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  • 1
    Call number: ZSP-166-261
    In: Berichte aus dem MARUM und dem Fachbereich Geowissenschaften der Universität Bremen
    Type of Medium: Series available for loan
    Pages: 130, A41 S.
    Series Statement: Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen 261
    Classification: D.3.
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
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    PANGAEA
    In:  Supplement to: Pape, Thomas; Geprägs, Patrizia; Hammerschmidt, Sebastian; Wintersteller, Paul; Wei, Jiangong; Fleischmann, Timo; Bohrmann, Gerhard; Kopf, Achim J (2014): Hydrocarbon seepage and its sources at mud volcanoes of the Kumano forearc basin, Nankai Trough subduction zone. Geochemistry, Geophysics, Geosystems, 15(6), 2180-2194, https://doi.org/10.1002/2013GC005057
    Publication Date: 2020-01-17
    Description: Twelve submarine mud volcanoes (MV) in the Kumano forearc basin within the Nankai Trough subduction zone were investigated for hydrocarbon origins and fluid dynamics. Gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from MVs 2, 4, 5, and 10. Molecular ratios (C1/C2〈250) and stable carbon isotopic compositions (d13C-CH4 〉-40 per mil V-PDB) indicate that hydrate-bound hydrocarbons (HCs) at MVs 2, 4, and 10 are derived from thermal cracking of organic matter. Considering thermal gradients at the nearby IODP Sites C0009 and C0002, the likely formation depth of such HCs ranges between 2300 and 4300 m below seafloor (mbsf). With respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of HCs fueling the MVs is derived from sediments of the Cretaceous to Tertiary Shimanto belt below Pliocene/Pleistocene to recent basin sediments. Considering their sizes and appearances hydrates are suggested to be relicts of higher MV activity in the past, although the sporadic presence of vesicomyid clams at MV 2 showed that fluid migration is sufficient to nourish chemosynthesis-based organisms in places. Distributions of dissolved methane at MVs 3, 4, 5, and 8 pointed at fluid supply through one or few MV conduits and effective methane oxidation in the immediate subsurface. The aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane-containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth.
    Type: Dataset
    Format: application/zip, 31 datasets
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  • 3
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    PANGAEA
    In:  Supplement to: Sahling, Heiko; Römer, Miriam; Pape, Thomas; Bergès, Benoit; dos Santos Ferreira, Christian; Boelmann, Jan; Geprägs, Patrizia; Tomczyk, Michal; Nowald, Nicolas; Dimmler, Werner; Schroedter, Leah; Glockzin, Michael; Bohrmann, Gerhard (2014): Gas emissions at the continental margin west of Svalbard: mapping, sampling, and quantification. Biogeosciences, 11(21), 6029-6046, https://doi.org/10.5194/bg-11-6029-2014
    Publication Date: 2020-01-17
    Description: We mapped, sampled, and quantified gas emissions at the continental margin west of Svalbard during R/V Heincke cruise He-387 in late summer 2012. Hydroacoustic mapping revealed that gas emissions were not limited to a zone just above 396 m below sea level (m b.s.l.). Flares from this depth gained significant attention in the scientific community in recent years because they may be caused by bottom water-warming induced hydrate dissolution in the course of global warming and/or by recurring seasonal hydrate formation and decay. We found that gas emissions occurred widespread between about 80 and 415 m b.s.l. which indicates that hydrate dissolution might only be one of several triggers for active hydrocarbon seepage in that area. Gas emissions were remarkably intensive at the main ridge of the forlandet moraine complex in 80 to 90 m water depths, and may be related to thawing permafrost. Focused seafloor investigations were performed with the remotely operated vehicle (ROV) "Cherokee". Geochemical analyses of gas bubbles sampled at about 240 m b.s.l. as well as at the 396 m gas emission sites revealed that the vent gas is primarily composed of methane (〉 99.70%) of microbial origin (average d13C = -55.7 per mil V-PDB). Estimates of the regional gas bubble flux from the seafloor to the water column in the area of possible hydrate decomposition were achieved by combining flare mapping using multibeam and single beam echosounder data, bubble stream mapping using a ROV-mounted horizontally-looking sonar, and quantification of individual bubble streams using ROV imagery and bubble counting. We estimated that about 53 × 10**6 mol methane were annually emitted at the two areas and allow a large range of uncertainty due to our method (9 to 118 × 10**6 mol yr**-1). These amounts, first, show that gas emissions at the continental margin west of Svalbard were in the same order of magnitude as bubble emissions at other geological settings, and second, may be used to calibrate models predicting hydrate dissolution at present and in the future, third, may serve as baseline (year 2012) estimate of the bubble flux that will potentially increase in future due to ever-increasing global-warming induced bottom water-warming and hydrate dissolution.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 4
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    PANGAEA
    In:  Supplement to: Römer, Miriam; Torres, Marta E; Kasten, Sabine; Kuhn, Gerhard; Graham, Alastair G C; Mau, Susan; Little, Crispin T S; Linse, Katrin; Pape, Thomas; Geprägs, Patrizia; Fischer, David; Wintersteller, Paul; Marcon, Yann; Rethemeyer, Janet; Bohrmann, Gerhard; Shipboard scientific party ANT-XXIX/4 (2014): First evidence of widespread active methane seepage in the Southern Ocean, off the sub-Antarctic island of South Georgia. Earth and Planetary Science Letters, 403, 166-177, https://doi.org/10.1016/j.epsl.2014.06.036
    Publication Date: 2020-01-17
    Description: An extensive submarine cold-seep area was discovered on the northern shelf of South Georgia during R/V Polarstern cruise ANT-XXIX/4 in spring 2013. Hydroacoustic surveys documented the presence of 133 gas bubble emissions, which were restricted to glacially-formed fjords and troughs. Video-based sea floor observations confirmed the sea floor origin of the gas emissions and spatially related microbial mats. Effective methane transport from these emissions into the hydrosphere was proven by relative enrichments of dissolved methane in near-bottom waters. Stable carbon isotopic signatures pointed to a predominant microbial methane formation, presumably based on high organic matter sedimentation in this region. Although known from many continental margins in the world's oceans, this is the first report of an active area of methane seepage in the Southern Ocean. Our finding of substantial methane emission related to a trough and fjord system, a topographical setting that exists commonly in glacially-affected areas, opens up the possibility that methane seepage is a more widespread phenomenon in polar and sub-polar regions than previously thought.
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 5
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    PANGAEA
    In:  Supplement to: Wenau, Stefan; Spieß, Volkhard; Pape, Thomas; Fekete, Noemi (2015): Cold seeps at the salt front in the Lower Congo Basin II: The impact of spatial and temporal evolution of salt-tectonics on hydrocarbon seepage. Marine and Petroleum Geology, 67, 880-893, https://doi.org/10.1016/j.marpetgeo.2014.09.021
    Publication Date: 2020-01-17
    Description: This study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front, i.e., the seaward boundary of salt-induced deformation in the Lower Congo Basin (LCB). Seafloor topography, backscatter data and TV-sled observations indicate active fluid seepage from the seafloor directly at the salt front, whereas suspected seepage sites appear to be inactive at a distance of 〉10 km landward of the deformation front. High resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region. The unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt-tectonic deformation facilitates seafloor seepage at the salt front. Bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area. Onlap structures associated with fan deposits which were formed after the onset of salt-tectonic deformation represent potential traps for gas, which may hinder gas migration towards seafloor seeps. Faults related to the thrusting of salt bodies seawards also disrupt along-strata gas migration pathways. Additionally, the development of an effective gas hydrate seal after the cessation of active salt-induced uplift and the near-surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt-tectonic deformation. This process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects Congo Fan deposits on the abyssal plain. These observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting.
    Type: Dataset
    Format: application/zip, 7 datasets
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  • 6
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    Unknown
    PANGAEA
    In:  Supplement to: Blumenberg, Martin; Pape, Thomas; Seifert, Richard; Bohrmann, Gerhard; Schlömer, Stefan (2018): Can hydrocarbons entrapped in seep carbonates serve as gas geochemistry recorder? Geo-Marine Letters, 38(2), 121-129, https://doi.org/10.1007/s00367-017-0522-6
    Publication Date: 2020-01-17
    Description: The geochemistry of seep gases is useful for an understanding of the local petroleum system. Here it was tested whether individual light hydrocarbons in seep gases are representatively entrapped in authigenic carbonates that formed near active seep sites. If applicable, it would be possible to extract geochemical information not only on the origin but also on the thermal maturity of the hydrocarbon source rocks from the gases entrapped in carbonates in the past. Respective data could be used for a better understanding of paleoenvironments and might directly serve as calibration point for, amongst others, petroleum system modeling. For this approach, (sub)-recent seep carbonates from the Black Sea (Paleodnjepr region and Batumi seep area), two sites of the Campeche Knoll region in the Gulf of Mexico, and the Venere mud volcano (Mediterranean Sea) were selected. These seep carbonates derive from sites for which geochemical data on the currently seeping gases exist. During treatment with phosphoric acid, methane and higher hydrocarbons were released from all carbonates, but in low concentrations. Compositional studies demonstrate that the ratio of methane to the sum of higher hydrocarbons (C1/(C2+C3)) is (partly strongly) positively biased in the entrapped gas fraction. δ13C values of C1 were determined for all samples and, for the samples from the Gulf of Mexico and the Mediterranean Sea, also of C2 and C3. The present dataset from six seep sites indicates that information on the seeped methane can be—although with a scatter of several permil—recorded in seep carbonate matrices, but other valuable information like the composition and δ13C of ethane and propane appears to be modified or lost during, for example, enclosure or at an early stage of diagenesis.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 7
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 18292 data points
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  • 8
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 17156 data points
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  • 9
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 9496 data points
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  • 10
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 17436 data points
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