Eocene cooling linked to early flow across the Tasmanian Gateway

  • Peter K. Bijl
    Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD, Utrecht, The Netherlands;
  • James A. P. Bendle
    Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
  • Steven M. Bohaty
    Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, United Kingdom;
  • Jörg Pross
    Paleoenvironmental Dynamics Group, Institute of Geosciences, University of Frankfurt, 60438 Frankfurt, Germany;
  • Stefan Schouten
    NIOZ Royal Netherlands Institute for Sea Research, 1790 AB, Den Burg, Texel, The Netherlands;
  • Lisa Tauxe
    Geosciences Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0220;
  • Catherine E. Stickley
    Department of Geology, University of Troms, N-9037 Troms, Norway;
  • Robert M. McKay
    Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand;
  • Ursula Röhl
    MARUM–Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany;
  • Matthew Olney
    Department of Geology, University of South Florida, Tampa, FL 33620; and
  • Appy Sluijs
    Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD, Utrecht, The Netherlands;
  • Carlota Escutia
    Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Cientificas (Spain)–Universite de Granada, 18002 Granada, Spain
  • Henk Brinkhuis
    Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD, Utrecht, The Netherlands;
  • Adam Klaus
    United States Implementing Organization, Integrated Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station, TX 77845;
  • Annick Fehr
    RWTH Aachen University, Institute for Applied Geophysics and Geothermal Energy, Mathieustrasse 6, D-52074 Aachen, Germany;
  • Trevor Williams
    Borehole Research Group, Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964;
  • Stephanie A. Carr
    Department of Chemistry and Geochemistry, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401;
  • Robert B. Dunbar
    Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305-2115;
  • Jhon J. Gonzàlez
    Instituto Andaluz de Ciencias de la Tierra, CSIC-Universite de Granada, 18002 Granada, Spain;
  • Travis G. Hayden
    Department of Geology, Western Michigan University, Kalamazoo, MI 49008;
  • Masao Iwai
    Department of Natural Science, Kochi University, Kochi 780-8520, Japan;
  • Francisco J. Jimenez-Espejo
    Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho 2-15, Yokosuka 237-0061, Japan;
  • Kota Katsuki
    Marine Center for Advanced Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan;
  • Gee Soo Kong
    Petroleum and Marine Research Division, Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon 305-350, Republic of Korea;
  • Mutsumi Nakai
    Education Department, Daito Bunka University, 1-9-1 Takashima-daira, Itabashi-ku, Tokyo 175-8571, Japan;
  • Sandra Passchier
    Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043;
  • Stephen F. Pekar
    School of Earth and Environmental Sciences, Queens College, 65-30 Kissena Boulevard, Flushing, NY 11367;
  • Christina Riesselman
    Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305-2115;
  • Toyosaburo Sakai
    Department of Geology, Utsunomiya University, 350 Mine-Machi, Utsunomiya 321-8505, Japan;
  • Prakash K. Shrivastava
    Antarctica Division, Geological Survey of India, NH5P, NIT, Faridabad 121001, Harlyana, India;
  • Saiko Sugisaki
    Department of Polar Science, Graduate University of Advanced Study, 10-3 Midori-cho, Tachikawa City, Tokyo 190-8518, Japan;
  • Shouting Tuo
    School of Ocean and Earth Science, Tongji University, 1239 Spring Road, Shanghai 200092, People’s Republic of China;
  • Tina van de Flierdt
    Department of Earth Science and Engineering, Imperial College London, SW7 2AZ London, UK;
  • Kevin Welsh
    School of Earth Sciences, University of Queensland, St Lucia, Brisbane QLD 4072, Australia; and
  • Masako Yamane
    Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

抄録

<jats:p> The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO <jats:sub>2</jats:sub> ). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO <jats:sub>2</jats:sub> forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling. </jats:p>

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