Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico

Pohlman, John W.; Ruppel, Carolyn D.; Hutchinson, Deborah R.; Downer, Ross; Coffin, Richard B.

doi:10.1016/j.marpetgeo.2008.01.016

Cited by 66 publications

(56 citation statements)

References 55 publications

(73 reference statements)

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“…1 filter fitted above a titanium screen, filtered through a 0.2-m-pore-size Gelman polysulfone disposable filter, and subsequently extruded into a precleaned (10% HCl) 50-ml plastic syringe attached to the bottom of the squeezer assembly (41). During PGC0807, pore water for sulfate analysis was extracted by pressure squeezing (ϳ3 bar) and filter sterilized with 0.2-m-pore-size acrodisc polyethersulfone (PES) syringe filters (Pall Corporation) (35).…”

Section: Methodsmentioning

confidence: 99%

Macroscopic Biofilms in Fracture-Dominated Sediment That Anaerobically Oxidize Methane

Briggs

Pohlman

Torres

et al. 2011

Appl Environ Microbiol

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Methane release from seafloor sediments is moderated, in part, by the anaerobic oxidation of methane (AOM) performed by consortia of archaea and bacteria. These consortia occur as isolated cells and aggregates within the sulfate-methane transition (SMT) of diffusion and seep-dominant environments. Here we report on a new SMT setting where the AOM consortium occurs as macroscopic pink to orange biofilms within subseafloor fractures. Biofilm samples recovered from the Indian and northeast Pacific Oceans had a cellular abundance of 10 7 to 10 8 cells cm ؊3 . This cell density is 2 to 3 orders of magnitude greater than that in the surrounding sediments. Sequencing of bacterial 16S rRNA genes indicated that the bacterial component is dominated by Deltaproteobacteria, candidate division WS3, and Chloroflexi, representing 46%, 15%, and 10% of clones, respectively. In addition, major archaeal taxa found in the biofilm were related to the ANME-1 clade, Thermoplasmatales, and Desulfurococcales, representing 73%, 11%, and 10% of archaeal clones, respectively. The sequences of all major taxa were similar to sequences previously reported from cold seep environments. PhyloChip microarray analysis detected all bacterial phyla identified by the clone library plus an additional 44 phyla. However, sequencing detected more archaea than the PhyloChip within the phyla of Methanosarcinales and Desulfurococcales. The stable carbon isotope composition of the biofilm from the SMT (؊35 to ؊43‰) suggests that the production of the biofilm is associated with AOM. These biofilms are a novel, but apparently widespread, aggregation of cells represented by the ANME-1 clade that occur in methane-rich marine sediments.

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Section: Methodsmentioning

confidence: 99%

Macroscopic Biofilms in Fracture-Dominated Sediment That Anaerobically Oxidize Methane

Briggs

Pohlman

Torres

et al. 2011

Appl Environ Microbiol

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“…In summary, AOM in the methane seep area results in alkalinity increase in both pore water and sea water [49,50]. Methane is oxidized to HCO 3 − by SO 4 2− , a process in favor of CO 3 2− accumulation.…”

Section: Authigenic Minerals and Microstructures Of Sedimentsmentioning

confidence: 93%

Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea

et al. 2011

Journal of Geological Research

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Several authigenic minerals were identified by XRD and SEM analyses in shallow sediments from the Southeast Hainan Basin, on the northern slope of South China Sea. These minerals include miscellaneous carbonates, sulphates, and framboidal pyrite, and this mineral assemblage indicates the existence of gas hydrates and a methane seep. The assemblage and fabric features of the minerals are similar to those identified in cold-seep sediments, which are thought to be related to microorganisms fostered by dissolved methane. Chemical composition of pore water shows that the concentrations of SO 2− 4 , Ca 2+ , Mg 2+ , and Sr 2+ decrease clearly, and the ratios of Mg 2+ to Ca 2+ and Sr 2+ to Ca 2+ increase sharply with depth. These geochemical properties are similar to those where gas hydrates occur in the world. All results seem to indicate clearly the presence of gas hydrates or deep water oil (gas) reservoirs underneath the seafloor.

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“…Without an upward DIC flux into the SMT, the d 13 C-DIC minimum observed at the SMT is very low (down to −65‰ [Pohlman et al, 2008]). In these cases, the carbon isotopic signature is dominated by 13 C-depleted methane carbon converted to DIC by AOM.…”

Section: Authigenic Carbonate Formationmentioning

confidence: 95%

“…[49] We recognize that the results presented here are distinct from cases where the DIC concentration below the SMT does not increase so that there is no upward DIC flux [e.g., Kastner et al, 2008b;Pohlman et al, 2008;Ussler and Paull, 2008].…”

Section: Authigenic Carbonate Formationmentioning

confidence: 99%

Modeling sulfate reduction in methane hydrate-bearing continental margin sediments: Does a sulfate-methane transition require anaerobic oxidation of methane?

Malinverno

Pohlman

2011

Geochem. Geophys. Geosyst.

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[1] The sulfate-methane transition (SMT), a biogeochemical zone where sulfate and methane are metabolized, is commonly observed at shallow depths (1-30 mbsf) in methane-bearing marine sediments. Two processes consume sulfate at and above the SMT, anaerobic oxidation of methane (AOM) and organoclastic sulfate reduction (OSR). Differentiating the relative contribution of each process is critical to estimate methane flux into the SMT, which, in turn, is necessary to predict deeper occurrences of gas hydrates in continental margin sediments. To evaluate the relative importance of these two sulfate reduction pathways, we developed a diagenetic model to compute the pore water concentrations of sulfate, methane, and dissolved inorganic carbon (DIC). By separately tracking DIC containing 12 C and 13 C, the model also computes d 13 C-DIC values. The model reproduces common observations from methane-rich sediments: a welldefined SMT with no methane above and no sulfate below and a d 13 C-DIC minimum at the SMT. The model also highlights the role of upward diffusing 13 C-enriched DIC in contributing to the carbon isotope mass balance of DIC. A combination of OSR and AOM, each consuming similar amounts of sulfate, matches observations from Site U1325 (Integrated Ocean Drilling Program Expedition 311, northern Cascadia margin). Without AOM, methane diffuses above the SMT, which contradicts existing field data. The modeling results are generalized with a dimensional analysis to the range of SMT depths and sedimentation rates typical of continental margins. The modeling shows that AOM must be active to establish an SMT wherein methane is quantitatively consumed and the d 13 C-DIC minimum occurs. The presence of an SMT generally requires active AOM.

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Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico

Cited by 66 publications

References 55 publications

Macroscopic Biofilms in Fracture-Dominated Sediment That Anaerobically Oxidize Methane

Macroscopic Biofilms in Fracture-Dominated Sediment That Anaerobically Oxidize Methane

Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea

Modeling sulfate reduction in methane hydrate-bearing continental margin sediments: Does a sulfate-methane transition require anaerobic oxidation of methane?

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