Megaplume bubble process visualization by 3D multibeam sonar mapping

Wilson, Douglas S.; Leifer, Ira; Maillard, E.

doi:10.1016/j.marpetgeo.2015.07.007

Cited by 26 publications

(19 citation statements)

References 33 publications

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“…After nearly stabilizing, atmospheric CH 4 concentrations are increasing again, although the underlying reasons remain poorly understood (Nisbet et al, 2015). Despite likely increasing future natural emissions from global warming feedbacks (Rigby et al, 2008) and anthropogenic activities (Kirschke et al, 2013;Wunch et al, 2009), many source estimates have large uncertainties with greater uncertainty in future trends. This is particularly relevant for Arctic sources where global warming is the strongest (Graversen et al, 2008).…”

Section: Arctic Methanementioning

confidence: 99%

“…Sonar is the most common survey approach and has been used on concentrated seep areas covering ∼ 1000 m 2 in the North Sea (Schneider von Deimling et al, 2007Wilson et al, 2015), far more dispersed and weaker seepage in the Black Sea of ∼ 2500 plumes in an area of ∼ 20 km 2 , and offshore Svalbard where a few hundred plumes were observed in an area of ∼ 15 km 2 (Veloso et al, 2015). Sonar can also be used from remotely operated vehicles for the deep sea, e.g., Muyakshin and Sauter (2010) for the Haakon Mosby mud volcano (3 plumes).…”

Section: Arctic Methanementioning

confidence: 99%

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Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

et al. 2017

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Abstract. Sonar surveys provide an effective mechanism for mapping seabed methane flux emissions, with Arctic submerged permafrost seepage having great potential to significantly affect climate. We created in situ engineered bubble plumes from 40 m depth with fluxes spanning 0.019 to 1.1 L s −1 to derive the in situ calibration curve (Q(σ )). These nonlinear curves related flux (Q) to sonar return (σ ) for a multibeam echosounder (MBES) and a single-beam echosounder (SBES) for a range of depths. The analysis demonstrated significant multiple bubble acoustic scattering -precluding the use of a theoretical approach to derive Q(σ ) from the product of the bubble σ (r) and the bubble size distribution where r is bubble radius. The bubble plume σ occurrence probability distribution function ( (σ )) with respect to Q found (σ ) for weak σ well described by a power law that likely correlated with small-bubble dispersion and was strongly depth dependent. (σ ) for strong σ was largely depth independent, consistent with bubble plume behavior where large bubbles in a plume remain in a focused core.(σ ) was bimodal for all but the weakest plumes. Q(σ ) was applied to sonar observations of natural arctic Laptev Sea seepage after accounting for volumetric change with numerical bubble plume simulations. Simulations addressed different depths and gases between calibration and seep plumes. Total mass fluxes (Q m ) were 5.56, 42.73, and 4.88 mmol s −1 for MBES data with good to reasonable agreement (4-37 %) between the SBES and MBES systems. The seepage flux occurrence probability distribution function ( (Q)) was bimodal, with weak (Q) in each seep area well described by a power law, suggesting primarily minor bubble plumes. The seepage-mapped spatial patterns suggested subsurface geologic control attributing methane fluxes to the current state of subsea permafrost.

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Section: Arctic Methanementioning

confidence: 99%

Section: Arctic Methanementioning

confidence: 99%

Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

et al. 2017

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“…It is suggested that carefully located deep ADCP may be able to resolve a rotation within a plume and could be used to test our suggestion that maintenance of the tight axial shape of the plumes is at least partially due to the formation of a vortex tube. Multibeam sonar data may also be useful for determining some of the plume internal structure and rotation (e.g., von Wilson et al, 2015). Instrumentation specifically set up for volumetric water mass assessment, or a number of AUVs having very sensitive internal navigation would be needed to identify plume morphology and rotation.…”

Section: Discussion and Conceptual Modelmentioning

confidence: 99%

“…Undirected hydrostatic pressures decrease during bubble ascent resulting in gas exsolution and bubble expansion and fragmentation, which in turn results in increased buoyancy, possible expansion of the bubble plume, and changes in the interfacial tension of hydrate-shelled bubbles. Vortex tube generation could explain the consistent relatively slender morphologies associated with plumes seen in multibeam data (Solomon et al, 2009;Colbo et al, 2014;Skarke et al, 2014;Smith et al, 2014;Tudino et al, 2014;Weber et al, 2014;Garcia-Pineda et al, 2015;Wilson et al, 2015) and recent observations indicate that vertical rise of buoyant plumes may be augmented by spiral flow geometries (von Deimling et al, 2015). Because the reflection and scattering from a bubble plume is a bulk effect, rotation has not been observed in seismic reflection data.…”

Section: Axialized Plumes In Vortex Tubesmentioning

confidence: 96%

Submarine vortices derived from natural gas hydrate conversion: a mechanism for ocean mixing

Barnard

Max

Gualdesi³

2017

Medit. Mar. Sci.

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We propose that the source water for some abyssal undular vortices cored by cool, low-salinity water identified at depths in excess of 2,500 m in the deepwater region of the Eastern Mediterranean Basin may be related to conversion of natural gas hydrate (NGH) in abyssal marine sediments. The conditions for extensive formation of NGH in the gas hydrate stability zones (GHSZ) of the upper seafloor sediments existed in this region during previous glacial episodes when colder water supported a thicker GHSZ. Seafloor warming during the most recent interglacial caused thinning of the GHSZ at its base and has driven endothermic NGH dissociation that would have released large volumes of low-salinity water and gas that would tend to pond below the base GHSZ. Periodically, trapped low-salinity water and gas would be released into the sea through the overlying sediments. Buoyant low-salinity water masses, supersaturated with gas and locally containing free gas would ascend and introduce a dynamic element into an otherwise generally static environment. As a result of the interaction of the rise of this buoyant plume and Coriolis acceleration the ascending mass would begin to rotate and form a vortex tube in midwater. NGH conversion within the seafloor introduces large coherent masses of low-salinity, lower-temperature water containing a buoyant free gas fraction from near-surface reservoirs into the abyssal depths even where there may only be a weak natural gas petroleum system.

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“…Currents distort the momentum plume, compressing it in the upstream direction and extending it in the downstream direction (McClimans et al, 2000;Leifer et al, 2009). Detrainment of suspended material from the bubble plume can segregate detritus and upwelled fluids into the downstream momentum plume ) including small, dissolving bubbles (Wilson et al, 2015). As noted, the major difference between the PROVESS and 22/4b sites is the presence of the FIC and the bubble megaplume at the latter location.…”

Section: Bubble Plumes and Vertical Fluid Motionsmentioning

confidence: 90%

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

Nauw

Линке

Leifer

2015

Marine and Petroleum Geology

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The presence of a seasonal thermocline likely plays a key role in restraining methane released from a seabed source in the deeper water column, thereby inhibiting exchange to the atmosphere. The bubble plume itself, however, generates an upward motion of fluid, e.g. upwelling and may thereby be partially responsible for an early breakdown of the seasonal thermocline. Measurements at site 22/4b, located at (57 o 55'N, 1 o 38'E) in the UK Central North Sea, 200 km east of the Scottish mainland, where gas is still being released since a blow out in 1990, have been used to identify the generation of the seasonal thermocline, and thus, the depth of the upper mixed layer and its breakdown in autumn. Data derived from two landers, containing an Acoustic Doppler Current Profiler and a Conductivity Temperature Depth recorder, were used to determine the mixed layer depth and the breakdown of the thermocline. Mixing of upper layer fluid into the lower layer has been inferred from large amplitude variations in the near-bottom temperature. The ADCPs estimate velocity profiles in four beam directions using Doppler shifted frequency from acoustic pings sent out and received by four different transducers in a specific configuration. Besides that, the intensity of the backscattered sound per transducer is also recorded. Bubbles from the nearby plume contaminate the signal during part of the tidal cycle, but in bubble free periods, the mixed layer depth can be estimated using the acoustic backscatter signal as local maxima. Results show that the thermocline broke down between mid-October and early November, several weeks earlier than the breakdown of the thermocline in nearby/comparable areas, likely caused by bubble-induced downwelling at the site. The early breakdown of the thermocline was accompanied by multiple occurrence of a strong jet-like structure, associated with the seasonal tidal mixing front. 2

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Megaplume bubble process visualization by 3D multibeam sonar mapping

Cited by 26 publications

References 33 publications

Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

Submarine vortices derived from natural gas hydrate conversion: a mechanism for ocean mixing

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

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