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| Titel |
Towards improved cirque glacier reconstructions: differentiating glacial- from non-glacial sediments by means of environmental magnetism. |
| VerfasserIn |
Bjørn Christian Kvisvik, Øyvind Paasche, Svein Olaf Dahl |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250100067
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| Publikation (Nr.) |
 EGU/EGU2014-15948.pdf |
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| Zusammenfassung |
| Skriufonnen, a small cirque glacier (0.4 km2) in Southern Norway, has been monitored for
the last 10 years, revealing a short response time to on-going climate change. This is the only
remaining glacier in the central mountain massif known as Rondane where investigations of
past climate variability are scarce. A series of short (HTH, n=8) and long (piston, n=6) cores
from two lakes located downstream of Skriufonnen were retrieved and sediments were dated
and analysed. In order to complement and validate lake sediment interpretations i.e., the
potential connection to glacier variability, a number of soil samples was collected from the
surrounding catchment.
The six 110 mm piston cores (< 3.1 m length) and eight sediment surface cores were
analysed for grain size distribution, geochemical elements (ITRAX XRF-scanning),
organic matter content (LOI), magnetic parameters (magnetic susceptibility; surface
and bulk), anhysteretic remanent magnetization (ARM) and Saturation Isothermal
remanent magnetizations (sIRM). Consistent age-depth relationships were obtained by
AMS-C14 and Pb210 dates showing that the cores cover at least the last 10 000
years.
High-resolution analysis (XRF and MS) reveals centennial trends, but also distinct
changes in frequency and amplitude. A quiescent period during the Holocene Thermal
Optimum (9-6 ka) is followed by a sudden onset of Neoglacial (3.8 ka) activity
peaking at 2.4 ka. The Little Ice Age (LIA) peaked at 1800 AD. A weak magnetic
signal is observed in all cores. This is explained by the fact that Rondane is made of
Sparagmite, an arkosic sandstone partly consisting of metamorphosed sandstone
and conglomerate with high content of quarts (SiO2) (between 80 to 87 %) and
Feldspar. The Sparagmite is resistant to chemical weathering, making the soils dry and
sandy.
Catchment sediment samples, running in a transect all the way up from the lakes to the
glacier snout were sieved into various size classes (250, 125, 63, 38, 20 μm) prior to
measuring bulk susceptibility (Ïbulk) at 293K and 77K. The ratio between the two
measurements indicates the relative amount of paramagnetic versus ferromagnetic minerals,
and results indicate not only that the finest fractions increase in strength as one gets closer to
the glacier front, but also that there are long periods in the cores which is dominated by
paramagnetic minerals.
The approach employed here suggests that the combination of catchment samples with
high-resolution analysis of lake sediment cores provide a more accurate reconstruction of past
glacier variability, and has resulted in the first continuous cirque glacier reconstruction from
this area. |
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