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Climate threshold at the Eocene-Oligocene transition: Antarctic ice sheet influence on ocean circulation

By
Kenneth G Miller
Kenneth G Miller
Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA
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James D Wright
James D Wright
Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA
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Miriam E Katz
Miriam E Katz
Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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Bridget S Wade
Bridget S Wade
Department of Geology & Geophysics, Texas A&M University, College Station, Texas 77840, USA
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James V Browning
James V Browning
Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA
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Benjamin S Cramer
Benjamin S Cramer
Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA
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Yair Rosenthal
Yair Rosenthal
Institute of Marine & Coastal Sciences and Department of Earth and Planetary Sciences, Rutgers University, New Brunswick, New Jersey 08901, USA
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Published:
April 01, 2009

We present an overview of the Eocene-Oligocene transition from a marine perspective and posit that growth of a continent-scale Antarctic ice sheet (25 × 106 km3) was a primary cause of a dramatic reorganization of ocean circulation and chemistry. The Eocene-Oligocene transition (EOT) was the culmination of long-term (107 yr drawdown and related cooling that triggered a 0.5‰–0.9‰ transient pre-scale) CO2 cursor benthic foraminiferal δ18O increase at 33.80 Ma (EOT-1), a 0.8‰ δ18O increase at 33.63 Ma (EOT-2), and a 1.0‰ δ18O increase at 33.55 Ma (oxygen isotope event Oi-1). We show that a small (~25 m) sea-level lowering was associated with the precursor EOT-1 increase, suggesting that the δ18O increase primarily reflected 1–2 °C of cooling. Global sea level dropped by 80 ± 25 m at Oi-1 time, implying that the deep-sea foraminiferal δ18O increase was due to the growth of a continent-sized Antarctic ice sheet and 1–4 °C of cooling. The Antarctic ice sheet reached the coastline for the first time at ca. 33.6 Ma and became a driver of Antarctic circulation, which in turn affected global climate, causing increased latitudinal thermal gradients and a “spinning up” of the oceans that resulted in: (1) increased thermohaline circulation and erosional pulses of Northern Component Water and Antarctic Bottom Water; (2) increased deep-basin ventilation, which caused a decrease in oceanic residence time, a decrease in deep-ocean acidity, and a deepening of the calcite compensation depth (CCD); and (3) increased diatom diversity due to intensified upwelling.

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Contents

GSA Special Papers

The Late Eocene Earth—Hothouse, Icehouse, and Impacts

Christian Koeberl
Christian Koeberl
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Alessandro Montanari
Alessandro Montanari
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Geological Society of America
Volume
452
ISBN print:
9780813724522
Publication date:
April 01, 2009

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