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Robust constraints on past CO2 climate forcing from the boron isotope proxy

Robust constraints on past CO2 climate forcing from the boron isotope proxy
Robust constraints on past CO2 climate forcing from the boron isotope proxy
The atmospheric concentration of the greenhouse gas carbon dioxide, CO2, is intimately coupled to the carbon chemistry of seawater, such that the radiative climate forcing from CO2 can be changed by an array of physical, geochemical and biological ocean processes. For instance, biological carbon sequestration, seawater cooling and net CaCO3 dissolution are commonly invoked as the primary drivers of CO2 change that amplify the orbitally-paced ice age cycles of the late Pleistocene. Based on first-principle arguments with regard to ocean chemistry we demonstrate that seawater pH change (ΔpH) is the dominant control that effectively sets CO2 radiative forcing (ΔF) on orbital timescales, as is evident from independent late Pleistocene reconstructions of pH and CO2. In short, all processes relevant for CO2 on orbital timescales, including temperature change, cause pH to change to bring about fractional CO2 change so as to yield a linear relationship of ΔpH to CO2 climate forcing. Further, we show that ΔpH and CO2 climate forcing can be reconstructed using the boron isotope pH-proxy more accurately than absolute pH or CO2, even if seawater boron isotope composition is poorly constrained and without information on a second carbonate system parameter. Thus, our formalism relaxes otherwise necessary assumptions to allow the accurate determination of orbital timescale CO2 radiative forcing from boron isotope-pH reconstructions alone, thereby eliminating a major limitation of current methods to estimate our planet’s climate sensitivity from the geologic record.
2572-4525
1099-1115
Hain, M.P.
72efed7b-e866-4af9-8be9-a11312d84dd0
Foster, G.L.
fbaa7255-7267-4443-a55e-e2a791213022
Chalk, T.
0021bbe6-6ab1-4a30-8542-654d0f2d1a0a
Hain, M.P.
72efed7b-e866-4af9-8be9-a11312d84dd0
Foster, G.L.
fbaa7255-7267-4443-a55e-e2a791213022
Chalk, T.
0021bbe6-6ab1-4a30-8542-654d0f2d1a0a

Hain, M.P., Foster, G.L. and Chalk, T. (2018) Robust constraints on past CO2 climate forcing from the boron isotope proxy. Paleoceanography and Paleoclimatology, 33 (10), 1099-1115. (doi:10.1029/2018PA003362).

Record type: Article

Abstract

The atmospheric concentration of the greenhouse gas carbon dioxide, CO2, is intimately coupled to the carbon chemistry of seawater, such that the radiative climate forcing from CO2 can be changed by an array of physical, geochemical and biological ocean processes. For instance, biological carbon sequestration, seawater cooling and net CaCO3 dissolution are commonly invoked as the primary drivers of CO2 change that amplify the orbitally-paced ice age cycles of the late Pleistocene. Based on first-principle arguments with regard to ocean chemistry we demonstrate that seawater pH change (ΔpH) is the dominant control that effectively sets CO2 radiative forcing (ΔF) on orbital timescales, as is evident from independent late Pleistocene reconstructions of pH and CO2. In short, all processes relevant for CO2 on orbital timescales, including temperature change, cause pH to change to bring about fractional CO2 change so as to yield a linear relationship of ΔpH to CO2 climate forcing. Further, we show that ΔpH and CO2 climate forcing can be reconstructed using the boron isotope pH-proxy more accurately than absolute pH or CO2, even if seawater boron isotope composition is poorly constrained and without information on a second carbonate system parameter. Thus, our formalism relaxes otherwise necessary assumptions to allow the accurate determination of orbital timescale CO2 radiative forcing from boron isotope-pH reconstructions alone, thereby eliminating a major limitation of current methods to estimate our planet’s climate sensitivity from the geologic record.

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Hain et al 2018 accepted version - Accepted Manuscript
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Accepted/In Press date: 12 September 2018
e-pub ahead of print date: 17 September 2018
Published date: October 2018

Identifiers

Local EPrints ID: 425023
URI: http://eprints.soton.ac.uk/id/eprint/425023
ISSN: 2572-4525
PURE UUID: 118dc221-d20a-4572-a38f-3dd2494c9b39
ORCID for G.L. Foster: ORCID iD orcid.org/0000-0003-3688-9668
ORCID for T. Chalk: ORCID iD orcid.org/0000-0002-2880-3847

Catalogue record

Date deposited: 09 Oct 2018 16:30
Last modified: 26 Nov 2021 06:48

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Contributors

Author: M.P. Hain
Author: G.L. Foster ORCID iD
Author: T. Chalk ORCID iD

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