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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