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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. Source


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. Source


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. Source


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. Source


Wacker L.,ETH Zurich | Lippold J.,Heidelberg Academy of science | Molnar M.,ETH Zurich | Molnar M.,Hungarian Academy of Sciences | Schulz H.,University of Tubingen
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. Source

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