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  • 1
    Online Resource
    Online Resource
    Structure and drivers of cold seep ecosystems (2009)
    Associated volumes
    Details Availability
    In: Oceanography, Rockville, MD : The Oceanography Society, 1988, 22(2009), 1, Seite 92-109, 2377-617X
    In: volume:22
    In: year:2009
    In: number:1
    In: pages:92-109
    Description / Table of Contents: Submarine hydrocarbon seeps are geologically driven "hotspots" of increased biological activity on the seabed. As part of the HERMES project, several sites of natural hydrocarbon seepage in the European seas were investigated in detail, including mud volcanoes and pockmarks, in study areas extending from the Nordic margin, to the Gulf of Cádiz, to the Mediterranean and Black seas. High-resolution seabed maps and the main properties of key seep sites are presented here. Individual seeps show ecosystem zonation related to the strength of the methane flux and distinct biogeochemical processes in surface sediments. A feature common to many seeps is the formation of authigenic carbonate constructions. These constructions exhibit various morphologies ranging from large pavements and fragmented slabs to chimneys and mushroom-shaped mounds, and they form hard substrates colonized by fixed fauna. Gas hydrate dissociation could contribute to sustain seep chemosynthetic communities over several thousand years following large gas-release events.
    Type of Medium: Online Resource
    Pages: Ill., graph. Darst
    ISSN: 2377-617X
    Language: English
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  • 2
    Online Resource
    Online Resource
    Escape of methane gas from the seabed along the West Spitsbergen continental margin (2009)
    Associated volumes
    Details Availability
    In: Geophysical research letters, Hoboken, NJ : Wiley, 1974, 36(2009), 1944-8007
    In: volume:36
    In: year:2009
    In: extent:5
    Description / Table of Contents: More than 250 plumes of gas bubbles have been discovered emanating from the seabed of the West Spitsbergen continental margin, in a depth range of 150400 m, at and above the present upper limit of the gas hydrate stability zone (GHSZ). Some of the plumes extend upward to within 50 m of the sea surface. The gas is predominantly methane. Warming of the northward-flowing West Spitsbergen current by 1°C over the last thirty years is likely to have increased the release of methane from the seabed by reducing the extent of the GHSZ, causing the liberation of methane from decomposing hydrate. If this process becomes widespread along Arctic continental margins, tens of Teragrams of methane per year could be released into the ocean.
    Type of Medium: Online Resource
    Pages: 5 , graph. Darst
    ISSN: 1944-8007
    DOI: 10.1029/2009GL039191
    Language: English
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  • 3
    Electronic Resource
    Electronic Resource
    Magmatism at rifted continental margins (1987)
    [s.l.] : Nature Publishing Group
    Nature 330 (1987), S. 439-444 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The intense volcanism and uplift observed on many rifted continental margins, forming basaltic seaward-dipping reflector sequences, is accompanied by the emplacement of a thick igneous section at depth. Partial melting by decompression of passively upwelling asthenosphere that is hotter than ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/330439a0
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    Paper (German National Licenses)
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  • 4
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    The response of methane hydrate beneath the seabed offshore Svalbard to ocean warming during the next three centuries (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 40 (19). pp. 5159-5163.
    Details
    Publication Date: 2017-09-01
    Description: Methane is a potent greenhouse gas and large-scale rapid release of methane from hydrate may have contributed to past abrupt climate change inferred from the geological record. The discovery in 2008 of over 250 plumes of methane gas escaping from the seabed of the West Svalbard continental margin at ~400 m water depth (mwd) suggests that hydrate is dissociating in the present-day Arctic. Here we model the dynamic response of hydrate-bearing sediments over a period of 2300 years and investigate ocean warming as a possible cause for present-day and likely future dissociation of hydrate, within 350–800 mwd, west of Svalbard. Future temperatures are given by two climate models, HadGEM2 and CCSM4, and scenarios, Representative Concentration Pathways (RCPs) 8.5 and 2.6. Our results suggest that over the next three centuries 5.3–29 Gg yr−1 of methane may be released to the Arctic Ocean on the West Svalbard margin.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/grl.50985
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard (2012)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 117 (B9). B09102.
    Details
    Publication Date: 2018-04-27
    Description: Active gas venting occurs on the uppermost continental slope off west Svalbard, close to and upslope from the present-day intersection of the base of methane hydrate stability (BMHS) with the seabed in about 400 m water depth in the inter-fan region between the Kongsfjorden and Isfjorden cross-shelf troughs. From an integrated analysis of high-resolution, two-dimensional, pre-stack migrated seismic reflection profiles and multibeam bathymetric data, we map out a bottom simulating reflector (BSR) in the inter-fan region and analyze the subsurface gas migration and accumulation. Gas seeps mostly occur in the zone from which the BMHS at the seabed has retreated over the recent past (1975–2008) as a consequence of a bottom water temperature rise of 1°C. The overall margin-parallel alignment of the gas seeps is not related to fault-controlled gas migration, as seismic evidence of faults is absent. There is no evidence for a BSR close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted BMHS. While the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the BMHS and gas hydrate dissociation, the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted BMHS limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011JB009126
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Methane in shallow subsurface sediments at the landward limit of the gas hydrate stability zone offshore western Svalbard (2017)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 198 . pp. 419-438.
    Details
    Publication Date: 2020-02-06
    Description: Offshore western Svalbard plumes of gas bubbles rise from the seafloor at the landward limit of the gas hydrate stability zone (LLGHSZ; ∼400 m water depth). It is hypothesized that this methane may, in part, come from dissociation of gas hydrate in the underlying sediments in response to recent warming of ocean bottom waters. To evaluate the potential role of gas hydrate in the supply of methane to the shallow subsurface sediments, and the role of anaerobic oxidation in regulating methane fluxes across the sediment–seawater interface, we have characterised the chemical and isotopic compositions of the gases and sediment pore waters. The molecular and isotopic signatures of gas in the bubble plumes (C1/C2+ = 1 × 104; δ13C-CH4 = −55 to −51‰; δD-CH4 = −187 to −184‰) are similar to gas hydrate recovered from within sediments ∼30 km away from the LLGHSZ. Modelling of pore water sulphate profiles indicates that subsurface methane fluxes are largely at steady state in the vicinity of the LLGHSZ, providing no evidence for any recent change in methane supply due to gas hydrate dissociation. However, at greater water depths, within the GHSZ, there is some evidence that the supply of methane to the shallow sediments has recently increased, which is consistent with downslope retreat of the GHSZ due to bottom water warming although other explanations are possible. We estimate that the upward diffusive methane flux into shallow subsurface sediments close to the LLGHSZ is 30,550 mmol m−2 yr−1, but it is 〈20 mmol m−2 yr−1 in sediments further away from the seafloor bubble plumes. While anaerobic oxidation within the sediments prevents significant transport of dissolved methane into ocean bottom waters this amounts to less than 10% of the total methane flux (dissolved + gas) into the shallow subsurface sediments, most of which escapes AOM as it is transported in the gas phase.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.gca.2016.11.015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Dynamics of gas hydrates off Svalbard (2009)
    In:  [Talk] In: 69. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG), 23.03.-26.03, Kiel .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 8
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    Gas hydrate quantification from ocean-bottom seismometer data along the continental margin of western Svalbard (2009)
    In:  [Talk] In: EGU General Assembly, 19.04.-24.04, Vienna, Austria .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 9
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    Escape of methane gas from the seabed along the West Spitsbergen continental margin (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L15608.
    Details
    Publication Date: 2017-10-13
    Description: More than 250 plumes of gas bubbles have been discovered emanating from the seabed of the West Spitsbergen continental margin, in a depth range of 150– 400 m, at and above the present upper limit of the gas hydrate stability zone (GHSZ). Some of the plumes extend upward to within 50 m of the sea surface. The gas is predominantly methane. Warming of the northward-flowing West Spitsbergen current by 1° C over the last thirty years is likely to have increased the release of methane from the seabed by reducing the extent of the GHSZ, causing the liberation of methane from decomposing hydrate. If this process becomes widespread along Arctic contine ntal margins, tens of Teragrams of methane per year could be released into the ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009GL039191
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Variability of Acoustically Evidenced Methane Bubble Emissions Offshore Western Svalbard (2019)
    Wiley | AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 46 (15). pp. 9072-9081.
    Details
    Publication Date: 2022-01-31
    Description: Large reservoirs of methane present in Arctic marine sediments are susceptible to rapid warming, promoting increasing methane emissions. Gas bubbles in the water column can be detected, and flow rates can be quantified using hydroacoustic survey methods, making it possible to monitor spatiotemporal variability. We present methane (CH4) bubble flow rates derived from hydroacoustic data sets acquired during 11 research expeditions to the western Svalbard continental margin (2008-2014). Three seepage areas emit in total 725-1,125 t CH4/year, and bubble fluxes are up to 2 kg.m(-2).year (-1). Bubble fluxes vary between different surveys, but no clear trend can be identified. Flux variability analyses suggest that two areas are geologically interconnected, displaying alternating flow changes. Spatial migration of bubble seepage was observed to follow seasonal changes in the theoretical landward limit of the hydrate stability zone, suggesting that formation/dissociation of shallow hydrates, modulated by bottom water temperatures, influences seafloor bubble release. Plain Language Summary It has been speculated that the release of methane (a potent greenhouse gas) from the seafloor in some Arctic Ocean regions is triggered by warming seawater. Emissions of gas bubbles from the seafloor can be detected by ship-mounted sonars. In 2008, a methane seepage area west of Svalbard was hydroacoustically detected for the first time. This seepage was hypothesized to be caused by dissociation of hydrates (ice-like crystals consisting of methane and water) due to ocean warming. We present an analysis of sonar data from 11 surveys conducted between 2008 and 2014. This study is the first comparison of methane seepage-related hydroacoustic data over such a long period. The hydroacoustic mapping and quantification method allowed us to assess the locations and intensity of gas bubble release, and how these parameters change over time, providing necessary data for numerical flux and climate models. No trend of increasing gas flow was identified. However, we observed seasonal variations potentially controlled by seasonal formation and dissociation of shallow hydrates. The hydrate formation/dissociation process is likely controlled by changes of bottom water temperatures. Alternating gas emissions between two neighboring areas indicate the existence of fluid pathway networks within the sediments.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
    DOI: 10.1029/2019GL082750
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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