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  • 1
    Publication Date: 2018-09-13
    Description: In the past two decades, the behavior of lithium (Li) isotopes has been studied in various marine systems, including mid-ocean ridge and sediment-hosted hydrothermal systems, subduction zone settings and normal coastal and deep-sea sediments recovered by the Ocean Drilling Program (ODP). Major processes identified to cause deviations from the seawater isotopic composition are adsorption/desorption reactions, formation and transformation of silicate minerals, and leaching of Li from sediments or underlying crust at high temperature. As a result of the accomplished work, Li isotopes are considered a promising tracer for the diagenetic evolution and provenance of pore fluids in overpressured sedimentary environments. Here, we present Li concentration and isotope data of 18 cold seep locations and reference fluids from shallow marine sediments, a sediment-hosted hydrothermal system and two Mediterranean brine basins. The new reference data and literature data of hydrothermal fluids and pore fluids from the ODP follow an empirical relationship reflecting increasing Li release and decreasing isotope fractionation during clay mineral authigenesis with increasing temperature. Lithium concentration and isotope data of cold seep fluids are mostly in agreement with this empirical relationship. Ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite-illite is an important sink for light pore water Li in deeply buried continental margin sediments. Deviations from the general relationship are attributed to the varying proportion of weatherable (e.g. volcanogenic) components and to transport-related fractionation trends. A simple transport-reaction model was applied to simulate Li isotope fractionation during upwelling of pore fluids to the seafloor. It is demonstrated that slow pore water advection (order of mm a-1) suffices to convey much of the deep-seated diagenetic Li signal into shallow sediments. If carefully applied, Li isotope systematics may, thus, provide a valuable record of fluid/mineral interaction that has been inherited several hundreds or thousands of meters below the seafloor.
    Language: English
    Type: http://purl.org/eprint/type/ConferencePaper
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  • 2
    Publication Date: 1967-02-01
    Print ISSN: 0028-1042
    Electronic ISSN: 1432-1904
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
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  • 3
    Publication Date: 2012-12-01
    Description: Background: The moss Physcomitrella patens contains C18- as well as C20-polyunsaturated fatty acids that can be metabolized by different enzymes to form oxylipins such as the cyclopentenone cis(+)-12-oxo phytodienoic acid. Mutants defective in the biosynthesis of cyclopentenones showed reduced fertility, aberrant sporophyte morphology and interrupted sporogenesis. The initial step in this biosynthetic route is the conversion of a fatty acid hydroperoxide to an allene oxide. This reaction is catalyzed by allene oxide synthase (AOS) belonging as hydroperoxide lyase (HPL) to the cytochrome P450 family Cyp74. In this study we characterized two AOS from P. patens, PpAOS1 and PpAOS2. Results: Our results show that PaAOS1 is highly active with both C18 and C20-hydroperoxy-fatty acid substrates, whereas PpAOS2 is fully active only with C20-substrates, exhibiting trace activity (~1000-fold lower kcat/KM) with C18 substrates. Analysis of products of PpAOS1 and PpHPL further demonstrated that both enzymes have an inherent side activity mirroring the close inter-connection of AOS and HPL catalysis. By employing site directed mutagenesis we provide evidence that single amino acid residues in the active site are also determining the catalytic activity of a 9-/13-AOS -- a finding that previously has only been reported for substrate specific 13-AOS. However, PpHPL cannot be converted into an AOS by exchanging the same determinant. Localization studies using YFP-labeled AOS showed that PpAOS2 is localized in the plastid while PpAOS1 may be found in the cytosol. Analysis of the wound-induced cis(+)-12-oxo phytodienoic acid accumulation in PpAOS1 and PpAOS2 single knock-out mutants showed that disruption of PpAOS1, in contrast to PpAOS2, results in a significantly decreased cis(+)-12-oxo phytodienoic acid formation. However, the knock-out mutants of neither PpAOS1 nor PpAOS2 showed reduced fertility, aberrant sporophyte morphology or interrupted sporogenesis. Conclusions: Our study highlights five findings regarding the oxylipin metabolism in P. patens: (i) Both AOS isoforms are capable of metabolizing C18- and C20-derived substrates with different specificities suggesting that both enzymes might have different functions. (ii) Site directed mutagenesis demonstrated that the catalytic trajectories of 9-/13-PpAOS1 and PpHPL are closely inter-connected and PpAOS1 can be inter-converted by a single amino acid exchange into a HPL. (iii) In contrast to PpAOS1, PpAOS2 is localized in the plastid where oxylipin metabolism takes place. (iv) PpAOS1 is essential for wound-induced accumulation of cis(+)-12-oxo phytodienoic acid while PpAOS2 appears not to be involved in the process. (v) Knock-out mutants of neither AOS showed a deviating morphological phenotype suggesting that there are overlapping functions with other Cyp74 enzymes.
    Electronic ISSN: 1471-2229
    Topics: Biology
    Published by BioMed Central
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  • 4
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    PANGAEA
    In:  Supplement to: Ehlert, Claudia; Doering, Kristin; Wallmann, Klaus; Scholz, Florian; Sommer, Stefan; Grasse, Patricia; Geilert, Sonja; Frank, Martin (2016): Stable silicon isotope signatures of marine pore waters – Biogenic opal dissolution versus authigenic clay mineral formation. Geochimica et Cosmochimica Acta, 191, 102-117, https://doi.org/10.1016/j.gca.2016.07.022
    Publication Date: 2020-01-17
    Description: Dissolved silicon isotope compositions have been analysed for the first time in pore waters (δ30SiPW) of three short sediment cores from the Peruvian margin upwelling region with distinctly different biogenic opal content in order to investigate silicon isotope fractionation behaviour during early diagenetic turnover of biogenic opal in marine sediments. The δ30SiPW varies between +1.1‰ and +1.9‰ with the highest values occurring in the uppermost part close to the sediment–water interface. These values are of the same order or higher than the δ30Si of the biogenic opal extracted from the same sediments (+0.3‰ to +1.2‰) and of the overlying bottom waters (+1.1‰ to +1.5‰). Together with dissolved silicic acid concentrations well below biogenic opal saturation, our collective observations are consistent with the formation of authigenic alumino-silicates from the dissolving biogenic opal. Using a numerical transport-reaction model we find that approximately 24% of the dissolving biogenic opal is re-precipitated in the sediments in the form of these authigenic phases at a relatively low precipitation rate of 56 μmol Si cm−2 yr−1. The fractionation factor between the precipitates and the pore waters is estimated at −2.0‰. Dissolved and solid cation concentrations further indicate that off Peru, where biogenic opal concentrations in the sediments are high, the availability of reactive terrigenous material is the limiting factor for the formation of authigenic alumino-silicate phases.
    Type: Dataset
    Format: application/zip, 6 datasets
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  • 5
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 1072 data points
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  • 6
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    PANGAEA
    In:  Supplement to: Scholz, Florian; Severmann, Silke; McManus, James; Hensen, Christian (2014): Beyond the Black Sea paradigm: The sedimentary fingerprint of an open-marine iron shuttle. Geochimica et Cosmochimica Acta, 127, 368-380, https://doi.org/10.1016/j.gca.2013.11.041
    Publication Date: 2020-01-17
    Description: We present iron (Fe) concentration and Fe isotope data for a sediment core transect across the Peru upwelling area, which hosts one of the ocean's most pronounced oxygen minimum zones (OMZs). The lateral progression of total Fe to aluminum ratios (FeT/Al) across the continental margin indicates that sediments within the OMZ are depleted in Fe whereas sediments below the OMZ are enriched in Fe relative to the lithogenic background. Rates of Fe loss within the OMZ, as inferred from FeT/Al ratios and sedimentation rates, are in agreement with benthic flux data that were calculated from pore water concentration gradients. The mass of Fe lost from sediments within the OMZ is within the same order of magnitude as the mass of Fe accumulating below the OMZ. Taken together, our data are in agreement with a shuttle scenario where Fe is reductively remobilized from sediments within the OMZ, laterally transported within the anoxic water column and re-precipitated within the more oxic water below the OMZ. Sediments within the OMZ have increased 56Fe/54Fe isotope ratios relative to the lithogenic background, which is consistent with the general notion of benthic release of dissolved Fe with a relatively low 56Fe/54Fe isotope ratio. The Fe isotope ratios increase across the margin and the highest values coincide with the greatest Fe enrichment in sediments below the OMZ. The apparent mismatch in isotope composition between the Fe that is released within the OMZ and Fe that is re-precipitated below the OMZ implies that only a fraction of the sediment-derived Fe is retained near-shore whereas another fraction is transported further offshore. We suggest that a similar open-marine shuttle is likely to operate along many ocean margins. The observed sedimentary fingerprint of the open-marine Fe shuttle differs from a related transport mechanism in isolated euxinic basins (e.g., the Black Sea) where the laterally supplied, reactive Fe is quantitatively captured within the basin sediments. We suggest that our findings are useful to identify OMZ-type Fe cycling in the geological record.
    Type: Dataset
    Format: text/tab-separated-values, 492 data points
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  • 7
  • 8
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    PANGAEA
    In:  Supplement to: Hensen, Christian; Scholz, Florian; Nuzzo, Marianne; Valadares, Vasco; Gràcia, Eulàlia; Terrinha, Pedro; Liebetrau, Volker; Kaul, Norbert E; Silva, Sonia; Martinez-Loriente, Sara; Bartolome, Rafael; Piñero, Elena; Magalhães, Vitor H; Schmidt, Mark; Weise, Stephan M; Cunha, Marina Ribeiro; Hilário, Ana; Perea, Hector; Rovelli, Lorenzo; Lackschewitz, Klas S (2015): Strike-slip faults mediate the rise of crustal-derived fluids and mud volcanism in the deep sea. Geology, 43(4), 339-342, https://doi.org/10.1130/G36359.1
    Publication Date: 2020-01-17
    Description: We report on newly discovered mud volcanoes located at about 4500 m water depth 90 km west of the deformation front of the accretionary wedge of the Gulf of Cadiz, and thus outside of their typical geotectonic environment. Seismic data suggest that fluid flow is mediated by a 〉400-km-long strike-slip fault marking the transcurrent plate boundary between Africa and Eurasia. Geochemical data (Cl, B, Sr, 87Sr/86Sr, Delta18O, DeltaD) reveal that fluids originate in oceanic crust older than 140 Ma. On their rise to the surface, these fluids receive strong geochemical signals from recrystallization of Upper Jurassic carbonates and clay-mineral dehydration in younger terrigeneous units. At present, reports of mud volcanoes in similar deep-sea settings are rare, but given that the large area of transform-type plate boundaries has been barely investigated, such pathways of fluid discharge may provide an important, yet unappreciated link between the deeply buried oceanic crust and the deep ocean.
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 9
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    PANGAEA
    In:  Supplement to: Völker, David; Scholz, Florian; Geersen, Jacob (2011): Analysis of submarine landsliding in the rupture area of the 27 February 2010 Maule earthquake, Central Chile. Marine Geology, 288(1-4), 79-89, https://doi.org/10.1016/j.margeo.2011.08.003
    Publication Date: 2020-01-17
    Description: The comparison of bathymetric datasets compiled before and after the Mw = 8.8 Maule Earthquake of the 27 February 2010 offshore Central Chile proves that no new submarine landslides on a size scale detectable with hull-mounted bathymetric echosounders (features of a horizontal size of 〉 1 km) formed as a direct consequence of the ground shaking. Gravity coring around a pre-existing slide feature offshore Concepción (BioBio Slide), however, documents that (1) a number of events occurred as retrogressive failures of the BioBio Slide wall, the youngest of which is 700?1000 years old, and that (2) a very recent small scale slide structure resulted from non-destructive imbricate stacking of a thin sediment layer. Pore water geochemical data show that this event post-dates the Maule Earthquake, suggesting that it was triggered by one of the numerous aftershocks. The absence of larger failures and the presence of a small slide let us propose that in contrast to apparent logic, frequent violent earthquakes at convergent margins do not necessarily pose a particular tsunami risk by landslides. The frequent shaking might even limit the slide volume and therefore their tsunami hazard, as instead of rare and large slides, frequent smaller slides are induced.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 10
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 539 data points
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