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Bachofer F.,University of Tubingen | Queneherve G.,University of Tubingen | Marker M.,Heidelberger Akademie der Wissenschaften | Hochschild V.,University of Tubingen
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. Source

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. Source

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. Source

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. Source

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. Source

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