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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Analysis of soil lipids may contribute to an improved understanding of atmosphere to soil carbon fluxes, soil organic matter source differentiation and pollutant accumulation. Soil lipids, mostly originating from plants and microorganisms, have traditionally been analysed by non-automated extraction and separation methods, which produce several lipid fractions, operationally defined by polarity. Here we present a combination of fast, automated and reproducible techniques, adopted from organic geochemical studies, for preparative separation of individual soil lipid fractions with increasing polarity. These techniques involve commercially available instruments, including accelerated solvent extraction and a two-step automated medium-pressure liquid chromatography procedure. The method yields eight lipid fractions consisting of five fractions fully amenable to gas chromatography/mass spectrometry (GC/MS) (aliphatic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, carboxylic acids), and three fractions of highly polar or high molecular weight compounds (bases, very long-chain wax esters (C40+), high polarity compounds) that were not measurable with GC/MS under standard conditions. We tested the method on five agricultural soils. Results show that (i) mass recoveries for the individual fractions are reproducible, (ii) within individual fractions compound distribution patterns are reproducible, as demonstrated for alkanes and carboxylic acids, and (iii) individual fractions represent distinct and clean compound classes, free of interfering substances detectable by GC/MS. Thus, automated separation can be a fast, effective and reproducible procedure for fractionation of complex mixtures of soil lipids into clean compound classes, directly suitable for a variety of molecular (e.g. GC/MS) and isotopic characterizations (e.g. gas chromatography coupled with isotope ratio monitoring mass spectrometry or accelerator mass spectrometry).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ammonia oxidation is the first step in nitrification, a key process in the global nitrogen cycle that results in the formation of nitrate through microbial activity. The increase in nitrate availability in soils is important for plant nutrition, but it also has considerable impact on ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 441.2006, 7093, E5-, (2 S.) 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Wignall et al. suggest that the abrupt negative δ13Corg shifts that we recognize in our data set could be localized features caused by recycling of isotopically light marine carbon. This overlooks two important lines of evidence: that the early Toarcian ...
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  • 4
    Publication Date: 2019-02-01
    Description: The 541 ± 4 Ma-old magnesian, weakly peraluminous, calc-alkalic Donkerhoek Onanis granite is part of the ca. 6000 km2 large Donkerhoek batholith in the Southern Zone of the Damara orogen of Namibia. Linear major and trace element variations and decreasing MgO, FeO, Al2O3, CaO, K2O, Na2O, Ba and Sr concentrations with increasing SiO2 indicate that this part of the batholith represent a coherent mass and underwent fractional crystallization processes. The Donkerhoek Onanis granites are isotopically evolved (initial εNd: −4.7 to −12.3, initial 87Sr/86Sr: 0.7099–0.7157) with moderately radiogenic Pb isotope ratios (206Pb/204Pb: 17.26–18.22; 207Pb/204Pb: 15.59–15.67; 208Pb/204Pb: 37.60–38.06). Beside heterogeneities imparted by the sources, an evaluation of LREE fractionation and Nd isotope data suggests that AFC processes also modified some samples. Based on the chemical and isotope data, the Donkerhoek Onanis granites cannot be derived by partial melting of Al- and Fe-rich metasedimentary rocks of the Kuiseb formation in which they intruded. Instead, melting of meta-igneous crustal sources with Proterozoic crustal residence ages is more likely. Three igneous to meta-igneous rock suites from the area (Matchless amphibolites, Proterozoic mafic to felsic gneisses from the southern Kalahari craton basement, syn-tectonic Salem granodiorites to granites) are potential sources. An evaluation of chemical and isotope data suggests that remelting of early syn-orogenic Salem-type granites is the most likely process which would also explain the existence of ca. 563 ± 4 Ma-old zircon in the Donkerhoek Onanis granites. Comparison of the Donkerhoek Onanis granites with experimentally derived melt compositions from an intermediate igneous parent indicates temperatures between 800 and 850 °C. It is suggested that the Pan-African igneous activity in this part of the Damara Belt was a moderate-temperature intra-crustal event. Although there are some compositional similarities with juvenile granites generated in subduction zones, unradiogenic Pb isotope ratios and moderately radiogenic Sr and unradiogenic Nd isotopes suggest that reprocessed crustal rocks are more likely sources. Previously obtained high δ18O values of the Donkerhoek Onanis granites ranging from 11.8 to 13.6‰, covering the range of δ18O values obtained on Salem-type granites from the area (12.5–13.3‰) confirm this view. In contrast to igneous processes along active continental margins that produce juvenile batholiths with calc-alkaline affinities, this igneous event was not a major crust-forming episode and the Donkerhoek Onanis granites represent reprocessed crustal material.
    Type: Article , PeerReviewed
    Format: text
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  • 5
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract In the Central European Zechstein Basin, the Permian Kupferschiefer has been deposited under marine anoxic conditions. From a lagoon at the southwest border of the Zechstein Sea, today part of the Lower Rhine Basin, 30 core samples have been studied by means of organic geochemical methods. Within the area investigated, the depth of the Kupferschiefer horizon increases from about 350 m in the south to about 1000 m in the north. Furthermore, the Kupferschiefer has been thermally affected in the western part by the intrusive body of the so-called Krefeld High. This geological situation opens the possibility to investigate differences of short term and long term temperature effects on the biological marker distribution within a sediment layer of a largely uniform faciès type. Depth related changes in the hopane, sterane and diasterene/diasterane distributions are compared to those changes induced by the Krefeld High. The composition of aromatic steroid hydrocarbons is used to discuss time-temperature effects. It is shown that depth related values of maturation parameters can only be interpreted by taking into account post-depositional tectonic events. Samples from tectonic horst structures show higher maturation values than one would expect from the present day depth.
    Abstract: Résumé Dans le bassin du Zechstein d'Europe Centrale, les Kupferschiefer permiens ont été déposés dans des conditions marines anoxiques. Dans un paléo-lagon situé à la bordure sud-ouest de la mer du Zechstein, et qui fait partie aujourd'hui du Bassin du Bas-Rhin, 30 échantillons, provenant de carottes, ont fait l'objet d'une étude de géochimie organique. Dans la région ainsi étudiée, la profondeur de l'horizon des Kupferschiefer augmente, du sud au nord, de 350 m à 1.000 m. D'autre part, les Kupferschiefer ont subi, dans leur partie ouest, l'influence thermique du corps intrusif du «Dôme de Krefeld». Cette situation géologique fournit la possibilité d'étudier les effets à long terme et à court terme de la température sur la distribution des marqueurs biologiques au sein d'un niveau sédimentaire de faciès uniforme. Les modifications dans la répartition de l'hopane, du stérane et du diastérène/diasterane en fonction de la profondeur sont comparées à celles qui sont provoquées par le Dôme de Krefeld. Les effets temps-température sont discutés à partir de la composition des hydrocarbures stéroïdes aromatiques. Les auteurs montrent que la valeur des paramètres de maturation liés à la profondeur ne peuvent être interprétés sans que l'on prenne en considération les événements tectoniques postsédimentaires. Des échantillons provenant de structures en horst montrent un degré d'évolution plus élevé que celui auquel on s'attend d'après leur profondeur actuelle.
    Notes: Zusammenfassung Aus dem Bereich der heutigen Niederrheinischen Bucht wurden an 30 Kernproben des Kupferschiefers organischgeochemische Untersuchungen durchgeführt. Innerhalb des Untersuchungsgebiets nimmt die Teufe des Kupferschieferhorizonts von 350 m im Süden auf über 1000 m im Norden zu. Organisch-geochemische Reifeparameter zeigen an, daß der Kupferschiefer im Westen durch den Intrusivkörper des Krefelder Gewölbes thermisch beeinflußt worden ist. Aufgrund dieser Situation bietet sich die Möglichkeit, Unterschiede im Einfluß von kurzzeitigen und langzeitigen Temperatureinwirkungen auf die Verteilung von Chemofossilien in einem faziell einheitlichen Horizont zu studieren. Teufenabhängige Variationen der Hopan-, Steran-, Diasteran- und Diasterenverteilungen lassen sich mit den zusätzlich durch den Intrusivkörper verursachten Veränderungen vergleichen. Die Verteilungsmuster der aromatischen Steroide werden zur Deutung von Zeit-Temperatur-Effekten im Verlauf der Diagenese herangezogen. Die ermittelten Meßwerte der Reifeparameter lassen sich nur interpretieren, wenn postsedimentäre tektonische Bewegungen nach der Ablagerung des Kupferschiefers in Betracht gezogen werden. Die aus Horsten stammenden Proben zeigen höhere Reifegrade an als entsprechend ihrer heutigen Teufe zu erwarten.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0040-4020
    Keywords: 24,25-dinorarbora-1,3,5(10),9(11)-tetraene ; 24,25-dinorarbora-1,3,5,7,9- pentaene ; des-A-arbora-5,7,9-triene ; isolation from sediments and structural identification by NMR spectroscopy. ; pentacyclic triterpene-derived aromatic hydrocarbons
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 9
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 10
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
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