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  • 1
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    Porewater chemistry and magnetic parameters of a sediment core from SG1 station in the South-Eastern Mediterranean Sea (2020)
    PANGAEA
    Details
    Publication Date: 2023-02-12
    Description: A 6 m long sediment core was collected from Station SG-1 using a piston corer during a cruise on the R.V. Bat-Galim in January 2017. The sediment core was sliced onboard at intervals of 30 cm within minutes of core collection. For headspace measurements of CH~4~, approximately 1.5 mL of sediment was taken from the top of each sediment slice. This sediment was transferred immediately into N~2~-flushed crimped bottles containing 5 mL of 1.5 N NaOH. Sediment samples from the top 5 cm of each sediment slice were transferred to vials under anaerobic conditions, and porewater was extracted from them on the same day by centrifugation at 4°C under an N~2~ atmosphere. The supernatant was filtered through a 0.22 μm filter and was analyzed for dissolved Fe^2+^, sulfide, and sulfate. The sediment was dried in an ambient temperate under N~2~ atmosphere, the dry sediment was analyzed for different iron minerals fractions following the sequential extraction protocol from Poulton and Canfield (2005, doi:10.1016/j.chemgeo.2004.09.003). The 30 cm core segments were split along their length and sampled for magnetic analysis by pushing non-magnetic plastic sampling boxes of 23x23x19 mm into the split halves at ~5 cm intervals. The different microbial respiration pathways cause changes in the porewater chemistry and in the sediment mineralogy due to the reduction and dissolution of iron minerals. In this study, we linked the different respiration processes to the magnetic parameters of a 6 m sediment core from the South-Eastern Mediterranean Sea. In the sulfate-methane transition zone (SMTZ), we observed a decrease in the sediment magnetic properties, due to the dissolution of detrital magnetic minerals, followed by pyrite precipitation. In the upper methanic zone, where iron-reduction occurs, we observed an increase in magnetic properties due to precipitation of authigenic ferrimagnetic minerals.
    Keywords: Anhysteretic remanent magnetization, Intensity, per unit mass; Anhysteretic remanent magnetization/saturation isothermal remanent magnetization ratio; ARM Susceptibility/susceptibility ratio; DEPTH, sediment/rock; early diagenesis; Eastern Mediterranean Sea; Iron 2+; Iron reduction; Isothermal remanent magnetization, Intensity, per unit mass; Magnetite; Methane, porewater; Methanogenesis; Natural remanent magnetization, Intensity per unit mass; Porewater chemistry; Saturation isothermal remanent magnetization/kappa ratio; Sedimentary magnetism; SE-Mediterranean_SG-1; S-ratio (hematite/magnetite); Sulfate; Susceptibility, frequency dependence; Susceptibility, specific, low-field mass-normalized
    Type: Dataset
    Format: text/tab-separated-values, 567 data points
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    DATA PANGAEA
  • 2
    Electronic Resource
    Electronic Resource
    Synthesis and metabolic fate of purine nucleotides in cultured fibroblasts from normal subjects and from purine overproducing mutants
    Amsterdam : Elsevier
    BBA Section Nucleic Acids And Protein Synthesis 521 (1978), S. 452-458 
    Details
    ISSN: 0005-2787
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0005-2787(78)90286-1
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    Paper (German National Licenses)
    Fulltext
  • 3
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    lron-Coupled Anaerobic Oxidation of Methane Performed by a Mixed Bacterial-Archaeal Community Based on Poorly Reactive Minerals (2017)
    ACS
    In:  Environmental Science & Technology, 51 (21). pp. 12293-12301.
    Details
    Publication Date: 2020-02-06
    Description: Anaerobic oxidation of methane (AOM) was shown to reduce methane emissions by over 50% in freshwater systems, its main natural contributor to the atmosphere. In these environments iron oxides can become main agents for AOM, but the underlying mechanism for this process has remained enigmatic. By conducting anoxic slurry incubations with lake sediments amended with 13C-labeled methane and naturally abundant iron oxides the process was evidenced by significant 13C-enrichment of the dissolved inorganic carbon pool and most pronounced when poorly reactive iron minerals such as magnetite and hematite were applied. Methane incorporation into biomass was apparent by strong uptake of 13C into fatty acids indicative of methanotrophic bacteria, associated with increasing copy numbers of the functional methane monooxygenase pmoA gene. Archaea were not directly involved in füll methane oxidation, but their crucial participation,likely being mediators in electron transfer, was indicated by specific inhibition of their activity that fully stopped iron-coupled AOM. By contrast, inhibition of sulfur cycling increased 13C-methane turnover, pointing to sulfur species involvement in a competing process. Our findings suggest that the mechanism of iron-coupled AOM is accomplished by a complex microbemineral reaction network, being likely representative of many similar but hidden interactions sustaining life under highly reducing low energy conditions.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1021 /acs.est.7603126
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Iron oxides stimulate anaerobic methane oxidation [Earth, Atmospheric, and Planetary Sciences] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-10-08
    Description: Seep sediments are dominated by intensive microbial sulfate reduction coupled to the anaerobic oxidation of methane (AOM). Through geochemical measurements of incubation experiments with methane seep sediments collected from Hydrate Ridge, we provide insight into the role of iron oxides in sulfate-driven AOM. Seep sediments incubated with 13C-labeled methane showed...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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    PAPER CURRENT
  • 5
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    A unique isotopic fingerprint of sulfate-driven anaerobic oxidation of methane (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-06-23
    Description: The largest reservoir of the powerful greenhouse gas methane is in marine sediments, and catastrophic release of this methane has been invoked to explain climate perturbations throughout Earth history. Marine methane oxidation is mainly coupled anaerobically to microbial sulfate reduction, which both limits and controls the release of methane from this sedimentary reservoir to the rest of Earth’s surface. Methane can be transported within the pore space of marine sediments either via diffusion or as bubbles. When methane travels in bubbles, these bubbles often are not completely oxidized and reach the overlying water where the methane emerges from the sediment in cold seeps. Although paleo–cold seeps can be identified by geological features such as carbonate mounds, a geochemical signature for cold seeps remains elusive. We demonstrate, using the sulfur and oxygen isotope composition of sulfate, that a unique isotopic signature emerges during microbial sulfate reduction coupled to methane oxidation in bubbling cold seeps. This isotope signature differs from that when sulfate is reduced by either organic matter oxidation or by the slower, diffusive flux of methane within marine sediments. We also show, through a comparison with the literature, that this unique isotope fingerprint is preserved in the rock record in authigenic buildups of barite associated with methane cold seeps.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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    PAPER CURRENT
  • 6
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    Pore fluids in Dead Sea sediment core reveal linear response of lake chemistry to global climate changes (2017)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2017-03-08
    Description: Pore fluids extracted from a 456 m sediment core, recovered within the framework of a multinational and International Continental Scientific Drilling Program (ICDP) co-sponsored effort at the bottom of the terminal Dead Sea, recorded the chemical variations in the deep lake over the past 220 k.y. Mg 2+ and Br – were shown to be conservative in the pore fluids, increasing in concentration during interglacial periods, diluting during glacials, and providing excellent proxies for deep lake net water balance changes. Furthermore, the Na/Cl ratio recorded the process of halite precipitation and dissolution induced by these hydrological changes. Mg 2+ and Br – records follow a glacial-interglacial pattern, such as observed in atmospheric CO 2 concentrations and global sea-surface temperatures, albeit with a phase offset. At the end of the last interglacial (ca. 116 ka), there is a delay in onset of dilution of the deep lake, most likely due to the limnological transition from holomictic to meromictic conditions. The increase in deep lake concentrations at Last Glacial Termination I is delayed as a result of freshwater input into the deep lake during the cooler Younger Dryas period. There is a persistent relationship between precipitation in the watershed and North Atlantic sea-surface temperatures, similar to conditions observed over the past instrumental record. Deviations from the long-term trends occurred during interglacial periods, Marine Isotope Stages MIS 5e and MIS 1, when the deep Dead Sea was significantly diluted, and coincided with Mediterranean sapropel layers S5 and S1.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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    PAPER CURRENT
  • 7
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    Subfossil trees suggest enhanced Mediterranean hydroclimate variability at the onset of the Younger Dryas (2018)
    In:  Scientific Reports
    Details
    Publication Date: 2020-02-12
    Description: Nearly 13,000 years ago, the warming trend into the Holocene was sharply interrupted by a reversal to near glacial conditions. Climatic causes and ecological consequences of the Younger Dryas (YD) have been extensively studied, however proxy archives from the Mediterranean basin capturing this period are scarce and do not provide annual resolution. Here, we report a hydroclimatic reconstruction from stable isotopes (δ18O, δ13C) in subfossil pines from southern France. Growing before and during the transition period into the YD (12 900–12 600 cal BP), the trees provide an annually resolved, continuous sequence of atmospheric change. Isotopic signature of tree sourcewater (δ18Osw) and estimates of relative air humidity were reconstructed as a proxy for variations in air mass origin and precipitation regime. We find a distinct increase in inter-annual variability of sourcewater isotopes (δ18Osw), with three major downturn phases of increasing magnitude beginning at 12 740 cal BP. The observed variation most likely results from an amplified intensity of North Atlantic (low δ18Osw) versus Mediterranean (high δ18Osw) precipitation. This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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