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The regional impact of abrupt glacial climate variability remains poorly constrained for arid southwestern Asia, particularly winter dynamics during Marine Isotope Stage 3, due to limited paleoarchives in the Middle East. Here, we present continuous speleothem records of δ18O and δ13C with robust chronologies for southwestern and central Iran, spanning ∼50–30 ka. Stable‐isotope signals in the two stalagmites are generally uncorrelated and do not exhibit a consistent response to Greenland stadials or interstadials; however, both show a positive δ18O excursion that coincides with Heinrich event 4. We explore the potential mechanisms for intermittent coupling of speleothem δ18O across Iran through isotope‐enabled atmospheric modeling outputs, from which we utilize the spatial δ18O gradient as a proxy for wintertime westerly versus southerly jet strength. Our results suggest that during Heinrich event 4 and several Greenland stadials, stronger westerly winds enhanced Mediterranean moisture contributions to both sites and reduced aridity in southern Iran. Plain Language Summary: Stalagmites are useful archives to reconstruct the climate of the past. In order to shed light on the past climate of western Asia and the response of this region to the rapid climate changes, here we present two stalagmites from central and southwestern Iran that span 50,000 to 30,000 yrs ago. Our findings suggest that during extreme cold events, the moisture originates mostly from the west, whereas out of these extraordinarily cold periods moisture comes mostly from the south. Key Points: Continuous high‐resolution speleothem record of climatic change in southwestern and central Iran between 50 and 30 kaDecoupled responses of stable‐isotope gradients in central and southern Iran to glacial climate variability, except during Heinrich event 4Decreased impact of southerly moisture sources and reinforced westerlies during extreme cold events [ABSTRACT FROM AUTHOR]

ABSTRACT A flowstone from the central European Abaliget Cave (Mecsek Mts, Hungary) provides a record of uninterrupted calcite deposition between ∼160 and ∼124 ka, covering most of Marine Isotope Stage (MIS) 6 and part of 5e. δ18O values of three lateral drill cores show synchronous high-frequency (millennial-scale) variability during MIS 6, interpreted as stadials and interstadials, and a 3.4‰ rise at the MIS 6/5e boundary. The interstadials are mostly symmetrical in shape and show consistently lower δ18O values than calcite formed during MIS 5e. The rises (decreases) in δ18O are followed by drops (increases) in δ13C with a delay of 1-2 ka, implying enhanced (reduced) soil bioproductivity. This period of highly variable climate is bracketed by two broad δ18O minima. The first minimum between ∼160 and ∼148 ka coincided with a maximum in ice-rafted detritus in the eastern North Atlantic. The second one from ∼134 to ∼129 ka occurred during Heinrich 11, before the rapid and large δ18O increase at ∼128 ka. [ABSTRACT FROM AUTHOR]

The Devils Hole Ridge, a small block of Paleozoic carbonate rocks surrounded by the Amargosa Desert in southern Nevada, is located at the discharge end of the Ash Meadows regional carbonate groundwater flow system. The massif hosts the famous Devils Hole, a near-vertical extensional fracture which intersects slightly thermal groundwater (33.6 °C) and whose walls are coated below the water table by thick mammillary calcite. The latter was deposited continuously over the last ca. 600 kyr, indicating that the water underneath Devils Hole Ridge was supersaturated with respect to calcite during this time span. Rocks, located more than 9 m above the present-day water table, remained in the unsaturated (vadose) zone. Continuous, long-term presence of thermal water and the extensional tectonic setting, creating underground thermal lakes in open fractures, is associated with intense dissolution above the water table. Condensation corrosion is responsible for modifications of the morphology of the subaerial parts of the tectonic caves. We also describe, for the first time, the Devils Hole Prospect Cave, which was created almost entirely by condensation corrosion. Caves and cavities in the Devils Hole Ridge are an interesting example of hypogene speleogenesis, by condensation corrosion, operating above an aquifer which was demonstrably supersaturated with respect to calcite for hundreds of thousands of years. [ABSTRACT FROM AUTHOR]

Cryogenically formed carbonate particles represent a rather new class of speleothems whose origin is directly linked to the presence of perennial ice in the subsurface. Recent studies concluded that dating these deposits provides important time constraints on the presence and the thickness of permafrost, e.g., during the last glacial period. More precisely, these carbonates record episodes of progressive karst water freezing. Such conditions have been associated with periods of permafrost thawing allowing the infiltration of meltwater into formerly dry, frozen caves. To shed more light on the origin of the coarsely crystalline variety of these cryogenic cave carbonates--CCCcoarse for short--we examined a high-elevation cave site in the western part of the Austrian Alps which is located in an area dominated by permafrost features and transformed from an ice cave into an essentially ice-free cave during the past decade. Two side chambers of the main gallery revealed cryogenic calcite deposits whose isotopic composition indicates that they formed in individual pools of water carved in ice which underwent very slow freezing under closed-system conditions, i.e., enclosed in ice. 230Th dating shows that most of these carbonates formed ca. 2600 yr BP. Based on comparisons with other palaeoclimate archives in the Alps this thawing episode did not occur during a climate optimum, nor did CCCcoarse form in this cave during, e.g., the Roman or the Medieval Warm Periods. Our results suggest that the occurrence of CCCcoarse, at least in mountain regions characterized by discontinuous permafrost, may be more stochastic than previously thought. Given the inherent heterogeneity of karst aquifers and the important role of localized water infiltration in modifying the thermal structure of the subsurface, we caution against attributing CCCcoarse occurrences solely to peak warming conditions, while confirming the unique significance of these deposits in providing robust age constraints on permafrost thawing episodes. [ABSTRACT FROM AUTHOR]

Coarse crystalline cryogenic cave carbonates (CCCcoarse) 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 CCCcoarse formed as no modern analogue setting is known. Here, we report the first findings of sub-recent, albeit inactive, CCCcoarse 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 CO2, 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 CCCcoarse resulted from the re-freezing of this water in the still cold karst cavities. [ABSTRACT FROM AUTHOR]

The interpretation of stable isotope ratios in speleothem calcite is complex, and only in a few cases, unequivocal relationships with palaeoclimate parameters have been attained. A major issue is temperature, which has an effect on both the isotope incorporation into calcite and on environmental processes. Here, a field approach is taken, by studying the isotopic composition of calcites from monitored caves located in steep altitudinal topography in the northern Italian Alps. These create a thermal gradient (3-12 °C) apt to study the effects of temperature on the speleothem isotope record. Our data indicate that the magnitude of oxygen isotope disequilibrium effects, calculated as an offset from the experimentally determined equilibrium, decreases with increased elevation (cooler temperatures) and faster drip rate. Carbon isotope values exhibit 13C enrichment at high altitudes (colder temperatures) and slow drip rates. The results obtained support modelling and laboratory cave analogue experiments that indicate temperature, drip rate, pCO2 and supersaturation are important factors controlling stable isotope fractionation, but also stress the significance of ventilation and evaporation in the cave environment. It is proposed that the effects on stable isotope ratios observed along the altitudinal gradient can be analogues for glacial to interglacial temperature changes in regions which were extensively glaciated in the past. [ABSTRACT FROM AUTHOR]

Here we explore the potential of magnesium (δ26Mg) isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semiarid to arid (Morocco), the warm-temperate (Germany), the equatorial-humid (Peru) and the cold-humid (Austria) climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and disequilibrium processes governs the δ26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rainwater or snow as well as soil and host rock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ26Mg values (GDA: -4.26±0.07‰and HK3: -4.17±0.15 ‰), and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value of all stalagmites (NC-A and NC-B δ26Mg: -3.96±0.04 ‰) but only minor variations in Mg-isotope composition, which is consistent with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ26Mg: -4.01±0.07 ‰; BU 4 mean δ26Mg: -4.20±0.10 ‰) suggest changes in outside air temperature was the principal driver rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: -3.00±0.73 ‰; SPA 59: -3.70±0.43 ‰) are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity and weathering balance. Several δ26Mg values of the Austrian and two δ26Mg values of the German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well-calibrated leaching and precipitation experiments. [ABSTRACT FROM AUTHOR]

Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present highresolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation. [ABSTRACT FROM AUTHOR]

Large changes of the climate can dramatically affect the environment surrounding and within a cave. This variability, including temperature shifts, can change the amount of in-cave isotopic fractionation affecting speleothems, potentially leaving these records difficult to interpret. Here, caves located in steep altitudinal topography in the Northern Italian Alps are used to create a thermal gradient (3-12 °C) to study the effects of temperature on the speleothem isotope record. The data indicate that the amount of incave oxygen isotope fractionation is reduced to minimum values of around 0.25‰ with cooler temperatures and under faster dripping stalactites, which infers that such sites would be most suitable for palaeoclimate reconstruction. However, when considering the possible freezing periods, reduced saturation index and fluctuating drip rates, such sites appear less than ideal for study on long timescales. The importance of picking the best site(s) within a cave for palaeoclimate reconstruction is paramount, to reduce the in-cave fractionation and gain a record that reflects climate changes. A method for rapid determination of calcite fractionation is demonstrated here, through prior cave monitoring of dripwaters and calcite precipitates, permitting an informed choice of speleothems for further study. [ABSTRACT FROM AUTHOR]

The geochemical signature of many speleothems used for reconstruction of past continental climates is affected by kinetic isotope fractionation. This limits quantitative paleoclimate reconstruction and, in cases where the kinetic fractionation varies with time, also affects relative paleoclimate interpretations. In carbonate archive research, clumped isotope thermometry is typically used as proxy for absolute temperatures. In the case of speleothems, however, clumped isotopes provide a sensitive indicator for disequilibrium effects. The extent of kinetic fractionation co-varies in Δ47 and δ18O so that it can be used to account for disequilibrium in δ18O and to extract the past drip-water composition. Here we apply this approach to stalagmites from Bunker Cave (Germany) and calculate drip-water δ18Ow values for the Eemian, Marine Isotope Stage (MIS) 3, and the Holocene, relying on independent temperature estimates and accounting for disequilibrium. Applying the co-variation method to modern calcite precipitates yields drip-water δ18Ow values in agreement with modern cave drip-water δ18Ow of -7.9 ± 0.3‰, despite large and variable disequilibrium effects in both calcite δ18Oc and Δ47. Reconstructed paleo-drip-water δ18Ow values are lower during colder periods (e.g., MIS 3: -8.5 ± 0.4‰ and the early Holocene at 11 kyr: -9.3 ± 0.1‰) and show higher values during warmer climatic periods (e.g., the Eemian: -7.5 ± 0.2‰ and the Holocene Climatic Optimum: -7.2 ± 0.3‰). This new approach offers a unique possibility for quantitative climate reconstruction including the assessment of past hydrological conditions while accounting for disequilibrium effects. [ABSTRACT FROM AUTHOR]

Here we present high-resolution stable isotope and lamina thickness profiles as well as radiocarbon data for the Holocene stalagmite ER 76 from Grotta di Ernesto (North-Eastern Italy), which was dated by combined U-series dating and lamina counting. ER 76 grew between 8 ka (thousands of years before 2000 AD) and today, with a hiatus from 2.6 to 0.4 ka. Data from nine meteorological stations show a significant influence of the North Atlantic Oscillation (NAO) on winter precipitation in the cave region. Spectral analysis of the stable isotope signals of ER 76 reveals significant peaks at periods of 110, 60-70, 40-50, 32-37 and around 25 a. Except for the cycle between 32 and 37 a all periodicities have corresponding peaks in power spectra of solar variability, and the 25-a cycle may correspond to NAO variability. This suggests that climate variability in Northern Italy was influenced by both solar activity and the NAO during the Holocene. Six periods of warm winter climate in the cave region were identified. These are centred at 7.9, 7.4, 6.5, 5.5, 4.9 and 3.7 ka, and their duration ranges from 100 to 400 a. The two oldest warm phases coincide with the deposition of sapropel S1 in the Mediterranean Sea indicating that the climate in the cave region was influenced by this prominent pluvial phase in the Mediterranean area. For the younger warm phases it is difficult to establish a supra-regional climate pattern, and some of them may, thus, reflect regional climate variability. This highlights the complexity of regional and supra-regional scale Holocene climate patterns. [ABSTRACT FROM AUTHOR]

The stable oxygen isotope parameter δ18O remains the most widely utilised speleothem proxy for past climate reconstructions. Uncertainty can be introduced into stalagmite δ18O from a number of factors, one of which is the heterogeneity of groundwater flow in karstified aquifers. Here, we present a lumped parameter hydrological model, KarstFor, which is capable of generating monthly simulations of surface water -- ground water -- stalagmite δ18O for more than thousand year time periods. Using a variety of climate input series, we use this model for the first time to compare observational with modelled (pseudoproxy) stalagmite δ18O series for a site at Assynt, NW Scotland, where our knowledge of δ18O systematics is relatively well understood. The use of forward modelling allows us to quantify the relative contributions of climate, peat and karst hydrology, and disequilibrium effects in stalagmite δ18O, from which we can identify potential stalagmite δ18O responses to climate variability. Comparison of the modelled and actual stalagmite δ18O for two stalagmites from the site demonstrates that for the period of overlapping growth, the two series do not correlate with one another, but forward modelling demonstrates that this falls within the range explicable by differences in flow routing to the stalagmites. Pseudoproxy δ18O stalagmite series highlight the potential significance of peat hydrology in controlling stalagmite δ18O over the last 1000 years at this site. [ABSTRACT FROM AUTHOR]

Accurate and precise chronologies are essential in understanding the rapid and recurrent climate variations of the Last Glacial - known as Dansgaard-Oeschger (D-O) events - found in the Greenland ice cores and other climate archives. The existing chronological uncertainties during the Last Glacial, however, are still large. Radiometric age data and stable isotopic signals from speleothems are promising to improve the absolute chronology. We present a record of several precisely dated stalagmites from caves located at the northern rim of the Alps (NALPS), a region that favours comparison with the climate in Greenland. The record covers most of the interval from 120 to 60 ka at an average temporal resolution of 2 to 22 yr and 20-age uncertainties of ca. 200 to 500 yr. The rapid and large oxygen isotope shifts of 1 to 4.5‰ occurred within decades to centuries and strongly mimic the Greenland D-O pattern. Compared to the updated Greenland ice-core timescale (GICC05modelext) the NALPS record confirms the timing of rapid warming and cooling transitions between 118 and 106 ka, but suggests younger ages for D-O events between 106 and 60 ka. As an exception, the timing of the rapid transitions into and out of the stadial following GI 22 is earlier in NALPS than in the Greenland ice-core timescale. In addition, there is a discrepancy in the duration of this stadial between the icecore and the stalagmite chronology (ca. 2900 vs. 3650 yr). The short-lived D-O events 18 and 18.1 are not recorded in NALPS, provoking questions with regard to the nature and the regional expression of these events. NALPS resolves recurrent short-lived climate changes within the cold Greenland stadial and warm interstadial successions, i.e. abrupt warming events preceding GI 21 and 23 (precursor-type events) and at the end of GI 21 and 25 (rebound-type events), as well as intermittent cooling events during GI 22 and 24. Such superimposed events have not yet been documented outside Greenland. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to measure the mass and energy balance of ice within the Eisriesenwelt cave in Austria. Data from meteorological measurements show the basic features of a dynamically ventilated cave system with a well distinguished winter and summer regime. It concludes that the reliability of the calculated energy balance regarding diverse measurement uncertainties and show that the annual mass balance of the ice depends on cave air temperature.

The article reports on a study regarding the highest density of ice-bearing caves at Eisriesenwelt cave in Austria. The study conducted visual core inspections, quasi-continuous measurements, stable water isotope and electrolytic conductivity profiles to analyze tritium and radiocarbon. It suggests undergoing further studies that would greatly help better understand high-frequency variability as well as the systematic changes seen in total ion content, cryocalcite and water isotope.

Dripwater hydrology and hydrogeochemistry is particularly useful in constraining the meaning of speleothem palaeoclimate archives, for example using δ18O signatures. Here, we calibrate the relationship between δ18O in precipitation, percolation waters and contemporary calcite deposits, at Tartair cave, Sutherland, NW Scotland, an Atlantic site sensitive to regional changes both of temperature and precipitation. Monthly precipitation displayed a 7.1‰ range in δ18O, a negative linear relationship with rainfall amount, and no correlation with temperature. Autogenically-derived cave percolation waters show little variation in δ18O during the same period and their annual weighted mean is the same as that of the local precipitation. This evidence together with hydrological data and electroconductivity values indicates that percolation waters are well mixed and dominated by stored water. Calculated values of δ18O of calcite deposited in this cave environment indicate that the cave deposits are forming close to isotopic equilibrium and kinetic effects are negligible. Comparison of a high-resolution δ18O stalagmite record with the instrumental record of climate indicates that isotopically heavy values are reflective of relatively cold, dry conditions (and vice-versa for warm, wet condition) and hence that stalagmite oxygen isotopes provide an appropriate means of investigating the palaeoclimate in this location. [ABSTRACT FROM AUTHOR]