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Leifer I.,Bubbleology Research International | Leifer I.,University of California at Santa Barbara
Marine and Petroleum Geology | Year: 2015

A new approach to estimating seabed bubble emissions was applied to a ROV video survey of the 22/4b blowout crater in the UK North Sea. Video was analyzed to identify and classify bubble plumes and other seabed features. Plume occurrence then was gridded into quadrats and the total number of plumes in the crater's active portion estimated. Almost all of the seepage in the 40 × 45 m crater was localized within a 20 by 18-m ellipse. All five major plumes in this ellipse were measured by direct capture with mean emission of 1.34 L s-1 at 12 bar (range 0.54-3.5 L s-1). The primary source of variability (71%) was temporal, demonstrated by repeat measurements of a single vent. Overall, temporal variability was consistent with highly fluid migration through a thick, near-seabed, coarse-grained sediment bed underlying the 22/4b crater seabed. Occurrence data were converted to flux based on direct capture measurements, survey video, and laboratory experiments where video was collected of bubble plumes of known flow for comparison with field video. The derived best-estimate, total seabed emission flux was 90 L s-1 with an estimated uncertainty of 50%, within a scenario uncertainty range of 50-142 L s-1. This is equivalent to 100 million L dy-1 at Standard Temperature and Pressure or an annualized 25 kton. However, long-term monitoring data showing large temporal variability suggests extrapolation to an annual basis is inappropriate. © 2015 Elsevier Ltd.

Warzinski R.P.,U.S. National Energy Technology Laboratory | Lynn R.,URS Corporation | Haljasmaa I.,URS Corporation | Leifer I.,Bubbleology Research International | And 4 more authors.
Geophysical Research Letters | Year: 2014

Predicting the fate of subsea hydrocarbon gases escaping into seawater is complicated by potential formation of hydrate on rising bubbles that can enhance their survival in the water column, allowing gas to reach shallower depths and the atmosphere. The precise nature and influence of hydrate coatings on bubble hydrodynamics and dissolution is largely unknown. Here we present high-definition, experimental observations of complex surficial mechanisms governing methane bubble hydrate formation and dissociation during transit of a simulated oceanic water column that reveal a temporal progression of deep-sea controlling mechanisms. Synergistic feedbacks between bubble hydrodynamics, hydrate morphology, and coverage characteristics were discovered. Morphological changes on the bubble surface appear analogous to macroscale, sea ice processes, presenting new mechanistic insights. An inverse linear relationship between hydrate coverage and bubble dissolution rate is indicated. Understanding and incorporating these phenomena into bubble and bubble plume models will be necessary to accurately predict global greenhouse gas budgets for warming ocean scenarios and hydrocarbon transport from anthropogenic or natural deep-sea eruptions. Key Points Complex surface mechanisms govern hydrate formation and dissociation on bubblesSurface hydrate morphology and coverage characteristics linked to hydrodynamicsNew mechanistic insights may have important implications for bubble plume models ©2014. American Geophysical Union. All Rights Reserved.

Leifer I.,Bubbleology Research International | Judd A.,Alan Judd Partnership
Marine and Petroleum Geology | Year: 2015

The 22/4b blowout occurred in the UK sector of the North Sea in November 1990, but during a survey in September 2011 strong gas emissions still were occurring. This manuscript summarizes the findings of the 2011 survey and subsequent studies, considering them in the context of previous investigations, and the regional geologic and oceanographic environments.The seabed crater formed during the initial event is still there, as is a previously-undiscovered secondary crater. Seabed bubble flux estimates indicate methane emission rates of 90 L s-1 at the time; however, this methane's fate(s) remains unclear. The very strong thermocline that persists for more than half the year acts as an effective barrier to upward migration, despite the presence of strong upwelling flows around the bubble plume. Clearly a large proportion of the methane is advected away from the site to be either oxidized microbially in the water column, or released to the atmosphere as a result of normal sea:air gas exchange processes. Nevertheless, a significant atmospheric methane anomaly persists in the vicinity of the blowout site. This has been constrained to likely less than 0.72 Mscfd (5 kTon yr-1) and possibly less than 0.36 Mscfd (2.5 kton yr-1).During the late-fall to early spring months (when there is no thermocline), direct methane emissions to the atmosphere are expected to increase significantly. Also, long-term monitoring has shown that periodic eruptive events occur, which likely expel great quantities of methane. These demonstrate the dynamic nature of the system and suggest that migration pathways in and between the deep sub-seabed and seabed remain active.The 22/4b Study resulted in the development and adaptation of novel techniques that are applicable to other studies of seabed seepage and the development of a number of critical hypotheses with application to megaplume seepage by natural migration pathways or from the result of anthropogenic intervention. © 2015 Elsevier Ltd.

Shakhova N.,University of Alaska Fairbanks | Shakhova N.,Russian Academy of Sciences | Semiletov I.,University of Alaska Fairbanks | Semiletov I.,Russian Academy of Sciences | And 10 more authors.
Nature Geoscience | Year: 2014

Vast quantities of carbon are stored in shallow Arctic reservoirs, such as submarine and terrestrial permafrost. Submarine permafrost on the East Siberian Arctic Shelf started warming in the early Holocene, several thousand years ago. However, the present state of the permafrost in this region is uncertain. Here, we present data on the temperature of submarine permafrost on the East Siberian Arctic Shelf using measurements collected from a sediment core, together with sonar-derived observations of bubble flux and measurements of seawater methane levels taken from the same region. The temperature of the sediment core ranged from-1.8 to 0C. Although the surface layer exhibited the lowest temperatures, it was entirely unfrozen, owing to significant concentrations of salt. On the basis of the sonar data, we estimate that bubbles escaping the partially thawed permafrost inject 100-630 mg methane m-2 d-1 into the overlying water column. We further show that water-column methane levels had dropped significantly following the passage of two storms. We suggest that significant quantities of methane are escaping the East Siberian Shelf as a result of the degradation of submarine permafrost over thousands of years. We suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere, respectively. © 2014 Macmillan Publishers Limited.

Tratt D.M.,The Aerospace Corporation | Buckland K.N.,The Aerospace Corporation | Hall J.L.,The Aerospace Corporation | Johnson P.D.,The Aerospace Corporation | And 6 more authors.
Remote Sensing of Environment | Year: 2014

Airborne thermal-infrared (TIR) imaging spectrometry techniques have been used to detect and track methane and other gaseous emissions from a variety of discrete sources in diverse environmental settings, and to enable estimation of the strength of each plume. The high spatial resolution (1-2m) permits attribution of chemical plumes to their source, while the moderate spectral resolution (44nm across the 7.5-13.5μm TIR band) enables identification and quantification of the gaseous plume constituents, even when one is present in considerably greater concentration than the others. Raw imagery was quantitatively analyzed using matched filtering and adaptive coherence techniques. Experiments under controlled conditions demonstrated successful detection of methane point sources at release rates as low as 2.2kg/h (~1dm3/s at NTP). © 2014 Elsevier Inc.

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