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  • Elsevier  (25)
  • Springer  (3)
  • Wiley  (2)
  • Kiel : GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel  (1)
  • Kiel : GEOMAR, Helmholtz-Zentrum für Ozeanforschung
  • 2020-2024  (30)
  • 2000-2004  (1)
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  • 1
    Keywords: Forschungsbericht ; Meeresbergbau ; Umweltbelastung
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (39 Seiten, 1,58 MB) , Illustrationen, Diagramme
    Language: German , English
    Note: Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden , Förderkennzeichen BMBF 03F0812A , Verbundnummer 01183428 , Sprache der Kurzfassungen: Deutsch, Englisch
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  • 2
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 68 (21). pp. 4335-4354.
    Publication Date: 2017-09-08
    Description: Extensive methane hydrate layers are formed in the near-surface sediments of the Cascadia margin. An undissociated section of such a layer was recovered at the base of a gravity core (i.e. at a sediment depth of 120 cm) at the southern summit of Hydrate Ridge. As a result of salt exclusion during methane hydrate formation, the associated pore waters show a highly elevated chloride concentration of 809 mM. In comparison, the average background value is 543 mM. A simple transport-reaction model was developed to reproduce the Cl- observations and quantify processes such as hydrate formation, methane demand, and fluid flow. From this first field observation of a positive Cl- anomaly, high hydrate formation rates (0.15–1.08 mol cm-2 a-1) were calculated. Our model results also suggest that the fluid flow rate at the Cascadia accretionary margin is constrained to 45–300 cm a-1. The amount of methane needed to build up enough methane hydrate to produce the observed chloride enrichment exceeds the methane solubility in pore water. Thus, most of the gas hydrate was most likely formed from ascending methane gas bubbles rather than solely from CH4 dissolved in the pore water.
    Type: Article , PeerReviewed
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  • 3
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    Elsevier | Cell Press
    Publication Date: 2023-10-06
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2023-10-06
    Description: Uncertainties concerning deep-seabed mining relate to the expected impacts on the abyssal benthic and pelagic environment and its ecosystems but also include geopolitical, economic, societal and cultural uncertainty. The uncertain impacts from mining lead to anxiety and a low societal acceptance for the activity and are not the same for everybody at the same time. Hence, uncertainty is an important element of the risk involved in deep-seabed mining. This chapter describes the different risks involved, develops a methodology for risk assessment for the exploitation of marine mineral resources that takes into consideration the state of knowledge and evolving research on deep-sea ecosystems, and informs on possible environmental threshold values in relation to deep-seabed mining operations.
    Type: Book chapter , NonPeerReviewed
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  • 5
    Publication Date: 2024-06-17
    Description: The crises of climate change and biodiversity loss are interlinked and must be addressed jointly. A proposed solution for reducing reliance on fossil fuels, and thus mitigating climate change, is the transition from conventional combustion-engine to electric vehicles. This transition currently requires additional mineral resources, such as nickel and cobalt used in car batteries, presently obtained from land-based mines. Most options to meet this demand are associated with some biodiversity loss. One proposal is to mine the deep seabed, a vast, relatively pristine and mostly unexplored region of our planet. Few comparisons of environmental impacts of solely expanding land-based mining versus extending mining to the deep seabed for the additional resources exist and for biodiversity only qualitative. Here, we present a framework that facilitates a holistic comparison of relative ecosystem impacts by mining, using empirical data from relevant environmental metrics. This framework (Environmental Impact Wheel) includes a suite of physicochemical and biological components, rather than a few selected metrics, surrogates, or proxies. It is modified from the “recovery wheel” presented in the International Standards for the Practice of Ecological Restoration to address impacts rather than recovery. The wheel includes six attributes (physical condition, community composition, structural diversity, ecosystem function, external exchanges and absence of threats). Each has 3–5 sub attributes, in turn measured with several indicators. The framework includes five steps: (1) identifying geographic scope; (2) identifying relevant spatiotemporal scales; (3) selecting relevant indicators for each sub-attribute; (4) aggregating changes in indicators to scores; and (5) generating Environmental Impact Wheels for targeted comparisons. To move forward comparisons of land-based with deep seabed mining, thresholds of the indicators that reflect the range in severity of environmental impacts are needed. Indicators should be based on clearly articulated environmental goals, with objectives and targets that are specific, measurable, achievable, relevant, and time bound.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2024-06-07
    Description: The impact of oxygen on the preservation of organic matter in marine surface sediments is still controversial. We revisited this long-standing debate by determining the burial efficiency of sedimentary organic matter in the Black Sea, the largest anoxic and euxinic basin in the modern ocean. Surface sediments were sampled in the Danube paleodelta on the northwestern margin of the Black Sea at 420–1550 m water depth. Steady-state modeling of solid species (particulate organic carbon and nitrogen) and solutes (ammonium, sulfate, and total alkalinity) in sediments was performed to quantify rates of mass accumulation, particulate organic matter (POM) degradation, and POM burial. We develop a novel analytical model to quantify these rates applying an inverse modelling approach to down core data accounting for molecular diffusion, sediment burial and compaction. Our model results indicate that 56.7 ± 6.6 % of the particulate organic matter deposited in the study area is not degraded in surface sediments but accumulates below 10 cm sediment depth. This burial efficiency is substantially higher than those previously derived for seafloor areas underlying oxygenated bottom waters. Hence, our study confirms previous studies showing that euxinic bottom water conditions promote the preservation of particulate organic matter in marine sediments.
    Type: Article , PeerReviewed
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  • 7
    Publication Date: 2023-02-08
    Description: Highlights • Gas release from wells may counteract efforts to mitigate greenhouse gas emissions. • An approach for assessing methane release from marine decommissioned wells. • This gas release largely depends on the presence of shallow gas accumulations. • Methane release from hydrocarbon wells represents a major source in the North Sea. Abstract Hydrocarbon gas emissions from with decommissioned wells are an underreported source of greenhouse gas emissions in oil and gas provinces. The associated emissions may partly counteract efforts to mitigate greenhouse gas emissions from fossil fuel infrastructure. We have developed an approach for assessing methane leakage from marine decommissioned wells based on a combination of existing regional industrial seismic and newly acquired hydroacoustic water column imaging data from the Central North Sea. Here, we present hydroacoustic data which show that 28 out of 43 investigated wells release gas from the seafloor into the water column. This gas release largely depends on the presence of shallow gas accumulations and their distance to the wells. The released gas is likely primarily biogenic methane from shallow sources. In the upper 1,000 m below the seabed, gas migration is likely focused along drilling-induced fractures around the borehole or through non-sealing barriers. Combining available direct measurements for methane release from marine decommissioned wells with our leakage analysis suggests that gas release from investigated decommissioned hydrocarbon wells is a major source of methane in the North Sea (0.9-3.7 [95% confidence interval = 0.7-4.2] kt yr−1 of CH4 for 1,792 wells in the UK sector of the Central North Sea). This means hydrocarbon gas emissions associated with marine hydrocarbon wells are not significant for the global greenhouse gas budget, but have to be considered when compiling regional methane budgets.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 8
    Publication Date: 2023-02-08
    Description: Highlights • Combining porewater geochemistry, geochemical modeling and subsurface geophysical data in order to understand the fluid flow system of Kerch seep area. • This seep area is not in steady state. • Methane transport is in the form of gas bubbles not porewater advection. • High surface temperatures are the result of hydrate formation and not an indication for elevated geothermal gradients. • Modeling says this seep is young (〈500 years old). Abstract High-resolution 3D seismic data in combination with deep-towed sidescan sonar data and porewater analysis give insights into the seafloor expression and the plumbing system of the actively gas emitting Kerch seep area, which is located in the northeastern Black Sea in around 900 m water depth, i.e. well within the gas hydrate stability zone (GHSZ). Our analysis shows that the Kerch seep consists of three closely spaced but individual seeps above a paleo-channel-levee system of the Don Kuban deep-sea fan. We show that mounded seep morphology results from sediment up-doming due to gas overpressure. Each of the seeps hosts its own gas pocket underneath the domes which are fed with methane of predominantly microbial origin along narrow pipes through the GHSZ. Methane transport occurs dominantly in the form of gas bubbles decoupled from fluid advection. Elevated sediment temperatures of up to 0.3 °C above background values are most likely the result of gas hydrate formation within the uppermost 10 m of the sediment column. Compared to other seeps occurring within the GHSZ in the Black Sea overall only scarce gas indications are present in geoacoustic and geophysical data. Transport-reaction modeling suggests that the Kerch seep is a young seep far from steady state and probably not more than 500 years old.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2023-02-08
    Description: Highlights • Total amount of generated biogenic methane is estimated at ~3100 Gt. • Total amount of generated thermogenic methane is estimated at ~1,560 Gt. • The Maykop formation is partially productive in the central basin and not yet fully productive towards the basin peripherals. A new numerical model reconstructing the depositional history (98–0 Ma) of the Western Black Sea sub-basin is presented. The model accounts for changing boundary conditions (i.e. water depth, bottom water temperature, heat flow evolution over time) and estimates the rates and total amounts of the in-situ biogenic methane generation and thermally-driven organic matter maturation in the source rocks. The overall thermogenic and biogenic gas generation predicted by the model is estimated at ~1560 Gt and ~3100 Gt, respectively.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2023-02-08
    Description: Highlights • Physical properties obtained from core and log data at the Danube deep sea fan are reported. • Core-log-seismic integration defines stratigraphic framework at the S2 channel. • All data suggest no gas hydrate is present at drill sites within uncertainties of methods employed. Abstract Drilling, coring, and geophysical logging were performed with the MARUM-MeBo200 seafloor drilling rig to investigate gas hydrate occurrences of the Danube deep sea fan, off Romania, Black Sea. Three sites within a channel-levee complex were investigated. Geophysical log data of P-wave velocity, electrical resistivity, and spectral gamma ray are combined with core-derived physical properties of porosity, magnetic susceptibility, and bulk density. Core- and log physical property data are used to define a time-depth conversion by synthetic seismogram modeling, which is then used to interpret the seismic data. Individual polarity reversed reflectors within the stratigraphic column drilled are linked to reduction in P-wave velocity and bulk density. Those reflectors (and associated reflection packages) are accompanied by distinct and systematic changes in sediment porosity, magnetic susceptibility, and electrical resistivity. Overall, the sediments at drill site GeoB22605 (MeBo-17) represent the younger (upper) levee sequence of the channel, that has been eroded at drill site GeoB22603 (MeBo-16). Splicing seismic data across the channel from the East (MeBo-16) to the West (MeBo-17) demonstrates the continuation of reflectors underneath the channel. The upper ∼50 m below seafloor (mbsf) at site MeBo-16 do not stratigraphically belong to the same sequence of the (deeper) levee-deposits. Above the marked erosional unconformity, sediments at Site MeBo-16 are likely derived by a mixture of repeated slump-events (identified as seismically transparent units) interbedded with hemi-pelagic sedimentation. Similarly, sediments within the upper ∼20 mbsf at Site MeBo-17 are not stratigraphically the same levee-deposits, but are derived by a mixture of slump-events (also seen in the marked seafloor amphitheatre architecture of a large failure complex extending further upslope) and hemi-pelagic sedimentation. All observations combined show that the seismically observed stratigraphic pattern represents a reflectivity sequence mostly driven by variations in density (porosity) and correspondingly by changes in P-wave velocity and electrical resistivity. All observations from the geophysical log- and core, as well as geochemical data do show no evidence for the presence of any significant gas hydrates within the drilled/cored sequences.
    Type: Article , PeerReviewed
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