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Causes of ice-age intensification across the Mid-Pleistocene Transition

Causes of ice-age intensification across the Mid-Pleistocene Transition
Causes of ice-age intensification across the Mid-Pleistocene Transition
During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.
Boron Isotopes, Middle Pleistocene, geochemistry, Carbon Dioxide, PALAEOCLIMATE
13114-13119
Chalk, Thomas
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Hain, Mathis
d31486bc-c473-4c34-a814-c0834640876c
Foster, Gavin
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Rohling, Eelco
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Sexton, Philip F.
e461e50e-fb4e-4d13-9013-5155be9f90ce
Badger, Marcus P.S.
f1bb5cb5-b886-4676-a2d2-f58a748301ff
Cherry, Soraya
36a106d0-868f-4865-90fb-5105292b87fd
Hasenfratz, Adam
27554712-1745-4997-b4f6-50f53ad3f557
Haug, G.H.
39dd0949-c65e-4f26-ad5f-41ddb5bafadb
Jaccard, S.L.
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Martínez-García, Alfredo
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Palike, Heiko
b9bf7798-ad8c-479b-8487-dd9a30a61fa5
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Chalk, Thomas
0021bbe6-6ab1-4a30-8542-654d0f2d1a0a
Hain, Mathis
d31486bc-c473-4c34-a814-c0834640876c
Foster, Gavin
fbaa7255-7267-4443-a55e-e2a791213022
Rohling, Eelco
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Sexton, Philip F.
e461e50e-fb4e-4d13-9013-5155be9f90ce
Badger, Marcus P.S.
f1bb5cb5-b886-4676-a2d2-f58a748301ff
Cherry, Soraya
36a106d0-868f-4865-90fb-5105292b87fd
Hasenfratz, Adam
27554712-1745-4997-b4f6-50f53ad3f557
Haug, G.H.
39dd0949-c65e-4f26-ad5f-41ddb5bafadb
Jaccard, S.L.
2ca25b07-e88d-442b-b655-c05fd1f1f79b
Martínez-García, Alfredo
29c2896b-3a8c-4457-b640-5c3ac1b9d272
Palike, Heiko
b9bf7798-ad8c-479b-8487-dd9a30a61fa5
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Chalk, Thomas, Hain, Mathis, Foster, Gavin, Rohling, Eelco, Sexton, Philip F., Badger, Marcus P.S., Cherry, Soraya, Hasenfratz, Adam, Haug, G.H., Jaccard, S.L., Martínez-García, Alfredo, Palike, Heiko and Wilson, Paul A. (2017) Causes of ice-age intensification across the Mid-Pleistocene Transition. Proceedings of the National Academy of Sciences, 114 (50), 13114-13119. (doi:10.1073/pnas.1702143114).

Record type: Article

Abstract

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

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Accepted/In Press date: 26 October 2017
e-pub ahead of print date: 27 November 2017
Published date: 12 December 2017
Keywords: Boron Isotopes, Middle Pleistocene, geochemistry, Carbon Dioxide, PALAEOCLIMATE

Identifiers

Local EPrints ID: 415926
URI: https://eprints.soton.ac.uk/id/eprint/415926
PURE UUID: 99271ba6-5e06-4a91-b271-51b2f76a85c7
ORCID for Thomas Chalk: ORCID iD orcid.org/0000-0002-2880-3847
ORCID for Eelco Rohling: ORCID iD orcid.org/0000-0001-5349-2158

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Date deposited: 28 Nov 2017 17:31
Last modified: 14 Mar 2019 05:25

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Contributors

Author: Thomas Chalk ORCID iD
Author: Mathis Hain
Author: Gavin Foster
Author: Eelco Rohling ORCID iD
Author: Philip F. Sexton
Author: Marcus P.S. Badger
Author: Soraya Cherry
Author: Adam Hasenfratz
Author: G.H. Haug
Author: S.L. Jaccard
Author: Alfredo Martínez-García
Author: Heiko Palike
Author: Paul A. Wilson

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