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  • 1
    Online Resource
    Online Resource
    Methane sources, distributions, and fluxes from cold vent sites at Hydrate Ridge, Cascadia Margin (2005)
    Associated volumes
    Details Availability
    In: Global biogeochemical cycles, Hoboken, NJ : Wiley, 1987, 19(2005), 1944-9224
    In: volume:19
    In: year:2005
    In: extent:21
    Type of Medium: Online Resource
    Pages: 21 , graph. Darst
    ISSN: 1944-9224
    DOI: 10.1029/2004GB002266
    Language: English
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  • 2
    Online Resource
    Online Resource
    Methane sources feeding cold seeps on the shelf and upper continental slope off central Oregon, USA (2009)
    Associated volumes
    Details Availability
    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 10(2009), 11, 1525-2027
    In: volume:10
    In: year:2009
    In: number:11
    In: extent:21
    Description / Table of Contents: We report on a bathymetric mapping and remotely operated vehicle surveys along the 100600 m region offshore Oregon from 43ʿ50?N to 44°18'N. We interpret our results in light of available geophysical data, published geotectonic models, and analogous observations of fluid venting and carbonate deposition from 44°30'N to 45°00'N. The methane seepage is defined by juxtaposition of a young prism, where methane is generated by bacterial activity and its release is modulated by gas hydrate dynamics, against older sequences that serve as a source of thermogenic hydrocarbons that vent in the shelf. We hypothesize that collision of a buried ridge with the Siletz Terrane results in uplift of gas hydrate bearing sediments in the oncoming plate and that the resulting decrease in pressure leads to gas hydrate dissociation and methane exolution, which, in turn, may facilitate slope failure. Oxidation of the released methane results in precipitation of carbonates that are imaged as high backscatter along a 550 ± 60 m benthic corridor.
    Type of Medium: Online Resource
    Pages: 21 , Ill., graph. Darst
    ISSN: 1525-2027
    URL: http://www.agu.org/journals/gc/gc0911/2009GC002518/
    DOI: 10.1029/2009GC002518
    Language: English
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  • 3
    Online Resource
    Online Resource
    In situ hydrocarbon concentrations from pressurized cores in surface sediments, northern Gulf of Mexico (2007)
    Associated volumes
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    In: Marine chemistry, Amsterdam [u.a.] : Elsevier Science, 1972, 107(2007), 4, Seite 498-515, 0304-4203
    In: volume:107
    In: year:2007
    In: number:4
    In: pages:498-515
    Description / Table of Contents: Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct- Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C1 through C5) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg -1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH4. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH4 concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis.
    Type of Medium: Online Resource
    Pages: Ill., graph. Darst
    ISSN: 0304-4203
    DOI: 10.1016/j.marchem.2007.08.008
    Language: English
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  • 4
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    (Table 1) Analysis of pore water (PW) and hydrocarbon gases (HC) on sediment samples after degassing, and the recovery pressure (pressure) on SO174 samples (2007)
    PANGAEA
    Details
    Publication Date: 2023-07-10
    Keywords: 152; 153; 158; 166; 170; Analysis; Bush Hill; Center for Marine Environmental Sciences; DAPC; Device type; Dynamic autoclave piston corer; Elevation of event; Event label; Latitude of event; Location type; Longitude of event; MAC; MARUM; Multi autoclave corer; OTEGA II; Pressure, water; Sample, optional label/labor no; SO174/1; SO174/1_118; SO174/1_63; SO174/1_90; SO174/1_97; SO174/2; SO174/2_152; SO174/2_153; SO174/2_158; SO174/2_166; SO174/2_170; Sonne
    Type: Dataset
    Format: text/tab-separated-values, 42 data points
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  • 5
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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
    Publication Date: 2018-03-16
    Description: 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.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2004GB002266
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    In-situ hydrocarbon concentrations from pressurized cores in surface sediments, Northern Gulf of Mexico (2007)
    Elsevier
    In:  Marine Chemistry, 107 (4). pp. 498-515.
    Details
    Publication Date: 2017-08-22
    Description: Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct–Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C1 through C5) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg− 1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH4. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH4 concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marchem.2007.08.008
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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