Methane under-saturated fluids in deep-sea sediments: Implications for gas hydrate stability and rates of dissolution

Lapham, L.; Chanton, Jeffrey P.; Chapman, Ross; Martens, Christopher S.

doi:10.1016/j.epsl.2010.07.016

Cited by 34 publications

(47 citation statements)

References 64 publications

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“…At the MC118 site, gas hydrate bearing sediments have been found at depths greater than 0.5 m ( Fig. 2; Sassen et al, 2006;Lapham et al, 2008;McGee et al, 2009a,b;Lapham et al, 2010) (Davidson et al, 1983), the unusually high δ 18 O values of MC118 carbonates are best explained by gas hydrate decomposition.…”

Section: Gas Hydrate In the Shallow Subsurface: Insights From Oxygen mentioning

confidence: 93%

Time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from Gulf of Mexico Gas Hydrate Seafloor Observatory

et al. 2014

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Section: Gas Hydrate In the Shallow Subsurface: Insights From Oxygen mentioning

confidence: 93%

Time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from Gulf of Mexico Gas Hydrate Seafloor Observatory

et al. 2014

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“…Considering the magnitude of dissolution rates (0.5-30 mm yr 21 ) calculated for buried hydrates surrounded by methane-undersaturated pore water [Lapham et al, 2010], we propose that hydrate dissolution at MVs 2, 4, 5, and 10 was already ongoing for several months at least at the time of our investigation. Very low methane concentrations (<1 lmol L 21 ) in the uppermost sediments demonstrate that methane released during hydrate decomposition is effectively consumed by AOM [Hoehler et al, 1994;Miyazaki et al, 2009] in overlying sediments ( Figure 3).…”

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confidence: 99%

Hydrocarbon seepage and its sources at mud volcanoes of the Kumano forearc basin, Nankai Trough subduction zone

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Hammerschmidt

et al. 2014

Geochem Geophys Geosyst

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Twelve submarine mud volcanoes (MV) in the Kumano forearc basin within the Nankai Trough subduction zone were investigated for hydrocarbon origins and fluid dynamics. Gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from MVs 2, 4, 5, and 10. Molecular ratios (C 1 /C 2 < 250) and stable carbon isotopic compositions (d 13 C-CH 4 >240& V-PDB) indicate that hydratebound hydrocarbons (HCs) at MVs 2, 4, and 10 are derived from thermal cracking of organic matter. Considering thermal gradients at the nearby IODP Sites C0009 and C0002, the likely formation depth of such HCs ranges between 2300 and 4300 m below seafloor (mbsf). With respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of HCs fueling the MVs is derived from sediments of the Cretaceous to Tertiary Shimanto belt below Pliocene/Pleistocene to recent basin sediments. Considering their sizes and appearances hydrates are suggested to be relicts of higher MV activity in the past, although the sporadic presence of vesicomyid clams at MV 2 showed that fluid migration is sufficient to nourish chemosynthesis-based organisms in places. Distributions of dissolved methane at MVs 3, 4, 5, and 8 pointed at fluid supply through one or few MV conduits and effective methane oxidation in the immediate subsurface. The aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane-containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth.

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“…The dissolution of gas hydrates driven by methane undersaturation of the surrounding bottom waters or pore waters has been the subject of several studies (e.g., Egorov et al 1999;Dickens 2001aDickens , 2003Rehder et al 2004;Bigalke et al 2009). Only recently, Lapham et al (2010) presented the first high-resolution in situ methane pore-water profiles of sediments overlying deep-sea gas hydrates of the northern Cascadia margin and the northern Gulf of Mexico. Their measurements revealed that the pore fluids of sediments immediately surrounding the gas hydrate deposits were largely undersaturated with respect to methane concentration in equilibrium with methane gas hydrate, and that AOM accounted for some of this undersaturation.…”

Section: Discussionmentioning

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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Methane under-saturated fluids in deep-sea sediments: Implications for gas hydrate stability and rates of dissolution

Cited by 34 publications

References 64 publications

Time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from Gulf of Mexico Gas Hydrate Seafloor Observatory

Time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from Gulf of Mexico Gas Hydrate Seafloor Observatory

Hydrocarbon seepage and its sources at mud volcanoes of the Kumano forearc basin, Nankai Trough subduction zone

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

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