Neogene ice volume and ocean temperatures

Insights from infaunal foraminiferal Mg/Ca paleothermometry

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

Research output: Contribution to journalArticle

30 Citations (Scopus)

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 δ18O 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 δ18O 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. Key Points Foraminifer O. umbonatus Mg/Ca has low sensitivity to changing seawater Mg/Ca Greater than modern ice volume followed Middle Miocene Climate Transition Plio-Pleistocene glaciation preceded by a change in Pacific Ocean overturning.

Original languageEnglish (US)
Pages (from-to)1437-1454
Number of pages18
JournalPaleoceanography
Volume30
Issue number11
DOIs
StatePublished - Nov 1 2015

Fingerprint

Neogene
bottom water
ice
water temperature
Ocean Drilling Program
calibration
glaciation
Eocene
climate
temperature
Miocene
Pleistocene
seawater
benthic foraminifera
Paleocene
temperature gradient
foraminifera
ice sheet
Oligocene
Northern Hemisphere

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Palaeontology

Keywords

  • Antarctica
  • Mg/Ca
  • Miocene
  • Neogene
  • paleothermometry
  • temperature

Cite this

Lear, C. H., Coxall, H. K., Foster, G. L., Lunt, D. J., Mawbey, E. M., Rosenthal, Y., ... Wilson, P. A. (2015). Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry. Paleoceanography, 30(11), 1437-1454. https://doi.org/10.1002/2015PA002833
Lear, Caroline H. ; Coxall, Helen K. ; Foster, Gavin L. ; Lunt, Daniel J. ; Mawbey, Elaine M. ; Rosenthal, Yair ; Sosdian, Sindia M. ; Thomas, Ellen ; Wilson, Paul A. / Neogene ice volume and ocean temperatures : Insights from infaunal foraminiferal Mg/Ca paleothermometry. In: Paleoceanography. 2015 ; Vol. 30, No. 11. pp. 1437-1454.
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Lear, CH, Coxall, HK, Foster, GL, Lunt, DJ, Mawbey, EM, Rosenthal, Y, Sosdian, SM, Thomas, E & Wilson, PA 2015, 'Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry', Paleoceanography, vol. 30, no. 11, pp. 1437-1454. https://doi.org/10.1002/2015PA002833

Neogene ice volume and ocean temperatures : Insights from infaunal foraminiferal Mg/Ca paleothermometry. / Lear, Caroline H.; Coxall, Helen K.; Foster, Gavin L.; Lunt, Daniel J.; Mawbey, Elaine M.; Rosenthal, Yair; Sosdian, Sindia M.; Thomas, Ellen; Wilson, Paul A.

In: Paleoceanography, Vol. 30, No. 11, 01.11.2015, p. 1437-1454.

Research output: Contribution to journalArticle

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T2 - Insights from infaunal foraminiferal Mg/Ca paleothermometry

AU - Lear, Caroline H.

AU - Coxall, Helen K.

AU - Foster, Gavin L.

AU - Lunt, Daniel J.

AU - Mawbey, Elaine M.

AU - Rosenthal, Yair

AU - Sosdian, Sindia M.

AU - Thomas, Ellen

AU - Wilson, Paul A.

PY - 2015/11/1

Y1 - 2015/11/1

N2 - 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 δ18O 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 δ18O 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. Key Points Foraminifer O. umbonatus Mg/Ca has low sensitivity to changing seawater Mg/Ca Greater than modern ice volume followed Middle Miocene Climate Transition Plio-Pleistocene glaciation preceded by a change in Pacific Ocean overturning.

AB - 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 δ18O 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 δ18O 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. Key Points Foraminifer O. umbonatus Mg/Ca has low sensitivity to changing seawater Mg/Ca Greater than modern ice volume followed Middle Miocene Climate Transition Plio-Pleistocene glaciation preceded by a change in Pacific Ocean overturning.

KW - Antarctica

KW - Mg/Ca

KW - Miocene

KW - Neogene

KW - paleothermometry

KW - temperature

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