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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-2019-163
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-163
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 Jan 2020

Submitted as: research article | 16 Jan 2020

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This preprint is currently under review for the journal CP.

Early Eocene vigorous ocean overturning and its contribution to a warm Southern Ocean

Yurui Zhang1, Thierry Huck1, Camille Lique1, Yannick Donnadieu2,3, Jean-Baptiste Ladant4, Marina Rabineau5, and Daniel Aslanian6 Yurui Zhang et al.
  • 1Univ Brest, CNRS, IRD, Ifremer, Laboratoired’Océanographie Physique et Spatiale (LOPS), IUEM, Brest, France
  • 2Laboratoire des Sciences du Climat et de l’Environnement, LSCE-IPSL, CEA/CNRS/UVSQ, Université Paris-Saclay, Gif-sur-Yvette, France
  • 3Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France
  • 4Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA
  • 5CNRS, Laboratoire Géosciences Océan (LGO, UMR 6538 CNRS, Univ Brest, Univ Bretagne-Sud), IUEM, Plouzané, France
  • 6IFREMER, Unité deRecherche Géosciences Marines, Centre de Bretagne, Plouzané, France

Abstract. The early Eocene (~ 55 Ma) is the warmest period, and most likely characterized by the highest atmospheric CO2 concentrations, of the Cenozoic era. Here, we analyze simulations of the early Eocene performed with the IPSL-CM5A2 coupled climate model set up with paleogeographic reconstructions of this period from the DeepMIP project, with different levels of atmospheric CO2, and compare them with simulations of the modern conditions. This allows us to explore the changes of the ocean circulation and the resulting ocean meridional heat transport. At a CO2 level of 840 ppm, the Early Eocene simulation is characterized by a strong abyssal overturning circulation in the Southern Hemisphere (40 Sv at 60º S), fed by deep water formation in the three sectors of the Southern Ocean. Deep convection in the Southern Ocean is favored by the closed Drake and Tasmanian passages, which provide western boundaries for the build-up of strong subpolar gyres in the Weddell and Ross seas, in the middle of which convection develops. The strong overturning circulation, associated with the subpolar gyres, sustains the poleward advection of saline subtropical water to the convective region in the Southern Ocean, maintaining deep-water formation. This salt-advection feedback mechanism works similarly in the present-day North Atlantic overturning circulation. The strong abyssal overturning circulation in the 55 Ma simulations primarily results in an enhanced poleward ocean heat transport by 0.3–0.7 PW in the Southern Hemisphere compared to modern conditions, reaching 1.7 PW southward at 20° S, and contributing to maintain the Southern Ocean and Antarctica warm in the Eocene. Simulations with different atmospheric CO2 levels show that the ocean circulation and heat transport are relatively insensitive to CO2-doubling.

Yurui Zhang et al.

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Latest update: 26 Feb 2020
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Short summary
The early Eocene (~ 55 Ma ago) was an extreme warm period and accompanied by high atmospheric CO2 level. We explore the relationships between the ocean dynamics and this warm climate, with the aid of the IPSL climate model. Our results show that the Eocene was characterized by a strong overturning circulation, associated with deep water formation in the Southern Ocean, which is analogous to the present-day North Atlantic. Consequently, poleward ocean heat transport was strongly enhanced.
The early Eocene (~ 55 Ma ago) was an extreme warm period and accompanied by high atmospheric...
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