The Cryosphere Discuss., 7, 419-440, 2013
www.the-cryosphere-discuss.net/7/419/2013/
doi:10.5194/tcd-7-419-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal The Cryosphere (TC). Please refer to the corresponding final paper in TC.
Alpine permafrost thawing during the Medieval Warm Period identified from cryogenic cave carbonates
M. Luetscher1, M. Borreguero2, G. E. Moseley1, C. Spötl1, and R. L. Edwards3
1Institute of Geology and Palaeontology, University of Innsbruck, Austria
2Swiss Society of Speleology, Switzerland
3Department of Geology and Geophysics, University of Minnesota, USA

Abstract. Coarse crystalline cryogenic cave carbonates (CCCcoarse) 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 CCCcoarse formed as no modern analogue setting is known. Here, we report the first findings of sub-recent, albeit inactive, CCCcoarse 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 described 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 CO2 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 permafrozen catchment above the cave allowed water infiltration into the karst system. The growth of CCCcoarse resulted from the re-freezing of this water in the still cold karst cavities.

Citation: Luetscher, M., Borreguero, M., Moseley, G. E., Spötl, C., and Edwards, R. L.: Alpine permafrost thawing during the Medieval Warm Period identified from cryogenic cave carbonates, The Cryosphere Discuss., 7, 419-440, doi:10.5194/tcd-7-419-2013, 2013.
 
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