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The Younger Dryas stadial was characterised by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between - 2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m , which persisted for 233 ± 54 d per year. By identifying modern analogues from climate reanalysis data, we demonstrate that the inferred temperature and snow cover characteristics for the British Isles during the Younger Dryas are best explained by extreme temperature seasonality, comparable to continental parts of today's Arctic Archipelago. Such a climate for the British Isles necessitates a winter sea ice margin at approximately 45° N in the North Atlantic Ocean. [ABSTRACT FROM AUTHOR]

The Younger Dryas Stadial was characterized by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between - 2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution, ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ±2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ±54 days per year. [ABSTRACT FROM AUTHOR]

The investigation of cryogenic cave minerals (CCMs) has developed in recent decades to be a particularly valuable proxy for palaeo-permafrost reconstruction. Due to difficulties, however, in obtaining reliable chronologies with the so-called “fine” form of these minerals, such studies have thus far utilised the “coarse” form. In this study, we successfully investigate the northernmost-known deposit of fine-grained cryogenic cave minerals (CCMs), which are situated in Cove Cave (Greenlandic translation: Eqik Qaarusussuaq), a low-elevation permafrost cave in northeast Greenland (80° N). The Cove Cave CCMs display a complex mineralogy that consists of fine-grained cryogenic cave carbonates (CCCfine) as well as sulphate minerals (gypsum, eugsterite, mirabilite, and löweite). In comparison to CCCfine from the mid-latitudes, positive δ13C values (7.0 to 11.4 ‰) recorded in Cove Cave are similar. In contrast, Cove Cave CCCfine δ18O values are ca. 8 to 16 ‰ lower. Furthermore, despite previous CCCfine dating efforts being unsuccessful, here we demonstrate that precise dating is possible with both isochron-based 230Th/U dating and 14C dating if the dead carbon fraction is reliably known. The dating result (65 ± 17 a BP; 1885 ± 17 CE) shows that the CCMs formed during the late Little Ice Age, a time interval characterised by cold temperatures and abundant permafrost in northeast Greenland, making water infiltration into Cove Cave dependent on water amount and latent heat. We relate the CCM formation to a combination of black carbon deposition and anomalously high temperatures, which occurred over a few days, in the summer of 1889 CE. Such extreme conditions led to widespread melting over large areas of the Greenland ice sheet. We propose that the anomalous (weather) conditions of 1889 CE also affected northeast Greenland, where the enhanced melting of a local ice cap resulted in water entering the cave and rapidly freezing. While CCCfine and gypsum likely precipitated concurrently with freezing, the origin of the other sulphate minerals might not be purely cryogenic but could be linked to subsequent sublimation of this ice accumulation in the very dry cave environment. [ABSTRACT FROM AUTHOR]

Cryogenic cave carbonates (CCCs) are a type of speleothem, typically dated with 230Th/U disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre- to centimetre-sized loose crystals and crystal aggregates on the floors of cave chambers, so they lack a framework that would allow ages to be validated by stratigraphic order. Correction factors for the initial 230 Th (230 Th 0) are often based on the bulk-earth-derived initial 230Th/232Th activity ratio ((230Th/232Th)0), which is a well-established approach when 230 Th 0 is moderately low. For samples with elevated levels of 230 Th 0 , however, accuracy can be improved by constraining (230Th/232Th)0 independently. Here, we combine detailed morphological observations from three CCC patches found in Water Icicle Close Cavern in the Peak District (UK) with 230Th/U analyses. We find that individual CCC crystals show a range of morphologies that arise from non-crystallographic branching in response to the chemical evolution of the freezing solution. Results of 230Th/U dating indicate that samples with a large surface area relative to the sample volume are systematically more affected by contamination with 230 Th 0. By fitting isochrons to these results, we test whether the CCCs in a patch formed during the same freezing event, and demonstrate that (230Th/232Th)0 can deviate substantially from the bulk-earth-derived value and can also vary between the different CCC patches. Where CCCs display elevated 230 Th 0 , isochrons are a useful tool to constrain (230Th/232Th)0 and obtain ages with improved accuracy. Detritus absorbed to the crystal surface is shown to be the most likely source of 230 Th 0. Our results suggest that some previously published CCC ages may merit re-assessment, and we provide suggestions on how to approach future dating efforts. [ABSTRACT FROM AUTHOR]

Paleolithic antiquity of parietal art in Ignatievskaya cave, Southern Ural, is supported by its subject (Late Pleistocene animals) as well as by paleontological and palynological data, and 14C dates from cultural layers associated with artistic activity (17.8−16.3 cal ka BP; association is established by finds of ochre in these layers). However, three 14C dates of charcoal motifs yielded younger, Holocene ages (7.4−6.0 cal ka BP). In this study, we constrain the age of parietal art in the cave by 230Th dating of flowstone that brackets the paintings. Flowstone did not form in the cave between c. 78 and 10 ka BP, due to widespread permafrost in northern Eurasia at that time. Our 230Th dates do not support the middle Holocene age of art in Ignatievskaya cave and are consistent with its Upper Paleolithic antiquity instead. [ABSTRACT FROM AUTHOR]

Uranium--uranium (234U--238U) disequilibrium dating can determine the age of secondary carbonates over greater time intervals than the well-established 230Th--234U dating method. Yet it is rarely applied due to unknowns in the initial δ234U (δ234Ui) value, which result in significant age uncertainties. In order to understand the δ234Ui in Devils Hole 2 cave, Nevada, we have determined 110 δ234Ui values from phreatic calcite using 230Th-234U disequilibrium dating. The sampled calcite was deposited in Devils Hole 2 between 4 and 590 ka, providing a long-term look at δ234Ui variability over time. We then performed multilinear regression among the δ234Ui values and correlative δ18O and δ13C values. The regression can be used to estimate the δ234Ui value of Devils Hole calcite based upon its measured δ18O and δ13C values. Using this approach and the measured present-day δ234U values of Devils Hole 2 calcite, we calculated 110 independent 234U-238U ages. In addition, we used newly measured δ18O, δ13C, and present-day δ234U values to calculate 10 234U-238U ages that range between 676 and 731 ka, thus allowing us to extend the Devils Hole chronology beyond the 230Th--234U-dated chronology while maintaining an age precision of ~2 %. Our results indicate that calcite deposition at Devils Hole 2 cave began no later than 736±11 kyr ago. The novel method presented here may be applied to future speleothem studies in similar hydrogeological settings, given appropriate calibration studies. [ABSTRACT FROM AUTHOR]

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 (δ18O calc) that grew along the northern rim of the Alps (NALPS), enabling direct chronological comparisons with δ18O records from Greenland ice cores (δ18O ice). In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18O calc 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 δ18O calc 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 δ18O calc record and the Asian monsoon composite speleothem δ18O calc 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) 05 modelext 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 δ18O calc variability during the last glacial period in the northern Alps, we also offer preliminary considerations regarding the controls on mean δ18O calc for given stadials and interstadials. We find that, as expected, δ18O calc 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 δ18O calc 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. [ABSTRACT FROM AUTHOR]

Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates that the climate can change state, the mechanisms that drive that change, and the leads, lags and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using speleothems from the northern rim of the Alps (NALPS), enabling direct chronological comparisons with highly similar shifts in Greenland ice cores. In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18O chronology over the interval 118.3 to 63.7 ka using eleven,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 15 stalagmites from seven caves. Where speleothems grew synchronously, major transitional events between stadials and interstadials (and vice versa) are all in agreement within uncertainty. Ramp-fitting analysis further reveals good agreement between the NALPS19 speleothem δ18O record, the GICC05modelext NGRIP ice-core δ18O record, and the Asian Monsoon composite speleothem δ18O record. In contrast, NGRIP ice-core δ18O on AICC2012 appears to be considerably too young. We also propose a longer duration for the interval covering Greenland Stadial (GS) 22 to GS-21.2 in line with the Asian monsoon and NGRIP-EDML. Given the near-complete record of δ18O variability during the last glacial period in the northern Alps, we offer preliminary considerations regarding the controls on mean δ18O. We find that as expected, δ18O values became increasingly more depleted with distance from the oceanic source regions, and increasingly depleted with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ18O values that are too high in comparison to lower-elevation sites, thus indicating a summer bias in the recorded signal. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ18O such as "pre-cursor" events GS-16.2, GS-17.2, GS-21.2, and GS-23.2, as well as the "within-interstadial" GS-24.2 event. Our new high-precision chronology shows that each of these δ18O depletions occurred shortly following rapid rises in sea level associated with increased ice-rafted debris and southward shifts in the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately-sized ice sheets may have been responsible for the cold reversals causing the AMOC to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events. [ABSTRACT FROM AUTHOR]