Dissolved hydrocarbon flux from natural marine seeps to the southern California Bight

Clark, J. M.; Washburn, Libe; Hornafius, J. Scott; Luyendyk, Bruce P.

doi:10.1029/2000jc000259

Cited by 84 publications

(63 citation statements)

References 35 publications

(13 reference statements)

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“…While it appears that in the former case the plume of dissolved methane was more uniform, in the latter one this was not the case. Heterogeneity in the near-field dissolved methane plume has been observed earlier (Clark et al, 2000), although at distances larger than the ones in our case, and hence on the second station measurements might have been influenced either by changing currents or the ship's drifting around the anchor, or both.…”

Section: Resultssupporting

confidence: 58%

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Effects of methane outgassing on the Black Sea atmosphere

et al. 2006

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Abstract. Methane in air and seawater was measured in the Eastern Black Sea during the 10-18 December 1999 BIGBLACK project cruise. The measurements allowed for the calculation of supersaturation ratios and methane fluxes across the air-sea interface. CH 4 mixing ratios in air were generally in the 1.8-2.0 ppmv range, while surface (4 m depth) seawater concentrations varied from 4 to 93 ppmv. Above active seep areas, the water was supersaturated to around 500% with respect to the overlying atmosphere. Accordingly, flux densities varied greatly and were up to 3300 umol m −2 day −1 . In the Sevastopol harbour, supersaturations up to around 3000%, similar to those at the Danube Delta, were observed, while in the Istanbul harbour supersaturations could not be determined because the very high values of water concentrations led to detector saturation. Simple modelling shows that the observed fluxes do not have any substantial impact on the methane content of the Black Sea atmosphere, as they would only raise its concentrations by less than 50 ppt. On the other hand, calculations performed as part of the CRIMEA project show that mud volcano eruptions could episodically raise the methane concentrations well above their regional background for several tens of kilometres downwind. These calculations, which also apply to mud volcano eruptions elsewhere on the globe, indicate that the spatial extend and the magnitude of the atmospheric perturbation is such that its observation might lie within the capabilities of existing satellite instrumentation such as SCIAMACHY on ENVISAT.

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Section: Resultssupporting

confidence: 58%

“…Underwater seepages have been investigated by many authors in various parts of the world (e.g. Judd et al, 1997;Hornafius et al, 1999;Clark et al, 2000;Klusman et al, 2000), and have been found to result in elevated methane concentrations in the surface waters overlying these seeps (e.g. Cynar and Yayanos, 1992;Ward, 1992).…”

Section: Introductionmentioning

confidence: 99%

Effects of methane outgassing on the Black Sea atmosphere

et al. 2006

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“…In the shallow Coal Oil Point seep field, most of the CH 4 reaches the atmosphere directly (Clark et al, 2005) from mixing in the near field (Clark et al, 2000) and in the far (down-current) field when winds strengthen as typically occurs diurnally for coastal California. The same is true for the shallow ESAS where virtually all seabed CH 4 (dissolved and gaseous) is emitted in the WWML and escapes to the atmosphere directly by bubbles or through air-sea gas exchange by frequent storms (Shakhova et al, 2014).…”

Section: Marine Seepage Fate and Bubble Processesmentioning

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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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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“…Mean seep gas composition is 87.5% methane, 5.1% ethane, 3.1% propane and 1.3% carbon dioxide along with trace gases of heavier hydrocarbons and hydrogen sulfide (Clark et al, 2000). Some emission sites are constant, others eruptive.…”

Section: Study Sitementioning

confidence: 99%