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Abstract: Speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system. However, the climatological meaning of many speleothem records cannot be interpreted unequivocally; this is particularly so for more subtle shifts and shorter time periods, but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward. An explicit description of speleothem records as time series draws attention to the nature and importance of the signal filtering processes by which the weather, the seasons, and longer-term climatic and other environmental fluctuations become encoded in speleothems. We distinguish five sources of variation that influence speleothem geochemistry, i.e. atmospheric, vegetation/soil, karstic aquifer, primary speleothem crystal growth and secondary alteration, and give specific examples of their influence. The direct role of climate diminishes progressively through these five factors. We identify and review a number of processes identified in recent and current work that bear significantly on the conventional interpretation of speleothem records, for example: [(1)] speleothem geochemistry can vary seasonally and hence a research need is to establish the proportion of growth attributable to different seasons and whether this varies over time; [(2)] whereas there has traditionally been a focus on monthly mean δ18O data of atmospheric moisture, current work emphasizes the importance of understanding the synoptic processes that lead to characteristic isotope signals, since changing relative abundance of different weather types might control their variation on the longer-term; [(3)] the ecosystem and soil zone overlying the cave fundamentally imprint the carbon and trace element signals and can show characteristic variations with time; [(4)] new modelling on aquifer plumbing allows quantification of the effects of aquifer mixing; [(5)] recent work has emphasized the importance and seasonal variability of CO2-degassing leading to calcite precipitation upflow of a depositional site on carbon isotope and trace element composition of speleothems; [(6)] although much is known about the chemical partitioning between water and stalagmites, variability in relation to crystal growth mechanisms and kinetics is a research frontier; [(7)] aragonite is susceptible to conversion to calcite with major loss of chemical information, but the controls on the rate of this process are obscure. Analytical factors are critical in generating high-resolution speleothem records. A variety of methods of trace element analysis is available, but standardization is a common problem with the most rapid methods. New stable isotope data on Irish stalagmite CC3 compares rapid laser-ablation techniques with the conventional analysis of micromilled powders and ion microprobe methods. A high degree of comparability between techniques for δ18O is found on the millimeter to centimeter scale, but a previously described high-amplitude oxygen isotope excursion around 8.3 ka is identified as an analytical artefact related to fractionation of the laser-analysis associated with sample cracking. High-frequency variability of not less than 0.5‰ may be an inherent feature of speleothem δ18O records. [Copyright &y& Elsevier]

Past climate archives show the Last Interglacial (LIG) period as similar to slightly warmer than current temperatures. However, there is a lack of LIG proxy evidence regarding variations of the climate across large topographic features and how this manifests at different altitudes. Here, we analysed two flowstones from Bigonda Cave, northeast Italy, to reconstruct LIG climate conditions in a region where precipitation is strongly influenced by the presence of the Alps. Stable isotope ratios, trace element concentrations and speleothem petrography from 133 ka to 105 ka allowed the detection of various hydroclimate and environmental conditions. Composite speleothem δ18O records from northeast Italy were found to closely follow the Northern Hemisphere summer insolation curve, attesting to the influence of solar isolation on Earth's hydroclimate. Our reconstructions indicate a northward shift of the Intertropical Convergence Zone during the LIG maximum, permitting Atlantic-derived moisture to travel further east across North Africa than at present, before being directed north towards the Alps. The latter part of the LIG exhibited frequent, extreme precipitation events in the SE Prealps due to orographic lifting of moisture from both the Atlantic and Mediterranean seas. Socio-economic planning must prepare for extreme autumnal flooding events and serious summer droughts, particularly important in vulnerable mountainous regions. • Last Interglacial speleothem multi-proxy records from the NE Italian Prealps. • Three infiltration sources identified permits robust hydroclimate reconstruction. • Solar insolation was the main forcing mechanism of the oxygen isotope record. • The LIG was punctuated by hot dry summers and extreme cave flooding events. [ABSTRACT FROM AUTHOR]

A precisely dated speleothem isotope record from the Sieben Hengste cave system, Switzerland, reveals a Last Interglacial (LIG) climate optimum centred at 128.1 ± 1.2 ka. The oxygen isotope signal is consistent with a temperature-dominated record and shows a strong correlation with the modelled Greenland δ18O signal. The comparison with speleothems formed during the Last Glacial Maximum (LGM) in the same cave indicates a 4–5‰ difference in δ18O between peak LIG and peak LGM conditions, suggesting peak LIG temperatures being up to 3 °C higher than the Holocene average. Pollen extracted from the stalagmite indicates a vegetation response delayed by up to 3 ka with maximum pollen concentrations recorded at 125 ± 2.2 ka. Our results support a regional vegetation dominated by thermophile tree species including Corylus (hazel), Quercus robur-type (oak), Ulmus (elm), Tilia (lime tree) and Hedera (ivy), consistent with slightly warmer conditions than today. Despite the relatively low pollen concentration, the speleothem-based pollen spectra are consistent with regional pollen assemblage zones from paleolake sediments and provide the first direct paleovegetation evidence of thermophilization during the LIG at high altitudes in the Alps. • A Last Interglacial speleothem underlines the ocean control on the North Alpine climate. • The speleothem δ18O signal reveals a temperature-dominated record. • The Last Interglacial thermal optimum is dated at 128.1 ± 1.2 ka. • A delay is observed between the temperature and local vegetation response. • First palynological evidence of high-altitude thermophilization during the LIG. [ABSTRACT FROM AUTHOR]

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]

Climate change during the Little Ice Age (LIA) was characterized by globally widespread but spatiotemporally incoherent cooling with high regional variability. However, the onset, termination, internal structure, and underlying forcing mechanisms of the LIA remain unclear. Here we present a U-Th-dated stalagmite record with an average sampling resolution of 0.8 years and mean age uncertainty less than 4 years from Shijiangjun Cave, Southwest China (SW China). We have characterized the dynamics of the Asian summer monsoon (ASM) on interdecadal to centennial timescales during the LIA at unprecedented accuracy and precision. The onset of the LIA occurred at about 1300 (A.D.) and six weak-ASM events were identified at 1340–1380, 1445–1480, 1520–1540, 1600–1630, 1650–1670, and 1695–1730 (A.D.), respectively. The overall climate variability in Chinese monsoon regions is inconsistent with that in Northwest China (NW China). During the coldest period of the LIA (i.e. after 1500 CE), SW China exhibited a cold and dry pattern, while NW China experienced a cold and wet climate. Moreover, our records from the Asian-Australian monsoon (AAM) region showed coherent changes during the LIA, arguing against the interhemispheric "see-saw" model on interdecadal-centennial timescales. Documented solar minima, lower Northern Hemisphere temperature, and positive phases of PDO and ENSO during the LIA weakened the Asian-Australian summer monsoon, decreasing precipitation throughout the AAM regions. • The onset of Little Ice Age (LIA) occurred at 1300 CE. • Six weak Asian Summer monsoon events were identified in the LIA. • During the coldest period of the LIA, SW-China showed a cold-dry pattern. • Asian-Australian monsoon (AAM) regions experienced coherent change in the LIA. • Change in temperature and ocean-atmosphere circulation weakened the AAM in LIA. [ABSTRACT FROM AUTHOR]

Calcium carbonate (CaCO 3) deposits from Roman aqueducts are an innovative archive to obtain local high-resolution palaeoenvironmental and archaeological data in interdisciplinary studies. Deposits from one of the aqueducts of the Roman city of Gerasa provide a record of 59 years during the 1st to 3rd centuries CE, divided into three sequences separated by plaster layers. Annual carbonate layers show an alternation of sparite, formed in winter, and micrite, formed in summer. Brown bands at the base of many sparite layers probably correspond to large rainstorms in early winter. A fine lamination present in the brown bands may be diurnal in origin. Stable isotope and trace element data confirm annual layering, indicate strongly variable flow rate in the aqueduct and show truncations that may have been associated with drying up of the channel in some years. The trace element pattern is typical of a relatively small aquifer with a rapid response to precipitation. The trace element composition changes abruptly from the first to the second carbonate sequence, suggesting that a spring was added to increase the flow rate. Deformation twins in calcite crystals at the top of the second sequence may be due to earthquake damage after 48 years of use. The presence of abundant clay in the carbonate sequence, especially in the third sequence, suggests seismic damage to the channel. The channel was usually replastered after damage. The aqueduct went out of use sometime after the mid-2nd to mid-3rd century CE. The carbonate archive stores key information on groundwater quantity and composition and indirectly on air temperature, rainfall, extreme environmental events and land use at sub-annual resolution. Unlabelled Image • Carbonate deposits give information on functioning of a Roman aqueduct in Jordan • Stable isotopes and trace elements reveal environmental data from the Roman period • Data on air temperature and precipitation are present with up to daily resolution • The aqueduct was impacted by event horizons of earthquakes, droughts and floods • The aqueduct functioned for at least 59 years [ABSTRACT FROM AUTHOR]

Investigations of interstadials during early stages of glacial periods are of special interest, because they featured large-scale transformations of the climate system and the build-up of land-based ice sheets. Lacustrine sediment sequences are considered to be important natural archives that register past climate and environmental signals. Here, we present new multi-proxy data obtained from a palaeolake succession preserved in the inner-alpine terrace of Unterangerberg, Eastern Alps. These sediments formed during the second Early Würmian Interstadial, equivalent to Marine Isotope Stage (MIS) 5a, and were used to reconstruct changes in lake conditions and to infer past air temperatures. The sediment geochemical data and subfossil aquatic biota provide evidence of a cyclic lake–fen–lake development during this interstadial. The proxy records reveal stable lacustrine conditions with dense charophyte meadows and abundant aquatic fauna during the early part of the interstadial, a progressive shallowing of the lake resulting in the spreading out of fen vegetation in the middle part, and a transition from wetland to a renewed shallow lake stage towards the end of the interstadial. Chironomids were used to reconstruct mean July air temperatures, employing a combined Norwegian-Swiss chironomid temperature inference model. The reconstruction indicates a temperature close to present-day values of ca. 18 °C in the middle part of the record, while temperatures of ca. 13–14 °C are recorded for the lower and upper parts. The proxy data from this palaeolake provide evidence of heat and drought in the middle part of MIS 5a, supported by the chironomid-based temperature reconstruction. Our reconstruction shows a climate pattern broadly similar to that found in pollen-based estimates of mean July air temperatures from sites in the northern Alpine foreland and compares well to other European palaeoclimatic reconstructions of MIS 5a climate. • Palaeoenvironmental data from MIS 5a lacustrine deposits in the Alps are reported. • Proxy records provide evidence of cyclic lake–fen–lake development. • Quantitative estimates of summer temperatures are based on chironomid assemblages. • Cool conditions are inferred for the beginning and end of the interstadial sequence. • Hot and dry summers occurred in the middle part of MIS 5a. [ABSTRACT FROM AUTHOR]

The climate during the last glacial cycle was characterized by abrupt millennial-scale changes superimposed on long-term orbital control. This study examines this climate variability for northeast Iberia for the time interval 118.9 to 36.9 kyr using a multi-proxy approach (δ18O, δ13C and Mg/Ca) applied to a stalagmite that covers this period continuously. During Marine Isotope Stage (MIS) 5 and 4, δ18O is controlled by orbital pacing, whereby more humid conditions prevailed during minima in boreal summer precession. In contrast, during MIS 3 δ18O lags precession and co-varies with δ13C (ρ = 0.53, p-value < 0.001, n = 500), suggesting a common control of both isotopes by reduced precipitation during dry periods. δ13C shows a positive correlation with Mg/Ca, reflecting water availability, vegetation productivity and microbial activity in the catchment of the cave's drip water. The δ13C values exhibit a response to Heinrich Stadials (HS) and other cold marine events (e.g. C26 to C23), as well as Dansgaard-Oeschger oscillations (D-O). The Last Interglacial ended at 108.6 ± 0.3 kyr at this site. Two periods with a marked "W-shape" pattern in δ13C can be recognized between 70 and 50 kyr (hereafter multi-event). The older multi-event (including HS-6 and D-O 18) is characterized in the North Atlantic by high IRD discharges and cold sea-surface temperatures, while the two phases attending to the hydrology in the study area suggest dry conditions prior to HS-6. A dry climate prevailed during the younger multi-event (including HS-5a and D-O 15), coincident with an increase in productivity-related foraminifera species at lower latitudes, suggesting a reinforcement of the trade winds associated with a stronger Hadley Cell. • First continuous speleothem record from Europe covering MIS 5e to 3. • Precession-paced control of first-order δ18O variability during MIS 5. • Reduced precipitation controlled δ18O and δ13C millennial variability during MIS 4 and 3. • Late demise of the Last Interglacial in NE Iberia. • New insights into the climate variability during HS-6 and 5a, and D-O 15 and 18. [ABSTRACT FROM AUTHOR]

Cave air temperatures in four caves in the European Alps show statistically significant warming trends of about 0.2 °C per decade over the last two decades (2000-2020). These trends are about half as large as those observed outside and are characterized by a remarkable spatial and temporal consistency. The investigated caves represent different types in terms of their ventilation regime and one of them also hosts perennial ice. Key observation sites are located in cave sections where the temporal variability of air temperature is strongly attenuated compared to outside conditions and data from different cave sections show that the main results are valid for large parts of the investigated caves. Continued warming will lead to broad changes in alpine cave environments, including changes in strength and direction of air flow in caves, karst hydrology and subsurface ecosystems. The observed subsurface warming has a particular strong effect on the long-term preservation of perennial ice present in some of these caves. This is shown for an ice cave in the Austrian Alps, where enhanced melt of ice correlates with the observed warming. This cave (and similar ones) will not be able to hold perennial ice beyond the next decade., Competing Interests: Declarations Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

The Marine Isotope Stage (MIS) 11c interglacial and its preceding glacial termination represent an enigmatically intense climate response to relatively weak insolation forcing. So far, a lack of radiometric age control has confounded a detailed assessment of the insolation-climate relationship during this period. Here, we present 230 Th-dated speleothem proxy data from northern Italy and compare them with palaeoclimate records from the North Atlantic region. We find that interglacial conditions started in subtropical to middle latitudes at 423.1 ± 1.3 thousand years (kyr) before present, during a first weak insolation maximum, whereas northern high latitudes remained glaciated (sea level ~ 40 m below present). Some 14.5 ± 2.8 kyr after this early subtropical onset, peak interglacial conditions were reached globally, with sea level 6-13 m above present, despite weak insolation forcing. We attribute this remarkably intense climate response to an exceptionally long (~15 kyr) episode of intense poleward heat flux transport prior to the MIS 11c optimum., (© 2024. The Author(s).)

Frozen water is the most widespread type of ice present in ice caves and forms ice stalagmites and stalactites as well as floor ice, which is often several meters thick. Organic macroremains are commonly rare in this type of cave ice, which makes it difficult to establish a chronology and severely limits the use of such ice deposits as paleoenvironmental archives. Here, the chronology of such ice deposits in the inner part of the glaciated Eisriesenwelt, one of the world's largest ice caves located in the European Alps of Austria, is determined by a combination of radiocarbon and 230 Th dating of cryogenic calcite. The data suggest that this cave ice has formed over the last three millennia, with a marked increase in the average accumulation rate during the thirteenth century, coinciding with the onset of the Little Ice Age in the Alps. Data from a second site closer to the entrance suggests that large parts of this tourist cave were likely ice-free during the Medieval Warm Period and that a substantial part of the ice is probably a relic of the Little Ice Age. The current warming has already penetrated deeper into the cave than during the Medieval Warm Period, although air exchange during the warm season is restricted by a door at the cave entrance., (© 2024. The Author(s).)

Quaternary climate changes are driven in part by variations in the distribution and strength of insolation due to orbital parameters. Continental climate variability is well documented for the most recent glacial-interglacial cycles, yet few records extend further back in time. Such records are critically needed to comprehensively assess the entire spectrum of natural climate variability against the backdrop of anthropogenic warming. Here, we apply uranium isotope geochronology to calcite deposits to date groundwater-table changes in Devils Hole cave, Nevada. The deposits record multi-meter groundwater-table fluctuations over the last 750,000 years, reflecting the long-term evolution of hydroclimate in this presently arid region. During periods between glacial or interglacial extremes, the water table responded sensitively to variations in 65°N summer insolation, likely caused by the increasing extent of North American ice sheets during cold period, which steered moisture-laden trajectories towards the southwestern USA. These orbitally-driven hydroclimatic changes are superimposed on a tectonically-driven long-term decline in the regional groundwater table observed prior to 438,000 ± 14,000 years ago., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2024.)

Damage to speleothems is a common phenomenon in mid-latitude caves, and multiple causes have been proposed. Here we report on one of such type of damage, namely stalagmites that are broken and partially sheared near their base but are still in upright position. Such stalagmites occur in the Obir Caves (Austria) associated with cryogenic cave carbonates, demonstrating the former presence of cave ice. 230 Th dating suggests damage to the speleothems during the Last Glacial Maximum. Numerical modelling combined with laboratory measurements demonstrates that internal deformation within a cave ice body cannot fracture stalagmites, even on a steep slope. Instead, temperature changes lead to thermoelastic stresses within an ice body that reach values equaling to and exceeding the tensile strength of even large stalagmites. Differences in thermal expansion coefficients cause a sharp vertical jump in stress between the stalagmite and the surrounding ice body, and the ice lifts the stalagmite as it expands with increasing temperature. This study refutes the previously accepted model that flow of ice breaks stalagmites, and suggests a link between glacial climate variability and corresponding cooling and warming cycles in the subsurface that weaken and eventually fracture stalagmites due to the opposing thermoelastic properties of calcite and ice., (© 2023. The Author(s).)

Estimating groundwater recharge under various climate conditions is important for predicting future freshwater availability. This is especially true for the water-limited region of the southern Great Basin, USA. To investigate the response of groundwater recharge to different climate states, we calculate the paleo recharge to a groundwater basin in southern Nevada over the last 350,000 years. Our approach combines a groundwater model with paleo-water-table data from Devils Hole cave. The minimum water-table during peak interglacial conditions was more than 1.6 m below modern levels, representing a recharge decline of less than 17% from present-day conditions. During peak glacial conditions, the water-table elevation was at least 9.5 m above modern levels, representing a recharge increase of more than 233-244% compared to present-day conditions. The elevation of the Devils Hole water-table is 3-4 times more sensitive to groundwater recharge during dry interglacial periods, compared to wet glacial periods. This study can serve as a benchmark for understanding long-term effects of past and future climate change on groundwater resources., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2023.)

The variability of the northern westerlies has been considered as one of the key elements for modern and past climate evolution. Their multiscale behavior and underlying control mechanisms, however, are incompletely understood, owing to the complex dynamics of Atlantic sea-level pressures. Here, we present a multi-annually resolved record of the westerly drift over the past 6,500 years from northern Italy. In combination with more than 20 other westerly-sensitive records, our results depict the non-stationary westerly-affected regions over mainland Europe on multi-decadal to multi-centennial time scales, showing that the direction of the westerlies has changed with respect to the migrations of the North Atlantic centers of action since the middle Holocene. Our findings suggest the crucial role of the migrations of the North Atlantic dipole in modulating the westerly-affected domain over Europe, possibly modulated by Atlantic Ocean variability., (© 2022. The Author(s).)

Our understanding of climate dynamics during millennial-scale events is incomplete, partially due to the lack of their precise phase analyses under various boundary conditions. Here we present nine speleothem oxygen-isotope records from mid-to-low-latitude monsoon regimes with sub-centennial age precision and multi-annual resolution, spanning the Heinrich Stadial 2 (HS2) - a millennial-scale event that occurred at the Last Glacial Maximum. Our data suggests that the Greenland and Antarctic ice-core chronologies require +320- and +400-year adjustments, respectively, supported by extant volcanic evidence and radiocarbon ages. Our chronological framework shows a synchronous HS2 onset globally. Our records precisely characterize a centennial-scale abrupt "tropical atmospheric seesaw" superimposed on the conventional "bipolar seesaw" at the beginning of HS2, implying a unique response/feedback from low-latitude hydroclimate. Together with our observation of an early South American monsoon shift at the HS2 termination, we suggest a more active role of low-latitude hydroclimate dynamics underlying millennial events than previously thought., (© 2022. The Author(s).)

Protracted droughts lasting years to decades constitute severe threats to human welfare across the Indian subcontinent. Such events are, however, rare during the instrumental period ( ca . since 1871 CE). In contrast, the historic documentary evidence indicates the repeated occurrences of protracted droughts in the region during the preinstrumental period implying that either the instrumental observations underestimate the full spectrum of monsoon variability or the historic accounts overestimate the severity and duration of the past droughts. Here we present a temporally precise speleothem-based oxygen isotope reconstruction of the Indian summer monsoon precipitation variability from Mawmluh cave located in northeast India. Our data reveal that protracted droughts, embedded within multidecadal intervals of reduced monsoon rainfall, frequently occurred over the past millennium. These extreme events are in striking temporal synchrony with the historically documented droughts, famines, mass mortality events, and geopolitical changes in the Indian subcontinent. Our findings necessitate reconsideration of the region's current water resources, sustainability, and mitigation policies that discount the possibility of protracted droughts in the future.

The Little Ice Age (LIA; ca. 1450-1850 C.E.) is the best documented cold period of the past millennium, characterized by high-frequency volcanism, low solar activity, and high variability of Arctic sea-ice cover. Past studies of LIA Atlantic circulation changes have referenced the North Atlantic Oscillation (NAO), but recent studies have noted that LIA climate patterns appear to possess complexity not captured by an NAO analogue. Here, we present a new precipitation-sensitive stalagmite record from northern Italy that covers the past 800 years. We show that in the early LIA (1470-1610 C.E.), increased atmospheric ridging over northern Europe split the climatological westerlies away from central and northern Europe, possibly caused by concurrent Artic sea-ice reduction. With ongoing ice melting in the northern high latitudes and decreasing solar irradiance in the coming years, the early LIA may potentially serve as an analogue for European hydroclimatic conditions in the coming decades., (© 2022. The Author(s).)

The Liangzhu culture in the Yangtze River Delta (YRD) was among the world’s most advanced Neolithic cultures. Archeological evidence suggests that the Liangzhu ancient city was abandoned, and the culture collapsed at ~4300 years ago. Here, we present speleothem records from southeastern China in conjunction with other paleoclimatic and archeological data to show that the Liangzhu culture collapsed within a short and anomalously wet period between 4345 ± 32 and 4324 ± 30 years ago, supporting the hypothesis that the city was abandoned after large-scale flooding and inundation. We further show that the demise of Neolithic cultures in the YRD occurred within an extended period of aridity that started at ~4000 ± 45 years ago. We suggest that the major hydroclimatic changes between 4300 and 3000 years ago may have resulted from an increasing frequency of the El Niño–Southern Oscillation in the context of weakened Northern Hemisphere summer insolation.

Paleolithic antiquity of parietal art in Ignatievskaya cave, Southern Ural, is supported by its subject (Late Pleistocene animals) as well as by paleontological and palynological data, and 14 C dates from cultural layers associated with artistic activity (17.8-16.3 cal ka BP; association is established by finds of ochre in these layers). However, three 14 C dates of charcoal motifs yielded younger, Holocene ages (7.4-6.0 cal ka BP). In this study, we constrain the age of parietal art in the cave by 230 Th dating of flowstone that brackets the paintings. Flowstone did not form in the cave between c. 78 and 10 ka BP, due to widespread permafrost in northern Eurasia at that time. Our 230 Th dates do not support the middle Holocene age of art in Ignatievskaya cave and are consistent with its Upper Paleolithic antiquity instead., Competing Interests: The authors declare that there are no conflict of interests., (© 2021 The Authors. Geoarchaeology published by Wiley Periodicals LLC.)

The Barbegal watermill complex, a unique cluster of 16 waterwheels in southern France, was the first known attempt in Europe to set up an industrial-scale complex of machines during the culmination of Roman Civilization in the second century CE. Little is known about the state of technological advance in this period, especially in hydraulics and the contemporary diffusion of knowledge. Since the upper part of the Barbegal mill complex has been destroyed and no traces of the wooden machinery survived, the mode of operation of these mills has long remained elusive. Carbonate incrustations that formed on the woodwork of the mills were used to reconstruct its structure and function, revealing a sophisticated hydraulic setup unique in the history of water mills. The lower mills used an elbow shaped flume to bring water onto overshot millwheels. This flume was specially adapted to the small water basins and serial arrangement of the mills on the slope. Carbonate deposits from ancient water systems are therefore a powerful tool in archaeological reconstructions and provide tantalizing insights into the skills of Roman engineers during a period of history that is the direct predecessor of our modern civilization.

Madagascar and the Mascarene Islands of Mauritius and Rodrigues underwent catastrophic ecological and landscape transformations, which virtually eliminated their entire endemic vertebrate megafauna during the past millennium. These ecosystem changes have been alternately attributed to either human activities, climate change, or both, but parsing their relative importance, particularly in the case of Madagascar, has proven difficult. Here, we present a multimillennial (approximately the past 8000 years) reconstruction of the southwest Indian Ocean hydroclimate variability using speleothems from the island of Rodrigues, located ∼1600 km east of Madagascar. The record shows a recurring pattern of hydroclimate variability characterized by submillennial-scale drying trends, which were punctuated by decadal-to-multidecadal megadroughts, including during the late Holocene. Our data imply that the megafauna of the Mascarenes and Madagascar were resilient, enduring repeated past episodes of severe climate stress, but collapsed when a major increase in human activity occurred in the context of a prominent drying trend., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard-Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic-Asian Monsoon-Westerlies directionality of climatic recovery., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)

The causes of Neanderthal-modern human (MH) turnover are ambiguous. While potential biocultural interactions between the two groups are still little known, it is clear that Neanderthals in southern Europe disappeared about 42 thousand years ago (ka) after cohabitation for ~3,000 years with MH. Among a plethora of hypotheses on Neanderthal extinction, rapid climate changes during the Middle to Upper Palaeolithic transition (MUPT) are regarded as a primary factor. Here we show evidence for stable climatic and environmental conditions during the MUPT in a region (Apulia) where Neanderthals and MH coexisted. We base our findings on a rare glacial stalagmite deposited between ~106 and ~27 ka, providing the first continuous western Mediterranean speleothem palaeoclimate archive for this period. The uninterrupted growth of the stalagmite attests to the constant availability of rainfall and vegetated soils, while its δ 13 C-δ 18 O palaeoclimate proxies demonstrate that Apulia was not affected by dramatic climate oscillations during the MUPT. Our results imply that, because climate did not play a key role in the disappearance of Neanderthals in this area, Neanderthal-MH turnover must be approached from a perspective that takes into account climatic and environmental conditions favourable for both species.

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.

Despite its thermodynamical metastability at near-surface conditions, aragonite is widespread in marine and terrestrial sediments. It abundantly forms in living organisms, and its abiotic formation is favored in waters of a Mg 2+ /Ca 2+ ratio > 1.5. Here, we provide crystallographic evidence of a nanocrystalline CaCO 3 polymorph, which precipitates before aragonite in a cave. The new phase, which we term monoclinic aragonite (mAra), is crystallographically related to ordinary, orthorhombic aragonite. Electron diffraction tomography combined with structure determination demonstrates that mAra has a layered aragonite structure, in which some carbonates can be replaced by hydroxyls and up to 10 atomic % of Mg can be incorporated. The diagnostic electron diffraction features of mAra are diffuse scattering and satellite reflections along aragonite {110}. Similar features have previously been reported-although unrecognized-from biogenic aragonite formed in stromatolites, mollusks, and cyanobacteria as well as from synthetic material. We propose that mAra is a widespread crystalline CaCO 3 that plays a hitherto unrecognized key role in metastable aragonite formation.

The projected long-term drying of the southwest (SW) United States in response to climate warming raises a sobering alarm for this already water-limited region, yet the climatic controls on moisture availability over longer time scales remain a topic of debate. Here, we present a 350,000-year record of past water table fluctuations in Devils Hole 2 cave that are driven by variations in recharge amount to the local groundwater flow system. Because of the unprecedented length and precision of our record, we can observe variations in regional moisture availability over the last three glacial-interglacial cycles at a millennial-scale resolution. The timing of past water table rises and falls (>9 m in amplitude) closely coincides with the expansion and reduction of Northern Hemisphere ice volume, which in turn influences the position and intensity of westerly winter storms on orbital time scales. Superimposed on this long-term trend are millennial-scale highstands recorded during the last glaciation that coincide with North Atlantic Heinrich events. Earlier millennial-scale highstands provide the first evidence of multiple short-lived wet periods in the SW United States linked to coeval cooling intervals in the North Atlantic during marine isotope stages 6 and 8. The Devils Hole 2 water table record is currently the longest independently dated paleomoisture record in the SW United States and thus provides a critical testbed to examine the controls on regional moisture availability over larger time scales.

Shulgan-Tash (Kapova) cave in southern Ural, Russia, is the easternmost European site hosting Late Paleolithic cave art. Most of the 195+ drawings catalogued in the cave are made with red natural pigment (ochre), and only a handful of drawings are made with charcoal, see "Catalogue of images" [4], "Höhlenmalerei im Ural: Kapova und Ignatievka; die altsteinzeitlichen Bilderhöhlen im sudlichen Ural," [5]. "Constraining the ages of the Late Palaeolithic cave paintings in the Shulgan-Tash cave, Southern Urals, Russia" [6]. None of the charcoal drawings were directly dated by 14 C method so far. Black lines delineating a figure similar to the outline of a fox are known in the cave. Here we present data on the 14 C AMS date of charcoal with which the lines were drawn. Calibration of the data was performed using the Bomb13NH1 dataset, see "Atmospheric radiocarbon for the period 1950-2010" [7] and the IntCal13 dataset, see "IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP" [8]. The calibrated age distribution has maximum probability density (65.3%) between 1877 and 1918.

Rationale: CO 2 is the main driver of many chemical processes in cave environments. Understanding CO 2 fluxes in a given cave system through monitoring campaigns has become a standard procedure in a wide variety of fields such as paleoclimatology or show cave management. However, conventional methods lack the resolution of isotopic data to capture many transient processes occurring in caves., Methods: A novel approach using isotope ratio infrared spectrometry (IRIS) to monitor cave air pCO 2 , δ 13 C and δ 18 O values in situ was tested and compared with conventional monitoring methods (handheld pCO 2 meter and discrete cave air samples for conventional isotope ratio mass spectrometry). This also involved the development of a field-deployable experimental setup to operate the equipment in rough cave environments., Results: Comparison between data obtained by means of a Thermo Fisher Scientific Delta Ray IRIS instrument shows overall good agreement with conventional monitoring methods in terms of pCO 2 and δ 13 C values. In addition, IRIS allows the δ 18 O values of cave air CO 2 to be measured., Conclusions: IRIS allows identification and tracking of processes at various timescales ranging from transient visitor impact on the cave atmosphere to seasonal trends in cave ventilation. However, the need for an uninterrupted power supply (110/220 V AC) and the relatively large dimensions of the equipment (698 × 1092 × 704 mm, 80 kg) limit the number of caves where deployment of the instrument is feasible. Copyright © 2017 John Wiley & Sons, Ltd., (Copyright © 2017 John Wiley & Sons, Ltd.)