of unique palaeogeographic maps, we carry out an ensemble of 19 General Circulation Model simulations covering this period, one simulation per stratigraphic stage. By maintaining atmospheric CO2 concentration constant across the simulations, we are able to identify the contribution from palaeogeographic and solar forcing to global change across the CPE, and explore the underlying mechanisms. We find that global mean surface temperature is remarkably constant across the simulations, resulting from a cancellation of opposing trends from solar and palaeogeographic change. However, there are significant modelled variations on a regional scale. The stratigraphic stage–stage transitions which exhibit greatest climatic change are associated with transitions in the mode of ocean circulation, themselves often associated with changes in ocean gateways, and amplified by feedbacks related to emissivity and planetary albedo. We also find some control on global mean temperature from continental area and global mean orography. Our results have important implications for the interpretation of single-site palaeo proxy records. In particular, our results allow the non-CO2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change. This “adjustment factor” is used to adjust sea surface temperatures, as the deep ocean is not fully equilibrated in the model. The adjustment factor is illustrated for seven key sites in the CPE, and applied to proxy data from Falkland Plateau, and we provide data so that similar adjustments can be made to any site and for any time period within the CPE. Ultimately, this will enable isolation of the CO2-forced climate signal to be extracted from multiple proxy records from around the globe, allowing an evaluation of the regional signals and extent of polar amplification in response to CO2 changes during the CPE. Finally, regions where the adjustment factor is constant throughout the CPE could indicate places where future proxies could be targeted in order to reconstruct the purest CO2-induced temperature change, where the complicating contributions of other processes are minimised. Therefore, combined with other considerations, this work could provide useful information for supporting targets for drilling localities and outcrop studies.
1814-9332
1181-1198
Lunt, Daniel J.
931ecfb5-1f50-412c-8f01-a46d69b1f82f
Farnsworth, Alex
2be2b60e-d93a-4e07-bcf9-0147ad328e7a
Loptson, Claire
a4859030-910a-453f-a30f-fe206d837ef3
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Markwick, Paul
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O'Brien, Charlotte L.
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Pancost, Richard D.
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Robinson, Stuart A.
5bc07ad4-35e6-4d20-b984-516bb747d940
Wrobel, Neil
fceb9d37-fee9-43e6-a50f-498a3164bbac
Lunt, Daniel J.
931ecfb5-1f50-412c-8f01-a46d69b1f82f
Farnsworth, Alex
2be2b60e-d93a-4e07-bcf9-0147ad328e7a
Loptson, Claire
a4859030-910a-453f-a30f-fe206d837ef3
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Markwick, Paul
fb6da003-9a49-4b6d-b6d7-29c15c3c9226
O'Brien, Charlotte L.
621c5c3a-b752-4e5d-80f0-3c79a651c6bf
Pancost, Richard D.
5914e19e-7777-4304-9fd8-86e2e9cfe8a1
Robinson, Stuart A.
5bc07ad4-35e6-4d20-b984-516bb747d940
Wrobel, Neil
fceb9d37-fee9-43e6-a50f-498a3164bbac

Lunt, Daniel J., Farnsworth, Alex, Loptson, Claire, Foster, Gavin L., Markwick, Paul, O'Brien, Charlotte L., Pancost, Richard D., Robinson, Stuart A. and Wrobel, Neil (2016) Palaeogeographic controls on climate and proxy interpretation. Climate of the Past, 12 (5), 1181-1198. (doi:10.5194/cp-12-1181-2016).

Record type: Article

Abstract

During the period from approximately 150 to 35?million years ago, the Cretaceous–Paleocene–Eocene (CPE), the Earth was in a “greenhouse” state with little or no ice at either pole. It was also a period of considerable global change, from the warmest periods of the mid-Cretaceous, to the threshold of icehouse conditions at the end of the Eocene. However, the relative contribution of palaeogeographic change, solar change, and carbon cycle change to these climatic variations is unknown. Here, making use of recent advances in computing power, and a set of unique palaeogeographic maps, we carry out an ensemble of 19 General Circulation Model simulations covering this period, one simulation per stratigraphic stage. By maintaining atmospheric CO2 concentration constant across the simulations, we are able to identify the contribution from palaeogeographic and solar forcing to global change across the CPE, and explore the underlying mechanisms. We find that global mean surface temperature is remarkably constant across the simulations, resulting from a cancellation of opposing trends from solar and palaeogeographic change. However, there are significant modelled variations on a regional scale. The stratigraphic stage–stage transitions which exhibit greatest climatic change are associated with transitions in the mode of ocean circulation, themselves often associated with changes in ocean gateways, and amplified by feedbacks related to emissivity and planetary albedo. We also find some control on global mean temperature from continental area and global mean orography. Our results have important implications for the interpretation of single-site palaeo proxy records. In particular, our results allow the non-CO2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change. This “adjustment factor” is used to adjust sea surface temperatures, as the deep ocean is not fully equilibrated in the model. The adjustment factor is illustrated for seven key sites in the CPE, and applied to proxy data from Falkland Plateau, and we provide data so that similar adjustments can be made to any site and for any time period within the CPE. Ultimately, this will enable isolation of the CO2-forced climate signal to be extracted from multiple proxy records from around the globe, allowing an evaluation of the regional signals and extent of polar amplification in response to CO2 changes during the CPE. Finally, regions where the adjustment factor is constant throughout the CPE could indicate places where future proxies could be targeted in order to reconstruct the purest CO2-induced temperature change, where the complicating contributions of other processes are minimised. Therefore, combined with other considerations, this work could provide useful information for supporting targets for drilling localities and outcrop studies.

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Accepted/In Press date: 26 April 2016
e-pub ahead of print date: 20 May 2016
Published date: 20 May 2016
Organisations: Geochemistry

Identifiers

Local EPrints ID: 399098
URI: https://eprints.soton.ac.uk/id/eprint/399098
ISSN: 1814-9332
PURE UUID: b4b1bfa0-4158-45cc-a738-87f44e92441d
ORCID for Gavin L. Foster: ORCID iD orcid.org/0000-0003-3688-9668

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Date deposited: 04 Aug 2016 11:02
Last modified: 10 Dec 2019 01:40

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Contributors

Author: Daniel J. Lunt
Author: Alex Farnsworth
Author: Claire Loptson
Author: Gavin L. Foster ORCID iD
Author: Paul Markwick
Author: Charlotte L. O'Brien
Author: Richard D. Pancost
Author: Stuart A. Robinson
Author: Neil Wrobel

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