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Riechelmann D.F.C.,Johannes Gutenberg University Mainz | Riechelmann D.F.C.,Ruhr University Bochum | Schroder-Ritzrau A.,Heidelberg Academy of science | Scholz D.,Johannes Gutenberg University Mainz | And 4 more authors.
Journal of Hydrology | Year: 2011

Monitoring cave environments is important to understand processes in karst systems. If stalagmites from a specific cave are used as archives of past climate variability, a quantitative understanding of the soil-karst-speleothem system is crucial. The monitoring program performed in Bunker Cave (NW Germany), which includes monthly collection of climatological data as well as air and water samples from the cave and the overlying soil since 2006, is a prerequisite for the interpretation of speleothem data from the cave in terms of climate variability.The results show that Bunker Cave is a homogeneously ventilated cave with rather low pCO2 values of 580-1200ppmv, which lacks strong seasonal variations. The δ18O value of cave drip water reflects the mean annual composition of the rain water, and the seasonal variability is strongly attenuated indicating a well-mixed karst aquifer. Hence, stalagmites from Bunker Cave should be well suited to record interannual/decadal climate trends.Seven drip sites in two cave chambers show three different types of discharge behaviour including slow seasonal drip, fast seasonal drip, and seepage-flow. The drip-rate patterns of most drip sites are consistent with the main infiltration events, taking into account a delay of several months. An instantaneous response to precipitation (i.e., piston-flow) is not observed for any drip site indicating a specific water capacity threshold in the soil/karst aquifer. Prior Calcite Precipitation (PCP) was also identified especially during times of low discharge. Though PCP is not as pronounced at Bunker Cave as in other caves, it probably has an influence on the Mg/Ca ratios of the stalagmites. © 2011 Elsevier B.V.

Fohlmeister J.,Heidelberg Academy of science | Vollweiler N.,Heidelberg Academy of science | Vollweiler N.,Heidelberg Center for the Environment | Spotl C.,University of Innsbruck | Mangini A.,Heidelberg Academy of science
Holocene | Year: 2013

We present an update (COMNISPA II) of a precisely dated, high-resolution speleothem δ18O record from the Austrian Alps. COMNISPA II consists of five stalagmites from Spannagel Cave, which have comparable δ18O values within periods of simultaneous growth and show similar δ18O variations on centennial to millennial timescales. This allows combining the five stalagmites to one composite record using a newly developed statistical approach. The COMNISPA II stack differs slightly from the previous version, but is better constrained because of additional stalagmites used for the reconstruction and a more objective method used for constructing the composite record. Furthermore, the record now covers the last 11 ka and shows variations in δ18O values by about 2‰. As previously shown, these variations compare well with other records in central Europe and the North Atlantic, and thus reflect a large-scale climate evolution. © The Author(s) 2012.

Christl M.,ETH Zurich | Lippold J.,Heidelberg Academy of science | Steinhilber F.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Bernsdorff F.,Heidelberg Academy of science | Mangini A.,Heidelberg Academy of science
Quaternary Science Reviews | Year: 2010

In this study we present a reconstruction of the global 10Be production rate over the past 250,000 years from three marine sediment cores located in high accumulation environments in the North-, northwest-, and South Atlantic Ocean (ODP Sites 983, 1063 and 1089). The 10Be records are corrected for oceanic transport processes and Principal Component Analysis (PCA) is used to extract the common signal from the three records, which we interpreted as variations of the global 10Be production rate. The reconstruction presented here may serve as (i) a record of past flux of Galactic Cosmic Rays (GCR), (ii) a proxy for past geomagnetic dipole strength, and (iii) as a global matching tool to synchronize marine archives with ice cores and terrestrial records. © 2010 Elsevier Ltd.

Fohlmeister J.,Heidelberg Academy of science | Scholz D.,University of Mainz | Kromer B.,Heidelberg Academy of science | Mangini A.,Heidelberg Academy of science
Geochimica et Cosmochimica Acta | Year: 2011

C isotopes in cave drip water are affected by both the C isotope composition of soil air and host rock carbonate. Furthermore, the C isotope composition of cave drip water strongly depends on the calcite dissolution system, i.e., open, closed and intermediate conditions. Here, we present a calcite dissolution model, which calculates the 14C activity and δ13C value of the dissolved inorganic carbon of the drip water. The model is based on the chemical equations describing calcite dissolution (H2O+CaCO3+CO2⇔Ca2++2HCO3-). The most important improvement, relative to previous models, is the combination of the open and closed system conditions in order to simulate the C isotope composition during intermediate states of calcite dissolution and the application to carbon isotope measurements on cave drip waters from Grotta di Ernesto, Italy. The major changes in the C isotope composition of the drip water occur in response to variations in the open-closed system ratio. Additionally, the 14C activity and the δ13C value of the drip water depend on changes in the partial pressure of soil CO2. Radiocarbon and δ13C values of the Grotta di Ernesto drip water are well reproduced by the model. © 2011 Elsevier Ltd.

Wacker L.,ETH Zurich | Lippold J.,Heidelberg Academy of science | Molnar M.,ETH Zurich | Molnar M.,Hungarian Academy of Sciences | Schulz H.,University of Tübingen
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2013

Carbonate shells from foraminifera are often analysed for radiocarbon to determine the age of deep-sea sediments or to assess radiocarbon reservoir ages. However, a single foraminiferal test typically contains only a few micrograms of carbon, while most laboratories require more than 100 μg for radiocarbon dating with an accelerator mass spectrometry (AMS) system. The collection of the required amount of foraminifera for a single analyses is therefore time consuming and not always possible. Here, we present a convenient method to measure the radiocarbon content of foraminifera using an AMS system fitted with a gas ion source. CO2 is liberated from 150 to 1150 μg of carbonate in septum sealed vials by acid decomposition of the carbonate. The CO2 is collected on a zeolite trap and subsequently transferred to a syringe from where it is delivered to the ion source. A sample of 400 μg (50 μg C) typically gives a 12C- ion source current of 10-15 μA over 20 min, yielding a measurement precision of less than 7 per mil for a modern sample. Using this method, we were able to date a single 560 μg Cibicides pseudoungerianus test at 14,030 ± 160 radiocarbon years. Only a minor modification to our existing gas handling system was required and the system is fully automatable to further reduce the effort involved for sample preparation. © 2012 Elsevier B.V. All rights reserved.

Fohlmeister J.,Heidelberg Academy of science | Kromer B.,Heidelberg Academy of science | Mangini A.,Heidelberg Academy of science
Radiocarbon | Year: 2011

The imprint of the radiocarbon bomb peak was detected in the top of stalagmite ER-77 from Grotta di Ernesto (NE Italy). This recently grown stalagmite reveals a reservoir age, also known as dead carbon fraction (dcf), of ~1050 14C yr, or 12%. By applying a 14C soil-karst model, the age spectrum of soil organic matter (SOM) as well as the CO2 contribution of the single SOM reservoirs to the total soil CO2 can be derived. Under the assumption of constant vegetation, meaning both vegetation density and the age spectrum of SOM, it is possible to derive the soil-air 14C activity of the past using the 14C calibration curve (IntCal04). Hence, it is also possible to calculate an artificial stalagmite 14C data set covering the last 25,000 yr with parameters determined for stalagmite ER-77. With this artificially constructed data set, we derived the hypothetical atmospheric 14C activity by using the common method of applying a constant dcf on the modeled 14C data set of the stalagmite. This theoretical approach allows to analyze the impact of a constant and variable SOM age spectrum on atmospheric 14C reconstructions performed with real stalagmite 14C measurements. We observe deviations between IntCal04 and the atmospheric 14C activity as derived with our modeled 14C data set, which are larger for older SOM than for younger SOM and vary in time up to 2 pMC, depending on the strength of the variations in the atmospheric 14C level. This value is comparable with the 1-σ uncertainty given by IntCal04 for the last glacial. For a varying SOM age spectrum, the deviations between the calibration curve and 14C level of the atmosphere reconstructed with a stalagmite exceed 3 pMC, which is larger than the 1-σ uncertainty of IntCal04. In general, the SOM has smoothing, shifting, and 14C-depleting effects on the stalagmite 14C record and, therefore, on the stalagmite-derived atmospheric 14C activity. In this study, changes in soil-air pCO2 and carbonate dissolution conditions, which have also an important impact on the 14C record of a stalagmite, are not accounted for. © 2011 by the Arizona Board of Regents on behalf of the University of Arizona.

Mudelsee M.,Climate Risk Analysis | Mudelsee M.,Alfred Wegener Institute for Polar and Marine Research | Fohlmeister J.,Heidelberg Academy of science | Scholz D.,Johannes Gutenberg University Mainz
Climate of the Past | Year: 2012

A fundamental problem in paleoclimatology is to take fully into account the various error sources when examining proxy records with quantitative methods of statistical time series analysis. Records from dated climate archives such as speleothems add extra uncertainty from the age determination to the other sources that consist in measurement and proxy errors. This paper examines three stalagmite time series of oxygen isotopic composition (δ18O) from two caves in western Germany, the series AH-1 from the Atta Cave and the series Bu1 and Bu4 from the Bunker Cave. These records carry regional information about past changes in winter precipitation and temperature. U/Th and radiocarbon dating reveals that they cover the later part of the Holocene, the past 8.6 thousand years (ka). We analyse centennial- to millennial-scale climate trends by means of nonparametric Gasser-Müller kernel regression. Error bands around fitted trend curves are determined by combining (1) block bootstrap resampling to preserve noise properties (shape, autocorrelation) of the δ18O residuals and (2) timescale simulations (models StalAge and iscam). The timescale error influences on centennial- to millennial-scale trend estimation are not excessively large. We find a "mid-Holocene climate double-swing", from warm to cold to warm winter conditions (6.5 ka to 6.0 ka to 5.1 ka), with warm-cold amplitudes of around 0.5‰ δ18O; this finding is documented by all three records with high confidence. We also quantify the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the current warmth. Our analyses cannot unequivocally support the conclusion that current regional winter climate is warmer than that during the MWP. © Author(s) 2012.

Fohlmeister J.,Heidelberg Academy of science
Quaternary Geochronology | Year: 2012

Proxy records of dated environmental archives like stalagmites are used for reconstruction of past climate and therefore are of fundamental interest for the paleoclimate community. However, dating conditions are often not perfect to obtain precise ages with small uncertainties. On this matter, the use of statistical approaches applied to reproduced climate signals of several nearby situated specimens, like stalagmites from one cave, can help to reduce age uncertainties. A new method implemented in MATLAB uses a Monte Carlo approach on absolute age determinations to find the best correlation between climate proxies of several signal reproducing adjacent archives. Therefore, the program is able to combine climatic proxies to construct a composite record. This " intra-site correlation age modelling" (iscam) approach offers great advantages. The age uncertainty can be significantly reduced within the overlapping time intervals and it can be tested if the signal of interest is indeed similar in both records. Additionally, iscam allows to enlarge the time span of a single record while at the same time the signal to noise ratio of the combined record improves in periods where replicates exist. Significance levels of the correlation can be calculated against the red-noise background from a first order autoregressive process (AR1), which allows to determine adequate age uncertainties. The method was designed to synchronize time series of nearby locations, where changes in the climate signal occur simultaneously. Applying this method to geographically dispersed locations might not be appropriate due to unknown leads and lags in the climate system. © 2012 Elsevier B.V.

Wassenburg J.A.,Ruhr University Bochum | Immenhauser A.,Ruhr University Bochum | Richter D.K.,Ruhr University Bochum | Jochum K.P.,Max Planck Institute for Chemistry | And 5 more authors.
Geochimica et Cosmochimica Acta | Year: 2012

The occurrence of aragonite in speleothems has commonly been related to high dripwater Mg/Ca ratios, because Mg is known to be a growth inhibitor for calcite. Laboratory aragonite precipitation experiments, however, suggested a more complex array of controlling factors. Here, we present data from Pleistocene to Holocene speleothems collected from both a dolostone and a limestone cave in northern Morocco. These stalagmites exhibit both lateral and stratigraphic calcite-to-aragonite transitions. Aragonite fabrics are well-preserved and represent primary features. In order to shed light on the factors that control alternating calcite and aragonite precipitation, elemental (Mg, Sr, Ba, U, P, Y, Pb, Al, Ti and Th) abundances were measured using LA-ICP-MS, and analysed with Principal Component Analysis. Samples were analyzed at 100-200 μm resolution across stratigraphic and lateral transitions. Carbon and oxygen isotope ratios were analysed at 100 μm resolution covering stratigraphic calcite-to-aragonite transitions. Results show that the precipitation of aragonite was driven by a decrease in effective rainfall, which enhanced prior calcite precipitation. Different geochemical patterns are observed between calcite and aragonite when comparing data from the Grotte de Piste and Grotte Prison de Chien. This may be explained by the increased dripwater Mg/Ca ratio and enhanced prior aragonite precipitation in the dolostone cave versus lower dripwater Mg/Ca ratio and prior calcite precipitation in the limestone cave. A full understanding for the presence of lateral calcite-to-aragonite transitions is not reached. Trace elemental analysis, however, does suggest that different crystallographic parameters (ionic radius, amount of crystal defect sites, adsorption potential) may have a direct effect on the incorporation of Sr, Mg, Ba, Al, Ti, Th and possibly Y and P. © 2012 Elsevier Ltd.

Griffiths M.L.,University of California at Irvine | Fohlmeister J.,Heidelberg Academy of science | Drysdale R.N.,University of Melbourne | Hua Q.,Australian Nuclear Science and Technology Organisation | And 4 more authors.
Quaternary Geochronology | Year: 2012

Over the past decade, a number of speleothem studies have used radiocarbon (14C) to address a range of palaeoclimate problems. These have included the use of the bomb pulse 14C to anchor chronologies over the last 60 years, the combination of U-Th and 14C measurements to improve the radiocarbon age-calibration curve, and linking atmospheric 14C variations with climate change. An issue with a number of these studies is how to constrain, or interpret, variations in the amount of radioactively dead carbon (i.e. the dead carbon fraction, or DCF) that reduces radiocarbon concentrations in speleothems. In this study, we use 14C, stable-isotopes, and trace-elements in a U-Th dated speleothem from Flores, Indonesia, to examine DCF variations and their relationship with above-cave climate over the late Holocene and modern era. A strong association between the DCF and hydrologically-controlled proxy data suggests that more dead carbon was being delivered to the speleothem during periods of higher cave recharge (i.e. lower δ18O, δ13C and Mg/Ca values), and hence stronger summer monsoon. To explore this relationship, we used a geochemical soil-karst model coupled with 14C measurements through the bomb pulse to disentangle the dominant components governing DCF variability in the speleothem. We find that the DCF is primarily controlled by limestone dissolution associated with changes in open- versus closed-system conditions, rather than kinetic fractionation and/or variations in the age spectrum of soil organic matter above the cave. Therefore, we infer that periods of higher rainfall resulted in a higher DCF because the system was in a more closed state, which inhibited carbon isotope exchange between the karst water dissolved inorganic carbon and soil-gas CO2, and ultimately led to a greater contribution of dead carbon from the bedrock. © 2012.

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