Neogene ice volume and ocean temperatures; insights from infaunal foraminiferal Mg/Ca paleothermometry

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doi: 10.1002/2015PA002833
Author(s): 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.
Author Affiliation(s): Primary:
Cardiff University, School of Earth and Ocean Sciences, Cardiff, United Kingdom
Stockholm University, Sweden
University of Southampton, United Kingdom
Bristol University, United Kingdom
Rutgers University, United States
Yale University, United States
Volume Title: Paleoceanography
Source: Paleoceanography, 30(11), p.1437-1454. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0883-8305 CODEN: POCGEP
Note: In English. 108 refs.; illus., incl. 2 tables, sketch map
Summary: 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. Abstract Copyright (2015), . The Authors.
Year of Publication: 2015
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Calcium; Cenozoic; Equatorial Pacific; Foraminifera; Ice sheets; Indian Ocean; Invertebrata; Isotope ratios; Isotopes; Leg 113; Leg 122; Leg 130; Magnesium; Marine environment; Maud Rise; Metals; Mg/Ca; Microfossils; Neogene; North Pacific; Northwest Pacific; O-18/O-16; ODP Site 690; ODP Site 761; ODP Site 806; Ocean Drilling Program; Ontong Java Plateau; Oridorsalis umbonatus; Oxygen; Pacific Ocean; Paleoclimatology; Paleoenvironment; Paleotemperature; Pleistocene; Protista; Quaternary; Southern Ocean; Stable isotopes; Tertiary; Trace elements; Volume; Weddell Sea; West Pacific; Wombat Plateau
Coordinates: S164414 S164413 E1153206 E1153206
N001906 N001907 E1592142 E1592140
S650938 S650937 E0011218 E0011218
Record ID: 2017050185
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom