The lithological characteristics of natural gas hydrates in permafrost on the Qinghai of China

The environment is seriously threatened by the methane emitted as permafrost melts. Studying deposits of natural gas hydrates that include methane is therefore important. This study presents a novel approach based on the rock Archie formula to discover the porosity and saturation of gas hydrates. The relationship between resistivity and porosity and the porosity of hydrates was studied, and the results showed that the resistivity of hydrate reservoirs was closely related to porosity and hydrate saturation, and the polarization rate was only related to the concentration of natural gas hydrates and had nothing to do with porosity. Using the multi-channel time domain induced polarization (MTIP) method, the profile with five boreholes in the Muli area of the permafrost area of the Qinghai-Tibet Plateau was observed, and the thickness of the shallow permafrost distribution and the underground structure were inferred based on the resistivity of the MTIP data. The polarization rate and hydrate saturation of the inversion assessed the presence of hydrates in the Muli region. The results show that the MTIP method can be used to detect the thickness of permafrost distribution, determine fault boundaries, reveal the distribution of natural gas transport paths, and evaluate the presence of natural gas hydrates.

Distributed natural gas venting offshore along the Cascadia margin

Widespread gas venting along the Cascadia margin is investigated from acoustic water column data and reveals a nonuniform regional distribution of over 1100 mapped acoustic flares. The highest number of flares occurs on the shelf, and the highest flare density is seen around the nutrition-rich outflow of the Juan de Fuca Strait. We determine ∼430 flow-rates at ∼340 individual flare locations along the margin with instantaneous in situ values ranging from ∼6 mL min⁻¹ to ∼18 L min⁻¹. Applying a tidal-modulation model, a depth-dependent methane density, and extrapolating these results across the margin using two normalization techniques yields a combined average in situ flow-rate of ∼88 × 10⁶ kg y⁻¹. The average methane flux-rate for the Cascadia margin is thus estimated to ∼0.9 g y⁻¹m⁻². Combined uncertainties result in a range of these values between 4.5 and 1800% of the estimated mean values.

Methane venting is a widespread phenomenon at the Cascadia margin, however a comprehensive database of methane vents at this margin is lacking. Here the authors show that the margin-wide average methane flow-rate ranges from ~4 × 10⁶ to ~1590 × 10⁶ kg y⁻¹ and is on average around 88 ± 6 × 10⁶ kg y⁻¹.

Spatial and seasonal variability of CH4 in the eastern Gulf of Cadiz (SW Iberian Peninsula)

Methane (CH₄) concentrations were measured along three sections of the eastern Gulf of Cadiz (designated "Guadalquivir", "Sancti Petri" and "Trafalgar") during eight cruises in 2014 and 2015. The concentration of CH₄ varied from 3.6 to 19.7nmolkg^-1 (CH₄ saturation percent of 122 and 916%), showing seasonal variation. The highest values were found in December 2014 and November 2015. In most of the sampling area the highest concentration of CH₄ was found in subsurface waters at depths close to the thermocline, and in the bottom waters near the coast. The seawater-air flux of CH₄ ranged between 0.8 and 59.7μmolm^-2d^-1, showing seasonal variation in function of the temperature of the surface water. In the "Guadalquivir" and "Sancti Petri" sections, the CH₄ fluxes increased with proximity to the coast; this may be a result of continental inputs and CH₄ emissions from sediments. The whole study area behaves as a source of CH₄ to the atmosphere with mean values of 0.5 and 0.6GgCH₄yr^-1 in 2014 and 2015, respectively.

Macroscopic biofilms in fracture-dominated sediment that anaerobically oxidize methane

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.