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

Badger, Marcus; Chalk, Thomas B; Foster, Gavin L; Bown, Paul R; Gibbs, Samantha J; Sexton, Philip; Schmidt, Daniela N; Pälike, Heiko; Mackensen, A and Pancost, Richard D (2019). Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels. Climate of the Past, 15 pp. 539–554.

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DOI (Digital Object Identifier) Link: https://doi.org/10.5194/cp-15-539-2019
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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 kyrs, 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 (δ11B) of foraminifer shells. Here we present alkenone and δ11B-based pCO2 reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to pCO2 in the alkenone record compared to contemporaneous ice core and δ11B 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.

Item Type: Journal Item
Copyright Holders: 2018 The Authors
ISSN: 1814-9324
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 57510
Depositing User: Marcus Badger
Date Deposited: 08 Nov 2018 09:29
Last Modified: 17 Aug 2019 14:20
URI: http://oro.open.ac.uk/id/eprint/57510
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