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The Saharo-Arabian desert is part of the largest near-continuous chain of drylands stretching from north-western Africa to the northern China. This harsh and often hyper-arid belt acts as a transition zone separating major biogeographic realms, including the Palearctic, Afrotropics and Indomalayan. This aridity is thought responsible for the creation of unique geographic endemism between Africa and Eurasia. However, there are no direct hydroclimate records from the Arabian hyper-arid interior before the mid-Pleistocene, leaving the terrestrial hydroclimate and the role of Arabia as a biogeographic crossroads or barrier largely unknown.We use desert speleothems preserved from the northern Arabian interior to identify past humid phases over the last 8 million years. These are particularly useful terrestrial climate archives as they act as underground rain gauges, requiring a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Our data reveal evidence of multiple ‘windows of opportunity’ of climate amelioration, allowing biogeographic exchange and dispersals to occur across the Arabian hyper-arid zone. Further, the novel analyses of the isotopic composition (d18O and d2H) of speleothem fluid inclusion waters, representing ‘fossil rainwater’, reveal the diminishing influence of tropical rain-belt precipitation in Arabia across Earth’s transition from a largely ‘ice-free’ northern hemisphere to an ‘ice-age’ world. The extent of Arabian aridity may thus be important in controlling biogeographic dispersals through the Arabian corridor, becoming increasingly less favourable through time. This is supported by fossil evidence which suggest that exchange between biogeographic regions across the Old World Savannah Biome were favoured in the Late Miocene, but became increasingly latitudinally fragmented from the Pliocene onwards. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally.

Four stalagmites were sampled from different excavations in Dechencave (western Germany) and dated to Marine Isotope Stage (MIS) 9. MIS 9 is a very interesting interglacial due to its comparatively high concentration of greenhouse gasses (Lang & Wolff, 2011) and high temperatures (Petit et al., 1999), which are on the same level as during early industrial times (Robertson et al., 2001). Speleothem records from this time period are rare, in particular from central Europe. The stalagmites were precisely dated by the 230Th/U-method using MC-ICP-MS (Mainz University) and stable carbon and oxygen isotope composition were measured using CF-IRMS (Mainz University).The stalagmites grew from 343 to 326 ka BP including Termination IV and MIS 9e. The stable oxygen isotope records of the four stalagmites show rapidly increasing values reflecting the temperature increase during the termination. The timing of this increase agrees well with the timing of Termination IV in the LR04 benthic foraminifera stack (Lisiecki & Raymo, 2005). However, the duration of the termination is shorter in the stalagmites than in the LR04 benthic foraminifera stack (Lisiecki & Raymo, 2005). The stable carbon isotope data decrease, but later and more gradually than the stable oxygen isotope data. This indicates a delayed and more gradual response of the evolving vegetation in response to the warming during Termination IV. Lang, N., Wolff, E.W., 2011. Interglacial and glacial variability from the last 800 ka in marine, ice and terrestrial archives. Climate of the Past 7, 361-380.Lisiecki, L.E., Raymo, M.E., 2005. A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography 20.Petit, J.R., Jouzel, J., Raynaud, D., Barkov, N.I., Barnola, J.M., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., Delmotte, M., Kotlyakov, V.M., Legrand, M., Lipenkov, V.Y., Lorius, C., Pépin, L., Ritz, C., Saltzman, E., Stievenard, M., 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399, 429.Robertson, A., Overpeck, J., Rind, D., Mosley-Thompson, E., Zielinski, G., Lean, J., Koch, D., Penner, J., Tegen, I., Healy, R., 2001. Hypothesized climate forcing time series for the last 500 years. Journal of Geophysical Research: Atmospheres 106, 14783-14803.

Speleothems are terrestrial paleoclimate archives that occur abundantly in the low and mid latitudes. They archive changes in the past hydroclimate in many ways, including the rate of calcium carbonate accumulation – their growth rate. However, determining speleothem growth rates, and in particular growth rate changes, is challenging due to speleothem inherent features such as growth hiatuses, and large and abrupt growth rate changes. Low dating resolution poses an additional problem, as the U/Th measurements that allow for precise dating are time-consuming and expensive.Here, we analyze speleothem growth rates during the Holocene – an ideal period for method testing due to the high abundance of speleothem records in the SISALv2 database. In particular, we compare speleothem growth rates in the early (12-8 kyr BP), mid (8-4 kyr BP) and the late Holocene (4-0 kyr BP). Using synthetically-modelled stalagmites, we test the strengths and weaknesses of state-of-the-art age-depth modelling methods to determine a set of necessary requirements to quantify speleothem growth rates and growth rate changes. Using these, we find slightly higher growth rates in the early Holocene within speleothems that cover at all periods. Comparing growth rates of speleothems that cover only one of the respective periods in the Holocene did not distinguish any period of highest or lowest growth rate. Detailed regional studies and comparison to model data are used to further interpret these results. Reliably determining growth rate changes in the Holocene may help in further understanding and characterizing hydroclimate changes as archived in speleothems also beyond the Holocene.

We present speleothem fluid inclusion δ18Of and δ2Hf values from Larga Cave, Puerto Rico, that cover the interval between 46.2 and 15.3 ka on the millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The data set can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line (GMWL), which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where one cluster comprises samples from cold and dry periods, such as the Heinrich and Greenland stadials (HSs and GSs), as well as parts of the LGM, which exhibit very high δ18Of and δ2Hf values. We interpret this enrichment as being caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials (GIs), but also for some from HS 2 and 3, the δ18Of and δ2Hf values plot on the meteoric water line and modification of fluid inclusion water due to “in-cave” evaporation are found to be negligible. Consequently, variations of recent glacial hydro-climate and temperatures in the western tropical Atlantic can be constrained. In general, δ18Of values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of 2–3 ∘C during the LGM compared to modern cave temperatures. Reconstructed cave temperatures yield an average cooling of −1.4 ± 2.8 ∘C for HS 2 and −3.6 ± 2.2 ∘C for HS 3. Higher δ18Of values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during interstadial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable to or only slightly weaker than today.

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 CaCO3-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 CO2 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 CaCO3-DIC fractionation. Consequently, predicting the CaCO3-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 CO2(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.

The south-eastern Gorny Altai is one of the most hazardous seismogenic area in the north of Central Asia. We present a synthesis of field, 230Th-U geochronological, mineralogical and geochemical data collected on seven Quaternary travertines. All travertines occur within the zones of active faults that border the Chuya and Kurai intermontane basins. Travertine cement mainly comprises calcite (with minor amounts of aragonite), which cements alluvial, alluvial fan, and colluvial deposits. The results of 230Th-U dating suggest that deposition of the travertines was triggered by large paleoearthquakes in the last eight thousand years. Several stages of travertine formation with ages 9–11 ka BP correspond to the known period of strong paleoseismicity in the region (8–16 ka BP). The 123 ka BP travertine resulted from a slip triggered by the Middle Pleistocene deglaciation, while that of 400 ka BP represents seismic motions likely associated with the main Cenozoic orogenic phase. All travertine forming events fall within warm and wet climatic phases (interglacials). Large earthquakes activated faults and caused a rapid rise along them of ambient-temperature bicarbonate groundwater, which was previously sealed in deep-seated Upper Neoproterozoic–Paleozoic limestone-dolostone aquifers. Rapid CO2 degassing of the spring water was the most important control of calcite or aragonite precipitation. Such travertines represent an important tool for paleoseismological research in seismically active regions.

The carbon isotopic signature inherited from soil/epikarst processes may be modified by degassing and prior calcite precipitation (PCP) before its imprint on speleothem calcite. Despite laboratory demonstration of PCP effects on carbon isotopes and increasingly sophisticated models of the governing processes, to date, there has been limited effort to deconvolve the dual PCP and soil/epikarst components in measured speleothem isotopic time series. In this contribution, we explore the feasibility, advantages, and disadvantages of using trace element ratios and δ44Ca to remove the overprinting effect of PCP on measured δ13C to infer the temporal variations in the initial δ13C of dripwater. In 8 examined stalagmites, the most widely utilized PCP indicators Mg/Ca and δ44Ca covary as expected. However, Sr/Ca does not show consistent relationships with δ44Ca so PCP is not universally the dominant control on Sr/Ca. From δ44Ca and Mg/Ca, our calculation of PCP as fCa, fraction of initial Ca remaining at the deposition of the stalagmite layer, yields multiple viable solutions depending on the assumed δ44Ca fractionation factor and inferred variation in DMg. Uncertainty in the effective fractionation of δ13C during degassing and precipitation contributes to uncertainty in the absolute value of estimated initial δ13C. Nonetheless, the trends in initial δ13C are less sensitive to these uncertainties. In coeval stalagmites from the same cave spanning 94 to 82 ka interval, trends in calculated initial δ13C are more similar than those in measured δ13C, and reveal a common positive anomaly initial δ13C during a stadial cooling event. During deglaciations, the trend of greater respiration rates and higher soil CO2 is captured in the calculated initial δ13C, despite the tendency of higher interglacial dripwater situation to favor more extensive PCP.

The transition along the strike of the Sunda subduction zone, from oceanic subduction in the west to subduction of continental Australian lithosphere in the east is envisioned as one of the canonical examples of the structural changes that take place within an overriding plate when a continental lithosphere wedge enters a subduction zone. Yet, the along-strike offset of the trench toward the Australian margin represents a structural response opposite to the predictions of numerical models. To understand this paradox, we analyse the morphotectonic evolution of Sumba island located at the transition from oceanic to continental Indo-Australian lithosphere subduction. Drainage evolution allows us to constrain the topographic evolution of the island since the Pliocene. Flights of uplifted coral reef terraces document Quaternary deformation. Focal mechanisms of shallow crustal earthquakes constrain the current stress field. Together, these data reveal that the island is affected by dextral en-échelon folding. Offshore, west of the island, reverse and strike-slip focal mechanisms evidence an active dextral transpressional zone. The emergence of the island and dextral shearing of the accretionary prism were triggered by subduction of the western lateral boundary of the Australian continental margin. We contend that the Plio-Quaternary tectonic evolution of the region, with transpression and migration of the trench toward the Australian margin is primarily dictated by shear stress transfer from the lower plate to the overriding plate, favored by strong interplate coupling, and by southwestward escape of the Savu-Sumba block following the impingement of the Australian continental margin against Timor island.

The global development and modern distribution of arid zones in subtropical regions (drylands) are likely associated with the global cooling marking the dawn of the Quaternary (~2.6 Ma). This coincides with global shifts in ocean circulation patterns, the intensification of the Walker-Hadley circulation, declining atmospheric CO2, the initiation of glacial–interglacial cycles and the intensification of Northern Hemisphere glaciation, the combination of which has led to the current global distribution of non-polar deserts at ~30° latitude. Although modern drylands represent Earth’s largest terrestrial biome, covering ~46% of global land surfaces and supporting a global population of ~3 billion people, it is currently unclear how drylands will change under future climate change scenarios. Speleothems, preserved in arid-zone caves, are particularly useful terrestrial climate archives as they act as underground rain gauges, which require a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Here, we present new data from speleothems during past ‘warm periods’ from the Arabian hyper-arid zone. We apply a novel technique of extracting speleothem fluid inclusions waters to reconstruct the isotopic composition (d18O and d2H) of ‘fossil rainwater’ preserved in the speleothem fabric pristinely over millions of years. Speleothem evidence suggests that during the last 7 million years, the Sahara-Arabian desert experienced numerous intermittent humid phases, typically occurring with periods of low global ice-volume and warmer global temperatures. We further explore tropical push-pull mechanisms driving heating of the deep tropics and subsequent expansion of the tropical zone and synchronicity of humid phases regionally. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally.

Trace element to Ca ratios in speleothems have emerged as important proxies that reflect local environmental conditions. However, interpretations of speleothem trace element records can be challenging due to various processes. Positive correlations between speleothem Mg/Ca and Sr/Ca have often been interpreted to reflect prior calcite precipitation (PCP), a process potentially modulated by rainfall variability. For quantitative interpretation of PCP, the distribution coefficients for Mg and Sr (DMg and DSr) are required. Here, we use ten cave monitoring calcite and drip water datasets to investigate the influence of temperature and drip water and calcite Mg/Ca and Sr/Ca ratios on speleothem calcite DMg and DSr. The datasets cover a large range of climatic and geological settings resulting in a large range of drip water Mg/Ca ratios. Speleothem calcite DSr shows a positive correlation with the calcite Mg/Ca ratio. Furthermore, DMg shows a clear temperature dependence (DMg = 0.013*e0.035*T). Previous work proposed that the slope of a trend line through a plot of ln(Sr/Ca) versus ln(Mg/Ca) of a speleothem trace element dataset is between 0.709 and 1.003 if dominated by PCP. However, this only holds true if the initial drip water Mg/Ca and Sr/Ca ratios as well as DSr and DMg are constant for the whole dataset. We use an excel-based PCP model (see Electronic Annex) to assess the potential influence of PCP on drip water and speleothem Mg/Ca and Sr/Ca ratios and simulate different initial drip water Ca, Mg, and Sr concentrations corresponding to limestone, dolostone, and mixed host rock compositions. In the case of enhanced PCP and high Mg/Ca ratios, calcite DSr increases progressively with the mean Mg/Ca ratio of the speleothem time series resulting in steeper slopes of ln(Sr/Ca) versus ln(Mg/Ca) of up to 1.45. We show that PCP can induce slopes ranging from 0.709 (or even shallower) up to 1.45. This large range suggests that the previously applied criteria to detect PCP in speleothem records were too strict and may lead to unjustified exclusion of PCP as a potential interpretation of speleothem and drip water trace element ratios. Thus, the number of speleothem Mg/Ca and Sr/Ca datasets that potentially reflect past changes in effective rainfall may be larger than previously suggested.

In the Alps, the Adriatic plate convergence provoked eastward lateral extrusion compensated by strike-slip faulting and N-directed thrusting. Since the Miocene, these complex processes have led to several paleostress phases. Since the Quaternary phase is the least recognized, we used karst cave passages as the geomorphic displacement indicators. This study presents an overview of 190 Quaternary fault ruptures in totally 27 caves in the Eastern Alps, some radiometrically dated, and the paleostress analysis based on cave passages offset. Reactivated faults have been registered with their orientation, slip vector and offset, in caves adjacent to major fault systems of the Eastern Alps. The paleostress was computed using the multiple inversion method for heterogeneous fault-slip data.Most active faults in caves along the southern part of the sinistral Vienna Basin Transfer Fault were NW-SE, and NNE-SSW oriented and revealed mostly normal to sinistral kinematics and cumulative offsets of a few mm to a couple of cms. The associated extensional paleostress state comprised the E-W σ3 in agreement with the opening mode of the Vienna Basin. At sinistral Mur-Mürz Fault, the active faults striking NNE-SSE and ENE-WSW operated under a strike-slip regime with σ1 NE-SW. In the eastern segment of sinistral Salzach-Ennstal-Mariazell-Puchberg fault associated strike-slip paleostress regime with horizontal SE-NE σ1, and subhorizontal SE-trending σ3. This stress regime was computed from reverse, oblique reverse, oblique normal, and sinistral strike-slip reactivated faults documented in the Hochschwab massif. The central segment of Salzach-Ennstal-Mariazell-Puchberg fault is adjoin to Totes Gebirge and Dachstein massifs. In the western part of Totes Gebirge, three stress regimes were recorded. N-S and NW-SE striking oblique normal strike-slip faults revealed an extensional regime with NE σ3. Two strike-slip regimes with NE-SW σ1 and subhorizontal σ3 gently inclined to SE and NW were calculated from mostly steep oblique reverse NNE to NW striking faults with offsets up to a few decimetres. In the Dachstein massif, two paleostress phases were identified: the extensional regime with σ3 subhorizontally tilted to NE and the strike-slip regime with N-S σ1. Tens of active, mostly oblique normal strike-slip faults were documented in massifs adjacent to sinistral Königsee-Lammertal-Traunsee Fault: Hoher Göll, Tennengebirge and Hagengebirge. The dominating associated paleostress is an extensional regime with NE-SW σ3. The polyphase sinistral and reverse-dextral NE-SW faults with Late Pleistocene to Early Holocene reactivations and up to 40 cm offsets, identified at the sinistral Obir Fault attributed to the dextral Periadriatic Line. Neither the strike-slip regime with ENE-plunging σ1 nor the other strike-slip regime with σ1 WNW oriented to fit the regional stress setting. It probably resulted from large-scale complex Karawanken Mts. transpressive shear zone deformation.In conclusion, the paleostress multiple inversions from the Quaternary cave passage ruptures kinematic data brought original information on the paleostress regime over a significant portion of the Eastern Alps in their latest deformational period.

Speleothems from well-monitored Cloşani Cave (Romania), have provided excellent records of past rainfall amount and European winter hydro-climate variability (Warken et al., 2018). Here we present new data allowing to extend the precipitation history of Central-Eastern Europe back to the Last Glacial Maximum (LGM) as well as MIS 3. High-precision 230Th/U ages show that the two analysed speleothems (C09-1 and C09-2) grew nearly continuously during the past 20 ka, with only one growth interruption between c. 11 and 9.7 ka BP. In addition, C09-2 also covers the Dansgaard/Oeschger (D/O) Stadials/Interstadials 16 to 14 between 60 and 52 ka BP. Consistently with previous results, the speleothem proxies (δ18O and δ13C values, as well as laser ablation ICPMS trace element profiles) provide a comprehensive picture of local and regional hydro-climate variability on centennial to glacial/interglacial timescales.Over the course of the record, all proxies reveal millennial-scale features associated with prominent transitions during MIS 3, i.e., D/O events 16 to 14, as well as during the deglaciation, i.e., the Bølling-Allerød (BA) and Younger Dryas (YD). Local wetness as indicated by Mg/Ca ratios exhibits large variability, including pronounced swings between dry conditions during MIS 3 interstadials, and wetter conditions during stadials. After speleothem growth re-initiated at 20 ka BP, Mg/Ca ratios indicate a progressive drying until 15 ka BP, followed by an interval with enhanced variability from the Late Glacial to the Early Holocene. During the subsequent mid to late Holocene, from 8 ka BP to present, the local hydroclimate was characterized by relatively stable conditions. This dataset thus provides new insights into Central-Eastern European precipitation variability, and possibly also into its linkages to the North Atlantic realm.References:Warken, S.F., Fohlmeister, J., Schröder-Ritzrau, A., Constantin, S., Spötl, C., Gerdes, A., Esper, J., Frank, N., Arps, J., Terente, M., Riechelmann, D.F.C., Mangini, A., Scholz, D., (2018). Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record. Earth and Planetary Science Letters 499, 122-133. DOI: 10.1016/j.epsl.2018.07.027

To reliably predict future changes, it is crucial to understand the response of the climate system to past changes in radiative forcing, which are investigated using climate models as well as information extracted from paleoclimate archives such as speleothems. Hydrological changes in past, present, and future are, however, far less understood and more uncertain than changes in temperature.Speleothems are terrestrial archives in the low to mid latitudes. Their growth rate changes are hypothesized to reflect local changes in precipitation amount, albeit the response may be non-linear and subject to karst specific processes. Full coverage of glacial-interglacial cycles and high precision dating through U/Th measurements makes them a suitable archive to assess and constrain state-dependent precipitation changes. However, speleothem inherent features, such as growth hiatuses or large and abrupt changes in growth rates, are a challenge for current age-depth modelling methods.Here, we compare modelled precipitation amount from the Paleoclimate Modeling Intercomparison Project (PMIP), in particular time slices of the Last Glacial Maximum (around 21.000 years before present) and the Mid-Holocene (around 6.000 years before present) to growth rate changes of speleothems from the global speleothem database SISALv2. We perform case studies on a large ensemble of synthetic speleothems to systematically assess the resolution of age measurements necessary to reliably detect and model growth rate changes. These synthetic speleothems cover a large range of characteristic speleothem features observed in the SISALv2 database and are analyzed by six different age-depth modeling methods (linear regression, linear interpolation, copRa, StalAge, Bacon, and Bchron). Comparing the simulated changes with speleothems selected from SISALv2 according to these criteria can thus help to constrain past precipitation changes and subsequently confine uncertainty of future changes.

Although damaged speleothems have been widely investigated to study paleo-earthquake records in caves, only few reports could directly link damages to specific recent earthquakes. We mapped before the 2017 Mw 6.6 Bodrum–Kos earthquake the so-far unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece), which is located at the transition between the Aegean and Anatolian region and is known for its strong seismicity. The cave formed along an active normal fault and records numerous broken columns and flowstones sealed by younger speleothems. New 230Th/U-ages show that paleoseismic events occurred since the formation of the cave, which is older than the limit of the dating method. During a cave visit 2 months after the 2017 Mw 6.6 Bodrum–Kos earthquake we noted that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, have been chipped off by movements along the fractures and were lying on flowstones covered by greenish biofilms. Removal of the broken fragments demonstrated that the chlorophyll pigment below the position of the fragments did not show a colour difference to the surrounding area, which is exposed to the daylight of the cave entrance. The preservation of the photoautotrophic biofilm, which can survive only a few months without daylight, suggests that the stalactites have been broken by the 2017 Mw 6.6 Bodrum–Kos earthquake, which also caused the collapse of several buildings on the island of Kos only 4 km S of Pserimos. We conclude that earthquake capable of causing small shear displacements on fractures can damage speleothems. However, other delicate speleothems including long and slim stalactites remained undamaged.

The first-row transition metals Cu, Ni, and Co show a strong binding affinity to natural organic matter. Compared to dissolved elements and stable water isotopes, they may be transported rapidly through the soil and host rock into caves in response to infiltration events. This study aims to assess the potential of transition metal ratios as indicators for infiltration changes in response to the seasonal and/or event-based rainfall variation.We developed a protocol to analyze Cu, Ni, and Co in the cave drip water using collision cell ICP-QMS without extensive sample pretreatment. The high Ca matrix leads to significant isobaric interferences on all isotope masses. Our method includes a correction of these matrix effects and yields results with comparable accuracy and reproducibility to other published methods. We applied this protocol to drip water samples from Larga Cave (Puerto Rico) covering at least two full annual cycles between 2014 and 2019 on a bimonthly scale.The analysis of external reference materials yielded a reproducibility between 4.7% and 9.2% (relative standard deviation), validating the accuracy of the matrix correction method. The limit of detection is0.04 ppb for Cu,0.02 ppb for Ni, and0.008 ppb for Co. The analysis of drip water samples from Larga Cave reveals pronounced changes of several orders of magnitude in all Element (El) to Ca, Cu/Ni, and Cu/Co ratios in response to seasonal infiltration changes. In addition, we observe a partly even stronger response after major tropical storms and heavy precipitation events of the period of record, for example, tropical storm "Bertha" (2014) and the category 5 hurricanes "Irma" and "Maria" (both 2017).Transition metal ratios can be accurately measured in cave drip waters with high Ca matrix. At our tropical site, these are promising tracers of infiltration changes in response to changes in the amount of rainfall, providing the first step toward tropical cyclone reconstruction using trace elements in speleothems.

Hells Bells are underwater secondary carbonates discovered in sinkholes (cenotes) southeast of Cancun on the north-eastern Yucatán Peninsula, Mexico. These authigenic calcite precipitates, reaching a length of up to 4 m, most likely grow in the pelagic redoxcline. Here, we report on detailed 230Th/U-dating and in-depth geochemical and stable isotope analyses of specimens from cenotes El Zapote, Maravilla and Tortugas. Hells Bells developed during the end of MIS5b/c (~96–90 thousand years ago) and again since the early Holocene, with active growth until present day. The temporal evolution of the geochemistry and isotope composition of Hells Bells calcites appears closely linked to the mid to late Holocene sea-level rise, which reflects changing hydrological conditions of the aquifer. A stabilization of sea level combined with aquifer occlusion during the past ~8 thousand years probably led to a reduction in hydraulic conductivity and a desalinization of the freshwater layer as indicated by decreasing Sr/Ca values. In addition, initial (234U/238U) activity ratios (δ234U0) in the Bells calcite decrease from 55 to 15‰ as sea level converges toward its present state. We propose that the Holocene sea-level rise drives desalinization and subsequent deceleration of leaching of excess 234U from the previously unsaturated bedrock.

The abstract is available here: https://uscholar.univie.ac.at/o:1624693

(IF 4.45: Q1); International audience; The emerged coral reef terrace sequence at Cape Laundi, on the north coast of Sumba Island (Indonesia), with at least 18 successive strandlines, remains poorly dated in spite of numerous previous data. The age discrepancies within these coral reef terraces (CRTs) were previously explained by their polycyclic nature, triggered by marine erosion and reoccupation of old coral colonies by new ones. This study aims at highlighting these processes, as well as the continental denudation that participates in the partial stripping of the thin superficial coral reef layer overlying the pre-existing surface, exhuming older coral colonies. For this purpose, we use a combined analysis of 36Cl cosmogenic concentrations, new 230Th/U ages, and previous dating in order to quantify denudation rates affecting the sequence and to highlight the role of marine erosion in reworking the lowest CRT surface. Our results demonstrate that 1) the lowermost CRT is composite, i.e., formed by different reefal limestone units constructed and eroded during successive highstands of the last interglacial, 2) following the last deglaciation, this CRT has been subjected again to coastal erosion and reoccupation during the Mid Holocene highstand, 3) its distal edge is affected by the current marine erosion and shows denudation rates higher by one to two orders of magnitude (from 279 ± 0.4 to 581 ± 0.4 mm ka−1) than the continental denudation values of higher CRTs (14.7 ± 8.3 mm ka−1 on average), 4) at the scale of a single CRT surface, variations in continental denudation rates are caused by epikarstification roughness, and 5) the distal edges have the highest continental denudation rate due to diffusion and regressive erosion produced by the runoff occurring along the steep downward cliff.

We present speleothem fluid inclusion δ18Of and δ2Hf values from Larga Cave, Puerto Rico, that covers the interval between 46.2 to 15.3 ka before present on millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The dataset can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where the first cluster comprises samples from cold and dry periods, such as Heinrich and Greenland stadials, as well as parts of the LGM, which exhibit very high δ18Of and δ2Hf values. We interpret this enrichment as caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials, but also for some from Heinrich Stadial 2 and 3, the δ18Of and δ2Hf values plot on the meteoric water line and modification of fluid inclusion water due to “in-cave” evaporation is found negligible. Consequently, variations of last glacial hydro-climate and temperature in the western tropical Atlantic can be constrained. In general, δ18Of values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of c. 3 °C during the LGM compared to modern cave temperature. During Heinrich Stadials 2 and 3, reconstructed cave temperatures yield an additional cooling of 2.9 ± 2.6 °C and 4.4 ± 0.6 °C, respectively. Higher δ18Of values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during interstadial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable or only slightly weaker than today.

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 Bolling/Allerod interstadial.

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.

Three small stalagmites from Zoolithencave (southern Germany) show visible laminae, which consist of a clear and a brownish, pigmented layer pair. This potentially provides the opportunity to construct precise chronologies by counting annual laminae. The growth period of the three stalagmites was constrained by the 14C bomb peak in the youngest part of all three stalagmites and 14C-dating of a piece of charcoal in the consolidated base part of stalagmite Zoo-rez-2. These data suggest an age of AD 1970 for the top laminae and a lower age limit of AD 1973–1682 or AD 1735–1778. Laminae were counted and their thickness determined on scanned thin sections of all stalagmites. On stalagmites Zoo-rez-1 and -2, three tracks were measured near the growth axes, each separated into three sections at prominent anchor laminae (I, II, III). Each section was replicated three times (a, b, c). For Zoo-rez-3, only one track was measured. The total number of laminae counted for Zoo-rez-1 ranges from 138 to 177, for Zoo-rez-2 from 119 to 145, and for Zoo-rez-3 from 159 to 166. The numbers agree well with the range constrained by the bomb peak and the age of the charcoal, which supports the annual origin of the laminae. The replicated measurements of the different tracks as well as the three different tracks on the stalagmites Zoo-rez-1 and -2 were cross-dated using the TSAP-Win® tree-ring software. This software is very useful for cross-dating because it enables to insert or delete missing or false laminae as well as identifying common pattern by shifting the series back and forth in time. However, visual inspection of the thin sections was necessary to confirm detection of missing or false laminae by TSAP-Win®. For all three Zoo-rez speleothems, cross-dating of the mean lamina thickness series was not possible due to a missing common pattern. The cross-dating procedure results in three refined chronologies for the three Zoo-rez stalagmites of ranging from AD 1821–1970 (Zoo-rez-1), AD 1835–1970 (Zoo-rez-2), and AD 1808–1970 (Zoo-rez-3).

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.\ud \ud 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.\ud \ud 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.\ud \ud 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.

South-eastern Spain is one of the driest regions in Europe and thus, prone to drought. Terrestrial climate records covering the late Glacial and Holocene from this area are sparse. Here, we present a flowstone record from Cueva Victoria, south-eastern Spain, which covers the late Glacial (15 ka) to the mid-Holocene (7 ka) including the Younger Dryas (YD). Between the onset of the Bølling/Allerød (B/A) and the early Holocene, flowstone δ18O values progressively decrease in accordance with sea-surface temperatures in the Alboran Sea, indicating an increase in precipitation in south-eastern Spain and a supra-regional signal of North Atlantic temperature change. At the same time, decreasing δ13C values suggest progressively increasing precipitation and vegetation density. This trend is interrupted by both colder and drier conditions during the YD. Between 9.7 ± 0.3 and 7.8 ± 0.2 ka, a large positive excursion of the δ13C values indicates a strong reduction in vegetation density, probably as a consequence of very dry spring/summer conditions. In combination with the continuously low speleothem δ18O values and a nearly unchanged growth rate, this suggests increased seasonality (i.e. drier spring/summer conditions, but not a strong reduction in annual precipitation). This is consistent with several other climate records from the Western Mediterranean region, showing that the Western Mediterranean realm (Spain, Italy) experienced pronounced spring/summer drought during this time interval. Interestingly, the timing of this dry period coincided with the African Humid Period. This may be part of a teleconnection with the North African Monsoon via the Hadley cell circulation.