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| Titel |
Testing hypotheses of the cause of peripheral thinning of the Greenland Ice Sheet: is land-terminating ice thinning at anomalously high rates? |
| VerfasserIn |
A. Sole, T. Payne, J. Bamber, P. Nienow, W. Krabill |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 2, no. 2 ; Nr. 2, no. 2 (2008-12-16), S.205-218 |
| Datensatznummer |
250000536
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| Publikation (Nr.) |
 copernicus.org/tc-2-205-2008.pdf |
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| Zusammenfassung |
Recent observations have shown that the periphery of the Greenland ice sheet
(GrIS) is thinning rapidly and that this thinning is greatest around
marine-terminating outlet glaciers. Several theories have been proposed
which provide a link between climate and ice thinning. We present surface
elevation change (dh/dt) data from NASA's Program for Arctic Regional
Climate Assessment (PARCA) laser altimetry surveys for fourteen and eleven
of the largest outlet glaciers in Southern Greenland from 1993 to 1998 and
1998 to 2006 respectively to test the applicability of these theories to the
GrIS.
Initially, outlet glacier dh/dt data are compared with data from concurrent
surveys over inland ice (slow flowing ice that is not obviously draining
into an outlet glacier) to confirm the effect of ice flow on surface
thinning rates. Land-terminating and marine-terminating outlet glacier
dh/dt
data are then compared from 1993 to 1998 and from 1998 to 2006. Finally,
ablation anomalies (the difference between the "normal" ablation rate from
1970 to 2000 and the ablation rate in the time period of interest)
calculated with a positive degree day model are compared to both
marine-terminating and land-terminating outlet glacier dh/dt data.
Our results support earlier conclusions that certain marine-terminating
outlet glaciers have thinned much more than land-terminating outlet glaciers
during both time periods. Furthermore we show that these differences are not
limited to the largest, fastest-flowing outlet glaciers – almost all
marine-terminating outlet glaciers are thinning more than land-terminating
outlet glaciers. There was a four fold increase in mean marine-terminating
outlet glacier thinning rates below 1000 m elevation between the periods
1993 to 1998 and 1998 to 2006, while thinning rates of land-terminating
outlet glaciers remained statistically unchanged. This suggests that a
change in a controlling mechanism specific to the thinning rates of
marine-terminating outlet glaciers occurred in the late 1990s and that this
change did not affect thinning rates of land-terminating outlet glaciers.
Thinning rates of land-terminating outlet glaciers are statistically the
same as ablation anomalies, while thinning rates of marine-terminating
outlet glaciers are not. Thinning of land-terminating outlet glaciers
therefore seems to be a response to changes in local mass balance
(principally increases in air temperature) while thinning of
marine-terminating outlet glaciers is principally controlled by ice
dynamics. The mechanism by which this dynamic thinning occurs is still not
clear although its association with marine-terminating outlet glaciers
suggests perturbations at marine termini (calving) as the likely cause. |
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