Clim. Past Discuss., 9, 1297-1319, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Mid-pliocene Atlantic meridional overturning circulation not unlike modern?
Z.-S. Zhang1,2,3, K. H. Nisancioglu1,2,4, M. A. Chandler5, A. M. Haywood6, B. L. Otto-Bliesner7, G. Ramstein8, C. Stepanek9, A. Abe-Ouchi10,11, W.-L. Chan10, F. J. Bragg12, C. Contoux9,13, A. M. Dolan6, D. J. Hill6,14, A. Jost13, Y. Kamae15, G. Lohmann8,16, D. J. Lunt11, N. A. Rosenbloom7, L. E. Sohl5, and H. Ueda15
1UNI Research, Allegaten 55, 5007, Bergen, Norway
2Bjerknes Centre for Climate Research, Allegaten 55, 5007, Bergen, Norway
3Nansen-Zhu International Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, 100029, Beijing, China
4Department of Earth Science, University of Bergen, Allegaten 41, 5007, Bergen, Norway
5CCSR/GISS, Columbia University, New York, USA
6School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, S29JT, UK
7National Center for Atmospheric Research, Boulder, Colorado, USA
9Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
10Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan
11Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
12BRIDGE, School of Geographical Sciences, University of Bristol, University Road, Bristol, BS8 1SS, UK
13Sisyphe, CNRS/UPMC Univ Paris 06, Paris, France
14British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
15Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
16Institute for Environmental Physics, University of Bremen, Bremen, Germany

Abstract. In the Pliocene Model Intercomparison Project (PlioMIP), eight state-of-the-art coupled climate models have simulated the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Ma). Here, we compare the Atlantic Meridional Overturning Circulation (AMOC), northward ocean heat transport and ocean stratification simulated with these models. None of the models participating in the PlioMIP simulates a strong mid-Pliocene AMOC as suggested by earlier proxy studies. Rather, there is no consistent increase in AMOC maximum among the PlioMIP models. The only consistent change in AMOC is a shoaling of the overturning cell in the Atlantic, and a reduced influence of North Atlantic Deep Water (NADW) at depth in the basin. Furthermore, the simulated mid-Pliocene Atlantic northward heat transport is similar to the pre-industrial. These simulations demonstrate that the reconstructed high latitude mid-Pliocene warming can not be explained as a direct response to an intensification of AMOC and concomitant increase in northward ocean heat transport by the Atlantic.

Citation: Zhang, Z.-S., Nisancioglu, K. H., Chandler, M. A., Haywood, A. M., Otto-Bliesner, B. L., Ramstein, G., Stepanek, C., Abe-Ouchi, A., Chan, W.-L., Bragg, F. J., Contoux, C., Dolan, A. M., Hill, D. J., Jost, A., Kamae, Y., Lohmann, G., Lunt, D. J., Rosenbloom, N. A., Sohl, L. E., and Ueda, H.: Mid-pliocene Atlantic meridional overturning circulation not unlike modern?, Clim. Past Discuss., 9, 1297-1319, doi:10.5194/cpd-9-1297-2013, 2013.
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