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Environmental change in the subtropics during the late middle Eocene greenhouse and global implications

Okafor, CU; Thomas, DJ; Wade, BS; Firth, J; (2009) Environmental change in the subtropics during the late middle Eocene greenhouse and global implications. Geochemistry, Geophysics, Geosystems , 10 (7) , Article Q07003. 10.1029/2009GC002450. Green open access

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Abstract

[1] Oxygen isotope records from ODP Site 1052 (Blake Nose, subtropical North Atlantic Ocean) indicate significant short-term, high-amplitude variability (up to 1.4‰ in about 2500 to 4000 years) during the late middle Eocene (37.9–37.5 Ma). These variations reflect a combination of changes in sea surface temperature and the oxygen isotope composition of the regional seawater. In order to independently evaluate the magnitude of SST changes at Blake Nose and better understand the nature of environmental change during the late middle Eocene, we present planktonic foraminiferal Mg/Ca data combined with δ18O data from the same samples. The calculated Mg/Ca paleotemperatures indicate a decrease in SSTs over the study interval from ∼33 to 28°C at the same time that previously published foraminiferal δ18Ocalcite values from the same samples also decrease. Thus, the δ18Ocalcite values must reflect a significant component of seawater δ18O change in order to reconcile the opposite paleotemperature trends reflected by both proxies. Calculated δ18Oseawater values decreased from ∼3‰ at 37.83 Ma to ∼2‰ at 37.6 Ma. The combined trends of the SST and δ18Oseawater cannot be explained by an increase of continental ice over this time interval. Instead, the data favor an overall weakening of the hydrological cycle as global climate transitioned from the greenhouse to icehouse.

Type: Article
Title: Environmental change in the subtropics during the late middle Eocene greenhouse and global implications
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2009GC002450
Publisher version: http://doi.org/10.1029/2009GC002450
Language: English
Additional information: Copyright 2009 by the American Geophysical Union. This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Geochemistry & Geophysics, GEOCHEMISTRY & GEOPHYSICS, Ocean Drilling Program, middle Eocene, paleoceanograpy, PALAEOCENE/EOCENE THERMAL MAXIMUM, SEA-SURFACE TEMPERATURES, WESTERN NORTH-ATLANTIC, PLANKTONIC-FORAMINIFERA, BLAKE NOSE, OCEAN CIRCULATION, STABLE-ISOTOPES, ARCTIC-OCEAN, ICE VOLUME, CLIMATE
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1400885
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