Alpine permafrost thawing during the Medieval Warm Period identified from cryogenic cave carbonates
Coarse crystalline cryogenic cave carbonates (CCC<sub>coarse</sub>) dated to the last glacial period are common in central European caves and provide convincing evidence of palaeo-permafrost during this time. Little is known, however, about the exact nature of the environment in which CC...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-07-01
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| Series: | The Cryosphere |
| Online Access: | http://www.the-cryosphere.net/7/1073/2013/tc-7-1073-2013.pdf |
| Summary: | Coarse crystalline cryogenic cave carbonates (CCC<sub>coarse</sub>) dated to the last glacial period are common in central European caves and provide convincing evidence of palaeo-permafrost during this time. Little is known, however, about the exact nature of the environment in which CCC<sub>coarse</sub> formed as no modern analogue setting is known. Here, we report the first findings of sub-recent, albeit inactive, CCC<sub>coarse</sub> from a cave of the Western Alps which is located in the present-day permafrost zone. The globular shape and the presence of ubiquitous euhedral crystal terminations are comparable to previously reported aggregates from the last glacial period and strongly suggest that these aggregates formed subaqueously in pools lacking agitation. Furthermore, stable isotope values of mm-sized spheroids point to calcite precipitation in a closed system with respect to CO<sub>2</sub>, strongly supporting the hypothesis of a cryogenic origin associated with the freezing of water ponds. U-series analyses revealed three clusters of late Holocene calcite precipitation intervals between 2129 and 751 a b2k. These ages correlate with known periods of elevated summer temperatures, suggesting that warming and thawing of the frozen catchment above the cave allowed water infiltration into the karst system. The growth of CCC<sub>coarse</sub> resulted from the re-freezing of this water in the still cold karst cavities. |
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| ISSN: | 1994-0416 1994-0424 |