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| Titel |
Melt-induced speed-up of Greenland ice-sheet offset by efficient subglacial drainage |
| VerfasserIn |
Aud Sundal, Andrew Shepherd, Peter Nienow, Edward Hanna, Steven Palmer, Philippe Huybrechts |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051658
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| Zusammenfassung |
| Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets1-4,
but their impact on the Greenland Ice Sheet in a warming climate remains uncertain. While
some studies suggest that greater melting produces greater ice sheet acceleration4-5, others
have identified a long-term decrease in Greenland’s flow despite increased melting2. 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 speedup are positively
correlated with the degree of melting, mean summer flow rates are not because
glacier slowdown occurs, on average, when a critical runoff threshold of about 1.4
cm/day is exceeded. In contrast to the first half of summer, when flow is similar in
all years, speedup 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 due to basal
lubrication alone. Instead, it mirrors that of mountain glaciers6-7, where melt-induced
acceleration of flow is reduced once subglacial drainage becomes efficient. A model of ice
sheet flow that captures switching between cavity and channel drainage modes8 is
consistent with the runoff 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 dynamic evolution of subglacial drainage; a simple model
of basal lubrication alone misses key aspects of the ice sheet response to climate
warming.
References
1. Joughin, I. et al. Seasonal speedup along the western flank of the Greenland Ice Sheet.
Science 320, 781-783 (2008).
2. van de Wal, R.S.W. et al. Large and rapid melt-induced velocity changes in the ablation
zone of the Greenland Ice Sheet. Science 321, 111-113 (2008).
3. Bartholomew, I. et al. Seasonal evolution of subglacial drainage and acceleration in a
Greenland outlet glacier. Nature Geoscience 3, 408-411 (2010).
4. Zwally, H.J. et al. Surface melt-induced acceleration of Greenland ice-sheet flow.
Science 297, 218-222 (2002).
5. Parizek, B.R. and Alley, R.B. Implications of increased Greenland surface melt under
global-warming scenarios: Ice-sheet simulations. Quaternary Science Reviews 23, 1013-1027
(2004).
6. Bingham, R.G., et al. Intra-annual and intra-seasonal flow dynamics of a
High Arctic polythermal valley glacier. Annals of Glaciology, Vol 37 37, 181-188
(2003).
7. Truffer, M., et al. Record negative glacier balances and low velocities during the 2004
heatwave in Alaska, USA: implications for the interpretation of observations by Zwally and
others in Greenland. J. Glaciol. 51, 663-664 (2005).
8. Schoof, C. Ice-sheet acceleration driven by melt supply variability. Nature 468, 803
-806 (2010). |
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