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Large gas bubbles can reach the surface of pools of mud and lava where they burst, often through the formation and expansion of circular holes. Bursting bubbles release volatiles and generate spatter, and hence play a key role in volcanic degassing and volcanic edifice construction. Here, we study the ascent and rupture of bubbles using a combination of field observations at Pâclele Mici (Romania), laboratory experiments with mud from the Imperial Valley (California, USA), numerical simulations and theoretical models. Numerical simulations predict that bubbles ascend through the mud as elliptical caps that develop a dimple at the apex as they impinge on the free surface. We documented the rupture of bubbles in nature and under laboratory conditions using high-speed video. The bursting of mud bubbles starts with the nucleation of multiple holes, which form at a near-constant rate and in quick succession. The quasi-circular holes rapidly grow and coalesce, and the sheet evolves towards a filamentous structure that finally falls back into the mud pool, sometimes breaking up into droplets. The rate of expansion of holes in the sheet can be explained by a generalization of the Taylor-Culick theory, which is shown to hold independent of the fluid rheology.

Terrestrial mud volcanoes represent surface features of channels for subsurface methane transport and, therefore, constitute an important source of methane emission from natural environments. How microbial processes regulate methane emissions in terrestrial mud volcanoes has yet to be fully addressed. This study demonstrated the geochemical characteristics and microbial communities of four mud volcano and seep sites in two geological settings of Sicily, Italy. At sites within the accretionary wedge that exhibited higher methane and sulfate concentrations, the communities were dominated by members capable of catalyzing methane and sulfate metabolisms and organic degradation. In particular, both anaerobic and aerobic methanotrophs were abundant and their abundance distribution coincided with the geochemical transition. In contrast, the sites near Mount Etna were characterized by high fluid salinity, CO2, and low methane and sulfate concentrations, with communities consisting of halophilic organic degraders and sulfur metabolizers, along with a minor presence of aerobic methanotrophs. Substantial variations in community composition and geochemistry across spatial and vertical redox gradients suggest that physicochemical contexts imposed by the geology, fluid path, and source characteristics play a vital role in shaping community composition and cycling of methane, sulfur and organic carbon in Sicily mud volcanoes. [ABSTRACT FROM AUTHOR]

Situated between the petroliferous Cenozoic Zhujiang (Pearl) River Mouth Basin and the mud volcano-rich Mesozoic Dongsha Basin in the middle sector of the northern South China Sea, the Weitan Banks area has been previously mapped as a basement high that is composed of Mesozoic magmatic rocks. In this study, we present several favorable indicators for petroleum geology that were detected from geophysical profiling and benthic sampling in the area. A conspicuous hill was discovered, named "Zhongwei Hill", ∼80 m high above the ∼340 m deep seafloor and ∼1 km broad, in a depression with more than 7 km thick sedimentary strata. The Zhongwei Hill was seismically imaged with a mushroom-shaped structure and containing a cake-like crown, fluid flow pipes, and an ∼10 km broad anticline at depth. Thus, the hill represents a source-plumbing-eruption system. Shallow gas zones linked to deep fracture were found at or near the hill. Stratigraphic correlation indicates that the deep strata comprise the Jurassic and Paleogene strata, the major hosts of hydrocarbon source rocks. In addition to the hill, there are number of mounds from which three bottom water samples were collected and the samples are rich in dissolved methane with concentrations high up to ∼900 nmol/L, much higher than the background level (0.5–2 nmol/L). The benthic samples are rich in coarse sediment clastics, authigenic carbonate nodules, and deep-water habitats likely feeding on methanotrophic community. Given these observations and the context, we propose that the Zhongwei Hill represents a mud volcano, likely thermally driven, that seeps methane from Jurassic and Paleogene source layers, thus poses a favorable clue for significant hydrocarbon generation capacity in transitional zone of the Zhujiang River Mouth Basin and the Dongsha Basin. [ABSTRACT FROM AUTHOR]

One of the crucial tasks in studying the genesis and deep structure of mud volcanoes is to determine the origin of the erupted material and the depth of its original location, the so-called roots. The purpose of this study was to present the first results of stratigraphic control of solid emissions from the Yuzhno-Sakhalinsk Mud Volcano with local stratigraphic units. As a result of field work, a collection of rock material sampled from the mud volcano deposits and natural outcrops of the stratigraphic units typical of the study area has been compiled. According to lithological characteristics, sandstones, siltstones, clay-bearing carbonate, and carbonate rocks have been identified among the large detrital rocks in the solid emissions of the Yuzhno-Sakhalinsk Mud Volcano. The largest group of rock fragments was represented by the sandstone, which was different in its structural and textural characteristics. The first confirmations have been obtained that the mud volcano chamber extends beyond the traditionally accepted boundaries of the Bykov Formation. The preliminary results of stratigraphic control of large detrital rocks indicate the highest lithological similarity with the deposits from the Lower Bykov Subformation and Naiba Formation, suggesting that the main source (mud volcano chamber) of the erupted large detrital rocks lies within the depth range of 2,500 to 3,500 meters. Evidence of Cenozoic rock inclusion in the mud volcano process has also been found.

Deep‐sea chemosynthetic ecosystems are 'oases' of life powered by reducing geofluids, of which serpentinite‐hosted seeps are among the least studied. South Chamorro Seamount, a serpentine mud volcano on the Mariana Arc, has been known to host chemosynthesis‐based assemblages since 1996, but no detailed information on the fauna was published. Here, we revisited South Chamorro to characterise its biodiversity. We located two regions of chemosynthetic communities dominated by bathymodioline mussels, vesicomyid clams, and chaetopterid parchment worms: one on the northwestern flank ('Fryer Site') and one on the southern summit ('Summit Site'). We sampled a total of 20 species including 13 molluscs, five annelids, and two crustaceans – all present on the more active Summit Site but only a subset being found at Fryer Site. A mussel bed surrounding the Fryer Site was drilled by the Ocean Drilling Program in 2001 resulting in six holes, the deepest being 266 m (Hole 1200C). Cuttings ~50 cm deep still cover an approximately 60 m radius around Hole 1200C even 22 years later, and there is no sign of recovery. Low geofluid supply in serpentinite‐hosted seamounts may not allow decadal recovery of animal colonies, unlike a previous drilling site in an Okinawa Trough vent. [ABSTRACT FROM AUTHOR]

Diversity of extremophilic microorganisms in mud volcanoes is largely unexplored. Here we report the isolation of a novel alkaliphilic, mesophilic, fermentative bacterium (strain FN5sucT) from a terrestrial mud volcano located at the Taman Peninsula, Russia. Cells of strain FN5sucT are gram-stain-positive, non-sporeforming, motile rods. The temperature range for growth is 10–37°C, with an optimum at 30°C. The pH range for growth is 7.5–10.0, with an optimum at pH 9.0. The isolate utilizes various organic polymeric substances, organic acids, carbohydrates, and proteinaceous compounds. The end products of carbohydrates fermentation are acetate, CO2 and trace amounts of H2 and formate. The major cellular fatty acid compounds are C16:0, C16:1 ω7c, and monounsaturated dimethyl acetal C14:1. Phylogenetic analysis reveals that strain FN5sucT is most closely related to Petrocella atlantisensis = DSM 105309T (98.4% 16S rRNA gene identity). The total size of the genome of strain FN5sucT is 3.35 Mb, and a genomic DNA G+C content is 37.0 mol %. The genome contains complete glycolisis/glyconeogenesis pathway. We propose to assign strain FN5sucT to the genus Petrocella, as a new species, Petrocella pelovolcani sp. nov. The type strain is FN5sucT (=DSM 113898T = UQM 41591T). [ABSTRACT FROM AUTHOR]

Geothermal features, such as hot springs and mud volcanoes, host diverse microbial life, including many extremophile organisms. The physicochemical parameters of the geothermal feature, such as temperature, pH, and heavy metal concentration, can influence the alpha and beta diversity of microbial life in these environments, as can spatiotemporal differences between sites and sampling. In this study, water and sediment samples were collected and analyzed from eight geothermal sites at Yellowstone National Park, including six hot springs, a mud volcano, and an acidic lake within the same week in July 2019, and these geothermal sites varied greatly in their temperature, pH, and chemical composition. All samples were processed and analyzed with the same methodology and taxonomic profiles and alpha and beta diversity metrics determined with 16S rRNA sequencing. These microbial diversity results were then analyzed with respect to pH, temperature, and chemical composition of the geothermal features. Results indicated that predominant microbial species varied greatly depending on the physicochemical composition of the geothermal site, with decreases in pH and increases in dissolved heavy metals in the water corresponding to decreases in alpha diversity, especially in the sediment samples. Similarly, sites with acidic pH values had more similar microbial populations (beta diversity) to one another than to relatively neutral or alkaline pH geothermal sites. This study suggests that pH and/or heavy metal concentration is a more important driver for microbial diversity and population profile than the temperature for these sites and is also the first reported microbial diversity study for multiple geothermal sites in Yellowstone National Park, including the relatively new mud volcano Black Dragon’s Caldron, which erupted in 1948. [ABSTRACT FROM AUTHOR]

Microbial communities of terrestrial mud volcanoes are involved in aerobic and anaerobic methane oxidation, but the biological mechanisms of these processes are still understudied. We have investigated the taxonomic composition, rates of methane oxidation, and metabolic potential of microbial communities in five mud volcanoes of the Taman Peninsula, Russia. Methane oxidation rates measured by the radiotracer technique varied from 2.0 to 460 nmol CH4 cm−3 day−1 in different mud samples. This is the first measurement of high activity of microbial methane oxidation in terrestrial mud volcanos. 16S rRNA gene amplicon sequencing has shown that Bacteria accounted for 65–99% of prokaryotic diversity in all samples. The most abundant phyla were Pseudomonadota, Desulfobacterota, and Halobacterota. A total of 32 prokaryotic genera, which include methanotrophs, sulfur or iron reducers, and facultative anaerobes with broad metabolic capabilities, were detected in relative abundance >5%. The most highly represented genus of aerobic methanotrophs was Methyloprofundus reaching 36%. The most numerous group of anaerobic methanotrophs was ANME-2a-b (Ca. Methanocomedenaceae), identified in 60% of the samples and attaining relative abundance of 54%. The analysis of the metagenome-assembled genomes of a community with high methane oxidation rate indicates the importance of CO2 fixation, Fe(III) and nitrate reduction, and sulfide oxidation. This study expands current knowledge on the occurrence, distribution, and activity of microorganisms associated with methane cycle in terrestrial mud volcanoes. [ABSTRACT FROM AUTHOR]

Featured Application: Deep geoelectrical mapping of subsurface objectives. This work presents a case study of a geoelectrical exploration of understudied mud volcanoes in Romania, specifically the Pâclele Mici mud volcano from Buzău County. Using a geoelectrical technique facilitated by the distributed network of V-FullWaver equipment, we present, to our knowledge, the first deep 3D case study of a mud volcano in the country. The findings indicate that while geoelectrical surveys in such environments are met with important challenges in terms of soil conductivity, they nonetheless provide a viable approach to uncovering the complex structures and processes of mud volcanoes. We map a part of the mud volcano, showing that the active subsurface part corresponds only partly with what is visible on the surface, and suggest a framework for an in-depth analysis of the extensive mud volcano area. [ABSTRACT FROM AUTHOR]

In spite of wide distribution, the phenomenon of mud volcanism is fragmentarily studied by geoscientists, saying nothing about the role of the mud volcanoes as the geopark components or the independent geoheritage objects. In Azerbaijan (the eastern part) and the adjacent water area of the South Caspian basin, the mud volcanism has its most development in comparison with the rest parts of world. The mentioned area is considered as the host for over 350 mud volcanoes onshore and offshore, differing in type, morphology, dimensions, eruption activity and intensity of fluids’ emitting and even possible risks for the environment. Here, the mud volcanoes, being the unique and noticeable units of the local landscape, claim the attention of not only the geoscientists but also the domestic and foreign tourists. Consequently, it represents a good enough potential for promoting the future geotourism development of the region not only as the geopark component, but also as independent geoheritage units. The study characterizes the provinces of mud volcanoes distribution, their specific features, definitions and classification. Seven remarkable mud volcanoes from various provinces in Azerbaijan had been selected in the present paper. They are described not only as geological objects but also as the landscape units, scenic attraction and local landmarks. The detailed description as well as the images of the volcanoes can give the comprehensive view about the target of research. The study concludes that following the example of the described mud volcanoes, these geological edifices have the good enough potential to gain the status of geoheritage. [ABSTRACT FROM AUTHOR]

Large gas bubbles can reach the surface of pools of mud and lava where they burst, often through the formation and expansion of circular holes. Bursting bubbles release volatiles and generate spatter, and hence play a key role in volcanic degassing and volcanic edifice construction. Here, we study the ascent and rupture of bubbles using a combination of field observations at Pâclele Mici (Romania), laboratory experiments with mud from the Imperial Valley (California, USA), numerical simulations and theoretical models. Numerical simulations predict that bubbles ascend through the mud as elliptical caps that develop a dimple at the apex as they impinge on the free surface. We documented the rupture of bubbles in nature and under laboratory conditions using high-speed video. The bursting of mud bubbles starts with the nucleation of multiple holes, which form at a near-constant rate and in quick succession. The quasi-circular holes rapidly grow and coalesce, and the sheet evolves towards a filamentous structure that finally falls back into the mud pool, sometimes breaking up into droplets. The rate of expansion of holes in the sheet can be explained by a generalization of the Taylor–Culick theory, which is shown to hold independent of the fluid rheology.

Geothermal features, such as hot springs and mud volcanoes, host diverse microbial life, including many extremophile organisms. The physicochemical parameters of the geothermal feature, such as temperature, pH, and heavy metal concentration, can influence the alpha and beta diversity of microbial life in these environments, as can spatiotemporal differences between sites and sampling. In this study, water and sediment samples were collected and analyzed from eight geothermal sites at Yellowstone National Park, including six hot springs, a mud volcano, and an acidic lake within the same week in July 2019, and these geothermal sites varied greatly in their temperature, pH, and chemical composition. All samples were processed and analyzed with the same methodology and taxonomic profiles and alpha and beta diversity metrics determined with 16S rRNA sequencing. These microbial diversity results were then analyzed with respect to pH, temperature, and chemical composition of the geothermal features. Results indicated that predominant microbial species varied greatly depending on the physicochemical composition of the geothermal site, with decreases in pH and increases in dissolved heavy metals in the water corresponding to decreases in alpha diversity, especially in the sediment samples. Similarly, sites with acidic pH values had more similar microbial populations (beta diversity) to one another than to relatively neutral or alkaline pH geothermal sites. This study suggests that pH and/or heavy metal concentration is a more important driver for microbial diversity and population profile than the temperature for these sites and is also the first reported microbial diversity study for multiple geothermal sites in Yellowstone National Park, including the relatively new mud volcano Black Dragon’s Caldron, which erupted in 1948.

Gas hydrates were found in bottom sediments on the western slope of the Kuril Basin from the side of the Terpeniya Gulf (Okhotsk Sea) at 1020 m depths during expeditions in 2012 and 2013. However, on the eastern slope of the Tatar Strait, gas hydrates were sampled at an unusually shallow 322 m depth. During our research, we identified gas hydrate provinces based on both bottom water and sediment temperature measurement data and heat flow, earthquake, cold seep and sea current data analyses. These provinces have similar hydrological regimes, providing suitable temperature conditions for the existence of gas hydrates, to those at a 322 m depth in the Tatar Strait (Japan Sea) and at 725 and 1020 m depths on the slope of the Kuril Basin (Okhotsk Sea). [ABSTRACT FROM AUTHOR]

We identified 27 new mud volcanoes, including potential ones, in a part of the Hyuga-nada area, southwest offshore Japan, at the northern end of the Ryukyu Trench, based on subseafloor geological structures using geophysical investigations. These mud volcanoes exhibited high density and breadth and were likely connected to other mud volcano fields in the south. Acoustic investigations indicated subseafloor structures. Multiple acoustically transparent bodies were interpreted as a region containing gas. They were likely to appear along faults and below the bottom of valleys and sometimes reached the seafloor, expressing mud volcanoes onto the seafloor. They also indicated the wide distribution of subseafloor free-gas throughout the area. These acoustic investigations suggested that a swarm of mud volcanoes exists over the Hyuga-nada area, heterogeneously distributed along a series of plate convergent margins, the Nankai Trough, and the northern part of the Ryukyu Trench. [ABSTRACT FROM AUTHOR]

Mud volcanoes (MVs) are surface structures typically created by episodic discharge of fluids and solids, often associated to onshore and offshore accretionary prisms on convergent plate boundaries. Detailed investigations of ongoing activity and its associated morphological changes, as well as a better understanding of the temporal evolution of these highly dynamic systems, may improve the estimations of material fluxes from MVs drastically. Until today, approximately 70 individual MVs were discovered in the northern Ionian Sea in the Calabrian Arc (Central Mediterranean Sea), but only a few have been analyzed and described in detail. In this study, new evidence for recent recurring eruptive activity of the ~45 m-high and 1 km-wide Sartori MV situated in the clastic wedge of the Calabrian Arc is presented. High-resolution seafloor mapping as well as sediment temperature, geochemical, and sedimentological data received from two research cruises in 2016 and 2020 are used. Bathymetric and seafloor backscatter data (1 m scale) indicate the presence of two active eruption centers at the flat-topped Sartori MV. Elevated sediment temperature gradients at both eruption centers show that currently heat is transferred to the surface sediments. Pore water analyses indicate that fluids rising below the eruption centers are CH4-rich, Cl--poor, and SO42--free. Stable C and H isotopic compositions of methane suggest that it originates from a mix of primary microbial, secondary microbial, and/or thermogenic sources. A relatively shallow position of the sulfate-methane interface at both eruption centers also indicates the presence of upward fluid migration in recent times. Pore water modeling suggests that seawater has penetrated the surface sediments to a greater extent within the last few years. In contrast, centimeter-thick layers of hemipelagic sediments overlying mud breccia in sediment cores taken from both eruption centers show that no solid material has been ejected in recent times. Sediment core analyses combined with high-resolution seafloor mapping show an absence of rim-passing mudflows over the past ~10 ka. It is concluded that Sartori MV is an episodically active MV from which fluids with a comparatively low flux were released into the bottom water in recent times. [ABSTRACT FROM AUTHOR]

Mud volcanoes are geological structures observed throughout the world that arise from the upwelling of deep fluids along discontinuities in the subsoil. The detection of mud fluid migration pathways can be challenging, even when using Electrical Resistivity Tomography (ERT) as detectability issues may arise from complex geological settings. This paper presents new results from 2D and 3D ERT synthetic modelling for the investigation of the shallow, internal structure of terrestrial mud volcanoes. This study revealed the internal structure of the 'Cenerone-Pineto' mud volcano (Central Italy) and provided further clues as to its internal structure. The main results of the study are: the presence of a mud chamber, which represents the last phase of mud accumulation before final emission, not located beneath the crater but laterally offset, as well as the presence of a narrow, shallow feeder channel; these findings represent evidence of a much more complex structure than one would expect. This means that the mud volcano is not supplied with mud fluids directly from below as would be the case with an uprising of deep fluid along a near-vertical open fracture and that the shallow mud fluid reservoir is not correlated to the distribution of any mud volcano observed on the surface. Findings from this study are consistent with the observed structural features already noted in ERT and seismic field data collected at the 'Cenerone-Pineto' mud volcano and may be helpful in explaining the mechanisms and processes involved in mud volcanism in similar geological settings. [ABSTRACT FROM AUTHOR]

Microbial communities of terrestrial mud volcanoes are involved in aerobic and anaerobic methane oxidation, but the biological mechanisms of these processes are still understudied. We have investigated the taxonomic composition, rates of methane oxidation, and metabolic potential of microbial communities in five mud volcanoes of the Taman Peninsula, Russia. Methane oxidation rates measured by the radiotracer technique varied from 2.0 to 460 nmol CH4 cm−3 day−1 in different mud samples. This is the first measurement of high activity of microbial methane oxidation in terrestrial mud volcanos. 16S rRNA gene amplicon sequencing has shown that Bacteria accounted for 65–99% of prokaryotic diversity in all samples. The most abundant phyla were Pseudomonadota, Desulfobacterota, and Halobacterota. A total of 32 prokaryotic genera, which include methanotrophs, sulfur or iron reducers, and facultative anaerobes with broad metabolic capabilities, were detected in relative abundance >5%. The most highly represented genus of aerobic methanotrophs was Methyloprofundus reaching 36%. The most numerous group of anaerobic methanotrophs was ANME-2a-b (Ca. Methanocomedenaceae), identified in 60% of the samples and attaining relative abundance of 54%. The analysis of the metagenome-assembled genomes of a community with high methane oxidation rate indicates the importance of CO2 fixation, Fe(III) and nitrate reduction, and sulfide oxidation. This study expands current knowledge on the occurrence, distribution, and activity of microorganisms associated with methane cycle in terrestrial mud volcanoes.

An integrated study of mud volcanoes in the World Ocean is important for making assessment of potential geological-ecological disasters caused by rapid large-volume gas discharge into the water column and mud volcano eruptions at the bottom. The study of mud-volcanic activity in the past and determination of its periodicity are pioneering for the Baikal. The mud volcanoes and other hydrate-bearing structures are largely concentrated in the Middle Baikal basin along the tectonic faults. The most representative example of these phenomena is the "Gydratny" fault, four of six structures along which are mud volcanoes. An integrated geological-geophysical study (seismoacoustic and hydroacoustic sounding and geological sampling) of the "Novosibirsk" mud volcano, the largest and well-pronounced feature of the lake bottom relief, confirmed its structural identity with classical submarine mud volcanoes. The "Novosibirsk" mud volcano possesses all major elements of other single hydrate-bearing mud volcanoes of the lake which include volcanic cone in the bottom relief, vertical acoustically not transparent feeding channel, mud-volcanic breccia, gas saturation, and gas hydrates. This makes it one of the reference hydrate-bearing mud volcanic-type structures of Lake Baikal.The analysis of the bottom hydroacoustic profiling yielded evidence of the Late Pleistocene mud-volcanic eruptions shaped as two layers-flows at sub-bottom depths of 15 and 26 m (30 and 50 kyr ago, respectively). The presence of mud-volcanic breccia beneath the thin Holocene diatomic silt deposits testifies to the Holocene mud volcano activation due to the warm fluid rising from the depths to the volcano roots along the active segment of the tectonic fault in accordance with the model of the "Baikal-type" mud volcanism. Using the "Novosibirsk" mud volcano and the "Gydratny" fault as an example, it can be shown that the past tectonic activity of the Baikal basin may be determined based on the knowledge of the structure and evolution of the mud volcanoes of the lake.

The debate about the conceptual model of mud volcanoes functioning is still alive in the literature. A large part of the literature focuses on the characterization of the deep reservoir where expelled fluids are expected to originate. Another part of literature is focused on the study of the shallow system of mud volcanoes, which could influence the short‐term variations in mud volcanoes activity. We present and analyze a new data set of micro‐gravimetric data to study the area of the Nirano Salse, Italy. Unlike what is commonly assumed for the study area, our results suggest that the geomorphology of the Nirano Salse is not related to a caldera collapse above a shallow mud chamber, but to the surface expression of slip distribution of a fault termination along which the fluids ascended to the surface. We believe that gravimetric data can significantly improve the study of hydrocarbon seeps and mud volcanism. Plain Language Summary: Mud volcanoes are broadly distributed throughout the globe, both on‐and off‐shore. They are formed by the episodic eruption of mud and rock fragments. The eruptions are mainly driven by of gravitative instability, due to the overall low density of clay on surrounding soil types and fluid overpressures. To date, a physical conceptual model of the area of Nirano Salse (Northern Italy), ascribes the mud eruptions to the presence of over‐pressurized fluids that are expelled from a main deep reservoir. The latter is put into communication with the surface due to the episodical reactivation of pre‐existing faults or pipes. The debate about this conceptual model is still open. To improve it, a new data set of gravimetric data was acquired during 2022. Our results suggest that the morphology of the study area is due to the presence of an almost vertical fault, which acts as a preferential route for the ascent of deep fluids. Key Points: A microgravimetric survey coupled with laboratory density measurements allows to image the shallow to medium subsurface below mud volcanoesGravimetric data allow to distinguish between morphologies due to caldera collapse and the surface expression of slip along a faultFor the first time the attenuation volume caused by mud intrusion is imaged by gravimetry along a fault [ABSTRACT FROM AUTHOR]

Chemosynthetic ecosystems powered by microbial primary production are rare 'hot spots' of biological activity in the deep‐sea characterized by dense aggregations of specially adapted animal species. Among settings where such systems have been found, serpentinite‐hosted seep systems supported by alkaline geofluid are particularly understudied with just a few known sites worldwide. Mariana Forearc hosts the world's only series of active serpentinite mud volcanoes, but seep communities have only been reported from South Chamorro Seamount where large bathymodioline mussels dominate. Here, we report the discovery of a serpentinite‐hosted seep on the conical summit of Asùt Tesoru Seamount, Mariana Forearc. Named the 'Big Blue Seep', this field features white, likely carbonate crusts inhabited by animals, under which fluid seepage could be seen. We confirm 16 animal species, including typical seep‐associated fauna such as Desbruyeresia gastropods and Acharax awning‐clams. This is surprising as previous research expeditions did not notice any sign of chemosynthesis‐based ecosystems on this seamount, although the community is indeed difficult to spot due to the lack of large‐bodied epifauna such as mussels. The Big Blue Seep is adjacent to three drill holes made by the International Ocean Discovery Program expedition 366 (Holes U1496A‐C), which may have impact on seepage. Our findings represent the second chemosynthesis‐based ecosystem associated with serpentinite mud volcanism, suggestive of further such communities on other Mariana Forearc mud volcanoes. [ABSTRACT FROM AUTHOR]

Identification of methane origins remains a challenging work as current diagnostic signals are often not sufficient to resolve individual formation and post‐formation processes. To address such a knowledge gap in a tectonically active and fragmented terrain, samples from mud volcanoes, gas seeps, and springs distributed along structural features onshore and offshore of Taiwan were analyzed for their isotopic compositions of methane, nitrogen, helium, dissolved inorganic carbon, CO2, and water. Our analyses yielded Δ13CH3D and Δ12CH2D2 values ranging between +1.9‰ and +7.8‰ and between +3.0‰ and +19.9‰, respectively. A portion of the samples were characterized by values that represent the thermodynamic equilibrium at temperatures of 99°–260°C. These temperature estimates, together with the bulk isotopic compositions and local geothermal gradients (25°–30°C/km), suggest that methane was formed by thermal maturation of organic matter at depths of 2–9 km below the land surface and channeled upward along faults. Other samples were found to deviate from equilibrium by varying degrees. Considering the geological background, helium isotopic ratios, and nitrogen isotopologue compositions, and methanogens detected at some sites, these gases are either abiotic in origin or a mixture of microbial and thermogenic sources. Regardless of whether the equilibrium of methane isotopologues was reached, few sites hosted by sedimentary formations were characterized by mantle‐like helium signatures, indicating decoupled origins and potential degassing of helium from the relic igneous source. Overall, these results suggest the extraction of methane and other gases from multiple depths from strata fragmented by fault displacement in an active orogenic belt. Plain Language Summary: Mud volcanoes and gas seeps are distributed primarily in active tectonic regimes and represent the surface expression of subsurface fracture networks. They provide rapid access to probing subsurface characteristics for the generations of methane, other gases, and water. Identifying the exact mechanisms of methane formation remains a challenging work due to the lack of diagnostic signals with sufficient resolving power. This study employed a wide range of isotopic tools to constrain the origins of gases and water from mud volcanoes and seeps in Taiwan, where dual subductions and associated arc‐continent collision between the Philippine Sea and Eurasian plates have enabled the plumbing of gases and water in accordance with structure development and stratum deformation. Our results reveal a spectrum of geochemical characteristics that point to diverse formation mechanisms and conditions. In particular, deeply sourced thermogenic methane (from depths of 2–9 km) appears to constitute a major gas component at most sites, and is mixed by various degrees with abiotic methane pertinent to igneous bodies emplaced during subduction/collision, or microbial methane generated at shallow depths. Overall, the results address the temporal and spatial variations in gas origins prone to terrain fragmentation and dynamic structural control associated with mountain building. Key Points: Mud volcanoes and gas seeps provide rapid access to probing subsurface fluid characteristics in tectonically active regionsThermogenic methane constitutes a major component of hydrocarbons and forms at temperatures of 99°–260°CA wide spectrum of geochemical characteristics indicates diverse formation mechanisms and conditions that constrain gas and water origins [ABSTRACT FROM AUTHOR]

This work presents a case study of a geoelectrical exploration of understudied mud volcanoes in Romania, specifically the Pâclele Mici mud volcano from Buzău County. Using a geoelectrical technique facilitated by the distributed network of V-FullWaver equipment, we present, to our knowledge, the first deep 3D case study of a mud volcano in the country. The findings indicate that while geoelectrical surveys in such environments are met with important challenges in terms of soil conductivity, they nonetheless provide a viable approach to uncovering the complex structures and processes of mud volcanoes. We map a part of the mud volcano, showing that the active subsurface part corresponds only partly with what is visible on the surface, and suggest a framework for an in-depth analysis of the extensive mud volcano area.

Mud volcanoes (MVs) are surface structures typically created by episodic discharge of fluids and solids, often associated to onshore and offshore accretionary prisms on convergent plate boundaries. Detailed investigations of ongoing activity and its associated morphological changes, as well as a better understanding of the temporal evolution of these highly dynamic systems, may improve the estimations of material fluxes from MVs drastically. Until today, approximately 70 individual MVs were discovered in the northern Ionian Sea in the Calabrian Arc (Central Mediterranean Sea), but only a few have been analyzed and described in detail. In this study, new evidence for recent recurring eruptive activity of the ∼45 m-high and 1 km-wide Sartori MV situated in the clastic wedge of the Calabrian Arc is presented. High-resolution seafloor mapping as well as sediment temperature, geochemical, and sedimentological data received from two research cruises in 2016 and 2020 are used. Bathymetric and seafloor backscatter data (1 m scale) indicate the presence of two active eruption centers at the flat-topped Sartori MV. Elevated sediment temperature gradients at both eruption centers show that currently heat is transferred to the surface sediments. Pore water analyses indicate that fluids rising below the eruption centers are CH4-rich, Cl−-poor, and SO42−-free. Stable C and H isotopic compositions of methane suggest that it originates from a mix of primary microbial, secondary microbial, and/or thermogenic sources. A relatively shallow position of the sulfate–methane interface at both eruption centers also indicates the presence of upward fluid migration in recent times. Pore water modeling suggests that seawater has penetrated the surface sediments to a greater extent within the last few years. In contrast, centimeter-thick layers of hemipelagic sediments overlying mud breccia in sediment cores taken from both eruption centers show that no solid material has been ejected in recent times. Sediment core analyses combined with high-resolution seafloor mapping show an absence of rim-passing mudflows over the past ∼10 ka. It is concluded that Sartori MV is an episodically active MV from which fluids with a comparatively low flux were released into the bottom water in recent times.

We identified 27 new mud volcanoes, including potential ones, in a part of the Hyuga-nada area, southwest offshore Japan, at the northern end of the Ryukyu Trench, based on subseafloor geological structures using geophysical investigations. These mud volcanoes exhibited high density and breadth and were likely connected to other mud volcano fields in the south. Acoustic investigations indicated subseafloor structures. Multiple acoustically transparent bodies were interpreted as a region containing gas. They were likely to appear along faults and below the bottom of valleys and sometimes reached the seafloor, expressing mud volcanoes onto the seafloor. They also indicated the wide distribution of subseafloor free-gas throughout the area. These acoustic investigations suggested that a swarm of mud volcanoes exists over the Hyuga-nada area, heterogeneously distributed along a series of plate convergent margins, the Nankai Trough, and the northern part of the Ryukyu Trench.

Abstract The debate about the conceptual model of mud volcanoes functioning is still alive in the literature. A large part of the literature focuses on the characterization of the deep reservoir where expelled fluids are expected to originate. Another part of literature is focused on the study of the shallow system of mud volcanoes, which could influence the short‐term variations in mud volcanoes activity. We present and analyze a new data set of micro‐gravimetric data to study the area of the Nirano Salse, Italy. Unlike what is commonly assumed for the study area, our results suggest that the geomorphology of the Nirano Salse is not related to a caldera collapse above a shallow mud chamber, but to the surface expression of slip distribution of a fault termination along which the fluids ascended to the surface. We believe that gravimetric data can significantly improve the study of hydrocarbon seeps and mud volcanism.

Abstract Identification of methane origins remains a challenging work as current diagnostic signals are often not sufficient to resolve individual formation and post‐formation processes. To address such a knowledge gap in a tectonically active and fragmented terrain, samples from mud volcanoes, gas seeps, and springs distributed along structural features onshore and offshore of Taiwan were analyzed for their isotopic compositions of methane, nitrogen, helium, dissolved inorganic carbon, CO2, and water. Our analyses yielded Δ13CH3D and Δ12CH2D2 values ranging between +1.9‰ and +7.8‰ and between +3.0‰ and +19.9‰, respectively. A portion of the samples were characterized by values that represent the thermodynamic equilibrium at temperatures of 99°–260°C. These temperature estimates, together with the bulk isotopic compositions and local geothermal gradients (25°–30°C/km), suggest that methane was formed by thermal maturation of organic matter at depths of 2–9 km below the land surface and channeled upward along faults. Other samples were found to deviate from equilibrium by varying degrees. Considering the geological background, helium isotopic ratios, and nitrogen isotopologue compositions, and methanogens detected at some sites, these gases are either abiotic in origin or a mixture of microbial and thermogenic sources. Regardless of whether the equilibrium of methane isotopologues was reached, few sites hosted by sedimentary formations were characterized by mantle‐like helium signatures, indicating decoupled origins and potential degassing of helium from the relic igneous source. Overall, these results suggest the extraction of methane and other gases from multiple depths from strata fragmented by fault displacement in an active orogenic belt.

Mud volcanoes can cause various geohazards, so it is very important to know their activity level and their distribution. Surface sediments were collected from four submarine mud volcanoes (MVs) off Tanegashima (SW Japan), namely, MV1, MV2, MV3, and MV14. We extracted pore water from the surface sediments and investigated its chemical and isotopic compositions. The sodium (Na) and chloride (Cl-) concentrations decreased and the boron (B) and lithium (Li) concentrations increased with increasing depth, suggesting that some fluids with lower Na and Cl- concentrations and higher B and Li concentrations than seawater were supplied upward from the deep sub-seafloor. The fluid advection velocities estimated from the pore-water profiles differed for each MV, and those of MV3 were the fastest (14 cm/yr) in this study. The estimated equilibrium temperature with clay minerals using Na and Li concentrations were 93-134°C, corresponding to the temperature of environments around 3.7 to 5.3 km below the seafloor. This indicates that these components originated from these depths and that the origin depth did not reach the plate boundary in this area. The B isotope ratio in the pore water was extremely high up to +57 ‰, suggesting that it was strongly affected by adsorption onto the surface of the sediments. A higher B isotope ratio (+57 ‰) was detected in MV3, which was considered to be more active, indicating that more B was adsorbed onto clay minerals supplied from deeper depths.

An alkaliphilic, sulfate-reducing, anaerobic bacterium (strain H1T) was isolated from a terrestrial mud volcano at the Taman Peninsula, Russia. The cells of the isolate were gram-negative motile vibrios, 1 µm in diameter and 2.0–2.5 µm in length. Strain H1T grew at 14–42°C (optimum at 37°C), pH 8.5–10.5 (optimum at pH 9.5), and NaCl concentrations of 0.5–6% (wt/vol) (optimum at 0.5–1.5%); pyruvate, lactate, butyrate, caproate, or pelargonate were used as electron donors, and elemental sulfur, sulfite, or sulfate were used as electron acceptors. Pyruvate and lactate were fermented. No growth occurred in the presence of oxygen. Thiosulfate, DMSO, fumarate, nitrate, nitrite, arsenate, selenite, and Fe(III) were not used as electron acceptors. Elemental sulfur, thiosulfate, and sulfite were not disproportionated. Glucose, fructose, sucrose, trehalose, galactose, xylose, fumarate, citrate, yeast extract, and peptone were not fermented. Predominant fatty acids were C20:0 (54.2%), C22:0 (24.6%), and C18:0 (11.1%). The genome of strain H1T was 3.66 Mb in size and had G + C DNA content of 51.1%. The genome contained the genes encoding the enzymes of dissimilatory sulfate reduction and β-oxidation of fatty acids. According to the results of analysis of the 16S rRNA gene sequence, Desulfobotulus mexicanus was the organism most closely related to strain Н1Т (98.3% similarity). Based on its phenotypic characteristics and the data of phylogenetic analysis, affiliation of the isolate as member of a novel Desulfobotulus species, Desulfobotulus pelophilus sp. nov., is proposed, with the type strain H1T (=DSM 112796T = VKM B-3697Т =UQM 41590T). [ABSTRACT FROM AUTHOR]

A novel alkaliphilic sulfate-reducing bacterium, strain M08butT, was isolated from a salsa lake of terrestrial mud volcano (Taman Peninsula, Russia). Cells were rod-shaped, motile and Gram-stain-negative. The temperature range for growth was 15–42 °C (optimum at 30 °C). The pH range for growth was 7.0–11.0, with an optimum at pH 8.5–9.0 Strain M08butT used sulfate, thiosulfate, sulfite, dimethyl sulfoxide and arsenate as electron acceptors. Acetate, formate, butyrate, fumarate, succinate, glycerol and pyruvate were utilized as electron donors with sulfate. Fermentative growth was observed with fumarate, pyruvate, crotonate. Strain M08butT grew chemolithoautotrophically with H2 and CO2. The G + C content of the genomic DNA was 60.1%. The fatty acid profile of strain M08butT was characterized by the presence of anteiso-C15:0 as the major component (68.8%). The closest phylogenetic relative of strain M08butT was Desulfatitalea tepidiphila (the order Desulfobacterales) with 96.3% 16S rRNA gene sequence similarity. Based on the phenotypic, genotypic and phylogenetic characteristics of the isolate, strain M08butT is considered to represent a novel species of the genus Desulfatitalea, with proposed name Desulfatitalea alkaliphila sp. nov. The type strain of Desulfatitalea alkaliphila is M08butT (= KCTC 25382T = VKM B-3560T = DSM 113909T = JCM 39202T = UQM 41473T). [ABSTRACT FROM AUTHOR]

Many features indicative of natural gas and oil leakage are delineated in the deep-water Orange Basin offshore South Africa using 3D reflection seismic data. These features are influenced by the translational and compressional domains of an underlying Upper Cretaceous deep-water fold-and-thrust belt (DWFTB) system detaching Turonian shales. The origin of hydrocarbons is postulated to be from both: (a) thermogenic sources stemming from the speculative Turonian and proven Aptian source rocks at depth; and (b) biogenic sources from organic-rich sediments in the Cenozoic attributed to the Benguela Current upwelling system. The late Campanian surface has a dense population of > 950 pockmarks classified into three groups based on their variable shapes and diameter: giant (> 1500 m), crater (~ 700–900 m) and simple (< 500 m) pockmarks. A total of 85 simple pockmarks are observed on the present-day seafloor in the same area as those imaged on the late Campanian surface found together with mass wasting. A major slump scar in the north surrounds a ~ 4200 m long, tectonically controlled mud volcano. The vent of the elongated mud volcano is near-vertical and situated along the axis of a large anticline marking the intersection of the translational and compressional domains. Along the same fold further south, the greatest accumulation of hydrocarbons is indicated by a positive high amplitude anomaly (PHAA) within a late Campanian anticline. Vast economical hydrocarbon reservoirs have yet to be exploited from the deep-water Orange Basin, as evidenced by the widespread occurrence of natural gas/fluid escape features imaged in this study. [ABSTRACT FROM AUTHOR]

Abstract Mud volcano (MV) is one of the most important channels for deep seated volatile materials to migrate to Earth’s surface in the sedimentary basins at subduction zones. It plays a meaningful role of elemental budget in hydrosphere. Waters of MV fluid emitted from 46 mud pools in MV Lei-Gong-Huo (LGH) in eastern Taiwan were sampled from October 2015 to July 2016 monthly. Previous research indicates that the chemical characteristic of fluid expelled by MV LGH is dominated by two-end-member mixing of water–rock interaction with sedimentary and igneous rocks (Chao et al., Front Earth Sci 9:750436, 2022). Trace elements of 165 mud pool samples, including Al, Co, Ni, Cu, Zn, As, Br, Rb, Mo, Sb, I, Cs, Pb and U, were measured. The results show that waters of MV LGH reveal similar chemical characteristics to low-temperature ridge-flank hydrothermal spring and marine pore water in anoxic conditions coupled with the addition of clay dehydration. Principle component analysis (PCA) with previous published variables (Chao et al., Front Earth Sci 9:750436, 2022) indicates the important factors are the source of water–rock interaction, the surface ion exchange, the redox condition of mud pool, and the evaporation. In summary, the concentration of trace elements in the waters expelled by MV LGH is in the range of nM to pM. Their behaviors are dominated by secondary factors during and after migration such as surface ion exchange in response to changes in pressure and temperature, redox state of the mud pool, and evaporation. Trace elements in MV water are not suitable for fluid source or provenance studies.

Betula platyphylla is one of the main forest-forming species in Northeast Asia. In the Russian Far East, it forms birch and diverse mixed forests. Due to high germinative ability and growth rates, unpretentiousness, resistance to wind, drought, low and high temperatures, Betula platyphylla dominates after clear-cutting, fi and on pyroclastic deposits of volcanoes, and further forms favorable conditions for the restoration of zone coniferous forests. This paper studies the populations of Betula platyphylla under the various conditions of mid-mountain massifs, sea shores, active magmatic and mud volcanoes in the south of Sakhalin and Kuril Islands. Tree age and height were measured and macro- and micro-characteristics of the bark and wood of stems were identified in each habitat from 15 trees using the cleavages, cores and sections. The results of the study have shown that Betula platyphylla under the impact of natural stress is characterized by the formation of a low-growing multi-stemmed tree with significant damage and deformation of the crown, twisted eccentric stems and structural basal anomalies – woodknobs and gnarls. The structural reaction of the bark and wood of the Betula platyphylla, character for many woody plants adapted to extreme habitats, which manifests itself in a decrease in the bark thickness and its growth rate in mature trees was revealed on the Okhotsk coast and under the conditions of the mud volcano on Sakhalin. Under the conditions of gas-hydrothermal springs of magmatic volcanoes, the bark thickness growth rate increases up to 2.7 times compared to the norm, which is probably associated with the young age of trees (10–20 years). The data we have obtained additionally substantiate the adaptive significance of the life strategy of the Betula platyphylla as a fast-growing tree species and show that the bark thickness of woody plants and its growth rate can be the plant functional traits that characterize the natural landscape systems with varying degrees of intensity of ecological factors.

The methods of remote sensing of the Earth, due to their efficiency and information content, are widely used to research vegetation dynamics and monitor volcanic activity. The purpose of this work is to research the dynamics of the mud volcanic landscapes and vegetation cover of the Yuzhno-Sakhalinsk mud volcano, as well as its eruption, using Earth remote sensing data. The total area of the study area is 11.5 km2. The work was done in QGIS 3.16 program using Sentinel-2B satellite image, images from Google Earth program and graphic maps of the study area created by O.A. Melnikov and V.V. Ershov. An updated large-scale schematic map of the Yuzhno-Sakhalinsk mud volcano has been created, displaying all known volcanic eruption fields over the last 70 years, modern and extinct eruptive centers. A semi-automatic classification of the Sentinel-2B satellite image was carried out using the methods of supervised and unsupervised classification using the Semi-Automatic Classification Plugin module. Based on the results of two types of classification, the areas of vegetation classes of the study area were calculated and two maps of the vegetation cover of the Yuzhno-Sakhalinsk mud volcano were created on a scale of 1 : 50 000 as of 2018. The maps need to be refined, but they can already be used to analyze the dynamics of the vegetation cover of the study area. In our opinion, it is more expedient to apply unsupervised classification before conducting a field survey of the area of interest, and supervised classification after. The practical significance of satellite monitoring of the Yuzhno-Sakhalinsk mud volcano lies in the ability to quickly monitor its activity, assess the recreational load and study the impact of volcano activity on vegetation and the landscape as a whole.

Mud volcanoes are natural phenomena that provide an essential source of information about subsurface sediments and deep structures. The phenomenon is usually associated with hydrocarbon accumulations in deep-seated strata. More than 30% of all mud volcanoes in the world are concentrated in the South Caspian Basin. Gorgan plain, as a part of the south Caspian lowland, is a transition zone between uplifting zones of the Alborz and Kopet Dagh and the subsiding basin of the south Caspian. Four active mud volcanoes in the western parts of the Gorgan Plain have extrusion of gas and mud. The existence of the possible hydrocarbon contents in this plain caused a reflection seismic survey and exploratory wells were performed in this area by the National Iranian Oil Company. In this paper, we used 2-D reflection seismic data and well top data for the investigation of stratigraphy and structural setting of the Neftlijeh and Gharnyaregh mud volcanoes. According to the Well Report, the area sediments are composed of the Tertiary to Quaternary sediments of the SCB and underlying pre-Tertiary sequence of the Kopet-Dagh basin and a missing Oligocene, Eocene, Paleocene and upper Cretaceous deposition are observed in the well. The interpretation of the seismic section shows that the Caspian basin deposits reveal a partial deformation and increasingly sloping toward the depocenter, while the sequence of Kopet Dagh is folded. The Neftlijeh and Gharnyaregh mud volcanoes occurred on subsurface anticline axes of the Kopet Dagh and a cluster of conjugate normal faults developed into the Cenozoic formations above the hinge zone of these anticlines. The subsidence pattern is observable at the summit of the anticlines. The structure suggests the presence of a chamber within the crest of the anticline. It seems extrusion and material removal from this chamber caused subsidence and forming of the structure. The Oligo-Miocene Maykop Formation is the significant source of both the extruded mud and the petroleum in the south Caspian basin, which is not observed in the studied well due to later regional erosion. However, the Cheleken and Apsheron deposits, known as reservoir rocks, have a large thickness in the area. The Kashafrud Formations are considered as the main source rock for the Kopet Dagh basin and the Mozduran and Tirgan formations are known as reservoir rocks. The occurrence of the Late Eocene compressional tectonic phase and following the folding of the Mesozoic sedimentary created structural traps at the strata. In addition, continued diapirism and uplifting of the deep-seated strata led to the growth of extensional faults and fractures over the hinge zones. These structures provide effective pathways for gas and fluid ascent from deep reservoirs to the surface. Generally, the results suggest that these mud volcanoes have a spatial and genetic relationship with buried folds. It seems the location of Gharenyaregh and Neftelijeh mud volcanoes is controlled by subsurface anticlines and their feeding source originated from both the Tertiary (SCB) and Pre-Tertiary (Kopet Dagh) units. [ABSTRACT FROM AUTHOR]

The violent eruption of Karabetova Gora mud volcano on 6 May 2000 (Taman Peninsula, 45°12′16″ N; 36°47′05″ E) triggered gas ignition as a giant straight-flow vertical gas flare. The 400 m high, short-lived (~15 min) gas flare left no thermal halo on the ground surface, but the thermal shock caused melting or annealing of mud masses which became dispersed in ≤2 m3 blocks to distances within 30 m around the volcano conduit. The flare reached the maximum temperatures (~1400–1540 °C) at heights from 75 to 250 m, as estimated by a numerical simulation in SigmaFlow. Bulk melting of dehydrated mud masses was mostly limited to <1.5 cm near the surface of the blocks. Porous paralavas at the site consisted of low- and high-silica K-Al glasses (70%–80%) with residual unmolten grains of detrital quartz and fine (<30 µm) new phases: main intermediate members of the magnetite–ulvöspinel solid solutions and plagioclase (An45-61Ab37-44Or2-11 to An73-90Ab10-27Or0.5-1), minor cordierite (XFe = 26%–46%), pigeonite (XFe = 42%–60%), tridymite, cristobalite, and rare mullite. The metapelitic rocks affected by combustion metamorphism were heterogeneous in terms of phase composition and texture. They failed to attain homogeneity due to the high viscosity of anhydrous silicate melts and brevity of the thermal impact. The revealed features of rocks altered by a giant gas fire may serve as a proxy for phase transformation patterns in highly disequilibrium conditions of a thermal shock, far from the formation conditions of ordinary metamorphic rocks. [ABSTRACT FROM AUTHOR]

The key microbial group involved in anaerobic methane oxidation is anaerobic methanotrophic archaea (ANME). From a terrestrial mud volcano, we enriched a microbial community containing ANME-2a, using methane as an electron donor, Fe(III) oxide (ferrihydrite) as an electron acceptor, and anthraquinone-2,6-disulfonate as an electron shuttle. Ferrihydrite reduction led to the formation of a black, highly magnetic precipitate. A significant relative abundance of ANME-2a in batch cultures was observed over five subsequent transfers. Phylogenetic analysis revealed that, in addition to ANME-2a, two bacterial taxa belonging to uncultured Desulfobulbaceae and Anaerolineaceae were constantly present in all enrichments. Metagenome-assembled genomes (MAGs) of ANME-2a contained a complete set of genes for methanogenesis and numerous genes of multiheme c-type cytochromes (MHC), indicating the capability of methanotrophs to transfer electrons to metal oxides or to a bacterial partner. One of the ANME MAGs encoded respiratory arsenate reductase (Arr), suggesting the potential for a direct coupling of methane oxidation with As(V) reduction in the single microorganism. The same MAG also encoded uptake [NiFe] hydrogenase, which is uncommon for ANME-2. The MAG of uncultured Desulfobulbaceae contained genes of dissimilatory sulfate reduction, a Wood–Ljungdahl pathway for autotrophic CO2 fixation, hydrogenases, and 43 MHC. We hypothesize that uncultured Desulfobulbaceae is a bacterial partner of ANME-2a, which mediates extracellular electron transfer to Fe(III) oxide. [ABSTRACT FROM AUTHOR]

The article is devoted to the study of the geological structure of the lower parts of the Productive Series of the Lower Pliocene of the Kurovdagh field. It consists of an introduction, problem statement, research questions, research methodology, results, conclusion and list of references. The introduction provides basic information about the field under study, its geographical location, the history of geological and geophysical studies, the lithology of the section, the structure of the Kyurovdag fold and the oil and gas potential of the field. Oil and gas presence inthefield is related to the Absheron stage of Pleistocene, Akchagyl stage and Productive Series (horizons PS01—PS23) of Neogene. Despite the long-term production from the field, the lower parts of the Productive Series and underlying sediments have not been recovered and sufficiently studied by deep drilling due to the complicated surface and deepseismo-geological environment. It has been recommended to carry out a 3D seismic survey due to a high level of lateral one-fold reflections on seismic records. The major goals of the 3D seismic survey were studyingthe Kurovdagh field's geologic setting, obtaining characteristics previously unknown to geoscientists, and providing detailed research on velocity section to derive prognostic time-depth dependence. It was noted that thePetroalliance Services Company Limited geophysical company has performed a field seismic survey on request «The Caspian Energy Group» company. Processing of the acquired data used the FOCUS 5.4 software package manufactured by Paradigm Geophysical. For repeated interpretation of 3D seismic survey data, the 3D CDP data acquired from the field were used. The kinematic analysis by use of the 3 D cubes revealed the difference by the time shift, frequency spectrum, and amplitude range. The 3 D cubes were brought to a single formby time, phase, and amplitude. The further kinematic interpretation displayed the good quality of the data acquired from Kurovdagh area. The study applied PANGEYA® software for a multi-attribute geological and geophysical data analysis and the standard interpretation. For volumetric modeling of the productive layers of the Kurovdagh oil field, we used the PETREL.10.2 software package. The study targets included complex, lithologically, and tectonically sealed deposits of Productive Series PS01—PS09 and Akchagyl stage (AKCH). Productive layers are attributed to Neogene's Pliocene stage within the Caspian basin's limits. It is represented by a thick series of continental, coastal, and marine sediments (sand, clay, coarsely fragmented depositions) of 1600 m thickness and is unconformity laying over the Pontian stage and covered by the Akchagyl layers in a transgressive form. The Akchagyl stage is one of the stages of the Upper Pliocene which is made of clay, limestone, marl, sandstone, sand, and conglomerates. It became clear that the Kurovdagh field is characterized by a block type structure across the geological section. Block sizes are almost unchanged, evidencing conformance of structural stages and heritance of tectonic movements. Mud volcano and diapiric folding and their sizes are the major distinguishing features of the area.

Mud volcanoes are topographic features through which over-pressurized sediments are intruded upward and erupted, transporting fluids and sediments from the deep subsurface to the surface/seafloor. To understand material and biogeochemical cycling through mud volcanoes, we investigated the origins of sediments and fluids erupted by four submarine mud volcanoes off Tanegashima Island, along the northern Ryukyu Trench: MV#1–3 and MV#14. We estimated the ages of the source sequences of the mud volcano sediments to be middle to late Miocene based on nannofossils and 10Be ages. The sediments were characteristically enriched in illite. The similar mineral compositions and vitrinite reflectance values (0.42%–0.45%) of sediments erupted by the mud volcanoes strongly suggest that each is rooted in the same source sequence. Pore waters had Cl− concentrations ∼40% that of seawater and were proportionally enriched in 18O and depleted in D, indicating the addition of freshwater from the dehydration of clay minerals. However, the smectite and illite contents (

An eruption occurred on Dashli Island, 75 km from Baku, on 4th of July 2021, at 21:51 local time. The island is known as the mud volcano and has a history of eruption. We suspected that mud volcano eruption causes emergence on this island. Thus, the effect of this 2021 eruption is investigated using a remote sensing technique. Processed Sentinel-1 and 2 images are employed for this aim. We considered pre- and post-eruption scenarios to evaluate the effect of this eruption on the island. Satellite image classification is used to calculate shoreline changes. Results show that Dashli Island with an area of about 8.55 ha before eruption is now expanded to about 21.8 ha (about 155% increase). The DInSAR method is used to estimate the ground displacement of the island. According to the results, a two-year-displacement before the eruption was between 0.18 and 0.2 m, while a five-month-displacement after the eruption is estimated to be between 0.32 and 0.4 m. Considering ground displacement pre- and post-eruption we estimated 62000 m3 land gaining, due to emergence. We concluded that mud volcano can be counted as a feature of emergence in Dashli Island.

Seabed fluid flow is a widespread and important natural phenomenon in marine environments, which involves complex multi-physics, multi-process and multi-scale processes. The developments in offshore geophysical technology have facilitated the discovery of the widespread emissions of seabed fluids. For an overview on the state-of-the-art seabed fluid flow research and for obtaining a perspective on future research in the China Seas, we reviewed the data, reports, and publications particularly that associated with cold seeps such as pockmarks, seeps, domes, mud volcanoes, and gas hydrates in the Bohai Sea, the Yellow Sea, the East China Sea, and the South China Sea. This study presents the first report for seabed fluid flow on all China Seas with the basic information required to undertake additional analytical studies of these features. Furthermore, we explore processes responsible for them and their implications. Although the seabed fluid flow is widespread, dynamic, and influential, it is still poorly examined and understood. To understand seabed fluid flow in both time and space, it is important to investigate how and why these seabed fluids form and migrate.

An alkaliphilic, facultatively anaerobic bacterium (strain T05bT) was isolated from a terrestrial mud volcano on the Taman Peninsula, Russia. The cells of the isolate were motile spirilla 0.5 µm in diameter and 1.5–2.5 µm long. Strain T05bT grew at 6–42°C (optimum at 30°C), pH 8.0–11.0 (optimum at 9.0), and 0–14% NaCl (wt/vol). Lactate, formate, malate, pyruvate, H2, elemental sulfur, sulfite, thiosulfate, and sulfide were used as electron donors; nitrate, fumarate, elemental sulfur, sulfite, thiosulfate, dimethyl sulfoxide, arsenate, and oxygen could be used as electron acceptors. Nitrate was reduced to ammonium. Malate, pyruvate, and fumarate were fermented. Microaerobic growth was possible at up to 3% О2 (vol/vol). Strain T05bT did not use sulfate and Fe(III) as electron acceptors, was unable of elemental sulfur, sulfite or thiosulfate disproportionation, and did not ferment glucose, fructose, sucrose, lactate, formate, maleate, yeast extract, or peptone. The predominant fatty acids were C16:1 ω7 (45.9%), C16:0 (25.8%), and C18:1 ω7 (20.9%). The genome of strain T05bT was 2.46 Mb in size and had the G + C DNA content of 45.5%. It contained the genes encoding the following enzymes of energy metabolism: Nap nitrate reductase periplasmic complex, Phs/Psr thiosulfate/polysulfide reductase, Sqr sulfide:quinone oxidoreductase, and Arr respiratory arsenate reductase. According to analysis of the 16S rRNA gene nucleotide sequence, strain T05bT exhibited 98.61% similarity to the type strain of Sulfurospirillum alkalitolerans (phylum "Campylobacterota"). Based on its phenotypic characteristics and the results of phylogenetic analysis, assignment of the isolate to a new Sulfurospirillum species, Sulfurospirillum tamanensis sp. nov., is proposed, with the type strain T05bT (=DSM 112596T = VKM B-3538T). [ABSTRACT FROM AUTHOR]

Low-chlorinity springs sampled from ten sites on nine serpentinite mud volcanoes show systematic chemical gradients across the outer Mariana forearc that result from progressive devolatilization of the subducting Pacific plate. Sites range from 50 to 90 km from the trench axis corresponding to depths to the top of the plate of ∼15–29 km. Dissolved sulfate, Na/Cl, K, Rb, Cs, and B in the springs all increase regularly with distance from the trench, leached from subducting sediment and altered basalt in response to increasing temperature at depth from ∼80 to 350 °C. Sites nearer the trench have high Ca (up to 76 mmol/kg) and Sr, low alkalinity, and pH 10.7, whereas sites farther from the trench have almost no Ca and Sr, alkalinity (some carbonate but mostly hydroxyl) as high as 69 meq/kg, and pH 12.5. Springs with high alkalinity also have high methane (>44 mmol/kg) that feeds sulfate-reducing archaeal communities in the shallow subsurface and macrofauna at the seafloor. These distal springs form chimneys and crusts of CaCO 3 , whereas the proximal springs form chimneys of brucite. High alkalinity at the distal sites apparently results from carbonate dissolution at the top of the subducting plate; because serpentinization during ascent generates both high pH and H 2 , the resulting dissolved carbonate is reduced to methane such that carbonate alkalinity is replaced by hydroxyl alkalinity: 4H 2 + HCO 3 – → CH 4 + 2H 2 O + OH–. This reaction can account for the much higher pH of the distal springs. Chlorinity of the springs varies from 234 to 546 mmol/kg and is related to latitude N S rather than distance from the trench. Distal springs have otherwise similar compositions over this entire range of chlorinity, implying that chloride derives from depth rather than from mixing with seawater within the seamounts themselves. The range in chlorinity can readily be explained by serpentinization at reasonable water/rock mass ratios of 0.2–1.0 if 30–40% of the spring water originates as residual pore water in subducted sediment and basalt rather than as H 2 O+ of dehydration. The pH, alkalinity, and methane content of the springs increase abruptly, while Ca and Sr decrease, because carbonate dissolution joins dehydration as a major process at the top of the subducting plate at ∼70 km from the trench, where metabasites recovered from the serpentinite mud indicate the transition from lawsonite blueschist facies to epidote blueschist facies also occurs. Replacement of lawsonite by epidote drastically depletes the solution in Ca and shifts the equilibrium toward massive dissolution of subducted carbonate. Fluxes of sulfate, C, Na, K, Rb, Cs, B, Ca, and Sr in the forearc springs represent only a few percent of the amounts subducted, consistent with continued supply at greater depth. [ABSTRACT FROM AUTHOR]

The cause of the Lusi mud eruption remains controversial. The review by Miller and Mazzini (2017) firmly dismisses a role of drilling operations at the adjacent Banjarpanji-1 well and argues that the eruption was triggered by the M6.3 Yogyakarta earthquake some 254 km away. We disagree with these conclusions. We review drilling data and the daily drilling reports, which clearly confirm that the wellbore was not intact and that there was a subsurface blowout. Downhole pressure data from Lusi directly witness the birth of Lusi at the surface on the 29th of May 2006, indicating a direct connection between the well and the eruption. Furthermore, the daily drilling reports specifically state that Lusi activity was visibly altered on three separate occasions by attempts to kill the eruption by pumping dense fluid down the BJP-1 well, providing further evidence of a connection between the wellbore and Lusi. By comparison with other examples of newly initiated mud eruptions elsewhere by other earthquakes, the Yogyakarta earthquake was far away given its magnitude. The seismic energy density of the Yogyakarta earthquake was only 0.0043 J/m3, which is less than a quarter of the minimum 0.019 J/m3 seismic energy density that has ever been inferred to trigger other mud eruptions. We show that the Lusi area had previously experienced other shallow earthquakes with similar frequencies and stronger ground shaking that did not trigger an eruption. Finally, the data from the BJP-1 well indicates that there was no prior hydrodynamic connection between deep overpressured hydrothermal fluids and the shallow Kalibeng clays, and that there was no evidence of any liquefaction or remobilization of the Kalibeng clays induced by the earthquake. We thus strongly favor initiation by drilling and not an earthquake.

The cause of the Lusi mud eruption remains controversial. The review by Miller and Mazzini (2017) firmly dismisses a role of drilling operations at the adjacent Banjarpanji-1 well and argues that the eruption was triggered by the M6.3 Yogyakarta earthquake some 254 km away. We disagree with these conclusions. We review drilling data and the daily drilling reports, which clearly confirm that the wellbore was not intact and that there was a subsurface blowout. Downhole pressure data from Lusi directly witness the birth of Lusi at the surface on the 29th of May 2006, indicating a direct connection between the well and the eruption. Furthermore, the daily drilling reports specifically state that Lusi activity was visibly altered on three separate occasions by attempts to kill the eruption by pumping dense fluid down the BJP-1 well, providing further evidence of a connection between the wellbore and Lusi. By comparison with other examples of newly initiated mud eruptions elsewhere by other earthquakes, the Yogyakarta earthquake was far away given its magnitude. The seismic energy density of the Yogyakarta earthquake was only 0.0043 J/m3, which is less than a quarter of the minimum 0.019 J/m3 seismic energy density that has ever been inferred to trigger other mud eruptions. We show that the Lusi area had previously experienced other shallow earthquakes with similar frequencies and stronger ground shaking that did not trigger an eruption. Finally, the data from the BJP-1 well indicates that there was no prior hydrodynamic connection between deep overpressured hydrothermal fluids and the shallow Kalibeng clays, and that there was no evidence of any liquefaction or remobilization of the Kalibeng clays induced by the earthquake. We thus strongly favor initiation by drilling and not an earthquake.

The shallow migration path of mudflow of the mud volcano MV420 on the continental slope of the Canadian Beaufort Sea is investigated in terms of thermal and geotechnical characteristics. MV420 is a nearly flat topped active mud volcano that emits methane and fluidized mud. Its top is at a depth of water of 420 m, within the gas hydrate stability zone. During the summer 2017 IBRV Araon expedition, several measurements of marine heat flow were conducted in the area of juvenile mud mound/pond morphologies identified by multibeam bathymetry and backscatter intensity images obtained by the Monterey Bay Aquarium Research Institute’s autonomous underwater vehicle. The heat probe (a gravity corer with temperature, pressure, and tilt sensors) appeared to penetrate to a depth of >70 m below the seafloor. The sediment bulk density in the mudflow migration path of MV420, estimated by pressure change with controlled stretches of a winch cable, was 1.56 g/cm3. The subsurface temperature reaches up to 18°C and profiles show that the maximum local temperature occurs from 20 to 40 m below the seafloor, implying substantial vertical variability of geothermal gradients. Our finding of large positive and small negative geothermal gradients above and below the depth of the local temperature maximum may represent stagnant hot mud along the mudflow migration path, indicating a pulsative eruption of the mudflow. Gas hydrate is stable only within a few meter thick layer near the seafloor above the path because of the cold bottom water (0.4°C) covering the top of the mud volcano. Furthermore, the thermal conductivity of 0.939 W/m/K and the marine heat flow of 22.5 mW/m2 at a control site outside MV420 is estimated as the background heat flow in the slope, for which little data exists.

The continental subsurface harbors microbial populations highly enriched in uncultured taxa. OPB41 is an uncultured order-level phylogenetic lineage within the actinobacterial class Coriobacteriia. OPB41 bacteria have a wide geographical distribution, but the physiology and metabolic traits of this cosmopolitan group remain elusive. From two contrasting subsurface environments, a terrestrial mud volcano and a deep subsurface aquifer, located in the central part of Eurasia, within the Caucasus petroleum region, we have isolated two pure cultures of anaerobic actinobacteria belonging to OPB41. The cells of both strains are small non-motile rods forming numerous pili-like appendages. Strain M08DHBT is mesophilic, while strain Es71-Z0120T is a true thermophile having a broad temperature range for growth (25-77°C). Strain M08DHBT anaerobically reduces sulfur compounds and utilizes an aromatic compound 3,4-dihydroxybenzoic acid. Strain Es71-Z0120T is an obligate dissimilatory Fe(III) reducer that is unable to utilize aromatic compounds. Both isolates grow lithotrophically and consume molecular hydrogen or formate using either thiosulfate, elemental sulfur, or Fe(III) as an electron acceptor. Genomes of the strains encode the putative reductive glycine pathway for autotrophic CO2 fixation, Ni-Fe hydrogenases, putative thiosulfate/polysulfide reductases, and multiheme c-type cytochromes presumably involved in dissimilatory Fe(III) reduction. We propose to assign the isolated strains to the novel taxa of the species-order levels and describe strain M08DHBT as Anaerosoma tenue gen. nov., sp. nov., and strain Es71-Z0120T as Parvivirga hydrogeniphila gen. nov., sp. nov., being members of Anaerosomatales ord. nov. This work expands the knowledge of the diversity, metabolic functions, and ecological role of the phylum Actinomycetota. [ABSTRACT FROM AUTHOR]

Gases were sampled from 7 surface gas seeps including 2 mud volcanoes in the Niigata oil and gas basin. Based on the gas compositions and isotope compositions, the origin, maturity, migration, and alteration of gases were studied. A seep gas from the paddy field is interpreted to be microbial. The other 6 gases are thermogenic, or mixtures of thermogenic and microbia!・ The methane, ethane, and propane carbon isotope compositions suggest that the thermogenic gases were generated in the peak to late oil generation stage. Some gases show high C1 (C2 + C3), suggesting molecular fractionation during the migration to the surface. The 13C-enriched propane and heavy values (>+2 %) of CO2 in some gases, especially in gases from the mud volcanoes, indicate active processes of the secondary microbial methanogenesis accompanied 'by biodegradation of petroleum. The microbial processes could proceed during the residence time in the mud chambers, which are estimated to exist several hundred meters below the mud volcanoes. [ABSTRACT FROM AUTHOR]

Compared with the deeply buried marine gas hydrate deposits, gas hydrates in the shallow subsurface, close to and at the seafloor, have attracted more attention owing to their concentrated distribution, high saturation, and easy access. They accumulate at relatively shallow depths <100–120 m and occur as gas hydrate-bearing mounds (also known as hydrate outcrops, pingoes) at the seafloor derived from the growth of hydrates in the shallow subsurface or as pure hydrate chunks formed by gas leakage. This paper reviews and summarizes such gas hydrate systems globally from the perspective of gas sources, migration pathways, and accumulation processes. Here, we divided them into four categories: fault-chimney-controlled, diapir-fault-controlled, fault-controlled, and submarine mud volcano-controlled deposits. Gas chimneys originate immediately above the restricted regions, mostly affected by faults where high gas concentrations trigger elevated pore fluid pressures. Diapirism derives a dendritic network of growth faults facilitating focused gas discharge and hydrate formation near the seafloor. Furthermore, pre-existing faults or fractures created by overpressured gas from greater depths in accretionary tectonics at convergent margins act as preferential pathways channeling free gas upwards to the seafloor. Gas flux rates decrease from the submarine mud volcano center to its margins, creating a concentric pattern of distributing temperature, gas concentrations, and hydrate contents in shallow sediments around the mud volcano. Hydrate-bound hydrocarbons are commonly of thermogenic origin and correspond to high-background geothermal conditions, whereas microbial gas is dominant in a few cases. The presence of heavier hydrocarbons mitigates the inhibition of hydrate formation by salt or heat. Fluid migration and pathways could be compared to the "blood" and "bones" in an organic system, respectively. The root of a pathway serves as the "heart" that gathers and provides considerable free gas concentrations in a restricted area, thereby triggering pore fluid pressures as one important drive force for focused fluid flow in impermeable sediments (the organic system). Besides the suitable temperature and pressure conditions, a prerequisite for the formation and stability of hydrate deposits in the shallow subsurface and at the seafloor is the sufficient supply of gas-rich fluids through the hydrate stability zone. Thus, the proportion of gas migrating from deep sources is significantly larger than that trapped in hydrates. As such, such marine hydrate deposits seem more like temporary carbon storage rather than the main culprit for climate warming at least in a short period. [ABSTRACT FROM AUTHOR]