Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 13, 959-975, 2017
https://doi.org/10.5194/cp-13-959-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
27 Jul 2017
Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma
Nicholas R. Golledge1,2, Zoë A. Thomas3, Richard H. Levy2, Edward G. W. Gasson4, Timothy R. Naish1, Robert M. McKay1, Douglas E. Kowalewski5, and Christopher J. Fogwill3 1Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand
2GNS Science, Avalon, Lower Hutt 5011, New Zealand
3Climate Change Research Centre and PANGEA Research Centre, University of New South Wales, Sydney, NSW 2052, Australia
4Department of Geography, The University of Sheffield, Sheffield, S10 2TN, UK
5Department of Earth, Environment, and Physics, Worcester State University, Worcester, MA 01602, USA
Abstract. The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offline-coupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

Citation: Golledge, N. R., Thomas, Z. A., Levy, R. H., Gasson, E. G. W., Naish, T. R., McKay, R. M., Kowalewski, D. E., and Fogwill, C. J.: Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma, Clim. Past, 13, 959-975, https://doi.org/10.5194/cp-13-959-2017, 2017.
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We investigated how the Antarctic climate and ice sheets evolved during a period of warmer-than-present temperatures 4 million years ago, during a time when the carbon dioxide concentration in the atmosphere was very similar to today's level. Using computer models to first simulate the climate, and then how the ice sheets responded, we found that Antarctica most likely lost around 8.5  m sea-level equivalent ice volume as both East and West Antarctic ice sheets retreated.
We investigated how the Antarctic climate and ice sheets evolved during a period of...
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