Статті в журналах: "Seep gas"

1

Zhang, Wei, Jinqiang Liang, Qianyong Liang, Jiangong Wei, Zhifeng Wan, Junxi Feng, Wei Huang, et al. "Gas Hydrate Accumulation and Occurrence Associated with Cold Seep Systems in the Northern South China Sea: An Overview." Geofluids 2021 (October 5, 2021): 1–24. http://dx.doi.org/10.1155/2021/5571150.

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Studying deep-water cold seep systems is of great significance to gas hydrate exploration due to their close relationship. Various cold seep systems and related gas hydrate accumulations have been discovered in the northern South China Sea in the past three decades. Based on high-resolution seismic data, subbottom profiles, in situ submergence observations, deep drilling and coring, and hydrate gas geochemical analyses, the geological and geophysical characteristics of these cold seep systems and their associated gas hydrate accumulations in the Qiongdongnan Basin, the Shenhu area, the Dongsha area, and the Taixinan Basin have been investigated. Cold seep systems are present in diverse stages of evolution and exhibit various seabed microgeomorphic, geological, and geochemical features. Active cold seep systems with a large amount of gas leakage, gas plumes, and microbial communities and inactive cold seep systems with authigenic carbonate pavements are related to the variable intensity of the gas-bearing fluid, which is usually derived from the deep strata through mud diapirs, mud volcanoes, gas chimneys, and faults. Gas hydrates are usually precipitated in cold seep vents and deeper vertical fluid migration pathways, indicating that deep gas-bearing fluid activities control the formation and accumulation of gas hydrates. The hydrocarbons collected from cold seep systems and their associated gas hydrate reservoirs are generally mixtures of biogenic gas and thermogenic gas, the origin of which is generally consistent with that of deep conventional gas. We also discuss the paragenetic relationship between the gas-bearing fluid and the seafloor morphology of cold seeps and the deep-shallow coupling of gas hydrates, cold seeps, and deep petroleum reservoirs. It is reasonable to conclude that the deep petroleum systems and gas-bearing fluid activity jointly control the development of cold seep systems and the accumulation of gas hydrates in the northern South China Sea. Therefore, the favorable areas for conventional oil and gas enrichment are also prospective areas for exploring active cold seeps and gas hydrates.

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2

Zhang, Wei, Jinqiang Liang, Qianyong Liang, Jiangong Wei, Zhifeng Wan, Junxi Feng, Wei Huang, et al. "Gas Hydrate Accumulation and Occurrence Associated with Cold Seep Systems in the Northern South China Sea: An Overview." Geofluids 2021 (October 5, 2021): 1–24. http://dx.doi.org/10.1155/2021/5571150.

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Studying deep-water cold seep systems is of great significance to gas hydrate exploration due to their close relationship. Various cold seep systems and related gas hydrate accumulations have been discovered in the northern South China Sea in the past three decades. Based on high-resolution seismic data, subbottom profiles, in situ submergence observations, deep drilling and coring, and hydrate gas geochemical analyses, the geological and geophysical characteristics of these cold seep systems and their associated gas hydrate accumulations in the Qiongdongnan Basin, the Shenhu area, the Dongsha area, and the Taixinan Basin have been investigated. Cold seep systems are present in diverse stages of evolution and exhibit various seabed microgeomorphic, geological, and geochemical features. Active cold seep systems with a large amount of gas leakage, gas plumes, and microbial communities and inactive cold seep systems with authigenic carbonate pavements are related to the variable intensity of the gas-bearing fluid, which is usually derived from the deep strata through mud diapirs, mud volcanoes, gas chimneys, and faults. Gas hydrates are usually precipitated in cold seep vents and deeper vertical fluid migration pathways, indicating that deep gas-bearing fluid activities control the formation and accumulation of gas hydrates. The hydrocarbons collected from cold seep systems and their associated gas hydrate reservoirs are generally mixtures of biogenic gas and thermogenic gas, the origin of which is generally consistent with that of deep conventional gas. We also discuss the paragenetic relationship between the gas-bearing fluid and the seafloor morphology of cold seeps and the deep-shallow coupling of gas hydrates, cold seeps, and deep petroleum reservoirs. It is reasonable to conclude that the deep petroleum systems and gas-bearing fluid activity jointly control the development of cold seep systems and the accumulation of gas hydrates in the northern South China Sea. Therefore, the favorable areas for conventional oil and gas enrichment are also prospective areas for exploring active cold seeps and gas hydrates.

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3

Terentieva, Irina, Ilya Filippov, Aleksandr Sabrekov, and Mikhail Glagolev. "Mapping Onshore CH4 Seeps in Western Siberian Floodplains Using Convolutional Neural Network." Remote Sensing 14, no. 11 (June 2, 2022): 2661. http://dx.doi.org/10.3390/rs14112661.

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Onshore seeps are recognized as strong sources of methane (CH4), the second most important greenhouse gas. Seeps actively emitting CH4 were recently found in floodplains of West Siberian rivers. Despite the origin of CH4 in these seeps is not fully understood, they can make substantial contribution in regional greenhouse gas emission. We used high-resolution satellite Sentinel-2 imagery to estimate seep areas at a regional scale. Convolutional neural network based on U-Net architecture was implemented to overcome difficulties with seep recognition. Ground-based field investigations and unmanned aerial vehicle footage were coupled to provide reliable training dataset. The seep areas were estimated at 2885 km2 or 1.5% of the studied region; most seep areas were found within the Ob’ river floodplain. The overall accuracy of the final map reached 86.1%. Our study demonstrates that seeps are widespread throughout the region and provides a basis to estimate seep CH4 flux in entire Western Siberia.

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4

Argentino, Claudio, Stefano Conti, Chiara Fioroni, and Daniela Fontana. "Evidences for Paleo-Gas Hydrate Occurrence: What We Can Infer for the Miocene of the Northern Apennines (Italy)." Geosciences 9, no. 3 (March 20, 2019): 134. http://dx.doi.org/10.3390/geosciences9030134.

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The occurrence of seep-carbonates associated with shallow gas hydrates is increasingly documented in modern continental margins but in fossil sediments the recognition of gas hydrates is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and geochemical indicators for paleo-gas hydrate occurrence based on present-day analogues to investigate fossil seeps located in the northern Apennines. We recognized clathrite-like structures such as thin-layered, spongy and vuggy textures and microbreccias. Non-gravitational cementation fabrics and pinch-out terminations in cavities within the seep-carbonate deposits are ascribed to irregularly oriented dissociation of gas hydrates. Additional evidences for paleo-gas hydrates are provided by the large dimensions of seep-carbonate masses and by the association with sedimentary instability in the host sediments. We report heavy oxygen isotopic values in the examined seep-carbonates up to +6‰ that are indicative of a contribution of isotopically heavier fluids released by gas hydrate decomposition. The calculation of the stability field of methane hydrates for the northern Apennine wedge-foredeep system during the Miocene indicated the potential occurrence of shallow gas hydrates in the upper few tens of meters of sedimentary column.

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5

Wan, Zhifeng, Chongmin Chen, Jinqiang Liang, Wei Zhang, Wei Huang, and Pibo Su. "Hydrochemical Characteristics and Evolution Mode of Cold Seeps in the Qiongdongnan Basin, South China Sea." Geofluids 2020 (January 7, 2020): 1–16. http://dx.doi.org/10.1155/2020/4578967.

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Submarine cold seeps have recently attracted significant attention and are among the most effective indicators of gas hydrate in the oceans. In this study, remotely operated vehicle (ROV) observations, seismic profiles, core sediments, bottom seawater, and fluid vented from cold seeps in the deep-water Qiongdongnan Basin were used to investigate the origin and evolution of cold seeps and their relationships with gas hydrate. At stations A, B, and C, inactive cold seeps with dead clams, cold seep leakage with live clams, and active cold seeps with a rich mussel presence, respectively, were observed. The salinity and Na+ and Cl- concentrations of the cold seeps were different from those of typical seawater owing to gas hydrate formation and decomposition and fluid originating from various depths. The main ion concentrations of the bottom seawater at stations B and C were higher than those at station A, indicating the substantial effects of low-salinity cold seep fluids from gas hydrate decomposition. The Na+-Cl-, K+-Cl-, Mg2+-Cl-, and Ca2+-Cl- diagrams and rare earth element distribution curves of the water samples were strongly affected by seawater. The concentrations of trace elements and their ratios to Cl- in the bottom seawater were high at the stations with cold seeps, suggesting the mixing of other fluids rich in those elements. Biochemical reactions may also have caused the chemical anomalies. Samples of HM-ROV-1 indicated a greater effect of upward cold seep fluids with higher B/Cl-, Sr/Cl-, and Ba/Cl- values. Moreover, the Re/Cl- value varied between fluid vents, possibly due to differences in Re precipitation strength. Differences in cold seep intensity are also believed to occur between areas. The cold seep fluxes changed from large to small before finally disappearing, showing a close connection with gas hydrate formation and decomposition, and influenced the local topography and ecosystems.

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6

Rychert, Kevin M., and Thomas C. Weber. "Acoustic measurements of a controlled gas seep." Journal of the Acoustical Society of America 141, no. 5 (May 2017): 3524. http://dx.doi.org/10.1121/1.4987427.

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7

Sideleva, V. G., and T. Ya Sitnikova. "Differentiation of communities of macroinvertebrates and cottoid fish associated with methane seeps of different bottom landscapes of Lake Baikal." Proceedings of the Zoological Institute RAS 325, no. 4 (December 21, 2021): 469–84. http://dx.doi.org/10.31610/trudyzin/2021.325.4.469.

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The paper presents the results of the study of communities of macroinvertebrates and cottoid fish inhabiting methane seeps of Lake Baikal. For the analysis, we used video surveillance and collection of animals carried out with the help of "Mir" deep-water submersible, as well as NIOZ-type box-corer samplers from the board of a research vessel. Posolskaya Bank and Saint Petersburg methane seeps are located in different basins (southern and middle) and at different depths (300–500 m and ~ 1400 m), characterized by the different underwater landscapes (slope of underwater upland and hills formed by gas hydrates), by the structure of gas hydrates and their depth location in sediments, as well as the composition of microbial mats and communities of microorganisms of bottom sediments. Both seeps are characterized by bubble discharge of methane gas and the formation of highly productive communities of large invertebrates and cottoid fish on seep habitats. Seep animal communities consisted of species-depleted invertebrates and fish of the surrounding deep-water benthal of the Lake. We showed the similarities and differences in the composition of the faunas of two seeps, as well as the quantitative characteristics of taxonomic groups of macroinvertebrates and cottoid fishes. Obligate species have not been revealed on the methane seep Posolskaya Bank. For the methane seep Saint Petersburg, the gastropod species Kobeltocochlea tamarae Sitnikova, Teterina et Maximova, 2021 (Caenogastropoda: Benedictiidae) was designated as an obligate species; among bottom cottoid fishes, Neocottus werestschagini (Taliev, 1953) (Cottoidei: Abyssocottidae) had possible a transitional state to obligate. We presented the data on the assimilation by seep animals of mixed photo- and chemosynthetic food with different proportions of methane-derived carbon. A hypothesis has been substantiated that deep-water seep areas could serve as refugium for the preservation of endemic fauna during the Pliocene-Pleistocene glaciations of Lake Baikal.

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8

Mitchell, Garrett A., Larry A. Mayer, and Jamshid J. Gharib. "Bubble vent localization for marine hydrocarbon seep surveys." Interpretation 10, no. 1 (January 26, 2022): SB107—SB128. http://dx.doi.org/10.1190/int-2021-0084.1.

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Commercial success of marine seep hunting exploration campaigns involves acquisition of high-quality bathymetry and backscatter along with targeted coring of shallow geochemical sampling of seep sediments. The sharp lateral chemical gradient encompassing seafloor seeps requires accurate identification of seep sites from high-resolution acoustic data. Active seafloor seeps featuring plumes of gas bubbles and oil droplets rising into the water column can be imaged with modern multibeam echosounders providing an effective approach to remotely characterizing seafloor seeps. Interpreting the seafloor position of gas plume emissions in multibeam data using existing mapping methodology is hindered by slow processing due to large files sizes, a manual “by eye” qualitative assessment of each sonar ping searching for plume anomalies, skill and fatigue of the geoscientist, and environmental or acquisition artifacts that can mask the precise location of gas emission on the seafloor. These limitations of midwater backscatter mapping create a qualitative data set with varying inherent positional errors that can lead to missed or incorrect observations about seep-related seafloor features and processes. By vertically integrating midwater multibeam amplitude samples, a 2D midwater backscatter raster can be generated and draped over seafloor morphology, providing a quantitative synoptic overview of the spatial distribution of gas plume emission sites for more refined seafloor interpretation. We reprocess multibeam midwater data set from NOAA Cruise EX1402L2 in the northwestern Gulf of Mexico using a vertical amplitude stacking technique. Constructed midwater backscatter surfaces are compared with digitized plume positions collected during the survey for a comparison into assessing uncertainty in mapping approaches. Our results show that the accuracy of manually digitizing gas emission sites varies considerably when compared with the midwater backscatter amplitude maps. This quantitative plume mapping technique offers multiple advantages over traditional geopicking from cost effectiveness, offshore efficiency, repeatability, and higher accuracy, ultimately improving the detectability and sampling of active seafloor seeps through precisely located cores.

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9

Dando, P. R., S. C. M. O'Hara, S. J. Niven, U. Schuster, L. J. Taylor, and P. Jensen. "The effects of methane seepage at an intertidal/shallow subtidal site on the shore of the Kattegat, Vendsyssel, Denmark." Bulletin of the Geological Society of Denmark 41 (March 30, 1994): 65–79. http://dx.doi.org/10.37570/bgsd-1995-41-07.

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The effects of methane gas seepage were studied at an intertidal/shallow subtidal site on the Kattegat coast of Denmark. A 30 m wide zone, containing approximately 65 gas seeps, extended over 70 m seawards from the shore. This was characterised by the presence of slabs, pavement and small pillars of carbonate-cemented sandstone which formed a partially buried reef. The escaping gas contained 91-100% methane with some carbon dioxide, 0.6--0.9%, and hydrogen sulphide. The hydrogen sulphide concentration varied over time and between individual seeps. Gas flow rates of individual seeps ranged up to 211 h-1 and the estimated total flow was 110 I h-1• Seeps were often stopped by sand movement, but the overall gas flow from the site appeared to be constant. The escaping gas generated an interstitial water circulation and drew overlying seawater into the sediment. Water pumped out by the seeps was enriched in phosphate and ammonia. Sulphate reduction rates in the seep area were 1.1-17.1 m moles sulphate reduced and aerobic methane oxidation rates were 0.2 - 5.5 m moles methane consumed m-2 day-1• The composition of the flora and fauna surrounding the seeps was affected by the presence of hard substrate (the cemented sandstone). Epifauna was more abundant in the seep zone than elsewhere, whereas the macrobenthic infauna was reduced in the seep zone, possibly due to the cementation. The sediment was almost devoid of meiobenthic organisms, except nematodes. Nematode species numbers, abundance and biomass were lower at the seeps than 5-20 cm away. The nematode fauna penetrated deeper into the sediment close to the seeps than at the seeps themselves. This is explained by the interstitial water circulation at and close to the seeps. 14C measurements showed that little methane carbon was entering the food web surrounding the seeps.

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10

Ruff, S. Emil, Jennifer F. Biddle, Andreas P. Teske, Katrin Knittel, Antje Boetius, and Alban Ramette. "Global dispersion and local diversification of the methane seep microbiome." Proceedings of the National Academy of Sciences 112, no. 13 (March 16, 2015): 4015–20. http://dx.doi.org/10.1073/pnas.1421865112.

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Methane seeps are widespread seafloor ecosystems shaped by the emission of gas from seabed reservoirs. The microorganisms inhabiting methane seeps transform the chemical energy in methane to products that sustain rich benthic communities around the gas leaks. Despite the biogeochemical relevance of microbial methane removal at seeps, the global diversity and dispersion of seep microbiota remain unknown. Here we determined the microbial diversity and community structure of 23 globally distributed methane seeps and compared these to the microbial communities of 54 other seafloor ecosystems, including sulfate–methane transition zones, hydrothermal vents, coastal sediments, and deep-sea surface and subsurface sediments. We found that methane seep communities show moderate levels of microbial richness compared with other seafloor ecosystems and harbor distinct bacterial and archaeal taxa with cosmopolitan distribution and key biogeochemical functions. The high relative sequence abundance of ANME (anaerobic methanotrophic archaea), as well as aerobic Methylococcales, sulfate-reducing Desulfobacterales, and sulfide-oxidizing Thiotrichales, matches the most favorable microbial metabolisms at methane seeps in terms of substrate supply and distinguishes the seep microbiome from other seafloor microbiomes. The key functional taxa varied in relative sequence abundance between different seeps due to the environmental factors, sediment depth and seafloor temperature. The degree of endemism of the methane seep microbiome suggests a high local diversification in these heterogeneous but long-lived ecosystems. Our results indicate that the seep microbiome is structured according to metacommunity processes and that few cosmopolitan microbial taxa mediate the bulk of methane oxidation, with global relevance to methane emission in the ocean.

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11

Wu, Daidai, Nengyou Wu, Ying Ye, Mei Zhang, Lihua Liu, Hongxiang Guan, and Xiaorong Cong. "Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea." Journal of Geological Research 2011 (October 2, 2011): 1–10. http://dx.doi.org/10.1155/2011/592703.

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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 SO42-, Ca2+, Mg2+, and Sr2+ decrease clearly, and the ratios of Mg2+ to Ca2+ and Sr2+ to Ca2+ 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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12

Kinnaman, Franklin S., Justine B. Kimball, Luis Busso, Daniel Birgel, Haibing Ding, Kai-Uwe Hinrichs, and David L. Valentine. "Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas." Geo-Marine Letters 30, no. 3-4 (February 20, 2010): 355–65. http://dx.doi.org/10.1007/s00367-010-0184-0.

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13

Heeschen, K., M. Haeckel, I. Klaucke, M. K. Ivanov, and G. Bohrmann. "Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique." Biogeosciences Discussions 8, no. 3 (May 9, 2011): 4529–58. http://dx.doi.org/10.5194/bgd-8-4529-2011.

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Abstract. In the eastern Black Sea, we determined methane (CH4) concentrations, gas hydrate volumes and their vertical distribution from combined gas and chloride (Cl−) measurements within pressurized sediment cores. The total gas volume collected from the cores corresponds to concentrations of 1.2–1.4 mol of methane per kg porewater at in-situ pressure, which is equivalent to a gas hydrate saturation of 15–18% of pore volume and amongst the highest values detected in shallow seep sediments. At the central seep site, a high-resolution Cl− profile resolves the upper gas hydrate stability boundary and a continuous layer of hydrates in a sediment column of 120 cm thickness. Including this information, a more precise gas hydrate saturation of 22–24% pore volume can be calculated. This is higher in comparison to a saturation calculated from the Cl− profile alone, resulting in 14.4%. The likely explanation is an active gas hydrate formation from CH4 gas ebullition. The hydrocarbons at Batumi Seep are of shallow biogenic origin (CH4 > 99.6%), at Pechori Mound they originate from deeper thermocatalytic processes as indicated by the lower ratios of C1 to C2–C3 and the presence of C5.

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14

Heeschen, K. U., M. Haeckel, I. Klaucke, M. K. Ivanov, and G. Bohrmann. "Quantifying in-situ gas hydrates at active seep sites in the eastern Black Sea using pressure coring technique." Biogeosciences 8, no. 12 (December 8, 2011): 3555–65. http://dx.doi.org/10.5194/bg-8-3555-2011.

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Abstract. In the eastern Black Sea, we determined methane (CH4) concentrations, gas hydrate volumes, and their vertical distribution from combined gas and chloride (Cl−) measurements within pressurized sediment cores. The total gas volume collected from the cores corresponded to concentrations of 1.2–1.4 mol CH4 kg−1 porewater at in-situ pressure, which is equivalent to a gas hydrate saturation of 15–18% of pore volume and amongst the highest values detected in shallow seep sediments. At the central seep site, a high-resolution Cl− profile resolved the upper boundary of gas hydrate occurrence and a continuous layer of hydrates in a sediment column of 120 cm thickness. Including this information, a more precise gas hydrate saturation of 22–24% pore volume could be calculated. This volume was higher in comparison to a saturation calculated from the Cl− profile alone, resulting in only 14.4%. The likely explanation is an active gas hydrate formation from CH4 gas ebullition. The hydrocarbons at Batumi Seep are of shallow biogenic origin (CH4 > 99.6%), at Pechori Mound they originate from deeper thermocatalytic processes as indicated by the lower ratios of C1 to C2–C3 and the presence of C5.

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15

Feng, Junxi, Niu Li, Min Luo, Jinqiang Liang, Shengxiong Yang, Hongbin Wang, and Duofu Chen. "A Quantitative Assessment of Methane-Derived Carbon Cycling at the Cold Seeps in the Northwestern South China Sea." Minerals 10, no. 3 (March 12, 2020): 256. http://dx.doi.org/10.3390/min10030256.

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Widespread cold seeps along continental margins are significant sources of dissolved carbon to the ocean water. However, little is known about the methane turnovers and possible impact of seepage on the bottom seawater at the cold seeps in the South China Sea (SCS). We present seafloor observation and porewater data of six push cores, one piston core and three boreholes as well as fifteen bottom-water samples collected from four cold seep areas in the northwestern SCS. The depths of the sulfate–methane transition zone (SMTZ) are generally shallow, ranging from ~7 to <0.5 mbsf (meters below seafloor). Reaction-transport modelling results show that methane dynamics were highly variable due to the transport and dissolution of ascending gas. Dissolved methane is predominantly consumed by anaerobic oxidation of methane (AOM) at the SMTZ and trapped by gas hydrate formation below it, with depth-integrated AOM rates ranging from 59.0 and 591 mmol m−2 yr−1. The δ13C and Δ14C values of bottom-water dissolved inorganic carbon (DIC) suggest discharge of 13C- and 14C-depleted fossil carbon to the bottom water at the cold seep areas. Based on a two-endmember estimate, cold seeps fluids likely contribute 16–26% of the bottom seawater DIC and may have an impact on the long-term deep-sea carbon cycle. Our results reveal the methane-related carbon inventories are highly heterogeneous in the cold seep systems, which are probably dependent on the distances of the sampling sites to the seepage center. To our knowledge, this is the first quantitative study on the contribution of cold seep fluids to the bottom-water carbon reservoir of the SCS, and might help to understand the dynamics and the environmental impact of hydrocarbon seep in the SCS.

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16

Purwasatriya, Eko Bayu, and Gentur Waluyo. "Pembuatan Model Geologi Bawah Permukaan dengan Metode Geolistrik Dan Studi Stratigrafi pada Rembesan Gas DiJatilawang, Banyumas." Dinamika Rekayasa 7, no. 2 (August 2, 2011): 54. http://dx.doi.org/10.20884/1.dr.2011.7.2.50.

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<p>Banyumas basin is oneof sedimentary basin inIndonesia whichhasn’t proven yet its economical hydrocarbonreserves, although there are several oil and gas seeps in this area which is indicate mature source rocks had been migrated. One of itsgas seep is located on Karanglewas village, Jatilawang, Banyumas which hadbeen flowing its gases since tens years ago. Geoelectrical method and Stratigraphic studyare the methods usedin this research to built a geological subsurface model of Jatilawang’s gas seep.Geoelectrical method isintent to finding the distribution of gas seep over the area and also to finding the direction of fault structure which can be act asa path for gases to flowing up. Stratigraphic study comprise of lithology description, strike and dip measurement, and study of other secondary geological data. Interpreted subsurfacegeological model showing that sandstone dominated bed of Halang Formation is filled by gases and become gas pockets near the surface. Fault direction also interpreted from correlation of these gas pockets and resulting directionof N 115° E and dip of fault plane is45°.Gas flowing through fault and probably the source comes from gas cap of Jatilawang’s anticline. Predicted location of gas cap is about 610 meters to the south, and depthabout 620 meters.</p>

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17

Geng, Minghui, Ruwei Zhang, Shengxiong Yang, Jun Guo, and Zongheng Chen. "Focused Fluid Flow, Shallow Gas Hydrate, and Cold Seep in the Qiongdongnan Basin, Northwestern South China Sea." Geofluids 2021 (June 12, 2021): 1–11. http://dx.doi.org/10.1155/2021/5594980.

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The 3D seismic data acquired in the central Qiongdongnan Basin, northwestern South China Sea, reveal the presence of shallow gas hydrate, free gas, and focused fluid flow in the study area, which are indicated by multiple seismic anomalies, including bottom simulating reflectors, polarity reverses, pulldowns, minor faults, and gas chimneys intensively emplaced within the shallow strata. A new cold seep is also discovered at approximately 1520 m water depths with an ~40 m wide crater in the west part of the study area. Water column imaging, seafloor observation, and sampling using the remotely operated vehicle “Haima” demonstrate ongoing gas seepages and shallow gas hydrates at this site. Thermogenic gas in the study area migrates from the deep reservoir through the gas hydrate stability zone along deep faults and gas chimneys, forms shallow gas hydrate and free gas, and sustains localized gas seepage within this cold seep. The results provide insight into the relationship between shallow gas hydrate accumulation and deep hydrocarbon generation and migration and simultaneously have important implications for hydrocarbon explorations in the Qiongdongnan Basin, northwestern South China Sea.

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O'Hara, S. C. M., P. R. Dando, U. Schuster, A. Bennis, J. D. Boyle, F. T. W. Chui, T. V. J. Hatherell, S. J. Niven, and L. J. Taylor. "Gas seep induced interstitial water circulation: observations and environmental implications." Continental Shelf Research 15, no. 8 (July 1995): 931–48. http://dx.doi.org/10.1016/0278-4343(95)80003-v.

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19

Di, Pengfei, Dong Feng, Jun Tao, and Duofu Chen. "Using Time-Series Videos to Quantify Methane Bubbles Flux from Natural Cold Seeps in the South China Sea." Minerals 10, no. 3 (February 27, 2020): 216. http://dx.doi.org/10.3390/min10030216.

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Natural cold seeps are an important source of methane and other greenhouse gases to the ocean and atmosphere in the marine environment. Accurate quantification of methane bubble fluxes from cold seeps is vital for evaluating their influence on the global methane budget and climate change. We quantified the flux of gas bubbles released from two natural cold seep sites in the South China Sea: one seep vent in the Haima cold seeps (1400 m depth) and three seep vents at Site F (1200 m depth). We determined bubble diameter, size distribution, and bubble release rate using image processing techniques and a semiautomatic bubble-counting algorithm. The bubble size distributions fit well to log-normal distribution, with median bubble diameters between 2.54 mm and 6.17 mm. The average bubble diameters and release rates (4.8–26.1 bubbles s−1) in Site F was lower than that in Haima cold seeps (22.6 bubbles s−1), which may be attributed to a variety of factors such as the nature of the gas reservoir, hydrostatic pressure, migration pathways in the sediments, and pore size. The methane fluxes emitted at Haima cold seeps (12.6 L h−1) and at Site F (4.9 L h−1) indicate that the Haima and Site F cold seeps in the South China Sea may be a source of methane to the ocean. However, temporal variations in the bubble release rate and the geochemical characteristics of the seeps were not constrained in this study due to the short observational time interval.

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20

Wegener, G., M. Shovitri, K. Knittel, H. Niemann, M. Hovland, and A. Boetius. "Biogeochemical processes and microbial diversity of the Gullfaks and Tommeliten methane seeps (Northern North Sea)." Biogeosciences 5, no. 4 (August 18, 2008): 1127–44. http://dx.doi.org/10.5194/bg-5-1127-2008.

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Abstract. Fluid flow related seafloor structures and gas seeps were detected in the North Sea in the 1970s and 1980s by acoustic sub-bottom profiling and oil rig surveys. A variety of features like pockmarks, gas vents and authigenic carbonate cements were found to be associated with sites of oil and gas exploration, indicating a link between these surface structures and the underlying, deep hydrocarbon reservoirs. In this study we performed acoustic surveys and videographic observation at Gullfaks, Holene Trench, Tommeliten, Witch's Hole and the giant pockmarks of the UK Block 15/25, to investigate the occurrence and distribution of cold seep ecosystems in the Northern North Sea. The most active gas seep sites, i.e. Gullfaks and Tommeliten, were investigated in detail. At both sites, gas bubbles escaped continuously from small holes in the seabed to the water column, reaching the upper mixed surface layer. At Gullfaks a gas emitting, flat area of 0.1 km2 of sandy seabed covered by filamentous sulfur-oxidizing bacteria was detected. At Tommeliten, we found a patchy distribution of small bacterial mats indicating sites of gas seepage. Below the patches the seafloor consisted of sand from which gas emissions were observed. At both sites, the anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) was the major source of sulfide. Molecular analyses targeting specific lipid biomarkers and 16S rRNA gene sequences identified an active microbial community dominated by sulfur-oxidizing and sulfate-reducing bacteria (SRB) as well as methanotrophic bacteria and archaea. Stable carbon isotope values of specific, microbial fatty acids and alcohols from both sites were highly depleted in the heavy isotope 13C, indicating that the microbial community incorporates methane or its metabolites. The microbial community composition of both shallow seeps shows high similarities to the deep water seeps associated with gas hydrates such as Hydrate Ridge or the Eel River basin.

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Conti, Stefano, and Daniela Fontana. "Possible Relationships between Seep Carbonates and Gas Hydrates in the Miocene of the Northern Apennines." Journal of Geological Research 2011 (August 3, 2011): 1–9. http://dx.doi.org/10.1155/2011/920727.

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In the Miocene of the northern Apennines, a widespread carbonate precipitation was induced by the expulsion of methane-rich fluids. Numerous outcrops of carbonate masses share sedimentological, textural and geochemical features with present-day gas hydrate-associated carbonates. We hypothesize the contribution of paleo-gas hydrate destabilization on the base of the heavy oxygen isotope signature, the presence of distinctive sedimentary features (breccias, pervasive nonsystematic fractures, and soft sediment deformation), the close association between seep carbonates and sedimentary instability, and the huge dimensions of seep carbonates bearing brecciated structures.

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22

Wegener, G., M. Shovitri, K. Knittel, H. Niemann, M. Hovland, and A. Boetius. "Biogeochemical processes and microbial diversity of the Gullfaks and Tommeliten methane seeps (Northern North Sea)." Biogeosciences Discussions 5, no. 1 (February 25, 2008): 971–1015. http://dx.doi.org/10.5194/bgd-5-971-2008.

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Abstract. Fluid-flow related seafloor structures and gas seeps were detected in the North Sea in the 1970s and 1980s by acoustic sub-bottom profiling and oil rig surveys. A variety of features like pockmarks, gas vents and authigenic carbonate cements were found to be associated with sites of oil and gas exploration, indicating a link between these surface structures and underlying deep hydrocarbon reservoirs. In this study we performed acoustic surveys and videographic observation at Gullfaks, Holene Trench, Tommeliten, Witch's Hole and the giant pockmarks of the UK Block 15/25, to investigate the occurrence and distribution of cold seep ecosystems in the Northern North Sea. The most active gas seep sites, i.e. Gullfaks and Tommeliten, were investigated in detail: at both sites gas bubbles escaped continuously from small holes in the seabed to the water column, reaching the upper mixed surface layer as indicated by acoustic images of the gas flares. At Gullfaks a 0.1 km2 large gas emission site was detected on a flat sandy seabed, covered by filamentous sulfide-oxidizing bacteria. At Tommeliten we found a patchy distribution of small bacterial mats indicating sites of gas seepage. Here the seafloor consists of layers of sand and stiff clay, and gas emission was observed from small cracks in the seafloor. At both sites the anaerobic oxidation of methane (AOM) coupled to sulfate reduction is the major source of sulfide. Molecular analyses targeting specific lipid biomarkers and 16 S rRNA gene sequences identified an active microbial community dominated by sulfide-oxidizing and sulfate-reducing bacteria (SRB) as well as methanotrophic bacteria and archaea. Carbon isotope values of specific microbial fatty acids and alcohols were highly depleted, indicating that the microbial community at both gas seeps incorporates methane or its metabolites. The microbial community composition of both shallow seeps show high similarities to the deep water seeps associated with gas hydrates such as Hydrate Ridge or Eel River basin.

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23

Leifer, Ira, and Ken Wilson. "Quantified Marine Oil Emissions with a Video-Monitored, Oil Seep-Tent." Marine Technology Society Journal 38, no. 3 (September 1, 2004): 44–53. http://dx.doi.org/10.4031/002533204787511228.

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A video-monitored oil capture tent was developed and deployed during two field trips to quantify oil emissions from several sites in nearshore waters off Summerland Beach in Santa Barbara County, California, at a water depth of ∼5 m. The tent was a tall, inverted polyvinyl chloride plastic cone, which funneled oil into a video-observed sample collection jar. Sample jars were periodically retrieved and analyzed to determine oil and gas emissions at two seeps not associated with physical structures, and a suspected abandoned oil well, designated S-3. Oil and gas emissions at the seeps were ∼1 ml day−1 and ∼90 L day−1, respectively. At the S-3 site, emissions were 51 ml oil day−1 and 0.35 L gas day−1. The size distribution of bubbles at S-3 was sharply peaked at 1500-μm radius, and bubbles rose significantly slower than equivalent size non-oily bubbles, demonstrating the effect of oil on buoyancy loss. A method was developed to estimate from the measured rise velocities the oil-to-gas ratio of each bubble, calibrated with the sample analysis oil and gas fluxes. Autocorrelation showed strong peaks at 64.3 s and 120.0 s period, which were likely related. Other autocorrelation peaks at multiples of 8.2 s corresponded to Fourier spectrum peaks at 8 s and 23.4 s, and were proposed to relate to wave swell-induced surge. Other spectral peaks were observed at 4.9 s, 13.0 s, and 45-50 s period.

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24

Hadimuljono, Jonathan Setyoko, and Desi Yensusnimar. "Heavy Oil Seapage Characteristic in Cipari Area, Banyumas Central Java." Scientific Contributions Oil and Gas 44, no. 3 (March 4, 2022): 161–71. http://dx.doi.org/10.29017/scog.44.3.709.

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Oil seepage in Cipari, Banyumas, Central Java, has long been known. Although, Its occurrence had been reported in several publications, it's properties and characteristic, have not been explained in detail. Therefore, through field geology observation and laboratory analysis, this paper attempts to describe the oil seep characteristic, possible source rock origin, and its relationship with geological features in the surrounding area. Picnometer analysis resulted that this oil seep can be classified as heavy oil with 12n API Gravity. Gas Chromatography (GC) Gas Chromatography Mass Spectometry (GCMS) analysis revealed that Cipari oil seep is heavily biodegraded. Possible source rock of the oil seep was interpreted based on bicadinane and oleanane biomarkers, which indicated that source was deposited in fluvio-deltaic/transitional environment. Based on regional geology reference of Banyumas sub-Basin, it is inferred that the source rocks possibly shale or claystone of Paleogene sediment which was thermally mature, and deposited in transition to marine environment. Deep seated fault that extent from Majenang to Karangbolong areas is probably the main migration pathway of the oil seepage from the kitchen or deep reservoir to the surface. The Cipari anticline outcrop, which associated with faults and fractures, become the place where the oil seep occurs in the surface. Heavy biodegradation of the oil seep may possibly be accelerated by hydrothermal system during migration from the reservoir/kitchen area to the surface.

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Smit, Nadine T., Laura Villanueva, Darci Rush, Fausto Grassa, Caitlyn R. Witkowski, Mira Holzheimer, Adriaan J. Minnaard, Jaap S. Sinninghe Damsté, and Stefan Schouten. "Novel hydrocarbon-utilizing soil mycobacteria synthesize unique mycocerosic acids at a Sicilian everlasting fire." Biogeosciences 18, no. 4 (March 1, 2021): 1463–79. http://dx.doi.org/10.5194/bg-18-1463-2021.

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Abstract. Soil bacteria rank among the most diverse groups of organisms on Earth and actively impact global processes of carbon cycling, especially in the emission of greenhouse gases like methane, CO2 and higher gaseous hydrocarbons. An abundant group of soil bacteria are the mycobacteria, which colonize various terrestrial, marine and anthropogenic environments due to their impermeable cell envelope that contains remarkable lipids. These bacteria have been found to be highly abundant at petroleum and gas seep areas, where they might utilize the released hydrocarbons. However, the function and the lipid biomarker inventory of these soil mycobacteria are poorly studied. Here, soils from the Fuoco di Censo seep, an everlasting fire (gas seep) in Sicily, Italy, were investigated for the presence of mycobacteria via 16S rRNA gene sequencing and fatty acid profiling. The soils contained high relative abundances (up to 34 % of reads assigned) of mycobacteria, phylogenetically close to the Mycobacterium simiae complex and more distant from the well-studied M. tuberculosis and hydrocarbon-utilizing M. paraffinicum. The soils showed decreasing abundances of mycocerosic acids (MAs), fatty acids unique for mycobacteria, with increasing distance from the seep. The major MAs at this seep were tentatively identified as 2,4,6,8-tetramethyl tetracosanoic acid and 2,4,6,8,10-pentamethyl hexacosanoic acid. Unusual MAs with mid-chain methyl branches at positions C-12 and C-16 (i.e., 2,12-dimethyl eicosanoic acid and 2,4,6,8,16-pentamethyl tetracosanoic acid) were also present. The molecular structures of the Fuoco di Censo MAs are different from those of the well-studied mycobacteria like M. tuberculosis or M. bovis and have relatively δ13C-depleted values (−38 ‰ to −48 ‰), suggesting a direct or indirect utilization of the released seep gases like methane or ethane. The structurally unique MAs in combination with their depleted δ13C values identified at the Fuoco di Censo seep offer a new tool to study the role of soil mycobacteria as hydrocarbon gas consumers in the carbon cycle.

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Chen, Duo Fu, Dong Feng, Zheng Su, Zhi Guang Song, Guang Qian Chen, and Lawrence M. Cathles. "Pyrite crystallization in seep carbonates at gas vent and hydrate site." Materials Science and Engineering: C 26, no. 4 (May 2006): 602–5. http://dx.doi.org/10.1016/j.msec.2005.08.037.

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27

Blumenberg, Martin, Thomas Pape, Richard Seifert, Gerhard Bohrmann, and Stefan Schlömer. "Can hydrocarbons entrapped in seep carbonates serve as gas geochemistry recorder?" Geo-Marine Letters 38, no. 2 (August 26, 2017): 121–29. http://dx.doi.org/10.1007/s00367-017-0522-6.

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28

Schneider von Deimling, J., G. Rehder, J. Greinert, D. F. McGinnnis, A. Boetius, and P. Linke. "Quantification of seep-related methane gas emissions at Tommeliten, North Sea." Continental Shelf Research 31, no. 7-8 (May 2011): 867–78. http://dx.doi.org/10.1016/j.csr.2011.02.012.

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29

Decker, John, Philip Teas, Daniel Orange, and Bernie B. Bernard. "Sea bottom characteristics and geochemistry of oil and gas seeps in the Gulf of Mexico." Interpretation 10, no. 1 (January 12, 2022): SB49—SB62. http://dx.doi.org/10.1190/int-2021-0065.1.

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From 2015 to 2018, TGS conducted a comprehensive multiclient oil and gas seep mapping survey in the Gulf of Mexico (GOM). The basis for identifying seeps on the sea bottom was a high-resolution multibeam echosounder survey, mapping approximately 880,000 km2 of the sea bottom deeper than 750 m water depth, at a bathymetric resolution of 15 m, and a backscatter resolution of 5 m. We identified more than 5000 potential oil and/or gas seeps, and of those, we cored approximately 1500 for hydrocarbon geochemical analysis. The sea bottom features best related to hydrocarbon seepage in the GOM are high backscatter features, mud volcanoes, pock marks, brine pools, “popcorn” texture, fault traces, and anticlinal crests. We also tracked gas plumes in the water column back to the sea bottom to provide an additional criterion for hydrocarbon seepage. Cores from sea bottom targets recovered liquid oil, tar, and gas hydrates. Oil extract and gas analyses of samples from most target types produced values substantially higher than background in both oil and gas.

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Niemann, H., M. Elvert, M. Hovland, B. Orcutt, A. Judd, I. Suck, J. Gutt, et al. "Methane emission and consumption at a North Sea gas seep (Tommeliten area)." Biogeosciences 2, no. 4 (November 24, 2005): 335–51. http://dx.doi.org/10.5194/bg-2-335-2005.

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Abstract. The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea (56°29.90' N, 2°59.80' E, Norwegian Block 1/9, 75 m water depth). Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments as well as carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the AOM zone. This zone is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses of this horizon give evidence that AOM is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw−1 biphythanes, 140 ng g-dw−1 fatty acid ai-C15:0), cell numbers (1.5×108 cells cm−3), AOM and SR rates (3 nmol cm−3 d−1) in the Tommeliten AOM zone are 2–3 orders of magnitude lower compared to AOM zones of highly active deep water cold seeps such as Hydrate Ridge or the Gulf of Mexico.

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Niemann, H., M. Elvert, M. Hovland, B. Orcutt, A. Judd, I. Suck, J. Gutt, et al. "Methane emission and consumption at a North Sea gas seep (Tommeliten area)." Biogeosciences Discussions 2, no. 4 (November 30, 2005): 1197–241. http://dx.doi.org/10.5194/bgd-2-1197-2005.

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Abstract. The North Sea hosts large coal, oil and gas reservoirs of commercial value. Natural leakage pathways of subsurface gas to the hydrosphere have been recognized during geological surveys (Hovland and Judd, 1988). The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea. In this study, we report of an active seep site (56°29.90'N, 2°59.80'E) located in the Tommeliten area, Norwegian Block 1/9, at 75 m water depth. Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere during deep mixing situations. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments and carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the Sulphate-Methane Transition Zone (SMTZ). The SMTZ of Tommeliten is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses give evidence that AOM at the Tommeliten SMTZ is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw-1 biphythanes, 140 ng g-dw-1 fatty acid ai-C15:0), cell numbers (1.5x108 cells cm-3), AOM and SR rates (3 nmol cm-3 d-1 in the SMTZ are 2-3 orders of magnitude lower compared to AOM zones of highly active cold seeps such as Hydrate Ridge or the Gulf of Mexico.

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Leifer, Ira, Ken Wilson, John Tarpley, Robin Lewis, Randy Imai, Michael Sowby, Ken Mayer, and Carlton Moore. "FACTORS AFFECTING MARINE HYDROCARBON EMISSIONS IN AN AREA OF NATURAL SEEPS AND ABANDONED OIL WELLS - SUMMERLAND, CALIFORNIA." International Oil Spill Conference Proceedings 2005, no. 1 (May 1, 2005): 849–53. http://dx.doi.org/10.7901/2169-3358-2005-1-849.

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ABSTRACT A video-monitored oil-seep capture tent and an intertidal seep tank were developed and deployed to quantify emissions in shallow (5-m) nearshore waters and at an intertidal location at Summerland Beach, California. At two sites, where bubbles appeared clear, gas to oil ratios were 105:1; at a site where bubbles were dark, gas to oil ratio was 8.4:1. Nearshore oil emissions were conservatively estimated at 0.8 L dy’1. The size distribution of oily bubbles sharply peaked at 1500 µm, and the gas to oil ratio varied between bubbles. Oil affected the bubble's buoyancy and hydrodynamics. Time series of seabed emissions showed oil was mostly released in pulses. Several mechanisms that may cause variability in oil emissions were proposed. Intertidal oil emission were estimated a 12 L dy−1. Also, beach surveys showed less than trace amounts of beached oil and no oiled fauna over a 19-month period.

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33

Sen, Arunima, Emmelie K. L. Åström, Wei-Li Hong, Alexey Portnov, Malin Waage, Pavel Serov, Michael L. Carroll, and JoLynn Carroll. "Geophysical and geochemical controls on the megafaunal community of a high Arctic cold seep." Biogeosciences 15, no. 14 (July 25, 2018): 4533–59. http://dx.doi.org/10.5194/bg-15-4533-2018.

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Abstract. Cold-seep megafaunal communities around gas hydrate mounds (pingos) in the western Barents Sea (76∘ N, 16∘ E, ∼400 m depth) were investigated with high-resolution, geographically referenced images acquired with an ROV and towed camera. Four pingos associated with seabed methane release hosted diverse biological communities of mainly nonseep (background) species including commercially important fish and crustaceans, as well as a species new to this area (the snow crab Chionoecetes opilio). We attribute the presence of most benthic community members to habitat heterogeneity and the occurrence of hard substrates (methane-derived authigenic carbonates), particularly the most abundant phyla (Cnidaria and Porifera), though food availability and exposure to a diverse microbial community is also important for certain taxa. Only one chemosynthesis-based species was confirmed, the siboglinid frenulate polychaete Oligobrachia cf. haakonmosbiensis. Overall, the pingo communities formed two distinct clusters, distinguished by the presence or absence of frenulate aggregations. Methane gas advection through sediments was low, below the single pingo that lacked frenulate aggregations, while seismic profiles indicated abundant gas-saturated sediment below the other frenulate-colonized pingos. The absence of frenulate aggregations could not be explained by sediment sulfide concentrations, despite these worms likely containing sulfide-oxidizing symbionts. We propose that high levels of seafloor methane seepage linked to subsurface gas reservoirs support an abundant and active sediment methanotrophic community that maintains high sulfide fluxes and serves as a carbon source for frenulate worms. The pingo currently lacking a large subsurface gas source and lower methane concentrations likely has lower sulfide flux rates and limited amounts of carbon, insufficient to support large populations of frenulates. Two previously undocumented behaviors were visible through the images: grazing activity of snow crabs on bacterial mats, and seafloor crawling of Nothria conchylega onuphid polychaetes.

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34

Di, Pengfei, Dong Feng, and Duofu Chen. "Temporal Variation in Natural Gas Seep Rate and Influence Factors in the Lingtou Promontory Seep Field of the Northern South China Sea." Terrestrial, Atmospheric and Oceanic Sciences 25, no. 5 (2014): 665. http://dx.doi.org/10.3319/tao.2014.04.30.01(oc).

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35

Treude, T., and W. Ziebis. "Methane oxidation in permeable sediments at hydrocarbon seeps in the Santa Barbara Channel, California." Biogeosciences 7, no. 10 (October 13, 2010): 3095–108. http://dx.doi.org/10.5194/bg-7-3095-2010.

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Abstract. A shallow-water area in the Santa Barbara Channel, California, known collectively as the Coal Oil Point seep field, is one of the largest natural submarine hydrocarbon emission areas in the world. Both gas and oil are seeping constantly through a predominantly sandy seabed into the ocean. This study focused on the methanotrophic activity within the surface sediments (0–15 cm) of the permeable seabed in the so-called Brian Seep area at a water depth of ∼10 m. Detailed investigations of the sediment biogeochemistry of active gas vents indicated that it is driven by fast advective transport of water through the sands, resulting in a deep penetration of oxidants (oxygen, sulfate). Maxima of microbial methane consumption were found at the sediment-water interface and in deeper layers of the sediment, representing either aerobic or anaerobic oxidation of methane, respectively. Methane consumption was relatively low (0.6–8.7 mmol m−2 d-1) in comparison to gas hydrate-bearing fine-grained sediments on the continental shelf. The low rates and the observation of free gas migrating through permeable coastal sediments indicate that a substantial proportion of methane can escape the microbial methane filter in coastal sediments.

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36

Treude, T., and W. Ziebis. "Methane oxidation in permeable sediments at hydrocarbon seeps in the Santa Barbara Channel, California." Biogeosciences Discussions 7, no. 2 (March 17, 2010): 1905–33. http://dx.doi.org/10.5194/bgd-7-1905-2010.

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Abstract. A shallow-water area in the Santa Barbara Channel (California), known collectively as the Coal Oil Point seep field, is one the largest natural submarine oil and gas emission areas in the world. Both gas and oil are seeping constantly through a predominantly sandy seabed into the ocean. This study focused on the methanotrophic activity within the surface sediments (0–15 cm) of the permeable seabed in the so-called Brian Seep area at a water depth ~10 m. Detailed investigations of biogeochemical parameters in the sediment surrounding active gas vents indicated that methane seepage through the permeable seabed induces a convective transport of fluids within the surface sediment layer, which results in a deeper penetration of oxidants (oxygen, sulfate) into the sediment, as well as in a faster removal of potentially inhibiting reduced end products (e.g. hydrogen sulfide). Methanotrophic activity was often found close to the sediment-water interface, indicating the involvement of aerobic bacteria. However, biogeochemical data suggests that the majority of methane is consumed by anaerobic oxidation of methane (AOM) coupled to sulfate reduction below the surface layer (>15 cm), where sulfate is still available in high concentrations. This subsurface maximum of AOM activity in permeable sands is in contrast to known deep-sea seep habitats, where upward fluid advection through more fine-grained sediments leads to an accumulation of AOM activity within the top 10 cm of the sediments, because sulfate is rapidly depleted.

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ETIOPE, G., C. ZWAHLEN, F. S. ANSELMETTI, R. KIPFER, and C. J. SCHUBERT. "Origin and flux of a gas seep in the Northern Alps (Giswil, Switzerland)." Geofluids 10, no. 4 (November 2010): 476–85. http://dx.doi.org/10.1111/j.1468-8123.2010.00302.x.

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38

Blouet, Jean-Philippe, Patrice Imbert, and Anneleen Foubert. "Mechanisms of biogenic gas migration revealed by seep carbonate paragenesis, Panoche Hills, California." AAPG Bulletin 101, no. 08 (August 2017): 1309–40. http://dx.doi.org/10.1306/10171616021.

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39

Roche, Ben, Paul R. White, Jonathan M. Bull, Timothy G. Leighton, Jianghui Li, Colin Christie, and Joseph Fone. "Methods of acoustic gas flux inversion—Investigation into the initial amplitude of bubble excitation." Journal of the Acoustical Society of America 152, no. 2 (August 2022): 799–806. http://dx.doi.org/10.1121/10.0013220.

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Passive acoustic inversion techniques for measuring gas flux into the water column have the potential to be a powerful tool for the long-term monitoring and quantification of natural marine seeps and anthropogenic emissions. Prior inversion techniques have had limited precision due to lack of constraints on the initial amplitude of a bubble's excitation following its release into the water column ([Formula: see text]). [Formula: see text] is determined by observing the acoustic signal of bubbles released from sediment in a controlled experiment and its use is demonstrated by quantifying the flux from a volcanic CO2 seep offshore Panarea (Italy), improving the precision by 78%.

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40

Seliverstov, N. I., P. I. Torokhov, V. N. Dubrovsky, and S. G. Kokarev. "Active seeps and carbonates from the Kamchatsky Gulf (East Kamchatka)." Bulletin of the Geological Society of Denmark 41 (March 30, 1994): 50–54. http://dx.doi.org/10.37570/bgsd-1995-41-05.

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A zone of suginarine gas seepages was discovered on the seafloor of the Kamchatsky Gulf (East Kamchatkar, Gas plumes have been detected in the upper part of the Kamchatsky canyon within a depth range of 40-250 m. Sandstones with carbonate cementation were recovered from the seafloor near the seep locations. Cement occurs as calcite and Mg-calcite. the isotopic composition of carbon from carbonates (613C = -62%0 PDB provides grounds for believing that they originate as a result of methane oxidation.

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Chakraborty, Anirban, S. Emil Ruff, Xiyang Dong, Emily D. Ellefson, Carmen Li, James M. Brooks, Jayme McBee, Bernie B. Bernard, and Casey R. J. Hubert. "Hydrocarbon seepage in the deep seabed links subsurface and seafloor biospheres." Proceedings of the National Academy of Sciences 117, no. 20 (April 30, 2020): 11029–37. http://dx.doi.org/10.1073/pnas.2002289117.

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Marine cold seeps transmit fluids between the subseafloor and seafloor biospheres through upward migration of hydrocarbons that originate in deep sediment layers. It remains unclear how geofluids influence the composition of the seabed microbiome and if they transport deep subsurface life up to the surface. Here we analyzed 172 marine surficial sediments from the deep-water Eastern Gulf of Mexico to assess whether hydrocarbon fluid migration is a mechanism for upward microbial dispersal. While 132 of these sediments contained migrated liquid hydrocarbons, evidence of continuous advective transport of thermogenic alkane gases was observed in 11 sediments. Gas seeps harbored distinct microbial communities featuring bacteria and archaea that are well-known inhabitants of deep biosphere sediments. Specifically, 25 distinct sequence variants within the uncultivated bacterial phyla Atribacteria and Aminicenantes and the archaeal order Thermoprofundales occurred in significantly greater relative sequence abundance along with well-known seep-colonizing members of the bacterial genus Sulfurovum, in the gas-positive sediments. Metabolic predictions guided by metagenome-assembled genomes suggested these organisms are anaerobic heterotrophs capable of nonrespiratory breakdown of organic matter, likely enabling them to inhabit energy-limited deep subseafloor ecosystems. These results point to petroleum geofluids as a vector for the advection-assisted upward dispersal of deep biosphere microbes from subsurface to surface environments, shaping the microbiome of cold seep sediments and providing a general mechanism for the maintenance of microbial diversity in the deep sea.

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42

Hua, Zhi Li, and Zhong Hai Zhou. "Numerical Simulation of Deep Sea Gas Hydrate Plumes." Advanced Materials Research 1010-1012 (August 2014): 1719–22. http://dx.doi.org/10.4028/www.scientific.net/amr.1010-1012.1719.

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Plume is closely related to the presence of gas hydrates which can often be found in plume development area. By acoustic detection, plumes of bubbles in the seawater from shallow gas have been found by marine surveying instruments in some areas over the world. Based on the existed theory of plume porosity, acoustic echo profile of sedbed seep plumes are numerically calculated. Within the simulation results, according to the pattern of gas bubble change and movement in the seawater, process of methane plumes generation is simulated and directs the distribution of bubble radius and plume boundary as depth. Acoustic features of plume bubbles seeping from shallow gas are shown to be consistent with the field results.

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Gal, Frédérick, Eric Proust, and Wolfram Kloppmann. "Towards a Better Knowledge of Natural Methane Releases in the French Alps: A Field Approach." Geofluids 2019 (June 10, 2019): 1–16. http://dx.doi.org/10.1155/2019/6487162.

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We report investigations performed at some hydrocarbon gas seeps located in the French Subalpine Chains in zones of outcropping Jurassic black shales, increasing the reported number of such occurrences in this part of the Alps. We present the characteristics of each of the seeps, based on soil flux measurements and soil gas measurements. Gases emitted are CH4-rich (87–94%) with the exception of one site (78.5% CH4 + 8.2% CO2) where an active landslide may induce dilution by atmospheric air. CO2 is generally measured at low levels (<1.6%). Concentrations in C2H6 are more variable, from less than 1% to more than 2.3%. Gas is emitted over areas of various sizes. The smallest gas emission area measures only 60×20 cm, characterized by a strong hydrocarbon flux (release of about 100 kg of CH4 per year). At a second site, hydrocarbon emissions are measured over a surface of 12 m2. For this site, methane emission is evaluated at 235 kg per year and CO2 emission is 600 kg per year, 210 kg being related to gas seepage. At the third site, hydrocarbons are released over a 60 m2 area but strong gas venting is restricted to localized seeps. Methane emission is evaluated at 5.1 tons per year and CO2 emission at 1.58 tons per year, out of which 0.53 tons are attributed to gas seepage. Several historical locations remain uninvestigated at present, and numerous others may still be unknown. We outline strategies to search for such unrecorded sites. Considering the topography of the potential alpine and perialpine emission areas, the possibilities to detect gas emissions appear of the size recorded so far seem to be restricted to ground-based methods or to methods offering the possibility to point orthogonally to the soil towards the seep maximum. If such sites are to be investigated in the future in the frame of Environmental Baseline Assessment (EBA), even establishing appropriate monitoring protocols will be challenging.

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Baranov, B. V., L. I. Lobkovsky, K. A. Dozorova, and N. V. Tsukanov. "The fault system controlling methane seeps on the shelf of the Laptev Sea." Доклады Академии наук 486, no. 3 (May 30, 2019): 354–58. http://dx.doi.org/10.31857/s0869-56524863354-358.

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The paper presents data obtained during the 69th and 72nd expeditions of the research vessel Akademik Mstislav Keldysh (2017, 2018). A mechanism of methane discharge that explains the localization of the seep fields in a limited area of the outer shelf and suggesting a system of deep and surface faults is proposed. Along the deep faults, gas fluid is transferred to the upper strata of the sedimentary cover, where it is accumulated below the gas hydrate stability zone and the permafrost horizon. The surface faults of the outer shelf break this caprock, creating conduits for the gas to migrate to the surface and to jet-release into the water column.

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45

Bond, Alexander L., William C. Evans, and Ian L. Jones. "Avian Mortality Associated with a Volcanic Gas Seep at Kiska Island, Aleutian Islands, Alaska." Wilson Journal of Ornithology 124, no. 1 (March 2012): 146–51. http://dx.doi.org/10.1676/11-062.1.

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46

Canet, Carles, Pere Anadón, Pura Alfonso, Rosa M. Prol-Ledesma, Ruth E. Villanueva-Estrada, and Maite García-Vallès. "Gas-seep related carbonate and barite authigenic mineralization in the northern Gulf of California." Marine and Petroleum Geology 43 (May 2013): 147–65. http://dx.doi.org/10.1016/j.marpetgeo.2013.02.011.

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47

Greene, Chad A., and Preston S. Wilson. "Laboratory investigation of a passive acoustic method for measurement of underwater gas seep ebullition." Journal of the Acoustical Society of America 131, no. 1 (January 2012): EL61—EL66. http://dx.doi.org/10.1121/1.3670590.

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48

Bojanowski, Maciej J. "Oligocene cold-seep carbonates from the Carpathians and their inferred relation to gas hydrates." Facies 53, no. 3 (May 30, 2007): 347–60. http://dx.doi.org/10.1007/s10347-007-0109-1.

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49

Scoulding, Ben, Rudy Kloser, and Sven Gastauer. "Evaluation of unmanned surface vehicle acoustics for gas seep detection in shallow coastal waters." International Journal of Greenhouse Gas Control 102 (November 2020): 103158. http://dx.doi.org/10.1016/j.ijggc.2020.103158.

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Himmler, Tobias, Diana Sahy, Tõnu Martma, Gerhard Bohrmann, Andreia Plaza-Faverola, Stefan Bünz, Daniel J. Condon, Jochen Knies, and Aivo Lepland. "A 160,000-year-old history of tectonically controlled methane seepage in the Arctic." Science Advances 5, no. 8 (August 2019): eaaw1450. http://dx.doi.org/10.1126/sciadv.aaw1450.

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The geological factors controlling gas release from Arctic deep-water gas reservoirs through seabed methane seeps are poorly constrained. This is partly due to limited data on the precise chronology of past methane emission episodes. Here, we use uranium-thorium dating of seep carbonates sampled from the seabed and from cores drilled at the Vestnesa Ridge, off West Svalbard (79°N, ~1200 m water depth). The carbonate ages reveal three emission episodes during the Penultimate Glacial Maximum (~160,000 to 133,000 years ago), during an interstadial in the last glacial (~50,000 to 40,000 years ago), and in the aftermath of the Last Glacial Maximum (~20,000 to 5,000 years ago), respectively. This chronology suggests that glacial tectonics induced by ice sheet fluctuations on Svalbard mainly controlled methane release from Vestnesa Ridge. Data corroborate past methane release in response to Northern Hemisphere cryosphere variations and suggest that Arctic deep-water gas reservoirs are sensitive to temperature variations over Quaternary time scales.

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