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

Badger, M; Chalk, T; Foster, G; Bown, P; Gibbs, S; Sexton, P; Schmidt, D; ... Pancost, R; + view all (2019) Insensitivity of alkenone carbon isotopes to atmospheric CO₂ at low to moderate CO₂ levels. Climate of the Past , 15 (2) pp. 539-554. 10.5194/cp-15-539-2019. Green open access

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Abstract

Atmospheric pCO₂ 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 pCO₂ for the past 800 kyr, but at no point during this interval were CO₂ levels higher than today. Interpretation of older pCO₂ has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO₂: 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 pCO₂ 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 pCO₂ 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 pCO₂ 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 pCO₂.

Type: Article
Title: Insensitivity of alkenone carbon isotopes to atmospheric CO₂ at low to moderate CO₂ levels
Open access status: An open access version is available from UCL Discovery
DOI: 10.5194/cp-15-539-2019
Publisher version: https://doi.org/10.5194/cp-15-539-2019
Language: English
Additional information: © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License (https://creativecommons.org/licenses/by/4.0/).
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10070660
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