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  • Copernicus Publications (EGU)  (8)
  • HWU  (4)
  • Kiel : GEOMAR  (3)
  • ASLO (Association for the Sciences of Limnology and Oceanography)  (2)
  • 1
    Book
    Book
    Mineralische Rohstoffe aus der Tiefsee : Entstehung, Potential und Risiken (2019)
    Kiel : GEOMAR
    Details Availability
    Type of Medium: Book
    Pages: 34 Seiten , Illustrationen
    Parallel Title: GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel Parallele Sprachausgabe Mineral resources of the deep sea
    Language: German
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  • 2
    Book
    Book
    Mineral resources of the deep sea : formation, potential and risks (2020)
    Kiel : GEOMAR
    Details Availability
    Type of Medium: Book
    Pages: 34 Seiten , Illustrationen
    Parallel Title: GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel Parallele Sprachausgabe Mineralische Rohstoffe aus der Tiefsee
    Language: English
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  • 3
    Online Resource
    Online Resource
    Mineralische Rohstoffe aus der Tiefsee : Entstehung, Potential und Risiken (2019)
    Kiel : GEOMAR
    Details Availability
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (34 Seiten) , Illustrationen
    URL: https://www.geomar.de/fileadmin/content/service/presse/public-pubs/rohstoffbroschuere.pdf
    Language: German
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  • 4
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    Linked sediment and water-column methanotrophy at a man-made gas blowout in the North Sea: Implications for methane budgeting in seasonally stratified shallow seas (2016)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 61 (S1). S367-S386.
    Details
    Publication Date: 2019-02-01
    Description: Large quantities of the greenhouse gas methane (CH4) are stored in the seafloor. The flux of CH4 from the sediments into the water column and finally to the atmosphere is mitigated by a series of microbial methanotrophic filter systems of unknown efficiency at highly active CH4-release sites in shallow marine settings. Here, we studied CH4-oxidation and the methanotrophic community at a high-CH4-flux site in the northern North Sea (well 22/4b), where CH4 is continuously released since a blowout in 1990. Vigorous bubble emanation from the seafloor and strongly elevated CH4 concentrations in the water column (up to 42 µM) indicated that a substantial fraction of CH4 bypassed the highly active (up to ∼2920 nmol cm−3 d−1) zone of anaerobic CH4-oxidation in sediments. In the water column, we measured rates of aerobic CH4-oxidation (up to 498 nM d−1) that were among the highest ever measured in a marine environment and, under stratified conditions, have the potential to remove a significant part of the uprising CH4 prior to evasion to the atmosphere. An unusual dominance of the water-column methanotrophs by Type II methane-oxidizing bacteria (MOB) is partially supported by recruitment of sedimentary MOB, which are entrained together with sediment particles in the CH4 bubble plume. Our study thus provides evidence that bubble emission can be an important vector for the transport of sediment-borne microbial inocula, aiding in the rapid colonization of the water column by methanotrophic communities and promoting their persistence close to highly active CH4 point sources.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/lno.10388
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Estimation of the global inventory of methane hydrates in marine sediments using transfer functions (2013)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 10 (2). pp. 959-975.
    Details
    Publication Date: 2017-03-13
    Description: The accumulation of gas hydrates in marine sediments is essentially controlled by the accumulation of particulate organic carbon (POC) which is microbially converted into methane, the thickness of the gas hydrate stability zone (GHSZ) where methane can be trapped, the sedimentation rate (SR) that controls the time that POC and the generated methane stays within the GHSZ, and the delivery of methane from deep-seated sediments by ascending pore fluids and gas into the GHSZ. Recently, Wallmann et al. (2012) presented transfer functions to predict the gas hydrate inventory in diffusion-controlled geological systems based on SR, POC and GHSZ thickness for two different scenarios: normal and full compacting sediments. We apply these functions to global data sets of bathymetry, heat flow, seafloor temperature, POC input and SR, estimating a global mass of carbon stored in marine methane hydrates from 3 to 455 Gt of carbon (GtC) depending on the sedimentation and compaction conditions. The global sediment volume of the GHSZ in continental margins is estimated to be 60–67 × 1015 m3, with a total of 7 × 1015 m3 of pore volume (available for GH accumulation). However, seepage of methane-rich fluids is known to have a pronounced effect on gas hydrate accumulation. Therefore, we carried out a set of systematic model runs with the transport-reaction code in order to derive an extended transfer function explicitly considering upward fluid advection. Using averaged fluid velocities for active margins, which were derived from mass balance considerations, this extended transfer function predicts the enhanced gas hydrate accumulation along the continental margins worldwide. Different scenarios were investigated resulting in a global mass of sub-seafloor gas hydrates of ~ 550 GtC. Overall, our systematic approach allows to clearly and quantitatively distinguish between the effect of biogenic methane generation from POC and fluid advection on the accumulation of gas hydrate, and hence, provides a simple prognostic tool for the estimation of large-scale and global gas hydrate inventories in marine sediments.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-10-959-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Saturated CO2 inhibits microbial processes in CO2-vented deep-sea sediments (2013)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 10 (8). pp. 5639-5649.
    Details
    Publication Date: 2019-07-09
    Description: This study focused on biogeochemical processes and microbial activity in sediments of a natural deep-sea CO2 seepage area (Yonaguni Knoll IV hydrothermal system, Japan). The aim was to assess the influence of the geochemical conditions occurring in highly acidic and CO2 saturated sediments on sulfate reduction (SR) and anaerobic methane oxidation (AOM). Porewater chemistry was investigated from retrieved sediment cores and in situ by microsensor profiling. The sites sampled around a sediment-hosted hydrothermal CO2 vent were very heterogeneous in porewater chemistry, indicating a complex leakage pattern. Near the vents, droplets of liquid CO2 were observed emanating from the sediments, and the pH reached approximately 4.5 in a sediment depth 〉 6 cm, as determined in situ by microsensors. Methane and sulfate co-occurred in most sediment samples from the vicinity of the vents down to a depth of 3 m. However, SR and AOM were restricted to the upper 7-15 cm below seafloor, although neither temperature, low pH, nor the availability of methane and sulfate could be limiting microbial activity. We argue that the extremely high subsurface concentrations of dissolved CO2 (1000-1700 mM), which disrupt the cellular pH homeostasis, and lead to end-product inhibition. This limits life to the surface sediment horizons above the liquid CO2 phase, where less extreme conditions prevail. Our results may have to be taken into consideration in assessing the consequences of deep-sea CO2 sequestration on benthic element cycling and on the local ecosystem state.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.5194/bg-10-5639-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    A transfer function for the prediction of gas hydrate inventories in marine sediments (2010)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 7 . pp. 2925-2941.
    Details
    Publication Date: 2019-09-23
    Description: A simple prognostic tool for gas hydrate (GH) quantification in marine sediments is presented based on a diagenetic transport-reaction model approach. One of the most crucial factors for the application of diagenetic models is the accurate formulation of microbial degradation rates of particulate organic carbon (POC) and the coupled formation of biogenic methane. Wallmann et al. (2006) suggested a kinetic formulation considering the ageing effects of POC and accumulation of reaction products (CH4, CO2) in the pore water. This model is applied to data sets of several ODP sites in order to test its general validity. Based on a thorough parameter analysis considering a wide range of environmental conditions, the POC accumulation rate (POCar in g/m2/yr) and the thickness of the gas hydrate stability zone (GHSZ in m) were identified as the most important and independent controls for biogenic GH formation. Hence, depth-integrated GH inventories in marine sediments (GHI in g of CH4 per cm2 seafloor area) can be estimated as: GHI=a ·POCar·GHSZb ·exp(−GHSZc/POCar/d)+e with a = 0.00214, b = 1.234, c = −3.339, d = 0.3148, e = −10.265. The transfer function gives a realistic first order approximation of the minimum GH inventory in low gas flux (LGF) systems. The overall advantage of the presented function is its simplicity compared to the application of complex numerical models, because only two easily accessible parameters need to be determined.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-7-2925-2010
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Effects of climate change on methane emissions from seafloor sediments in the Arctic Ocean: A review (2016)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 61 (S1). pp. 301-309.
    Details
    Publication Date: 2019-09-24
    Description: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and seaair exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/lno.10307
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    CO2 injection into submarine sediments: disturbing news for methane-rich hydrates (2011)
    HWU
    In:  [Poster] In: 7. International Conference on Gas Hydrates (ICGH 2011), 17.-21.07.2011, Edinburgh, Scotland, United Kingdom . Proceedings of the 7th International Conference on Gas Hydrates (ICGH2011) ; 591/1-9 .
    Details
    Publication Date: 2012-03-16
    Description: The production of natural gas via injection of fossil-fuel derived CO2 into submarine gas hydrate reservoirs can be an example of tapping a hydrocarbon energy source in a CO2-neutral manner. However, the industrial application of this method is technically challenging. Thus, prior to feasibility testing in the field, multi-scale laboratory experiments and adapted reaction-modeling are needed. To this end, high-pressure flow-through reactors of 15 and 2000 mL sample volume were constructed and tested. Process parameters (P, T, Q, fluid composition) are defined by a fluid supply and conditioning unit to enable simulation of natural fluid-flow scenarios for a broad range of sedimentary settings. Additional Raman- and NMR-spectroscopy aid in identifying the most efficient pathway for CH4 extraction from hydrates via CO2 injection on both microscopic and macroscopic level. In this study we present experimental set-up and design of the highpressure flow-through reactors as well as CH4 yields from H4-hydrate decomposition experiments using CO2-rich brines and pure liquefied CO2.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 10
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    3-D numerical modeling of methane hydrate deposits (2011)
    HWU
    In:  In: Proceedings of the 7th International Conference on Gas Hydrates (ICGH2011). HWU, Edinburgh, 279/1-6.
    Details
    Publication Date: 2012-07-06
    Description: Within the German gas hydrate initiative SUGAR, we have developed a new tool for predicting the formation of sub-seafloor gas hydrate deposits. For this purpose, a new 2D/3D module simulating the biogenic generation of methane from organic material and the formation of gas hydrates has been added to the petroleum systems modeling software package PetroMod®. T ypically, PetroMod® simulates the thermogenic generation of multiple hydrocarbon components including oil and gas, their migration through geological strata, and finally predicts the oil and gas accumulation in suitable reservoir formations. We have extended PetroMod® to simulate gas hydrate accumulations in marine and permafrost environments by the implementation of algorithms describing (1) the physical, thermodynamic, and kinetic properties of gas hydrates; and (2) a kinetic continuum model for the microbially mediated, low temperature degradation of particulate organic carbon in sediments. Additionally, the temporal and spatial resolutions of PetroMod® were increased in order to simulate processes on time scales of hundreds of years and within decimeters of spatial extension. As a first test case for validating and improving the abilities of the new hydrate module, the petroleum systems model of the Alaska North Slope developed by IES (currently Shlumberger) and the USGS has been chosen. In this area, gas hydrates have been drilled in several wells, and a field test for hydrate production is planned for 2011/2012. The results of the simulation runs in PetroMod® predicting the thickness of the gas hydrate stability field, the generation and migration of biogenic and thermogenic methane gas, and its accumulation as gas hydrates will be shown during the conference. The predicted distribution of gas hydrates will be discussed in comparison to recent gas hydrate findings in the Alaska North Slope region.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
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