Mountain permafrost in the Central Pyrenees: insights from the Devaux ice cave

Abstract

Abstract. Ice caves are one of the least studied parts of the cryosphere, particularly those located in inaccessible permafrost areas at high altitudes or high latitudes. We characterize the climate dynamics and the geomorphological features of Devaux cave, an outstanding ice cave in the Central Pyrenees on the French–Spanish border. Two distinct cave sectors were identified based on air temperature and geomorphological observations. The first one comprises well-ventilated galleries with large temperature oscillations likely influenced by a cave river. The second sector corresponds to more isolated chambers, where air and rock temperatures stay below 0 ∘C throughout the year. Seasonal layered ice and hoarfrost occupy the first sector, while transparent, massive perennial ice is present in the isolated chambers. Cryogenic calcite and gypsum are mainly present within the perennial ice. During winter, the cave river freezes at the outlet, resulting in a damming and backflooding of the cave. We suggest that relict ice formations record past damming events with the subsequent formation of congelation ice. δ34S values of gypsum indicate that the sulfate originated from the oxidation of pyrite present in the bedrock. Several features including air and rock temperatures, the absence of drips, the small loss of ice in the past 7 decades, and the location of ice bodies in the cave indicate that the cave permafrost is the result of a combination of undercooling by ventilation and diffusive heat transfer from the surrounding permafrost, reaching a thickness of ∼ 200 m.

Cryogenic cave minerals recorded the 1889 CE melt event in northeastern Greenland

“…In some caves, the oc- currence of non-carbonate minerals of cryogenic origin has been reported (Dublyansky et al, 2017;Žák et al, 2018). Cryogenic gypsum and, locally, other sulfate minerals are mostly known from caves hosted in gypsum rock (Kadebskaya and Tschaikovskiy, 2015;Žák et al, 2018) but also from some limestone caves, where the sulfate is derived from pyrite oxidation (Bartolomé et al, 2023;Dublyansky et al, 2017). Mirabilite is known from several caves, where its existence has been tied to evaporative conditions (e.g.…”