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| Titel |
Detection of Supra-Glacial Lakes on the Greenland Ice Sheet Using MODIS Images |
| VerfasserIn |
Gauthier Verin, Ghislain Picard, Quentin Libois, Fabien Gillet-Chaulet, Antoine Roux |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106616
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| Publikation (Nr.) |
 EGU/EGU2015-6293.pdf |
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| Zusammenfassung |
| During melt season, supra-glacial lakes form on the margins of the Greenland ice sheet.
Because of their size exceeding several kilometers, and their concentration, they affect
surface albedo leading to an amplification of the regional melt. Furthermore, they foster
hydro-fracturing that propagate liquid water to the bedrock and therefore enhance the basal
lubrication which may affect the ice motion. It is known that Greenland ice sheet has strongly
responded to recent global warming. As air temperature increases, melt duration
and melt intensity increase and surface melt area extends further inland. These
recent changes may play an important role in the mass balance of the Greenland ice
sheet. In this context, it is essential to better monitor and understand supra-glacial
spatio-temporal dynamics in order to better assess future sea level rise. In this study MODIS
(Moderate Resolution Imaging Spectroradiometer) images have been used to detect
supra-glacial lakes. The observation site is located on the West margin of the ice sheet,
between 65°N and 70°N where the concentration of lake is maximum. The detection
is performed by a fully automatic algorithm using images processing techniques
introduced by Liang et al. (2012) which can be summarized in three steps: the selection
of usable MODIS images, mainly we exclude images with too many clouds. The
detection of lake and the automatic correction of false detections. This algorithm
is capable to tag each individual lake allowing a survey of all lake geometrical
properties over the entire melt season. We observed a large population of supra-glacial
lakes over 14 melt seasons, from 2000 to 2013 on an extended area of 70.000 km2.
In average, lakes are observed from June 9 ± 8.7 days to September 13 ± 13.9
days, and reach a maximum total area of 699 km2 ± 146 km2. As the melt season
progresses, lakes form higher in altitude up to 1800 m above sea level. Results
show a very strong inter-annual variability in term of date of melt and freeze up
onset, melt season duration, maximum total surface area and number of lakes. As it
has already been noticed, we observed a strong spatial persistence. Lakes tend to
form at the same place for several years, probably because of the ice sheet surface
topography. In order to investigate possible links with climatic parameters we calculated
positive degree day (PDD). The main result of this comparison is a strong correlation
between melt intensity and the altitude of lakes. During warmer summer, lakes
form higher in altitude and consequently the extent of melting increase. Recent
studies showed this trend is likely to continue and to increase in the years to come. |
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