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Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels

Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels
Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels

Atmospheric pCO 2 is a critical component of the global carbon system and is considered to be the major control of Earth's past, present, and future climate. Accurate and precise reconstructions of its concentration through geological time are therefore crucial to our understanding of the Earth system. Ice core records document pCO 2 for the past 800 kyr, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO 2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO 2 : the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ 11 B) of foraminifer shells. Here, we present alkenone and δ 11 B-based pCO 2 reconstructions generated from the same samples from the Pliocene and across a Pleistocene glacial- interglacial cycle at Ocean Drilling Program (ODP) Site 999. We find a muted response to pCO 2 in the alkenone record compared to contemporaneous ice core and δ 11 B records, suggesting caution in the interpretation of alkenone-based records at low pCO 2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO 2 .

1814-9324
539-554
Badger, Marcus P.S.
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Chalk, Thomas B.
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Foster, Gavin L.
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Bown, Paul R.
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Gibbs, Samantha J.
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Sexton, Philip F.
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Schmidt, Daniela N.
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Pälike, Heiko
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Mackensen, Andreas
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Pancost, Richard D.
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Badger, Marcus P.S.
f1bb5cb5-b886-4676-a2d2-f58a748301ff
Chalk, Thomas B.
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Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Bown, Paul R.
773e1a6d-1c12-4e57-af3b-ec981390a64a
Gibbs, Samantha J.
82dfbcbc-3a8a-40da-8a80-fe7ad83f3110
Sexton, Philip F.
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Schmidt, Daniela N.
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Pälike, Heiko
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Mackensen, Andreas
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Pancost, Richard D.
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Badger, Marcus P.S., Chalk, Thomas B., Foster, Gavin L., Bown, Paul R., Gibbs, Samantha J., Sexton, Philip F., Schmidt, Daniela N., Pälike, Heiko, Mackensen, Andreas and Pancost, Richard D. (2019) Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels. Climate of the Past, 15 (2), 539-554. (doi:10.5194/cp-15-539-2019).

Record type: Article

Abstract

Atmospheric pCO 2 is a critical component of the global carbon system and is considered to be the major control of Earth's past, present, and future climate. Accurate and precise reconstructions of its concentration through geological time are therefore crucial to our understanding of the Earth system. Ice core records document pCO 2 for the past 800 kyr, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO 2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO 2 : the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ 11 B) of foraminifer shells. Here, we present alkenone and δ 11 B-based pCO 2 reconstructions generated from the same samples from the Pliocene and across a Pleistocene glacial- interglacial cycle at Ocean Drilling Program (ODP) Site 999. We find a muted response to pCO 2 in the alkenone record compared to contemporaneous ice core and δ 11 B records, suggesting caution in the interpretation of alkenone-based records at low pCO 2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO 2 .

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Accepted/In Press date: 13 March 2019
Published date: 27 March 2019

Identifiers

Local EPrints ID: 430074
URI: https://eprints.soton.ac.uk/id/eprint/430074
ISSN: 1814-9324
PURE UUID: 0ef57695-b69d-4481-8d19-c0efea323feb
ORCID for Thomas B. Chalk: ORCID iD orcid.org/0000-0002-2880-3847
ORCID for Gavin L. Foster: ORCID iD orcid.org/0000-0003-3688-9668

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Date deposited: 11 Apr 2019 16:30
Last modified: 15 Aug 2019 00:39

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Contributors

Author: Marcus P.S. Badger
Author: Thomas B. Chalk ORCID iD
Author: Gavin L. Foster ORCID iD
Author: Paul R. Bown
Author: Philip F. Sexton
Author: Daniela N. Schmidt
Author: Heiko Pälike
Author: Andreas Mackensen
Author: Richard D. Pancost

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