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| Titel |
Past climate changes and permafrost depth at the Lake El'gygytgyn site: implications from data and thermal modeling |
| VerfasserIn |
Darius Mottaghy, Volker Rath, Georg Schwamborn |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083839
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| Zusammenfassung |
| This study focuses on the temperature field observed in boreholes drilled as part of
interdisciplinary scientific campaign targeting the El’gygytgyn crater lake in NE Russia.
Temperature data are available from two sites: the lake borehole 5011-1 located
near the center of the lake reaching 400Â m depth, and the land borehole 5011-3
at the rim of the lake, with a depth of 140Â m. Constraints on permafrost depth
and past climate changes are derived from 2D numerical simulation of the thermal
regime associated with the lake-related talik structure. The thermal properties of the
subsurface needed for these simulations are based on laboratory measurements of
representative cores from the quaternary sediments and the underlying impact-affected rock,
complemented by further information from geophysical logs and data from published
literature.
The temperature observations in the lake borehole 5011-1 are dominated by thermal
perturbations related to the drilling process, and thus only give reliable values for the
lowermost value in the borehole. Undisturbed temperature data recorded over more
than two years are available in the 140Â m deep land-based borehole 5011-3. The
analysis of these observations allows determination of not only the recent mean annual
ground surface temperature, but also the ground surface temperature history, though
with large uncertainties. Besides some signals to be attributed to the warming from
Pleistocene to Holocene, the data shows a strong evident for a comparatively large
amplitude of the Little Ice Age (up to 4Â K), with low temperatures prevailing far
into the 20th century. Other mechanisms like varying porosity may also have an
influence on the temperature profile, however, sensitivity studies imply a major
contribution from recent climate changes. We also address the issue of the possible
shortcomings when using 2D instead of 3D modeling. We show that in this case, due to the
large diameter-depth ratio of the lake, 2D modeling is sufficient for the studied
processes.
We also study the long-term monitoring data from the very shallow part (down to 20Â m)
in order to constrain thermal properties of the permafrost regime, such as thermal diffusivity
and porosity. |
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