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| Titel |
1,100,000 year history of Siberian permafrost based on U-Pb chronology of speleothems |
| VerfasserIn |
Anton Vaks, Andrew J. Mason, Sebastian F. M. Breitenbach, Alexander M. Kononov, Alexander V. Osintcev, Gideon M. Henderson |
| 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 |
250092667
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| Publikation (Nr.) |
 EGU/EGU2014-7027.pdf |
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| Zusammenfassung |
| We have used U-Pb dating of the speleothems from Siberian Ledyanaya Lenskaya Cave for
tracing of permafrost thawing events during the last 1.1 million years. Rain and snowmelt
waters can penetrate into caves only when the soil and subsoil temperatures are above 0°C
and permafrost above the cave is discontinuous or absent. Therefore, speleothems in
regions currently affected by permafrost provide a tracer of past permafrost thawing
events.
Ledyanaya Lenskaya Cave is located at 60°22’N-116°57’E, on the southern boundary
of continuous permafrost zone, with no present-day water seepage in the cave. Temperatures
in the region range from -32°C (January) to +18°C (July), with mean annual temperature of
~-6°C. U-Th dating of speleothems from this cave in a previous study [1] showed that
the youngest speleothem growth period occurred at 427±23 thousand years ago
(ka), during the early Marine Isotope Stage (MIS) 11. During this episode global
temperature was 1.5°C higher than pre-industrial levels, and ~0.7°C above the
present.
In the current study two horizons at the base of a stalagmite were dated using U-Pb
chronology [2]. Isochron ages of 1074.1 +7.9/-6.9 ka and 951.4 +3.6/-4.4 ka were obtained.
Timing of these permafrost thawing events correlates with events of exceptionally high
Pacific Warm Pool sea surface temperature (~+30°C)[3]. During these warm episodes the
average global temperature was 1.2-1.3°C higher than pre-industrial temperatures. These
findings put the threshold of thawing of the continuous permafrost near its southern
boundary slightly lower than it was found previously. The dating work is still in process
and is now focusing on growth periods older than MIS-11 but younger than 950
ka.
The oldest horizon of the stalagmite grew on the bedrock. This layer was probably
amongst the first vadose speleothems that formed after the cave was uplifted above the
groundwater table (associated with the nearby Lena River). Today the cave is ~50 meters
above the river. Therefore, it’s likely that the maximum uplift rate of the cave (plus Lena
River incision) is slightly less than 50 m/Myr.
References:
.1. Vaks, A., et al., Speleothems Reveal 500,000-Year History of Siberian Permafrost.
Science, 2013. 340 (6129): p. 183-186.
2. Mason, A.J., G.M. Henderson, and A. Vaks, An Acetic Acid-Based Extraction Protocol
for the Recovery of U, Th and Pb from Calcium Carbonates for U-(Th)-Pb Geochronology.
Geostandards and Geoanalytical Research, 2013. 37(3): p. 261-275.
3. Hansen, J., et al., Global temperature change. Proceedings of the National Academy of
Sciences, 2006. 103(39): p. 14288-14293. |
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