Gas hydrate destabilization: enhanced dewatering, benthic material turnover and large methane plumes at the Cascadia convergent margin

Suess, Erwin; Torres, Marta E; Bohrmann, Gerhard; Collier, Robert W.; Greinert, Jens; Линке, Петер; Rehder, Gregor; Tréhu, Anne M.; Wallmann, Klaus; Winckler, Gisela; Evelyn, Zuleger

doi:10.1016/s0012-821x(99)00092-8

Cited by 400 publications

(338 citation statements)

References 39 publications

Supporting

Mentioning

316

Contrasting

Unclassified

Order By: Relevance

“…The Barkley Canyon hydrates are unique compared with hydrates recovered from shallow (8 m) piston cores at other sites nearby in the northern Cascadia Margin [Riedel et al, 2002], and from Hydrate Ridge farther south off Oregon [Suess et al, 1999], which were of microbial origin.The digital images acquired during the ROPOS survey at Barkley Canyon revealed yellow or brownishyellow streaks in the exposed hydrates ( Figure 2), which are consistent with the presence of light oil in the hydrate.There was no evidence of gas venting from undisturbed sediment or by dissociation of hydrate. However, the sediments released gas bubbles, quantities of light oil, and small hydrate fragments when probed by the ROPOS mechanical arm.…”

Section: September 2004 Pages 361-368mentioning

confidence: 93%

Thermogenic gas hydrates in the northern Cascadia margin

et al. 2004

View full text Add to dashboard Cite

Gas hydrates are ice‐like solids that form in rigid cage structures under specific conditions of pressure, temperature, and gas and water concentration. Marine gas hydrates are stable in pore spaces of sediments in water depths greater than ∼300 m beneath the slopes of active and passive continental margins [Kvenvolden, 1988]. The lower limit of hydrate occurrence in marine sediments is determined by the geothermal gradient, so that the zone of hydrate stability is generally contained within the first few hundred meters of sediment. Continental hydrates occur in polar permafrost regions in the Arctic and Siberia. Most of the hydrates that have been discovered contain methane derived from microbial processes. Other hydrocarbons can also form hydrates, but in different structures of the surrounding water cages. Structure I, the most prevalent form, contains mostly (>99%) microbial methane, a small amount of ethane, and traces of C2+ hydrocarbons [Sassen et al, 2001]. Structure II and structure H hydrates contain significant quantities of thermogenic methane and larger, more complex hydrocarbons formed at high temperatures from fossil organic matter (i.e.,kerogen) or oil [Sassen and MacDonald, 1994].The gas origin is inferred from measurements of the carbon‐13 isotopic ratio (δ13); microbial methane is depleted in 13C (δ13 <−60‰) relative to thermogenic methane (δ13 from −20‰ to −50‰).

show abstract

Section: September 2004 Pages 361-368mentioning

confidence: 93%

Thermogenic gas hydrates in the northern Cascadia margin

et al. 2004

View full text Add to dashboard Cite

show abstract

“…Despite the growing interest in hydrocarbon seep systems, important factors modulating hydrocarbon flux are not well established. For seeps located in deep water and containing dissolved hydrocarbons, important factors include the advective flux of pore fluid through the subsurface (Tryon et al 2002), the formation of gas hydrate in the subsurface (Suess et al 1999), and the efficiency of anaerobic, methane-oxidizing communities (Boetius and Suess 2004). Factors known to impact gas seeps in shallow water include the pressure of the underlying gas reservoir (Quigley et al 1999), blockages or constrictions in fractures and subsequent large "blow-out" events (Leifer et al 2004), and an imprint of tides on seepage rates (Boles et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

et al. 2010

View full text Add to dashboard Cite

The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ∼200 m 2 area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ∼450 moles of CH 4 per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO 2 , which should act to dissolve carbonates. The average δ 13 C of the carbonates was −29.2±2.8‰ VPDB, compared to a range of −1.0 to +7.8‰ for CO 2 in the seep gas, indicating that CO 2 from the seep gas is quantitatively not as important as 13 Cdepleted bicarbonate derived from methane oxidation. Methane, with a δ 13 C of approximately −43‰, is oxidized and the resulting inorganic carbon precipitates as highmagnesium calcite and other carbonate minerals. This finding is supported by 13 C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ 13 C ranged from −84 to −25‰). The inconsistency in δ 13 C between the carbonates and the seeping CO 2 was resolved by discovering pockets of gas trapped near the base of the sediment column with δ 13 C-CO 2 values ranging from −26.9 to −11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment-bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation.

show abstract

“…Hydrate exposures at the sea floor [MacDonald et al, 1994;Suess et al, 1999] are particularly vulnerable to sudden releases, and this has been invoked in association with sea floor slumps [Dillon et al, 1998] and the resulting tsunamis [Hovland, 1999]. Over 1000 kg of hydrate were recently inadvertently recovered in a trawl net [Spence et al, 2001], and brought on board a fishing vessel.…”

Section: Introductionmentioning

confidence: 99%

Measurements of the fate of gas hydrates during transit through the ocean water column

Brewer

Paull

Peltzer

et al. 2002

Geophysical Research Letters

View full text Add to dashboard Cite

[1] We report on controlled experiments to document the fate of naturally occurring methane hydrate released from the sea floor (780 m, 4.3°C) by remotely operated vehicle (ROV) disturbance. Images of buoyant sediment-coated solids rising ($0.24 m/s) from the debris cloud, soon revealed clear crystals of methane hydrate as surficial material sloughed off. Decomposition and visible degassing began close to the predicted phase boundary, yet pieces initially of $0.10 m size easily survived transit to the surface ocean. Smaller pieces dissolved or dissociated before reaching the surface ocean, yet effectively transferred gas to depths where atmospheric ventilation times are short relative to methane oxidation rates.

show abstract

Gas hydrate destabilization: enhanced dewatering, benthic material turnover and large methane plumes at the Cascadia convergent margin

Cited by 400 publications

References 39 publications

Thermogenic gas hydrates in the northern Cascadia margin

Thermogenic gas hydrates in the northern Cascadia margin

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

Measurements of the fate of gas hydrates during transit through the ocean water column

Contact Info

Product

Resources

About