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Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry

Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry
Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry
Antarctic continental-scale glaciation is generally assumed to have initiated at the Eocene-Oligocene Transition, yet its subsequent evolution is poorly constrained. We reconstruct changes in bottom water temperature and global ice volume from 0 to 17?Ma using ?18O in conjunction with Mg/Ca records of the infaunal benthic foraminifer, O. umbonatus from Ocean Drilling Program (ODP) Site 806 (equatorial Pacific; ~2500?m). Considering uncertainties in core top calibrations and sensitivity to seawater Mg/Ca (Mg/Ca)sw, we produce a range of Mg/Ca-temperature-Mg/Casw calibrations. Our favored exponential temperature calibration is Mg/Ca?=?0.66?±?0.08 × Mg/Casw0.27±0.06 × e(0.114±0.02 × BWT) and our favored linear temperature calibration is Mg/Ca?=?(1.21?±?0.04?+?0.12?±?0.004 × BWT (bottom water temperature)) × (Mg/Casw?0.003±0.02) (stated errors are 2?s.e.). The equations are obtained by comparing O. umbonatus Mg/Ca for a Paleocene-Eocene section from Ocean Drilling Program (ODP) Site 690 (Weddell Sea) to ?18O temperatures, calculated assuming ice-free conditions during this peak warmth period of the Cenozoic. This procedure suggests negligible effect of Mg/Casw on the Mg distribution coefficient (DMg). Application of the new equations to the Site 806 record leads to the suggestion that global ice volume was greater than today after the Middle Miocene Climate Transition (~14?Ma). ODP Site 806 bottom waters cooled and freshened as the Pacific zonal sea surface temperature gradient increased, and climate cooled through the Pliocene, prior to the Plio-Pleistocene glaciation of the Northern Hemisphere. The records indicate a decoupling of deep water temperatures and global ice volume, demonstrating the importance of thresholds in the evolution of the Antarctic ice sheet.
Mg/Ca, paleothermometry, Antarctica, Neogene, temperature, Miocene
0883-8305
1437-1454
Lear, Caroline H.
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Coxall, Helen K.
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Foster, Gavin L.
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Lunt, Daniel J.
931ecfb5-1f50-412c-8f01-a46d69b1f82f
Mawbey, Elaine M.
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Rosenthal, Yair
0130f66f-7653-490b-b323-76956e66c9e1
Sosdian, Sindia M.
718c374a-7460-4c7e-a616-f93b1f0a46a5
Thomas, Ellen
a0dee1cb-6caa-4535-a994-a9a2bbe2fef2
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Lear, Caroline H.
c0caf74d-ed6c-4b04-b5c8-de8fc794943c
Coxall, Helen K.
aeeac8f5-cc62-4861-8805-4a2027b33b6c
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Lunt, Daniel J.
931ecfb5-1f50-412c-8f01-a46d69b1f82f
Mawbey, Elaine M.
ba9b907c-d736-4fc1-a72f-013cc6857fa2
Rosenthal, Yair
0130f66f-7653-490b-b323-76956e66c9e1
Sosdian, Sindia M.
718c374a-7460-4c7e-a616-f93b1f0a46a5
Thomas, Ellen
a0dee1cb-6caa-4535-a994-a9a2bbe2fef2
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Lear, Caroline H., Coxall, Helen K., Foster, Gavin L., Lunt, Daniel J., Mawbey, Elaine M., Rosenthal, Yair, Sosdian, Sindia M., Thomas, Ellen and Wilson, Paul A. (2015) Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry. Paleoceanography, 30 (11), 1437-1454. (doi:10.1002/2015PA002833).

Record type: Article

Abstract

Antarctic continental-scale glaciation is generally assumed to have initiated at the Eocene-Oligocene Transition, yet its subsequent evolution is poorly constrained. We reconstruct changes in bottom water temperature and global ice volume from 0 to 17?Ma using ?18O in conjunction with Mg/Ca records of the infaunal benthic foraminifer, O. umbonatus from Ocean Drilling Program (ODP) Site 806 (equatorial Pacific; ~2500?m). Considering uncertainties in core top calibrations and sensitivity to seawater Mg/Ca (Mg/Ca)sw, we produce a range of Mg/Ca-temperature-Mg/Casw calibrations. Our favored exponential temperature calibration is Mg/Ca?=?0.66?±?0.08 × Mg/Casw0.27±0.06 × e(0.114±0.02 × BWT) and our favored linear temperature calibration is Mg/Ca?=?(1.21?±?0.04?+?0.12?±?0.004 × BWT (bottom water temperature)) × (Mg/Casw?0.003±0.02) (stated errors are 2?s.e.). The equations are obtained by comparing O. umbonatus Mg/Ca for a Paleocene-Eocene section from Ocean Drilling Program (ODP) Site 690 (Weddell Sea) to ?18O temperatures, calculated assuming ice-free conditions during this peak warmth period of the Cenozoic. This procedure suggests negligible effect of Mg/Casw on the Mg distribution coefficient (DMg). Application of the new equations to the Site 806 record leads to the suggestion that global ice volume was greater than today after the Middle Miocene Climate Transition (~14?Ma). ODP Site 806 bottom waters cooled and freshened as the Pacific zonal sea surface temperature gradient increased, and climate cooled through the Pliocene, prior to the Plio-Pleistocene glaciation of the Northern Hemisphere. The records indicate a decoupling of deep water temperatures and global ice volume, demonstrating the importance of thresholds in the evolution of the Antarctic ice sheet.

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Published date: November 2015
Keywords: Mg/Ca, paleothermometry, Antarctica, Neogene, temperature, Miocene
Organisations: Geochemistry, Paleooceanography & Palaeoclimate

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Local EPrints ID: 388271
URI: http://eprints.soton.ac.uk/id/eprint/388271
ISSN: 0883-8305
PURE UUID: 191cbf33-0480-468b-b8db-e80277d1d1ad
ORCID for Gavin L. Foster: ORCID iD orcid.org/0000-0003-3688-9668

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Date deposited: 22 Feb 2016 16:37
Last modified: 10 Dec 2019 01:40

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Contributors

Author: Caroline H. Lear
Author: Helen K. Coxall
Author: Gavin L. Foster ORCID iD
Author: Daniel J. Lunt
Author: Elaine M. Mawbey
Author: Yair Rosenthal
Author: Sindia M. Sosdian
Author: Ellen Thomas
Author: Paul A. Wilson

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