Heidelberger Akademie der Wissenschaften

Heidelberg, Germany

Heidelberger Akademie der Wissenschaften

Heidelberg, Germany
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Scholz D.,Johannes Gutenberg University Mainz | Frisia S.,University of Newcastle | Borsato A.,University of Newcastle | Spotl C.,University of Innsbruck | And 5 more authors.
Climate of the Past | Year: 2012

Here we present high-resolution stable isotope and lamina thickness profiles as well as radiocarbon data for the Holocene stalagmite ER 76 from Grotta di Ernesto (north-eastern Italy), which was dated by combined U-series dating and lamina counting. ER 76 grew between 8 ka (thousands of years before 2000 AD) and today, with a hiatus from 2.6 to 0.4 ka. Data from nine meteorological stations in Trentino show a significant influence of the North Atlantic Oscillation (NAO) on winter temperature and precipitation in the cave region. Spectral analysis of the stable isotope signals of ER 76 reveals significant peaks at periods of 110, 60-70, 40-50, 32-37 and around 25 a. Except for the cycle between 32 and 37 a all periodicities have corresponding peaks in power spectra of solar variability, and the 25-a cycle may correspond to NAO variability. This suggests that climate variability in northern Italy was influenced by both solar activity and the NAO during the Holocene. Six periods of warm winter climate in the cave region were identified. These are centred at 7.9, 7.4, 6.5, 5.5, 4.9 and 3.7 ka, and their duration ranges from 100 to 400 a. The two oldest warm phases coincide with the deposition of sapropel S1 in the Mediterranean Sea indicating that the climate in the cave region was influenced by this prominent pluvial phase in the Mediterranean area. For the younger warm phases it is difficult to establish a supra-regional climate pattern, and some of them may, thus, reflect regional climate variability. This highlights the complexity of regional and supra-regional scale Holocene climate patterns. © Author(s) 2012.

Giry C.,University of Bremen | Felis T.,University of Bremen | Kolling M.,University of Bremen | Scholz D.,Heidelberger Akademie der Wissenschaften | And 4 more authors.
Earth and Planetary Science Letters | Year: 2012

Proxy reconstructions of tropical Atlantic sea surface temperature (SST) that extend beyond the period of instrumental observations have primarily focused on centennial to millennial variability rather than on seasonal to multidecadal variability. Here we present monthly-resolved records of Sr/Ca (a proxy of SST) from fossil annually-banded Diploria strigosa corals from Bonaire (southern Caribbean Sea). The individual corals provide time-windows of up to 68. years length, and the total number of 295. years of record allows for assessing the natural range of seasonal to multidecadal SST variability in the western tropical Atlantic during snapshots of the mid- to late Holocene. Comparable to modern climate, the coral Sr/Ca records reveal that mid- to late Holocene SST was characterised by clear seasonal cycles, persistent quasi-biennial and prominent interannual as well as inter- to multidecadal-scale variability. However, the magnitude of SST variations on these timescales has varied over the last 6.2. ka. The coral records show increased seasonality during the mid-Holocene consistent with climate model simulations indicating that southern Caribbean SST seasonality is induced by insolation changes on orbital timescales, whereas internal dynamics of the climate system play an important role on shorter timescales. Interannual SST variability is linked to ocean-atmosphere interactions of Atlantic and Pacific origin. Pronounced interannual variability in the western tropical Atlantic is indicated by a 2.35. ka coral, possibly related to a strengthening of the variability of the El Niño/Southern Oscillation throughout the Holocene. Prominent inter- to multidecadal SST variability is evident in the coral records and slightly more pronounced in the mid-Holocene. We finally argue that our coral data provide a target for studying Holocene climate variability on seasonal and interannual to multidecadal timescales, when using further numerical models and high-resolution proxy data. © 2012 Elsevier B.V.

Frisia S.,University of Newcastle | Fairchild I.J.,University of Birmingham | Fohlmeister J.,Heidelberger Akademie der Wissenschaften | Miorandi R.,Museo Tridentino di Science Naturali | And 2 more authors.
Geochimica et Cosmochimica Acta | Year: 2011

Diverse interpretations have been made of carbon isotope time series in speleothems, reflecting multiple potential controls. Here we study the dynamics of 13C and 12C cycling in a particularly well-constrained site to improve our understanding of processes affecting speleothem δ13C values. The small, tubular Grotta di Ernesto cave (NE Italy) hosts annually-laminated speleothem archives of climatic and environmental changes. Temperature, air pressure, pCO2, dissolved inorganic carbon (DIC) and their C isotopic compositions were monitored for up to five years in soil water and gas, cave dripwater and cave air. Mass-balance models were constructed for CO2 concentrations and tested against the carbon isotope data. Air advection forces winter pCO2 to drop in the cave air to ca. 500ppm from a summer peak of ca. 1500ppm, with a rate of air exchange between cave and free atmosphere of approximately 0.4days. The process of cave ventilation forces degassing of CO2 from the dripwater, prior to any calcite precipitation onto the stalagmites. This phase of degassing causes kinetic isotope fractionation, i.e. 13C-enrichment of dripwater whose δ13CDIC values are already higher (by about 1‰) than those of soil water due to dissolution of the carbonate rock. A subsequent systematic shift to even higher δ13C values, from -11.5‰ in the cave drips to about -8‰ calculated for the solution film on top of stalagmites, is related to degassing on the stalagmite top and equilibration with the cave air. Mass-balance modelling of C fluxes reveals that a very small percentage of isotopically depleted cave air CO2 evolves from the first phase of dripwater degassing, and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium. The systematic 13C-enrichment from the soil to the stalagmites at Grotta di Ernesto is independent of drip rate, and forced by the difference in pCO2 between cave water and cave air. This implies that speleothem δ13C values may not be simply interpreted either in terms of hydrology or soil processes. © 2010 Elsevier Ltd.

Dreybrodt W.,University of Bremen | Deininger M.,Heidelberger Akademie der Wissenschaften
Geochimica et Cosmochimica Acta | Year: 2014

To understand the effects of processes that influence the stable carbon and oxygen isotope ratios of DIC in a small planar water film, two model approaches have been developed in the past, a classical Rayleigh-approach and a kinetic model approach. Here we compare the effect of evaporation on the stable carbon and oxygen isotope ratios 13/12 and 18/16 of DIC, based on calculation with the two model approaches. For the Rayleigh-model, the isotope ratio increases, with increasing evaporation rate. For the kinetic-model the evolution of the isotope ratio, depends, in addition to the evaporation rate, on a fractionation parameter γ≈. 1, which results from different equilibrium concentrations with respect to calcite for the heavy and light isotopes in the DIC. In dependence on the evaporation rate, the isotope ratio increases faster, with increasing evaporation rate and reaches a maximum. After the maximum is reached it converges to an equilibrium isotope ratio, which is determined by γ. Both models results indicate, that the effect of evaporation on the stable carbon and oxygen isotope composition can be neglected for relative humidities greater than 85% and wind velocities smaller than 0.2. m/s. Close to ventilated cave sites, however, where humidity can be low and high wind speeds are possible significant changes of the isotope signal may arise. © 2013 Elsevier Ltd.

Mangini A.,Heidelberger Akademie der Wissenschaften | Godoy J.M.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Godoy M.L.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Kowsmann R.,Petrobras | And 4 more authors.
Earth and Planetary Science Letters | Year: 2010

Simultaneous 14C and Th/U dating of deep sea corals are useful for reconstructing the intensity of deep ocean circulation in the past, as they deliver the time between the gas exchange of the water with the atmosphere and the incorporation of the 14C in the carbonates (Adkins and Boyle, 1997; Adkins et al., 1998; Mangini et al., 1998). Th/U ages of deep sea corals sampled in sediment cores from locations off the coast of Brazil bathed by Antarctic Intermediate Water at depths between 600 and 800m group close to Heinrich events H2, H1 and the Younger Dryas. The Δ14C of the water bathing the corals starts to decrease approximately 2kyr before the Heinrich events and decreases to values 400% lower than the corresponding back tracked atmospheric values. The timing and the magnitude of the decrease is similar to that observed in intermediate water in the N. Pacific off Baja California (Marchitto et al., 2007) and in the Eastern Pacific (Stott et al., 2009). High ventilation ages, partly exceeding 4000years, are an unambiguous indication for a reduction of North Atlantic deep water formation during H2, H1 and the YD, as deduced from higher 231Pa/230Th activity ratios and from ΕNd in N. Atlantic Ocean sediments (McManus et al., 2004; Pahnke et al., 2008; Yu et al., 1996). They also could indicate a poorly oxygenated Southern Pacific Ocean at the end of the Heinrich events. © 2010 Elsevier B.V.

Wirsig C.,Heidelberger Akademie der Wissenschaften | Kowsmann R.O.,Petrobras | Miller D.J.,Petrobras | de Oliveira Godoy J.M.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Mangini A.,Heidelberger Akademie der Wissenschaften
Marine Geology | Year: 2012

Dating authigenic cold seep carbonates allows determining the timing of active seepage of hydrocarbon-rich fluids at continental margins and ultimately the detection of the geological factors affecting it. U/Th-dating has been selected in this study, the method having been successfully used before. However, incorporation of initial thorium in substantial amounts of detrital material, due to the precipitation of carbonates within the seabed, and post-depositional alteration potentially pose a major problem, violating the basic assumptions of the method. Here we report results from several samples from the Campos Basin off the coast of Brazil. They are unusual in their high δ13C values (mean of -10.0‰ VPDB), high detrital contents and being dominantly dolomite. Elevated 230Th/238U activity ratios indicate that most of the carbonates lost uranium during diagenesis. Isochrones are obtained from the unaffected samples yielding an age of 140.4±3.1ka. Vertical growth of the chimney must have been short and rapid since results from the top and bottom parts of the chimney concur within analytical uncertainties. Furthermore, profiles of U/Th radioisotope specific activity, δ234U and 232Th specific activity on two quarter slices of a carbonate chimney reveal the occurrence of three distinct diagenetic processes: U loss, U exchange with seawater and Th gain. © 2012 Elsevier B.V.

Bachofer F.,University of Tübingen | Queneherve G.,University of Tübingen | Marker M.,Heidelberger Akademie der Wissenschaften | Hochschild V.,University of Tübingen
Photogrammetrie, Fernerkundung, Geoinformation | Year: 2015

The lower member of the so called Manyara Beds is a distinct lacustrine sedimentary layer which indicates, with an elevation of more than 140 m above today's lake level, a high stand of the paleolake Manyara in the Monduli District in northern Tanzania. The Manyara Beds are rich in Pleistocene vertebrate fossils. In this study we focus on the delineation of this specific stratigraphic layer in order to yield new insights into paleontological settings, landscape evolution and to plan paleontological fieldwork. We compare the performance of a support vector classifier with a linear as well as a Gaussian kernel, with boosted regressiontree approaches to identify the lithostratigraphic layers of the Manyara Beds. For the identification of the lacustrine sediments, multispectral informationof ASTER satellite imagery and topographic indices derived from a digital elevation model were utilized as input feature sets. Acceptable classification accuracies were obtained with all methods. Thus, the Manyara Beds can be delineated and new sites with paleolake sediments were detected. The highest overall accuracy with 92% was provided by the support vector machine approach with a linear kernel for a binary classification problem. For a multi-class classification problem with three target classes the support vector classifier achieved 80% accuracy with a linear, as well as a Gaussian kernel. © 2015 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.

Wackerbarth A.,Heidelberger Akademie der Wissenschaften | Scholz D.,Johannes Gutenberg University Mainz | Fohlmeister J.,Heidelberger Akademie der Wissenschaften | Mangini A.,Heidelberger Akademie der Wissenschaften
Earth and Planetary Science Letters | Year: 2010

Stable isotope signals recorded in speleothems have provided important insights about past climate variability in recent years. Quantitative reconstruction of mean annual temperature and the amount of precipitation, however, remains difficult because the stable isotope signals are influenced by various processes. Here we present a drip water model, which shows how these climate parameters affect the oxygen isotope signal of cave drip water. In the model the dependence of the δ18O value of drip water on mean annual temperature is established by correlation to the amount of winter precipitation and winter temperature. Application of the model to two caves in western Germany reveals a strong influence of winter rainfall on the oxygen isotope composition of cave drip water in this region. Assuming equilibrium isotope fractionation between drip water and calcite, we provide a function relating the δ18O value of speleothem calcite to mean annual surface temperature. This function shows a clear anticorrelation between temperature and the δ18O value of speleothem calcite, which has been previously reported for several caves in central and northern Europe. By inverse application of this function, we tentatively reconstruct average temperatures for the period between 6 and 1.5ka from the δ18O signals of two stalagmites from Atta and Bunker Cave (western Germany). The resulting temperature curves are very sensitive to the value used for the correlation between the amount of winter precipitation and winter temperature. Since this correlation was probably not constant in the past, the reconstructed temperature curves are associated with substantial uncertainty. © 2010 Elsevier B.V.

Deininger M.,Heidelberger Akademie der Wissenschaften | Fohlmeister J.,Heidelberger Akademie der Wissenschaften | Scholz D.,Johannes Gutenberg University Mainz | Mangini A.,Heidelberger Akademie der Wissenschaften
Geochimica et Cosmochimica Acta | Year: 2012

In order to improve the understanding of variations of speleothem δ 18O and δ 13C values in the context of palaeoclimate research, it is important to quantify the isotope fractionation processes influencing the δ 18O and δ 13C values of stalagmites. Here we present an extended version of speleothem stable isotope model that accounts for evaporation and condensation effects during precipitation of calcite. The ISOLUTION-model allows to calculate the effect of evaporation on δ 18O calcite and δ 13C calcite values in dependence on relative humidity and wind velocity. Our results reveal that evaporation may have a significant effect on δ 18O calcite and δ 13C calcite due to the loss of H 2O from the solution layer and the related increase of the Ca 2+ concentration. This leads to higher precipitation rates and, consequently, larger isotope fractionation effects. The effect on speleothem δ 18O calcite and δ 13C calcite can be as high as changes caused by variations of temperature, drip interval, pCO 2.drip and pCO 2.cave. Furthermore, the change of pCO 2.cave due to ventilation effects, may also affect speleothem δ 18O calcite and δ 13C calcite values because of the effect of pCO 2.cave on the equilibrium concentrations of the CO 2-H 2O-CaCO 3-system and, thus, the calcite precipitation rate. The variability of other cave parameters (temperature, drip interval, pCO 2.drip, pCO 2.cave) can have a comparable effect on δ 18O calcite and δ 13C calcite values depending on the magnitude of variability. We validated the ISOLUTION-model by modelling the δ 18O calcite values from a cave-analogue experiment and successfully reproduced the values for high temperatures. © 2012 Elsevier Ltd.

Munsterer C.,Laboratory of Ion Beam Physics | Fohlmeister J.,Heidelberger Akademie der Wissenschaften | Christl M.,Laboratory of Ion Beam Physics | Schroder-Ritzrau A.,Heidelberger Akademie der Wissenschaften | And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2012

Monthly rain and drip waters were collected over a period of 10months at Bunker Cave, Germany. The concentration of 36Cl and the 36Cl/Cl-ratios were determined by accelerator mass spectrometry (AMS), while stable (35+37)Cl concentrations were measured with both, ion chromatography (IC) and AMS. The measured 36Cl-fluxes of (0.97±0.57)×10 4atomscm -2month -1 (0.97atomsm -2month -1) in precipitation were on average twice as high as the global mean atmospheric production rate. This observation is consistent with the local fallout pattern, which is characterized by a maximum at mid-latitudes. The stable chloride concentration in drip waters (ranging from 13.2 to 20.9mg/l) and the 36Cl-concentrations (ranging from 16.9×10 6 to 35.3×10 6atoms/l) are a factor of 7 and 10 above the values expected from empirical evapotranspiration formulas and the rain water concentrations, respectively. Most likely the additional stable Cl is due to human impact from a nearby urban conglomeration. The large 36Cl-enrichment is attributed to the local evapotranspiration effect, which appears to be higher than the calculated values and to additional bomb-derived 36Cl from nuclear weapons tests in the 1950s and 60s stored in the soil above the cave. In the densely vegetated soil above Bunker Cave, 36Cl seems not to behave as a completely conservative tracer. The bomb derived 36Cl might be retained in the soil due to uptake by minerals and organic material and is still being released now. Based on our data, the residence time of 36Cl in the soil is estimated to be about 75-85years. © 2012 Elsevier Ltd.

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