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  • Elsevier  (26)
  • Frontiers  (5)
  • AAAS (American Association for the Advancement of Science)  (1)
  • Kiel : GEOMAR, Helmholtz-Zentrum für Ozeanforschung
  • 2020-2024  (31)
  • 2000-2004  (1)
Document type
Publisher
Years
Year
  • 1
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    Rising methane gas bubbles form massive hydrate layers at the seafloor (2004)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 68 (21). pp. 4335-4354.
    Details
    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
    Format: text
    DOI: 10.1016/j.gca.2004.01.018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Seafloor integrity versus critical metal supply (2021)
    Elsevier | Cell Press
    Details
    Publication Date: 2023-10-06
    Type: Article , NonPeerReviewed
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    OceanRep: Article in a Scientific Journal - without review
  • 3
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    Degradation and accumulation of organic matter in euxinic surface sediments (2024)
    Elsevier
    Details
    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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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Industrial mining trial for polymetallic nodules in the Clarion-Clipperton Zone indicates complex and variable disturbances of meiofaunal communities (2024)
    Frontiers
    Details
    Publication Date: 2024-06-07
    Description: Following several small-scale benthic disturbance experiments, an industrial polymetallic nodule collector trial was conducted by the company Global Sea mineral Resources (GSR) in their exploration contract area in the Clarion-Clipperton Zone using the pre-prototype vehicle Patania II (PATII). In this study, meiofaunal (i.e., nematode abundance, ASV diversity and genus composition) and environmental (i.e., grain size, total organic carbon/total nitrogen and pigment) properties are compared between disturbance categories (i.e., Pre-impact, Collector Impact and Plume Impact). One week after the trial, proxies for food availability within the Collector Impact sediments were altered with lower total organic carbon (TOC) and pigment (i.e., CPE: sum of Chlorophyll a and phaeopigments) values. Albeit not significant, the observed decrease of nematode abundance and ASV diversity, further indicate the consequences of the removal of the ecologically important surface sediment layer within the PATII tracks. Next to sediment removal, exposed sediments were modified in different ways (e.g., central strips, parallel caterpillar imprints with alternating bands of depressions/ripples and interface patches) and were also subject to heavy collector-induced sediment blanketing. We propose that these cumulative impacts have led to intricate seabed modifications with various levels of disturbance intensity which resulted in the high meiofaunal variability observed. Adjacent nodule-rich areas (i.e., Plume Impact) received considerable levels of sediment deposition (2-3 cm) and were defined by significantly lower food sources (CPE, TOC, carbon to nitrogen ratio) and an observation of meiofaunal enrichment (i.e., higher average nematode abundance and ASV diversity; although statistically non-significant), but mechanisms behind these ecological changes (e.g., suspended material-surface fluxes, passive dispersal of fauna in the plume vs. active upward migration and “viability” of redeposited fauna) remain unresolved. We conclude that complex benthic pressure-response relationships associated with the PATII trial, combined with the high degree of natural spatial and temporal variability in abyssal meiofaunal communities and sedimentary parameters, complicates the quantitative assessment of deep-sea mining associated disturbances.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Carbon budget of methane seepages in the Haiyang 4 Area in the northern slope of the South China sea (2024)
    Elsevier
    Details
    Publication Date: 2024-07-03
    Description: Highlights • All investigated sites are in quiescent stage. Multi layers of clam shell debris were the ancient sediment surfaces during high methane flux. • Current fluxes contribute to less than 2 wt % of authigenic carbonates and 2 wt % iron sulfide minerals being precipitated in 600-800 cm sediment. • The sequestration of carbon could be 〉 50 mmol C cm-2 yr-1 under current in situ condition. Abstract Methane seepage records information of the local carbon cycle with respect to the generation, consumption and sequestration of carbon. Here presents the investigation of 7 gravity cores retrieved in 2004 during cruise SO-177 in the Haiyang 4 Area at the northern slope of the South China Sea. Porewater solutes, sulfate, methane, total alkalinity, sulfide and calcium demonstrate currently the weak seep activity. Local carbon cycling and sequestration is also revealed, that dominates by anaerobic oxidation of biogenic methane to dissolved bicarbonate inducing calcium carbonate and iron sulfide minerals (mainly pyrite) precipitation. A reactive transport model was employed to quantify the carbon cycle and budget. Model results show that current methane fluxes contribute to less than 2 wt % of authigenic carbonates and 2 wt % iron sulfide minerals being precipitated in 600–800 cm sediment depth. The sequestration of carbon could be 〉 50 mmol C cm−2 yr−1 under in situ condition. The observed increase of carbonate and iron sulfide minerals at ∼100 cm, however, require higher methane fluxes to shift the zone of anaerobic oxidation of methane upwards to around 1 m below the seafloor, which have occurred during sea level low stands in the geological past. The oscillation of seepage flux contributed to the formation of multiple layers of authigenic carbonates and pyrite, which indicates the high capability of carbon sink and is speculated to be induced by the dissociation of the underlying hydrates triggered by sea level drop and or temperature increase.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Greenhouse gas emissions from marine decommissioned hydrocarbon wells: leakage detection, monitoring and mitigation strategies (2020)
    Elsevier
    Details
    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
    Format: text
    Format: archive
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    New insights into geology and geochemistry of the Kerch seep area in the Black Sea (2020)
    Elsevier
    Details
    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
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Basin-scale estimates on petroleum components generation in the Western Black Sea basin based on 3-D numerical modelling (2020)
    Elsevier
    Details
    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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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Physical properties and core-log seismic integration from drilling at the Danube deep-sea fan, Black Sea (2020)
    Elsevier
    Details
    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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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Effects of a deep-sea mining experiment on seafloor microbial communities and functions after 26 years (2020)
    AAAS (American Association for the Advancement of Science)
    Details
    Publication Date: 2023-02-08
    Description: Future supplies of rare minerals for global industries with high-tech products may depend on deep-sea mining. However, environmental standards for seafloor integrity and recovery from environmental impacts are missing. We revisited the only midsize deep-sea disturbance and recolonization experiment carried out in 1989 in the Peru Basin nodule field to compare habitat integrity, remineralization rates, and carbon flow with undisturbed sites. Plough tracks were still visible, indicating sites where sediment was either removed or compacted. Locally, microbial activity was reduced up to fourfold in the affected areas. Microbial cell numbers were reduced by ~50% in fresh “tracks” and by 〈30% in the old tracks. Growth estimates suggest that microbially mediated biogeochemical functions need over 50 years to return to undisturbed levels. This study contributes to developing environmental standards for deep-sea mining while addressing limits to maintaining and recovering ecological integrity during large-scale nodule mining.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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