Planktonic and sediment-associated aerobic methanotrophs in two seep systems along the North American margin

Methane vents are of significant geochemical and ecological importance. Notable progress has been made towards understanding anaerobic methane oxidation in marine sediments, however, the diversity and distribution of aerobic methanotrophs in the water column are poorly characterized. Both environments play an essential role in regulating methane release from the oceans to the atmosphere. In this study, the diversity of particulate methane monooxygenase (pmoA) and 16S rRNA genes from two methane vent environments along the California continental margin was characterized. The pmoA phylotypes recovered from methane-rich sediments and the overlying water column differed. Sediments harbored the greatest number of unique pmoA phylotypes broadly affiliated with the Methylococcaceae family, whereas planktonic pmoA phylotypes formed three clades that were distinct from the sediment-hosted methanotrophs, and distantly related to established methanotrophic clades. Water-column associated phylotypes were highly similar between field sites, suggesting that planktonic methanotroph diversity is controlled primarily by environmental factors rather than geographical proximity. Analysis of 16S rRNA genes from methane-rich waters did not readily recover known methanotrophic lineages, with only a few phylotypes demonstrating distant relatedness to Methylococcus. The development of new pmo primers increased the recovery of monooxygenase genes from the water column and led to the discovery of a highly diverged monooxygenase sequence which is phylogenetically intermediate to Amo and pMMO. This sequence potentiates insight into the amo/pmo superfamily. Together, these findings lend perspective into the diversity and segregation of aerobic methanotrophs within different methane-rich habitats in the marine environment

Data management study. Appendix M - Contractor data requirements safety /SA/ FINAL report

Contractor data requirements to insure safety of personnel, facilities, and equipment of Voyager operation

Marine pore-water sulfate profiles indicate in situ methane flux from underlying gas hydrate

Marine pore-water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the Carolina Rise and Blake Ridge (U.S. Atlantic continental margin). Here, sulfate gradients are linear, implying that sulfate depletion is driven by methane flux from below, rather than by the flux of sedimentary organic matter from above. Thus, these linear sulfate gradients can be used to quantify and assess in situ methane flux, which is a function of the methane inventory below

New technique detects gas hydrates

As exploration and development moves into deep waters, the possibility of encountering gas hydrates within seafloor sediments becomes increasingly likely. The ability to accurately detect gas hydrates is key to producing deepwater fields, allowing operators to safely design and place offshore drilling and production platforms, subsea production equipment and flow lines, as well as pipelines

Bromeliad Catchments as Habitats for Methanogenesis in Tropical Rainforest Canopies

Tropical epiphytic plants within the family Bromeliaceae are unusual in that they possess foliage capable of retaining water and impounded material. This creates an acidic (pH 3.5–6.5) and anaerobic (<1 ppm O2) environment suspended in the canopy. Results from a Costa Rican rainforest show that most bromeliads (n = 75/86) greater than ~20 cm in plant height or ~4–5 cm tank depth, showed presence of methanogens within the lower anoxic horizon of the tank. Archaea were dominated by methanogens (77–90% of recovered ribotypes) and community structure, although variable, was generally comprised of a single type, closely related to either hydrogenotrophic Methanoregula or Methanocella, a specific clade of aceticlastic Methanosaeta, or Methanosarcina. Juvenile bromeliads, or those species, such as Guzmania, with shallow tanks, generally did not possess methanogens, as assayed by polymerase chain reaction specific for methanogen 16S rRNA genes, nor did artificial catchments (~100 ml volume), in place 6–12 months prior to sample collection. Methanogens were not detected in soil (n = 20), except in one case, in which the dominant ribotype was different from nearby bromeliads. Recovery of methyl coenzyme M reductase genes supported the occurrence of hydrogenotrophic and aceticlastic methanogens within bromeliad tanks, as well as the trend, via QPCR analysis of mcrA, of increased methanogenic capacity with increased plant height. Methane production rates of up to 300 nmol CH4 ml tank water−1 day−1 were measured in microcosm experiments. These results suggest that bromeliad-associated archaeal communities may play an important role in the cycling of carbon in neotropical forests

Sulfide mineralization in deep-water marine sediments related to methane transport, methane consumption, and methane gas hydrates

Patterns of sulfide sulfur concentration and sulfur isotopic composition (d34S) are perhaps related to upward methane transport, especially in sediments underlain by methane gas hydrate deposits. Increased methane delivery augments the affect of anaerobic methane oxidation (AMO) occurring at the sulfate-methane interface (SMI). Sulfate and methane co-consumption results in production of dissolved sulfide at the interface that is eventually sequestered within sulfide minerals (elemental sulfur, iron monosulfide, pyrite). We examine the sediments of two piston cores collected over the Blake Ridge gas hydrate deposits (offshore southeastern North America) by extracting total sedimentary sulfide using chromium reduction. We use an improved titration procedure to assay for sulfide sulfur concentration that involves addition of an excess amount of potassium iodate/potassium iodide (KIO3/KI) solution in order to completely oxidize dissolved sulfide to elemental sulfur. The remaining iodine ions are then back-titrated with sodium thiosulfate solution, avoiding leakage of hydrogen sulfide gas, thus increasing measurement accuracy. Our results show that authigenic sulfide sulfur generally increases in concentration downcore from ~0.05 to peak concentrations approaching 0.4 weight per cent sulfur. These results are consistent with localized sulfide production at the SMI and rapid sulfide mineral formation there. We will further test the hypothesis by examining d34S values of authigenic sulfide minerals, expecting to see enrichments in d34S near the interface. Discrete horizons showing sulfide mineralization with 34S enrichments potentially record periods of increased methane flux, highlighting an increased role for AMO as a biogeochemical process and perhaps identifying existence of underlying gas hydrates

Sulfide mineralization in deep-water marine sediments related to methane transport, methane consumption, and methane gas hydrates

Patterns of sulfide sulfur concentration and sulfur isotopic composition (d34 S) are perhaps related to upward methane transport, especially in sediments underlain by methane gas hydrate deposits. Increased methane delivery augments the effect of anaerobic methane oxidation (AMO) occurring at the sulfate-methane interface (SMI). Sulfate and methane co-consumption results in production of dissolved sulfide at the interface that is eventually sequestered within sulfide minerals (elemental sulfur, iron monosulfide, pyrite). We examine the sediments of two piston cores collected over the Blake Ridge gas hydrate deposits (offshore southeastern United States) by extracting total sedimentary sulfide using chromium reduction. We use an improved titration procedure to assay for sulfide sulfur concentration that involves addition of an excess amount of potassium iodate/potassium iodide (KIO3/KI) solution in order to completely oxidize dissolved sulfide to elemental sulfur. The remaining iodine ions are then back-titrated with sodium thiosulfate solution, avoiding leakage of hydrogen sulfide gas, thus increasing measurement accuracy. Our results show that authigenic sulfide sulfur generally increases in concentration downcore from ~0.05 to peak concentrations approaching 0.4 weight per cent sulfur (dry weight). These results are consistent with localized sulfide production at the SMI and rapid sulfide mineral formation there. We will further test the hypothesis by examining d34 S values of authigenic sulfide minerals, expecting to see enrichments in d34 S near the interface. Discrete horizons showing sulfide mineralization with 34S enrichments potentially record periods of increased methane flux, highlighting an increased role for AMO as a biogeochemical process and perhaps identifying existence of underlying gas hydrates

Are 34S-enriched Authigenic Sulfide Minerals a Proxy for Elevated Methane Flux and Gas Hydrates in the Geologic Record?

The sulfate–methane transition (SMT) zone is a diagenetic transition within anoxic marine sediments created by the metabolic activity of a consortium of sulfate-reducing bacteria and methane-oxidizing Archaea. As interstitial dissolved sulfate is consumed by microbially mediated sulfate reduction of sedimentary organic matter (SOM) and anaerobic oxidation of methane (AOM) large enrichments of 34S occur in the interstitial sulfate pool. These isotopic enrichments are transmitted to the dissolved sulfide pool (∑HS−) and subsequently into sulfide minerals (So, ∼FeS, FeS2). We investigate the sulfur isotopic composition of pore-water sulfate and sulfide minerals at three sites underlain by gas hydrates at the Blake Ridge. The isotopic composition of sulfate-sulfur is most positive at the SMT showing maximum values of +29.1, 49.6, 51.6‰ VCDT at each of the respective sites. δ34S values of bulk sulfide minerals tend to be more enriched in 34S at and below the SMT ranging from −12.7 to +23.6‰, corresponding to enrichments of 26.7–62.4‰ relative to the mean value of −38.8‰ in the sulfate reduction zone. Both enhanced delivery of methane to the SMT, and non-steady-state sedimentation appear necessary to create large 34S enrichments in sulfide minerals. Similar associations of AOM and large δ34S enrichments (\u3e0‰) occur in other gas hydrate terranes (Cascadia margin) but their exact origin is equivocal at present. An analysis of δ34S data from freshwater and marine sedimentary environments reveals that 34S enrichments within sulfide minerals occur under a range of conditions, but are statistically associated with AOM and systems not limited by dissolved interstitial iron. In methane-rich sediments, methane delivery to the SMT increases the role of AOM in sulfate depletion that impacts the formation and isotopic composition of authigenic sulfide minerals. We hypothesize that under certain diagenetic conditions large 34S enrichments within sulfide minerals in the geologic record potentially identify: (1) the former occurrence of AOM (2) present-day and “fossil” locations of the sulfate–methane transition zone; and (3) a diagenetic terrane, today characteristic of deep-water, methane-rich, marine sediments conducive to gas hydrate formation. Thus, 34S-enriched sulfide minerals preserved in modern and ancient continental-margin sediments may allow for the identification of AOM-related processes that occur in methane-rich sediments. Highlights ► Precipitation of authigenic sulfide minerals often occurs at the SMT because of AOM. ► Bulk sulfide minerals from Blake Ridge sediments display 34S enrichments at or below the SMT. ► A literature survey reveals a statistical link between sulfide minerals enriched in 34S and AOM. ► Corroborative diagenetic signatures may identify methane-rich sediments of the geologic past. ► Further hypothesis testing should occur in regions with underlying gas hydrate