Alpine permafrost thawing during the Medieval Warm Period identified from cryogenic cave carbonates

Abstract

Abstract. Coarse crystalline cryogenic cave carbonates (CCC coarse ) 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 coarse formed as no modern analogue setting is known. Here, we report the first findings of sub-recent, albeit inactive, CCC coarse 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 2 , 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 coarse resulted from the re-freezing of this water in the still cold karst cavities.

New Aspects of High-Mountain Palaeobiogeography: A Synthesis of Data from Forefields of Receding Glaciers and Ice Patches in the Tärna and Kebnekaise Mountains, Swedish Lapland

“…Futhermore, an Icelandic glacier has released a birch log originating from virtually the same time (Ives, 1991). In line with these findings, several other climate proxies from northern Europe indicate warmer-than-present conditions in the first decades of the Roman Empire (e.g., Hormes et al, 2004;Ljungqvist, 2009;Humlum et al, 2011;Esper et al, 2012;Kullman, 2013;Luetscher et al, 2013). Moreover, the discovery of this birch log adds to the insight that present-day glacier recession and associated warming are not unique phenomena during the past 4500 years (cf.…”

Cryogenic carbonates and cryogenic speleothem damage in the Za Hájovnou Cave (Javoříčko Karst, Czech Republic)

“…De pend ing on the thick ness of the layer of freez ing wa ter and thus also on the freez ing rate, two main groups of CCC have been rec og nized (Žák et al, 2008). Fine-grained types (CCC fine ; ab bre vi a tions af ter Luetscher et al, 2013) form dur ing rapid freez ing of a thin layer of wa ter, usually on the sur face of ice in caves with high air flow or in cave entrance sec tions. These had al ready been rec og nized in the 1930s (Kunský, 1939).…”

“…Dated oc cur rences of CCC coarse in caves of Cen tral Eu rope have been used to es ti mate the min i mum thick ness of Weichselian per ma frost (Žák et al, 2012). More rarely, CCC coarse sites in caves where air flow cool ing was pos si ble are lo cated at high el e va tions and are of Ho lo cene age (Luetscher et al, 2013;Spötl and Cheng, 2014;Colucci et al, 2017).…”

Permafrost-related hiatuses in stalagmites: Evaluating the potential for reconstruction of carbon cycle dynamics

“…Such conditions could have prevented speleothem growth from starting during MIS 9-5e, but it is possible that particularly warm periods during these interglacials could have led to episodic partial degradation of permafrost, and brief periods of inorganic speleothem growth. Cryogenic cave carbonate deposits may be able to resolve such brief and partial periods of thaw in more detail, as their formation typically precedes speleothem formation (Bazarova et al, 2014;Luetscher et al, 2013;Žák et al, 2012). Moreover, techniques employing ultra high-resolution measurements, e.g., nanoSIMS, synchrotron radiation, elemental mapping, or μXRF might be more successful at extracting very high frequency variations that allow more detailed insight into processes during these "skipped" interglacials, but would be difficult to interpret without additional chronological control.…”