An integrated view of the methane system in the pockmarks at Vestnesa Ridge, 79°N

Panieri, Giuliana; Bünz, Stefan; Fornari, Daniel J.; Escartı́n, J.; Serov, Pavel; Jansson, Pär; Torres, Marta E; Johnson, Joel E.; Hong, Wei‐Li; Sauer, Simone; García, Rafael Ortiz; Gracias, Nuno

doi:10.1016/j.margeo.2017.06.006

Cited by 78 publications

(108 citation statements)

References 115 publications

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“…Seafloor pockmarks and gas chimneys along the ridge are linked to faults and fractures (Plaza‐Faverola et al, ; Singhroha et al, ). Considering the suggested presence of thermogenic gas (Panieri et al, ; Plaza‐Faverola et al, ; Smith et al, ) in the study area, the study of fault/fracture systems is even more important as thermogenic gases have deeper origins (often below the GHSZ) and structural features affect the migration pathways of thermogenic gases. Faults at deeper depths in this region can be potential fluid migration pathways for deep sourced warm fluids (Knies et al, ; Dumke et al, ; Waghorn et al, ), whereas faults at the shallower depths within the GHSZ can be migration pathways or can also act as seals, as they can potentially be plugged with gas hydrates (Goswami et al, ; Madrussani et al, ).…”

Section: Study Areamentioning

confidence: 99%

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

et al. 2020

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Joint analysis of electrical resistivity and seismic velocity data is primarily used to detect the presence of gas hydrate‐filled faults and fractures. In this study, we present a novel approach to infer the occurrence of structurally controlled gas hydrate accumulations using azimuthal seismic velocity analysis. We perform this analysis using ocean‐bottom seismic data at two sites on Vestnesa Ridge, W‐Svalbard Margin. Previous geophysical studies inferred the presence of gas hydrates at shallow depths (up to ~190–195 m below the seafloor) in marine sediments of Vestnesa Ridge. We analyze azimuthal P‐wave seismic velocities in relation with steeply dipping near‐surface faults to study structural controls on gas hydrate distribution. This unique analysis documents directional changes in seismic velocities along and across faults. P‐wave velocities are elevated and reduced by ~0.06–0.08 km/s in azimuths where the raypath plane lies along the fault plane in the gas hydrate stability zone (GHSZ) and below the base of the GHSZ, respectively. The resulting velocities can be explained with the presence of gas hydrate‐ and free gas‐filled faults above and below the base of the GHSZ, respectively. Moreover, the occurrence of elevated and reduced (>0.05 km/s) seismic velocities in groups of azimuths bounded by faults suggests compartmentalization of gas hydrates and free gas by fault planes. Results from gas hydrate saturation modeling suggest that these observed changes in seismic velocities with azimuth can be due to gas hydrate saturated faults of thickness greater than 20 cm and considerably smaller than 300 cm.

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Section: Study Areamentioning

confidence: 99%

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

et al. 2020

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“…The widespread presence of a BSR provides evidence for the occurrence of gas hydrate in the Vestnesa Ridge sediments (Bünz et al, ; Hustoft et al, ; Petersen et al, ). Gas hydrates have been directly observed and sampled in several of the pockmarks that occur along the crest of the ridge (Panieri et al, ). The BSR is most pronounced at the crest of the ridge where topographically controlled fluid migration leads to the accumulation of free gas beneath the BSR (Bünz et al, ; Petersen et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…The BSR is most pronounced at the crest of the ridge where topographically controlled fluid migration leads to the accumulation of free gas beneath the BSR (Bünz et al, ; Petersen et al, ). Here we focus on the crest area of the eastern segment of the Vestnesa Ridge that is characterized by many active seepages of gas from pockmarks at the seafloor (Panieri et al, ; Smith et al, ). Different structural features like faults and fractures potentially play an important role in active seepage of methane gas in this area (Plaza‐Faverola et al, ; Singhroha et al, ).…”

Section: Introductionmentioning

confidence: 99%

Constraints on Gas Hydrate Distribution and Morphology in Vestnesa Ridge, Western Svalbard Margin, Using Multicomponent Ocean‐Bottom Seismic Data

2019

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Gas hydrates occur within sediments on the western Svalbard continental margin and the Vestnesa Ridge, a large sediment drift that extends in a west-northwest direction from the margin toward the mid-ocean ridge. We acquired multicomponent ocean-bottom seismic (OBS) data at 10 locations on the crest area of the eastern segment of the Vestnesa Ridge, an area with active gas seepage. P and S wave velocities are estimated using traveltime inversion, and self-consistent approximation/differential effective medium rock physics modeling is used to estimate gas hydrate and free gas saturation at OBS stations. We apply 1-D full waveform inversion at a selected OBS station to study detailed variations of P wave velocity near the bottom simulating reflection (BSR). High interval P wave velocity (Vp ≈ 1.73-1.82 km/s) and S wave velocity (>0.35 km/s) are observed in a layer above the BSR and low interval P wave velocity (Vp ≈ 1.28-1.53 km/s) in a layer below the BSR. We estimate 10-18% gas hydrate and 1.5-4.1% free gas saturation at different OBS stations in a layer above and below the BSR, respectively. We find significant variation in gas hydrate and free gas saturation across faults suggesting a structural control on the distribution of gas hydrate and free gas in the Vestnesa Ridge. Differences in gas hydrate saturation derived from P wave velocities and earlier estimates obtained from electromagnetic surveys indicate the presence of gas hydrates in faults and fractures. Moreover, beneath some OBS sites, the combined study of P and S waves, resistivity and seismic quality factor (Q), suggests the coexistence of free gas and gas hydrates.

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“…CH 4 in sediments may be present as hydrates, free (bubbles) and/or dissolved gas in pore water. CH 4 percolating upward is subject to anaerobic oxidation within the sulfate-methane transition zone (Boetius and Wenzhöfer 2013), but in high-velocity fluid flow systems, both dissolved CH 4 and bubbles can bypass this filter (Luff et al 2004;Panieri et al 2017).…”

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A new numerical model for understanding free and dissolved gas progression toward the atmosphere in aquatic methane seepage systems

Jansson

Férré

Silyakova

et al. 2019

Limnology & Ocean Methods

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We present a marine two‐phase gas model in one dimension (M2PG1) resolving interaction between the free and dissolved gas phases and the gas propagation toward the atmosphere in aquatic environments. The motivation for the model development was to improve the understanding of benthic methane seepage impact on aquatic environments and its effect on atmospheric greenhouse gas composition. Rising, dissolution, and exsolution of a wide size‐range of bubbles comprising several gas species are modeled simultaneously with the evolution of the aqueous gas concentrations. A model sensitivity analysis elucidates the relative importance of process parameterizations and environmental effects on the gas behavior. The parameterization of transfer velocity across bubble rims has the greatest influence on the resulting gas distribution, and bubble sizes are critical for predicting the fate of emitted bubble gas. High salinity increases the rise height of bubbles; whereas temperature does not significantly alter it. Vertical mixing and aerobic oxidation play insignificant roles in environments where advection is important. The model, applied in an Arctic Ocean methane seepage location, showed good agreement with acoustically derived bubble rise heights and in situ sampled methane concentration profiles. Coupled with numerical ocean circulation and biogeochemical models, M2PG1 could predict the impact of benthic methane emissions on the marine environment and the atmosphere on long time scales and large spatial scales. Because of its flexibility, M2PG1 can be applied in a wide variety of environmental settings and future M2PG1 applications may include gas leakage from seafloor installations and bubble injection by wave action.

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An integrated view of the methane system in the pockmarks at Vestnesa Ridge, 79°N

Cited by 78 publications

References 115 publications

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

Constraints on Gas Hydrate Distribution and Morphology in Vestnesa Ridge, Western Svalbard Margin, Using Multicomponent Ocean‐Bottom Seismic Data

A new numerical model for understanding free and dissolved gas progression toward the atmosphere in aquatic methane seepage systems

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