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Surface temperature is a fundamental parameter of Earth's climate. Its evolution through time is commonly reconstructed using the oxygen isotope and the clumped isotope compositions of carbonate archives. However, reaction kinetics involved in the precipitation of carbonates can introduce inaccuracies in the derived temperatures. Here, we show that dual clumped isotope analyses, i.e., simultaneous ∆47 and ∆48 measurements on the single carbonate phase, can identify the origin and quantify the extent of these kinetic biases. Our results verify theoretical predictions and evidence that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Further, we show that dual clumped isotope thermometry can achieve reliable palaeotemperature reconstructions, devoid of kinetic bias. Analysis of a belemnite rostrum implies that it precipitated near isotopic equilibrium and confirms the warmer-than-present temperatures during the Early Cretaceous at southern high latitudes. Some palaeotemperature proxies suffer from inaccuracies related to kinetic fractionations occurring during carbonate mineral growth. Here, the authors show that dual clumped isotope thermometry can identify the origin of these kinetic biases and allows for the reconstruction of accurate environmental temperatures. [ABSTRACT FROM AUTHOR]

Two small annually laminated stalagmites from Zoolithencave (southeastern Germany) grew between CE 1821 and 1970 (Zoo‐rez‐1) and CE 1835 and 1970 (Zoo‐rez‐2), respectively. Trace element concentrations were determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS). Samples for δ13C and δ18O analyses were micromilled on annual and subannual resolution. Soil and host rock samples were analyzed by X‐Ray Diffraction (XRD) and their elemental concentrations determined via inductively coupled plasma optical emission spectrometer (ICP‐OES). Trace element concentrations in the stalagmites show two groups in the principal component analyses: one with Mg, Ba, and Sr and another with Y, P, and Al, respectively. The second group reflects the content of detrital material. Increased weathering of soil minerals seems to have a strong influence on the silicate/carbonate weathering ratio controlling the variability of Mg, Ba, and Sr. Meteorological and Global Network of Isotopes in Precipitation (GNIP) station data were used to calculate the δ18O values of the drip water (infiltration‐weighted, mean annual, and the mean of the winter precipitation δ18O values) as well as the corresponding speleothem calcite. The δ18O values calculated by the infiltration‐weighted model show similar patterns and amplitudes as the measured δ18O values of the two stalagmites. This suggests that the δ18O values of speleothem calcite reflect the δ18O values of infiltration‐weighted annual precipitation, which zis related to mean annual temperature, resulting in a significant correlation between mean annual temperature and the measured δ18O values of stalagmite Zoo‐rez‐2. This relationship could potentially be used for quantitative climate reconstruction in the future by extending the time series back in time with further stalagmites from Zoolithencave. Key Points: Silicate versus carbonate weathering has an influence on speleothem trace elementsYttrium, phosphorus, and aluminum reflect detrital content of the speleothemsδ18O values of the stalagmites are a proxy for mean annual temperature [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]

Stable oxygen and carbon isotope ratios (d13C and d18O) are the most applied climate and environmental proxies in speleothems allowing to infer past changes in cave drip water d13C and d18O related to climate and environmental variations from above the cave. However, disequilibrium isotope fractionation processes can modify d13C and d18O values in speleothems, which is in most cases difficult to estimate due to inter-dependencies on various cave specific parameter. To better understand the effect of these disequilibrium isotope fractionation processes proxy system models were developed in recent years, such as the ISOLUTION model. Here the code of the ISOLUTION model is made available for the public and the speleothem community to be applied to research questions that arise from e.g. monitoring programs that investigate d13C and d18O values of in situ calcite precipitates on watch glasses or modern speleothem calcite, respectively. Another application of the ISOLUTION model is to investigate the dependence of calcite d13C and d18O on the variation of one or multiple cave specific parameter, such as cave air temperature, drip interval, cave air pCO2, Ca2+ concentration of the drip water as well as on relative humidity and wind velocity. This allows to quantitatively estimate the effect of disequilibrium isotope fractionation processes in individual caves and drip sites on speleothem d13C and d18O values for modern and past climates and may help to further elucidate the complex interplay of kinetic and disequilibrium isotope fractionation. [ABSTRACT FROM AUTHOR]

RATIONALE Milling of wood samples is a widely applied preparation method for pooling tree-rings from different trees or periods of several years for determination of δ13C and δ18O values. In this study, whole wood samples were milled using different procedures in order to evaluate potential effects of this preparation method on δ13C and δ18O values. METHODS Subsamples of a 5 cm3 wood piece of a single tree-ring from a lowland white fir were used. The samples were milled with different setups: (i) two and three stainless-steel balls, (ii) 3, 5 and 8 min milling time, and (iii) discontinuous and continuous milling. The δ13C values were measured using an elemental analyser connected to an IsoPrime mass spectrometer and δ18O values using a Thermo Scientific MAT 253 mass spectrometer and a TC/EA connected by a ConFlo IV. RESULTS The results show that varying the milling procedure does not alter the δ13C and δ18O values in comparison to non-milled blank samples. For shorter milling times, an increased variance of δ18O values is recorded, probably caused by isotopic gradient between early- and latewood portions of the tree-ring and thereby biasing the insufficiently homogenised samples. No overheating effects on the δ13C and δ18O values were detected. CONCLUSIONS Milling of wood samples for carbon and oxygen isotope analyses is an appropriate preparation method. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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: We derive equations describing the evolution of the carbon and oxygen isotope composition of the bicarbonate in a calcite precipitating solution on the surface of a stalagmite using a classical Rayleigh approach. The combined effects of calcite precipitation, degassing of CO2 and the buffering effect of the water reservoir are taken into account. Whereas δ13C shows a progressive increase to a final constant value, δ18O shows an initial isotopic enrichment, which exponentially decays due to the buffering effect of the water reservoir. The calculated evolution is significantly different for both carbon and oxygen isotopes than derived in a recent paper [Dreybrodt W. (2008) Evolution of the isotopic composition of carbon and oxygen in a calcite precipitating H2O–CO2–CaCO3 solution and the related isotopic composition of calcite in stalagmites. Geochim. Cosmochim. Acta 72, 4712–4724.]. Furthermore, we discuss the isotopic evolution of the bicarbonate in the solution for long residence times on the stalagmite surface, i.e., for . The equilibrium isotope ratio of the bicarbonate is then determined by isotopic exchange between the cave atmosphere and the bicarbonate in the solution and can be calculated by equilibrium isotope fractionation. For strongly ventilated caves exchange with the cave atmosphere will result in higher δ13C and δ18O values than those observed in a pure Rayleigh distillation scenario, for sparsely ventilated caves it will result in lower δ13C and δ18O values. [Copyright &y& Elsevier]

Abstract: Speleothem proxy data provide important information in continental palaeo-climate research due to their precise chronology and wide geographic distribution. Despite a continuously growing number of field and numerical studies designed to study stable isotope fractionation effects, many aspects remain a matter of debate. Here, carbon and oxygen isotope ratios from cave drip water and calcite precipitates sampled on watch glasses in the Bunker Cave (Western Germany) are compared with the values expected for isotopic equilibrium. Furthermore, the field data are compared with the results of a numerical model simulating stalagmite growth and stable isotope ratios. Two drip sites with different drip rates were investigated. Drip site TS 1 is characterised by a high drip rate, and drip water of this site is characterised by a high saturation index with respect to calcite. TS 1 shows no evidence of prior calcite precipitation. Conversely, drip site TS 8 shows a low drip rate, and drip water from this site is characterised by a low saturation index. TS 8 shows evidence of prior calcite precipitation. Whereas the mean δ13CDIC values of the drip water are significantly different between the two drip sites, the mean δ18Odrip water values are similar. Calcite precipitation rates are higher at watch glass site U I corresponding to drip site TS 1. This is probably due to the higher SIcalcite and drip rate. The δ18O and δ13C values of the calcite precipitated on watch glasses U IV corresponding to drip site TS 8 are significantly higher than those of the calcite collected on watch glasses U I. Calcite precipitation occurs close to isotopic equilibrium at watch glass site U I, whereas the calcite precipitated at watch glass site U IV shows clear evidence of isotopic disequilibrium. The results suggest that cave calcites precipitated at lower drip rates have higher δ13C and δ18O values than predicted by equilibrium precipitation. Furthermore, our data show that stalagmites from the same cave, which are fed by drip water with similar δ18O values, may have different δ18Ocalcite values. The δ13C and δ18O values predicted by the numerical model are generally lower by 1.9‰ and 0.8‰, respectively, than those of the natural cave calcite. Nevertheless, the first-order trends observed in the cave data are well reproduced by the model. The offset between cave and model data is probably due to the fractionation factors used in the model. [Copyright &y& Elsevier]

Abstract: In order to improve the understanding of variations of speleothem δ18O and δ13C values in the context of palaeoclimate research, it is important to quantify the isotope fractionation processes influencing the δ18O and δ13C values of stalagmites. Here we present an extended version of speleothem stable isotope model that accounts for evaporation and condensation effects during precipitation of calcite. The ISOLUTION-model allows to calculate the effect of evaporation on δ18Ocalcite and δ13Ccalcite values in dependence on relative humidity and wind velocity. Our results reveal that evaporation may have a significant effect on δ18Ocalcite and δ13Ccalcite due to the loss of H2O from the solution layer and the related increase of the Ca2+ concentration. This leads to higher precipitation rates and, consequently, larger isotope fractionation effects. The effect on speleothem δ18Ocalcite and δ13Ccalcite can be as high as changes caused by variations of temperature, drip interval, pCO2.drip and pCO2.cave. Furthermore, the change of pCO2.cave due to ventilation effects, may also affect speleothem δ18Ocalcite and δ13Ccalcite values because of the effect of pCO2.cave on the equilibrium concentrations of the CO2–H2O–CaCO3-system and, thus, the calcite precipitation rate. The variability of other cave parameters (temperature, drip interval, pCO2.drip, pCO2.cave) can have a comparable effect on δ18Ocalcite and δ13Ccalcite values depending on the magnitude of variability. We validated the ISOLUTION-model by modelling the δ18Ocalcite values from a cave-analogue experiment and successfully reproduced the values for high temperatures. [Copyright &y& Elsevier]

The curvature and slope of speleothem surfaces have been shown to affect the reaction rates in the aqueous carbonate system by altering the thickness of the CaCO 3 -precipitating solution. However, the effects of speleothem geometry and drip rate on the speleothem's carbon and oxygen isotopic composition have yet to be investigated. Over more strongly sloping surfaces, solutions are thinner and flow faster. The effects of thinner and faster-flowing solutions on the isotopic composition of carbonate minerals precipitated from these solutions are of opposite sense. Thinner solutions enhance rates of CO 2 degassing and mineral formation, increasing the degree of isotopic distillation of the dissolved inorganic carbon (DIC) reservoir and leading to larger isotopic fractionation between the carbonate mineral and the initial DIC. Concurrently, faster flow over the steeper surfaces results in shorter residence times of the solutions on the growing speleothem, thereby limiting the degree of isotopic distillation and CaCO 3 -DIC fractionation. Consequently, predicting the CaCO 3 -DIC isotopic fractionation as a function of drip rate, surface slope and flow distance is not trivial. Using an advection-diffusion-reaction model, we tested the sensitivity of the isotopic composition of calcite precipitated along inclined surfaces to the solution discharge (drip) rate and the surface slope. Calcite δ13C and δ18O values correlate well with the degree of prior calcite precipitation (PCP), which is identified as a major determinant of isotopic compositions in speleothems. Our results show that at low PCP, speleothem δ13C and δ18O values may initially decrease relative to calcite-DIC and calcite-water equilibrium due to expression of kinetic isotope effects of mineral precipitation. Upon progressive PCP, δ13C and δ18O values gradually increase due to continuous CO 2 (aq) formation and degassing. This shift in the isotopic composition of the calcite to lower-than-equilibrium and then higher-than-equilibrium values expands the regime of near-equilibrium compositions during the isotopic evolution. In turn, this may allow quantitative environmental reconstructions, even when the isotopic system is in disequilibrium. Under the simulated conditions, our model predicts maximal potential enrichments of 7 and 3‰ in the calcite δ13C and δ18O values, respectively. In addition, we found a strong dependence of the calcite δ13C and δ18O values on the drip rate and distance of flow, and a weak dependence on the surface slope. In fact, changes in drip rate alone may drive isotopic offsets of several permil, when all other environmental parameters are kept constant. According to our model, higher drip rates and shorter stalactites promote closer-to-equilibrium isotopic compositions of stalagmites, providing a higher signal-to-noise ratio, and minimizing variability that is unrelated to climate. [ABSTRACT FROM AUTHOR]

The equilibrium oxygen isotope fractionation factor between calcite and water (18α calcite/H2O) is an important quantity in stable isotope geochemistry and allows in principle to infer temperature variations from carbonate δ18O if carbonate formation occurred in thermodynamic equilibrium. For this reason, many studies intended to determine the value of the oxygen isotope fractionation factor between calcite and water (18α calcite/H2O) for a wide range of temperatures using modern cave calcite and the corresponding cave drip water or ancient speleothem carbonate and fluid inclusion samples. However, the picture that emerges from all of these studies indicates that speleothem calcite is not formed in thermodynamic equilibrium but under kinetic conditions, provoking a large variability of determined 18α calcite/H 2 O values. Here we present a conceptual framework that can explain the variability of 18α calcite/H 2 O values obtained by cave studies. Prior calcite precipitation (PCP) is calcite precipitation before cave drip water is dripping from the cave ceiling and impinges on the surface of a stalagmite or watch glass. Prior to the karst water dripping from the cave ceiling, PCP can occur in the karst above the cave as well as on the cave ceiling, the cave walls and on the surface of stalactites. We argue that PCP leads to increasing the δ18O value of the dissolved HCO 3 − (δ18O HCO3-), resulting in an oxygen isotope disequilibrium of the δ18O HCO3- values with respect to the δ18O value of water (δ18O H2O). The oxygen isotope disequilibrium between HCO 3 − and H 2 O is re-equilibrated by oxygen isotope exchange between H 2 O and HCO 3. Depending on the temperature, the re-equilibration time varies from hours to days and is usually much longer than the residence time of the drip water on stalactites, but much shorter than the time required to percolate through the karst. Therefore, while the oxygen isotope equilibrium between HCO 3 − and H 2 O is very likely re-established when PCP occurred in the karst, oxygen isotope disequilibrium conditions between HCO 3 − and H 2 O still prevail when PCP occurred inside a cave, e.g., on stalactites. If the oxygen isotope disequilibrium conditions between HCO 3 − and H 2 O is not re-established, the precipitated calcite will inherit the elevated δ18O value of the HCO 3 − and not be in oxygen isotope equilibrium with the corresponding drip water. Consequently, if the 18α calcite/H 2 O value is calculated from cave calcite samples affected by PCP, the derived value will be systematically biased. [ABSTRACT FROM AUTHOR]

Abstract Central European climate is strongly influenced by North Atlantic (Westerlies) and Siberian High circulation patterns, which govern precipitation and temperature dynamics and induce heterogeneous climatic conditions, with distinct boundaries between climate zones. These climate boundaries are not stationary and shift geographically, depending on long-term atmospheric conditions. So far, little is known about past shifts of these climate boundaries and the local to regional environmental response prior to the instrumental era. High resolution multi-proxy data (stable oxygen and carbon isotope ratios, S/Ca and Sr/Ca) from two Holocene stalagmites from Bleßberg Cave (Thuringia) are used here to differentiate local and pan-regional environmental and climatic conditions Central Germany through the Holocene. Carbon isotope and S/Ca and Sr/Ca ratios inform us on local Holocene environmental changes in and around the cave, while δ18O (when combined with independent records) serves as proxy for (pan-)regional atmospheric conditions. The stable carbon isotope record suggests repeated changes in vegetation density (open vs. dense forest), and increasing forest cover in the late Holocene. Concurrently, decreasing S/Ca values indicate more effective sulfur retention in better developed soils, with a stabilization in the mid-Holocene. This goes in hand with changes in effective summer infiltration, reflected in the Sr/Ca profile. Highest Sr/Ca values between 4 ka and 1 ka BP indicate intensified prior calcite precipitation resulting from reduced effective moisture supply. The region of Bleßberg Cave is sensitive to shifts of the boundary between maritime (Cfb) and continental (Dfb) climate and ideally suited to reconstruct past meridional shifts of this divide. We combined the Bleßberg Cave δ18O time series with δ18O data from Bunker Cave (western Germany) and a North Atlantic Oscillation (NAO) record from lake SS1220 (SW Greenland) to reconstruct the mean position of the Cfb-Dfb climate boundary. We further estimate the dynamic interplay of the North Atlantic Oscillation and the Siberian High and their influence on Central European climate. Repeated shifts of the Cfb-Dfb boundary over the last 4000 years might explain previously observed discrepancies between proxy records from Europe. Detailed correlation analyses reveal multi-centennial scale alternations of maritime and continental climate and, concurrently, waning and waxing influences of Siberian High and NAO on Central Europe. Highlights • U-series dated multi-proxy speleothem data from Bleßberg Cave, Thuringia cover the Holocene. • Local and pan-regional environmental and climatic changes are reconstructed. • Bleßberg Cave record is compared to data from W Germany and Greenland to infer maritime/continental climate regimes. • Waning/waxing of NAO and Siberian High influence on European climate is discussed for the last 4,000 years. [ABSTRACT FROM AUTHOR]

Speleothem records have been successfully calibrated against instrumental data, e.g., using stable oxygen isotope or annual growth lamina data considered as reliable recorders of air temperature or precipitation amount. We present the first high-resolution trace element (Mg/Ca, Sr/Ca, Ba/Ca) record providing the potential for quantitative climate reconstruction, deduced from stalagmites from Clo¸sani Cave, SW Romania.The calibration approach relies on a precise age control - in particular for the last 250 years, where the chronology is based on three independent dating methods. Chemical lamina counting is combined with the identification of the 20th century 14C bomb peak and 230Th/U dating. Long-term cave monitoring and model simulations of drip water and speleothem elemental variability support the inference that precipitation-relatedprocesses 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 whenconsidering age uncertainties and auto-correlation. This relationship is then used to develop a quantitative reconstruction of Holocene autumn/winter precipitation.During the last 3.6 ka, 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 theeastern 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]

The SISAL database v1 [1] is a comprehensive quality-controlled global compilation of oxygen and carbon isotope records from speleothems spanning large parts of the late Pleistocene compiled as a community effort supported by Past Global Changes (PAGES). The stable isotope records provide information on past changes in climate and the environment, both for reconstruction, as well as for comparison to climate model output.\\The chronology of the majority of the records is based on precise $^\text{230}$Th/U-dating, and speleothems are palaeoclimate archives with generally good chronological control. However, various types of age-depth modelling with different degrees of complexity (e.g., linear interpolation, etc.) have been used to construct the chronologies, and most of the records provide no estimates of age uncertainty. Some data sets have no age model at all. This limits the suitability for assessing abrupt transitions as well as the synchronicity of events across space. \\Here we apply six different age-depth modeling approaches to a representative subset from the SISAL database, to compare and evaluate their suitability as final SISAL chronologies for the next version of the database. The methods include linear models (linear regression, linear interpolation), fitting approaches (StalAge), ensemble-based methods (COPRA), as well as Bayesian models (OxCal, Bacon, Bchron). The subset of records from the SISAL database is representative in a sense that they include speleothems with ''well-behaved'' constant and continuous growth, variable growth rates, age outliers as well as growth interruptions.\\We find that for many speleothems, age models can be established, and that there is an overall consensus on the median, or most likely, age-depth trajectory. Not all methods are applicable in all situations, however, and the resulting confidence intervals differ. We compare and evaluate the methods also by applying them to virtually grown speleothems.\\We discuss challenges that arise (data inconsistencies, missing hiatuses, duplicated sample depths, multi-model integration) and the format we intend for the final chronologies. The new chronologies will allow to consider the impact of age uncertainty on analyses in the SISAL working group consistently across the database.\\[1] Atsawawaranunt \textit{et al}., The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems, Earth Syst. Sci. Data, 10, 1687-1713, https://doi.org/10.5194/essd-10-1687-2018, 2018. [ABSTRACT FROM AUTHOR]