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Climate of the Past An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/cp-2020-96
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-96
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  20 Jul 2020

20 Jul 2020

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This preprint is currently under review for the journal CP.

Eccentricity-paced atmospheric carbon-dioxide variations across the middle Miocene climate transition

Markus Raitzsch1,2, Jelle Bijma2, Torsten Bickert1, Michael Schulz1, Ann Holbourn3, and Michal Kučera1 Markus Raitzsch et al.
  • 1MARUM – Zentrum für Marine Umweltwissenschaften, Universität Bremen, Leobener Straße, 28359 Bremen, Germany
  • 2Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar-und Meeresforschung, Am Handelshafen 12, 27570, Bremerhaven, Germany
  • 3Christian-Albrechts-Universität, Institut für Geowissenschaften, 24118 Kiel, Germany

Abstract. The middle Miocene climate transition ~ 14 Ma marks a fundamental step towards the current “icehouse” climate, with a ~ 1 ‰ δ18O increase and a ~ 1 ‰ transient δ13C rise in the deep ocean, indicating rapid expansion of the East Antarctic Ice Sheet associated with a change in the operation of the global carbon cycle. The variation of atmospheric CO2 across the carbon-cycle perturbation has been intensely debated as proxy records of pCO2 for this time interval are sparse and partly contradictory. Using boron isotopes (δ11B) in planktonic foraminifers from drill site ODP 1092 in the South Atlantic, we show that long-term pCO2 variations between ~ 14.3 and 13.2 Ma were paced by 400 k.y. eccentricity cycles, with decreasing pCO2 at high eccentricity and vice versa. Our data support results from a carbon-cycle model study, according to which increased monsoon intensity at high eccentricity enhanced weathering and river fluxes in the tropics, resulting in increasing carbonate and organic carbon burial and hence decreasing atmospheric CO2. In this scenario, a combination of the eccentricity-driven climatic cycle and enhanced meridional deep-ocean circulation during Antarctic ice-sheet expansion may have both contributed to the pCO2 rise following Antarctic glaciation, acting as a negative feedback on the progressing glaciation and helping to stabilize the climate system on its way to the late Cenozoic “icehouse” world.

Markus Raitzsch et al.

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Markus Raitzsch et al.

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Short summary
Approximately 14 Ma ago, the East Antarctic Ice Sheet expanded to almost its current extent, but the role of CO2 in this major climate transition is not entirely known. We show that atmospheric CO2 might have varied on 400 k.y. cycles linked to the eccentricity of the earth's orbit. The resulting change in weathering and ocean carbon cycle affected atmospheric CO2 in a way that CO2 rose after Antarctica glaciated, helping to stabilize the climate system on its way to the “icehouse” world.
Approximately 14 Ma ago, the East Antarctic Ice Sheet expanded to almost its current extent, but...
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