Drip Site Research Articles

A Comparative Study of Cave System Calcium Isotope Ratios: Implications for Quantitative Reconstruction of Paleorainfall From Speleothems

AbstractVariations in speleothem calcium isotope ratios (δ44Ca) are thought to be uniquely controlled by prior carbonate precipitation (PCP) above a drip site and, when calibrated with modern data, show promise as a semi‐quantitative proxy for paleorainfall. However, few monitoring studies have focused on δ44Ca in modern cave systems. We present a multi‐year comparative study of δ44Ca, carbon isotopes (δ13C), and trace elemental ratios from cave drip waters, modern calcite, and host rocks from two cave systems in California—White Moon Cave (WMC) and Lake Shasta Caverns (LSC). Drip water and calcite δ44Ca from both caves indicate PCP‐driven enrichment, and we used a simple Rayleigh fractionation model to quantify PCP variability over the monitoring period. Modern calcite trace element and δ44Ca data positively correlate at WMC, but not at LSC, indicating a shared PCP control on these proxies at WMC but not at LSC. At both WMC and LSC, we observe an inverse relationship between PCP and rainfall amounts, though this relationship is variable across individual drip sites. Our modeled data suggest that WMC experiences ∼20% more PCP than LSC, consistent with the fact that WMC receives less annual rainfall. This work supports speleothem δ44Ca as an independent constraint on PCP that can aid in the interpretation of other hydrologically sensitive proxies and provide quantitative estimates of paleorainfall. Additional, long‐term monitoring studies from a variety of climate settings will be key for understanding δ44Ca variability in cave systems more fully and better constraining the relationship between PCP and rainfall.

Trace element partitioning controls on cave drip water compositions through prior calcite and aragonite precipitation

Speleothem trace element records can provide seasonal resolution climate reconstructions, but the interpretation can be challenging. Aragonite samples are understudied compared to calcite samples, despite that aragonite has 10x higher uranium concentrations and thus provide excellent dating precision. Here we present a high-resolution dataset of drip water trace elements (calcium, magnesium, strontium, barium, uranium) that are commonly affected by prior carbonate (calcite / aragonite) precipitation, a process often driven by effective rainfall. Our data suggest that prior calcite and aragonite precipitation can occur at the same drip site complicating the interpretation of strontium and uranium concentrations in aragonite speleothems. However, both processes can be distinguished with the “Sinclair test” through the trendline analysis of logarithmic relationships. Furthermore, our data show that aragonite speleothems slowly growing under relatively constant conditions are ideal to record variations in prior carbonate precipitation with its barium concentrations, independent from the prior carbonate precipitation mode.

Hydrogen and oxygen isotope signal transmission in rainfall, soil water, and cave drip water in Liangfeng Cave, Southwest China

δD and δ18O isotope signatures were widely used as tracers to investigate recharge processes of rainfall transfer into caves in the vadose zones of karst regions. The present research systematically monitored rainfall, soil water, and drip water at the Liangfeng Cave in Guilin City, China, from January 2020 to September 2022, as these aspects remain poorly quantified. The δD and δ18O compositions of rainfall were depleted during the rainy season and enriched during the dry season. The local meteoric water line (LMWL) was described as δD = 7.98δ18O + 11.52. The dry season is mainly characterized by resident soil water, with little mobile soil water, whereas the primary source of recharged drip water is stored bedrock water on the top of the cave. During the rainy season, resident and mobile soil water exchanged with each other, resulting in homogenous δD and δ18O compositions across different soil depths and indicating a lack of ecohydrological separation; however, δD and δ18O signature in drip water may differ from the original observed in rainfall, suggesting that the residence time affected the response time of the drip water to rain. Moreover, mixed stored older water in the overlying bedrock was the primary drip water recharge source each season; thus, drip water's isotope amplitude values were more depleted than rainfall's. Distinct flow paths also created differences in the lag time and amplitude at each drip site. During high-intensity rain, the isotopic signals were rapidly transmitted by preferential flow at different soil depths and via drip water. The δD and δ18O signals in the drip water showed significant depleted excursions several months after high-intensity rainfall. These findings indicate that ecohydrological separation did not occur under any circumstances within the study area, and care should be taken when interpreting significant depleted excursions of δD and δ18O signals in drip water during the summer monsoon or the amount of rainfall in stalagmites across seasonal or interannual scales.

Contemporaneously growing speleothems and their value to decipher in-cave processes – A modelling approach

In recent decades speleothems have become valuable climate archives and are of crucial importance for the investigation of past climate conditions. Albeit much progress has been made to understand speleothem proxies, it remains difficult to differentiate between a direct climate signal and variations, which occurred due to in-cave processes like prior carbonate precipitation (PCP), CO2 degassing or exchange between dissolved inorganic carbon and cave air CO2. Here, we investigate a large quantity of previously published data sets of stable C and O isotopic composition as well as growth rate of contemporaneously growing speleothems from the same cave site. We argue that differences in those paleoclimate proxies arise mainly by differences of drip site specific conditions as climate conditions for pairs of contemporaneously growing speleothems can be considered to be similar. To better understand the observed differences in the isotopic composition and growth rate of contemporaneously growing speleothems, we investigate the impact of in-cave processes using a speleothem isotope and growth model. Evolution of the isotope composition is modelled as a Rayleigh process, which includes CO2 degassing and carbonate precipitation, oxygen and carbon exchange between the bicarbonate and the drip water and between bicarbonate and cave air CO2. The model is able to calculate growth rates and accounts for carbonate deposition in form of prior carbonate precipitation as well as carbonate deposition at the speleothem top. We find that CO2 exchange and PCP are necessary to explain the observed isotopic and growth rate differences in previously published contemporaneously growing speleothems. Thus, both processes need to be accounted for in speleothem-based paleoclimate reconstructions, which highlight the importance of recent efforts to correct speleothem isotope records for cave-internal effects. Furthermore, this study demonstrates the advantage of investigating pairs of contemporaneously growing speleothems from one cave to evaluate the importance of cave-internal processes in individual caves and if they potentially changed over time.

Recharge variability in Australia's southeast alpine region derived from cave monitoring and modern stalagmite δ18O records

Oxygen isotopic (δ18O) variations in stalagmite records have the potential to provide new insights about past climates beyond the instrumental record. This paper presents the first high-resolution oxygen isotope time series of three coeval stalagmite records from the alpine region of south-eastern Australia covering the period 1922–2006 CE. We use extended surface and cave monitoring datasets, petrographic investigation, modelled recharge time series and farmed calcite precipitates to assess the controls on speleothem δ18O and investigate the coherence between three records from Harrie Wood Cave. The drip water response to recent interannual rainfall variability shows that cave drip water Cl−, δ18O and drip rate display a clear response to an increase in rainfall recharge. It is demonstrated that stalagmites from the same drip sites also record variability in interannual recharge, where an increase in δ18O values is observed with lower recharge, while a decrease in δ18O values correspond to higher recharge amounts. The three stalagmite δ18O records are in broad agreement, showing common responses to relatively higher recharge between 1945 and 1995 CE and the low recharge periods between 1937 and 1945 CE (World War II drought) and late 1996 to 2006 CE (beginning of the Millennium Drought). However, differences in the magnitude of the relative response of each stalagmite δ18O record varies. Based on evidence from our cave monitoring study and farmed calcites, we conclude that the differences between the three stalagmite records is attributed to variability in the contribution of preferential flows during recharge events and the store reservoir volume supplying the drip site. When the δ18O decreases in response to enhanced recharge, the speleothem δ13C also decreases, and this is interpreted to reflect a soil respiration response to changes in soil moisture availability due to recharge. Hence, stalagmite δ18O from the Australian alpine region can be applied to reconstruct periods of relatively higher and lower rainfall recharge and thus extend our knowledge of the timing and relative magnitude of droughts as well as past periods of higher recharge in this region.

Deciphering paleohydrology from the petrography and microstratigraphy of stalagmites (MIS 5 – Holocene, Moulis Cave, Ariège, S. France)

A stalagmite from Moulis Cave in the northern Pyrenean piedmont in SW France provides a discontinuous record between the last interglacial and the Holocene. The integrated study of petrography, microstratigraphy and internal architecture of the stalagmite documents paleohydrological history of the drip site during speleothem growth, including infiltration conditions and calcite saturation state of the water feeding the stalagmite. Following diagenetic screening which demonstrates the excellent state of preservation of the speleothem, a set of petrographical, mineralogical and geochemical analytical techniques was used to characterize: 1. the successive growth units and their bounding surfaces, including facies and nature of processes occurring at the level of each discontinuity, and 2. the morphological changes of the stalagmite apex and stacking pattern.Observations reveal that each bounding surface results from a particular group of events, the nature and effects of which are petrographically clearly identifiable. During the interstadials 5b-5a of the last interglacial, the stalagmite developed at a relatively moderate growth rate and under stable drip rate conditions, except at the onset of the 5b cooling. The highest growth rates are recorded during the Bølling-Allerød to Younger Dryas, and the Early-Middle Holocene. During the Younger Dryas, a cold and humid climate is suggested on the northern piedmont of the Pyrenean range while temperate and humid conditions prevailed during the Early Holocene. The Middle Holocene was still humid North of the Pyrenees, except during the cold and dry event at ∼6.2 kyrs. Finally, during the last growth phase of the stalagmite, the growth rate slowed down drastically in relation to increasing frequency of high infiltration events, possible floodings and a decreasing saturation of the drip water relatively to calcite.

Long-term elemental trends in drip waters from monitoring Bunker Cave: New insights for past precipitation variability

A seven-year (2006–2013) monitoring was conducted in Bunker Cave, northwest Germany. The monitoring programme incorporates cave air temperature, the amount of precipitation, drip rates at five drip sites (TS 1, 2, 3, 5, 8) in the cave, and the analyses of cation (Ca2+, Mg2+, Sr2+, Na+, K+) and anion (HCO3−, NO3−, SO42−, Cl−) concentrations of rain, soil, and drip waters with a monthly (2006–2011) and bimonthly (2012−2013) interval. Further, the Ca, Mg, and Sr concentrations of the two host rock components, limestone and dolomite, were analysed.The analysis of rain, soil, and drip waters allowed to distinguish between geogenic and anthropogenic influences on the hydrochemistry of the cave. The limestone is the source of Ca2+, Mg2+, Sr2+, and HCO3− in all drip waters, as well as SO42− from pyrite dissolution from the limestone. Chloride and NO3− were inserted by anthropogenic sources such as aerosols from road salt, fertilisers, and industry. Drip site TS 1 shows a strong seasonal drip rate, which is simultaneous with a seasonal variation in ion concentrations (Ca2+, Mg2+, Sr2+, HCO3−, SO42−), induced by younger water transported by fracture flow during episodes of fast drip rates. Drip water at drip site TS 5 is recharged by water which probably dissolves prior calcite precipitation (PCP), resulting in low and constant Mg2+ and Sr2+ concentrations. Drip water at drip sites TS 2, 3, and 8 are mainly influenced by PCP, whereas drip waters at TS 2 and 8 are additionally influenced by incongruent dolomite dissolution indicated by their increasing Mg2+ and stable Sr2+ concentrations. Furthermore, Cl− and SO42− concentrations show increasing and decreasing long-term trends for these three PCP-influenced drip waters at sites TS 2, 3, and 8, respectively.The decreasing pattern in infiltration/precipitation from 2000 to 2013 is not very pronounced; however, the continuous draining of the aquifer is visible in the decreasing drip rates over the seven-year monitoring period. This is reflected in the long-term increasing trends of Mg/Ca, Sr/Ca ratios induced by PCP, and Cl− concentrations, as well as in the decreasing long-term trend of the SO42− concentrations in drip waters of drip sites TS 2, 3, and 8.For a better understanding of the cave system with its complex processes, a multi-element-proxy long-term cave monitoring of rain, soil, and drip waters appears to be a reasonable step to be followed by the interpretation of the element proxies of speleothems. This monitoring emphasizes Mg/Ca and Sr/Ca ratios, as well as Cl− and in particular SO42− concentrations as potential past infiltration/precipitation proxies. Mg/Ca and Sr/Ca ratios are the strongest proxies to reconstruct infiltration/precipitation of measured elements in stalagmites, in cases Sr/Ca is not overprinted by growth rate influences. In addition, the sulphur concentration in speleothems may be an infiltration/precipitation proxy in the case of a geogenic source from the host rock.

A framework for triple oxygen isotopes in speleothem paleoclimatology

Speleothem oxygen isotope (δ18O) records provide key insight into the rate and timing of terrestrial paleoclimate changes during the late Quaternary. However, it can be difficult to deconvolve the δ18O signal into individual components, which include processes related to moisture source, moisture transport, temperature, precipitation amount, infiltration, and the cave environment. We developed a framework that uses triple oxygen isotope distributions in speleothems to refine interpretations of δ18O speleothem records. This framework identifies the influence of dominant processes on δ18O values through time by their characteristic (although not necessarily unique) trends in Δ′17O vs. δ′18O space, where Δ′17O = δ′17O – 0.528δ′18O and δ′xO = ln(δxO + 1). Following Guo and Zhou (2019a), we expect that ‘cave kinetic’ processes (e.g., fast degassing at the drip site, prior calcite precipitation) will drive positive trends between δ′18O and Δ′17O. In contrast, we can identify hydrologic processes from near-horizontal trends that reflect Rayleigh-type meteoric water processes and negative trends driven by changes in evaporation processes at the moisture source region or at the cave site, mineralization temperature, and seasonality in precipitation/infiltration amount. We applied this framework to four western USA speleothems from Cave of the Bells (Arizona), Leviathan Cave (Nevada), and Lehman Caves (Nevada). The Cave of the Bells and Leviathan data have near-horizontal to negative trends indicating δ18O variability was driven largely by changes in Rayleigh distillation of atmospheric moisture and moisture source conditions, supporting prior interpretations. We analyzed two Lehman Caves records because they were likely influenced by non-equilibrium processes and the data show weak to moderate negative trends. For sample LMC-12b, chosen for its extreme 7.5‰ δ18O range, the trend is statistically distinct from the near-horizontal Rayleigh-process trend and most consistent with changes in local evaporation intensity and infiltration seasonality as primary drivers. None of these records displays a positive covariation slope between δ′18O and Δ′17O, suggesting limited variability in cave kinetic processes through time or unknown limitations to the kinetic model of Guo and Zhou (2019a). Additionally, reconstructed formation waters for all sites fall near the Δ′17O vs. δ′18O Local Meteoric Water Line, a correlation we suggest as a novel test of the absolute magnitude of isotopic offset due to cave kinetic processes. More broadly, our framework adds context to the only other study of carbonate speleothem triple oxygen isotope composition (Sha et al., 2020). We find that positive to negative Δ′17O vs. δ′18O trends likely exist in speleothem data that may reasonably be expected from regional climate processes and that, combined with other proxy data, triple oxygen isotope data will be useful in constraining interpretations of δ18Ospeleothem records.

The knowledge and perceptions regarding antibiotic stewardship of the interns rotating at the Bloemfontein Academic Complex.

BackgroundAntibiotic resistance (ABR) is a global problem with the overuse of antibiotics accelerating this process. Antibiotic stewardship aims to optimise antibiotic treatment to enable cost-effective therapy and improve patients’ outcome whilst limiting ABR. The study aimed to evaluate intern medical doctors’ knowledge and perceptions about antibiotic stewardship and their perceptions regarding education on relevant topics.MethodsThis was a cross-sectional study on interns rotating at Bloemfontein Academic Complex. An anonymous, self-administered questionnaire was completed. The questionnaire recorded demographic information, perception and knowledge of antibiotic stewardship, and the quality of education as perceived by the interns.ResultsOf the 120 possible participants, 92 (76.7%) responded to all or part of the questionnaire. The median age of the respondents was 25 years, and 56.7% of the respondents were female. The mean score for the knowledge-based case scenarios was 5.4 out of 10. Only 4.4% participants could manage a drip site infection correctly, whilst 18.5% could treat Escherichia coli (E. coli) bacteraemia. The interns perceived that they have a lack of training and preparedness in certain areas of prescribing antibiotics. Though 77.2% of the interns had received education on starting antibiotic treatment, 29.3% claimed to be unsure when to start antibiotic therapy. Interns indicated that formal lectures (81.3%) and bedside tutorials (86.7%) have a high educational value.ConclusionIntern medical doctors do not have sufficient knowledge to establish antibiotic stewardship but have a desire for improvement. The results identified specific areas where better antibiotic training is required.

Heavy Metal Toxicity in Rice and its Effects on Human Health

Nowadays, rice is the staple food grain of billions of people worldwide. The scientific name of rice is Oryza sativa L. There are four types of rice found in all over the world. Heavy metals, such as arsenic, cadmium, lead, iron, etc. are also found in rice, which causes harmful effects in the human body. Recently, rice has also been identified as a major exposure route. Rice is the most important grain concerning human nutrition and calorie intake, providing more than one-fifth calories consumed worldwide by humans. Acute toxic effects of rice are lower risk of heart disease, diabetes, possibly stroke, obesity, etc. and the side effects of rice are swelling around the drip site, hearing changes, liver changes, sore mouth, diarrhea, flushing of the face, changes in blood pressure, etc.

Effects of an extreme flood event on an alpine karst system

The effects of an extreme storm (501 mm of rainfall in less than five days) were monitored in an alpine show cave to assess the characteristics of its aquifer unsaturated and saturated zones. The selected cave, Bossea (SW Piedmont, Italy), is an excellent test site for hydrological investigation of karst systems, because it hosts an underground karst laboratory since the late 70 s. The investigation was carried out by means of an integrated approach that combined measurements of flow discharge, physico-chemical parameters, major chemical components, and trace elements (metals, Rb, Ba, Sr and REE). The hydrology and hydrochemistry of the main underground river and two of its secondary tributaries (a drip site and a small secondary inflow) draining the unsaturated zone were monitored during the November 2016 flood, an exceptional hydrological event (estimated recurrence time of 200 years) that caused severe damages in the whole southwestern Piedmont region. The results of the 2016 monitoring were compared with those of another less extreme flood occurred in 2011 (recurrence time of 20 years). The karst system showed an impulsive response to flooding at the catchment and at the individual inflow scales, but each site exhibited a characteristic response due to the complex geological and structural setting of the cave system. The development of this karst system is, in fact, related to the lateral and vertical juxtaposition of rocks with different lithologies and mechanical properties, which form different hydrogeologic compartments. Coupling hydrograph, chemograph analysis and REE normalized patterns permitted to assess which compartments were activated during each phase of the floods. In particular, it was possible to recognize a progressive increasing contribution of the non-carbonate lithologies to flow during the peak of the flood for both the two unsaturated inflows and the main underground river, suggesting the activation of larger portions of the aquifer. However, the response of each individual unsaturated inflow is more influenced by its recharge system architecture rather than the magnitude of the meteorological event. Similar complex geological and lithological karst systems are typical of many areas characterized by orogenetic processes (Alps, Rocky Mountains, Caledonides, etc.), but despite them being relatively widespread, the hydrodynamics of these aquifers is still poorly understood. This study affirms that only long-term and well-integrated monitoring and sampling can help unravel the behavior of such complex karst systems.

A Randomized Controlled Trial of Intravenous N-Acetylcysteine in the Management of Anti-tuberculosis Drug-Induced Liver Injury.

Liver injury is a common complication of anti-tuberculosis therapy. N-acetylcysteine (NAC) used in patients with paracetamol toxicity with limited evidence of benefit in liver injury due to other causes. We conducted a randomized, double-blind, placebo-controlled trial to assess the efficacy of intravenous NAC in hospitalized adult patients with anti-tuberculosis drug-induced liver injury (AT-DILI). The primary endpoint was time for serum alanine aminotransferase (ALT) to fall below 100 U/L. Secondary endpoints included length of hospital stay, in-hospital mortality, and adverse events. Fifty-three participants were randomized to NAC and 49 to placebo. Mean age was 38 (SD±10) years, 58 (57%) were female, 89 (87%) were HIV positive. Median (IQR) serum ALT and bilirubin at presentation were 462 (266-790) U/L and 56 (25-100) μmol/L, respectively. Median time to ALT <100 U/L was 7.5 (6-11) days in the NAC arm and 8 (5-13) days in the placebo arm. Median time to hospital discharge was shorter in the NAC arm (9 [6-15] days) than in the placebo arm (18 [10-25] days) (HR, 1.73; 95% CI, 1.13-2.65). Mortality was 14% overall and did not differ by study arm. The study infusion was stopped early due to an adverse reaction in 5 participants receiving NAC (nausea and vomiting [3], anaphylaxis [1], pain at drip site [1]). NAC did not shorten time to ALT <100 U/L in participants with AT-DILI, but significantly reduced length of hospital stay. NAC should be considered in management of AT-DILI. South African National Clinical Trials Registry (SANCTR: DOH-27-0414-4719).

Drip water δ18O variability in the northeastern Yucatán Peninsula, Mexico: Implications for tropical cyclone detection and rainfall reconstruction from speleothems

This study examines the oxygen isotopic composition (δ18O values) of drip water, rainfall, and groundwater in the Río Secreto cave system, located in the Yucatán Peninsula, Mexico. The main motivation of this study was to determine the implications of drip water hydrology for the reconstruction of rainfall, droughts and tropical cyclone activity from stalagmite δ18O records. Monitoring of environmental and isotopic conditions was conducted for two years, from June 2017 to April 2019. This study provides the first instrumental evidence of an “amount effect” on interannual timescales in the Yucatán Peninsula. Observed bi-weekly to interannual variability in drip water δ18O values can be explained for individual drips by different integrations of rainfall amount in the time domain. Drip sites in two chambers (Stations A and B) integrate 4–15 months of rainfall accumulation. In a third chamber (Station LF) one drip site reflects the annual rainfall isotopic cycle with a positive offset and another, the largest rainfall events. During epikarst infiltration, the integration of rainfall amount by drip water source reservoirs determines the degree to which they “dilute” a tropical cyclone (TC) isotopic signature. TCs can be detected particularly when: (1) the water volume of the reservoir is low, such as during a persistent meteorological drought, and; (2) TCs have a sufficiently distinct isotopic signal relative to that of the reservoir prior to the event. TC isotopic signals can be masked or attenuated when drip water samples integrate more than a week and if significant rainfall events proceed the TC. In Río Secreto cave, reconstructing precipitation amount and detecting the TC isotopic signatures from stalagmite δ18O records is possible. Our analysis shows that stalagmite δ18O records are more likely to underestimate the magnitude of annual-scale droughts following normal hydroclimate conditions and more likely to record TCs during multiyear droughts than during normal or wet periods. Drip water monitoring results suggest that available stalagmite δ18O records from the Maya lowlands might be underestimating the intensity of paleo-drought events, such as the Terminal Classic droughts associated with the disintegration of the Maya civilization. This study complements the results from Lases-Hernandez et al. (2019) comparing two different sampling protocols of drip water collection. This study shows that a discrete sampling protocol is expected to approximate the amount-weighted isotopic composition of a drip, as long as it is conducted at a temporal resolution higher than the rainfall integration time by the drip reservoir. We highlight the importance of conducting multiyear monitoring of drip water and rainfall in order to interpret stalagmite δ18O as a paleoclimate proxy.

Farmed calcite δ13C at Ascunsă cave, Romania, and its relation with CO2

When calcite precipitates in caves, its carbon stable isotope signature can be modified by the CO2 outgassing gradient between drip water and cave atmosphere. This effect is modulated by the water residence time in the cave, from its emergence in the cave until the deposition of calcite. Moreover, CO2 solubility, calcite precipitation rate, and isotopic fractionation are controlled by temperature. Here, we present up to date results of an ongoing monitoring study at Ascunsa Cave (Romania), exploring the relationship between farmed calcite δ13C, drip rate, and CO2 outgassing. In addition to measuring CO2 concentration in cave air, we also measured the CO2 concentration in the headspace of a water-air equilibrator that collects drip water without exposing it to cave atmosphere, preventing outgassing. δ13C from calcite farmed at two neighboring stalagmites with different drip rates was also measured. Although caves have generally stable temperatures, we show here that temperature inside Ascunsa and Isverna caves has risen by more than 2°C over the course of a year, bearing important implications for stable isotopic fractionation equations and CO2 dynamics. Our results show that δ13C of farmed calcite has a strong relationship with drip rate at the slow dripping site, but no correlation at the faster dripping site. These two sites are also different when δ13C is compared to the outgassing gradient. At the slower drip site, δ13C and the outgassing gradient are directly correlated, whereas at the faster drip site their correlation is inverse. Our study brings new light onto speleothem δ13C behavior in general, and at Ascunsa Cave in particular, which is crucial for understanding the paleoclimate information captured by speleothems from this cave or elsewhere.

Lignin oxidation products as a potential proxy for vegetation and environmental changes in speleothems and cave drip water – a first record from the Herbstlabyrinth, central Germany

Abstract. 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.

The potential of near-entrance stalagmites as high-resolution terrestrial paleoclimate proxies: Application of isotope and trace-element geochemistry to seasonally-resolved chronology

Sub-annually resolved environmental proxies can be valuable archives of climate change, but they are rare in terrestrial settings, and it can be difficult to verify their annual nature. We suggest that speleothems that grow in well-ventilated zones of caves may preserve such high-resolution records. Near-entrance cave environments are characterized by year-round, near-atmospheric CO2 concentrations and are significantly influenced by surface air temperature fluctuations, particularly in temperate latitudes. Previous monitoring studies of a well-ventilated, temperate-latitude cave (Westcave Preserve, central Texas) have documented seasonal variations in the oxygen isotope composition of calcite grown on glass substrates (with winter δ18O maxima and summer δ18O minima) as well as seasonal variations in drip water trace element compositions. Extending this work to a stalagmite (WC-3) from the same drip site, we find that stalagmite δ18O variations are similar in magnitude to the seasonal δ18O variations previously observed for calcite grown on glass substrates, that stalagmite [Mg] variations have a similar seasonal period with winter minima and summer maxima, and that geochemical variations follow stalagmite growth fabric as mm-scale couplets comprising thin, slow-growing, compact sparry calcite laminae (winters) and thicker, fast-growing, porous-elongate columnar calcite laminae (summers). We interpret a high-resolution (weekly to monthly) 52-year record of δ18O, Mg, Sr, and Ba in WC-3, and report new monthly measurements of drip water and associated calcite grown on glass substrates. We find drip water δ18O and [Mg]/[Ca] are essentially invariant and that seasonal variations in WC-3 calcite δ18O and Mg concentration agree well with predicted temperature-dependent fractionation between water and calcite. WC-3 calcite Sr and Ba also vary, but with higher and more variable frequencies compared to δ18O and [Mg]. The annual nature of δ18O and [Mg] cycles is supported by monitoring and 14C bomb-peak chronology. We suggest that stalagmite δ18O and [Mg] vary primarily in response to large seasonal temperature changes in this setting, allowing for unambiguous differentiation between summer and winter calcite growth. From such δ18O- and [Mg]- derived sub-annual chronologies, the timing of enrichments in other geochemical species that are less directly coupled to external cave temperature (e.g., calcite Sr and Ba) can be considered as proxies of other important processes such as water-rock interaction in the epikarst, precipitation events, or subsurface respiration rates. The potential for this kind of multi-proxy, seasonally-resolved dating may add near-entrance stalagmites to the list (ice cores, lake varves, tree rings) of high-resolution terrestrial proxies available for paleoclimate studies.

Monitoring of selected caves as a prerequisite for the speleothem-based reconstruction of the Quaternary environment in Croatia

Quaternary palaeo-environmental changes that have taken place in Croatia are likely to be recorded in speleothems – secondary carbonate deposits precipitated in caves. Confident interpretation of well dated speleothem proxy records relies on modern monitoring programs, which we provided in three regionally different caves. Parallel monitoring of the surface and cave air temperature and relative humidity, precipitation and cave drip intensity, as well as stable isotope modification of meteoric and drip water was carried out in order to estimate the most reliable stalagmites for the interpretation of Quaternary landscape history. In all three caves, Nova Grgosova (239 m a.s.l.; Tcave = 11.2 °C) in central Croatia, Lokvarka (780 m a.s.l.; Tcave = 7.5 °C) in the mountainous part of Croatia, and Modrič (32 m a.s.l.; Tcave = 16.6 °C) in coastal Croatia, we selected the parts of the caves where the ambient cave conditions appeared to be appropriate for equilibrium deposition of calcite in terms of constant air temperature (seasonal amplitudes of 0.73, 0.38 and 0.45 °C, respectively) and relative humidity (100%). Both Atlantic and Mediterranean moisture influences were detected in all three caves, but of different intensities. Cave hydrological settings governed by karst aquifer properties were resolved by the comparison of the precipitation intensities and drip site responses to the rain events, and generally, seasonal rainwater isotopic signal was almost completely attenuated, except for one drip site. Such homogenized drip water and stable cave environmental settings give confidence for calcite deposition under equilibrium conditions, especially for Modrič and Nova Grgosova caves where speleothems' inner structures also look promising for potentially quality dating results and stable isotopic profiles. The fracture-flow drip regime of selected drip sites in Lokvarka Cave, and uncompleted homogenization of the water in the epikarst might point to speleothem samples that are unsuitable for resolving multi-annual Quaternary climate changes. This view is supported by the high porosity internal structure of some Lokvarka speleothems, so further monitoring, sampling and the thorough speleothem examination is therefore necessary for adequate interpretations of palaeo-environmental changes.

Sensitivity of Bunker Cave to climatic forcings highlighted through multi-annual monitoring of rain-, soil-, and dripwaters

The last two decades have seen a considerable increase in studies using speleothems as archives of past climate variability. Caves under study are now monitored for a wide range of environmental parameters and results placed in context with speleothem data. The present study investigates trends from a seven year long monitoring of Bunker Cave, northwestern Germany, in order to assess the hydraulic response and transfer time of meteoric water from the surface to the cave. Rain-, soil-, and dripwater were collected from August 2006 to August 2013 at a monthly to bimonthly resolution and their oxygen and hydrogen isotope composition was measured. Furthermore, drip rates were quantified. Due to different drip characteristics, annual mean values were calculated for the drip rates of each drip site. Correlations of the annual mean drip rate of each site with precipitation and infiltration demonstrate that the annual infiltration, and thus the annual precipitation control the inter-annual drip-rate variability for all except one site. The hydraulic response is not delayed on an annual basis. All drip sites display identical long-term trends, which suggests a draining of a common karst reservoir over these seven years of monitoring. Correlations of soil- and dripwater monthly δ18O and δD values with atmospheric temperature data reveal water transfer times of 3months to reach a depth of 40cm (soilwater at site BW 2) and 4months for 70cm depth (soilwater at site BW 1). Finally, the water reaches the cave chambers (15 to 30m below land surface) after ca. 2.5years. Consequently, a temporal offset of 29 to 31months (ca. 2.5years) between the hydraulic response time (no time lag on annual basis) and the water transfer time (time lag of 29 to 31months) was found, which is negligible with regard to Bunker Cave speleothems because of their slow growth rates. Here, proxies recording precipitation/infiltration and temperature are registered on a decadal scale. Variations in drip rate and thus precipitation and infiltration are recorded by δ13C and Mg/Ca ratios in speleothem calcite. Speleothem δ18O values reflect both temperature and precipitation signals due to drip rate-related fractionation processes. We document that long-term patterns in temperature and precipitation are recorded in dripwater patterns of Bunker Cave and that these are linked to the North Atlantic Oscillation (NAO).

A post-wildfire response in cave dripwater chemistry

Abstract. Surface disturbances above a cave have the potential to impact cave dripwater discharge, isotopic composition and solute concentrations, which may subsequently be recorded in the stalagmites forming from these dripwaters. One such disturbance is wildfire; however, the effects of wildfire on cave chemistry and hydrology remains poorly understood. Using dripwater data monitored at two sites in a shallow cave, beneath a forest, in southwest Australia, we provide one of the first cave monitoring studies conducted in a post-fire regime, which seeks to identify the effects of wildfire and post-fire vegetation dynamics on dripwater δ18O composition and solute concentrations. We compare our post-wildfire δ18O data with predicted dripwater δ18O using a forward model based on measured hydro-climatic influences alone. This helps to delineate hydro-climatic and fire-related influences on δ18O. Further we also compare our data with both data from Golgotha Cave – which is in a similar environment but was not influenced by this particular fire – as well as regional groundwater chemistry, in an attempt to determine the extent to which wildfire affects dripwater chemistry. We find in our forested shallow cave that δ18O is higher after the fire relative to modelled δ18O. We attribute this to increased evaporation due to reduced albedo and canopy cover. The solute response post-fire varied between the two drip sites: at Site 1a, which had a large tree above it that was lost in the fire, we see a response reflecting both a reduction in tree water use and a removal of nutrients (Cl, Mg, Sr, and Ca) from the surface and subsurface. Solutes such as SO4 and K maintain high concentrations, due to the abundance of above-ground ash. At Site 2a, which was covered by lower–middle storey vegetation, we see a solute response reflecting evaporative concentration of all studied ions (Cl, Ca, Mg, Sr, SO4, and K) similar to the trend in δ18O for this drip site. We open a new avenue for speleothem science in fire-prone regions, focusing on the geochemical records of speleothems as potential palaeo-fire archives.

Comparison of speleothem fabrics and microstratigraphic stacking patterns in calcite stalagmites as indicators of paleoenvironmental change

In the necessary task of obtaining high-resolution paleoclimate series from speleothems, the characterization of their internal microstratigraphy is a useful tool for: a) improving geochronology, and b) reaching a more complete knowledge of the speleothem formation and evolution through time and thus obtaining additional paleoenvironmental information. However, the development of standardized methodologies for microstratigraphic characterization is a pending task. In this paper, two different approaches allow construction of microstratigraphic logs for three stalagmites retrieved from two different caves. The logs correspond to vertical variations in speleothem fabrics and in microstratigraphic stacking patterns. The “fabrics logs” essentially provide information about the drip rate (sometimes used as a precipitation proxy) and the regularity or irregularity of each drip in the short-term. The “microstratigraphic stacking patterns logs” can be interpreted to obtain information about the changes in drip rates in the mid- and long-term. The results show a broad correlation between both kinds of logs that supports their validity as paleoenvironmental proxies. Fabrics formed under relatively constant and regular drips (columnar compact, open and elongated) usually constitute aggradational or progradational microstratigraphic stacking patterns. On the other hand, retractional stacking patterns are usually related with fabrics precipitated under more irregular drips (dendritic and columnar microcrystalline). However, this relation is not rigid and the information obtained from the logs is not equivalent, but complementary. The combination of both logs allows reconstruction of the hydrological history for each drip site. As all the obtained information derives directly from the drip conditions, drip effects result to be very important and can, in some cases, overwhelm the paleoclimate information recorded in each stalagmite.