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  • 1
    Electronic Resource
    Electronic Resource
    The Multiple Sources and Patterns of Methane inNorth Sea Waters (1998)
    Springer
    Aquatic geochemistry 4 (1998), S. 403-427 
    Details
    ISSN: 1573-1421
    Keywords: methane ; trace gases ; North Sea ; air-sea exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The methane concentration in the atmosphere andsurface water was surveyed along 58° N acrossthe North Sea. In addition, the vertical methanedistribution in the water column was determined at sixstations along the transect. The methane contents ofthe surface water as well as in the water column wereextremely inhomogeneous. Input by freshwater fromriver discharge and injection of methane from thesediment were both observed. The survey continued fromthe western side of the North Sea to the Elbe Riverestuary. The Elbe River appears to have low methaneconcentrations compared to other European rivers, itsaverage input into the North Sea is estimated to be70 nmol s-1 of methane. Near 58° N,1°40' E, an abandoned drill site releases about 25 % ofthe North Sea's emission of methane to the atmosphere.The advective methane transport induced by watercirculation was assessed for May 16, 1994, using a 3-DNorth Sea circulation model. For the period of thissurvey, the North Sea's source strength foratmospheric methane is estimated using in situwind velocities. In comparison to the advectivetransport by the water circulation, the gas flux tothe atmosphere appears to be the dominant sink ofNorth Sea methane. This flux is estimated to bebetween 1500 · 106 mol a-1 and 3100 ·106mol a-1, depending on the relationbetween wind speed and gas transfer velocity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009644600833
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Fluid and gas fluxes from the Logatchev hydrothermal vent area (2012)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 13 (7). Q07007.
    Details
    Publication Date: 2018-03-01
    Description: The Logatchev hydrothermal field at 14°45′N on the MAR is characterized by gas plumes that are enriched in methane and helium compared to the oceanic background. We investigated CH4 concentration and δ13C together with δ3He in the water column of that region. These data and turbidity measurements indicate that apart from the known vent fields, another vent site exists northeast of the vent field Logatchev 1. The distribution of methane and 3He concentrations along two sections were used in combination with current measurements from lowered acoustic Doppler current profilers (LADCP) to calculate the horizontal plume fluxes of these gases. According to these examinations 0.02 μmol s−1 of 3He and 0.21 mol s−1 of methane are transported in a plume that flows into a southward direction in the central part of the valley. Based on 3He measurements of vent fluid (22 ± 6 pM), we estimate a total vent flux in this region of about 900 L s−1 and a total flux of CH4 of 3.2 mol s−1.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2012GC004158
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Fluxes and fate of dissolved methane released at the seafloor at the landward limit of the gas hydrate stability zone offshore western Svalbard (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 120 (9). pp. 6185-6201.
    Details
    Publication Date: 2017-05-02
    Description: Widespread seepage of methane from seafloor sediments offshore Svalbard close to the landward limit of the gas hydrate stability zone (GHSZ) may, in part, be driven by hydrate destabilization due to bottom water warming. To assess whether this methane reaches the atmosphere where it may contribute to further warming, we have undertaken comprehensive surveys of methane in seawater and air on the upper slope and shelf region. Near the GHSZ limit at ∼400 m water depth, methane concentrations are highest close to the seabed, reaching 825 nM. A simple box model of dissolved methane removal from bottom waters by horizontal and vertical mixing and microbially mediated oxidation indicates that ∼60% of methane released at the seafloor is oxidized at depth before it mixes with overlying surface waters. Deep waters are therefore not a significant source of methane to intermediate and surface waters; rather, relatively high methane concentrations in these waters (up to 50 nM) are attributed to isopycnal turbulent mixing with shelf waters. On the shelf, extensive seafloor seepage at 〈100 m water depth produces methane concentrations of up to 615 nM. The diffusive flux of methane from sea to air in the vicinity of the landward limit of the GHSZ is ∼4-20 μmol m-2 d-1, which is small relative to other Arctic sources. In support of this, analyses of mole fractions and the carbon isotope signature of atmospheric methane above the seeps do not indicate a significant local contribution from the seafloor source.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015JC011084
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Methane cycling in the Weddell Sea determined via stable isotope ratios and CFC-11 (2004)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 18 (2). GB2012.
    Details
    Publication Date: 2018-03-16
    Description: The physical, chemical/biological processes that control the methane dynamics in the Weddell Sea are revealed by the distributions of methane (CH4), its stable carbon isotope ratio, δ13C-CH4, and the conservative transient tracer, chlorofluorocarbon-11 (CFC-11, CCl3F). In general, a nearly linear correlation between CH4 and CFC-11 concentrations was observed. Air-sea exchange is the major source of methane to this region, and the distribution of methane is controlled mainly by mixing between surface water and methane-poor Warm Deep Water. A significant influence of methane oxidation over the predominant two end-member mixing was only found in the Weddell Sea Bottom Water (WSBW) of the deep central Weddell Basin, where the turnover time of methane appears to be about 20 years. Mixing also controls most of the δ13C-CH4 distribution, but lighter than expected carbon isotopic ratios occur in the deep WSBW of the basin. From box model simulations, it appears that this “anomaly” is due to methane oxidation with a low kinetic isotope fractionation of about 1.004. The surface waters in the Weddell Sea and the Antarctic Circumpolar Current showed a general methane undersaturation of 6 to 25% with respect to the atmospheric mixing ratio. From this undersaturation and model-derived air-sea exchange rates, we estimate a net uptake of CH4 of roughly −0.5 μmol m−2 d−1 during austral autumn.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2003GB002151
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Distribution of methane in the water column of the Baltic Sea (2010)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 37 (12). L12604.
    Details
    Publication Date: 2018-12-20
    Description: The distribution of dissolved methane in the water column of the Baltic Sea was extensively investigated. A strong correlation between the vertical density stratification, the distribution of oxygen, hydrogen sulfide, and methane has been identified. A widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth. The deep basins in the central Baltic Sea show the strongest methane enrichments in stagnant anoxic water bodies (max. 1086 nM and 504 nM, respectively), with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations (saturation values of 206% and 120%, respectively). In general the more limnic basins in the northern part of the Baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium (between 106% and 116%). In contrast, the shallow Western Baltic Sea is characterized by high saturation values up to 746%.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010GL043115
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Hydrothermal activity at Hook Ridge in the Central Bransfield Basin, Antarctica (1999)
    Springer
    In:  Geo-Marine Letters, 18 (4). pp. 277-284.
    Details
    Publication Date: 2017-06-29
    Description: Hydrothermal activity in the Central Bransfield Basin revealed an active low-temperature vent field on top of a submarine volcanic structure. A temperature anomaly was detected and the sea floor showed various patches of white silica (opal-A) precipitate exposures and some yellow–brown Fe-oxyhydroxide crusts. Enriched dissolved methane concentrations were encountered. Sediment was near 24°C just after the grab came on deck. No dense population of chemosynthetically based macrofauna known from other hydrothermal venting areas was present, except for pogonophora. The observations suggest that the sedimented hydrothermal field at Hook Ridge is a low-temperature end-member branch from a deeper hydrothermal source.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s003670050080
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    An experiment demonstrating that marine slumping is a mechanism to transfer methane from seafloor gas-hydrate deposits into the upper ocean and atmosphere (2003)
    Springer
    In:  Geo-Marine Letters, 22 (4). pp. 198-203.
    Details
    Publication Date: 2017-05-24
    Description: The scientific community is engaged in a lively debate over whether and how venting from the gas-hydrate reservoir and the Earth’s climate is connected. The various scenarios which have been proposed are based on the following assumptions: the inventory of methane gas-hydrate deposits is locally enormous, the stability of marine gas-hydrate deposits can easily be perturbed by temperature and pressure changes, enough methane can be released from these deposits to contribute adequate volumes of this isotopically distinct greenhouse gas to alter the composition of oceanic or atmospheric methane reservoirs, and the mechanisms exist for the transfer of methane from deeper geologic reservoirs to the ocean and/or atmosphere. However, some potential transfer mechanisms have been difficult to evaluate. Here, we consider the possibility of marine slumping as a mechanism to transfer methane carbon from gas hydrates within the seafloor into the ocean and atmosphere. Our analyses and field experiments indicate that large slumps could release volumetrically significant quantities of solid gas hydrates which would float upwards in the water column. Large pieces of gas hydrate would reach the upper layers of the ocean before decomposing, and some of the methane would be directly injected into the atmosphere.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00367-002-0113-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Seepage of methane at Jaco Scar, a slide caused by seamount subduction offshore Costa Rica (2014)
    Springer
    In:  International Journal of Earth Sciences, 103 (7). pp. 1801-1815.
    Details
    Publication Date: 2019-09-23
    Description: Methane (CH4) concentrations and CH4 stable carbon isotopic composition (d13CCH4 ) were investigated in the water column within Jaco Scar. It is one of several scars formed by massive slides resulting from the subduction of seamounts offshore Costa Rica, a process that can open up structural and stratigraphical pathways for migrating CH4. The release of large amounts of CH4 into the adjacent water column was discovered at the outcropping lowermost sedimentary sequence of the hanging wall in the northwest corner of Jaco Scar, where concentrations reached up to 1,500 nmol L-1. There CH4-rich fluids seeping from the sedimentary sequence stimulate both growth and activity of a dense chemosynthetic community. Additional point sources supplying CH4 at lower concentrations were identified in density layers above and below the main plume from light carbon isotope ratios. The injected CH4 is most likely a mixture of microbial and thermogenic CH4 as suggested by d13CCH4 values between -50 and -62 % Vienna Pee Dee Belemnite. This CH4 spreads along isopycnal surfaces throughout the whole area of the scar, and the concentrations decrease due to mixing with ocean water and microbial oxidation. The supply of CH4 appears to be persistent as repeatedly high CH4 concentrations were found within the scar over 6 years. The maximum CH4 concentration and average excess CH4 concentration at Jaco Scar indicate that CH4 seepage from scars might be as significant as seepage from other tectonic structures in the marine realm. Hence, taking into account the global abundance of scars, such structures might constitute a substantial, hitherto unconsidered contribution to natural CH4 sources at the seafloor.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00531-012-0822-z
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Measurements of the fate of gas hydrates during transit through the ocean water column (2002)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 29 (22). p. 2081.
    Details
    Publication Date: 2018-02-20
    Description: We report on controlled experiments to document the fate of naturally occurring methane hydrate released from the sea floor (780 m, 4.3°C) by remotely operated vehicle (ROV) disturbance. Images of buoyant sediment-coated solids rising (∼0.24 m/s) from the debris cloud, soon revealed clear crystals of methane hydrate as surficial material sloughed off. Decomposition and visible degassing began close to the predicted phase boundary, yet pieces initially of ∼0.10 m size easily survived transit to the surface ocean. Smaller pieces dissolved or dissociated before reaching the surface ocean, yet effectively transferred gas to depths where atmospheric ventilation times are short relative to methane oxidation rates.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2002GL014727
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    N2O emissions from the northern Benguela upwelling system (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 46 (6). pp. 3317-3326.
    Details
    Publication Date: 2022-01-31
    Description: The Benguela Upwelling system (BUS) is the most productive of all eastern boundary upwelling ecosystems and it hosts a well‐developed oxygen minimum zone. As such, the BUS is a potential hotspot for production of N2O, a potent greenhouse gas derived from microbially‐driven decay of sinking organic matter. Yet, the extent at which near‐surface waters emit N2O to the atmosphere in the BUS is highly uncertain. Here we present the first high‐resolution surface measurements of N2O across the northern part of the BUS (nBUS). We found strong gradients with a three‐fold increase in N2O concentrations near the coast as compared with open ocean waters. Our observations show enhanced sea‐to‐air fluxes of N2O (up to 1.67 nmol m−2 s−1) in association with local upwelling cells. Based on our data we suggest that the nBUS can account for 13% of the total coastal upwelling source of N2O to the atmosphere.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1029/2018GL081648
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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