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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-112
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-112
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 06 Sep 2019

Submitted as: research article | 06 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Changes in the high latitude Southern Hemisphere through the Eocene-Oligocene Transition: a model-data comparison

Alan T. Kennedy-Asser1,2, Daniel J. Lunt1,2, Paul J. Valdes1,2, Jean-Baptiste Ladant3, Joost Frieling4, and Vittoria Lauretano2,5 Alan T. Kennedy-Asser et al.
  • 1BRIDGE, School of Geographical Sciences, University of Bristol, Bristol, UK
  • 2Cabot Institute for the Environment, University of Bristol, Bristol, UK
  • 3Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, USA
  • 4Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Princetonlaan 8a, 3584CB Utrecht, the Netherlands
  • 5Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK

Abstract. Global and regional climate changed dramatically with the expansion of the Antarctic Ice sheet at the Eocene-Oligocene Transition (EOT). These large-scale changes are generally linked to declining atmospheric pCO2 levels and/or changes in Southern Ocean gateways such as the Drake Passage around this time. To better understand the Southern Hemisphere regional climatic changes and the impact of glaciation on the Earth’s oceans and atmosphere at the EOT, we compiled a database of sea and land surface temperature reconstructions from a range of proxy records and compared this with a series of fully-coupled climate model simulations. Regional patterns in the proxy records of temperature show that cooling across the EOT was less at high latitudes and greater at mid-latitudes. Climate model simulations have some issues in capturing the zonal mean latitudinal temperature profiles shown by the proxy data, but certain simulations do show moderate-good performance at recreating the temperature patterns shown in the data. When taking into account the absolute temperature before and after the EOT, as well as the change in temperature across it, simulations with a closed Drake Passage before and after the EOT or with an opening of the Drake Passage across the EOT perform poorly, whereas simulations with a drop in atmospheric pCO2 in combination with ice growth generally perform better. This provides further support to previous research that changes in atmospheric pCO2 are more likely to have been the driver of the EOT climatic changes, as opposed to opening of the Drake Passage.

Alan T. Kennedy-Asser et al.
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Compiled proxy dataset A. T. Kennedy-Asser https://doi.org/10.17605/OSF.IO/BKN26

Alan T. Kennedy-Asser et al.
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Short summary
Global cooling and a major expansion of ice over Antarctica occurred ~34 millions years ago at the Eocene-Oligocene Transition (EOT). A large secondary proxy dataset of high latitude southern hemisphere temperature before, after and across the EOT is compiled and compared to simulations from two coupled climate models. Although there are some inconsistencies between the models and data, the comparison shows amongst other things that changes in ocean gateways were unlikely the cause of the EOT.
Global cooling and a major expansion of ice over Antarctica occurred ~34 millions years ago at...
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