34 research outputs found

    Biosignatures in chimney structures and sediment from the Loki's Castle low-temperature hydrothermal vent field at the Arctic Mid-Ocean Ridge

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    We investigated microbial life preserved in a hydrothermally inactive silica-barite chimney in comparison with an active barite chimney and sediment from the Loki's Castle low-temperature venting area at the Arctic Mid-Ocean Ridge (AMOR) using lipid biomarkers. Carbon and sulfur isotopes were used to constrain possible metabolic pathways. Multiple sulfur (ή34S, ∆33S) isotopes on barite over a cross section of the extinct chimney range between 21.1 and 22.5‰ in ή34S, and between 0.020 and 0.034‰ in Δ33S, indicating direct precipitation from seawater. Biomarker distributions within two discrete zones of this silica-barite chimney indicate a considerable difference in abundance and diversity of microorganisms from the chimney exterior to the interior. Lipids in the active and inactive chimney barite and sediment were dominated by a range of 13C-depleted unsaturated and branched fatty acids with ή13C values between −39.7 and −26.7‰, indicating the presence of sulfur-oxidizing and sulfate-reducing bacteria. The majority of lipids (99.5%) in the extinct chimney interior that experienced high temperatures were of archaeal origin. Unusual glycerol monoalkyl glycerol tetraethers (GMGT) with 0-4 rings were the dominant compounds suggesting the presence of mainly (hyper-) thermophilic archaea. Isoprenoid hydrocarbons with ή13C values as low as −46‰ also indicated the presence of methanogens and possibly methanotrophs

    A multiple sulfur record of super-large volcanic eruptions in Archaean pyrite nodules

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    Archaean supracrustal rocks carry a record of mass-independently fractionated S that is interpreted to be derived from UV-induced photochemical reactions in an oxygen-deficient atmosphere. Experiments with photochemical reactions of SO2 gas have provided some insight into these processes. However, reconciling experimental results with the multiple S isotopic composition of the Archaean sedimentary record has proven difficult and represents one of the outstanding issues in understanding the Archaean surface S-cycle. We present quadruple S isotope data (32S, 33S, 34S, 36S) for pyrite from Mesoarchaean carbonaceous sediments of the Dominion Group, South Africa, deposited in an acidic volcanic lake, which help reconcile observations from the Archaean sedimentary record with the results of photochemical experiments. The data, which show low S/S ratios (mostly â‰Ș 1) and very negative S/S ratios (−4 and lower), contrast with the composition of most Archaean sedimentary sulfides and sulfates, having S/ (the so-called ‘Archaean reference array’), but match those of modern photochemical sulfate aerosols produced in the stratosphere, following super-large volcanic eruptions, and preserved in Antarctic ice. These data are also consistent with the results of UV-irradiation experiments of SO2 gas at variable gas pressure. The S isotope composition of the Dominion Group pyrite is here interpreted to reflect the products of photolysis in a low-oxygen-level atmosphere at high SO2 pressure during large volcanic eruptions, mixed with Archaean ‘background’ (having a composition broadly similar to the Archaean reference array) S pools. It is inferred that high sedimentation rates in a terrestrial basin resulted in an instantaneously trapped input of atmospheric S during short-lasted depositional intervals, which faithfully represents transient photochemical signals in comparison with marine sedimentary records

    Moderate levels of oxygenation during the late stage of Earth's Great Oxidation Event

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    FOO and RS acknowledge financial support from the University of TĂŒbingen and the German Research Foundation (DFG Grant SCHO1071/11-1). FOO and MBA are thankful for support from the Natural Environment Research Council (NERC grant NE/V004824/1). The stable isotope facilities at IDYST were funded by the University of Lausanne. SK, YA and MIV-R acknowledge European Research Council (ERC) Starting Grant 636808 (O2RIGIN). AH and FOO acknowledge support from National Research Foundation of South Africa (NRF Grant 75892). SK also acknowledges the Ramon y Cajal contract (RYC2020-030014-I). Participation by AB was supported by Discovery and Accelerator Grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and ACS PF grant (624840ND2). EES acknowledges funding from a NERC Frontiers grant (NE/V010824/1). SWP acknowledges support from a Royal Society Wolfson Research Merit Award. MIV-R additionally acknowledges funding support from the German Research Foundation (DFG Grant VA 1568/1-1).The later stages of Earth's transition to a permanently oxygenated atmosphere during the Great Oxidation Event (GOE; ∌2.43–2.06 Ga) is commonly linked with the suggestion of an “oxygen overshoot” during the ∌2.22–2.06 Ga Lomagundi Event (LE), which represents Earth's most pronounced and longest-lived positive carbon isotope excursion. However, the magnitude and extent of atmosphere-ocean oxygenation and implications for the biosphere during this critical period in Earth's history remain poorly constrained. Here, we present nitrogen (N), selenium (Se), and carbon (C) isotope data, as well as bio-essential element concentrations, for Paleoproterozoic marine shales deposited during the LE. The data provide evidence for a highly productive and well-oxygenated photic zone, with both inner and outer-shelf marine environments characterized by nitrate- and Se oxyanion-replete conditions. However, the redoxcline subsequently encroached back onto the inner shelf during global-scale deoxygenation of the atmosphere-ocean system at the end of the LE, leading to locally enhanced water column denitrification and quantitative reduction of selenium oxyanions. We propose that nitrate-replete conditions associated with fully oxygenated continental shelf settings were a common feature during the LE, but nitrification was not sufficiently widespread for the aerobic nitrogen cycle to impact the isotopic composition of the global ocean N inventory. Placed in the context of Earth's broader oxygenation history, our findings indicate that O2 levels in the atmosphere-ocean system were likely much lower than modern concentrations. Early Paleoproterozoic biogeochemical cycles were thus far less advanced than after Neoproterozoic oxygenation.Publisher PDFPeer reviewe

    Phase 1 Trials of rVSV Ebola Vaccine in Africa and Europe.

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    BACKGROUND: The replication-competent recombinant vesicular stomatitis virus (rVSV)-based vaccine expressing a Zaire ebolavirus (ZEBOV) glycoprotein was selected for rapid safety and immunogenicity testing before its use in West Africa. METHODS: We performed three open-label, dose-escalation phase 1 trials and one randomized, double-blind, controlled phase 1 trial to assess the safety, side-effect profile, and immunogenicity of rVSV-ZEBOV at various doses in 158 healthy adults in Europe and Africa. All participants were injected with doses of vaccine ranging from 300,000 to 50 million plaque-forming units (PFU) or placebo. RESULTS: No serious vaccine-related adverse events were reported. Mild-to-moderate early-onset reactogenicity was frequent but transient (median, 1 day). Fever was observed in up to 30% of vaccinees. Vaccine viremia was detected within 3 days in 123 of the 130 participants (95%) receiving 3 million PFU or more; rVSV was not detected in saliva or urine. In the second week after injection, arthritis affecting one to four joints developed in 11 of 51 participants (22%) in Geneva, with pain lasting a median of 8 days (interquartile range, 4 to 87); 2 self-limited cases occurred in 60 participants (3%) in Hamburg, Germany, and Kilifi, Kenya. The virus was identified in one synovial-fluid aspirate and in skin vesicles of 2 other vaccinees, showing peripheral viral replication in the second week after immunization. ZEBOV-glycoprotein-specific antibody responses were detected in all the participants, with similar glycoprotein-binding antibody titers but significantly higher neutralizing antibody titers at higher doses. Glycoprotein-binding antibody titers were sustained through 180 days in all participants. CONCLUSIONS: In these studies, rVSV-ZEBOV was reactogenic but immunogenic after a single dose and warrants further evaluation for safety and efficacy. (Funded by the Wellcome Trust and others; ClinicalTrials.gov numbers, NCT02283099, NCT02287480, and NCT02296983; Pan African Clinical Trials Registry number, PACTR201411000919191.)

    An atmospheric source of S in Mesoarchaean structurally-controlled gold mineralisation of the Barberton Greenstone Belt

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    The Barberton Greenstone Belt of southern Africa hosts several Mesoarchaean gold deposits. The ores were mostly formed in greenschist facies conditions, and occur as hydrothermal alteration zones around extensional faults that truncate and post-date the main compressional structures of the greenstone belt. Ore deposition was accompanied by the intrusion of porphyries, which has led to the hypothesis that gold may have been sourced from magmas. Because the transport of Au in the hydrothermal fluids is widely believed to have involved S complexes, tracing the origin of S may place strong constraints on the origin of Au. We measured multiple S isotopes in sulfide ore from Sheba and Fairview mines of the Barberton Greenstone Belt to distinguish “deep” S sources (e.g. magmas) from “surface” S sources (i.e. rocks of the volcano-sedimentary succession that contain S processed in the atmosphere preserved as sulfide and sulfate minerals). Ion probe (SIMS) analyses of pyrite from ore zones indicate mass-independent fractionation of S isotopes (Δ33S = −0.6‰ to +1.0‰) and the distribution of the analyses in the Δ33S–ή34S space matches the distribution peak of previously published analyses of pyrite from the entire volcano-sedimentary succession. Notwithstanding that the H2O–CO2 components of the fluids may have been introduced from a deep source external to the greenstone belt rocks, the fact that S bears an atmospheric signature suggests the hypothesis that the source of Au should also be identified in the supracrustal succession of the greenstone belt. Our findings differ from conclusions of previous studies of other Archaean shear-hosted Au deposits based on mineralogical and isotopic evidence, which suggested a magmatic or mantle source for Au, and imply that there is no single model that can be applied to this type of mineralisation in the Archaean

    Karbonatbildung in der ozeanischen Kruste als Indikator fĂŒr Wasser-Gesteins-Wechselwirkungen

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    The main objective of this thesis was to elucidate the authigenesis of carbonate minerals in modern and Devonian ocean-floor volcanic rocks and to demonstrate that Late Devonian (Frasnian) pillow basalts from the Saxothuringian zone once harbored microbial life. The ultramafic-hosted Logatchev hydrothermal field (LHF) at the Mid-Atlantic Ridge, the Arctic Gakkel Ridge (GR) and the Late Devonian Frankenwald feature carbonate precipitates (aragonite, calcite, dolomite) in voids and fractures of different types of rocks. Carbonate veins cut the rock texture, postdating the emplacement and serpentinization of the upper mantle rocks. Petrographic and stable isotope (13C, 18O) patterns were compared in an attempt to understand the genesis of carbonate minerals in these settings. Specifically, were the carbonate sample from the modern seafloor settings and the Devonian analogue of hydrothermal origin, low-temperature abiogenic or biogenic origin? Aragonite is the most abundant carbonate mineral in serpentnites from the LHF and GR and occurs within massive sulfides of the LHF. 18O values of aragonite hosted in serpentinites and sulfides are consistent with precipitation from cold seawater. Most of the corresponding 13C values indicate a marine carbon source, while 13C values of sulfide-hosted aragonite as high as 3.6 may reflect residual carbon dioxide in the zone of methanogenesis. Calcite veins from LHF, by contrast, have low 18O values (as low as 20.0) and 13C values (as low as 5.8) indicative of precipitation from hydrothermal solutions dominated by magmatic carbon dioxide. To gain deeper insights in the formation of carbonates in hydrothermal environments, chemical and strontium isotopic composition of these different carbonates were analyzed to examine the conditions that led to their formation. Seawater-like 87Sr/86Sr ratios of aragonite in serpentinites from LHF are similar to those of aragonite from the GR, indicating aragonite formation from seawater at ambient conditions at both sites. Aragonite veins in sulfides from LHF also have seawater-like 87Sr/86Sr ratios, however, the rare earth element (REE) patterns show a clear positive europium (Eu) anomaly indicative of small (<1%) proportions of hydrothermal fluids. In contrast to aragonite, dolomite and calcite from the LHF precipitated at much higher temperatures, indicative of formation from evolved hydrothermal fluids. A simple mixing model based on strontium mass balance and enthalpy conservation indicates strongly variable conditions of fluid mixing and heat transfers involved in carbonate formation. Aragonite samples corroborate the stable isotope patterns and formed at low temperatures form pure seawater. Dolomite precipitated from a mixture of 97% seawater and 3% hydrothermal fluid that indicate conductive heating, probably of seawater prior to mixing. Hydrothermal serpentinite-hosted calcite formed from a mixture of 67% hydrothermal fluid and 33% seawater due to conductive cooling of hydrothermal fluid effusing a fault. REE patterns corroborate the results of the mixing model; since the calcite that formed from waters with the greatest hydrothermal contribution have REE that closely resemble those of vent fluids from the LHF. ή13C values of Late Devonian (Frasnian) calcite hosted in basalts indicate precipitation from seawater, while ή13C values of serpentinite-hosted calcite agree with mantle-derived carbon dioxide with a contribution of amagmatic carbon (for values low as −8.6), presumably methane. Low 18O values reflect diagenetic and metamorphic overprinting. Furthermore, Late Devonian pillow basalts from the Saxothuringian zone were found to contain abundant putative biogenic filaments, indicating that the volcanic rocks once harbored microbial life. The mineralized filaments are found in carbonate-filled vesicles, where they start to form on internal surfaces after seawater ingress. A biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms, their independence of crystal faces and cleavage plans, complex branching patterns, and internal segmentation. They became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron-rich environments. The results presented in this thesis give rise to a new and better understanding of carbonate formation in the ocean crust, especially in ultramafic-hosted hydrothermal environments. Further, the results highlight the important of mixing processes in the subseafloor of hydrothermal systems that led to the formation of carbonates and highlights that seafloor basalt may thus represent a common, perhaps universal niche for life in the oceanic crust

    Carbonate formation in the ocean crust as a proxy for water-rock interactions

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    The main objective of this thesis was to elucidate the authigenesis of carbonate minerals in modern and Devonian ocean-floor volcanic rocks and to demonstrate that Late Devonian (Frasnian) pillow basalts from the Saxothuringian zone once harbored microbial life. The ultramafic-hosted Logatchev hydrothermal field (LHF) at the Mid-Atlantic Ridge, the Arctic Gakkel Ridge (GR) and the Late Devonian Frankenwald feature carbonate precipitates (aragonite, calcite, dolomite) in voids and fractures of different types of rocks. Carbonate veins cut the rock texture, postdating the emplacement and serpentinization of the upper mantle rocks. Petrographic and stable isotope (13C, 18O) patterns were compared in an attempt to understand the genesis of carbonate minerals in these settings. Specifically, were the carbonate sample from the modern seafloor settings and the Devonian analogue of hydrothermal origin, low-temperature abiogenic or biogenic origin? Aragonite is the most abundant carbonate mineral in serpentnites from the LHF and GR and occurs within massive sulfides of the LHF. 18O values of aragonite hosted in serpentinites and sulfides are consistent with precipitation from cold seawater. Most of the corresponding 13C values indicate a marine carbon source, while 13C values of sulfide-hosted aragonite as high as 3.6 may reflect residual carbon dioxide in the zone of methanogenesis. Calcite veins from LHF, by contrast, have low 18O values (as low as 20.0) and 13C values (as low as 5.8) indicative of precipitation from hydrothermal solutions dominated by magmatic carbon dioxide. To gain deeper insights in the formation of carbonates in hydrothermal environments, chemical and strontium isotopic composition of these different carbonates were analyzed to examine the conditions that led to their formation. Seawater-like 87Sr/86Sr ratios of aragonite in serpentinites from LHF are similar to those of aragonite from the GR, indicating aragonite formation from seawater at ambient conditions at both sites. Aragonite veins in sulfides from LHF also have seawater-like 87Sr/86Sr ratios, however, the rare earth element (REE) patterns show a clear positive europium (Eu) anomaly indicative of small (<1%) proportions of hydrothermal fluids. In contrast to aragonite, dolomite and calcite from the LHF precipitated at much higher temperatures, indicative of formation from evolved hydrothermal fluids. A simple mixing model based on strontium mass balance and enthalpy conservation indicates strongly variable conditions of fluid mixing and heat transfers involved in carbonate formation. Aragonite samples corroborate the stable isotope patterns and formed at low temperatures form pure seawater. Dolomite precipitated from a mixture of 97% seawater and 3% hydrothermal fluid that indicate conductive heating, probably of seawater prior to mixing. Hydrothermal serpentinite-hosted calcite formed from a mixture of 67% hydrothermal fluid and 33% seawater due to conductive cooling of hydrothermal fluid effusing a fault. REE patterns corroborate the results of the mixing model; since the calcite that formed from waters with the greatest hydrothermal contribution have REE that closely resemble those of vent fluids from the LHF. &#948;13C values of Late Devonian (Frasnian) calcite hosted in basalts indicate precipitation from seawater, while &#948;13C values of serpentinite-hosted calcite agree with mantle-derived carbon dioxide with a contribution of amagmatic carbon (for values low as &#8722;8.6), presumably methane. Low 18O values reflect diagenetic and metamorphic overprinting. Furthermore, Late Devonian pillow basalts from the Saxothuringian zone were found to contain abundant putative biogenic filaments, indicating that the volcanic rocks once harbored microbial life. The mineralized filaments are found in carbonate-filled vesicles, where they start to form on internal surfaces after seawater ingress. A biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms, their independence of crystal faces and cleavage plans, complex branching patterns, and internal segmentation. They became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron-rich environments. The results presented in this thesis give rise to a new and better understanding of carbonate formation in the ocean crust, especially in ultramafic-hosted hydrothermal environments. Further, the results highlight the important of mixing processes in the subseafloor of hydrothermal systems that led to the formation of carbonates and highlights that seafloor basalt may thus represent a common, perhaps universal niche for life in the oceanic crust
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