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Regional-scale geothermal maps are the basis for calculations and mapping of the thermobaric stability zone of submarine gas hydrates. Global geothermal measurements (in particular, at the Eurasian continental margin of the Arctic Ocean) are sporadic. The lack of geotemperature data does not allow mapping of thermal fields using standard interpolation methods. This article presents a solution to this problem and the results of geothermal mapping of the Eurasian continental margin of the Arctic Ocean by extrapolation on a structural-tectonic basis following the age of tectonomagmatic activation of geological structures. The TEMAR-10 000 tectonic map of the Arctic was chosen as a structural-tectonic basis for zoning by age of tectonomagmatic activation. The geothermal studies were based on verified data from the Global Heat Flow Database, as well as published materials and the authors' original data. A geothermal database consisting of ~1000 geotemperature estimates has been compiled. Verification and statistical analysis of geothermal data in the Eurasian margin of the Arctic Ocean was performed. It has been established that the median values of heat flow are the most applicable for geothermal zoning on a structural-tectonic basis. The geothermal zoning of the Laptev Sea has been clarified based on seismic survey data on the position of the hydrate-related reflector, marking the phase boundary of the gas hydrate stability zone. For the first time, regional-scale geothermal mapping has been carried out at the Eurasian continental margin using actual measured and calculated geothermal data. The compiled geothermal map is the basis for calculating and mapping the gas hydrate stability zone. [ABSTRACT FROM AUTHOR]

A wide range of geological and geophysical methods was carried out on the Yamal Peninsula in the Arctic in the period 2014–2022. The results were analyzed together with data from remote sensing of the Earth. Fundamentally new data on the gas-dynamic mechanisms of dangerous processes in permafrost have been obtained. These data included catastrophic gas blowouts and explosions with the formation of giant craters. More than three thousand zones of powerful gas blowouts with the formation of craters at the bottom of thermokarst lakes, rivers, and the coast of the Kara Sea have been discovered. According to data on remote sensing of the Earth, large mud volcanic structures, located at the bottom of the Labvarto and Yambuto thermokarst lakes, were discovered on the Yamal Peninsula in 2022–2023 for the first time. Monitoring of their state with the use of retrospective satellite images showed the presence of periodic release of underground fluids, including gas. A conclusion was made about the discovery of active mud volcanoes on the Yamal Peninsula. [ABSTRACT FROM AUTHOR]

Russia has unique technical and technological experience of gas field development in permafrost regions. According to this experience, different environmental and geocryological conditions require different technical solutions. Such problems as considerable subzero temperatures in geologic sections, great ice saturation of subsurface sediments, and gas and gas hydrate accumulations inside permafrost and immediately below it cause a series of dangerous consequences when gas production wells are in operation. These include back freezing, breaking well casings, well site subsidence when in production; movement and deformation of the wellhead caused by thawing of the rock massif around the well column when in operation; sudden and strong gas blowouts during well drilling, completion, and operation. To prevent possible accidents, different technical and technological solutions are applied: zoning of the field area according to the degree of complexity of geocryological conditions and the correction of future gas well cluster locations to avoid zones with extremely complex conditions; preliminary degassing of permafrost zones by shallow slim wells in places of future production well clusters; mechanical support of unstable production wells; installation of passive and active heat-isolation systems to the well construction and inside ground around wellheads. Key messages received during the development of gas fields at complex geocryological conditions are (consistently): preliminary careful geological engineering surveys and zoning of the field area, well clusters placed in areas with relatively soft geocryological conditions, preliminary degassing of permafrost depth intervals, passive and active heat isolation installation to the sub-wellhead part of the production well and around wellhead, and mechanical strengthening of unstable wells. Current plans are underway to utilize this experience for new gas discoveries in the Russian Arctic. [ABSTRACT FROM AUTHOR]

Trigger mechanisms are proposed for gas hydrate decomposition, methane emissions, and glacier collapse in polar regions. These mechanisms are due to tectonic deformation waves in the lithosphere–asthenosphere system, caused by large earthquakes in subduction zones, located near the polar regions: the Aleutian arc, closest to the Arctic, and the Antarctica–Chilean and Tonga–Kermadec–Macquarie subduction zones. Disturbances of the lithosphere are transmitted over long distances (of the order of 2000–3000 km and more) at a speed of about 100 km/year. Additional stresses associated with them come to the Arctic and Antarctica several decades after the occurrence of seismic events. On the Arctic shelf, additional stresses destroy the microstructure of metastable gas hydrates located in frozen rocks at shallow depths, releasing the methane trapped in them and leading to filtration and emissions. In West Antarctica, these wave stresses lead to decreases in the adhesions of the covered glaciers with underlying bedrock, sharp accelerations of their sliding into the sea, and fault occurrences, reducing pressure on the underlying rocks containing gas hydrates, which leads to their decomposition and methane emissions. [ABSTRACT FROM AUTHOR]

The Vestnesa Ridge, located off the west Svalbard margin, is a >60 km long ridge consisting of fine-grained sediments that host a deep-marine gas hydrate and associated seepage system. Geological and geophysical observations indicate the predominance of vertical fluid expulsion through fractures with pockmarks expressed on the seafloor along the entire ridge. However, despite the apparent evidence for an extended free gas zone (FGZ) below the base of the gas hydrate stability zone (BGHSZ), present-day seafloor seepage has been confirmed only on the eastern half of the sedimentary ridge. In this study, we combine the relationships between aqueous phase pressure, capillary pressure, sediment clay fraction, porosity, and total stress to simulate how much gas is required to open preexisting fractures from the BGHSZ towards the seafloor. Data from four specific sites with different lithology and pressure regime along the ridge are used to constrain the simulations. Results demonstrate that fracturing is favored from the FGZ (with gas saturations < 0.1 and gas column heights < 15 m) towards the seafloor. Neglecting the capillary pressure overpredicts the size of the gas column by up to 10 times, leading to erroneous maximum gas vent volume predictions and associated ocean biosphere consequences. Further parametric analyses indicate that variations in the regional stress regime have the potential to modify the fracture criterion, thus driving the differences in venting across the ridge. Our results are in line with independent geophysical observations and petroleum system modeling in the study area, adding confidence to the proposed approach and highlighting the importance of the capillary pressure influence on gas pressure. [ABSTRACT FROM AUTHOR]

The article examines the regional patterns of rifting in the Arctic and assesses the impact of large (supra-regional) rift systems on the geological evolution of the region. Against the background of the description of main Arctic structures, the Atlantic–Arctic rift system (AARS) is described as a tectonotype of a large planetary geophorm that has evolved from continental rifting to spreading proper with the development of a full-fledged ocean. The main properties of this system are its development towards the North Pole, the longitudinal orientation of the rifts, their separation by latitudinal faults, and predominantly sinistral shear displacement of individual segments. We believe that such a structure reflects the influence of the rotational factor on distribution of lithospheric masses of the Earth. Their tendency to the equilibrium position relative to the rotation axis is implemented by movements towards the equator and along it. The outflow of masses to low latitudes makes possible the growth of the rift system, but does not contribute to its further development after reaching the Pole. This phenomenon is of general nature and determines the development of all longitudinal rift systems, which leads to their spatial convergence and attenuation of dynamics in the circumpolar space. Within the Arctic region, in addition to the Atlantic–Arctic system, areas of possible termination of the West Siberian, Okhotsk–Verkhoyansk, and East Pacific rift systems are considered. It is assumed that their evolution initiated the destruction of the continental lithosphere of the Arctic region and determined the subsequent transformations of its structure. Special attention is paid to the problems of the possible influence of rifting on the hydrocarbon generation due to serpentinization of hyperbasites, when the lithosphere is penetrated by faults to the upper mantle depths, as well as on the remobilization of gases as a result of the disturbance of both gas hydrate reservoirs and permafrost. It is shown that the greatest generation of methane is generally associated with the development of faults in the cold lithosphere and serpentinization of mantle rocks. [ABSTRACT FROM AUTHOR]

Archaea mediating anaerobic methane oxidation are key in preventing methane produced in marine sediments from reaching the hydrosphere; however, a complete understanding of how microbial communities in natural settings respond to changes in the flux of methane remains largely uncharacterized. We investigate microbial communities in gas hydrate-bearing seafloor mounds at Storfjordrenna, offshore Svalbard in the high Arctic, where we identify distinct methane concentration profiles that include steady-state, recently-increasing subsurface diffusive flux, and active gas seepage. Populations of anaerobic methanotrophs and sulfate-reducing bacteria were highest at the seep site, while decreased community diversity was associated with a recent increase in methane influx. Despite high methane fluxes and methanotroph doubling times estimated at 5–9 months, microbial community responses were largely synchronous with the advancement of methane into shallower sediment horizons. Together, these provide a framework for interpreting subseafloor microbial responses to methane escape in a warming Arctic Ocean. Archaea in marine sediment control the transfer of methane to the ocean, but microbial dynamics in these environments are poorly understood. Here the authors investigate marine sediments in the high Arctic, showing how methane influx quickly increases abundances of methane-consuming archaea and decreases total microbial community diversity. [ABSTRACT FROM AUTHOR]

Sub-sea Arctic methane and gas hydrate reservoirs are expected to be severely impacted by ocean temperature increase and sea-level rise. Our understanding of the gas emission phenomenon in the Arctic is however partial, especially in deep environments where the access is difficult and hydro-acoustic surveys are sporadic. Here, we report on the first continuous pore-pressure and temperature measurements over 4 days in shallow sediments along the west-Svalbard margin. Our data from sites where gas emissions have not been previously identified in hydro-acoustic profiles show that tides significantly affect the intensity and periodicity of gas emissions. These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume. Hence, the question remains as to whether sea-level rise may partially counterbalance the potential threat of submarine gas emissions caused by a warmer Arctic Ocean. This study investigates the effect of changing sea level on deep sea gas emissions in the Arctic. The results show that small decreases in sea-level favors gas release. This implies that sea-level rise may partially counterbalance the effect of warming oceans on gas emissions overall. [ABSTRACT FROM AUTHOR]

Cold seeps are characterized by high biomass, which is supported by the microbial oxidation of the available methane by capable microorganisms. The carbon is subsequently transferred to higher trophic levels. South of Svalbard, five geological mounds shaped by the formation of methane gas hydrates, have been recently located. Methane gas seeping activity has been observed on four of them, and flares were primarily concentrated at their summits. At three of these mounds, and along a distance gradient from their summit to their outskirt, we investigated the eukaryotic and prokaryotic biodiversity linked to 16S and 18S rDNA. Here we show that local methane seepage and other environmental conditions did affect the microbial community structure and composition. We could not demonstrate a community gradient from the summit to the edge of the mounds. Instead, a similar community structure in any methane-rich sediments could be retrieved at any location on these mounds. The oxidation of methane was largely driven by anaerobic methanotrophic Archaea-1 (ANME-1) and the communities also hosted high relative abundances of sulfate reducing bacterial groups although none demonstrated a clear co-occurrence with the predominance of ANME-1. Additional common taxa were observed and their abundances were likely benefiting from the end products of methane oxidation. Among these were sulfide-oxidizing Campilobacterota, organic matter degraders, such as Bathyarchaeota, Woesearchaeota, or thermoplasmatales marine benthic group D, and heterotrophic ciliates and Cercozoa. [ABSTRACT FROM AUTHOR]

Two areas with cold methane seeps on the outer shelf of the Laptev Sea were studied by two interdisciplinary expeditions onboard the RV Akademik Mstislav Keldysh in August–September of 2017 and 2018. These fields lie in water between depths of 63 and 73 m, and in a region of growing interest to the international community. Characteristic features of the methane seeps were obtained, which include their distribution and appearance on the seabed based on acoustic anomalies and seafloor observations. The cold seeps are part of a domain striking in a SW–NE direction along the Laptev Sea Rift System, Khatanga–Lomonosov Fracture Zone, and the Gakkel Ridge junction, and its structure was determined by shallow faults on the outer shelf. These faults are related to subsidence of the outer shelf cutting the caprock formed by permafrost and gas hydrates. Faults serve as conduits for an intense bubble methane discharge at the seabed. Shallow-water methane seep fauna were described for the first time in the Siberian Arctic. The frenulate siboglinid tubeworm Oligobrachia haakonmosbiensis was among the dominant species of the methane seep communities. A newly discovered gastropod species Frigidalvania sp. was also found in abundance at the seeps as well as an ophiuroid Ophiocten sericeum. Significant differences were observed between benthic communities of the two seep fields and background fauna including integral community parameters and the presence/absence of certain species. Development of shallow methane seep communities in the Laptev Sea apparently is related to extremely oligotrophic conditions in this area. [ABSTRACT FROM AUTHOR]

Paleoceanographic investigations in the Arctic and north Atlantic are crucial to understanding past and current climate change, in particular considering amounts of pressure-temperature sensitive gas stored in marine sediments of the region. Many paleoceanographic studies are based on foraminiferal oxygen and carbon stable isotope compositions (δ18O, δ13C) from either planktonic specimens, benthic specimens or both. However, in seafloor regions promixal to high upward methane fluxes, such as where seafloor gas emission and shallow gas hydrate-bearing sediment occur, foraminiferal δ18O and δ13C display a wide range of values. Our study focuses on foraminiferal stable isotope signatures in shallow sediment at core sites in the Arctic and North Atlantic affected by significant upward flow of methane. This includes cores with shallow sulfate methane transitions that are adjacent to seeps and containing gas hydrate. We place emphasis on potential effects due to gas hydrate dissociation and diagenesis. Gas hydrate dissociation is known to increase pore-water δ18O, but our results indicate that precipitation of methane-derived authigenic carbonate (MDAC) also affects the foraminiferal δ18O of both planktonic and benthic species. In addition to this post-depositional overprint, we investigate the potential bias of the stable isotope record due to ontogenetic effects. Our data show that the size fraction does not impact the isotopic signal of planktonic and benthic foraminifera. [ABSTRACT FROM AUTHOR]

Despite the long history of development in the Russian Arctic, it remains one of the least studied regions of the world and continues to raise important and complex questions for science, industry, and humanity in general. V.A. Kryukov (editor-in-chief of EKO) and E.S. Veselova (correspondent for EKO) interview the renowned geophysicist and academician M.I. Epov about the most relevant trends and issues of ongoing Arctic projects, the scientific research being conducted by Novosibirsk State University, and current approaches in the study of the Arctic. [ABSTRACT FROM AUTHOR]

Gutless marine worms of the family Siboglinidae have been found in the estuaries of the largest Arctic rivers Yenisei, Lena, and Mackenzie. Siboglinid metabolism is provided by symbiotic chemoautotrophic bacteria. Strong salinity stratification is characteristic of the estuaries of the largest Arctic rivers and ensures a high salinity at depths of 25-36 m, where siboglinids were found. High methane concentrations, which are necessary for siboglinid metabolism, result from dissociation of permafrost gas hydrates under the influence of river runoff in the conditions of Arctic warming., (© 2023. Pleiades Publishing, Ltd.)

We present results from a sediment core collected from a pockmark field on the Vestnesa Ridge (~ 80° N) in the eastern Fram Strait. This is the only deep-water gateway to the Arctic, and one of the northernmost marine gas hydrate provinces in the world. Eight 14C AMS dates reveal a detailed chronology for the last 14 ka BP. The δ 13C record measured on the benthonic foraminiferal species Cassidulina neoteretis shows two distinct intervals with negative values termed carbon isotope excursion (CIE I and CIE II, respectively). The values were as low as â'4.37‰ in CIE I, correlating with the BÃ,llingâ€"AllerÃ,d interstadials, and as low as â'3.41‰ in CIE II, correlating with the early Holocene. In the BÃ,llingâ€"AllerÃ,d interstadials, the planktonic foraminifera also show negative values, probably indicating secondary methane-derived authigenic precipitation affecting the foraminiferal shells. After a cleaning procedure designed to remove authigenic carbonate coatings on benthonic foraminiferal tests from this event, the 13C values are still negative (as low as â'2.75‰). The CIE I and CIE II occurred during periods of ocean warming, sea-level rise and increased concentrations of methane (CH4) in the atmosphere. CIEs with similar timing have been reported from other areas in the North Atlantic, suggesting a regional event. The trigger mechanisms for such regional events remain to be determined. We speculate that sea-level rise and seabed loading due to high sediment supply in combination with increased seismic activity as a result of rapid deglaciation may have triggered the escape of significant amounts of methane to the seafloor and the water column above. [ABSTRACT FROM AUTHOR]

Shear wave velocity data have been acquired at several marine gas hydrate drilling expeditions, including the India National Gas Hydrate Program Expedition 1 (NGHP-01), the Ocean Drilling Program (ODP) Leg 204, and Integrated Ocean Drilling Program (IODP) Expedition 311 (X311). In this study we use data from these marine drilling expeditions to develop an understanding of general grain-size control on the P- and S-wave properties of sediments. A clear difference in the downhole trends of P-wave (Vp) and S-wave (Vs) velocity and the Vp/Vs ratio from all three marine regions was observed: the northern Cascadia margin (IODP X311) shows the highest P-wave and S-wave velocity values overall and those from the India margin (Expedition NGHP-01) are the lowest. The southern Cascadia margin (ODP Leg 204) appears to have similar low P-wave and S-wave velocity values as seen off India. S-wave velocity values increase relative to the sites off India, but they are not as high as those seen on the northern Cascadia margin. Such regional differences can be explained by the amount of silt/sand (or lack thereof) occurring at these sites, with northern Cascadia being the region of the highest silt/sand occurrences. This grain-size control on P-wave and S-wave velocity and associated mineral composition differences is amplified when compared to the Arctic permafrost environments, where gas hydrate predominantly occurs in sand- and silt-dominated formations. Using a cross-plot of gamma ray values versus the Vp/Vs ratio, we compare the marine gas hydrate occurrences in these regions: offshore eastern India margin, offshore Cascadia margin, the Ignik-Sikumi site in Alaska, and the Mallik 5L-38 site in the Mackenzie Delta. The log-data from the Arctic permafrost regions show a strongly linear Vp–Vs relationship, similar to the previously defined empirical relationships by Greenberg and Castagna (1992). P- and S-wave velocity data from the India margin and ODP Leg 204 deviate strongly from these linear trends, whereas data from IODP X311 plot closer to the trend of the Arctic data sets and previously published relationships. Three new linear relationships for different grain size marine sediment hosts are suggested: a) mud-dominated (Mahanadi Basin, ODP Leg 204 & NGHP-01-17): Vs = 1.5854 × Vp − 2.1649 b) silty-mud (KG Basin): Vs = 0.8105 × Vp − 1.0223 c) silty-sand (IODP X311): Vs = 0.5316 × Vp − 0.4916 We investigate the relationship of gas hydrate saturation determined from electrical resistivity on the Vp/Vs ratio and found that the sand-dominated Arctic hosts show a clearly decreasing trend of Vp/Vs ratio with gas hydrate saturation. Though limited due to lower overall GH saturations, a similar trend is seen for sites from IODP X311 and at the ash-dominated NGHP-01-17 sediment in the Andaman Sea. Gas hydrate that occurs predominantly in fractured clay hosts show a different trend where the Vp/Vs ratio is much higher than at sand-dominated sites and remains constant or increases slightly with increasing gas hydrate saturation. This trend may be the result of anisotropy in fracture-dominated systems, where P- and S-wave velocities appear higher and Archie-based saturations of gas hydrate are overestimated. Gas hydrate concentrations were also estimated in these three marine settings and at Arctic sites using an effective medium model, combining P- and S-wave velocities as equally weighted constraints on the calculation. The effective medium approach generally overestimates S-wave velocity in high-porosity, clay-dominated sediments, but can be accurately used in sand-rich formations. [ABSTRACT FROM AUTHOR]

The western Svalbard continental margin contains thick sediment sequences with areas known to contain gas hydrates. Together with a dynamic tectonic environment, this makes the region prone to submarine slides. This paper presents results from geophysical mapping of the deepest part of the high Arctic environment, the Molloy Hole. The mapping includes multibeam bathymetry, acoustic backscatter and sub-bottom profiling. The geophysical data reveal seabed features indicative of sediment transport and larger-scale mass wasting. The large slide scar is here referred to as the Molloy Slide. It is located adjacent to the prominent Molloy Hole and Ridge system. The slide is estimated to have transported >65 km of sediments over the deep axial valley of the Molloy Ridge, and further into the Molloy Hole. A unique feature of this slide is that, although its run-out distance is relatively short (<5 km), it extends over an enormous vertical depth (>2,000 m) as a result of its position in a complex bathymetric setting. The slide was most likely triggered by seismic activity caused by seafloor spreading processes along the adjacent Molloy Ridge. However, gas-hydrate destabilization may also have played a role in the ensuing slide event. [ABSTRACT FROM AUTHOR]

Abstract: The SW Barents Sea is a large hydrocarbon-prone epi-continental Sea of the Norwegian Arctic region. A significant portion of the hydrocarbon gases generated in deep source rocks has leaked or migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The evolution of sedimentary basins of this region has controlled the leakage of these fluids through marine sediments. Understanding the distribution of various fluid-flow systems may enhance our knowledge of the evolution of different basins in the SW Barents Sea and could help find potential targets for future hydrocarbon exploration. We analyze approximately 3000 2D multi-channel seismic profiles and data from 60 wells covering the entire SW Barents Sea, to identify and classify fluid-flow features, and study their relationship to tectonic elements and geological history. Gas chimneys are the most abundant feature among various other fluid-flow features such as fluid leakage along faults and fractures, seepage pipes, and high amplitude anomalies potentially indicating trapped fluids. Large fluid-flow features, covering areas as large as 600 km2, occur close to known hydrocarbon fields such as Snøhvit, Skrugard, and Havis. The fluid-flow features occur above major deep-seated faults in the area suggesting a close relation to it. The number of fluid-flow features in the western part of the study area is significantly higher than in the eastern part. The amount of net erosion in the study area shows no direct control over the distribution of fluid-flow features, suggesting that the faults and distribution of mature source rocks control the fluid flow. The strong correlation between the locations of fluid-flow features and structural elements indicates that extensional tectonics, uplift and glaciations could have played major roles in the timing and activity of the fluid leakage, although erosion might have had an added effect. [Copyright &y& Elsevier]

In recent years, there has been considerable interest in the Arctic as a source for resources, as a potential zone for commercial shipping, and as a region that might experience conflict due to its strategic importance. With regards to energy resources, some studies suggest that the region contains upwards of 13 percent of global undiscovered oil, 30 percent of undiscovered gas, and multiples more of gas hydrates. The decreasing amount and duration of Arctic ice cover suggests that extraction of these resources will be increasingly commercially viable. Arctic and non-arctic states wish to benefit from the region's resources and the potential circum-polar navigation possibilities. This has led to concerns about the environmental risks of these operations as well as the fear that competition between states for resources might result in conflict. Unresolved offshore boundaries between the Arctic states exacerbate these fears. Yet, the risk of conflict seems overstated considering the bilateral and multilateral steps undertaken by the Arctic states to resolve contentious issues. This article will examine the potential impact of Arctic energy resources on global security as well as the regional environment and examine the actions of concerned states to promote their interests in the region. [ABSTRACT FROM AUTHOR]

Abstract: A mechanistic model is proposed to predict/explain hydrate saturation distribution in “converted free gas” hydrate reservoirs in sub-permafrost formations in the Arctic. This 1-D model assumes that a gas column accumulates and subsequently is converted to hydrate. The processes considered are the volume change during hydrate formation and consequent fluid phase transport within the column, the descent of the base of gas hydrate stability zone through the column, and sedimentological variations with depth. Crucially, the latter enable disconnection of the gas column during hydrate formation, which leads to substantial variation in hydrate saturation distribution. One form of variation observed in Arctic hydrate reservoirs is that zones of very low hydrate saturations are interspersed abruptly between zones of large hydrate saturations. The model was applied to data from Mount Elbert well, a gas hydrate stratigraphic test well drilled in the Milne Point area of the Alaska North Slope. The model is consistent with observations from the well log and interpretations of seismic anomalies in the area. The model also predicts that a considerable amount of fluid (of order one pore volume of gaseous and/or aqueous phases) must migrate within or into the gas column during hydrate formation. This paper offers the first explanatory model of its kind that addresses “converted free gas reservoirs” from a new angle: the effect of volume change during hydrate formation combined with capillary entry pressure variation versus depth. [Copyright &y& Elsevier]

Abstract: Gases were analyzed from well cuttings, core, gas hydrate, and formation tests at the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well, drilled within the Milne Point Unit, Alaska North Slope. The well penetrated a portion of the Eileen gas hydrate deposit, which overlies the more deeply buried Prudhoe Bay, Milne Point, West Sak, and Kuparuk River oil fields. Gas sources in the upper 200 m are predominantly from microbial sources (C1 isotopic compositions ranging from −86.4 to −80.6‰). The C1 isotopic composition becomes progressively enriched from 200 m to the top of the gas hydrate-bearing sands at 600 m. The tested gas hydrates occur in two primary intervals, units D and C, between 614.0 m and 664.7 m, containing a total of 29.3 m of gas hydrate-bearing sands. The hydrocarbon gases in cuttings and core samples from 604 to 914 m are composed of methane with very little ethane. The isotopic composition of the methane carbon ranges from −50.1 to −43.9‰ with several outliers, generally decreasing with depth. Gas samples collected by the Modular Formation Dynamics Testing (MDT) tool in the hydrate-bearing units were similarly composed mainly of methane, with up to 284 ppm ethane. The methane isotopic composition ranged from −48.2 to −48.0‰ in the C sand and from −48.4 to −46.6‰ in the D sand. Methane hydrogen isotopic composition ranged from −238 to −230‰, with slightly more depleted values in the deeper C sand. These results are consistent with the concept that the Eileen gas hydrates contain a mixture of deep-sourced, microbially biodegraded thermogenic gas, with lesser amounts of thermogenic oil-associated gas, and coal gas. Thermal gases are likely sourced from existing oil and gas accumulations that have migrated up-dip and/or up-fault and formed gas hydrate in response to climate cooling with permafrost formation. [Copyright &y& Elsevier]

promising method for gas hydrates exploration incorporates pre-stack seismic inversion data, elastic properties modeling, and seismic interpretation to predict saturation of gas hydrates ( Sgh). The technology can be modified slightly and used for predicting hydrate concentrations in shallow arctic locations as well. Examples from Gulf of Mexico Walker Ridge (WR) and Green Canyon (GC) protraction areas illustrate how Sgh was derived and used to support the selection of well locations to be drilled for gas hydrates in sand reservoirs by the Chevron-led Joint Industry Project (JIP) Leg II cruise in 2009. Concentrations of hydrates were estimated through the integration of seismic inversion of carefully conditioned pre-stack data, seismic stratigraphic interpretation, and shallow rock property modeling. Rock property trends were established by applying principles of rock physics and shallow sediment compaction, constrained by regional geological knowledge. No nearby sonic or density logs were available to define the elastic property trends in the zone of interest. Sgh volumes were generated by inverting pre-stack data to acoustic and shear impedance (PI and SI) volumes, and then analyzing deviations from modeled impedance trends. In order to enhance the quality of the inversion, we stress the importance of maximizing the signal to noise ratio of the offset data by conditioning seismic angle gathers prior to inversion. Seismic interpretation further plays an important role by identifying false anomalies such as hard, compact strata, which can produce apparent high Sgh values, and by identifying the more promising strata and structures for containing the hydrates. This integrated workflow presents a highly promising methodology, appropriate for the exploration of gas hydrates. [ABSTRACT FROM AUTHOR]

Abstract: Natural gas hydrate deposits have been estimated to store about 10% of gas in hydrate form (even with regard to a higher concentration of gas in hydrates), proceeding from the known ratio of dissolved-to-deposited gas. This high percentage is largely due to the fact that the buffer factor in natural gas hydrate deposits is lower than that for free gas because of less diverse structural conditions for gas accumulation. Therefore, the available appraisal of world resources of hydrated gas needs a revision. Hydrates in rocks are either syngenetic or epigenetic. Syngenetic hydrates originate from free or dissolved gas which was present in rocks in situ at the time when PT-conditions became favorable for gas hydrate formation. Epigenetic hydrates are derived from gas which came by migration into rocks with their PT-conditions corresponding to formation of gas hydrates. In addition to the optimum PT-conditions and water salinity, economic gas hydrate accumulation requires sustained supply of natural gas into a specific zone of gas hydrate formation. This condition is feasible only in the case of vertical migration of natural gas along faults, fractured zones, and lithologic windows, or, less often, as a result of lateral migration. Of practical importance are only the gas hydrate deposits produced by vertical or lateral gas migration. [Copyright &y& Elsevier]

Analysis of factual data on acoustic indicators of fluid occurrences, negative gravity anomalies based on satellite altimetry, tectonic deformations, and findings of ultramafic rocks and serpentinites was carried out. Such data make up stable sublatitudinal groups across the Atlantic Ocean. The image obtained suggests the following cause-and-effect series of processes: (1) tectonic deformations; (2) serpentinization of ultramafic rocks and generation of methane; and (3) accumulation of gas hydrates in the sedimentary cover near the continental margin. The second process is accompanied by the formation of negative gravity anomalies; the third process, by the specific reflection of fluids in the acoustic wave field. These facts provide a basis for forecasting the presence of gas hydrates based on reductions of the satellite altimetry data and regional maps of the sedimentary cover in the Atlantic and Arctic. [ABSTRACT FROM AUTHOR]

Detection of faults and other zones of weakness in shallow permafrost to a few hundreds of meters is extremely important for ensuring the safety during the production and transportation of fuels (oil and gas). The construction of line facilities (power lines and pipelines) should be preceded by detailed surveys in order to localize major areas of potential hazard. Furthermore, reliable geophysical methods are necessary for exploration of gas hydrates. This research aims at proving that induction-based electromagnetic surveys are applicable for permafrost studies and at finding new evidence for the similarity and difference of the permafrost structure in different regions of Northern Siberia. TEM curves are collected in several regions of Northern Siberia with continuous, mostly continuous, and discontinuous permafrost. Transient electromagnetic (TEM) surveys performed in the Russian Arctic image the permafrost structure to a depth of 500 m. The data are acquired with telemetric systems that allow varying the survey design and loop configuration. Advanced processing tools are used to provide geologically essential information from late-time records, while optimized inversion algorithms are applied to obtain high-quality layered resistivity models. The resulting geoelectric models reveal evident variations in the thickness of highly resistive frozen rocks and the presence of unfrozen patches. The induction surveys, which require no galvanic contact with the earth and no grounding, are inferred to be best suitable for imaging the frozen shallow subsurface. The TEM-based resistivity patterns clearly resolve the permafrost base, as well as the contours of unfrozen zones (taliks), lenses of saline water (cryopegs), gas hydrates, and frost heaving features. The reported results can make basis for the choice of geophysical methods for permafrost studies in such harsh conditions as the Russian Arctic. Furthermore, the presented resistivity patterns can make reference for future studies of permafrost in Northern Siberia. [ABSTRACT FROM AUTHOR]

A huge amount of carbon (C) is stored in permafrost regions. Climate warming and permafrost degradation induce gradual and abrupt carbon emissions into both the atmosphere and hydrosphere. In this paper, we review and synthesize recent advances in studies on carbon stocks in permafrost regions, biodegradability of permafrost organic carbon (POC), carbon emissions, and modeling/projecting permafrost carbon feedback to climate warming. The results showed that: (1) A large amount of organic carbon (1460–1600 PgC) is stored in permafrost regions, while there are large uncertainties in the estimation of carbon pools in subsea permafrost and in clathrates in terrestrial permafrost regions and offshore clathrate reservoirs; (2) many studies indicate that carbon pools in Circum-Arctic regions are on the rise despite the increasing release of POC under a warming climate, because of enhancing carbon uptake of boreal and arctic ecosystems; however, some ecosystem model studies indicate otherwise, that the permafrost carbon pool tends to decline as a result of conversion of permafrost regions from atmospheric sink to source under a warming climate; (3) multiple environmental factors affect the decomposability of POC, including ground hydrothermal regimes, carbon/nitrogen (C/N) ratio, organic carbon contents, and microbial communities, among others; and (4) however, results from modeling and projecting studies on the feedbacks of POC to climate warming indicate no conclusive or substantial acceleration of climate warming from POC emission and permafrost degradation over the 21st century. These projections may potentially underestimate the POC feedbacks to climate warming if abrupt POC emissions are not taken into account. We advise that studies on permafrost carbon feedbacks to climate warming should also focus more on the carbon feedbacks from the rapid permafrost degradation, such as thermokarst processes, gas hydrate destabilization, and wildfire-induced permafrost degradation. More attention should be paid to carbon emissions from aquatic systems because of their roles in channeling POC release and their significant methane release potentials. [ABSTRACT FROM AUTHOR]

Large amounts of methane are trapped as natural gas hydrate (NGH) in the sediments of the Arctic. Unlike NGH provinces offshore west of Svalbard (Vestnesa Ridge), NGH potential in Svalbard's fjords and near-shore environment is poorly constrained. In this study we modelled the NGH stability zone (GHSZ) to determine the NGH formation potential within the fjords of Svalbard. We applied a nearest neighbour interpolation method to dynamically derive statistical bottom-water temperature (BWT) trends from available CTD data. The BWT trends along with available geothermal gradient data constrained Svalbard-wide sub-bottom thermobaric models suitable for GHSZ modelling in the near subsurface. Analyses of source rock and fluid seepage data in Isfjorden, including 15 newly identified acoustic gas flares, indicate an active petroleum system with fluid migration reaching the seafloor with significant contributions of higher-order hydrocarbons to the gas feed. A GHSZ is predicted for most fjords at mean BWT conditions and 95:5 methane:ethane gas compositions. Suitable conditions for pure methane NGH formation are only met in the deepest parts of Isfjorden, Hinlopenstretet, Kross- and Kongsfjorden, and Rijpfjorden. Temporal constraints implemented along the well-defined Isfjorden transect indicated a notable negative response to water column warming. The predicted GHSZ across Svalbard's fjords is likely to disappear over the next few decades. [Display omitted] • The gas hydrate stability zone (GHSZ) is modelled for Svalbard's fjords. • Water column temperatures are calculated through a dynamic nearest neighbour approach. • Seeps, pockmarks and gas flares lie within the GHSZ's spatial extent in Isfjorden. • Natural gas in the shallow subsurface is potentially in hydrate form. • Strong temporal variability in hydrate stability is predicted. [ABSTRACT FROM AUTHOR]

The article is devoted to the four-year (2017–2020) monitoring of gas emissions from the bottom of the Seyakha Crater, located in the central part of the Yamal Peninsula (north of Western Siberia). The crater was formed on 28 June 2017 due to a powerful blowout, self-ignition and explosion of gas (mainly methane) at the site of a heaving mound in the river channel. On the basis of a comprehensive analysis of expeditionary geological and geophysical data (a set of geophysical equipment, including echo sounders and GPR was used) and remote sensing data (from space and with the use of UAVs), the continuing nature of the gas emissions from the bottom of the crater was proven. It was revealed that the area of gas seeps in 2019 and 2020 increased by about 10 times compared to 2017 and 2018. Gas in the cryolithosphere of the Arctic exists in free and hydrated states, has a predominantly methane composition, whereas this methane is of a biochemical, thermogenic and/or mixed type. It was concluded that the cryolithosphere of Yamal has a high level of gas saturation and is an almost inexhaustible unconventional source of energy resources for the serving of local needs. [ABSTRACT FROM AUTHOR]

A seismogenic trigger mechanism is proposed to explain the abrupt climate warming phases in the Arctic as a result of strong mechanical disturbances in the marginal region of the Arctic lithosphere. Those disturbances might have been caused by great earthquakes in the Aleutian subduction zone, and slowly propagated across the Arctic shelf and adjacent regions, triggering the methane release from permafrost and metastable gas hydrates, followed by greenhouse gas emissions into the atmosphere. The proposed mechanism is based on the identified correlation between the series of the great earthquakes in the Aleutian island arc, which occurred in the early and middle of the 20th century, and the two phases of sharp climate warming, which began in 1920 and 1980. There is a 20-year time lag between these events, which is explained by the time of arrival of deformation waves in the lithosphere (propagating with a velocity of about 100 km per year) at the Arctic shelf and adjacent land from the Aleutian subduction zone, the region of their generation. The trigger mechanism causing the methane release from permafrost and metastable gas hydrates is related to the destruction of micro-sized ice films covering gas hydrate particles, the elements highly important for hydrate self-preservation, as well as destruction of gas-saturated micropores in permafrost rocks due to the slight additional stresses associated with deformation waves, and thus emergence of conditions favorable for gas filtration and its subsequent emission. [ABSTRACT FROM AUTHOR]