Letter

Nature 458, 322-328 (19 March 2009) | doi:10.1038/nature07867; Received 25 July 2008; Accepted 11 February 2009

Obliquity-paced Pliocene West Antarctic ice sheet oscillations

T. Naish1,2, R. Powell3, R. Levy4,30, G. Wilson5, R. Scherer3, F. Talarico6, L. Krissek7, F. Niessen8, M. Pompilio9, T. Wilson7, L. Carter1, R. DeConto10, P. Huybers11, R. McKay1, D. Pollard12, J. Ross13, D. Winter4, P. Barrett1, G. Browne2, R. Cody1,2, E. Cowan14, J. Crampton2, G. Dunbar1, N. Dunbar13, F. Florindo15, C. Gebhardt8, I. Graham2, M. Hannah1, D. Hansaraj1,2, D. Harwood4, D. Helling8, S. Henrys2, L. Hinnov16, G. Kuhn8, P. Kyle13, A. Läufer17, P. Maffioli18, D. Magens8, K. Mandernack19, W. McIntosh13, C. Millan7, R. Morin20, C. Ohneiser5, T. Paulsen21, D. Persico22, I. Raine2, J. Reed23,4, C. Riesselman24, L. Sagnotti15, D. Schmitt25, C. Sjunneskog26, P. Strong2, M. Taviani27, S. Vogel3, T. Wilch28 & T. Williams29

  1. Antarctic Research Centre, Victoria University of Wellington, Kelburn Parade, PO Box 600, Wellington 6012, New Zealand
  2. GNS Science, 1 Fairway Drive, PO Box 30-368, Lower Hutt 5040, New Zealand
  3. Department of Geology & Environmental Geosciences, Northern Illinois University, DeKalb, Illinois 60115, USA
  4. ANDRILL Science Management Office, Department of Geosciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0340, USA
  5. University of Otago, Department of Geology, PO Box 56, Leith Street, Dunedin, Otago 9001, New Zealand
  6. Università di Siena, Dipartimento di Scienze delle Terra, Via Laterina 8, I-53100 Siena, Italy
  7. Ohio State University, Department of Geological Sciences, 275 Mendenhall Lab, 125 South Oval Mall, Columbus, Ohio 43210, USA
  8. Alfred Wegener Institute, Department of Geosciences, Postfach 12 01 6, Am Alten Hafen 26, D-27515 Bremerhaven, Germany
  9. Istituto Nazionale di Geofisica e Vulcanologia, Via della Faggiola 32, I-56126 Pisa, Italy
  10. Department of Geosciences, 233 Morrell Science Centre, University of Massachusetts, Amherst, Massachusetts 01003-9297, USA
  11. Department of Earth and Planetary Sciences, Harvard University, Massachusetts 02138, USA
  12. Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
  13. New Mexico Institute of Mining & Technology, Earth & Environmental Sciences, Socorro, New Mexico 87801, USA
  14. Department of Geology, Appalachian State University, ASU Box 32067, Boone, North Carolina 28608-2067, USA
  15. Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, I-00143 Rome, Italy
  16. Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA
  17. Federal Institute of Geosciences & Natural Resources, BGR, Stilleweg 2, D-30655 Hannover, Germany
  18. Università Milano-Bicocca, Dipartimento di Scienze Geologiche e Geotecnologie, Piazza della Scienza 4, I-20126 Milano, Italy
  19. Colorado School of Mines, Department of Chemistry & Geochemistry, 1500 Illinois Street, Golden, Colorado 80401, USA
  20. US Geological Survey, Mail Stop 403, Denver Federal Center, Denver, Colorado 80225, USA
  21. University of Wisconsin-Oshkosh, Department of Geology, 800 Algoma Boulevard, Oshkosh, Wisconsin 54901, USA
  22. Dipartimento di Scienze della Terra, Università degli Studi di Parma, Via Usberti 157/A, I-43100 Parma, Italy
  23. CHRONOS, Iowa State University, Department of Geological & Atmospheric Sciences, 275 Science I, Ames, Iowa 50011-3212, USA
  24. Department of Geological and Environmental Sciences, School of Earth Sciences, Stanford University, Stanford, California 94305, USA
  25. Department of Physics, Mailstop #615, University of Alberta, Edmonton, Alberta T6G 2G7, Canada
  26. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA
  27. CNR, ISMAR – Bologna, Via Gobetti 101, I-40129 Bologna, Italy
  28. Albion College, Department of Geology, Albion, Michigan 49224, USA
  29. Columbia University, Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA
  30. Present address: GNS Science, 1 Fairway Drive, PO Box 30368, Lower Hutt 5040, New Zealand.

Correspondence to: T. Naish1,2 Correspondence and requests for materials should be addressed to T.N. (Email: tim.naish@vuw.ac.nz).

Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (approx5–3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming3. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, approx40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to approx3 °C warmer than today4 and atmospheric CO2 concentration was as high as approx400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt8 under conditions of elevated CO2.

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