Gas-controlled seafloor doming

Koch, Stephanie; Berndt, Christian; Bialas, J.; Haeckel, Matthias; Crutchley, Gareth; Papenberg, Cord; Klaeschen, Dirk; Greinert, Jens

doi:10.1130/g36596.1

Cited by 59 publications

(91 citation statements)

References 22 publications

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“…At shallow depth, where the areas of high resistivity and the seismic conduits reach the seafloor, free gas may be prevailing as seafloor doming [ Koch et al , ] and active seafloor venting suggest.…”

Section: Discussionsupporting

confidence: 89%

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Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

et al. 2017

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Marine controlled source electromagnetic (CSEM) data have been collected to investigate methane seep sites and associated gas hydrate deposits at Opouawe Bank on the southern tip of the Hikurangi Margin, New Zealand. The bank is located in about 1000 m water depth within the gas hydrate stability field. The seep sites are characterized by active venting and typical methane seep fauna accompanied with patchy carbonate outcrops at the seafloor. Below the seeps, gas migration pathways reach from below the bottom‐simulating reflector (at around 380 m sediment depth) toward the seafloor, indicating free gas transport into the shallow hydrate stability field. The CSEM data have been acquired with a seafloor‐towed, electric multi‐dipole system measuring the inline component of the electric field. CSEM data from three profiles have been analyzed by using 1‐D and 2‐D inversion techniques. High‐resolution 2‐D and 3‐D multichannel seismic data have been collected in the same area. The electrical resistivity models show several zones of highly anomalous resistivities (>50 Ωm) which correlate with high amplitude reflections located on top of narrow vertical gas conduits, indicating the coexistence of free gas and gas hydrates within the hydrate stability zone. Away from the seeps the CSEM models show normal background resistivities between ~1 and 2 Ωm. Archie's law has been applied to estimate gas/gas hydrate saturations below the seeps. At intermediate depths between 50 and 200 m below seafloor, saturations are between 40 and 80% and gas hydrate may be the dominating pore filling constituent. At shallow depths from 10 m to the seafloor, free gas dominates as seismic data and gas plumes suggest.

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Section: Discussionsupporting

confidence: 89%

“…Analysis of new sediment echo sounder, 2‐D and 3‐D MCS data collected during cruise SO214 of R/V SONNE , provides further evidence of free gas entering the GHSZ [ Koch et al , , ]. 3‐D seismic images show that the gas conduits in fact are narrow elongated fracture systems perpendicular to the ridge axis [ Koch , ].…”

Section: Study Areamentioning

confidence: 99%

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

et al. 2017

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“…years BP (Sejrup et al, ). Furthermore, we observe a gentle shoaling of the Witch Ground Formation toward the class 1 pockmarks while S4.1 slightly dips down (Figure a), which may indicate sediment doming prior to pockmark formation (Barry et al, ; Koch et al, ). We therefore conclude that class 1 pockmarks formation initiated between 13,165 ± 55 and 26,595 ± 387 cal.…”

Section: Discussionmentioning

confidence: 62%

Pockmarks in the Witch Ground Basin, Central North Sea

Böttner

Berndt

Reinardy

et al. 2019

Geochem Geophys Geosyst

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Marine sediments host large amounts of methane (CH4), which is a potent greenhouse gas. Quantitative estimates for methane release from marine sediments are scarce, and a poorly constrained temporal variability leads to large uncertainties in methane emission scenarios. Here, we use 2‐D and 3‐D seismic reflection, multibeam bathymetric, geochemical, and sedimentological data to (I) map and describe pockmarks in the Witch Ground Basin (central North Sea), (II) characterize associated sedimentological and fluid migration structures, and (III) analyze the related methane release. More than 1,500 pockmarks of two distinct morphological classes spread over an area of 225 km2. The two classes form independently from another and are corresponding to at least two different sources of fluids. Class 1 pockmarks are large in size (>6 m deep, >250 m long, and >75 m wide), show active venting, and are located above vertical fluid conduits that hydraulically connect the seafloor with deep methane sources. Class 2 pockmarks, which comprise 99.5% of all pockmarks, are smaller (0.9–3.1 m deep, 26–140 m long, and 14–57 m wide) and are limited to the soft, fine‐grained sediments of the Witch Ground Formation and possibly sourced by compaction‐related dewatering. Buried pockmarks within the Witch Ground Formation document distinct phases of pockmark formation, likely triggered by external forces related to environmental changes after deglaciation. Thus, greenhouse gas emissions from pockmark fields cannot be based on pockmark numbers and present‐day fluxes but require an analysis of the pockmark forming processes through geological time.

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“…Despite the absence of chemoherm carbonates, multibeam [ Greinert et al ., ] and deep‐towed side scan sonar data [ Klaucke et al ., ; Dumke et al ., ] showed increased acoustic backscatter from the seafloor caused by harder sediments possibly due to the inception of carbonate precipitation and/or the occurrence of near‐surface gas hydrate (Figure ). When comparing the shape and size of this increased backscatter with geophysical subbottom profiler data, it becomes clear that the area of increased seafloor backscatter signal correlates with an elliptical gas chimney with dimensions of 400 m along the north‐south axis and 250 m from east to west [ Koch et al ., ] (Figure ).…”

Section: Study Areamentioning

confidence: 99%

A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

Luo

Dale

Haffert

et al. 2016

Geochem Geophys Geosyst

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Takahe seep, located on the Opouawe Bank, Hikurangi Margin, is characterized by a well-defined subsurface seismic chimney structure $80,500 m 2 in area. Subseafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure. Reaction-transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m. Model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas.

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Gas-controlled seafloor doming

Cited by 59 publications

References 22 publications

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

Pockmarks in the Witch Ground Basin, Central North Sea

A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

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