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| Titel |
Birth and demise of lakes on the Greenland Ice Sheet |
| VerfasserIn |
A. Malin Johansson, Peter Jansson, Ian A. Brown |
| 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 |
250055009
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| Zusammenfassung |
| The stability of ice sheets are a major concern under the ongoing climate change. Drainage of
supra-glacial lakes has been shown to be an important mechanism for enhanced
basal sliding and also for increased speed of the ice sheet. We have investigated the
initiation, evolution, disappearance and location of these lakes on the Greenland
ice sheet to obtain better understanding for the spatio-temporal variations in lake
distribution.
For this task we have used Moderate Resolution Imaging Spectroradiometer (MODIS)
images from 2007 and 2008 situated over part of the western Greenland Ice Sheet. The
images were collected every 5 days during the entire ablation season. We have used manual
delineation of lake extent to generate a temporally dense set of lake observations. The lakes in
each image were linked together in such a way that the lake evolution could be followed.
Lakes where then divided into transient lakes (available only in one image) and sustained
lakes (available in multiple images).
Using air temperature data from Kangerlussuaq and by applying a lapse rate approach we
have been able to link initiation and termination of lakes in relation to the estimated time and
elevation dependent temperature field. Our results quantitatively show that lake formation is
closely coupled to a threshold in energy input for melting; lakes disappear due
to two processes, draining during the summer season and freeze-over at the end
of the ablation season. Some lakes also drain only to re-appear later during the
season. The positive degree days needed to initiate lakes are; 38.2Ë C days for
2007 and 42.4Ë C days for 2008 and the mean life time expectancy were for 2007
22 days and in 2008 19.1 days. Given the error margins associated with the PDD
method the two years exhibit a marked similarity in energy input required for lake
initiation.
Lakes initiate at lower elevations (1500 m a.s.l.). This is probably related
to the steeper slopes at lower elevations limiting lake basin extent and at higher
elevations the available amount of energy is likely to be the constraining factor for
the evolution of these lakes, due to the less numerous PDD at these elevations. |
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