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Vast quantities of methane are trapped in oceanic hydrate deposits, and there is concern that a rise in the ocean temperature will induce dissociation of these hydrate accumulations, potentially releasing large amounts of carbon into the atmosphere. Because methane is a powerful greenhouse gas, such a release could have dramatic climatic consequences. The recent discovery of active methane gas venting along the landward limit of the gas hydrate stability zone (GHSZ) on the shallow continental slope (150 m to 400 m) west of Svalbard suggests that this process may already have begun, but the source of the methane has not yet been determined. This study performs 2‐D simulations of hydrate dissociation in conditions representative of the Arctic Ocean margin to assess whether such hydrates could contribute to the observed gas release. The results show that shallow, low‐saturation hydrate deposits, if subjected to recently observed or future predicted temperature changes at the seafloor, can release quantities of methane at magnitudes similar to what has been observed, and that the releases will be localized near the landward limit of the GHSZ. Both gradual and rapid warming is simulated, along with a parametric sensitivity analysis, and localized gas release is observed for most of the cases. These results resemble the recently published observations and strongly suggest that hydrate dissociation and methane release as a result of climate change may be a real phenomenon, that it could occur on decadal timescales, and that it already may be occurring. Key Points Seafloor warming can dissociate hydrates and cause methane release Shallow hydrates alone may contribute to significant release Methane release may occur under a wide range of sediment conditions

Seafloor methane release due to the thermal dissociation of gas hydrates is pervasive across the continental margins of the Arctic Ocean. Furthermore, there is increasing awareness that shallow hydrate-related methane seeps have appeared due to enhanced warming of Arctic Ocean bottom water during the last century. Although it has been argued that a gas hydrate gun could trigger abrupt climate change, the processes and rates of subsurface/atmospheric natural gas exchange remain uncertain. Here we investigate the dynamics between gas hydrate stability and environmental changes from the height of the last glaciation through to the present day. Using geophysical observations from offshore Svalbard to constrain a coupled ice sheet/gas hydrate model, we identify distinct phases of subglacial methane sequestration and subsequent release on ice sheet retreat that led to the formation of a suite of seafloor domes. Reconstructing the evolution of this dome field, we find that incursions of warm Atlantic bottom water forced rapid gas hydrate dissociation and enhanced methane emissions during the penultimate Heinrich event, the Bølling and Allerød interstadials, and the Holocene optimum. Our results highlight the complex interplay between the cryosphere, geosphere, and atmosphere over the last 30,000 y that led to extensive changes in subseafloor carbon storage that forced distinct episodes of methane release due to natural climate variability well before recent anthropogenic warming.

Submarine methane seepage can potentially be promoted by the dissociation of the marine hydrates surrounding the continental margins due to oceanic warming since the Last Glacial Maximum. This seepage could be archived by authigenic carbonates at seeping sites, but the time lag caused by heat transmission through the sediment column leads to an inconsistency between the ages of the carbonate and the period of bottom water warming. Here we present the records of the authigenic carbonate crust from drilling site D1 in the Mid‐Okinawa Trough. Uranium–thorium dating results show that the carbonate crust mainly grew downwards during 14–6 ka. Gas hydrates hosted in the relatively thin stability zone dissociated in a rapid response to bottom water warming and intensified the methane seepage. Our study better supports the hypothesis that a considerable amount of methane can be released from marine hydrates due to global climatic changes. Plain Language Summary Methane hydrates are ice‐like crystalline compounds and often found in deep‐ocean marine sediments. Ocean warming in the past could have destabilized methane hydrates and led to a rapid discharge of free methane gas. Geological information on this methane escape could be preserved by carbonate rocks. To date, the hypothesis of the control of ocean warming on hydrate melting since the Last Glacial Maximum (19,000–26,000 years ago) has not been fully tested. To examine this hypothesis, we used the rock samples of seep‐carbonate retrieved by seafloor drilling in the Mid‐Okinawa Trough. Uranium–thorium dating results show that the seep carbonates formed between 6,000 and 14,000 years ago. It took less time for heat to diffuse downwards from warming seawater to trigger hydrate melting at this location than in most of other oceans at similar water depths. The smaller time lag makes the carbonate rock age close to the period of ocean warming. Our results better support that global ocean warming could potentially release methane from gas hydrates during glacial–interglacial transitions. The consequent methane transport into the oceans and likely also the atmosphere might impact ocean acidification and climatic warming. Key Points Presentation of the chronology of methane seepage by dating authigenic carbonates collected from drilling core D1 in the Okinawa Trough Ocean warming–induced hydrate dissociation led to the downward growth of authigenic carbonate for 14–6 ka after the Last Glacial Maximum This carbonate record better supports the link of hydrate dissociation with ocean warming due to a smaller thermal lag effect

One of the most demanding environmental and economic challenges of this era is that of supplying the increasing global energy demand while reducing and neutralizing the CO 2 footprint. In this regard, the provision of a secure and diversified energy supply and the sequestration of CO 2 into geological formations are currently of great significance. However, the buoyant nature of CO 2 under the temperature and pressure conditions of typical geological sites leads to the risk of CO 2 leakage, and thus necessitates long-term monitoring. Therefore, the hydrate-based sequestration of CO 2 beneath oceanic sediments has become a desirable alternative to conventional geologic sequestration in some regions, with the potential to eliminate the risks of leaking CO 2 . Over the past decades, considerable progress has been made in the study of gas hydrates, including understanding their occurrence in nature, characterizing their behavior, and assessing their energy and exploitation potentials, along with the potential development of sustainable hydrate-based chemistry applications and technologies. Due to the significance and severity of plugged oil/gas flowlines, the early research was dominated by the inhibition of gas hydrates in order to provide flow assurance in pipelines. However, the discovery of vast natural gas hydrate resources has shifted scientific attention towards the possibility of storing CO 2 as a hydrate, and developing applications such as CO 2 capture and transportation, gas separation, cold storage, natural gas solidification, and CH 4 -CO 2 hydrate replacement. Hence, the present review examines the fundamental properties of gas hydrates, including their natural occurrence and distribution in geological sediments, along with their thermodynamic and kinetic behaviors with respect to the effects of promoting and inhibiting additives. In addition, natural gas hydrate (NGH) production methods and field-scale trials are reviewed. Furthermore, various concepts and experimental investigations pertaining to hydrate-based CO 2 sequestration pathways are reviewed in the final section, including sequestration in the deep ocean, sub-permafrost regions, and marine sediments, as well as the CH 4 -CO 2 hydrate replacement technique. Therefore, CO 2 hydrate storage in suitable depleted oil and gas fields has the potential to reduce infrastructure costs, with CH 4 -CO 2 hydrate replacement potentially providing additional economic incentives. However, long-term field trials in marine sediments with different compositions are required to assess the CO 2 storage potential of hydrate reservoirs, and the effectiveness of CH 4 -CO 2 hydrate replacement technique. Highlights Gas clathrate hydrates enormous energy potential and application for gas storage are introduced. Fundamental properties, occurrence, and geological distribution of gas hydrates are reviewed. Natural gas hydrate (NGH) production methods and field-scale trials are reviewed and discussed. Hydrate-based CO 2 storage pathways and experiments are reviewed and evaluated comprehensively. Field-scale trial of CH 4 -CO 2 hydrate replacement technique is reviewed and discussed. Future research is projected to be on novel techniques that enhance CH 4 -CO 2 replacement efficiency.

Widespread methane release from thawing Arctic gas hydrates is a major concern, yet the processes, sources, and fluxes involved remain unconstrained. We present geophysical data documenting a cluster of kilometer-wide craters and mounds from the Barents Sea floor associated with large-scale methane expulsion.Combined with ice sheet/gas hydrate modeling, our results indicate that during glaciation, natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates. Upon ice sheet retreat, methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters. We propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets.

∼90% of gas hydrates occur as pore‐filling or fracture‐filling morphology in clay‐rich marine sediments. Their dissociation releases gas with distinct environmental fates interacting with climate change. A well‐constrained model of hydrate distribution with different morphologies is urgently needed. We present a novel one based on drilling data worldwide. We identified a geomechanics‐controlled critical depth, typically several hundred meters below the seafloor, which limits the maximum occurrence depth of fracture‐filling hydrates. This relative positioning of critical depth and bottom of the gas hydrate stability zone (BGHSZ) determines hydrate distribution with various morphologies: pore‐filling hydrates develop and predominate below critical depth only when critical depth lies above BGHSZ, while only fracture‐filling hydrates occur above BGHSZ when critical depth exceeds BGHSZ. Critical depth increases with higher clay‐sized fractions or water depths, causing varying hydrate morphologies at specific depths along continental margins. This model is essential for evaluating hydrates' roles in global carbon cycle.

The anti-hydrate surface is considered as a promising solution to prevent gas hydrate blockages. Previously, superhydrophobic surfaces have been investigated. But their surface micro structures are easily damaged and lack durability, thereby leading to promote hydrate nucleation and increase the adhesion of hydrates to the wall. In this work a hydrophilic dual network gel coating Zr 4+ /D-Gel was proposed and tested for the inhibition tetrahydrofuran (THF) hydrates formation as an example and for the reduction of the adhesion force of hydrates on the wall surface. In comparison to the uncoated surface, the Zr 4+ /D-Gel hydrophilic coating significantly prolongs the induction time for THF hydrate formation and diminishes the adhesion strength of THF hydrates. Moreover, THF hydrates in contact with the Zr 4+ /D-Gel coating exhibit a cycle of formation and decomposition over time, and a distinct unfrozen water layer was observed at the solution edges during hydrate formation. This work may provide novel insights and direction for the safe and efficient exploitation and transportation of natural gas hydrates.

Anthropogenic global warming may be accelerated by a positive feedback from the mobilization of methane from thawing Arctic permafrost. There are large uncertainties about the size of carbon stocks and the magnitude of possible methane emissions. Methane cannot only be produced from the microbial decay of organic matter within the thawing permafrost soils (microbial methane) but can also come from natural gas (thermogenic methane) trapped under or within the permafrost layer and released when it thaws. In the Taymyr Peninsula and surroundings in North Siberia, the area of the worldwide largest positive surface temperature anomaly for 2020, atmospheric methane concentrations have increased considerably during and after the 2020 heat wave. Two elongated areas of increased atmospheric methane concentration that appeared during summer coincide with two stripes of Paleozoic carbonates exposed at the southern and northern borders of the Yenisey-Khatanga Basin, a hydrocarbon-bearing sedimentary basin between the Siberian Craton to the south and the Taymyr Fold Belt to the north. Over the carbonates, soils are thin to nonexistent and wetlands are scarce. The maxima are thus unlikely to be caused by microbial methane from soils or wetlands. We suggest that gas hydrates in fractures and pockets of the carbonate rocks in the permafrost zone became unstable due to warming from the surface. This process may add unknown quantities of methane to the atmosphere in the near future.

Vast amounts of methane hydrates are potentially stored in sediments along the continental margins, owing their stability to low temperature – high pressure conditions. Global warming could destabilize these hydrates and cause a release of methane (CH4) into the water column and possibly the atmosphere. Since the Arctic has and will be warmed considerably, Arctic bottom water temperatures and their future evolution projected by a climate model were analyzed. The resulting warming is spatially inhomogeneous, with the strongest impact on shallow regions affected by Atlantic inflow. Within the next 100 years, the warming affects 25% of shallow and mid‐depth regions containing methane hydrates. Release of methane from melting hydrates in these areas could enhance ocean acidification and oxygen depletion in the water column. The impact of methane release on global warming, however, would not be significant within the considered time span. Key Points Arctic bottom water temperatures will rise under climate warming Methane hydrates will be released in the coming decades The release will be limited in the next decades and lead to ocean acidification

Methane seepage from the upper continental slopes of Western Svalbard has previously been attributed to gas hydrate dissociation induced by anthropogenic warming of ambient bottom waters. Here we show that sediment cores drilled off Prins Karls Foreland contain freshwater from dissociating hydrates. However, our modeling indicates that the observed pore water freshening began around 8 ka BP when the rate of isostatic uplift outpaced eustatic sea-level rise. The resultant local shallowing and lowering of hydrostatic pressure forced gas hydrate dissociation and dissolved chloride depletions consistent with our geochemical analysis. Hence, we propose that hydrate dissociation was triggered by postglacial isostatic rebound rather than anthropogenic warming. Furthermore, we show that methane fluxes from dissociating hydrates were considerably smaller than present methane seepage rates implying that gas hydrates were not a major source of methane to the oceans, but rather acted as a dynamic seal, regulating methane release from deep geological reservoirs.