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We present a 500‐year precipitation‐sensitive record based on co‐varying speleothem δ18O values and Mg/Ca ratios from Larga cave in Puerto Rico. This multi‐proxy record shows that the evolution of rainfall in the northeastern Caribbean was characterized by alternating centennial dry and wet phases corresponding to reduced versus enhanced convective activity. These phases occurred synchronous with relatively cool and warm tropical Atlantic sea‐surface temperatures (SSTs), respectively. While the observed pattern suggests a close link of northeastern Caribbean rainfall to the Atlantic Multidecadal Variability, a regional comparison reveals intermittent regional heterogeneity especially on decadal timescales, which may be related to a superimposing influence of the Pacific and Atlantic basins. Furthermore, the speleothem‐based hydroclimate reconstruction indicates a significant volcanic impact during the past two centuries, and further reveals a potential solar signal in the preceding three centuries. We posit that the forcing likely shifted from solar to volcanic during the eighteenth century in being an important source of multidecadal to centennial Caribbean rainfall variability. The link between convective rainfall and natural forcing may be explained through a modulation of SST variations in the tropical Atlantic and Pacific oceans. Plain Language Summary: Climate change is expected to affect rainfall throughout the Caribbean and Central America, where over 200 million people are heavily dependent upon rain as their main source of freshwater. We have looked at how the amount of rainfall in the Caribbean has changed through time, and possible reasons for these changes, to inform predictions of future rainfall patterns for the region. Cave mineral deposits, also known as speleothems, can be used to assess the amount of regional rainfall in the past by looking at their slight changes over time in the mineral's chemical composition. We created a record of Caribbean rainfall spanning the last five centuries using a speleothem from Puerto Rico. Our results indicate that rainfall changes since the sixteenth century were strongly influenced by changes in temperatures of the surface waters of the Atlantic Ocean. We further found that changes in the sun's brightness and volcanic eruptions may alter Atlantic Ocean sea‐surface temperature, which in turn affect the overall changes in Caribbean rainfall patterns. Key Points: Speleothem‐based Puerto Rican rainfall reconstruction shows prominent multidecadal‐to‐centennial variability during the past five centuriesPuerto Rican rainfall fluctuations are linked to solar variations before the eighteenth century and volcanic forcing thereafterCaribbean Sea‐surface temperature anomalies as part of the Atlantic Multidecadal Variability emerge as robust precursor of rainfall amounts [ABSTRACT FROM AUTHOR]

This short article provides detailed descriptions of custom-made and commercially available hand-held drilling gear and options for water-flushing units specifically designed to obtained good-quality core material from speleothems even in remote cave regions. We use small-diameter (6-7 mm) diamond drill-core bits to obtain aliquots of calcite (as little as a few hundred milligrams) from the interior of the basal part of in-situ stalagmites. These small cores are used to date the onset of stalagmite growth and occasionally to obtain other compositional information. Larger diameter drill-core bits produce cores 25-32 mm in diameter and up to 1.3 m in length which reveal internal structures and provide axial transects for chemical and isotope analysis and material for preparation of thin sections. This system has been successfully employed to sample flowstone and thick stalagmites. Given the growing interest in speleothem as archives of past environmental change, careful sample selection is primordial to keep the impact of sampling in these unique environments at a minimum. Low-invasive drilling is an essential technique and maximizes the amount of information gained.

We examined 14 subaerially deposited speleothems retrieved from submerged caves in the northeastern Yucatán Peninsula (Mexico). These speleothems grew during the Middle to Late Quaternary and were dated by 230Th‐U techniques to provide upper depth limits for past sea levels. We report the first relative sea‐level limits for Marine Isotope Stages (MIS) 11 and 6, and present new evidence for sea‐level oscillations during MIS 5 and early MIS 1. For the latter periods, the origin of growth interruptions is evaluated by combining petrographic methods with trace element analyses. The MIS 5c sea‐level highstand probably occurred between 103.94 ± 0.58 ka and 96.82 ± 0.42 ka and must have exceeded ‐10.8 m (relative to present‐day local sea level). The minimum average rate of sea‐level fall over a 9.4 ka‐long period during the MIS 5e/5d transition is calculated from stalagmite and published coral data at 1.74 ± 0.37 m/ka. For the early Holocene, previous discrepancies with respect to a potential multimetre oscillation of local sea level were found to be challenging to reconcile with the existing speleothem data from the area. [ABSTRACT FROM AUTHOR]

The abrupt climate event Younger Dryas (YD) has been extensively studied; however, its structure is still poorly understood. Climate in northeastern Brazil is very sensitive to the latitudinal position of the intertropical convergence zone (ITCZ) associated with abrupt climate change in the Atlantic. Here, we report changes in the ITCZ position within the YD by using precise speleothem multiproxy records from northeastern Brazil. We provide evidence for a gradual northward migration of the ITCZ preceding poleward shifts of the westerlies and the polar front in northern high latitudes within the YD. This can be attributed to gradual increase in atmospheric CO2 concentration as a consequence of the weakening Atlantic Meridional Overturning Circulation (AMOC). We suggest that a persistent increase in atmospheric CO2 might have triggered a resumption of the AMOC and reorganization of the atmosphere circulation in the Atlantic during the mid‐YD. Plain Language Summary: The Younger Dryas (YD) is the most recent millennial‐scale abrupt climate event in Earth history. Although its origin has been extensively studied, its structure is still poorly understood. Climate in northeastern Brazil is very sensitive to the latitudinal position of the intertropical convergence zone (ITCZ) responds to abrupt climate change in the Atlantic (e.g., YD). By using stable isotope and trace element proxy records of speleothem from Toca da Boa Vista Cave, northeastern Brazil, together with other paleoclimatic records in the Atlantic realm, we provide evidence for a gradual northward migration of the ITCZ preceding poleward shifts of the westerlies and the polar front in northern high latitudes within the YD. This can be attributed to a gradual increase in atmospheric CO2 concentration under the situation of weakening Atlantic Meridional Overturning Circulation (AMOC). A persistent increase in atmospheric CO2 concentration might have triggered a resumption of the AMOC and reorganization of the atmosphere circulation in the Atlantic during the mid‐YD. Key Points: Speleothem and other paleoclimate records confirm a wet climate in tropical South America within the Younger DryasPrecise speleothem multiproxy records reflect a bipartition of the Younger Dryas precipitation in northeastern BrazilGradual South‐North climate transition in the Atlantic responded to a gradual increase in atmospheric CO2 within the YD [ABSTRACT FROM AUTHOR]

The climate of the western Mediterranean was characterized by a strong precipitation gradient during the Holocene driven by atmospheric circulation patterns. The scarcity of terrestrial paleoclimate archives has precluded exploring this hydroclimate pattern during Marine Isotope Stages 5 to 3. Here we present stable carbon and oxygen isotope records from three flowstones from southeast Iberia, which show that Dansgaard/Oeschger events were associated with more humid conditions. This is in agreement with other records from the Iberian Peninsula, the Mediterranean, and western Europe, which all responded in a similar way to millennial‐scale climate variability in Greenland. This general increase in precipitation during Dansgaard/Oeschger events cannot be explained by any present‐day or Holocene winter atmospheric circulation pattern. Instead, we suggest that changes in sea surface temperature played a dominant role in determining precipitation amounts in the western Mediterranean. Plain Language Summary: Climate events characterized by a sudden temperature increase of up to 10 °C occurring in less than a few decades during the last glacial are recorded in Greenland ice cores. These abrupt warmings, the Dansgaard/Oeschger events, affected large regions of the Northern Hemisphere. The understanding of the regional response in precipitation during these climate shifts is limited for the western Mediterranean, due to the restricted number of terrestrial climate records that cover the last glacial period at sufficient resolution. Speleothems and their stable isotope compositions allow to trace changes in climate and vegetation based on an accurate chronological framework. Here we present a speleothem stable isotope record that shows that the Dansgaard/Oeschger events were associated with increased rainfall and a denser vegetation in the western Mediterranean. A similar pattern was observed for western Europe and other parts of the Mediterranean, and we propose that this was related to generally higher sea surface temperatures of the surrounding oceans rather than a reorganization of atmospheric circulation. Key Points: Western Mediterranean precipitation responded to Greenland interstadials and stadials in a coherent mannerDansgaard/Oeschger interstadials were accompanied by humid climate conditions over the western MediterraneanAtmospheric circulation patterns did not induce spatial differences in precipitation during the last glacial as they did during the Holocene [ABSTRACT FROM AUTHOR]

The cave bear was a prominent member of the Upper Pleistocene fauna in Eurasia. While breakthroughs were recently achieved with respect to its phylogeny using ancient DNA techniques, it is still challenging to date cave bear fossils beyond the radiocarbon age range. Without an accurate and precise chronological framework, however, key questions regarding the palaeoecology cannot be addressed, such as the extent to which large climate swings during the last glacial affected the habitat and possibly even conditioned the final extinction of this mammal. Key to constraining the age of cave bear fossils older than the lower limit of radiocarbon dating is to date interlayered speleothems using 230Th/U. Here we report new results from one such site in the Eastern European Alps (Schwabenreith Cave), which yielded the highest density of bones of cave bear (Ursus spelaeus eremus). Although dating of the flowstones overlying this fossiliferous succession was partly compromised by diagenetic alteration, the 230Th/U dates indicate that the bear hibernated in this cave after about 113 ka and before about 109 ka. This time interval coincides with the equivalent of Greenland Stadial 25, suggesting possible climate control on the cave bear's habitat and behaviour. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

Coarsely crystalline carbonates that formed cryogenically in caves (CCC coarse for short) are important paleoenvironmental archives that provide evidence of former perennial ice deposits in currently ice-free caves and allow the timing of the past freezing conditions close to 0 °C in the subsurface to be determined. Despite their significance, the mode of formation of these deposits has never been observed in statu nascendi. We conducted a series of freezing experiments in an Alpine ice cave to test the conceptual model of CCC coarse formation in freezing pools of water in perennial ice deposits. Our results document a number of features associated with the freezing of such confined water bodies, including ice bulging, cracking and episodic expulsion of water. These observations help explain the degassing of carbon dioxide required to maintain carbonate precipitation in these semi-closed pockets of slowly freezing water. Our experiments yielded a range of morphological types of cryogenic calcite crystals and aggregates comparable to those reported from CCC coarse from currently ice-free caves elsewhere. The experimentally grown crystals also exhibit the same depleted O isotope composition characteristic of natural carbonates interpreted as being formed subaqueously in a semi-closed pools subject to freezing. The main difference to naturally formed CCC coarse is their smaller crystal size, reflecting the comparably short freezing time of our experiments of less than two weeks. This study confirms the conceptual model explaining the formation of CCC coarse in localized pools in ice and calls for a revision of the currently existing classification scheme for cryogenic cave carbonates. [ABSTRACT FROM AUTHOR]

The use of moonmilk for medical and other purposes in the Alps is documented since the 16th century. This article reviews speleological reports and sparse historical accounts about the extraction of moonmilk from 18 caves in the Eastern Alps of Austria in an artisan mining style. One such example from a cave in Tyrol is documented in detail, where moonmilk was mined until the beginning of the 20th century and which, due to its remote location, uniquely preserved traces of both the mining and processing style. [ABSTRACT FROM AUTHOR]

Aragonite is a common mineral in caves hosted in dolomitic bedrock, and in particular in those from warm climate regions. It is much less common in cold caves, such as in the Alps, where the vast majority of speleothems consist of low-Mg calcite. Here we report the occurrence of modern aragonite at very low temperatures, the first of its kind from an alpine cave. In the interior part of Obstanser Eishöhle, a high-alpine cave containing perennial ice in its near-entrance zone, aragonite forms stalactites and flowstones, which coexist with calcite and locally also hydromagnesite. Precipitation of aragonite occurs at saturation indices between 0.4 and 0.6 at 1.0 ± 0.4 °C. Modern 230 Th dates of the youngest aragonite deposits demonstrate that aragonite formation is an ongoing process. δ 13 C values are high and overlap with those of the host rock. A comparison between δ 18 O values of aragonite and drip water showed that modern aragonite formation does not occur at isotopic equilibrium. Surprisingly, no radiocarbon “bomb peak” was detected in these speleothems, despite their young age. In addition, these samples are characterized by extremely high reservoir ages between 8800 and 10,100 yr, the highest ever reported for a speleothem worldwide. These data are best reconciled with a model of karst dissolution largely decoupled from the soil zone. Oxidation of disseminated pyrite in the dark gray host rock gives rise to acidic solutions driving carbonate dissolution. The dolomitic nature of the bedrock, prior calcite precipitation and ventilation-enhanced degassing leads to high Mg/Ca ratios in the drip water favoring aragonite formation. These in-situ observations confirm previous findings that temperature is not the dominant control on calcite versus aragonite formation in caves. They also suggest that ancient aragonite speleothems should be examined carefully and ideally be compared to coeval calcite samples prior to interpreting their stable isotope data in terms of environmental/climatic changes. [ABSTRACT FROM AUTHOR]

We present an update (COMNISPA II) of a precisely dated, high-resolution speleothem δ18O record from the Austrian Alps. COMNISPA II consists of five stalagmites from Spannagel Cave, which have comparable δ18O values within periods of simultaneous growth and show similar δ18O variations on centennial to millennial timescales. This allows combining the five stalagmites to one composite record using a newly developed statistical approach. The COMNISPA II stack differs slightly from the previous version, but is better constrained because of additional stalagmites used for the reconstruction and a more objective method used for constructing the composite record. Furthermore, the record now covers the last 11 ka and shows variations in δ18O values by about 2‰. As previously shown, these variations compare well with other records in central Europe and the North Atlantic, and thus reflect a large-scale climate evolution. [ABSTRACT FROM PUBLISHER]

Marble beds in the Tux Valley, Tyrol, host a series of cave systems, currently hydrologically largely inactive, the largest of which (Spannagel Cave) has ca. 11 km of explored passages. Despite their high elevation and low interior air temperatures (only barely above 0°C) calcitic speleothems are not uncommon in these caves and have been the focus of a long-term paleoclimate research project. In this study we take advantage of this comprehensive data set of stalagmite and flowstone samples, whose chronology is precisely established by U-Th dating. We utilize these samples to provide temporal and spatial constraints on speleogenetic processes including the formation of prominent canyons and the occurrence of floods. The data show that in spite of its proximity to a modern glacier, Spannagel Cave's prominent erosion features date back at least three glacial cycles. Unconsolidated sand and gravel are wide-spread in this cave and represent till and glaciofluvial sediment washed into the cave between 48 and 13 kyr. The strikingly small hydrological impact of the last few glaciations (and deglaciations) is consistent with (a) the antiquity of these high-elevation caves whose origin seems to be unrelated to today's adjacent glacier, and (b) underscores the unique preservation potential of cave systems and their sedimentary inventory. This is in stark contrast to the high rates of glacial erosion on the surface above the cave. [ABSTRACT FROM AUTHOR]

Abstract: U–Pb dating is increasingly used to date speleothems that are too old for precise U–Th disequilibrium dating; however there is little data that can independently validate its application to such material. This study presents U–Pb ages for speleothems from the Spannagel Cave in the Austrian Alps including a detailed comparison with U–Th ages from an unusually U–rich sample that yields precise ages by both methods. Sample SPA4 is a flowstone with three growth phases separated by distinct hiatuses. For the youngest growth phase the U–Pb and U–Th ages are 267±1ka and 267±5ka respectively; the middle growth phase is 291±1 versus 295±11ka while for the oldest growth phase a single sub-sample, assuming the same initial Pb composition as for the younger phases, yields an age of 340±2ka compared to 353±9ka by U–Th. Correlation of these ages with the marine isotope stages confirms that these speleothems grew during glacial stages as suggested by previous work on the same sample. Sample SPA 15 has U–Th isotopic compositions indistinguishable from secular equilibrium; the U–Pb data on the main growth phase of this sample give an age of 551±10ka, whereas a single analysis from the oldest phase suggests it may be on the order of 40ka older. This detailed comparison of U–Pb and U–Th ages provides important support for the potential validity of the U–Pb method in older samples beyond the range of U–Th. [ABSTRACT FROM AUTHOR]

Abstract: Here we present the first U-series dated stable oxygen isotope record in continental Europe that covers the entire tripartite Penultimate Interglacial, i.e. Marine Isotope Stages 7.5 to 7.1. This record was obtained from a U-rich stalagmite from Spannagel Cave in the Austrian Alps which is largely devoid of kinetic isotope fractionation effects which comprised previously studied flowstone from this site. Composed of dense, columnar calcite this speleothem apparently grew without significant interruption for ca. 50 ka, albeit at a very slow rate. The age model was established based on 23 individual U/Th TIMS dates using a combination of a Bayesian approach, which includes additional information using stratigraphic constraints, and the mixed-effect regression model. The resulting record shows three prominent maxima in δ18O (MIS 7.5, 7.3 and 7.1) separated by a long earlier and a shorter later cold period (MIS 7.4 and 7.2, respectively). The mid points of the transitions into the three warm phases occurred at 240±3, 215±2 and 200±3 ka and the MIS 7/6 transition was dated to 190±3 ka. The timing of these climate transitions is supported by other samples from the same cave and agrees within analytical uncertainties with U/Th-dated evidence from corals, marine aragonitic sediments and submerged stalagmites, as well as with orbitally tuned deep-sea records. Good agreement was also found with new speleothem data from China as far as MIS 7.1 and 7.5 are concerned, whereas MIS 7.3 apparently started earlier and MIS 7.2 lasted longer than in the Alps. Comparing the European speleothem data with Antarctic ice cores reveals obvious differences in age (the latter suggesting an earlier start and a generally shorter duration of the three warm episodes). In essence, this study underscores the great potential of speleothems as accurate and precise chronometers of Pleistocene climate change and emphasizes the need for similar studies in other continents (including submerged caves) in order to improve the imperfect chronological framework of MIS 7. [Copyright &y& Elsevier]

Abstract: Three different techniques are currently in use to microsample speleothem (and tufa) specimens at moderate to high spatial resolution, manual microdrilling using a dentist drill, semi automated micromilling, and laser ablation. While a separate handling step is involved in the first two techniques — transferring the sample powder to an on-line carbonate preparation system linked to an isotope ratio mass spectrometer — the laser is directly interfaced with the mass spectrometer via a gas preparation device. In this study we compare stable C and O isotope results obtained by these three preparation techniques using continuous He-flow mass spectrometry on the same speleothem samples. The overall consistency of the results is satisfactorily high, in particular between the micromill and the laser data. Although the precision of the laser data is slightly lower than analyses obtained by the other two methods (in particular with respect to δ18O), the speed of acquisition renders laser ablation a useful reconnaissance technique for rapidly analyzing long sections of speleothems. Micromilling is the method of choice to obtain highly spatially resolved isotope data of high analytical precision, while microdrilling is still an low-cost alternative for sampling at comparably low resolution, e.g. of fast growing stalagmites. [Copyright &y& Elsevier]

Abstract: Calcitic flowstones are present in fractures of a Pleistocene breccia near Innsbruck, Austria, and record periods of carbonate precipitation in the unsaturated zone between 101,500 ± 1500 and 70,300 ± 1800 yr, constrained by U-series disequilibrium dates. The occurrence of these speleothems, their low carbon isotopic composition, and the lack of infiltrated siliciclastic material demonstrate that the central Inn valley – which harbored one of the most extensive valley glaciers during the last glacial maximum – was ice-free during Marine Isotope Stages 5c to 5a. Climatically warm periods are separated by distinct drops in the oxygen isotopic composition of the speleothem calcite, attributed to strong and possibly seasonally biased atmospheric cooling. During these intervening stadials, which mirror those identified in the Greenland ice cores and marine sea-surface temperature records, calcite deposition apparently came to a halt, but the Inn Valley remained ice-free. The youngest calcite layer formed between ∼74,000 and ∼70,000 yr and places a maximum age limit on the likely expansion of alpine glaciers during the Marine Isotope Stage 5/4 transition, consistent with other speleothem records. [Copyright &y& Elsevier]

We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Multiple proxies were used to reconstruct Caribbean hydroclimate and vegetation variability on orbital to millennial timescales. In particular, our proxies indicate a shift to more abundant C4 (compared to C3) vegetation and/or reduced soil activity during the Last Glacial Maximum. Our results confirm the close link of Caribbean precipitation to North Atlantic climate variability, insolation and the strength of the AMOC. The associated variations in Caribbean SSTs and the shift of the ITCZ led to substantial changes of the hydrological cycle. During Heinrich stadials and the Younger Dryas, climatic conditions in Cuba were comparably cool and/or dry. In contrast, warm Dansgaard/Oeschger cycles were accompanied by wetter conditions. This is in agreement with previous evidence for the Holocene, when North Atlantic cold (warm) events coincided with drier (wetter) conditions in Cuba. However, our record suggests that this connection was less dominant during MIS 4 to 2, displayed by a weaker response of Cuban precipitation proxies to North Atlantic climatic shifts than during MIS 5 in particular. We hypothesize that this weaker connection was mediated by the southerly shifted ITCZ inducing a weakening of the northern branch of the Caribbean Low Level Jet which usually transports moisture into the northern Caribbean. This is strikingly evident during the deglacial, when driest and/or coolest conditions prevailed in western Cuba from HS 1 into the Younger Dryas, including the Bølling/Allerød interstadial. • We present a speleothem stable isotope and trace element record from Cuba covering the last 96 ka. • Our results confirm the link of Caribbean precipitation to NA climate, insolation and the AMOC. • Last glacial NA cold (warm) (inter)-stadials coincided with drier (wetter) conditions in Cuba. • During the LGM, our data suggest a shift to more abundant C4 vegetation and/or reduced soil activity. • We observe a weaker sensitivity to NA climate during MIS 4 to 2 compared to MIS5 and the Holocene. [ABSTRACT FROM AUTHOR]

Cryogenic cave carbonates (CCCs) genetically related to permafrost are of special interest in paleoclimate research. Their 230Th/U ages provide unique information about the former presence and depth of permafrost in presently permafrost-free areas. Details of CCC formation processes and their diagnostic features, however, remain incompletely understood. In this paper, we report the results of a study of CCCs from two northern Eurasian caves, currently located in permafrost-free rocks. CCCs in the caves occur in a wide range of grain sizes (micrometers to several centimeters). Stable isotope values of different CCC morphotypes (size range of 0.1 to 4 mm) plot within relatively tight clusters in δ18O-δ13C space, regardless of their grain size, indicating that CCCs of the same morphotype, but of different size, formed simultaneously at certain freezing stages. The clusters conform to an overall negative "freezing trend" in δ18O-δ13C space. The position on the trend indicates the relative age of individual morphotypes; scatter of the data in δ18O-δ13C space suggests multiple episodes of freezing (permafrost formation). The systematic characterization of CCC morphologies and the study of fine-size fractions of CCCs provide important insights into the processes involved in CCC formation in caves located in permafrost. [ABSTRACT FROM AUTHOR]

Abstract Here we present novel cave-analogue experiments directly investigating stable carbon and oxygen isotope fractionation between the major involved species of the carbonate system (HCO 3 −, CO 2 , CaCO 3 and H 2 O). In these experiments, which were performed under controlled conditions inside a climate box, a thin film of solution flew down an inclined marble or glass plate. After different distances of flow and, thus, residence times on the plate, pH, electrical conductivity, supersaturation with respect to calcite, precipitation rate as well as the δ18O and δ13C values of the dissolved inorganic carbon (DIC) and the precipitated CaCO 3 were obtained. Progressive precipitation of CaCO 3 along the plate is accompanied by degassing of CO 2 and stable isotope fractionation, and the system is driven out of isotope equilibrium. We observe a strong enrichment of the δ13C values with increasing residence time and a smaller enrichment in δ18O. The temporal evolution of the δ18O and δ13C values of both the DIC and the precipitated CaCO 3 can be explained by a Rayleigh fractionation model, but the observed enrichment in δ13C values is much larger than expected based on isotope equilibrium fractionation factors. Our setup enables to determine the fractionation between CaCO 3 and HCO 3 −, i.e., ε CaCO3/HCO3−. Carbon isotope fractionation, 13ε CaCO3/HCO3− , is strongly negative for all experiments and much lower than equilibrium isotope fractionation (0–1‰). In addition, 13ε CaCO3/HCO3− decreases with increasing residence time on the plate, and thus decreasing supersaturation with respect to calcite. Thus, isotope fractionation depends on precipitation rate and consequently occurs under kinetic conditions. This is in contrast to previous studies, which found no rate-dependence and no or even a positive carbon isotope fractionation between CaCO 3 and HCO 3 −. Oxygen isotope fractionation, 18ε CaCO3/HCO3− , is also negative and dependent on precipitation rate. Since no literature values for 18ε CaCO3/HCO3− are available, we calculated 18ε CaCO3/HCO3− using equilibrium oxygen isotope fractionation factors between water and calcite and water and HCO 3 −, respectively. At the beginning of the plate, the fractionation is in agreement with the fractionation calculated using fractionation factors determined in cave systems. The observed fractionation between CaCO 3 and water, 1000ln18α, is also in good agreement with the values determined in cave systems and shows a very similar temperature dependence 1000 ln 18 α = 16.516 ± 1.267 ∗ 10 3 T − 26.141 ± 4.356. However, with progressive precipitation of CaCO 3 along the plate, the system is forced out of isotope equilibrium with the water, and 1000ln18α increases. The large, negative, rate-dependent isotope fractionations observed in this study suggest that precipitation of speleothem calcite is strongly kinetically controlled and may, thus, have a large effect on speleothem δ18O and δ13C values. Since these values may erroneously be interpreted as reflecting changes in past temperature, precipitation and/or vegetation density, these results have important implications for paleoclimate reconstructions from speleothems. [ABSTRACT FROM AUTHOR]

We present the first high-resolution trace element (Mg/Ca, Sr/Ca, Ba/Ca) record from a stalagmite in southwestern Romania covering the last 3.6 ka, which provides the potential for quantitative climate reconstruction. Precise age control is based on three independent dating methods, in particular for the last 250 yr, where chemical lamina counting is combined with the identification of the 20th century radiocarbon bomb peak and 230 Th/U dating. Long-term cave monitoring and model simulations of drip water and speleothem elemental variability indicate that precipitation-related processes are the main drivers of speleothem Mg/Ca ratios. Calibration against instrumental climate data shows a significant anti-correlation of speleothem Mg/Ca ratios with autumn/winter (October to March) precipitation (r = −0.61, p < 0.01), which is statistically robust when considering age uncertainties and auto-correlation. This relationship is used to develop a quantitative reconstruction of autumn/winter precipitation. During the late Holocene, our data suggest a heterogeneous pattern of past regional winter hydroclimate in the Carpathian/Balkan realm, along with intermittent weakening of the dominant influence of North Atlantic forcing. In agreement with other regional paleo-hydrological reconstructions, the observed variability reveals periodically occurring strong NW–SE hydro-climate gradients. We hypothesize, that this pattern is caused by shifts of the eastern edge of the area of influence of the NAO across central-eastern Europe due to the confluence of North Atlantic forcing, and other climatic features such as the East Atlantic/Western Russia (EAWR) pattern. [ABSTRACT FROM AUTHOR]

Carbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient D SO 4  = (mSO 4 /mCO 3 ) solid /(mSO 4 /mCO 3 ) solution . High crystal growth rates (driven by either pH or saturation state) encouraged higher values of D SO 4 because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, D SO 4 was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO 2 could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of D SO 4 were compared with D SO 4 values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, D SO 4 (×10 5 ) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted D SO 4 values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of D SO 4 obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind D SO 4 and will enhance the use of speleothem CAS as a palaeoenvironmental proxy. [ABSTRACT FROM AUTHOR]

Previous studies point to a discrepancy in the timing of the maximum extent of the Alpine glaciation during the last glacial cycle (Würmian) in the Western Alps. Work carried out on the Lyon palaeoglacier lobe in France suggests that the glacial maximum occurred during Marine Isotope Stage (MIS) 4, while more recent studies on the Rhône palaeoglacier lobe in Switzerland provide evidence of a maximum during MIS 2. Here, we present new chronological data from the karst region of the Western Bauges (French Alps). Between 500 m and 1200 m a.s.l. several karst systems were in lateral position to the Isère palaeoglacier. This palaeoglacier invaded the Bauges limestone massif and the Chéran valley by a transfluence controlled by the Frêne pass at 980 m a.s.l. Allochthonous glacier-derived gravel and sand interbedded with speleothems are present in caves, providing terminus ante quem and post quem age constraints on the timing of several glacial advances. Other speleothems were submerged by rising water levels in the karst due to damming by the glacier. Finally, some speleothems show shatter marks caused by the impact of pebbles transported by highly turbulent meltwaters. 25 U/Th dates of speleothems cover MIS 9 to 1. For MIS 4 to 2, they allow, indirectly, to constrain the different glacial advances into the Bauges limestone massif and to re-evaluate the timing of the maximum Alpine glaciation during the Würmian in this part of the Western Alps. Although the new data and observations do not exclude the possibility of a maximum glacier advance during MIS 2, they argue for a maximum advance during MIS 4 and a local, smaller one during MIS 2. [Display omitted] • Clastic deposits in caves of the western Bauges record several phases of glaciation. • U-Th speleothems dates (MIS 9 to 1) constrain the age of these deposits. • The glacial retreat was followed by a phase of karst "cleaning". • These results hint towards a larger MIS 4 advance than during MIS 2. [ABSTRACT FROM AUTHOR]

Speleothem stable carbon isotope (δ 13 C) records provide important paleoclimate and paleo-environmental information. However, the interpretation of these records in terms of past climate or environmental change remains challenging because of various processes affecting the δ 13 C signals. A process that has only been sparsely discussed so far is carbon isotope exchange between the gaseous CO 2 of the cave atmosphere and the dissolved inorganic carbon (DIC) contained in the thin solution film on the speleothem, which may be particularly important for strongly ventilated caves. Here we present a novel, complete reaction diffusion model describing carbon isotope exchange between gaseous CO 2 and the DIC in thin solution films. The model considers all parameters affecting carbon isotope exchange, such as diffusion into, out of and within the film, the chemical reactions occurring within the film as well as the dependence of diffusion and the reaction rates on isotopic mass and temperature. To verify the model, we conducted laboratory experiments under completely controlled, cave-analogue conditions at three different temperatures (10, 20, 30 °C). We exposed thin (≈0.1 mm) films of a NaHCO 3 solution with four different concentrations (1, 2, 5 and 10 mmol/l, respectively) to a nitrogen atmosphere containing a specific amount of CO 2 (1000 and 3000 ppmV). The experimentally observed temporal evolution of the pH and δ 13 C values of the DIC is in good agreement with the model predictions. The carbon isotope exchange times in our experiments range from ca. 200 to ca. 16,000 s and strongly depend on temperature, film thickness, atmospheric pCO 2 and the concentration of DIC. For low pCO 2 (between 500 and 1000 ppmV, as for strongly ventilated caves), our time constants are substantially lower than those derived in a previous study, suggesting a potentially stronger influence of carbon isotope exchange on speleothem δ 13 C values. However, this process should only have an influence in case of very long drip intervals and slow precipitation rates. [ABSTRACT FROM AUTHOR]

Speleothems can be precisely dated by U-series disequilibrium methods. One basic assumption of the 230 Th/U-dating method is that the system remains closed and U and Th isotopes are neither lost nor added after deposition. For stalagmites, this requirement is usually fulfilled due to their protected environment in caves. However, undersaturated drip water may lead to diagenesis of speleothem CaCO 3 and altered 230 Th/U-ages. Here we present a detailed petrographic investigation using thin sections and 230 Th/U-ages of a stalagmite from the Riesenberghöhle, northern Germany, which grew during Marine Isotope Stages 5e, c and a. The occurrence of a mosaic fabric in large parts of the stalagmite in combination with several age inversions is a clear indication for diagenetic alteration. We discuss the potential diagenetic processes and quantitatively model their influence on the 230 Th/U ages. Post-depositional U loss leads to increasing ( 230 Th/ 238 U) activity ratios and, thus, apparently older ages. In contrast, post-depositional addition of U results in decreased ( 230 Th/ 238 U) activity ratios and apparently younger ages. Comparison with our modelling results suggests that diagenesis occurred early after deposition. Initial and post-depositional detrital contamination probably played a minor role for the observed age inversions. [ABSTRACT FROM AUTHOR]

Abstract: There is developing interest in cave aerosols due to the increasing awareness of their impacts on the cave environment and speleothem; this paper provides the first attempt to synthesize the issues. Processes of cave aerosol introduction, transport, deposition, distribution and incorporation are explored, and reviewed from existing literature. Key issues of specific aerosol processes of distribution and production as well as cave location and morphology effects are highlighted through the presentation of preliminary monitoring data. This study identifies the strong relationship between cave ventilation, cave aerosols and their consequent spatial distribution. The contribution of cave aerosol deposition to speleothem geochemistry is modelled and evaluated using a mass balance framework. As an example, speleothem trace element data from Obir Cave (Austria) are compared with aerosol inputs to evaluate their significance. The mass balance study demonstrates that generally, under normal continuous growth and environmental conditions aerosol deposition will be of only minor importance. However, it highlights specific scenarios in which aerosol contributions will be significant: speleothem hiatuses (or slow growth), high aerosol deposition, and secondary microbiological feedback. [Copyright &y& Elsevier]

Abstract: We present a speleothem stable oxygen isotope record for the last 12.5ka based on two stalagmites from western Cuba. The δ 18O signal is interpreted to represent past precipitation variability. Both stalagmites show a pronounced transition from higher δ 18O values (indicating drier conditions) to more negative δ 18O values (suggesting wetter conditions) between 10 and 6ka. This transition is also visible in a planktonic δ 18O record off Haiti. On orbital timescales, the δ 18O value of Caribbean precipitation, thus, strongly resembles the oxygen isotope composition of Caribbean surface water. On millenial timescales, the speleothem δ 18O record shows a high correlation to a North Atlantic sea surface temperature (SST) record off West Africa as well as a similarity with the Bond events. Periods of lower North Atlantic SST correspond to less precipitation in the Caribbean and vice versa. The potential teleconnection to the Caribbean may reflect the position of the Intertropical Convergence Zone because a further southward position of the ITCZ leads to reduced precipitation in the northern Caribbean. [Copyright &y& Elsevier]

Abstract: Sulphur emitted into the atmosphere from industrial activity is regarded as a key mechanism in forcing recent climate and has impacts upon the environment and human health at both local and regional scales. Trace amounts of sulphate present within speleothem carbonate can be used to provide an emissions inventory for regional sulphur loading to the atmosphere where sulphur isotopes can be extracted and used as a tool for provenance. However, speleothem sulphur concentrations are low and manual techniques for sulphur isotope analysis allow only low sampling resolution. SIMS (Secondary Ionisation Mass Spectrometry) is used here to develop records of sulphur isotopic change in speleothems from the Italian and Austrian Alps, where annual laminae are less than 100µm thick. Analysis at annual resolution over the past 100years demonstrates an excursion in sulphur isotopic composition from values close to the carbonate bedrock end-member composition in the pre-industrial era, to values isotopically depleted in 34 S. This trend is mirrored by increasing concentrations of sulphate and is suggested to reflect the increase in SO2 emissions with industrial activity. Subsequent decline in speleothem sulphate concentrations in one of the stalagmites reflects the recent European decline in industrial atmospheric SO2 content and is matched by a rebound in sulphur isotopic composition to values more enriched in 34 S. Superimposed on this general secular trend are smaller (annual) variations in concentration reflecting cave environmental conditions. High magnitude events of short duration, potentially reflect volcanic inputs of SO2 or the incorporation of dust particulates into the speleothem carbonate. This is the first micro-analysis of carbonate-associated sulphate (CAS) sulphur isotopes by SIMS. SIMS analysis of δ 34S–SO4 in speleothem carbonate reveals a high resolution archive depicting a regional sulphur emissions inventory for SO2 loading to the atmosphere. [Copyright &y& Elsevier]

Conflicting reconstructions of Holocene variability of the East Asian summer monsoon (EASM) from speleothem versus other types of proxy records have yielded widely divergent estimates of its phase relationship with the Indian summer monsoon (ISM) and Northern Hemisphere summer insolation (NHSI). This apparent discrepancy has been partly attributed to the uncertainties in the climatic representation of Chinese speleothem oxygen isotope (δ18O) records. Here we present a composite speleothem δ18O record of the last ∼14 kyr from Shennong Cave in southeastern China and model-simulated data of rainfall and meteoric δ18O over eastern China. Our synthesis of the proxy-model data suggests that the spatial patterns in both speleothem δ18O and paleo-rainfall over eastern China during the Holocene are diverse at orbital and multi-millennial scales. Our findings imply that: 1) speleothem δ18O in the EASM regime is largely controlled by the large-scale circulation and concomitant latitudinal shifts of the monsoon rain belt; notwithstanding the heterogeneous spatiotemporal pattern of Holocene rainfall as inferred from various proxy records, a coherent orbital-scale speleothem δ18O variability across most Asian monsoon regions (except southeastern China) indeed stems from the NHSI-forced changes in overall monsoon intensity; overall monsoon intensity is not equivalent to monsoon rainfall amount but a manifestation of the large-scale atmospheric circulation; 2) divergent phase relationships with NHSI between speleothem δ18O and other proxy records are consistent with—rather than contradictory to—the NHSI forcing mechanism. Speleothem δ18O and rainfall records reflect two different aspects of the monsoon dynamics. These results may thus, largely help to reconcile the divergent views of the Holocene Asian monsoon variability. • Holocene speleothem δ18O and rainfall show heterogeneous pattern in eastern China. • East Asian speleothem δ18O reflects large-scale circulation and monsoon rain belt shift. • Divergent phases between speleothem and other proxy records are not contradictory. [ABSTRACT FROM AUTHOR]