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| Titel |
Development of empirical data sets to further constrain glacial modeling in southwestern Greenland |
| VerfasserIn |
Vincent Rinterknecht, Yuri Gorokhovich |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044367
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| Zusammenfassung |
| Direct dating of the retreat of the southwestern margin of the Greenland Ice Sheet (GIS)
coupled with spatial analysis and glacial modeling have the potential to better constrain the
timing of the retreat of the ice margin, the thickness of the former ice sheet as well as its
response to climate change.
We measured 10Be concentrations in 12 samples collected along a longitudinal and
altitudinal transects from Sisimiut to within 10 km of the Isunguata Sermia Glacier ice
margin on the southwestern coast of Greenland. Along the longitudinal transect, we collected
three perched boulders and two bedrocks. In addition, seven perched boulders were
sampled along a vertical transect in a valley within 10 km of the Isunguata Sermia
Glacier ice margin. The results constrain the height of the ice sheet during the last
glacial maximum (LGM) between 500 m and 840 m (including the 120 m relative
sea level depression at the time of the LGM, 21 kyr BP). From the transect we
estimate the thinning of the ice sheet at the end of the deglaciation between 12.3 ± 1.5
10Be kyr (n = 2) and 8.3 ± 1.2 10Be kyr (n = 3) to be ~6 cm.yr-1 over this time
period.
In addition, we conducted a spatial analysis of the lake shape distribution, an
important geomorphological indicator in previously glaciated areas. Since glacial
sediment deposition or erosion act on large areas, distribution of lakes can reflect the
intensity of glacial erosional/depositional processes and their spatial extent. Landsat
imagery was used to extract lake outlines from our study area on the widest ice-free
coastal margin of the southwestern Greenland north of Kangerlussuaq. Analysis
included image classification and spatial analysis of lakes with elevation data using
geographic information system tools. A morphometric index was applied to extract kettle
lakes as indicators of a specific glacial process – ice stagnation. The analysis shows
that the highest concentrations of lakes within the study area occupy the elevation
range between 164 and 361 m above sea level. This conclusion is supported by
the above surface exposure ages. The widespread distribution of modeled kettle
lakes within the same elevation range and across the study area suggests that the
last deglaciation process was accompanied by abandonment of blocks of stagnant
ice.
Our data are now being fed into the next generation of numerical reconstructions, using
parallel ice sheet models, capable of closely replicating the range and pattern of ice
flow velocities observed in the present GIS at high horizontal resolution (1-5 km).
Ice thickness simulations by recent models are within the range of 1,100 – 1,300
m over the last deglaciation, largely overestimating our empirical and analytical
results. The goals of this and future studies are (1) to test the overestimated glacial
reconstructions (height of the ice sheet) of the southwestern sector of the GIS proposed
by the current models and (2) to reconstruct the deglacial history of the region. |
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