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Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates at which the climate can change state, the mechanisms that drive such changes, and the leads, lags, and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using δ18O from speleothems (δ18Ocalc) that grew along the northern rim of the Alps (NALPS), enabling direct chronological comparisons with δ18O records from Greenland ice cores (δ18Oice). In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18Ocalc chronology over the interval 118.3 to 63.7 ka using 11, newly available, clean, precisely dated stalagmites from five caves. Using only the most reliable and precisely dated records, this period is now 90 % complete and is comprised of 16 stalagmites from seven caves. Where speleothems grew synchronously, the timing of major transitional events in δ18Ocalc between stadials and interstadials (and vice versa) are all in agreement on multi-decadal timescales. Ramp-fitting analysis further reveals that, except for one abrupt change, the timing of δ18O transitions occurred synchronously within centennial-scale dating uncertainties between the NALPS19 δ18Ocalc record and the Asian monsoon composite speleothem δ18Ocalc record. Due to the millennial-scale uncertainties in the ice core chronologies, a comprehensive comparison with the NALPS19 chronology is difficult. Generally, however, we find that the absolute timing of transitions in the Greenland Ice Core Chronology (GICC) 05modelext and Antarctic Ice Core Chronology (AICC) 2012 are in agreement on centennial scales. The exception to this is during the interval of 100 to 115 ka, where transitions in the AICC2012 chronology occurred up to 3000 years later than in NALPS19. In such instances, the transitions in the revised AICC2012 chronology of Extier et al. (2018) are in agreement with NALPS19 on centennial scales, supporting the hypothesis that AICC2012 appears to be considerably too young between 100 and 115 ka. Using a ramp-fitting function to objectively identify the onset and the end of abrupt transitions, we show that δ18O shifts took place on multi-decadal to multi-centennial timescales in the North Atlantic-sourced regions (northern Alps and Greenland) as well as the Asian monsoon. Given the near-complete record of δ18Ocalc variability during the last glacial period in the northern Alps, we also offer preliminary considerations regarding the controls on mean δ18Ocalc for given stadials and interstadials. We find that, as expected, δ18Ocalc values became increasingly lighter with distance from the oceanic source regions, and increasingly lighter with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ18Ocalc values that are heavier than expected in comparison to lower-elevation sites, possibly caused by a summer bias in the recorded signal of the high-elevation site, or a winter bias in the low-elevation site. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ18O such as the Greenland Stadial (GS)-16.2, GS-17.2, GS-21.2, and GS-23.2 “precursor” events, as well as the “within-interstadial” GS-24.2 cooling event. Our new high-precision chronology shows that each of these δ18O depletions occurred in the decades and centuries following rapid rises in sea level associated with increased ice-rafted debris and southward shifts of the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately sized ice sheets may have been responsible for the cold reversals causing the Atlantic Meridional Overturning Circulation to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events.

This study explores the significance of show caves as subterranean geoheritage sites, focusing on their potential for sustainable cave tourism. The primary objective is to comprehensively assess caves, considering speleological, infrastructure, and tourist values, while developing sustainable tourism strategies. For this, a novel methodology was created that involves literature review, field surveys, assessments and stakeholder consultations, which is applied in the evaluation of nine show caves in Switzerland. By addressing potential challenges and negative impacts, we analyze current tourism development and propose mitigation strategies. Combining quantitative and qualitative analyses, including geological, ecological, and cultural factors, the study offers a comprehensive evaluation, contributing a practical methodology for cave management, as well as cave tourism planning. The findings provide insights beyond academia, guiding stakeholders involved in cave tourism development, and striving to balance ecosystem preservation with sustainable economic growth.

High-latitude or high-altitude caves often preserve ice deposits that contain valuable signals of past climate conditions, sometimes even reflecting regional and local atmospheric variability. Phases of aggradation or degradation of underground ice can also provide insights into the temporal evolution of Alpine permafrost. Such data are typically obtained from ice cores, which require a well-constrained chronological framework to be meaningful. In recent years, several dating methods have been developed or refined for glacier and ice sheet cores. However, some of these techniques have not yet been applied to cave ice. In this study, the 39Ar dating technique using Argon Trap Trace Analysis is applied for the first time to an underground ice deposit in the southeastern Alps, specifically in the Canin-Kanin massif (Julian Alps). The results are compared with pollen markers extracted from the ice, with U-Th dating of cryogenic cave carbonates found in situ within the same ice block, and with radiocarbon (14C) dating of the water-insoluble organic carbon fraction embedded in the ice. This integrated approach enabled dating the ice deposit to the end of the Little Ice Age, at the onset of the subsequent warming phase.

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.

Understanding the carbon cycle of the terrestrial critical zone, extending from the tree canopy to the aquifer, is crucial for accurate quantification of its total carbon storage and for modelling terrestrial carbon stock responses to climate change. Caves and their catchments offer a natural framework to sample and analyse carbon in unsaturated zone reservoirs across various spatial and temporal scales. In this study, we analyse the concentration, stable carbon isotopic ratio (δ13C), and radiocarbon (14C) compositions of CO2 from the atmosphere, boreholes (0.5 to 5 m depth), and cave sampled every 2 months over 2 years at Milandre cave in northern Switzerland. High concentrations of up to 35 000 ppmV CO2 are measured in the boreholes. The δ13C values of CO2 in the boreholes reflect the δ13C of C3 plants (∼ −26 ‰), which dominate the catchment ecosystem. Shallow meadow boreholes host older CO2 in winter and modern CO2 in summer, while forest ecosystems consistently export modern CO2 (F14C = ∼ 1) to the unsaturated zone. Cave CO2 concentrations exceed atmospheric levels and are diluted by temperature-driven seasonal ventilation. Keeling plot intercepts indicate that the cave CO2, which mixes with atmospheric CO2, is younger in summer (F14C = 0.94) and older in winter (F14C = 0.88), with a δ13C consistent with the C3-plant-dominated catchment. Mixing models utilizing drip water dissolved inorganic carbon 14C suggest that varying carbonate dissolution and degassing dynamics do not explain the F14C variation and concurrent δ13C stability of the mixing endmember. Rather, contributions from aged carbon reservoirs in the deeper unsaturated zone are likely. This study provides valuable insights into CO2 source dynamics and cycling within the karstic critical zone, highlighting the impact of seasonal variations and ecological factors on downward carbon export from terrestrial ecosystems.

Understanding the carbon cycle of the terrestrial critical zone, extending from the tree canopy to the aquifer, is crucial for accurate quantification of its total carbon storage and for modelling terrestrial carbon stock responses to climate change. Caves and their catchments offer a natural framework to sample and analyse carbon in unsaturated zone reservoirs across various spatial and temporal scales. In this study, we analyse the concentration, stable carbon isotopic ratio ([delta].sup.13 C), and radiocarbon (.sup.14 C) compositions of CO.sub.2 from the atmosphere, boreholes (0.5 to 5 m depth), and cave sampled every 2 months over 2 years at Milandre cave in northern Switzerland. High concentrations of up to 35 000 ppmV CO.sub.2 are measured in the boreholes. The [delta].sup.13 C values of CO.sub.2 in the boreholes reflect the [delta].sup.13 C of C.sub.3 plants (â¼ -26 0/00), which dominate the catchment ecosystem. Shallow meadow boreholes host older CO.sub.2 in winter and modern CO.sub.2 in summer, while forest ecosystems consistently export modern CO.sub.2 (F.sup.14 C = â¼ 1) to the unsaturated zone. Cave CO.sub.2 concentrations exceed atmospheric levels and are diluted by temperature-driven seasonal ventilation. Keeling plot intercepts indicate that the cave CO.sub.2, which mixes with atmospheric CO.sub.2, is younger in summer (F.sup.14 C = 0.94) and older in winter (F.sup.14 C = 0.88), with a [delta].sup.13 C consistent with the C.sub.3 -plant-dominated catchment. Mixing models utilizing drip water dissolved inorganic carbon .sup.14 C suggest that varying carbonate dissolution and degassing dynamics do not explain the F.sup.14 C variation and concurrent [delta].sup.13 C stability of the mixing endmember. Rather, contributions from aged carbon reservoirs in the deeper unsaturated zone are likely. This study provides valuable insights into CO.sub.2 source dynamics and cycling within the karstic critical zone, highlighting the impact of seasonal variations and ecological factors on downward carbon export from terrestrial ecosystems.

Understanding the carbon cycle of the terrestrial critical zone, extending from the tree canopy to the aquifer, is crucial for accurate quantification of its total carbon storage and for modelling terrestrial carbon stock responses to climate change. Caves and their catchments offer a natural framework to sample and analyse carbon in unsaturated zone reservoirs across various spatial and temporal scales. In this study, we analyse the concentration, stable carbon isotopic ratio (δ13C), and radiocarbon (14C) compositions of CO2 from the atmosphere, boreholes (0.5 to 5 m depth), and cave sampled every 2 months over 2 years at Milandre cave in northern Switzerland. High concentrations of up to 35 000 ppmV CO2 are measured in the boreholes. The δ13C values of CO2 in the boreholes reflect the δ13C of C3 plants (∼ -26 ‰), which dominate the catchment ecosystem. Shallow meadow boreholes host older CO2 in winter and modern CO2 in summer, while forest ecosystems consistently export modern CO2 (F14C = ∼ 1) to the unsaturated zone. Cave CO2 concentrations exceed atmospheric levels and are diluted by temperature-driven seasonal ventilation. Keeling plot intercepts indicate that the cave CO2, which mixes with atmospheric CO2, is younger in summer (F14C = 0.94) and older in winter (F14C = 0.88), with a δ13C consistent with the C3-plant-dominated catchment. Mixing models utilizing drip water dissolved inorganic carbon 14C suggest that varying carbonate dissolution and degassing dynamics do not explain the F14C variation and concurrent δ13C stability of the mixing endmember. Rather, contributions from aged carbon reservoirs in the deeper unsaturated zone are likely. This study provides valuable insights into CO2 source dynamics and cycling within the karstic critical zone, highlighting the impact of seasonal variations and ecological factors on downward carbon export from terrestrial ecosystems.

Ancient 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.

The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7 ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5–23.5 ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3 ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation.

This research develops a conceptual model of a karst system subject to mountain permafrost. The transient thermal response of a frozen rock cleft after the rise in the atmospheric temperature above the melting temperature of water is investigated using numerical simulations. Free convection in liquid water (i.e. buoyancy-driven flow) is considered. The density increase in water from 0 to 4 °C causes warmer meltwater to flow downwards and colder upwards, resulting in significant enhancement of the heat transferred from the ground surface to the melting front. Free convection increases the melting rate by approximately an order of magnitude compared to a model based on thermal conduction in stagnant water. The model outcomes are compared qualitatively with field data from the Monlesi ice cave (Switzerland) and confirm the agreement between real-world observations and the proposed model when free convection is considered.