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CO2 drawdown following the middle Miocene expansion of the Antarctic Ice Sheet

Authors

  • Marcus P. S. Badger,

    Corresponding author
    1. School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, UK
    2. Organic Geochemistry Unit, The Cabot Institute and Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Bristol, UK
    • School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol, UK
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  • Caroline H. Lear,

    1. School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, UK
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  • Richard D. Pancost,

    1. Organic Geochemistry Unit, The Cabot Institute and Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Bristol, UK
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  • Gavin L. Foster,

    1. Bristol Isotope Group, School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol, UK
    2. Now at Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton Waterfront Campus, Southampton, UK
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  • Trevor R. Bailey,

    1. Geology Department, Amgueddfa Cymru-National Museum Wales, Cardiff, UK
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  • Melanie J. Leng,

    1. Department of Geology, University of Leicester, Leicester, UK and NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham, UK
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  • Hemmo A. Abels

    1. Stratigraphy / Paleontology, Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
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Corresponding author: Marcus P.S. Badger, School of Earth Sciences, Bristol University, Wills Memorial Building, Queens Rd, Bristol, BS8 1RJ, UK. (marcus.badger@bristol.ac.uk)

Abstract

[1] The development of a permanent, stable ice sheet in East Antarctica happened during the middle Miocene, about 14 million years (Myr) ago. The middle Miocene therefore represents one of the distinct phases of rapid change in the transition from the “greenhouse” of the early Eocene to the “icehouse” of the present day. Carbonate carbon isotope records of the period immediately following the main stage of ice sheet development reveal a major perturbation in the carbon system, represented by the positive δ13C excursion known as carbon maximum 6 (“CM6”), which has traditionally been interpreted as reflecting increased burial of organic matter and atmospheric pCO2 drawdown. More recently, it has been suggested that the δ13C excursion records a negative feedback resulting from the reduction of silicate weathering and an increase in atmospheric pCO2. Here we present high-resolution multi-proxy (alkenone carbon and foraminiferal boron isotope) records of atmospheric carbon dioxide and sea surface temperature across CM6. Similar to previously published records spanning this interval, our records document a world of generally low (~300 ppm) atmospheric pCO2 at a time generally accepted to be much warmer than today. Crucially, they also reveal a pCO2 decrease with associated cooling, which demonstrates that the carbon burial hypothesis for CM6 is feasible and could have acted as a positive feedback on global cooling.

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