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  • 1
    Online-Ressource
    Online-Ressource
    Biomasse und Stoffwechsel-Leistungen benthischer Formaniferen (1986)
    Kiel
    Details Verfügbarkeit
    Schlagwort(e): Hochschulschrift
    Beschreibung / Inhaltsverzeichnis: - In der vorliegenden Arbeit war es möglich, die Lebensäußerungen benthischer Foraminiferen der Kieler Bucht und der Norwegischen See zu beobachten, unter möglichst natürlichen Bedingungen zu hältern und somit größere Individuenzahlen für die biochemischen Analysen verfügbar zu halten. Es konnten eindeutige Kriterien zur Ansprache lebender Individuen getroffen werden: 1. die durch das Gehäuse durchscheinende Plasmafüllung 2. die Ausbildung von Detrius-/Plasmastopfen im Mündungsbereich des Gehäuses 3. die Pseudopodien-Aktivität. Die Biomasse von Ammotium cassis konnte erstmals in einer allometrischen Wachstumskurve dargestellt werden, der Wachstumsexponent beträgt 2,38. Der ATP-Gehalt der Foraminiferen ist als Maß für die Plasmabiomasse geeignet. Es konnte mit der ATP - Bestimmng an Ammotium cassis und Reophax dentaliniformis regularis eine Ruhephase von einer Aktivphase unterschieden und diese Einteilung durch entsprechende Lebensbeobachtungen unterstützt werden. Das Kphlenstoff: ATP-Verhältnis stellt aktive Foraminiferen (180:1) in den Bereich zwischen Prokaryonten (250:1) und der mehrzelligen Meiofauna (50:1). Hierbei macht Elphidium incertum eine Ausnahme und weist Meiofauna-Werte auf. Die mit zwei Meßmethoden (ETS und Wäremproduktion) ermittelten Respirationsraten zeigen eine gute Übereinstimmung. Die hier untersuchten Foraminiferen sind von der größenspezifischen Stoffwechselrate her aktiver als andere Einzeller und liegen auf dem Niveau der Meiofauna. Die ATP-Umsatzgeschwindigkeiten liegen bei Ammotium cassis (Kieler Bucht) und Rhabdammina abyssorum (Norwegische See) im Größenbereich von Bakterien. Aus der Kombination der Meßwerte von Wärmeproduktion und ETS ergeben sich bei Ammotium cassis Hinweise auf fakultative Anaerobiose. Bei den Lebendbeobachtungen konnten Foraminiferen auch in O2-freien Sedimentschichten gefunden werden. Dieses verhalten erfordert die Fähigkeit, zeitweise Anaerobiose betreiben zu können, was die Laboranalysen bestätigen.
    Materialart: Online-Ressource
    Seiten: 1 Online-Ressource (129 Seiten = 5 MB) , Karten, Illustrationen, Graphen
    Ausgabe: 2020
    URL: https://oceanrep.geomar.de/id/eprint/50562
    Sprache: Deutsch
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  • 2
    Buch
    Buch
    LOTUS : long-term observatory for the study of control mechanisms for the formation and destabilisation of gas hydrates ; collaborative research project on marine gashydrates ; final report (2004)
    Kiel
    Details Verfügbarkeit
    Schlagwort(e): Forschungsbericht ; Gashydrate
    Materialart: Buch
    Seiten: Getr. Zählung [97] Bl , Ill., graph. Darst
    Sprache: Englisch
    Anmerkung: Förderkennzeichen BMBF 03G0565A/F , Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden , Auch als elektronische Ressource vorh , Enth.: P. Linke: Synthesis; Subproject 1: In situ long-term observatories for the study of trigger mechanisms of the formation and destabilisation of near surface marine gas hydrates; Subproject 2: The fate of methane water column; Subproject 3: Chronology and geochemical dynamics of near-surface gas hydrate deposits; Subproject 4: Modelling methane fluxes and biogeochemical processes in hydrate-bearing surface sediments
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  • 3
    Online-Ressource
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    Lebendbeobachtungen und Untersuchungen des Energiestoffwechsels benthischer Foraminiferen aus dem Europäischen Nordmeer (1989)
    Kiel
    Details Verfügbarkeit
    Schlagwort(e): Hochschulschrift
    Materialart: Online-Ressource
    Seiten: Online-Ressource (130 Seiten = 5 MB) , Illustrationen, Graphen, Karten
    URL: https://oceanrep.geomar.de/43459/
    Sprache: Deutsch
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  • 4
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    Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule Earthquake, Central Chile (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (11). pp. 4802-4813.
    Details
    Publikationsdatum: 2020-06-29
    Beschreibung: Seafloor seepage of hydrocarbon-bearing fluids has been identified in a number of marine forearcs. However, temporal variations in seep activity and the structural and tectonic parameters that control the seepage often remain poorly constrained. Subduction-zone earthquakes for example, are often discussed to trigger seafloor seepage but causal links that go beyond theoretical considerations have not yet been fully established. This is mainly due to the inaccessibility of offshore epicentral areas, the infrequent occurrence of large earthquakes, and challenges associated with offshore monitoring of seepage over large areas and sufficient time periods. Here, we report visual, geochemical, geophysical, and modelling results and observations from the Concepción Methane Seep Area (offshore Central Chile) located in the rupture area of the 2010 Mw. 8.8 Maule earthquake. High methane concentrations in the oceanic water column and a shallow sub-bottom depth of sulfate penetration indicate active methane seepage. The stable carbon isotope signature of the methane and hydrocarbon composition of the released gas indicate a mixture of shallow-sourced biogenic gas and a deeper sourced thermogenic component. Pristine fissures and fractures observed at the seafloor together with seismically imaged large faults in the marine forearc may represent effective pathways for methane migration. Upper-plate fault activity with hydraulic fracturing and dilation is in line with increased normal Coulomb stress during large plate-boundary earthquakes, as exemplarily modelled for the 2010 earthquake. On a global perspective our results point out the possible role of recurring large subduction-zone earthquakes in driving hydrocarbon seepage from marine forearcs over long timescales.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2016GC006498
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  • 5
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    Quantifying tidally-driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (10). pp. 6918-6932.
    Details
    Publikationsdatum: 2018-02-26
    Beschreibung: Continental shelves are predominately (~70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ~3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1-D model linking the benthic turbulence to the sediment pore water exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low-flow periods. The study reveals that the benthic hydrodynamics, sediment permeability, and pore water redox oscillations are all intimately linked and crucial parameters determining the oxygen availability. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2014JC010303
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  • 6
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    Discovery of a natural CO2 seep in the German North Sea: implications for shallow dissolved gas and seep detection (2011)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 116 . C03013.
    Details
    Publikationsdatum: 2019-09-23
    Beschreibung: A natural carbon dioxide (CO2) seep was discovered during an expedition to the southern German North Sea (October 2008). Elevated CO2 levels of ∼10–20 times above background were detected in seawater above a natural salt dome ∼30 km north of the East-Frisian Island Juist. A single elevated value 53 times higher than background was measured, indicating a possible CO2 point source from the seafloor. Measured pH values of around 6.8 support modeled pH values for the observed high CO2 concentration. These results are presented in the context of CO2 seepage detection, in light of proposed subsurface CO2 sequestering and growing concern of ocean acidification. We explore the boundary conditions of CO2 bubble and plume seepage and potential flux paths to the atmosphere. Shallow bubble release experiments conducted in a lake combined with discrete-bubble modeling suggest that shallow CO2 outgassing will be difficult to detect as bubbles dissolve very rapidly (within meters). Bubble-plume modeling further shows that a CO2 plume will lose buoyancy quickly because of rapid bubble dissolution while the newly CO2-enriched water tends to sink toward the seabed. Results suggest that released CO2 will tend to stay near the bottom in shallow systems (〈200 m) and will vent to the atmosphere only during deep water convection (water column turnover). While isotope signatures point to a biogenic source, the exact origin is inconclusive because of dilution. This site could serve as a natural laboratory to further study the effects of carbon sequestration below the seafloor.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010JC006557
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  • 7
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    Fluid venting in the eastern Aleutian subduction zone (1998)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 103 (B2). pp. 2597-2614.
    Details
    Publikationsdatum: 2018-04-25
    Beschreibung: Fluid venting has been observed along 800 km of the Alaska convergent margin. The fluid venting sites are located near the deformation front, are controlled by subsurface structures, and exhibit the characteristics of cold seeps seen in other convergent margins. The more important characteristics include (1) methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges; (2) prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps, over‐steepened folds or outcrops of bedding planes; (3) calcium carbonate and barite precipitates at the surface and subsurface of vents; and (4) carbon isotope evidence from tissue and skeletal hard parts of biota, as well as from carbonate precipitates, that vents expel either methane‐ or sulfide‐dominated fluids. A biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5.5±0.7 L m−2 d−1 for tectonics‐induced water flow [Wallmann et al., 1997b]. A geophysical estimate of dewatering from the same area [von Huene et al., 1997] based on sediment porosity reduction shows a fluid loss of 0.02 L m−2 d−1 for a 5.5 km wide converged segment near the deformation front. Our video‐guided surveys have documented vent biota across a minimum of 0.1% of the area of the convergent segment off Kodiak Island; hence an average rate of 0.006 L m−2 d−1 is estimated from the biogeochemical approach. The two estimates for tectonics‐induced water flow from the accretionary prism are in surprisingly good agreement.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/97JB02131
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  • 8
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    Sea Floor Methane Hydrates at Hydrate Ridge, Cascadia Margin (2001)
    AGU (American Geophysical Union)
    In:  In: Natural gas hydrates: occurrence, distribution, and detection. , ed. by Paull, C. Geophysical Monograph Series, 124 . AGU (American Geophysical Union), Washington, DC, pp. 87-99.
    Details
    Publikationsdatum: 2017-06-27
    Materialart: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1029/GM124p0087
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  • 9
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    Efficiency of benthic filter: Biological control of the emission of dissolved methane from sediments containing shallow gas hydrates at Hydrate Ridge (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (GB2019).
    Details
    Publikationsdatum: 2018-03-16
    Beschreibung: In marine sedimentary environments, microbial methanotrophy represents an important sink for methane before it leaves the seafloor and enters the water column. Using benthic observatories in conjunction with numerical modeling of pore water gradients, we investigated seabed methane emission rates at cold seep sites with underlying gas hydrates at Hydrate Ridge, Cascadia margin. Measurements were conducted at three characteristic sites which have variable fluid flow and sulfide flux and sustain distinct chemosynthetic communities. In sediments covered with microbial mats of Beggiatoa, seabed methane efflux ranges from 1.9 to 11.5 mmol m−2 d−1. At these sites of relatively high advective flow, total oxygen uptake was very fast, yielding rates of up to 53.4 mmol m−2 d−1. In sediments populated by colonies with clams of the genus Calyptogena and characterized by low advective flow, seabed methane emission was 0.6 mmol m−2 d−1, whereas average total oxygen uptake amounted to only 3.7 mmol m−2 d−1. The efficiency of methane consumption at microbial mat and clam field sites was 66 and 83%, respectively. Our measurements indicate a high potential capacity of aerobic methane oxidation in the benthic boundary layer. This layer potentially restrains seabed methane emission when anaerobic methane oxidation in the sediment becomes saturated or when methane is bypassing the sediment matrix along fractures and channels.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2004GB002389
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  • 10
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    Methane sources, distributions, and fluxes from cold vent sites at Hydrate Ridge, Cascadia Margin (2005)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 19 . GB2016.
    Details
    Publikationsdatum: 2018-03-16
    Beschreibung: To constrain the fluxes of methane (CH4) in the water column above the accretionary wedge along the Cascadia continental margin, we measured methane and its stable carbon isotope signature (δ13C-CH4). The studies focused on Hydrate Ridge (HR), where venting occurs in the presence of gas-hydrate-bearing sediments. The vent CH4 has a light δ13C-CH4 biogenic signature (−63 to −66‰ PDB) and forms thin zones of elevated methane concentrations several tens of meters above the ocean floor in the overlying water column. These concentrations, ranging up to 4400 nmol L−1, vary by 3 orders of magnitude over periods of only a few hours. The poleward undercurrent of the California Current system rapidly dilutes the vent methane and distributes it widely within the gas hydrate stability zone (GHSZ). Above 480 m water depth, the methane budget is dominated by isotopically heavier CH4 from the shelf and upper slope, where mixtures of various local biogenic and thermogenic methane sources were detected (−56 to −28‰ PDB). The distribution of dissolved methane in the working area can be represented by mixtures of methane from the two primary source regions with an isotopically heavy background component (−25 to −6‰ PDB). Methane oxidation rates of 0.09 to 4.1% per day are small in comparison to the timescales of advection. This highly variable physical regime precludes a simple characterization and tracing of “downcurrent” plumes. However, methane inventories and current measurements suggest a methane flux of approximately 3 × 104 mol h−1 for the working area (1230 km2), and this is dominated by the shallower sources. We estimate that the combined vent sites on HR produce 0.6 × 104 mol h−1, and this is primarily released in the gas phase rather than dissolved within fluid seeps. There is no evidence that significant amounts of this methane are released to the atmosphere locally.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2004GB002266
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