Impact of anaerobic oxidation of methane on the geochemical cycle of redox-sensitive elements at cold-seep sites of the northern South China Sea

Hu, Yu; Dong, Feng; Liang, Qianyong; Xia, Zhen; Chen, Linying; Chen, Duofu

doi:10.1016/j.dsr2.2015.06.012

Cited by 86 publications

(52 citation statements)

References 79 publications

(116 reference statements)

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“…Previous studies have used geochemical indicators, such as the concentration of sulfate [SO , and the carbon isotopic composition of dissolved inorganic carbon (δ 13 C-DIC) and dissolved organic carbon (δ 13 C-DOC) to attribute the source of CH 4 in groundwater (Valentine and Reeburgh, 2000;Kotelnikova, 2002;Antler, 2014;Green-Saxena et al, 2014;Antler et al, 2015;Hu et al, 2015;Segarra et al, 2015;Sela-Adler et al, 2015;Currell et al, 2016). Other studies have shown that the presence of active methanogenesis can be determined using isotopes of hydrogen in the CH 4 (δ 2 H-CH 4 ) and the surrounding formation water (δ 2 H-H 2 O) (Schoell, 1980;Whiticar and Faber, 1986;Whiticar, 1999;Currell et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures

et al. 2017

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Abstract. Geochemical and microbiological indicators of methane (CH 4 ) production, oxidation and migration processes in groundwater are important to understand when attributing sources of gas. The processes controlling the natural occurrence of CH 4 in groundwater must be understood, especially when considering the potential impacts of the global expansion of coal seam gas (CSG) production on groundwater quality and quantity. We use geochemical and microbiological data, along with measurements of CH 4 isotopic composition (δ 13 C-CH 4 ), to determine the processes acting upon CH 4 in a freshwater alluvial aquifer that directly overlies coal measures targeted for CSG production in Australia. Measurements of CH 4 indicate that there is biogenic CH 4 in the aquifer; however, microbial data indicate that there are no methanogenic archaea in the groundwater. In addition, geochemical data, particularly the isotopes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), as well as the concentration of SO 2− 4 , indicate limited potential for methanogenesis in situ. Microbial community analysis also shows that aerobic oxidation of CH 4 occurs in the alluvial aquifer. The combination of microbiological and geochemical indicators suggests that the most likely source of CH 4 , where it was present in the freshwater aquifer, is the upward migration of CH 4 from the underlying coal measures.

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Section: Introductionmentioning

confidence: 99%

Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures

et al. 2017

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“…That is, concentrations of successive samples do not display a high degree of scatter. This is expected for pore water profiles in sediment where diffusion dominates (Froelich et al, 1979;Klump and Martens, 1981;Schulz, 2000;Torres and Kastner, 2009;Hu et al, 2015). However, for some dissolved species whose concentrations do not appreciably change over depth (e.g., Ba 2+ and Ca 2+ ), scatter exists beyond that predicted from analytical precision.…”

Section: General Observationsmentioning

confidence: 85%

“…Nonetheless, it is possible that local CH 4 venting, perhaps related to and mediated by bubble transport, could occur away from transects and cores of SWERUS Leg 2. Certainly, the chemistry of advecting fluids toward seafloor features such as mud volcanoes and cold seeps typically differs from the much broader surrounding region (Luff and Wallmann, 2003;Coffin et al, 2007;Hiruta et al, 2009;Hu et al, 2010;Coffin et al, 2014;Hu et al, 2015). However, in such cases, even the encompassing area typically has shallow SMTs.…”

Section: Signatures Of Aom and Osrmentioning

confidence: 99%

“…Some authors have used changes in DIC and SO 2− 4 concentrations between the seafloor and the SMT to infer the relative importance of AOM and OSR in marine sediments (Kastner et al, 2008b;Luo et al, 2013;Hu et al, 2015). This idea can be expressed by comparing (DIC+Ca 2+ +Mg 2+ ) and SO 2− Figure 9.…”

Section: Signatures Of Aom and Osrmentioning

confidence: 99%

“…3). Good examples include the Baltic Sea (Jørgensen et al, 1990), Black Sea , Blake Ridge Borowski et al, 2001), Cariaco Trench (Reeburgh, 1976), Cascadia margin (Torres and Kastner, 2009), Gulf of Mexico (Kastner et al, 2008a;Hu et al, 2010;Smith and Coffin, 2014), Hydrate Ridge (Claypool et al, 2006), offshore Namibia (Niewohner et al, 1998), offshore Peru (Donohue et al, 2006), South China Sea (Luo et al, 2013;Hu et al, 2015), and Sea of Japan (Expedition Scientists, 2014). Moreover, in regions dominated by diffusion, fluxes of dissolved CH 4 can be estimated using Eq.…”

Section: Pore Water Chemistry Above Methane-charged Sedimentmentioning

confidence: 99%

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Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations

et al. 2017

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Abstract. Continental slopes north of the East Siberian Sea potentially hold large amounts of methane (CH 4 ) in sediments as gas hydrate and free gas. Although release of this CH 4 to the ocean and atmosphere has become a topic of discussion, the region remains sparingly explored. Here we present pore water chemistry results from 32 sediment cores taken during Leg 2 of the 2014 joint Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) expedition. The cores come from depth transects across the slope and rise extending between the Mendeleev and the Lomonosov ridges, north of Wrangel Island and the New Siberian Islands, respectively. Upward CH 4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO 2− 4 ), alkalinity, and the δ 13 C of dissolved inorganic carbon (DIC), is negligible at all stations east of 143 • E longitude. In the upper 8 m of these cores, downward SO 2− 4 flux never exceeds 6.2 mol m −2 kyr −1 , the upward alkalinity flux never exceeds 6.8 mol m −2 kyr −1 , and δ 13 C composition of DIC (δ 13 C-DIC) only moderately decreases with depth (−3.6 ‰ m −1 on average). Moreover, upon addition of Zn acetate to pore water samples, ZnS did not precipitate, indicating a lack of dissolved H 2 S. Phosphate, ammonium, and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment and supports very low organic carbon turnover rates. A single core on the Lomonosov Ridge differs, as diffusive fluxes for SO 2− 4 and alkalinity were 13.9 and 11.3 mol m −2 kyr −1 , respectively, the δ 13 C-DIC gradient was 5.6 ‰ m −1 , and Mn 2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that abundant CH 4 , including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based on assumption.

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In Situ Raman Detection of Gas Hydrates Exposed on the Seafloor of the South China Sea

Zhang

Luan

et al. 2017

Geochem Geophys Geosyst

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Gas hydrates are usually buried in sediments. Here we report the first discovery of gas hydrates exposed on the seafloor of the South China Sea. The in situ chemical compositions and cage structures of these hydrates were measured at the depth of 1,130 m below sea level using a Raman insertion probe (RiP‐Gh) that was carried and controlled by a remotely operated vehicle (ROV) Faxian. This in situ analytical technique can avoid the physical and chemical changes associated with the transport of samples from the deep sea to the surface. Natural gas hydrate samples were analyzed at two sites. The in situ spectra suggest that the newly formed hydrate was Structure I but contains a small amount of C3H8 and H2S. Pure gas spectra of CH4, C3H8, and H2S were also observed at the SCS‐SGH02 site. These data represent the first in situ proof that free gas can be trapped within the hydrate fabric during rapid hydrate formation. We provide the first in situ confirmation of the hydrate growth model for the early stages of formation of crystalline hydrates in a methane‐rich seafloor environment. Our work demonstrates that natural hydrate deposits, particularly those in the early stages of formation, are not monolithic single structures but instead exhibit significant small‐scale heterogeneities due to inclusions of free gas and the surrounding seawater, there inclusions also serve as indicators of the likely hydrate formation mechanism. These data also reinforce the importance of correlating visual and in situ measurements when characterizing a sampling site.

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Impact of anaerobic oxidation of methane on the geochemical cycle of redox-sensitive elements at cold-seep sites of the northern South China Sea

Cited by 86 publications

References 79 publications

Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures

Biogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures

Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations

In Situ Raman Detection of Gas Hydrates Exposed on the Seafloor of the South China Sea

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