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Orbital forcing, ice volume, and CO 2 across the Oligocene-Miocene Transition

Orbital forcing, ice volume, and CO 2 across the Oligocene-Miocene Transition
Orbital forcing, ice volume, and CO 2 across the Oligocene-Miocene Transition

Paleoclimate records suggest that a rapid major transient Antarctic glaciation occurred across the Oligocene-Miocene transition (OMT; ca. 23 Ma; ~50-m sea level equivalent in 200–300 kyr). Orbital forcing has long been cited as an important factor determining the timing of the OMT glacial event. A similar orbital configuration occurred 1.2 Myr prior to the OMT, however, and was not associated with a major climate event, suggesting that additional mechanisms play an important role in ice sheet growth and decay. To improve our understanding of the OMT, we present a boron isotope-based CO 2 record between 22 and 24 Ma. This new record shows that δ 11 B/CO 2 was comparatively stable in the million years prior to the OMT glaciation and decreased by 0.7‰ (equivalent to a CO 2 increase of ~65 ppm) over ~300 kyr during the subsequent deglaciation. More data are needed, but we propose that the OMT glaciation was triggered by the same forces that initiated sustained Antarctic glaciation at the Eocene-Oligocene transition: long-term decline in CO 2 to a critical threshold and a superimposed orbital configuration favorable to glaciation (an eccentricity minimum and low-amplitude obliquity change). When comparing the reconstructed CO 2 increase with estimates of δ 18 O sw during the deglaciation phase of the OMT, we find that the sensitivity of the cryosphere to CO 2 forcing is consistent with recent ice sheet modeling studies that incorporate retreat into subglacial basins via ice cliff collapse with modest CO 2 increase, with clear implications for future sea level rise.

Antarctica, boron isotopes, CO, cryosphere, Miocene, OMT
2572-4517
Greenop, Rosanna
9a08d945-03bb-41b9-b8f2-f6e84731057e
Sosdian, Sindia M.
718c374a-7460-4c7e-a616-f93b1f0a46a5
Henehan, Michael J.
1dae087e-6389-4f29-b966-26929951881d
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Lear, Caroline H.
c0caf74d-ed6c-4b04-b5c8-de8fc794943c
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Greenop, Rosanna
9a08d945-03bb-41b9-b8f2-f6e84731057e
Sosdian, Sindia M.
718c374a-7460-4c7e-a616-f93b1f0a46a5
Henehan, Michael J.
1dae087e-6389-4f29-b966-26929951881d
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Lear, Caroline H.
c0caf74d-ed6c-4b04-b5c8-de8fc794943c
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022

Greenop, Rosanna, Sosdian, Sindia M., Henehan, Michael J., Wilson, Paul A., Lear, Caroline H. and Foster, Gavin L. (2019) Orbital forcing, ice volume, and CO 2 across the Oligocene-Miocene Transition. Paleoceanography and Paleoclimatology. (doi:10.1029/2018PA003420).

Record type: Article

Abstract

Paleoclimate records suggest that a rapid major transient Antarctic glaciation occurred across the Oligocene-Miocene transition (OMT; ca. 23 Ma; ~50-m sea level equivalent in 200–300 kyr). Orbital forcing has long been cited as an important factor determining the timing of the OMT glacial event. A similar orbital configuration occurred 1.2 Myr prior to the OMT, however, and was not associated with a major climate event, suggesting that additional mechanisms play an important role in ice sheet growth and decay. To improve our understanding of the OMT, we present a boron isotope-based CO 2 record between 22 and 24 Ma. This new record shows that δ 11 B/CO 2 was comparatively stable in the million years prior to the OMT glaciation and decreased by 0.7‰ (equivalent to a CO 2 increase of ~65 ppm) over ~300 kyr during the subsequent deglaciation. More data are needed, but we propose that the OMT glaciation was triggered by the same forces that initiated sustained Antarctic glaciation at the Eocene-Oligocene transition: long-term decline in CO 2 to a critical threshold and a superimposed orbital configuration favorable to glaciation (an eccentricity minimum and low-amplitude obliquity change). When comparing the reconstructed CO 2 increase with estimates of δ 18 O sw during the deglaciation phase of the OMT, we find that the sensitivity of the cryosphere to CO 2 forcing is consistent with recent ice sheet modeling studies that incorporate retreat into subglacial basins via ice cliff collapse with modest CO 2 increase, with clear implications for future sea level rise.

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Accepted/In Press date: 14 January 2019
e-pub ahead of print date: 18 January 2019
Additional Information: An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.Further reproduction or electronic distribution is not permitted.
Keywords: Antarctica, boron isotopes, CO, cryosphere, Miocene, OMT

Identifiers

Local EPrints ID: 429475
URI: http://eprints.soton.ac.uk/id/eprint/429475
ISSN: 2572-4517
PURE UUID: e15edbc7-ed08-4606-8bf6-505595cdedcd
ORCID for Gavin L. Foster: ORCID iD orcid.org/0000-0003-3688-9668

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Date deposited: 27 Mar 2019 17:30
Last modified: 18 Feb 2021 17:14

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Contributors

Author: Rosanna Greenop
Author: Sindia M. Sosdian
Author: Michael J. Henehan
Author: Paul A. Wilson
Author: Caroline H. Lear
Author: Gavin L. Foster ORCID iD

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