Cold Seeps Research Articles

Natural 14C abundances and stable isotopes suggest discrete uptake routes for carbon and nitrogen in cold seep animals

Cold seeps, where geofluids containing methane and other hydrocarbons originating from the subseafloor seeps through the sediment surface, play important roles in the elemental and energy flux between sediment and seawater. These seep sites often harbor communities of endemic animals supported by chemolithoautotrophic bacteria, either through symbiosis or feeding. Despite these animal communities being intensively studied since their discovery in the 1980’s, the contribution of carbon from seep fluid to symbiotic microbes and subsequently host animals remains unclear. Here, we used natural-abundance radiocarbon to discern carbon sources: the ambient bottom water or the seeping geofluid. The 14C concentrations were measured for vesicomyid clams, a parasitic calamyzine polychaete, and a siboglinid tubeworm species from four different cold seep sites around Japan. We found most vesicomyid clams exhibiting 14C concentrations slightly lower than that of the ambient bottom water, suggesting up to 9% of C for chemolithoautotrophy originates from geofluid DIC. The different extent of fluid contribution across species may be explained by different routes to incorporate DIC and/or different DIC concentrations in the geofluid at each seep site. Stable nitrogen isotopic compositions further suggested N incorporation from geofluids in these clams, where the burrowing depth may be a key factor in determining their δ15N values. The siboglinid tubeworm showed a clear dependency for geofluid DIC, with a contribution of > 40%. Our results demonstrate the effectiveness of 14C analyses for elucidating the nutritional ecology of cold seep animals and their symbionts, as was previously shown for hydrothermal vent ecosystems.

Registering from space intensive gas seeps on the sea surface due to damage to Nord Stream 1 and Nord Stream 2 gas pipelines

Registering from space intensive gas seeps on the sea surface due to damage to Nord Stream 1 and Nord Stream 2 gas pipelines

Integrative taxonomy reveals a new species of deep-sea squat lobster (Galatheoidea, Munidopsidae) from cold seeps in the Gulf of Mexico

The western Atlantic Ocean harbors a diverse fauna of squat lobsters, particularly in the family Munidopsidae. This study introduces Munidopsis sednasp. nov., a species only found in the Gulf of Mexico and the first species reported to be endemic to cold seeps in the western Atlantic. Our investigation incorporates morphological analyses including micro-CT scanning evidence, multilocus molecular phylogeny, and mtDNA phylogeography, as well as ecological data derived from in situ observations and geographic distribution patterns to substantiate the recognition of the new species. Shallow molecular divergences and multiple morphological differences differentiate the new species from its closest relative, M. longimanus (A. Milne-Edwards, 1880). Additionally, we explore the potential scenario for ecological speciation within this newly identified taxon and discuss its significance in the context of conservation efforts in the Gulf of Mexico.

First record of the family Callianopsidae (Decapoda: Axiidea) and a new species of Vulcanocalliax from the Hikurangi Margin off Aotearoa New Zealand, with a key to species of Callianopsidae

IntroductionThe Aotearoa New Zealand ghost shrimp of the infraorders Axiidea and Gebiidea have never been comprehensively reviewed, with recent work uncovering a diverse regional fauna representing eight of the 14 known families.MethodsUsing standard morphological and DNA sequencing tools, the family Callianopsidae is, for the first time, recorded off New Zealand, represented by a new species of Vulcanocalliax.ResultsThe new species was found near hydrocarbon seeps on the Hikurangi Margin, on the eastern New Zealand continental slope, and is only the second species now known in this genus. The single congener, V. arutyunovi, is only known from a mud volcano in the Gulf of Cádiz, off the Iberian Peninsula. Vulcanocalliax sp. nov. was formerly reported as an unnamed host of a new endemic New Zealand rhizocephalan barnacle Parthenopea australis and is here formally described as Vulcanocalliax beervana sp. nov.DiscussionThe new species differs, e.g., in the shape of the anterior carapace margin (convexly rounded and without elevated postantennal shoulder present in V. arutyunovi), the ocular peduncle having a convex anterolateral margin (compared to a straight margin), and the uropodal exopod has a dorsomedian ridge, lacking the elevated anterior portion that is distinct in V. arutyunovi. This brings the number of described New Zealand ghost shrimp species to 18. A key to all known Callianopsidae is provided.ZOOBANKLSID urn:lsid:zoobank.org:pub:4EDE6CE1-B644-4FFB-94CA-C8725A7549DD.

MINERAL PHYSICS ANALYSIS OF ALLUVIAL ROCKS AS A SOURCE OF SHALLOW HYDROCARBON SEEPAGE IN BELIS VILLAGE, WARU BASIN, EASTERN SERAM ISLAND, MALUKU PROVINCE

Belis Village is located in the Waru basin adjacent to the Bula basin on the eastern part of Seram Island and has potential shallow hydrocarbon manifestations. This research aims to determine the mineralogical characteristics of the rocks that make up shallow hydrocarbon manifestations at the research location. The research method used is physical analysis of minerals including petrographic analysis and XRD methods. The analysis results of the XRD method show an abundance of quartz minerals at 58%, followed by clay minerals at 35%, opaque minerals at 25%, and the rest in the form of cavities while feldspar minerals are secondary minerals. The results of the XRD analysis show that the more dominant mineral is protoenstatite (MgSio3) with an average abundance of 70.33% as a carrier of shallow hydrocarbon seeps, Quartz (SiO2) with an average abundance of 18.46%, and Clinoestatite with an average abundance of 11.21% as a mineral associated with shallow hydrocarbon seeps.

Synergetic effects of chlorinated paraffins and microplastics on microbial communities and nitrogen cycling in deep-sea cold seep sediments

Chlorinated paraffins (CPs) and microplastics (MPs) are commonly found in deep-sea cold seep sediments, where nitrogen cycling processes frequently occur. However, little is known about their combined effects on sedimentary microbial communities and nitrogen cycling in these environments. This study aimed to investigate the synergistic impacts of CPs and MPs on microbial communities and nitrogen cycling in deep-sea cold seep sediments through microcosm experiments. Our results demonstrated that the presence of CPs and MPs induced significant alterations in microbial community composition, promoting the growth of Halomonas. Furthermore, CPs and MPs were found to enhance nitrification, denitrification and anammox processes, which was evidenced by the higher abundance of genes associated with nitrification and denitrification, as well as increased activity of denitrification and anammox in the CPs and MPs-treatment groups compared to the control group. Additionally, the enhanced influence of CPs and MPs on denitrification was expected to promote nitrate-dependent and sulfate-dependent anaerobic oxidation of methane, thereby resulting in less methane released into the environment. These findings shed light on the potential consequences of simultaneous exposure to CPs and MPs on biogeochemical nitrogen cycling in deep-sea cold seep sediments.

A Spatially Restricted Distribution of Thermophilic Endospores in Laptev Sea Shelf Sediments Suggests a Limited Dispersal by Local Geofluids.

Thermospores, the dormant resting stages of thermophilic bacteria, have been shown to be frequent but enigmatic components of cold marine sediments around the world. Multiple hypotheses have been proposed to explain their distribution, emphasizing their potential as model organisms for studying microbial dispersal via ocean currents. In the Arctic Ocean, the abundance and diversity of thermospores have previously been assumed to be low. However, this assessment has been based on data mainly from the western fjords of Svalbard, thus leaving most of the Arctic unexplored. Here, we expand the knowledge about the distribution of thermospores in the Arctic Ocean by investigating the abundance and diversity of thermospores in heated shelf sediments from three sites in the outer Laptev Sea. Two of the sites are located in an area with methane-emitting cold seeps with a thermogenic source signature suggestive of an origin in a deep hydrocarbon reservoir, while the third site is a reference site not known to be impacted by seepage. We found that activity of viable thermospore populations was more prominent at one of the investigated seep sites. This finding is supported by both radiotracer growth experiments showing thermophilic, sulfate-reducing activity triggered by heating, as well as 16S gene sequence analyses showing significantly enriched ASVs affiliated to the phylum Firmicutes following high-temperature incubations. An enrichment of the sulfate-reducing, endospore-forming class Desulfotomaculia in heated samples compared to unheated samples was also observed. Furthermore, several ASVs identified at the seep site are closely related to thermospore-producing bacteria associated with the deep biosphere, including hydrocarbon and hydrothermal systems. Based on the combined information from induced activity, estimated abundance, and phylogenetic composition using 16S rRNA gene sequencing, we propose likely source environments and dispersal vectors for thermospores in the Arctic Ocean.

Air Injection into Condensate Reservoirs in the Middle and Late Stages Increases Recovery with Thermal Miscible Mechanism

Summary Condensate gas reservoirs in the middle and late stages of development are faced with problems such as formation pressure reduction, serious retrograde condensation, and oil and gas seepage channel plugging, which make it difficult to further improve oil and gas recovery by conventional development methods. For this kind of condensate gas reservoir, in this paper we put forward air injection technology as a development means, taking the K condensate gas reservoir in the Tarim Oilfield as the research object. We explored the thermal oxidation characteristics and displacement efficiency of condensate oil/volatile oil by air injection through the thermal oxidation displacement experiment. In addition, we determined quantitatively the minimum miscibility pressure (MMP) of oil samples at high temperature and the correlation between MMP and temperature through a high-temperature, high-pressure slimtube experiment, and clarified the mechanism of “thermally assisted miscible” through fine full-component numerical simulations under high-temperature and high-pressure conditions, which indoor experiments could not achieve. The results showed that condensate oil/volatile oil can form a stable thermal front by injecting air, and the oil displacement efficiency is more than 90%. The MMP of flue gas produced by condensate oil and oxidation reaction decreases gradually with temperature increase, and the MMP is only 11 MPa at 260°C. The high temperature formed by oxidation heat release forces the oil phase into the gas phase, and the extraction of flue gas makes C2-C4 in the oil phase increase continuously, both of which promote the realization of heat-assisted evaporation miscible phase. This thermal-assisted miscible-phase mechanism makes air injection displacement technology an innovative replacement technology for greatly improving the recovery efficiency of condensate gas reservoirs in the middle and late development stages.

High rates of hydrogen sulfide emissions measured from marginal oil wells near Austin and San Antonio, Texas

Marginal oil and gas wells, or wells that produce less than 15 barrels of oil equivalent per day, represent 80% of actively producing wells in the United States, although they produce less than 10% of energy supply. Marginal wells are a disproportionate source of methane (CH4) relative to their production, and they emit harmful air pollutants, such as benzene and other hydrocarbons found in oil and natural gas. We made direct measurements of CH4 and hydrogen sulfide (H2S) emissions from 46 wellheads in the Luling Field, Caldwell County, Texas, just east of the Austin/San Antonio Metroplex. We found that these wells are venting natural gas and are a large source of hydrogen sulfide (H2S), a poisonous air pollutant. Hydrogen sulfide emission rates ranged from 0 to 5 ± 0.5 g H2S hr−1 with an average emission rate of 1.6 ± 0.1 g H2S hr−1. We also found ambient concentrations of H2S at dangerous levels (>100 ppm) near many of the wells. Methane emission rates were in line with previous studies of marginal wells, ranging from 0.0 to 2770 ± 390 g CH4 hr−1, with a skewed distribution and average emission rate of 710 ± 100 g CH4 hr−1. Oil production records from Texas were incomplete: some wells had oil production data from the year of sampling, but many had no production data for several years or decades, although they were actively pumping while we were on site. Interviews with local residents indicate that the closing of the county gas processing plant and subsequent loss of gathering lines may be the cause of gas venting and CH4 and H2S emissions from production sites. This deserves further scrutiny, as marginal wells in this region are a major source of H2S, a health hazard to people living and working nearby.

Diffusion behavior assessment of underwater active venting for combustible gases: An experimental study with helium instead of hydrogen

In the active venting process of the burn pond, the hydrogen diffusion behavior underwater directly affects their uniformity on the water surface and the stability of the safety burning. A series of visualization experiments are conducted to assess the influence of disposal structure, flow rate, and water seal depth on the diffusion area and fountain height for rising plume formation. Helium is used as a substitute for hydrogen in the experiments. The study demonstrates that the plume structure is notably smaller in bubble cap mode compared to the nozzle mode, regardless of the conditions. This mode minimizes water surface fluctuation efficiently, making it ideal for constructing a disposal-array burn pond with multiple bubble cap units. Additionally, through dimensionless analysis, the study quantifies the parameters related to water surface stability with various venting conditions, thus establishing a foundation for the underwater active venting of hydrogen and other combustible gases.

Numerical Analysis of Explosion Characteristics of Vent Gas from 18650 LiFePO<sub>4</sub> Batteries with Different States of Charge

Numerical Analysis of Explosion Characteristics of Vent Gas from 18650 LiFePO<sub>4</sub> Batteries with Different States of Charge

Unveiling vertical migration patterns of the mesopelagic fish Ceratoscopelus warmingii in cold seep ecosystems: A trophic niche perspective

Ceratoscopelus warmingii, a common mesopelagic fish in cold seep ecosystems, plays a crucial role in transferring energy and materials between different water layers, thereby influencing deep-sea carbon cycling and storage. In August 2023, we collected samples from four depths (75 m, 400 m, 500 m, and 600 m) in cold seep waters to analyze the trophic niche characteristics of C. warmingii using stable isotope techniques. The results indicated significant differences in δ13C and δ15N values among the water layers, with mean δ13C and δ15N values of −19.85 ‰±0.33 ‰ and 8.41 ‰±0.62 ‰, respectively. Indicators of trophic structure showed distinct vertical differentiation, with the width of the trophic niche decreasing as depth increased. At 75 m and 400 m, the consistency of CR and NR indicators and high trophic niche overlap indicated similar food sources, confirming vertical migration behavior. In contrast, at 500 m, the MNND and SDNND values suggested a more stable trophic structure, while at 600 m, changes in feeding sources pointed to a distinct population. The Standard Ellipse Area of Overlap (SEAc) was highest between 75 m and 400 m, while the divergence of trophic ecological niches at 600 m, with different food sources, suggests that cold seep ecosystems at this depth provide a relatively stable trophic structure for C. warmingii and support the formation of an independent population. In cold seep ecosystems, C. warmingii employs adaptive trophic strategies to optimize survival under varying habitat conditions at different depths. This vertical trophic differentiation reduces intraspecific competition and enhances population stability in deep-sea habitats. This study enhances our understanding of the trophic niche and vertical migration of C. warmingii in cold seep ecosystems, significantly contributing to our knowledge of biodiversity, energy flow, and material cycling in these unique environments.

The Implications of Seeping Hydrocarbon Gases in the Gunsan Basin, Central Yellow Sea, off the Southwest of Korea

A detailed analysis of high-resolution (3.5 kHz) chirp seismic profiles acquired in the Gunsan Basin of the central Yellow Sea revealed that hydrocarbon gases are actively seeping via the formation of many plumes. The uppermost sedimentary layer was acoustically confirmed to be fully or partially charged with gases. Somewhat favored by the low-tide period, episodic gas seepage is mainly associated with the underlying fault systems of Cretaceous-Cenozoic sedimentary strata in the southwestern part of the basin. Catastrophic gas expulsion seems to have formed a crater at the sidewall of a sedimentary ridge and two diapirs. Here, methane is poorly concentrated but rich in the heavy carbon isotope (δ13C, −52.6‰ to −44.7‰ The Vienna Peedee Belemnite [VPDB]), indicating that methane formed mainly through biodegradation of heavy oils at depth remains in the shallow sediments following its expulsion. Episodic rapid upward advection of porewater is also manifest by unmixed heavy methane trapped in the upper part of the primary biogenic methane (δ13C, about −90‰ VPDB)-filled sediment core. These findings imply that the Gunsan Basin fulfills the requirements for possible generation and preservation of oil and gas, like the petroliferous basins of eastern China and the Yellow Sea.

Study on the effective drainage range of long horizontal borehole for goaf gas drainage

AbstractLaying long horizontal borehole (LHB) in mining‐induced strata fractures for coal‐bed gas drainage in the goaf is a pivotal method for eliminating safety hazards, preventing atmospheric pollution, and realizing gas utilization. A crucial premise of this method is to determine the effective drainage range of the borehole, a key parameter directly affecting boreholes spacing and drainage efficiency. In this study, a model of gas seepage during LHB drainage within a circular equipotential boundary was presented, and the complex variable function theory and the mirror principle were adopted for deriving the complex potential function of gas flow under the condition of LHB drainage and the drainage volume function of a single center borehole. Besides, the main indicator to determinate the effective drainage range of LHB was given. Specifically, the indicator refers to the distance between the turning point (the point at which the change rate of the gas flow velocity is −0.002 around the borehole) and the center of the borehole. Subsequently, numerical simulation was conducted to obtain the effective drainage range of LHB within mining‐induced fractures of overlying strata, that is, 4 m < r < 7 m. Furthermore, discussion of the effective drainage range of LHB was carried out by analyzing gas flow velocity distributions and LHB drainage volumes. A case study demonstrates that a double‐borehole layout with a 10 m spacing can effectively control pressure‐relief gas in the goaf. Meanwhile, such a layout can achieve well‐balanced drainage efficiency of each borehole with a minimal difference of 0.31 m3 min−1, which is only about 7.9% of the average drainage volume of the two boreholes. The above results verify that the determined effective drainage range of LHB is reasonable. The research results can provide references for determining the drainage range of LHB in multi‐borehole layout of coal mines, and then determining the spacing of LHBs arrangement, thereby improving the efficiency of gas extraction.

Diagenetic features recorded in sedimentary rocks within a gas chimney: A case study from the Makassar Strait, offshore Indonesia

Methane seeps, prevalent in ocean basins globally, indicate upward methane migration from the subsurface, often evident as gas chimneys in seismic reflection data. The footprint of this methane migration is often indicated by methane-derived authigenic carbonate (MDAC), a product of anaerobic oxidation of methane (AOM). Despite extensive research on MDAC from present-day seafloors and outcrops, understanding methane migration footprints from subsurface rock samples remains limited. Therefore, this study aims to investigate methane migration footprints from subsurface rock samples taken from a proven area of gas migration. This study utilized cutting samples from well XS-01 located in the Makassar Strait, offshore Indonesia. The well was drilled through a gas chimney into Oligocene carbonate reservoirs hosting a substantial methane column (102 m). Analysis of 44 cutting samples involved petrographic examination, Scanning Electron Microscope (SEM) imaging, and X-ray Diffraction (XRD) analysis to discern mineralogical content and diagenetic features signaling the presence of gas. A diagenetic texture called clotted peloidal micrite (CPM) was discovered within foraminifera fossils and around fractures based on petrographic analysis. CPM is a type of MDAC and predominantly occurs in fine-grained, siliciclastic rocks, indicating gas migration. This migration is interpreted to occur: (i) during the early burial stages originating from microbial activity since the Oligocene (biogenic gas); (ii) following matured source rock that reached its peak maturity from the Middle Eocene to the Pliocene (thermogenic gas); or (iii) interference of these two processes. The migration route persists until present day as evidenced by gas chimney and seabed pockmarks identified in seismic reflection data. This study emphasizes the importance of subsurface rock samples, such as cuttings, in uncovering gas migration footprints. Especially, where seismic data is unavailable or could not image fluid flow features. In addition, this study also provides a new perspective on diagenesis along methane migration route, complementing most of the research that is primarily focused on reservoir diagenesis.

Distribution of methane in the upper water layer of the northern Black Sea: Seasonal and daily trends and seawater-air emissions

We report on methane (CH4) concentration measurements in the northern Black Sea area conducted during 6 cruises with R/V Professor Vodyanitsky from 2017 to 2019. Our work is a multi-season study at a uniform station grid covering an area of 88 × 103 km2 and including three latitudinal transects that comprises both surface and vertical profile water-column measurements. The main goal of the work was to assess the seasonal patterns of vertical CH4 structure in the aerobic water column (upper 100 m) and its emission to the atmosphere.In surface waters, the mean dissolved CH4 concentration ranged from 2.6 nmol L−1 detected in November 2018 to 11.5 nmol L−1 measured in June–July 2018, respectively. Calculated CH4 seawater-air fluxes and saturations were mostly positive (i.e. net flux to atmosphere), and winter fluxes (2.6 μmol m−2 d−1) were higher than summer fluxes (1.6 μmol m−2 d−1) due to the higher wind speed. The integral CH4 flux from the whole study area (88 × 103 km2) ranged from 84 to 235 kM day−1.It was shown that, on average, the methane concentration in the upper layer for deep-water stations where the seabed is located at depths >160 m (σt >16.2) was lower compared to stations at shallow water depths (28–140 m, σt <16.2). The most distinct difference was obtained for the summer season (June–July 2018) and a less significant difference – for spring (April–May 2019) and winter season (November–December 2018). During these seasons the water column was also considerably less saturated in CH4 compared to the entire monitoring period. We observed subsurface maxima, which were generally located at the base of the thermocline and exceeded 100 nmol L−1 at some stations. Exceptions were observed in October 2019 (cruise 110), when vertical CH4 distributions were characterized by two-peaks at ∼20 and ∼50 m depth. The strong influence of the thermohaline structure on the water column CH4 distribution has also been shown in studies of daily dynamics of CH4 vertical profiles in the shallow water region. Despite the high variability of CH4 concentrations, significant similarities in vertical distributions of CH4 and chlorophyll-a for which sub-surface maxima coincided at some stations, are shown. Extremely high concentrations of CH4 (up to 351 nmol L−1) in the near-bottom water layer were revealed during all seasons at the station near the Dnieper paleo-channel at the northwestern edge of the study area. This enrichment is assumed to be caused by methane emissions from gas seeps densely located in this region.

A review of benthic foraminiferal oxygen and carbon isotopes

Stable isotopes in the calcium carbonate of benthic foraminifera provide important paleoenvironmental information about seawater/sedimentary porewaters that these foraminifera live in. Oxygen isotopes provide essential insights about variations in deep water temperatures and sea-level/ice volume changes, while carbon isotopes provide information about sea-water carbon/nutrient cycling. In this review we look into detail at the direct and indirect mechanisms that contribute to stable oxygen and carbon isotope signals in Rotaliid benthic foraminifera. This includes effects from ontogenetic- and calcification mechanisms, and the impact of methane seeps and post-depositional diagenesis. We conclude our review with an overview of current challenges and provide recommendations for future research endeavors aimed at outstanding knowledge gaps in understanding how these biomineralizers control their stable isotopes.

Depth dimension in seepage detection: Insights for exploration and geological gas storage surveillance

The search for surface hydrocarbon seeps has historically served as a fundamental tool in the early stages of oil and gas exploration. However, as easily detectable surface hydrocarbon seeps become increasingly scarce, advancement in analytical capabilities have shifted the focus towards detecting ultra-trace levels of hydrocarbons, commonly referred to as microseepages. While it is critical to understand the distribution of hydrocarbon microseepage for assessing petroleum systems and optimizing exploration efforts, the role of sampling depth in the detection of microseepage remains poorly understood. In this study, we investigated the influence of sampling depth on microseepage detection, using passive soil-gas sampling techniques at depths ranging from 0.5 to 10 m at sites with hydrocarbon-bearing reservoirs and dry wells. Organic geochemical analysis, including thermal desorption-gas chromatography-mass spectrometry (GC-MS), was employed to identify and quantify hydrocarbon and nonhydrocarbon compounds.The study result demonstrates that sampling at the Minimal Interference Zone (MIZ) depths of 5 m or greater significantly mitigates the risk of interference signals, thereby enabling the identification and quantification of hydrocarbon microseepages at trace and ultra-trace concentrations. At these depths, the attenuation of non-hydrocarbon compounds was observed, making the hydrocarbon signal markedly more distinguishable. Geochemical characterization of the samples revealed spatial and vertical heterogeneity in the distribution of hydrocarbon compounds, indicative of variations in the microseepage mechanisms potentially influenced by factors such as sedimentary basin settings and secondary alterations associated with the vadose zone. By utilizing passive soil-gas sampling techniques coupled with GC-MS, this study emphasizes the importance of sampling depth to improve the detection of reliable microseepage signal while reducing interference and background noise. The proposed technique not only refines existing methodologies for petroleum system assessments but also paves the way for broader geological applications. Specifically, the approach offers critical insights for the development of high-resolution geochemical surveys adaptable for surface background profiling in CO2 sequestration projects to monitor for storage efficiency and seal integrity.

Postglacial ocean methane release from the northern South China Sea

Methane release into seawater and the atmosphere as a result of cold seepage activity is a sensitive indicator of global environmental change during the last glacial period. However, the link between postglacial ocean methane escape and possible increases in atmospheric methane concentration remains unclear, which hinders the evaluation of methane impact on climatic variability. In this study, lipid biomarkers were analyzed on samples from the Shenhu area in the South China Sea to reconstruct the marine gas hydrate variability since the last glacial time. The reconstructed methane release during the cool Last Glacial Maximum and Younger Dryas agreed well with previous findings. Interestingly, our results identified a pronounced methane outgassing at the end of Heinrich 1, which was likely triggered by the abrupt increase in intermediate water temperature. The occurrence of this gas hydrate dissociation before the drastic rise in atmospheric methane during Bølling-Allerød implied that the change in the gas hydrate reservoir could likely indirectly contribute to the initiation of the warming event, though more global evidence needs to be provided in the future.

Revealing the kinetic behaviors of hydrate formation on bubble surface with different pressure gradients in deep-sea methane seepage areas of the South China Sea

In the deep-sea methane seepage environment, hydrate formation on the methane bubbles is a crucial pathway for methane transformation, and plays an important role in determining whether seepage methane can enter the surface ocean. While how the pressure determines the hydrate formation process in different water depths remains unclear. In this study, we investigated the formation kinetic characteristics and microstructure evolution of methane hydrate on suspended gas bubbles within varied pressure conditions. The pressure range (4–14 MPa) was in the deep-sea methane seepage environment. The results indicated that pressure obviously affected the hydrate film formation characteristics. As pressure increased, the lateral growth rate of the hydrate film accelerated, the hydrate crystal particles became smaller, and the initial hydrate film surface became smoother. Raman spectroscopy results showed that pressure changes did not obviously alter the microporous evolution on the hydrate film surface, that the gas-phase/water-phase Raman peak area ratio exhibited similar trends. The dissolved methane concentration under different pressure conditions was not the primary factor affecting hydrate thickening, rather, it depended mainly on the driving force. This study is of great significance in revealing the characteristics of methane hydrate formation and methane transfer in the oceanic methane seepage environment.