Letter

Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier

Received:
Accepted:
Published online:

Abstract

The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels1. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate2, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway3. Understanding this recent retreat requires a detailed knowledge of grounding-line history4, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

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Acknowledgements

We thank D. Pomraning for help with designing and manning the hot-water drill equipment. Logistic and safety support was provided by K. Gibbon, D. Einerson, E. Steinarsson, F. McCarthy, S. Consalvi, S. King, the PIG support camp personnel, and the National Science Foundation (NSF) Antarctic support team. We particularly thank E. Steinarsson for his help with sediment coring. This research project was supported by NSF’s Office of Polar Programs under NSF grants including ANT-0732926 and ANT 0732730; by funding from NASA’s Cryospheric Sciences Program; by New York University Abhu Dabi grant 1204; and by the Natural Environment Research Council–British Antarctic Survey Polar Science for Planet Earth Programme. Work at the Lawrence Livermore National Laboratory (LLNL) was performed under contract DE-AC52-07NA27344; LLNL-JRNL-697878.

Author information

Affiliations

  1. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK

    • J. A. Smith
    • , M. Shortt
    • , A. Jenkins
    • , C.-D. Hillenbrand
    • , H. F. J. Corr
    • , N. Farley
    •  & D. G. Vaughan
  2. Center for Permafrost (CENPERM), Department of Geosciences and Natural Resource Management, University of Copenhagen, 1350 Copenhagen K, Denmark

    • T. J. Andersen
  3. Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA

    • A. M. Gaffney
  4. Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775-7320, USA

    • M. Truffer
  5. Department of Oceanography, Naval Postgraduate School, Monterey, California 93943, USA

    • T. P. Stanton
  6. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • R. Bindschadler
  7. Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA

    • P. Dutrieux
  8. Institute for Geophysics and Geology, University of Leipzig, Talstrasse 35, D-04103 Leipzig, Germany

    • W. Ehrmann
  9. Department of Earth Sciences, University of Geneva, 13 Rue des Maraîchers, CH-1205 Geneva, Switzerland

    • N. Farley
    •  & S. Crowhurst
  10. Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK

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Contributions

J.A.S., R.B., D.G.V. and H.F.J.C. conceived the study, and M.S., M.T. and T.P.S. conducted the fieldwork. J.A.S. and N.F. were responsible for sediment-core analysis and J.A.S. led the writing of the paper. T.J.A. measured 210Pb and 137Cs levels and developed the age models. A.M.G. measured plutonium isotopes on the PIG B core. P.D. and A.J. provided the bathymetric compilation, multibeam imagery and knowledge of the seafloor beneath Pine Island Glacier, and C-.D.H. contributed expertise on glacial sedimentology and data interpretation. W.E. is responsible for analysis of clay minerals, organic carbon and total nitrogen, and S.C. performed the X-ray fluorescence (XRF) scanning. All authors contributed to data interpretation and writing of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to J. A. Smith.

Reviewer Information Nature thanks M. Baskaran, M. Jakobsson and J. Wellner for their contribution to the peer review of this work.

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