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  • Wiley  (8)
  • ASLO (Association for the Sciences of Limnology and Oceanography)  (2)
  • GEOMAR Helmholtz-Zentrum für Ozeanforschung  (2)
  • Springer  (2)
  • AAAS (American Association for the Advancement of Science)  (1)
  • 2015-2019  (15)
Document type
Publisher
Years
Year
  • 1
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    The Character and Formation of Elongated Depressions on the Upper Bulgarian Slope (2018)
    Springer
    In:  Journal of Ocean University of China, 17 (3). pp. 555-562.
    Details
    Publication Date: 2021-02-08
    Description: Seafloor elongated depressions are indicators of gas seepage or slope instability. Here we report a sequence of slope-parallel elongated depressions that link to headwalls of sediment slides on upper slope. The depressions of about 250 m in width and several kilometers in length are areas of focused gas discharge indicated by bubble-release into the water column and methane enriched pore waters. Sparker seismic profiles running perpendicular and parallel to the coast, show gas migration pathways and trapped gas underneath these depressions with bright spots and seismic blanking. The data indicate that upward gas migration is the initial reason for fracturing sedimentary layers. In the top sediment where two young stages of landslides can be detected, the slope-parallel sediment weakening lengthens and deepens the surficial fractures, creating the elongated depressions in the seafloor supported by sediment erosion due to slope-parallel water currents.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1007/s11802-018-3460-7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Testing a thermo-chemo-hydro-geomechanical model for gas hydrate-bearing sediments using triaxial compression laboratory experiments (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 18 (9). pp. 3419-3437.
    Details
    Publication Date: 2020-02-06
    Description: Natural gas hydrates are considered a potential resource for gas production on industrial scales. Gas hydrates contribute to the strength and stiffness of the hydrate-bearing sediments. During gas production, the geomechanical stability of the sediment is compromised. Due to the potential geotechnical risks and process management issues, the mechanical behavior of the gas hydrate-bearing sediments needs to be carefully considered. In this study, we describe a coupling concept that simplifies the mathematical description of the complex interactions occurring during gas production by isolating the effects of sediment deformation and hydrate phase changes. Central to this coupling concept is the assumption that the soil grains form the load-bearing solid skeleton, while the gas hydrate enhances the mechanical properties of this skeleton. We focus on testing this coupling concept in capturing the overall impact of geomechanics on gas production behavior though numerical simulation of a high-pressure isotropic compression experiment combined with methane hydrate formation and dissociation. We consider a linear-elastic stress-strain relationship because it is uniquely defined and easy to calibrate. Since, in reality, the geomechanical response of the hydrate-bearing sediment is typically inelastic and is characterized by a significant shear-volumetric coupling, we control the experiment very carefully in order to keep the sample deformations small and well within the assumptions of poroelasticity. The closely coordinated experimental and numerical procedures enable us to validate the proposed simplified geomechanics-to-flow coupling, and set an important precursor toward enhancing our coupled hydro-geomechanical hydrate reservoir simulator with more suitable elastoplastic constitutive models.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2017GC006901
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Mind the seafloor (2018)
    AAAS (American Association for the Advancement of Science)
    In:  Science, 359 (6371). pp. 34-36.
    Details
    Publication Date: 2021-02-08
    Description: Research and regulations must be integrated to protect seafloor biota from future mining impacts Summary: As human use of rare metals has diversified and risen with global development, metal ore deposits from the deep ocean floor are increasingly seen as an attractive future resource. Japan recently completed the first successful test for zinc extraction from the deep seabed, and the number of seafloor exploration licenses filed at the International Seabed Authority (ISA) has tripled in the past 5 years. Seafloor-mining equipment is being tested, and industrial-scale production in national waters could start in a few years. We call for integrated scientific studies of global metal resources, the fluxes and fates of metal uses, and the ecological footprints of mining on land and in the sea, to critically assess the risks of deep-sea mining and the chances for alternative technologies. Given the increasing scientific evidence for long-lasting impacts of mining on the abyssal environment, precautionary regulations for commercial deep-sea mining are essential to protect marine ecosystems and their biodiversity.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1126/science.aap7301
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Linked sediment and water-column methanotrophy at a man-made gas blowout in the North Sea: Implications for methane budgeting in seasonally stratified shallow seas (2016)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 61 (S1). S367-S386.
    Details
    Publication Date: 2019-02-01
    Description: Large quantities of the greenhouse gas methane (CH4) are stored in the seafloor. The flux of CH4 from the sediments into the water column and finally to the atmosphere is mitigated by a series of microbial methanotrophic filter systems of unknown efficiency at highly active CH4-release sites in shallow marine settings. Here, we studied CH4-oxidation and the methanotrophic community at a high-CH4-flux site in the northern North Sea (well 22/4b), where CH4 is continuously released since a blowout in 1990. Vigorous bubble emanation from the seafloor and strongly elevated CH4 concentrations in the water column (up to 42 µM) indicated that a substantial fraction of CH4 bypassed the highly active (up to ∼2920 nmol cm−3 d−1) zone of anaerobic CH4-oxidation in sediments. In the water column, we measured rates of aerobic CH4-oxidation (up to 498 nM d−1) that were among the highest ever measured in a marine environment and, under stratified conditions, have the potential to remove a significant part of the uprising CH4 prior to evasion to the atmosphere. An unusual dominance of the water-column methanotrophs by Type II methane-oxidizing bacteria (MOB) is partially supported by recruitment of sedimentary MOB, which are entrained together with sediment particles in the CH4 bubble plume. Our study thus provides evidence that bubble emission can be an important vector for the transport of sediment-borne microbial inocula, aiding in the rapid colonization of the water column by methanotrophic communities and promoting their persistence close to highly active CH4 point sources.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/lno.10388
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Effects of climate change on methane emissions from seafloor sediments in the Arctic Ocean: A review (2016)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 61 (S1). pp. 301-309.
    Details
    Publication Date: 2019-09-24
    Description: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and seaair exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/lno.10307
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    An abyssal hill fractionates organic and inorganic matter in deep-sea surface sediments (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 42 (18). pp. 7663-7672.
    Details
    Publication Date: 2017-04-10
    Description: Current estimates suggest that more than 60% of the global seafloor are covered by millions of abyssal hills and mountains. These features introduce spatial fluid-dynamic granularity whose influence on deep-ocean sediment biogeochemistry is unknown. Here we compare biogeochemical surface-sediment properties from a fluid-dynamically well-characterized abyssal hill and upstream plain: (1) In hill sediments, organic-carbon and -nitrogen contents are only about half as high as on the plain while proteinaceous material displays less degradation; (2) on the hill, more coarse-grained sediments (reducing particle surface area) and very variable calcite contents (influencing particle surface charge) are proposed to reduce the extent, and influence compound-specificity, of sorptive organic-matter preservation. Further studies are needed to estimate the representativeness of the results in a global context. Given millions of abyssal hills and mountains, their integrative influence on formation and composition of deep-sea sediments warrants more attention.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GL065658
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Gas migration through Opouawe Bank at the Hikurangi margin offshore New Zealand (2016)
    Springer
    In:  Geo-Marine Letters, 36 (3). pp. 187-196.
    Details
    Publication Date: 2019-09-23
    Description: This study presents 2D seismic reflection data, seismic velocity analysis, as well as geochemical and isotopic porewater compositions from Opouawe Bank on New Zealand’s Hikurangi subduction margin, providing evidence for essentially pure methane gas seepage. The combination of geochemical information and seismic reflection images is an effective way to investigate the nature of gas migration beneath the seafloor, and to distinguish between water advection and gas ascent. The maximum source depth of the methane that migrates to the seep sites on Opouawe Bank is 1,500–2,100 m below seafloor, generated by low-temperature degradation of organic matter via microbial CO2 reduction. Seismic velocity analysis enabled identifying a zone of gas accumulation underneath the base of gas hydrate stability (BGHS) below the bank. Besides structurally controlled gas migration along conduits, gas migration also takes place along dipping strata across the BGHS. Gas migration on Opouawe Bank is influenced by anticlinal focusing and by several focusing levels within the gas hydrate stability zone.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1007/s00367-016-0441-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (12). pp. 4817-4835.
    Details
    Publication Date: 2019-02-01
    Description: Takahe seep, located on the Opouawe Bank, Hikurangi Margin, is characterized by a well-defined subsurface seismic chimney structure ca. 80,500 m2 in area. Sub-seafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure. Reaction-transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m. Model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas. The dissolution of gas (up to 3761 mmol m−2 yr−1) dwarfed the rate of methanogenesis within the simulated sediment column (2.6 mmol m−2 yr−1). Dissolved methane is mainly consumed by anaerobic oxidation of methane (AOM) at the base of the sulfate reduction zone and trapped by methane hydrate formation below it, with maximum rates in the central part of the chimney (946 and 2420 mmol m−2 yr−1, respectively). A seep-wide methane budget was constrained by combining the biogeochemical model results with geophysical data and led to estimates of AOM rates, gas hydrate formation and benthic dissolved methane fluxes of 3.68 × 104 mol yr−1, 73.85 × 104 mol yr−1and 1.19 × 104 mol yr−1, respectively. A much larger flux of methane probably escapes in gaseous form through focused bubble vents. The approach of linking geochemical model results with spatial geophysical data put forward here can be applied elsewhere to improve benthic methane turnover rates from limited single spot measurements to larger spatial scales.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GC006643
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Charakterisierung von Gashydratlagerstätten und Überwachung des Erdgasförderprozesses : Abschlussbericht SUGAR II : (A: Methoden zur Exploration und Überwachung von Gashydrat-Lagerstätten) : Laufzeit des Vorhabens: 1.7.2011-30.6.2014, Förderkennzeichen BMBF 03G0819A (2015)
    GEOMAR Helmholtz-Zentrum für Ozeanforschung
    In:  GEOMAR Helmholtz-Zentrum für Ozeanforschung, Kiel, Germany, 48 pp.
    Details
    Publication Date: 2019-04-10
    Type: Report , NonPeerReviewed
    Format: text
    DOI: 10.2314/GBV:848039963
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    OceanRep: Report - other report
  • 10
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    SUGAR III - Submarine Gashydrat Ressourcen; Teil B: Exploration einer Feldtest-Lokation und geomechanisches Verhalten beim Gashydratabbau; Teilvorhaben GEOMAR: Charakterisierung der Gashydratvorkommen im Donautiefseefächer : öffentlicher Schlussbericht für die Technische Informationsbibliothek (TIB) an der Universität Hannover : Laufzeit des Vorhabens und Berichtszeitraum: 01.01.2015-31.03.2018. SUGAR III - submarine gas hydrate resources; part B: exploration of a field test location and geomechanical behavior during gas hydrate exploitation; subproject GEOMAR: characterization of gas hydrate accumulations in the Danube deep-sea fan, Förderkannzeichen: 03G0856A (2018)
    GEOMAR Helmholtz-Zentrum für Ozeanforschung
    In:  GEOMAR Helmholtz-Zentrum für Ozeanforschung, Kiel, 98 pp.
    Details
    Publication Date: 2019-05-03
    Description: GEOMAR's project was integrated into the large-scale collaborative project SUGAR-III with 19 partners from industry and academia that was also coordinated by GEOMAR. The ain of the project was to characterize the gas hydrate accumulations in the Danube deep-sea fan geophysically and geochemically, to develop a three-dimensional geological model of the deposit and simulate its formation over geological time scales using the hydrate module developed in the PetroMod software, to investigate the problem of geomechanical destabilization and sand production occurring during hydrate exploitation by means of high-pressure experiments, to further develop the SUGAR gas hydrate technologies on geophysical data analysis, geological basin modelling and geomechanical test units in collaboration with the industrial project partners.
    Type: Report , NonPeerReviewed
    Format: text
    DOI: 10.2314/GBV:1663478228
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    OceanRep: Report - other report
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