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  • 1
    Publication Date: 2018-07-18
    Description: Although it has been more than 30 years since the discovery of deep-sea hydrothermal vents, comprehending the interconnections between hydrothermal venting and microbial life remains a challenge. Here we investigate abiotic-biotic linkages in low-temperature hydrothermal biotopes at Desperate and Lilliput on the southern Mid-Atlantic Ridge. Both sites are basalt-hosted and fluids exhibit the expected chemical signatures. However, contrasting crustal permeabilities have been proposed, supporting pervasive mixing at Desperate but restricting circulation at Lilliput. In Desperate fluids, sulfide and O2 were readily available but H2 hardly detectable. Under incubation conditions (oxic unamended, sulfide-spiked, oxic and anoxic H2 -spiked at 18°C), only sulfide oxidation by Thiomicrospira fuelled biomass synthesis. Microbial phylogenies from Desperate incubation experiments resembled those of the natural samples suggesting that the incubation conditions mimicked the environment. In Lilliput fluids, O2 was limited, whereas sulfide and H2 were enriched. Autotrophy appeared to be stimulated by residual sulfide and by amended H2 . Yet, based on bacterial phylogenies only conditions in anoxic H2 -spiked Lilliput incubations appeared similar to parts of the Lilliput habitat. In anoxic H2 -spiked Lilliput enrichments Campylobacteraceae likely supported biomass production through H2 oxidation. We argue that the diverging circulation patterns arising from different subseafloor permeabilities act as major driving forces shaping these biotope structures.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2015-03-16
    Description: During the international GEA-II expedition to Sør Rondane (East Antarctica), large aggregates of crystalline gypsum were found within blue-ice moraines on the south side of the Sør Rondane Mountains at an elevation of ca. 2000 m and ca. 250 km inland of the present coastline. Gypsum aggregates reach one meter in diameter with individual crystal length up to 20 cm. Apparently, the gypsum grows in-situ and as a result of sublimation of the blue ice on the gravel of the moraine. Individual cobbles and sand are incorporated into the gypsum aggregates. The gypsum does not show signs of transport. In thin section, the gypsum shows an irregular growth zoning and in part bent cleavage planes. Abundant primary fluid inclusions are present parallel to the growth zoning as well as parallel to cleavage plains. This type of gypsum formation is enigmatic and has never been described before. It might indicate an important and thus far unknown process, characterising a special way of interaction between the lithosphere and the cryosphere. Preliminary Sr-isotope data indicate relatively high values and suggest crustal affinities. A preliminary set of sulfate sulfur (δ34SSO4) and oxygen (δ18OSO4) isotope data reveals values ranging from +7.0 and +29.6 ‰ (δ34SSO4) and between -16.7 and +0.3 ‰ (δ18OSO4). Samples display a positive correlation between δ34S and δ18O. Thus, Sulfur isotope values are highly variable and offer different conclusions with respect to potential sulfate sources. None of the gypsum samples displays a sulfur isotopic composition reflecting a pure seawater sulfate (i.e. sea spray) origin. Two samples yielded δ34SSO4 values of +7.0 and +9.0 ‰, most others are distinctly more positive than modern seawater sulfate (i.e., above +21.0 ‰), with a maximum value of +29.6 ‰. In general, the sulfur isotope values more positive than modern seawater sulfate suggest bacterial sulfate reduction. The low δ34SSO4 values are comparable to values measured previously for continental sulfate and are similar to a single pyrite sample from a black schist sample, ca. 150 km to the W, Steingarden area (this study). The oxygen isotopic composition for the blue ice gypsum samples is also characterized by rather variable including strongly negative δ18OSO4 values. Negative sulfate oxygen isotope values possibly reflect an 18O depleted continental source such as Antarctic glacial waters that could have fostered the oxidative weathering of sulfide sulfur. The observed variability could reflect different stages of bacterial sulfate reduction.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The evolution of the Earth’s atmosphere is marked by a transition from an early atmosphere with very low oxygen content to one with an oxygen content within a few per cent of the present atmospheric level. Placing time constraints on this transition is of interest because it identifies ...
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1165
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Description / Table of Contents: Abstract Combined hydrochemical, geochemical and isotopic investigations of solid and dissolved sulphur- and carbon-species from different aquifer levels allow to distinguish two geochemical cycles: The first one is represented by the sedimentary pyrites which have been formed during the Tertiary by bacterial sulplate reduction. These pyrites are characterized by strongly depleted δ 14 S-signatures. In accordance with a recent origin, the groundwater composition reflects the current sulphur- and carbon-cycling representing the second one. The activity of sulphate reducing bacterian can be deduced from a decrease of the sulphate concentration with depth and a simultaneous increase in δ 14 S- and δ 18 O-values as well as increasing hydrogen sulphide concentrations. Dissolved organic carbon, the substrate and electron-donor for the bacterial sulphate reduction, appears to be the limiting factor as its average concentration reaches only 1.6 mg/l. The concentration of dissolved inorganic carbon is slightly higher in the deeper groundwater levels. Due to its clearly negative carbon-isotope signature it can be identified as a product of biogenic oxidation of organic material.
    Notes: Kurzfassung Durch den kombinierten Einsatz von isotopengeochemischen und hydrochemischen Untersuchungsmethoden an Sedimenten und Grundwässern der Niederrheinischen Bucht können die in den Aquiferen vorhandenen festen und gelösten Schwefel- und Kohlenstoff-Verbindungen zwei zeitlich getrennten Stoffkreisläufen zugeordnet werden. Während die sedimentären Pyrite, die dominierende Schwefelverbindung innerhalb der marinen Sande, durchschnittlich stark an 34 S verarmt sind und bereits im Tertiär gebildet wurden, läßt sich aus den gelösten Wasserinhaltsstoffen der jungen Grundwässer auf den rezenten Schwefel- und Kohlenstoff-Kreislauf schließen. In den unteren anaeroben Grundwasserstockwerken der durch Braunkohleeinschaltungen gegliederten Sande kann die Aktivität sulfatreduzierter Bakterien durch die Abnahme der Sulfatkonzentration bei gleichzeitigem Anstieg der zugehörigen δ 14 S- und δ 18 O-Werte im Sinne einer Rayleigh-Fraktionierung sowie durch erhöhte Schwefelwasserstoffkonzentration belegt werden. Gelöster organischer Kohlenstoff, der als Elektronendonator für die bakterielle Sulfatreduktion dient, ist mit durchschnittlich 1,6 mg/l vermutlich der limitierende Faktor dieses Prozesses. Gelöster anorganischer Kohlenstoff tritt in den tieferen Grundwasserstockwerken in leicht erhöhten Konzentrationen auf und kann aufgrund seiner deutlich negativ Kohlenstoff-Isotopensignatur als Produkt der Oxidation organischer Substanz identifiziert werden.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The oxidation of the Earth's crust and the increase in atmospheric oxygen early in Earth history have been linked to the accumulation of reduced carbon in sedimentary rocks. Trends in the carbon isotope composition of sedimentary organic carbon and carbonate show that during the Proterozoic aeon ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 362 (1993), S. 118-118 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] DES MARAIS ET AL. REPLY — We summarized the evidence that 〈 5org increased and that net isotope discrimination (〈 5carb - 〈 5org) decreased substantially during the Proterozoic1 (see figure left). These trends, which emerge from 〈 5carb and 〈 5org data obtained by several ...
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  • 7
    Publication Date: 2011-08-24
    Description: The oxidation of the earth's crust and the increase in atmospheric oxygen early in earth history have been linked to the accumulation of reduced carbon in sedimentary rocks. Trends in the carbon isotope composition of sedimentary organic carbon and carbonate show that during the Proterozoic aeon (2.5-0.54 Gyr ago) the organic carbon reservoir grew in size, relative to the carbonate reservoir. This increase, and the concomitant release of oxidizing power in the environment, occurred mostly during episodes of global rifting and orogeny.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 359; 6396; p. 605-609.
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  • 8
    Publication Date: 2017-05-18
    Description: Seamounts can provide conduits for the entry and exit of hydrothermal fluids in ocean basins. However, only a few ridge flank hydrothermal systems that discharge through seamounts have been discovered, all located on relatively young crust. We have retrieved samples from 126 m.y. old Henry Seamount, an extinct volcano near the youngest Canary island of El Hierro, that provide evidence for Holocene low-temperature hydrothermal fluid discharge. This is the first documented finding of such activity at the Canary archipelago. The samples include shells from vesicomyid clams 〈18.6 k.y. old, massive barite, and trachytes that are pervasively barite metasomatized. Sulfur, oxygen, and strontium isotope ratios of barite indicate that the fluid contained residual sulfate from microbial reduction at the recharge site and reacted with basement rocks. Recharge probably occurred at basement outcrops of El Hierro's submarine flank at 25–30 km distance, the driving force for hydrothermal circulation through old crust being provided by increased basal heat flow from Canary magmatism. The data show that island flanks may provide important recharge sites for seawater circulation and that even old and small seamounts can contribute to heat and mass exchange between ocean crust and seawater.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2014-02-11
    Description: Mass-independently fractionated sulfur isotopes (MIF-S) provide strong evidence for an anoxic atmosphere during the Archean. Moreover, the temporal evolution of MIF-S shows increasing magnitudes between 2.7 and 2.5 Ga until the start of the Great Oxidation Event (G.O.E.) at around 2.4 Ga. The conclusion of a completely anoxic atmosphere up to the G.O.E. is in contrast to recent studies on redox-sensitive elements, which suggest slightly oxidizing conditions during continental weathering already several hundred million years prior to the G.O.E. In order to investigate this apparent inconsistency, we present multiple sulfur isotopes for 2.71 Ga pyritic black shales derived from the Kidd Creek area, Ontario, Canada. These samples display high positive Δ33S values up to 3.8‰ and the typical late Archean slope in Δ36S/Δ33S of −0.9. In contrast, the time period before (3.2–2.73 Ga) is characterized by greatly attenuated MIF-S magnitudes and a slope in Δ36S/Δ33S of −1.5. We attribute the increase in Δ33S magnitude as well as the contemporaneous change in the slope of Δ36S/Δ33S to changes in the relative reaction rate of different MIF-S source reactions and changes in atmospheric sulfur exit channels. Both of these are dependent on atmospheric CH4:CO2 and O2 mixing ratios. We propose a distinct change in atmospheric composition at 2.7 Ga resulting from increased fluxes of oxygen and methane as the best explanation for the observed Neoarchean MIF-S record. Our data and modeling results suggest that oxygenic photosynthesis was a major contributor to primary productivity 2.7 billion years ago.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2017-02-20
    Description: The Cycladic blueschist belt, Greece, is mostly submerged below sea level and regional correlations are difficult to establish. Marbles are widespread within the belt and locally used as marker horizons to subdivide monotonous schist sequences. However, owing to the lack of distinctive petrographic characteristics, the marbles have not been used for island-to-island correlations. This study aims to investigate the potential of Sr-, C- and O-isotope compositions of marbles as a tool for unravelling the litho- and/or tectonostratigraphic relationships across the Cycladic islands, and as a proxy for the time of sediment formation. For this purpose, we have studied metamorphic carbonate rocks from the islands of Tinos, Andros, Syros, Sifnos and Naxos. Identical 87Sr/86Sr values for certain marble horizons occurring on Tinos, Andros and Sifnos are interpreted to document coeval regional carbonate precipitation. The 87Sr/86Sr values of the apparently least altered samples intersect the seawater curve multiple times within the most likely time interval of original carbonate precipitation (〈 240 Ma; as indicated by previously published ion probe U–Pb zircon data) and thus an unequivocal age assignment is not possible. Very broad temporal correlations are possible, but more subtle distinctions are not feasible. On Andros, the overlapping Sr-isotope values of marbles representing the lowest and highest parts of the metamorphic succession are in accordance with a model suggesting isoclinal folding or thrusting of a single horizon, or very fast sedimentation. In contrast, distinct 87Sr/86Sr values for samples from Tinos, representing different levels of the metamorphic succession, suggest that these rocks represent a temporal succession and not the tectonic repetition of a single horizon. Based on Sr-,O- and C-isotope characteristics alone the time equivalence ofmarbles occurring on different islands could not be documented unambiguously. However, by using various combinations of these parameters, some occurrences can be discriminated from the overall sample population. The new data further accentuate the general potential of coupled Sr-, C- and O-isotope characteristics for identification of archaeological provenance and complement existing datasets for Aegean marbles.
    Type: Article , PeerReviewed
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