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

Brewer, Peter G.; Paull, C. K.; Peltzer, Edward T.; Ussler, William; Rehder, Gregor; Friederich, Gernot

doi:10.1029/2002gl014727

Cited by 43 publications

(31 citation statements)

References 15 publications

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“…In sandy sediment, the hydrate tends to fill the existing pore structure of the sediment, potentially entraining sufficient sediment to prevent the hydrate/sediment mixture from floating, while in fine-grained sediments, bubble and hydrate grow by fracturing the cohesion of the sediment, resulting in irregular blobs of bubbles (Gardiner et al, 2003;Boudreau et al, 2005) or pure hydrate. Brewer et al (2002) and Paull et al (2003) tried the experiment of stirring surface sediments from Hydrate Ridge using the mechanical arm of a submersible remotely operated vehicle, and found that hydrate did manage to shed its sediment load enough to float. Hydrate pieces of 0.1 m survived a 750 m ascent through the water column.…”

Section: Fate Of Methane Hydrate In the Water Columnmentioning

confidence: 99%

Methane hydrate stability and anthropogenic climate change

2007

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Abstract. Methane frozen into hydrate makes up a large reservoir of potentially volatile carbon below the sea floor and associated with permafrost soils. This reservoir intuitively seems precarious, because hydrate ice floats in water, and melts at Earth surface conditions. The hydrate reservoir is so large that if 10% of the methane were released to the atmosphere within a few years, it would have an impact on the Earth's radiation budget equivalent to a factor of 10 increase in atmospheric CO 2 .Hydrates are releasing methane to the atmosphere today in response to anthropogenic warming, for example along the Arctic coastline of Siberia. However most of the hydrates are located at depths in soils and ocean sediments where anthropogenic warming and any possible methane release will take place over time scales of millennia. Individual catastrophic releases like landslides and pockmark explosions are too small to reach a sizable fraction of the hydrates. The carbon isotopic excursion at the end of the Paleocene has been interpreted as the release of thousands of Gton C, possibly from hydrates, but the time scale of the release appears to have been thousands of years, chronic rather than catastrophic.The potential climate impact in the coming century from hydrate methane release is speculative but could be comparable to climate feedbacks from the terrestrial biosphere and from peat, significant but not catastrophic. On geologic timescales, it is conceivable that hydrates could release as much carbon to the atmosphere/ocean system as we do by fossil fuel combustion.

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Section: Fate Of Methane Hydrate In the Water Columnmentioning

confidence: 99%

Methane hydrate stability and anthropogenic climate change

2007

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“…Changi ng processes can be observed in realtime, and both qualitative and qu antitati v e data can be obtained. The novel in situ spectroscopic tech niques we have devised will enhance m any CO 2 and gas hydrate studies (e.g., Brewer et al, 2002a;Brewer et al, 2002b;Rehder et al, 2002;Rehd er et al, 200 4), and can be extended to a v ery wide r ange of o cean science, inclu ding hydroth ermal vent studies.…”

Section: Comparison With Raman Measurementsmentioning

confidence: 99%

Determination of gas bubble fractionation rates in the deep ocean by laser Raman spectroscopy

2006

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A new d eep-sea l aser Ram an spectrom eter (DORISS -Deep Ocean Raman In Situ Spectromet er) is used to ob serv e the preferenti al dissoluti on of CO 2 into seawater from a 50%-50% CO 2 -N 2 gas mi xture in a set of experimen ts that test a proposed met hod of CO 2 sequestrati on i n the deep ocean. In a fir st set of experiments performed at 300 m depth, an open-bott omed 1000 cm 3 cube was used to contai n the gas mixture; and in a second set of experiment s a 2.5 cm 3 funnel was used t o hold a bubbl e of t he gas mixtur e in front of the sampli ng optic. By ob servi ng th e ch anging ratios of the CO 2 and N 2 Raman bands we were abl e to determi ne the g as flux and the mass tran sfer co efficient at 300 m depth and com pare th em to t heoreti cal calcul ations for air-sea gas ex change. Although each exp eriment had a differ ent config uration, comparable result s were obt ained. As expected, th e ratio of CO 2 to N 2 drops off at an expon ential rate as CO 2 i s preferen tially di ssolved i n seawater. In fitting th e dat a with theoretical gas flux calculation s, the boundary layer thick ness was det ermined t o be ~42 µm for the gas cube, and ~165 µm for the gas funnel reflecting different boundary l ayer t urbulence. The mass tran sfer co efficient s for CO 2 are k L = 2.82 x 10 -5 m/s for the gas cube experiment, and k L = 7.98 x 10 -6 m/s for the gas funnel experim ent.

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“…where J Ba 2+ is the diffusive flux of Ba 2+ , ϕ the porosity, D sed the tortuosity-and temperature-corrected diffusion coefficient of Ba 2+ in the sediment, calculated from the diffusion coefficient in free solution (D 0 ) of 147.6 cm 2 year -1 (5°C) after Boudreau (1997), and dC/ dx is the concentration gradient of Ba 2+ in pore water. As it is not possible to determine past changes in the upward Ba 2+ gradient, the present-day Ba 2+ gradients recorded at the two sites were used.…”

Section: Calculation Of Barite Precipitation Timementioning

confidence: 99%

“…The mass and distribution of hydrates can change over time when variations in pressure, temperature, and salinity (PTS), as well as in the methane saturation state of the surrounding fluids and in methane fluxes occur. The decomposition of gas hydrates induced by changes in PTS is referred to as dissociation (e.g., Brewer et al 2002); the decomposition of gas hydrates due to methane undersaturation is termed dissolution (e.g., Egorov et al 1999;Rehder et al 2004;Bigalke et al 2009;Lapham et al 2010). Methane undersaturation in marine sediments can be produced through the sulfatedependent anaerobic oxidation of methane (AOM; Lapham et al 2010), which was shown to typically occur above and within gas hydrate-bearing sediments (e.g., Borowski et al 1996Borowski et al , 1999Bohrmann et al 1998;Boetius et al 2000;Dickens 2001b;Treude et al 2003;Orcutt et al 2004;Snyder et al 2007a, b).…”

Section: Introductionmentioning

confidence: 99%

Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan

et al. 2012

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The geochemical cycling of barium was investigated in sediments of pockmarks of the northern Congo Fan, characterized by surface and subsurface gas hydrates, chemosynthetic fauna, and authigenic carbonates. Two gravity cores retrieved from the so-called Hydrate Hole and Worm Hole pockmarks were examined using high-resolution pore-water and solid-phase analyses. The results indicate that, although gas hydrates in the study area are stable with respect to pressure and temperature, they are and have been subject to dissolution due to methane-undersaturated pore waters. The process significantly driving dissolution is the anaerobic oxidation of methane (AOM) above the shallowest hydrate-bearing sediment layer. It is suggested that episodic seep events temporarily increase the upward flux of methane, and induce hydrate formation close to the sediment surface. AOM establishes at a sediment depth where the upward flux of methane from the uppermost hydrate layer counterbalances the downward flux of seawater sulfate. After seepage ceases, AOM continues to consume methane at the sulfate/methane transition (SMT) above the hydrates, thereby driving the progressive dissolution of the hydrates "from above". As a result the SMT migrates downward, leaving behind enrichments of authigenic barite and carbonates that typically precipitate at this biogeochemical reaction front. Calculation of the time needed to produce the observed solid-phase barium enrichments above the present-day depths of the SMT served to track the net downward migration of the SMT and to estimate the total time of hydrate dissolution in the recovered sediments. Methane fluxes were higher, and the SMT was located closer to the sediment surface in the past at both sites. Active seepage and hydrate formation are inferred to have occurred only a few thousands of years ago at the Hydrate Hole site. By contrast, AOM-driven hydrate dissolution as a consequence of an overall net decrease in upward methane flux seems to have persisted for a considerably longer time at the Worm Hole site, amounting to a few tens of thousands of years.

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

Cited by 43 publications

References 15 publications

Methane hydrate stability and anthropogenic climate change

Methane hydrate stability and anthropogenic climate change

Determination of gas bubble fractionation rates in the deep ocean by laser Raman spectroscopy

Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan

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