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  • AGU (American Geophysical Union)  (8)
  • American Society of Limnology and Oceanography  (3)
  • Marine Technology Society  (3)
  • 1
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    Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule Earthquake, Central Chile (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (11). pp. 4802-4813.
    Details
    Publication Date: 2020-06-29
    Description: Seafloor seepage of hydrocarbon-bearing fluids has been identified in a number of marine forearcs. However, temporal variations in seep activity and the structural and tectonic parameters that control the seepage often remain poorly constrained. Subduction-zone earthquakes for example, are often discussed to trigger seafloor seepage but causal links that go beyond theoretical considerations have not yet been fully established. This is mainly due to the inaccessibility of offshore epicentral areas, the infrequent occurrence of large earthquakes, and challenges associated with offshore monitoring of seepage over large areas and sufficient time periods. Here, we report visual, geochemical, geophysical, and modelling results and observations from the Concepción Methane Seep Area (offshore Central Chile) located in the rupture area of the 2010 Mw. 8.8 Maule earthquake. High methane concentrations in the oceanic water column and a shallow sub-bottom depth of sulfate penetration indicate active methane seepage. The stable carbon isotope signature of the methane and hydrocarbon composition of the released gas indicate a mixture of shallow-sourced biogenic gas and a deeper sourced thermogenic component. Pristine fissures and fractures observed at the seafloor together with seismically imaged large faults in the marine forearc may represent effective pathways for methane migration. Upper-plate fault activity with hydraulic fracturing and dilation is in line with increased normal Coulomb stress during large plate-boundary earthquakes, as exemplarily modelled for the 2010 earthquake. On a global perspective our results point out the possible role of recurring large subduction-zone earthquakes in driving hydrocarbon seepage from marine forearcs over long timescales.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2016GC006498
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Novel online digital video and high-speed data broadcasting via standard coaxial cable onboard marine operating vessels (2015)
    Marine Technology Society
    In:  Marine Technology Society Journal, 49 (1). pp. 7-18.
    Details
    Publication Date: 2017-12-19
    Description: A recently developed deep-sea telemetry (DST), based on the digital subscriber line technology, has been successfully used to equip various remotely operated underwater devices with online video control, high-speed data transmission, and power supply via standard coaxial cables with a length of up to 8,000 m. The system has been applied to study and sample the extreme saline and high-temperature conditions of the Red Sea brines and to detect gas emissions at abandoned wells in the North Sea. In both applications, it has been integrated into a water sampler rosette, providing live video streaming and internal recording from commercial high-definition and analog cameras as well as simultaneous data transmission from a suite of sensors to record and sample the distribution of dissolved gases (e.g., methane and CO2) and oceanographic parameters. This combination makes an ideal survey and monitoring tool for leak detection even in harsh subsea environments. The DST has also been used to deploy landers at selected spots at the seafloor. In combination with remotely operated vehicle (ROV) deployments, this technique can be used to increase significantly the efficiency of ROV bottom time during deep-water operations. The high quality of the video transmission, ease of operation, and versatile application make this novel system superior to existing conventional analog transmission systems.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4031/MTSJ.49.1.2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    A sediment flow-through system to study the impact of shifting fluid and methane flow regimes on the efficiency of the benthic methane filter (2014)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 12 . pp. 25-45.
    Details
    Publication Date: 2019-09-23
    Description: The efficiency of the “benthic microbial methane filter” at marine cold seeps is controlled by diffusive sulfate supply from the overlying seawater and advective methane flux from deep reservoirs. High fluid fluxes reduce the penetration depth of sulfate and limit the filter to a very narrow zone close to the sediment-water interface. Here, we introduce a new sediment-flow-through (SLOT) system, to mimic the balance between fluid/methane flow and sulfate supply in natural sediments. SLOT enables anaerobic incubations of intact sediment cores under natural flow regimes. In addition to traditional in- and outflow sampling, geochemical parameters can be monitored along the sediment core using microsensors and rhizons. In a first test run, two cores with gassy sediments from the Eckernförde Bay (Baltic Sea) were incubated and monitored for 310 days under low (11.2 cm y–1) and high fluid flow (112.1 cm y–1) conditions. Rates of anaerobic oxidation of methane (AOM) were one order of magnitude higher (3.07 mmol m–2 d–1) in the high flow compared to the low flow regime (0.29 mmol m–2 d–1), whereas methane efflux was twice as high (0.063 and 0.033 mmol m–2 d–1, respectively). Sediment profiles of sulfide, sulfate, total alkalinity, pH, redox, and other parameters offered important information on the nature and dynamics of the biogeochemical reactions in the sediment cores including methanotrophy, sulfate reduction, carbonate precipitation, and sulfide oxidation. The SLOT system proofed to be an effective device to study the temporal evolution of biogeochemical parameters in intact sediments subjected to advective fluid transport.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2014.12.25
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Quantifying tidally-driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (10). pp. 6918-6932.
    Details
    Publication Date: 2018-02-26
    Description: Continental shelves are predominately (~70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ~3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1-D model linking the benthic turbulence to the sediment pore water exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low-flow periods. The study reveals that the benthic hydrodynamics, sediment permeability, and pore water redox oscillations are all intimately linked and crucial parameters determining the oxygen availability. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2014JC010303
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Recent Development in IR Sensor Technology for Monitoring Subsea Methane Discharge (2013)
    Marine Technology Society
    In:  Marine Technology Society Journal, 47 (3). pp. 27-36.
    Details
    Publication Date: 2018-09-18
    Description: Recently developed methane sensors, based on infrared (IR) absorption technology, were successfully utilized for subsea methane release measurements. Long-term investigation of methane emissions (fluid flux determination) from natural methane seeps in the Hikurangi Margin offshore New Zealand were performed by using seafloor lander technology. Small centimeter-sized seep areas could be sampled at the seafloor by video-guided lander deployment. In situ sensor measurements of dissolved methane in seawater could be correlated with methane concentrations measured in discrete water samples after lander recovery. High backscatter flares determined by lander-based Acoustic Doppler Current Profiler (ADCP) measurement indicate bubble release from the seafloor. Highest methane concentrations determined by the IR sensor coincided with periods of high ADCP backscatter signals. The high fluid release cannot be correlated with tidal changes only. However, this correlation is possible with variability in spatial bubble release, sudden outbursts, and tidal changes in more quiescent seepage phases. A recently developed IR sensor (2,000 m depth-rated) with a detection limit for methane of about 1 ppm showed good linearity in the tested concentration range and an acceptable equilibration time of 10 min. The sensor was successfully operated offshore Santa Barbara by a small work-class ROV at a natural methane seep (Farrar Seep). High background methane concentration of 50 nmol L−1 was observed in the coastal water, which increases up to 560 nmol L−1 in dissolved methane plumes south of the seepage area. ROV- and lander-based sensor deployments have proven the applicability of IR sensor technology for the determination of subsea methane release rates and plume distribution. The wide concentration range, low detection limit, and its robust detection unit enable this technology for both subsea leak detection and oceanographic trace gas investigations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4031/MTSJ.47.3.8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Natural CO2 seeps offshore Panarea – A test site for subsea CO2 leak detection technology (2015)
    Marine Technology Society
    In:  Marine Technology Society Journal, 49 (1). pp. 19-30.
    Details
    Publication Date: 2017-12-19
    Description: During RV Poseidon cruise POS469 (May 2014), the distribution of pCO2 in the near field of submarine volcanic gas flares in shallow water depths down to 50 m below sea level was continuously monitored using three different and independent methodologies. In situ nondispersive infrared (NDIR) spectrometry, pH measurements, and onboard membrane inlet mass spectrometry (MIMS) were used to determine the fate of rising CO2 bubbles and the dissolved CO2 plume patterns in a 300 × 400-m working area. The in situ sensor carrier platform, a towed video-controlled water sampling rosette, equipped with CTD sensors, guaranteed excellent ground truthing of seafloor characteristics and bubble discharge. Sensor data and nearseafloor observations indicated that the gas bubbles (〈9 mm in diameter, 〉97 vol.% of CO2) dissolved very rapidly within the first 10 m above seafloor. Bottom water masses enriched with pCO2 (up to 1,100 μatm) show low pH values (up to 7.80) and tend to spread rather downslope west than following the measured weak current in SSE-SSW direction. The 3-D evaluation of pCO2 plume is a valuable tool to backtrace the origin of CO2 leakage when compared with local current regimes, water column CTD data, and seafloor bathymetry. Seep sites offshore Panarea can be used for studying CO2 leakage behavior and testing measuring strategies in shallow waters. Moreover, this area is a naturally designed laboratory to improve existing physicochemical and oceanographic transport models for subsea CO2 leakage.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.4031/MTSJ.49.1.3
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Discovery of a natural CO2 seep in the German North Sea: implications for shallow dissolved gas and seep detection (2011)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 116 . C03013.
    Details
    Publication Date: 2019-09-23
    Description: A natural carbon dioxide (CO2) seep was discovered during an expedition to the southern German North Sea (October 2008). Elevated CO2 levels of ∼10–20 times above background were detected in seawater above a natural salt dome ∼30 km north of the East-Frisian Island Juist. A single elevated value 53 times higher than background was measured, indicating a possible CO2 point source from the seafloor. Measured pH values of around 6.8 support modeled pH values for the observed high CO2 concentration. These results are presented in the context of CO2 seepage detection, in light of proposed subsurface CO2 sequestering and growing concern of ocean acidification. We explore the boundary conditions of CO2 bubble and plume seepage and potential flux paths to the atmosphere. Shallow bubble release experiments conducted in a lake combined with discrete-bubble modeling suggest that shallow CO2 outgassing will be difficult to detect as bubbles dissolve very rapidly (within meters). Bubble-plume modeling further shows that a CO2 plume will lose buoyancy quickly because of rapid bubble dissolution while the newly CO2-enriched water tends to sink toward the seabed. Results suggest that released CO2 will tend to stay near the bottom in shallow systems (〈200 m) and will vent to the atmosphere only during deep water convection (water column turnover). While isotope signatures point to a biogenic source, the exact origin is inconclusive because of dilution. This site could serve as a natural laboratory to further study the effects of carbon sequestration below the seafloor.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010JC006557
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Simple, robust eddy correlation amplifier for aquatic dissolved oxygen and hydrogen sulfide flux measurements (2011)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 9 . pp. 340-347.
    Details
    Publication Date: 2018-08-15
    Description: The aquatic application of the eddy correlation (EC) technique is growing more popular and is gradually becoming a standard method for resolving benthic O2 fluxes. By including the effects of the local hydrodynamics, the EC technique provides greater insight into the nature of benthic O2 exchange than traditional methods (i.e., benthic chambers and lander microprofilers). The growing popularity of the EC technique has led to a greater demand for easily accessible and robust EC instrumentation. Currently, the EC instrumentation is limited to two commercially available systems that are still in the development stage. Here, we present a robust, open source EC picoamplifier that is simple in design and can be easily adapted to both new and existing acoustic Doppler velocimeters (ADV). The picoamplifier has a response time of 〈 0.1 ms and features galvanic isolation that ensures very low noise contamination of the signal. It can be adjusted to accommodate varying ranges of microelectrode sensitivity as well as other types of amperometric microelectrodes. We show that the extracted flux values are not sensitive to reduced microelectrode operational ranges (i.e., lower resolution) and that no signal loss results from using either a 16- or 14-bit analog-to-digital converter. Finally, we demonstrate the capabilities of the picoamplifier with field studies measuring both dissolved O2 and H2S EC fluxes. The picoamplifier presented here consistently acquires high-quality EC data and provides a simple solution for those who wish to obtain EC instrumentation. The schematic of the amplifier’s circuitry is given in the Web Appendix.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.4319/lom.2011.9.340
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Fluid venting in the eastern Aleutian subduction zone (1998)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 103 (B2). pp. 2597-2614.
    Details
    Publication Date: 2018-04-25
    Description: Fluid venting has been observed along 800 km of the Alaska convergent margin. The fluid venting sites are located near the deformation front, are controlled by subsurface structures, and exhibit the characteristics of cold seeps seen in other convergent margins. The more important characteristics include (1) methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges; (2) prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps, over‐steepened folds or outcrops of bedding planes; (3) calcium carbonate and barite precipitates at the surface and subsurface of vents; and (4) carbon isotope evidence from tissue and skeletal hard parts of biota, as well as from carbonate precipitates, that vents expel either methane‐ or sulfide‐dominated fluids. A biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5.5±0.7 L m−2 d−1 for tectonics‐induced water flow [Wallmann et al., 1997b]. A geophysical estimate of dewatering from the same area [von Huene et al., 1997] based on sediment porosity reduction shows a fluid loss of 0.02 L m−2 d−1 for a 5.5 km wide converged segment near the deformation front. Our video‐guided surveys have documented vent biota across a minimum of 0.1% of the area of the convergent segment off Kodiak Island; hence an average rate of 0.006 L m−2 d−1 is estimated from the biogeochemical approach. The two estimates for tectonics‐induced water flow from the accretionary prism are in surprisingly good agreement.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/97JB02131
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Acoustic imaging of natural gas seepage in the North Sea: Sensing bubbles under control of variable currents (2010)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 8 . pp. 155-171.
    Details
    Publication Date: 2018-08-15
    Description: Natural seepage from the seafloor is a worldwide phenomenon but quantitative measurements of gas release are rare, and the entire range of the dynamics of gas release in space, time, and strength remains unclear so far. To mitigate this, the hydroacoustic device GasQuant (180 kHz, multibeam) was developed to monitor the tempo-spatial variability of gas bubble releases from the seafloor. GasQuant was deployed in 2005 on the seafloor of the seep field Tommeliten (North Sea) for 36 h. This in situ approach provides much better spatial and temporal resolution of seeps than using conventional ship-born echo sounders. A total of 52 gas vents have been detected. Detailed time series analysis revealed a wide range of gas release patterns ranging from very short periodic up to 50 min long-lasting events. The bulk gas seepage in the studied area is active for more than 70% of observation time. The venting clearly exhibits tidal control showing a peak in the second quarter of the tidal pressure cycle, where pressure drops fastest. The hydroacoustic results are compared with video observations and bubble flux estimates from remotely operated vehicle dives described in the literature. An advanced approach for identifying and visualizing rising bubbles in the sea by hydroacoustics is presented in which water current data were considered. Realizing that bubbles are moved by currents helps to improve the detection of gas bubbles in the data, better discriminate bubbles against fish echoes, and to enhance the S/N ratio in the per se noisy acoustic data.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2010.8.155
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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