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Characteristics of supra-glacial lakes on the south-west Greenland Ice Sheet
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Glaciologi)
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Glaciologi)
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Glaciologi)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Supra-glacial lake form and store melt water during the ablation season every year on the Greenland Ice Sheet (GrIS). This melt water influences both the surface and basal water fluxes. Using an adaptive object-oriented classification approach supra-glacial lakes on the west GrIS are mapped in Terra Moderate Resolution Imaging Spectroradiometer (MODIS) imagery 2001–2010. Lake size shape and distribution parameters are extracted for approximately 5-day intervals from the available cloud free imagery. Using temperature data measured within this region we correlate the lake parameters to melt proxies such ascumulative positive degree days (PDD). The analysis shows that simple parameters such as number of lakes and mean lake area, measures that have been used to describe the development of the surface hydrological system, are largely uncorrelated with melt proxies. Years with higher relative melt, expressed as negative surface mass balances and high PDDs, may exhibit long, predominantly mild melt seasons. Alternatively, a short but intense melt season may have occurred. Given the short duration of the time series, it is difficult to establish statistical relationships between parameters. However, parameters such as median lake size, reflectance and distance between lakes may provide valuable ancillary information to measures such as total lake area, median lake area and lake size distribution data.

Keyword [en]
Greenland Ice Sheet, Supra-glacial lakes, Ice melting, Remote sensing, MODIS
National Category
Climate Research
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-74507OAI: oai:DiVA.org:su-74507DiVA: diva2:510114
Available from: 2012-03-15 Created: 2012-03-15 Last updated: 2012-03-16
In thesis
1. Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet
Open this publication in new window or tab >>Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concerns about the stability of the ice sheet. Melt water generated at the surface is temporarily stored in supra-glacial lakes on the ice sheet. Connections between melt water generation, storage and ice sheet dynamics highlight the importance of the surface hydrological system.

In this thesis different methods are used that improve our ability to observe the supra-glacial lake system on the west Greenland Ice Sheet. This region of the Greenland Ice Sheet has the most extensive supra-glacial hydrological system with a dense network of streams connecting lakes that can exceed several square kilometres in area. Synthetic Aperture Radar (SAR) and visible-near infrared (VNIR) images are used to explore the potential of different sensor systems for regular observations of the supra-glacial lakes. SAR imagery is found to be a useful complement to VNIR data. VNIR data from moderate resolution sensors are preferred as these provide high temporal resolution data, ameliorating problems with cloud cover.

The dynamic nature of the lakes makes automated classification difficult and manual mapping has been widely used. Here a new method is proposed that improves on existing methods by automating the identification and classification of lakes, and by introducing a flexible system that can capture the full range of lake forms. Applying our new method we are better able to analyse the evolution of lakes over a number of melt seasons. We find that lakes initiate after approximately 40 positive degree days. Most lakes exist for less than 20 days before draining, or later in the season, and less often, freezing over. Using the automated method developed in this thesis lakes have been mapped in imagery from 2001–2010 at approximately five day intervals.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology (INK), Stockholm University, 2012. 28 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 31
Keyword
Supra-glacial lakes, Greenland Ice Sheet, Ice melting, Remote sensing, SAR, MODIS, Time-series analysis
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-74509 (URN)978-91-7447-465-7 (ISBN)
Public defence
2012-04-20, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2012-03-29 Created: 2012-03-15 Last updated: 2013-04-02Bibliographically approved

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