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  • 1
    Language: English
    In: Geo-Marine Letters, 2012, Vol.32(5), pp.489-499
    Description: The central Chilean subduction zone between 35°S and 37°S was investigated in order to identify, document and possibly understand fluid flow and fluid venting within the forearc region. Several areas were mapped using multibeam bathymetry and backscatter, high-resolution sidescan sonar, chirp subbottom profiling and reflection seismic data. On a subsequent cruise ground-truthing observations were made using a video sled. In general, this dataset shows surprisingly little evidence of fluid venting along the mid-slope region, in contrast to other subduction zones such as Central America and New Zealand. There were abundant indications of active and predominantly fossil fluid venting along the upper slope between 36.5°S and 36.8°S at the seaward margin of an intraslope basin. Here, backscatter anomalies suggest widespread authigenic carbonate deposits, likely the result of methane-rich fluid expulsion. There is unpublished evidence that these fluids are of biogenic origin and generated within the slope sediments, similar to other accretionary margins but in contrast to the erosional margin off Central America, where fluids have geochemical signals indicating an origin from the subducting plate.
    Keywords: Methane ; Sonar Systems ; Subduction Zones ; Carbonates ; Continental Margins ; Sediments (Geology);
    ISSN: 0276-0460
    E-ISSN: 1432-1157
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  • 2
    Language: English
    In: Geology, May, 2013, Vol.41(5), p.551(4)
    Description: Methane seepage at south Hydrate Ridge (offshore Oregon, United States), one of the best-studied examples of gas venting through gas hydrates, is the seafloor expression of a vigorous fluid flow system at depth. The seeps host chemosynthetic ecosystems and release significant amounts of carbon into the ocean. With new three-dimensional seismic data, we image strata and structures beneath the ridge in unprecedented detail to determine the geological processes controlling the style of focused fluid flow. Numerical fluid flow simulations reveal the influence of free gas within a stratigraphic unit known as Horizon A, beneath the base of gas hydrate stability (BGHS). Free gas within Horizon A increases the total mobility of the composite water-gas fluid, resulting in high fluid flux that accumulates at the intersection between Horizon A and the BGHS. This intersection controls the development of fluid overpressure at the BGHS, and together with a well-defined network of faults, reveals the link between the gas hydrate system at depth and methane seepage at the surface. doi: 10.1130/G34057.1
    Keywords: Motor Vehicle Drivers ; Seepage (Hydrology) ; Methane ; Gas Hydrates ; Hydrates
    ISSN: 0091-7613
    E-ISSN: 19432682
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  • 3
    Language: English
    In: Marine Geology, 2010, Vol.272(1), pp.49-58
    Description: Cold seeps on Opouawe Bank, situated in around 1000 m water depth on the Hikurangi Margin offshore North Island. New Zealand, were investigated using multibeam bathymetry, 75 and 410 kHz sidescan sonar imagery, and 2–8 kHz Chirp sediment echosounder data. Towed video camera observations allowed ground-truthing the various geoacoustic data. At least eleven different seep locations displaying a range of seep activity were identified in the study area. The study area consists of an elongated, northward-widening ridge that is part of the accretionary Hikurangi Margin and is well separated from direct terrigenous input by margin channels surrounding the ridge. The geoacoustic signature of individual cold-seep sites ranged from smooth areas with slightly elevated backscatter intensity resulting from high gas content or the presence of near-surface gas hydrates, to rough areas with widespread patches of carbonates at the seafloor. Five cold seeps also show indications for active gas emissions in the form of acoustic plumes in the water column. Repeated sidescan sonar imagery of the plumes indicates they are highly variable in intensity and direction in the water column, probably reflecting the control of gas emission by tides and currents. Although gas emission appears strongly focused in the Wairarapa area, the actual extents of the cold seep structures are much wider in the subsurface as is shown by sediment echosounder profiles, where large gas fronts were observed.
    Keywords: Hikurangi Margin ; Cold Seeps ; Sidescan Sonar ; Methane ; Gas Bubbles ; Temporal Variability ; Spatial Variability ; Oceanography ; Geology
    ISSN: 0025-3227
    E-ISSN: 1872-6151
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  • 4
    Language: English
    In: Geo-Marine Letters, 2016, Vol.36(3), p.165(10)
    Description: To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1007/s00367-015-0431-5 Byline: Ingo Klaucke (1), Christian Berndt (1), Gareth Crutchley (2), Wu-Cheng Chi (3), Saulwood Lin (4), Sina Muff (1) Abstract: Within the accretionary prism offshore SW Taiwan, widespread gas hydrate accumulations are postulated to occur based on the presence of a bottom simulating reflection. Methane seepage, however, is also widespread at accretionary ridges offshore SW Taiwan and may indicate a significant loss of methane bypassing the gas hydrate system. Four Way Closure Ridge, located in 1,500 m water depth, is an anticlinal ridge that would constitute an ideal trap for methane and consequently represents a site with good potential for gas hydrate accumulations. The analysis of high-resolution bathymetry, deep-towed sidescan sonar imagery, high-resolution seismic profiling and towed video observations of the seafloor shows that Four Way Closure Ridge is and has been a site of intensive methane seepage. Continuous seepage is mainly evidenced by large accumulations of authigenic carbonate precipitates, which appear to be controlled by the creation of fluid pathways through faulting. Consequently, Four Way Closure Ridge is not a closed system in terms of fluid migration and seepage. A conceptual model of the evolution of gas hydrates and seepage at accretionary ridges suggests that seepage is common and may be a standard feature during the geological development of ridges in accretionary prisms. The observation of seafloor seepage alone is therefore not a reliable indicator of exploitable gas hydrate accumulations at depth. Author Affiliation: (1) GEOMAR Helmholtz-Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148, Kiel, Germany (2) GNS Science, P.O. Box 30-368, Lower Hutt, 5040, New Zealand (3) Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC (4) Institute of Oceanography, National Taiwan University, Roosevelt Road, Taipei, Taiwan, ROC Article History: Registration Date: 25/11/2015 Received Date: 26/04/2015 Accepted Date: 25/11/2015 Online Date: 04/12/2015 Article note: Responsible guest editor: M. De Batist
    Keywords: Methane – Analysis ; Sonar Systems – Analysis ; Gas Hydrates – Analysis ; Carbonates – Analysis ; Hydrates – Analysis
    ISSN: 0276-0460
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Geo-Marine Letters, June, 2014, Vol.34(2-3), p.169(16)
    Description: Byline: Ines Dumke (1), Ingo Klaucke (1), Christian Berndt (1), Jorg Bialas (1) Abstract: Cold seeps on the Hikurangi Margin off New Zealand exhibit various seabed morphologies producing different intensity patterns in sidescan backscatter images. Acoustic backscatter characteristics of 25 investigated seep sites fall into four distinct types characterised by variations in backscatter intensity, distribution and inferred structural heights. The types reflect different carbonate morphologies including up to 20-m-high structures (type 1), low-relief crusts (type 2), scattered blocks (type 3) and carbonate-free sites (type 4). Each seep corresponds to a single type intermediates were not observed. This correlates well with published data on seep fauna at each site, with the four types representing three different faunal habitats of successive stages of seep development. Backscatter signatures in sidescan sonar images of cold seeps may therefore serve as a convenient proxy for variations in faunal habitats. Author Affiliation: (1) GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, Kiel, 24148, Germany Article History: Registration Date: 29/01/2014 Received Date: 15/05/2013 Accepted Date: 26/01/2014 Online Date: 12/03/2014 Article note: Responsible editors: B.W. Flemming and M.T. Delafontaine
    Keywords: Carbonates ; Ocean Bottom ; Sonar Systems
    ISSN: 0276-0460
    E-ISSN: 14321157
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  • 6
    Language: English
    In: Journal of Asian Earth Sciences, March 2, 2012, Vol.46, p.78(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jseaes.2011.11.003 Byline: Pachoenchoke Jintasaeranee (a)(c), Wilhelm Weinrebe (a), Ingo Klaucke (a), Anond Snidvongs (b)(d), Ernst R. Flueh (a) Keywords: Andaman Sea; Submarine landslides; Tsunami; Bathymetry; Sounding Abstract: a* We present a new detailed multibeam bathymetry and subbottom profilers. a* The Andaman Sea outer slope within Thai EEZ was investigated for the first time. a* The slope inclines westward and southward with gradient higher than 4[degrees] further north. a* Previously unknown features are identified such as mud-dome and plateaus. a* One location of translational submarine landslide is studied. Author Affiliation: (a) Leibniz Institute of Marine Sciences at Kiel University (IFM-GEOMAR), Dienstgebaude Ostufer, Wischhofstr. 1-3, 24148 Kiel, Germany (b) Southeast Asia START Regional Center, Chulawich 1 Building, 5th Floor, Chulalongkorn University, Henri Dunant Road, Bangkok 10330, Thailand (c) Department of Aquatic Science, Faculty of Science, Burapha University, 169 Long-Hard Bangsaen Road, Mueang, Chonburi 20131, Thailand (d) Department of Marine Science, Faculty of Science, Chulalongkorn University, 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand Article History: Received 21 June 2010; Revised 2 November 2011; Accepted 2 November 2011
    Keywords: Landslides ; Tsunamis ; Submarines ; Universities And Colleges
    ISSN: 1367-9120
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: The Journal of the Acoustical Society of America, 05/2008, Vol.123(5), pp.3349-3349
    Description: The backscattering signal on sidescan sonar images is to a large degree dependent on the incident angle of the acoustic beam onto the seafloor. As sidescan sonar systems are often used for mapping seafloor lithologies, it is necessary to reduce or even remove the effect of different backscattering strengths caused by varying incidence angles. This study evaluates the influence of seafloor morphology on the acoustic backscattering signal of the deep-towed IFM-GEOMAR DTS-1 sidescan sonar system. Data used are from the Pacific continental slope offshore Nicaragua in a water depth between 800 and 2400 metres. There authigenic carbonate patches formed by cold fluid venting are imaged with a high backscattering level. The carbonates are often located on top or on the flanks of mound structures with a strong morphology. The specific DTS-1 backscattering function is determined on normal, uniform seafloor sediment, and then applied in a new processing algorithm to the raw data of two test areas. The change in amplitude strength when considering seafloor morphology is calculated. The topographic influence on the backscattering signal can be quite significant when imaging mound structures. Nevertheless the high backscatter on mounds is not completely removed, leading to the conclusion that it originates from a different seafloor lithology and roughness.
    Keywords: Mathematical Models ; Backscatter ; Continental Slope ; Lithology ; Ocean Floor ; Imaging Techniques ; Bottom Topography Effects ; Seafloor Mapping ; Topographic Influences ; Acoustics ; Algorithms ; Topography ; Asw, Nicaragua ; I, Pacific ; Marine ; Propagation of Sound ; Physical Oceanography ; Submarine Topography/Bottom Forms/Sea-Floor Features (551.462);
    ISSN: 0001-4966
    Source: CrossRef
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  • 8
    Language: English
    In: Deep-Sea Research Part I, November 2017, Vol.129, pp.1-9
    Description: Reliable very deep shipborne SBE 911plus Conductivity Temperature Depth (CTD) data to within 60 m from the bottom and Kongsberg EM122 0.5° × 1° multibeam echosounder data are collected in the Challenger Deep, Mariana Trench. A new position and depth are given for the deepest point in the world's ocean. The data provide insight into the interplay between topography and internal waves in the ocean that lead to mixing of the lowermost water masses on Earth. Below 5000 m, the vertical density stratification is weak, with a minimum buoyancy frequency N = 1.0 ± 0.6 cpd, cycles per day, between 6500 and 8500 m. In that depth range, the average turbulence is coarsely estimated from Thorpe-overturning scales, with limited statistics to be ten times higher than the mean values of dissipation rate ε = 3 ± 2 × 10 m s and eddy diffusivity K = 2 ± 1.5 × 10 m s estimated for the depth range between 10,300 and 10,850 m, where N = 2.5 ± 0.6 cpd. Inertial and meridionally directed tidal inertio-gravity waves can propagate between the differently stratified layers. These waves are suggested to be responsible for the observed turbulence. The turbulence values are similar to those recently estimated from CTD and moored observations in the Puerto Rico Trench. Yet, in contrast to the Puerto Rico Trench, seafloor morphology in the Mariana Trench shows up to 500 m-high fault scarps on the incoming tectonic plate and a very narrow trench, suggesting that seafloor topography does not play a crucial role for mixing.
    Keywords: New Deepest Point Estimate ; Challenger Deep ; Mariana Trench ; Improved Deep Ctd Observations ; Turbulence Parameter Estimates ; Inertio-Gravity Tidal Wave Propagation ; Biology ; Oceanography
    ISSN: 0967-0637
    E-ISSN: 1879-0119
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  • 9
    Language: English
    In: Marine Geology, 2010, Vol.275(1), pp.1-19
    Description: Fluid escape structures on the Nile Deep Sea Fan were investigated during the MEDIFLUX MIMES expedition in 2004. Mud volcanoes, pockmarks and authigenic carbonate structures were surveyed for the first time with a high-resolution deep-towed 75 kHz sidescan sonar and a 2–8 kHz Chirp sediment echosounder. In combination with existing multibeam bathymetry and detailed seafloor in situ geological observations, these new data allowed detailed seep analyses. About 60 gas flares were detected acoustically in the water column from the sidescan sonar raw data at water depths from 770 to 1700 m. These gas flares coincide at the seabed with 1) the centres of the mud volcanoes where mud is also extruded, 2) the borders of the mud volcanoes where the emitted gases contribute to the precipitation of authigenic carbonates, and 3) to the edges of broad sheets of authigenic carbonates. Subsurface sediments are commonly disturbed by ascending fluids throughout the delta, with an abundance of seep-related carbonate structures on the seafloor. The feeder channels below mud volcanoes, similar to the gas conduits below the widespread carbonate crust structures and pockmarks, are relatively narrow and, for the vast majority of them, do not exceed a few metres in diameter. The seeps on the Nile Deep Sea Fan clearly follow lineations on the seafloor that we can relate to faults.
    Keywords: Nile Deep Sea Fan ; Seepage ; Backscatter ; Sidescan Sonar ; High-Resolution ; Gas Chimneys ; Mud Volcanoes ; Authigenic Carbonates ; Oceanography ; Geology
    ISSN: 0025-3227
    E-ISSN: 1872-6151
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  • 10
    Language: English
    In: Marine Geology, 2010, Vol.275(1), pp.53-65
    Description: Based on multibeam bathymetry, high-resolution deep-towed sidescan sonar and Chirp subbottom profiling 32 cold seep sites, already identified in Sahling et al. (2008a), have been studied in an approximately 1000 km large area ranging from 800 to 2600 m water depth along the middle slope of the active continental margin offshore Nicaragua. Ground truthing is available from towed camera surveys and coring on seven of the structures. The seeps occur in different settings on the slope: upslope and along the headwall of large submarine slides, as isolated eroded massifs, and forming linear ridges between deeply incised canyons. The seep sites show a wide range regarding their size and morphology, their backscatter intensity patterns, their structure in subbottom profiles, and their fluid venting activity inferred from seafloor observations. Surface extension of the seep sites ranges from less than 200 to more than 1500 m in diameter, and relief height varies between no relief and 180 m. Indications of extruded materials such as mud flows are not observed in the area of the seep sites. Instead the seeps are characterized by high proportions of authigenic carbonates. The carbonates occur as crusts, detritus, or single layers embedded in the seafloor sediments. They appear as high backscatter intensities on sidescan sonar images. On some seep sites living vent fauna indicative of active seepage is observed, but gas bubbles have not been observed. To explain the high morphological variability of the features, we propose a generic model including the interaction of several processes: (1) episodic fluid venting and associated authigenic carbonate formation; (2) background sedimentation and subsidence; (3) linear erosion along canyons and denudation on the slope surface.
    Keywords: Mound Structures ; Cold Seeps ; Fluid Venting ; Sedimentation ; Erosion ; Sidescan Sonar ; Nicaragua ; Oceanography ; Geology
    ISSN: 0025-3227
    E-ISSN: 1872-6151
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