Abstract Monte Perdido Glacier, located in the central Pyrenees, is one of the southernmost glaciers in Europe. Due to climate change, this glacier is suffering an accelerated mass loss, especially in the last decades. If the current trends persist, this glacier is expected to disappear in the next 50 years. As part of the efforts of the scientific community to increase the knowledge about this glacier, this research presents the first microstructural characterization of the Monte Perdido Glacier, focused on a high-impurity concentration segment that belongs to an ice core drilled in 2017. The results reveal the ice has a layering defined by air bubbles and non-soluble impurities. The bubble-defined layering exhibits features of both a primary (sedimentary) and a secondary (strain-induced) origin. We found a clear inverse correspondence between the particle concentration and the grains' size and roundness index. A preliminary micro-Raman characterization of the particles shows the occurrence of atacamite, anatase (likely related to ancient mining activities in the vicinity of the glacier) and quartz. The latter could be an indicator of mineral dust, probably suggesting the arrival of dust-laden air masses from the north of the African continent.

Caving accidents are rare, but when they occur, they represent a unique logistical and medical challenge. Retrieving the patient to the surface often means navigating stretchers through narrow corridors with limited options for monitoring and interventions. Because the patient is usually not fasting, opioids and sedatives should be used with extreme caution. Therefore, alternative analgesic techniques such as locoregional nerve blocks are a promising strategy to improve patient comfort and safety during cave rescues. In this article, we describe 2 cases in which portable point-of-care ultrasound equipment was used to supplement clinical assessment and provide locoregional anesthesia to facilitate patient evacuation and transport. In this context, we discuss the role of portable ultrasound-guided locoregional anesthesia in cave rescue and in the global preclinical context. In summary, our cases demonstrated that the administration of ultrasound-guided prehospital locoregional anesthesia is a safe, rapid, and effective procedure even in extreme situations such as cave rescues. The advent of portable, high-quality ultrasound equipment may open the door for more widespread application of this technique in the global preclinical setting.

Previous glacial intervals were punctuated by abrupt climate transitions between cold (stadial) and warm (interstadial) conditions. Many mechanisms leading to stadial-interstadial variability have been hypothesized with ice volume being a commonly involved element. Here, we test to which extent insolation modulated stadial-interstadial oscillations occurred during the penultimate glacial. We present a replicated and precisely dated speleothem record covering the period between 200 and 130 ka before present from caves located in the European Alps known to be sensitive to millennial-scale variability. We show that the widely proposed relationship between sea level change and stadial-interstadial variability was additionally modulated by solar insolation during this time interval. We find that interstadials occurred preferentially near maxima of Northern Hemisphere summer insolation, even when sea level remained close to its minimum during peak glacial periods. We confirm these observations with model simulations that accurately reproduce the frequency and duration of interstadials for given sea-level and insolation forcing. Our results imply that summer insolation played an important role in modulating the occurrence of stadial-interstadial oscillations and highlight the relevance of insolation in triggering abrupt climate changes.

The cycling of subsurface karst CO2 is not well constrained in terms of its source and transportation pathway. The classical model suggests that cave CO2 is produced by the respiration of soils and vegetation in the catchment. In contrast, several new studies have proposed that the dominant source of CO2 is from the respiration of older organic matter situated deeper within the karst, or from the degassing of supersaturated drip water.We present over a year of monitoring data from Milandre cave, northern Switzerland, whereby we evaluated the 14CO2 and δ13CO2 composition of the atmosphere in the cave catchment, catchment soil gas, well gas, and cave air. Drip waters located throughout the cave also underwent various analysis. The cave 14CO2 is more depleted compared to the soil and gas samples. The Keeling plot intercept of atmospheric and cave δ13CO2 is ~-26‰, indicating a dominant contribution from biological respiration. The dissolved inorganic carbon from various cave drips have an F14C from ~ 0.84 to 0.96 and δ13C from ~ -16‰ to -11‰. F14C and δ13C are inversely correlated.  Considering both the 14C and δ 13C results, this suggests either a source of CO2 from an aged reservoir of respiring organic matter contributing to the cave gas or substantial influence from degassing of 14C fossil carbonate CO2 from drip water. These results have implications for the understanding of the subterranean carbon cycle and the interpretation of speleothem carbon isotope records for paleoclimate studies.

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.

AbstractShow caves are great natural attractions and constitute important economic engines for particular rural areas. However, cave management requires knowledge of the cave dynamics to ensure adequate exploitation and conservation (e.g. number of visitors, amount of CO2, other impacts). Show caves located close to the hydrological base level can be affected by a sudden rise of the water level in response to rainfall events, exposing touristic facilities, visitors and staff to flood risk. Here we present a monitoring campaign in Las Güixas show cave, a small tourist cave located in the Central Pyrenees, to guide in developing an adequate flood risk management plan (FRMP). Cave monitoring includes temperature, relative humidity, CO2 concentration and water level measurements to characterize the different cave sections, as well as to assess the possible influence of the visitors on the cave dynamics. The tourist section is very well ventilated due to intense air flow associated with a chimney effect, and therefore CO2 remains low and temperature shows high thermal oscillations throughout the year. During the maximum number of visits per day, the CO2 generated by the tourists increases, however, is quickly reduced by the ventilation. Water level monitoring shows clear rises depending on the amount of rainfall and snowmelt in the catchment area. However, the water level does not always respond to given rainfall amounts in the same way, indicating that the water retained in the karst system plays an important role. Water can flood the tourist section forcing to cancel the following visits which generates economic losses. In addition, the higher water flow increases the natural inputs of CO2 in the cave atmosphere due to degassing. Las Güixas cave monitoring shows that anthropogenic CO2 emissions remain substantially lower than CO2 concentrations during the flood events.KeywordsCave monitoringEnvironmental conditionsFlood risk managementKarst hydrologyNatural heritage preservationShow caveWater level

AbstractDuring a flood inside a cave, sands and silts are transported through the cave system and deposited as (i) a coating of this detritus on speleothem surfaces and (ii) a flood bed accumulated on the cave passages which are protected from the main water stream. After the floodwater level drops, speleothem deposition is restarted and detrital coatings get trapped inside the carbonate laminae, while detrital flood bed sequences may contain clay laminae and water drops features at their contacts. When this process is unique and continuous (in the case of speleothems) record of paleofloods in a particular region is obtained. Typically, speleothems and detrital sequences close to usual groundwater table, record ordinary floods. On the contrary, sequences deposited in areas above the usual epiphreatic zone are expected to register extraordinary floods. Here, we present the geomorphosedimentary and chronological (U/Th, OSL) information derived from the Ojo de Val Junquera Cave (Iberian Range, Spain). The cave comprises two sub-horizontal levels connected by shafts and ramps. The lower level corresponds with an ephemeral spring and includes six siphons. Stalagmites from the upper level show single sand layers and brownish bands in relation to past low/high-frequency flood episodes, respectively. U/Th ages show that speleothems grew during Marine Isotope Stages (MIS) 9, 8, 7, 6, 3, 2 and 1. In the lower level, at the epiphreatic zone, a poorly consolidated detrital infill is formed by sands and gravels, indicating that the cave outlet was once blocked by these sediments, with an age (OSL) of 377 ± 39 ka (MIS 10–11). The study of detrital sediment facies and their chronology allow discerning between extreme and regular floods to provide high resolution records of extreme floods under climate variability up to a millennial scale in the Western Mediterranean.KeywordsSpeleothemsPaleofloodsSedimentsMorphosedimentary records

AbstractAncient environmental DNA retrieved from sedimentary records (sedaDNA) can complement fossil-morphological approaches for characterizing Quaternary biodiversity changes. PCR-based DNA metabarcoding is so far the most widely used method in environmental DNA studies, including sedaDNA. However, degradation of ancient DNA and potential contamination, together with the PCR amplification drawbacks, have to be carefully considered. Here we tested this approach on speleothems from an Alpine cave that, according to a previous palynomorphological study, have shown to contain abundant pollen grains. This offers a unique opportunity for comparing the two methods and, indirectly, trying to validate DNA-based results. The plant taxa identified by sedaDNA are fewer than those by pollen analysis, and success rate of PCR replicates is low. Despite extensive work performed following best practice for sedaDNA, our results are suboptimal and accompanied by a non-negligible uncertainty. Our preliminary data seem to indicate that paleoenvironmental DNA may be isolated from speleothems, but the intrinsic weakness of PCR-based metabarcoding poses a challenge to its exploitation. We suggest that newly developed methods such as hybridization capture, being free from PCR drawbacks and offering the opportunity to directly assess aDNA authenticity, may overcome these limitations, allowing a proper exploitation of speleothems as biological archives.

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 ºC 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 back-flooding of the cave. We suggest that relict ice formations record past damming events with subsequent congelation. δ34S values of gypsum indicate that the sulfate originated from the oxidation of pyrite present in the bedrock. Several features including the air and rock temperatures, the absence of drips, the low loss of ice, and the location of ice bodies in the cave indicate the cave permafrost is the result of a combination of undercooling by ventilation and diffusive heat transfer from the surrounding permafrost, reaching ~200 m below the surface.

<p>Globally, near-surface permafrost is likely to warm, thin or disappear in many areas subject to future climate warming and wetting, creating a positive atmospheric feedback where the permafrost is rich in carbon. Unfortunately, substantial uncertainty exists as to the extent and timing of thawing in response to atmospheric forcing. Cryogenic cave carbonates (CCCs),  a recently described type of speleothem, precipitate when cave ice forms and thus provide opportunities to constrain periods when permafrost was present at a given cave site. Here, we present a unique dataset comprising 38 <sup>230</sup>Th/U ages of CCCs from two caves in the Mendips, southwest England (51°N), and two caves in the Peak District, central England (53°N), all of which are currently ice-free. Whilst many ages are clean, reliable and high precision, the accuracy of those containing initial <sup>230</sup>Th<sup></sup>is improved greatly by constructing isochrons and applying further statistical methods.</p><p>The ages of CCCs reveal two distinct periods of isothermal permafrost conditions, peaking during i) the early Bølling–Allerød interstadial at approximately 14,463 ± 145 yBP<em>*</em> and ii) the late Younger Dryas around 11,719 ± 229 yBP. Such isothermal conditions (i.e., where values of mean annual ground temperature are commonly a fraction of a degree below 0°C and exist through much of the depth profile of permafrost) are thought to represent the later stages of permafrost warming prior to its disappearance. We attribute this isothermal, disequilibrium permafrost evolution during the last deglaciation of the British–Irish Ice Sheet to climatic variations linked to North Atlantic sea-ice extent and seasonality.</p><p><em>*years before 1950</em></p>