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Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage

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Abstract

Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets1,2,3,4,5,6,7, but their impact on the Greenland ice sheet in a warming climate remains uncertain8. Although some studies suggest that greater melting produces greater ice-sheet acceleration7,9, others have identified a long-term decrease in Greenland’s flow despite increased melting3. Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting. Although peak rates of ice speed-up are positively correlated with the degree of melting, mean summer flow rates are not, because glacier slowdown occurs, on average, when a critical run-off threshold of about 1.4 centimetres a day is exceeded. In contrast to the first half of summer, when flow is similar in all years, speed-up during the latter half is 62 ± 16 per cent less in warmer years. Consequently, in warmer years, the period of fast ice flow is three times shorter and, overall, summer ice flow is slower. This behaviour is at odds with that expected from basal lubrication alone7,9. Instead, it mirrors that of mountain glaciers10,11,12, where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient. A model of ice-sheet flow that captures switching between cavity and channel drainage modes13 is consistent with the run-off threshold, fast-flow periods, and later-summer speeds we have observed. Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet’s response to climate warming.

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Figure 1: Ice-velocity map of the study area.
Figure 2: Ice-velocity profiles along six glaciers in the study area.
Figure 3: Ice speed-up relative to winter during years of high and low surface melting.

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Acknowledgements

This work was supported by the UK NERC National Centre for Earth Observation, a Philip Leverhulme Prize to A.S. and by the EU FP7 Ice2Sea project (publ. no. 026). European Remote Sensing satellite synthetic aperture radar data were provided by the European Space Agency Vectra Consortium. We thank R. van de Wal for providing positive degree-day data.

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Authors and Affiliations

  1. School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK ,

    Aud Venke Sundal, Andrew Shepherd & Steven Palmer

  2. School of Geosciences, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP, UK ,

    Peter Nienow

  3. Department of Geography, University of Sheffield, Winter Street, Sheffield, S10 2TN, UK,

    Edward Hanna

  4. Earth System Sciences & Departement Geografie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium ,

    Philippe Huybrechts

Authors
  1. Aud Venke Sundal
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  2. Andrew Shepherd
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  3. Peter Nienow
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  4. Edward Hanna
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  5. Steven Palmer
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  6. Philippe Huybrechts
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Contributions

A.S. designed the research. A.V.S. produced the ice velocity data. E.H. and P.H. produced the run-off data. A.V.S. and A.S. analysed the data sets and produced the results. A.V.S. and A.S. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Andrew Shepherd.

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The authors declare no competing financial interests.

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Supplementary Information

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Sundal, A., Shepherd, A., Nienow, P. et al. Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage. Nature 469, 521–524 (2011). https://doi.org/10.1038/nature09740

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