Letter

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks

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Abstract

Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost1,2. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes3,4. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates5. It is thought1,2 that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study1, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth6 and drift direction7. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today8,9, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks11,12. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI13. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet.

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Acknowledgements

M.G.W. is funded by a UK Natural Environment Research Council (NERC) PhD studentship (LCAG/247 RG72013) held at the Scott Polar Research Institute, University of Cambridge. The OSO0910 expedition with Swedish icebreaker Oden was carried out as collaboration between the Swedish Polar Research Secretariat, the Swedish Research Council, and the US National Science Foundation (NSF). Part of the data shown in Extended Data Fig. 2 was collected on UK NERC-funded cruise JR179.

Author information

Affiliations

  1. Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge CB2 1ER, UK

    • Matthew G. Wise
    •  & Julian A. Dowdeswell
  2. Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden

    • Martin Jakobsson
  3. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK

    • Robert D. Larter

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Contributions

J.A.D. and R.D.L. conceived the idea for the study. M.G.W. made the measurements on the multibeam bathymetry data and analysed the results. M.J. was responsible for collection and processing of the IB/RB Oden multibeam bathymetry data. M.G.W. wrote the initial manuscript and all co-authors commented on and provided input to drafts and the final version.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Matthew G. Wise or Julian A. Dowdeswell.

Reviewer Information Nature thanks T. Scambos and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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