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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.

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.

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., EGUsphere

We present speleothem fluid inclusion ��18Of and ��2Hf 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 ��18Of and ��2Hf 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 ��18Of and ��2Hf 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, ��18Of 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 ��18Of 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 intersta-dial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable to or only slightly weaker than today.

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.

Although quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to using the speleothem data for data-model comparisons. Here, we illustrate this using 456 globally distributed speleothem delta O-18 records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates the process of procuring large numbers of records if data-model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotope values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model's ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotope data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on delta O-18 values, the optimum period for the modern observational baseline and the selection of an appropriate time window for creating means of the isotope data for palaeo-time-slices. European Geosciences Union - W2017/413; Irish Centre for Research in Applied Geosciences (iCRAG); European Association of Geochemistry (Early Career Ambassadors program 2017); Quaternary Research Association UK; Navarino Environmental Observatory, Stockholm University; University College Dublin, Savillex (UK) - SF1428; Ibn Zohr University, Morocco; University of Reading; European Research Council - 694481; Natural Environment Research Council (JPI-Belmont project "PAleao-Constraints on Monsoon Evolution and Dynamics (PACMEDY)"); Geological Survey Ireland - 2017-SC-056; Royal Irish Academy; Deutsche Forschungsgemeinschaft - RE3994/2-1; Past Global Changes (PAGES) programme; info:eu-repo/semantics/publishedVersion

Here, we present the first quantitative speleothem record of lignin oxidation products (LOPs), which has been determined in a Holocene stalagmite from the Herbstlabyrinth Cave in central Germany. In addition, we present LOP results from 16 months of drip water monitoring. Lignin is only produced by vascular plants and therefore has the potential to be an unambiguous vegetation proxy and to complement other vegetation and climate proxies in speleothems. We compare our results with stable isotope and trace element data from the same sample. In the stalagmite, LOP concentrations show a similar behavior to P, Ba and U concentrations, which have previously been interpreted as vegetation proxies. The LOP S∕V and C∕V ratios, which are usually used to differentiate between angiosperm and gymnosperm and woody and non-woody vegetation, show complex patterns suggesting additional influencing factors, such as transport and microbiological effects. The drip water from a fast drip site shows a seasonal pattern of LOPs with low LOP concentrations in winter and higher LOP concentrations in summer. These results indicate the potential of LOPs as a new proxy for vegetational and environmental changes in speleothems but also demonstrate the complexity and the current limitations of our understanding of the transport of lignin from the soil into the cave and the speleothems.

Speleothems provide a great opportunity for paleoclimate reconstruction because they occur almost worldwide and can be dated very precisely using the U-series disequilibrium method. The most commonly used climate proxies are stable isotope values (δ18O and δ13C) and trace elements. However, these are influenced by a variety of surface and in-cave processes, which results in a non-trivial interpretation of the speleothem proxy signals. The last glacial period and in particular the Marine Isotope Stage (MIS) 3 is, compared to the recent warm phase, the Holocene, characterised by larger climate oscillations. These are detectable in δ18O records from Greenland ice cores and also climate archives in Europe, such as pollen or tree ring records. Unfortunately, little direct proxy evidence is available from central Europe, and the climatic and environmental conditions during MIS 3 remain largely enigmatic. Speleothem records from central Europe during MIS 3 are limited due to cold climate conditions and mainly restricted to the warmer southern or alpine regions. Here we present the first results of two flowstones from Bleßberg Cave in Germany. Preliminary 230Th/U-ages make these flowstones the most northern continental growth of speleothems during MIS 3 in central Europe. Thus, these samples provide the unique opportunity to reconstruct climate variability during parts of the last glacial period. With the combination of several different proxies, such as stable isotopes, trace elements and the results from cave monitoring, we will be able to obtain detailed insights into environmental conditions in central Europe during MIS 3 and the Late Glacial.

Characterizing the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, correlating climate events between records, assessing climate periodicities, identifying potential triggers and evaluating climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) working group showed that age model uncertainties are not systematically reported in the published literature, and these are only available for a limited number of records (ca. 15 %, n = 107/691). To improve the usefulness of the SISAL database, we have (i) improved the database's spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age- depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age models and their uncertainties as well as the expansion of the database to include new records and the qualitycontrol measures applied. This paper also documents the age-depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age-depth models, including age-depth temporal uncertainties for 512 speleothems.

Characterising the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, for correlating climate events between records, for assessing climate periodicities, identifying potential triggers, and to evaluate climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) Working Group showed that age-model uncertainties are not systematically reported in the published literature and these are only available for a limited number of records (ca. 15 %, n = 107/691). To improve the usefulness of the SISAL database, we have (i) improved the database’s spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age-depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age-models and their uncertainties as well as the expansion of the database to include new records and the quality-control measures applied. This paper also documents the age-depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age-depth models, including age-depth temporal uncertainties for 512 speleothems. SISALv2 is available at https://doi.org/10.17864/1947.242 (Comas-Bru et al., 2020).

Speleothem δ18O values are commonly used to infer past climate variability. However, both non-linear karst hydrological processes and in-cave disequilibrium isotope fractionation are recognised and hinder the interpretation of δ18O values. In recent years, proxy system models (PSMs) have emerged to quantitatively assess the confounding effects of these processes. This study presents the first integrated stalagmite δ18O PSM (Karstolution) by coupling an existing karst hydrology with an in-cave fractionation PSM. The new modelling framework not only couples the two models, but also includes diffuse flow modelling, coupling of drip rate with infiltration, linking of surface with cave temperature, and incorporates cave seasonality effects. We test Karstolution using a cave monitoring dataset from Golgotha Cave, SW Australia. The predictive capacity of the model is assessed by comparing the output to stalagmite δ18O values. By comparing with observed stalagmite δ18O values, this study is also the first to quantify in-cave disequilibrium both kinetic isotopic fractionation in a speleothem and informs the conclusion that hydroclimatic processes contributes more to the variability of stalagmite δ18O values at Golgotha Cave than does in-cave processes. This is further supported via a sensitivity analysis performed by simulating the impacts of a wider range of cave temperature, ventilation, drip interval and pCO2 values than measured.

Stable hydrogen isotopes ratios of lignin methoxyl groups (expressed as δ2HLM) of wood have been shown to reflect the climate-sensitive δ2H values of precipitation (expressed as δ2Hprecip) modulated by a large uniform negative isotope fractionation. However, a detailed calibration study among temporal variabilities of δ2HLM in tree-ring series, site-specific δ2Hprecip and climate parameters has not been performed yet. Here, we present annually resolved δ2HLM values from nine tree-ring series (derived from four Fagus sylvatica L. trees) collected near stations of the Global Isotope Network of Isotopes in Precipitation (GNIP) and the Deutsche Wetterdienst (DWD) meteorological observatory at Hohenpeißenberg (southern Germany; ~ 48° N, 11° E). The measured nine δ2HLM tree-ring series (common period of overlap 1916-2015) show a strong coherency as indicated by highly significant (p 2HLM chronology shows highest correlations with annually averaged data of δ2Hprecip as well as temperature particularly when using the year defined from previous September to current August (r = 0.73 and 0.56, respectively, p 2HLM chronology shows enhanced correlations with land and sea surface air temperature for multiple (broadly combined) areas across Western Europe (r > 0.6, p 2HLM chronology (r = 0.71, p n = 100). Therefore, δ2HLM values of mid-latitudinal tree-ring archives are considered suitable for large-scale mean annual temperature reconstructions and are therefore able to improve the paleoclimatic potential of Late Holocene tree-ring archives.

Here we present a sensitive method to analyze lignin oxidation products (LOPs) in speleothems and cave drip water to provide a new tool for paleo-vegetation reconstruction. Speleothems are valuable climate archives. However, compared to other terrestrial climate archives, such as lake sediments, speleothems contain very little organic matter. Therefore, very few studies on organic biomarkers in speleothems are available. Our new sensitive method allows us to use LOPs as vegetation biomarkers in speleothems. Our method consists of acid digestion of the speleothem sample followed by solid-phase extraction (SPE) of the organic matter. The extracted polymeric lignin is degraded in a microwave-assisted alkaline CuO oxidation step to yield monomeric LOPs. The LOPs are extracted via SPE and finally analyzed via ultrahigh-performance liquid chromatography (UHPLC) coupled to electrospray ionization (ESI) and high-resolution Orbitrap mass spectrometry (HRMS). The method was applied to stalagmite samples with a sample size of 3–5 g and cave drip water samples with a sample size of 100–200 mL from the Herbstlabyrinth-Advent Cave in Germany. In addition, fresh plant samples, soil water, and powdered lignin samples were analyzed for comparison. The concentration of the sum of eight LOPs (Σ8) was in the range of 20–84 ng g−1 for the stalagmite samples and 230–440 ng L−1 for the cave drip water samples. The limits of quantification for the individual LOPs ranged from 0.3–8.2 ng per sample or 1.5–41.0 ng mL−1 of the final sample solution. Our method represents a new and powerful analytical tool for paleo-vegetation studies and has great potential to identify the pathways of lignin incorporation into speleothems.

Supplemental material, Supplement_Budsky for Speleothem δ13C record suggests enhanced spring/summer drought in south-eastern Spain between 9.7 and 7.8 ka – A circum-Western Mediterranean anomaly? by Alexander Budsky, Denis Scholz, Jasper A Wassenburg, Regina Mertz-Kraus, Christoph Spötl, Dana FC Riechelmann, Luis Gibert, Klaus Peter Jochum and Meinrat O Andreae in The Holocene

Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (δ18O, δ13C) measurements are referenced by distance from the top or bottom of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information on the full range of measurements carried out on each speleothem and information on the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data. The compiled data are available at http://dx.doi.org/10.17864/1947.147 .

A flight of marine terraces along the Cuban coast records Quaternary sea-level highstands and a general slowly uplifting trend during the Pleistocene. U/Th dating of these limestone terraces is difficult because fossil reef corals have been affected by open system conditions. Terrace ages are thus often based on geological and geomorphological observations. In contrast, the minimum age of the terraces can be constrained by dating speleothems from coastal mixing (flank margin) caves formed during past sea-level highstands and carving the marine limestones. Speleothems in Santa Catalina Cave have ages >360ka and show various cycles of subaerial-subaqueous corrosion and speleothem growth. This suggests that the cave was carved during the MIS 11 sea-level highstand or earlier. Some stalagmites grew during MIS 11 through MIS 8 and were submerged twice, once at the end of MIS 11 and then during MIS 9. Phreatic overgrowths (POS) covering the speleothems suggest anchialine conditions in the cave during MIS 5e. Their altitude at 16m above present sea level indicates a late Pleistocene uplift rate of

The connection between climatic change and social response is complex because change articulates a number of inter-related factors. Human decisions are filtered by social buffers – including social memory, risk perception, and cultural priorities – and the rate and scale of climate change is usually much larger than the scale of human decision-making. In this article, we provide information on climate change based on precisely dated speleothems with the response evident in archaeological sites that have radiocarbon date ranges within the same time frame. A stalagmite recovered from within the catchment area for aquifer recharge of the Pre-Arawak site of Angostura in Barceloneta, Puerto Rico, shows that a significant wet period occurred between 3.9 and 3.1 ka (primarily centered at 3.5 ka). We investigate the effect that this increase in precipitation had on the earliest occupations on the island in the context of palaeoenvironmental, geoarchaeological, and archaeological records from Angostura, Maruca, and Paso del Indio. Our analysis suggests the presence of two different adaptation strategies: settlement relocation and microlandscape modification. Our study concludes that the social response to change cannot be seen as monolithic given that human behavior, even within the same period, addresses the needs of individual groups with different priorities. This multiplicity of responses can indeed enhance resilience as social support can continue through alliances and exchanges, strengthening social bonds that can help buffer catastrophes. The results can help shed light on the range of adaptation strategies to change encompassed within the manifestations of social resilience or vulnerability.

The last four interglacials (intervals during which global ice volume was similar to, or less than, that of our current warm stage) correspond to the warmest parts of the marine oxygen isotope stages MIS 5, 7, 9, 11. These interglacials ffollowed the 100-kyr rhythm of eccentricity, but each had different insolation regimes, different durations, different ice volumes and different sea-level heights, bur atmospheric greenhouse gas concentrations were similar and reached values which, by and large, were close to those of the current interglacial (Holocene or MIS1) before the industrial revolution led to the artificial enrichment of the atmosphere's greenhouse gas concentrations via the burning of fossil fuels ... The last four interglacials (intervals during which global ice volume was similar to, or less than, that of our current warm stage) correspond to the warmest parts of the marine oxygen isotope stages MIS 5, 7, 9, 11. These interglacials ffollowed the 100-kyr rhythm of eccentricity, but each had different insolation regimes, different durations, different ice volumes and different sea-level heights, bur atmospheric greenhouse gas concentrations were similar and reached values which, by and large, were close to those of the current interglacial (Holocene or MIS1) before the industrial revolution led to the artificial enrichment of the atmosphere's greenhouse gas concentrations via the burning of fossil fuels ...

International audience; The last four interglacials (intervals during which global ice volume was similar to, or less than, that of our current warm stage) correspond to the warmest parts of the marine oxygen isotope stages marine isotopic age (MIS) 5, 7, 9, and 11. These interglacials followed the 100-kyr rhythm of eccentricity, but each had different insolation regimes, different durations, different ice volumes, and different sea-level heights. However, atmospheric greenhouse gas concentrations were similar and reached values, which, largely, were close to those of the current interglacial (Holocene or MIS 1) before the industrial revolution led to the artificial enrichment of the atmosphere's greenhouse gas concentrations via the burning of fossil fuels. This chapter summarizes the state of knowledge on each of the climatic warm intervals.

Mithilfe von fossilen Riffkorallen ist eine exakte Rekonstruktion der Meeresspiegelschwankungen der Vergangenheit möglich. Ein bekanntes Problem bei der Uranreihen-Datierung fossiler Riffkorallen sind initiale (234U/238U) Aktivitätsverhältnisse, die nicht durch den radioaktiven Zerfall in einem geschlossenen System erklärt werden können. Dieses Phänomen ist unter dem Begriff diagenetische Veränderungen bekannt. In der vorliegenden Arbeit werden fossile Riffkorallen aus Aqaba, Jordanien, und Barbados, Westindische Inseln, untersucht. Die Porites Korallen aus Aqaba zeigen einen hohen Grad diagenetischer Veränderungen und sind daher ideal geeignet, um die diagenetischen Prozesse zu untersuchen. Mithilfe eines numerischen Modells wird gezeigt, dass die Aktivitätsverhältnisse dieser Korallen durch nachträgliche Uranaufnahme gefolgt von teilweisem Verlust des aufgenommenen Urans erklärt werden können. Auf dieser Basis wird ein Korrekturverfahren (das Isochronenverfahren) entwickelt, das es ermöglicht, glaubwürdige Uranreihen-Alter für Korallen zu berechnen, die nicht mit den herkömmlichen Methoden datiert werden können. Die Acropora palmata und Diploria strigosa Korallen aus Barbados zeigen einen geringeren Grad diagenetischer Veränderungen. Es wird gezeigt, dass diese Korallen durch einen anderen Prozess beeinflusst wurden als die Korallen aus Aqaba. Daher können sie nicht mit der Isochronenmethode datiert werden. Dennoch ist es möglich, Höhe, Beginn und Dauer des Meeresspiegel Hochstands während des Marinen Isotopen Stadiums (MIS) 6.5 (~175000 Jahre vor heute) zu bestimmen. MIS 6.5 ist eine außergewöhnliche Klimaphase innerhalb der letzen 300000 Jahre. Die vorliegende Meeresspiegelkurve ist die erste, exakt datierte, direkte Meeresspiegelrekonstruktion für das Marine Isotopen Stadium 6.5.

Ziel des Projekts CheckExtrema ist, Anzeichen auf Überflutungsereignisse in der Region Franken anhand von historischen und geologischen Informationen zu erkennen, und vergangene Überschwemmungsereignisse mithilfe geeigneter historischer und geologischer Archive in einem gemeinsamen Überschneidungszeitraum zu identifizieren. Als geologisches Archiv wurde Stalagmit KTH-2 (Kleine Teufelshöhle, Fränkische Schweiz) mittels 14C- und 230Th/U-Methode datiert und hochaufgelöst auf die stabilen Isotopenverhältnisse von Sauerstoff (δ18O) und Kohlenstoff (δ13C) sowie die spezifischen Spurenelementmuster von Mg, P etc. analysiert. Parallel dazu wurde das Staats- und Stadtarchiv Nürnberg im Zeitraum 1400 bis 1800 n. Chr. auf Informationen über Überschwemmungsereignisse durchsucht. Um die Datenauflösung der δ18O-Verhältnisse im Überschneidungszeitraum zu erhöhen, wurde zusätzlich zu der konventionellen δ18O-Messmethode (Micromill + IR-MS; 90 µm) eine mit 7 und 15 µm höchstaufgelöste Isotopenanalyse mittels Sekundärionen-Massenspektrometrie (SIMS) durchgeführt. Für eine zuverlässigere Interpretation der Klimaproxies wurde in der Kleinen Teufelshöhle (KTH) und der benachbarten Zoolithenhöhle (ZooH) im Zeitraum 2016-2019 ein Monitoring-Programm durchgeführt, bei dem die Parameter der Höhlenatmosphären und die Tropfraten an fünf Tropfstellen hochaufgelöst aufgezeichnet, Tropf- und Niederschlagswässer mit ein- bis vierwöchiger Auflösung hochaufgelöst beprobt und frische Calcit-Präzipitate entnommen wurden. Die Temperaturen innerhalb der Höhlen spiegeln die Oberflächentemperaturen mit Abweichungen < 1 °C sehr gut wider. Bei hohen rel. Feuchtigkeiten von ≈ 100 % können evaporative Prozesse weitestgehend ausgeschlossen werden. Geringere (höhere) CO2-Gehalte über die Wintermonate (Sommermonate) deuten auf gut bewetterte Höhlen hin. Die fünf Tropfstellen zeigen eine breite Tropfratencharakteristik mit schnellen (langsamen) Tropfraten und schneller (fehlender) Reaktion auf Infiltrationsereignisse. Die Auflösung des Frankendolomits läuft weitestgehend kongruent ab. Die Mg/Ca- und Sr/Ca-Verhältnisse im Tropfwasser werden über variierende PCP-Raten und variierende Karstwasserverfügbarkeiten gesteuert. Temporär erhöhte Gehalte von Na, K, Al, Fe, Zn und P werden mit einer erhöhten Silikatverwitterungsrate und der Anwesenheit von Kolloiden im Tropfwasser begründet. HCO3- ist das dominierende Anion im Tropfwasser. Ein SICalcit > 0 zeigt eine konstante Übersättigung der Karstwässer an. An fast allen Tropfstellen findet ganzjährig Calcitpräzipitation statt. Das δ18O-Inputsignal des Niederschlags zeigt eine Temperaturabhängigkeit von 0,22 ‰/°C. Aufgrund der geringeren Infiltration im Sommer spiegeln die δ18O-Werte im Tropfwasser vor allem das leichtere δ18O-Inputsignal des Winterniederschlags wider. Im Hinblick auf die δ18O-Werte fällt das Calcitmaterial zum Großteil im isotopischen Gleichgewicht mit dem Tropfwasser aus. Die Temperaturabhängigkeit der Fraktionierung beläuft sich auf -0,39 ‰/°C. Die δ13C-Werte des Calcitmaterials fallen vereinzelt im isotopischen Gleichgewicht mit dem DIC des Tropfwassers aus. Schwerere δ13C-Werte deuten auf eine erhöhte CO2-Entgasung oder Ungleichgewichts- und/oder kinetische Fraktionierungsprozesse hin. Stalagmit KTH-2 ist bis 2004 n. Chr. gewachsen. Rezentes Wachstum wurde dabei über die Identifikation des 14C-Bombenpeaks festgestellt. Im Zeitraum 1000-2004 n. Chr. weist Stal-KTH-2 Wachstumsraten von 21 und 7 µm/a auf, was einer jährlichen Auflösung der δ18O-SIMS-Analyse entspricht. Zwei direkt nebeneinander gelegte δ18O-SIMS-Messlinien zeigen untereinander eine hohe Übereinstimmung von rp = 0,59 (p < 0,001, n = 963, rsp = 0,60). Im Vergleich zu dem IR-MS-Datensatz zeigen die beiden SIMS-Datensätze einen gleichmäßigen Offset von ca. 1,2 ‰, der mit dem Matrixeffekt zwischen dem kristallinen Marmor-Standard und dem Calcitmaterial begründet wird. Die normalisierten gemittelten δ18O-SIMS-Daten stimmen bei einer Angleichung der SIMS- an die IR-MS-Auflösung mit einem rp von 0,62 (p < 0,001, n = 84, rsp = 0,60) gut mit dem IR-MS-Datensatz überein. Kalte und trockene Winterverhältnisse zur Zeit der Kleinen Eiszeit (LIA, 1450-1800 n. Chr.) resultierten aufgrund eines verringerten Einflusses des leichteren δ18O-Winterniederschlags in schwereren δ18O-Werten in Stal-KTH-2. Ein Rückgang der Vegetation und der mikrobiellen Aktivität hatten schwerere δ13C-Werte und höhere P-Gehalte und das Auftreten von PCP erhöhte Mg/Ca-Verhältnisse zur Folge. Über den 30-jährigen gleitenden Häufigkeitsverlauf in einer Hochwasser-Chronologie für Nürnberg aus dem historischen Archiv werden im Zeitraum 1300-2000 n. Chr. sechs Hochwasser-/Kälteperioden identifiziert. Dass diese auch im Verlauf der δ18O-Verhältnisse in Stal-KTH-2 erkannt werden, lässt darauf schließen, dass in diesen Zeiträumen aufgrund kalter (und trockener) Winterverhältnisse Hochwässer durch Eisstau häufig auftreten konnten und dadurch gleichzeitig schwerere δ18O-Werte in Stal-KTH-2 gespeichert wurden. Zeitgleich zu den Hochwasser-/Kälteperioden werden NAO--Bedingungen und eine verringerte Sonneneinstrahlung beobachtet. Kurzzeitig schwerere δ18O-Verhältnisse konnten mit bekannten Vulkanausbrüchen in Verbindung gebracht werden. Ein Anstieg der δ18O- und δ13C-Verhältnisse hin zu schwereren Werten im jüngsten Wachstumsbereich von Stal-KTH-2 kann mit der Erschließung der Großen Teufelshöhle und der dadurch verursachten stärkeren Höhlenventilation begründet werden. Die Ablagerung von Detritusmaterial auf der Tropfsteinoberfläche resultierte in einem Anstieg der Spurenelementkonzentrationen.

The sensitivity of tropical Atlantic precipitation patterns to the mean position of the Intertropical Convergence Zone (ITCZ) at different time scales is well‐known. However, recent research suggests a more complex behavior of the northern hemispheric tropical rain belt related to the ITCZ in the western tropical Atlantic. Here we present a precisely dated speleothem multi‐proxy record from a well‐monitored cave in Puerto Rico, covering the period between 46.2 and 15.3 ka. The stable isotope and trace element records document a pronounced response of regional rainfall to abrupt climatic excursions in the North Atlantic across the Last Glacial such as Heinrich stadials and Dansgaard/Oeschger events. The annual to multidecadal resolution of the proxy time series allows substructural investigations of the recorded events. Spectral analysis suggests that multidecadal to centennial variability persisted in the regional hydroclimate mainly during interstadial conditions but also during the Last Glacial Maximum. In particular, we observe a strong agreement between the speleothem proxy data and the strength of the Atlantic meridional overturning circulation, supporting a persistent link of oceanic forcing to regional precipitation. Comparison to other paleo‐precipitation records enables the reconstruction of past changes in position, strength, and extent of the ITCZ in the western tropical Atlantic in response to millennial‐ and orbital‐scale global climate change., Plain Language Summary: It is important to understand the climatic circumstances of how rainfall in the western tropical Atlantic varies under a changing climate to better manage the water supply for millions of people. However, it is not well understood how rainfall varied in the past, especially during the Last Glacial period, a time of strong climate variability and abrupt climate changes. Here, we use a stalagmite from Puerto Rico to create a new record of past changes in rainfall in this region. For this purpose, we analyzed proxy data that reveal a series of wet and dry periods during the Last Glacial corresponding to rapid global climate shifts. Our rainfall‐sensitive stalagmite record captured changes of the tropical rain belt on various timescales and shows that this variability in rainfall is closely connected to changes in the strength of the ocean circulation. This suggests that the link between the ocean and the atmosphere is more robust than previously assumed. The comparison of our record with other rainfall‐sensitive records from Central America and the northern Caribbean allows for a detailed reconstruction of the spatial and temporal changes of the western tropical Atlantic rain belt., Key Points: Puerto Rican speleothem record documents multidecadal to millennial‐scale precipitation variability between 46.2 and 15.3 ka. Climate proxies show a distinct rainfall response to abrupt North Atlantic climate change including Heinrich and Dansgaard/Oeschger events. Compilation of regional precipitation records allows to reconstruct past changes in ITCZ patterns in the western tropical Atlantic., National Science Foundation (NSF) http://dx.doi.org/10.13039/501100000930, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

In situ laser ablation analyses rely on the microanalytical homogeneity of reference materials (RMs) and a similar matrix and mass fraction between unknown samples and RMs to obtain reliable results. Suitable carbonate and phosphate RMs for determination of Sr isotope ratios in such materials are limited. Thus, we determined Sr-87/Sr-86 ratios of several carbonate (JCt-1, JCp-1, MACS-1, MACS-3) and phosphate (MAPS-4, MAPS-5, NIST SRM 1400, NIST SRM 1486) international RMs using dissolved samples and two different multi-collector inductively coupled plasma-mass spectrometers (MC-ICP-MS). Our Sr isotope data are in agreement with published data and have an improved measurement precision for some RMs. For MACS-1, we present the first Sr-87/Sr-86 value. We tested the suitability of these materials for microanalytical analyses by LA-MC-ICP-MS, with two different laser ablation systems: a conventional nanosecond laser and a state-of-the-art femtosecond laser. We investigated the RMs micro-homogeneity and compared the data with our solution data. Both laser ablation systems yielded identical Sr-87/Sr-86 ratios within uncertainty to the solution data for RMs with low interferences of REEs. Therefore, these carbonate and phosphate RMs can be used to achieve accurate and precise results for insitu Sr isotope investigations by LA-MC-ICP-MS of similar materials.