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Clarifying the mechanical characteristics of gas hydrate-bearing sediments (GHBS) from a mechanical perspective is crucial for ensuring the long-term, safe, and efficient extraction of natural gas hydrates. In this study, seabed soft clay from the northern South China Sea was utilized to prepare clayey silt samples, aligning with gradation curves related to hydrate extraction projects in the Shenhu area of the South China Sea. Utilizing the high-pressure low-temperature hydrate triaxial testing system (ETAS), twelve sets of triaxial shear tests were conducted. The results highlight that increases in hydrate saturation and confining pressure significantly enhance GHBS' strength and stiffness, with more pronounced volume expansion observed during shearing. These tests have elucidated the mechanical responses of GHBS. Subsequently, empirical formulas were developed to characterize their properties under varying conditions. Additionally, based on the experimental data, the micro-mechanisms of GHBS were analyzed, suggesting that hydrates notably contribute to the filling and cementing effects in GHBS, with these effects varying with changes in hydrate saturation and confining pressure. This study contributes to a deeper understanding of the fundamental mechanical properties of GHBS. [ABSTRACT FROM AUTHOR]

With the exploration, development, and research of deep‐sea resources, there is an urgent need for long‐term and continuous observation data of the deep‐sea seabed boundary layer. The traditional method of deep‐sea seabed survey and sampling based on scientific research vessels has the discontinuity of observation data in space and time scales. There are some problems in the seabed in situ observation method based on the seabed observation network for low mobility and high operation and maintenance costs, restricting the in‐depth understanding of the dynamic change process of the deep‐sea floor. To solve the above problems, an open and modular data acquisition control system was designed based on an embedded system and signal processing technology. In terms of the physical, chemical, geological, and ecosystem characteristics of the seafloor or near the seafloor boundary layer, various functional sensors and instrumentation were matched to form an independent underwater integrated measurement or experimental device, eventually realizing in situ multiparameter and long‐time series observations of the seafloor. The system data acquisition and control test were completed through laboratory experiments, which verified the feasibility of the system design. The research showed important theoretical and technical reference significance for the exploration and development of resources in the submarine boundary layer and the promotion of deep‐sea scientific research. [ABSTRACT FROM AUTHOR]

The accumulation of authigenic carbonate in marine sediments has been regarded as a significant contributor to the carbon cycle over Earth's history. However, accurate quantification of the extent of authigenic carbonate formation in both modern and ancient oceans has been challenging due to limited approaches. Here, we analyzed calcium, magnesium, dissolved inorganic carbon, and alkalinity pore‐water profiles of 153 sites influenced by methane diffusion from the northern South China Sea. By combining these data with published data of diffusive sulfate flux, we found a significant positive correlation between carbonate precipitation rate and sulfate flux in the subseafloor. This correlation can be used to quantify the regional extent of authigenic carbonate formation, representing an advantage over a spatial interpolation approach. We therefore propose that the observed correlation can serve as a new approach for quantifying authigenic carbonate formation in shallow sediments along continental margins for both modern and ancient oceans. Plain Language Summary: Carbonate mineral precipitation through removing seawater dissolved inorganic carbon—the marine carbonate factory—plays a critical role in shaping marine carbon cycling and global climate. The formation of authigenic carbonate from pore‐water of marine sediments represents a variable share of the marine carbonate factory throughout geological history. However, it is challenging to quantify the extent of such authigenic carbonate formation. By analyzing pore‐water parameters from 153 sites influenced by methane diffusion of the northern South China Sea, we found a significant positive correlation between the rate of carbonate precipitation and the diffusive flux of sulfate into shallow sediments. Given the existence of estimates on the sizes of the seawater sulfate pool and diffusive fluxes of sulfate into sediments over Earth's history, we propose that the observed correlation can be used for quantifying authigenic carbonate formation in shallow sediments along continental margins through time, which will greatly advance our understanding for past carbon cycling and its relation to climate. Key Points: Porewater parameters from 153 sites of the northern South China Sea were evaluated to quantify the extent of authigenic carbonate formationRate of carbonate formation strongly correlates with diffusive flux of sulfate into sediments affected by methane diffusionA correlation of carbonate formation rate with sulfate flux is used to quantify most of authigenic carbonate formation in shallow sediments [ABSTRACT FROM AUTHOR]

The sources and sinks of dissolved CH4 in offshore waters are becoming diversified with the rapid increase in human activities. The concentration and air–sea exchange flux of dissolved CH4 present new characteristics of more intense spatiotemporal evolution, and the contribution to atmospheric CH4 continues to increase. Herein, a new model based on navigable air–sea exchange flux observations was proposed, which replaced the traditional station-based sampling analysis and testing method, realizing the synchronous measurement of methane in the atmosphere and surface seawater carried by ships. Based on the Marine Geological Survey project of the China Geological Survey, comprehensive environmental surveys were conducted in April 2018, September 2018, and June 2019 in the Qiongdongnan area in the northern part of the South China Sea, and the dissolved methane content in the sea surface atmosphere and surface seawaters in 2019 were simultaneously obtained. The methane exchange flux ranges of the southeastern sea area were calculated as −0.001~−0.0023 μmol·m−2·d−1 and −0.00164~−0.00395 μmol·m−2·d−1 by using the Liss and Merlivat formula (LM86), the Wanninkhof formula (W92), and the field-measured wind speed. The feasibility of the navigational air–sea methane exchange flux observation system was proven in a sea trial, and the measurement accuracy and observation efficiency of air-sea flux were improved with the designed system, providing a new technical means for further research on multiscale air–sea interactions and global climate change. [ABSTRACT FROM AUTHOR]

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

E-waste recycling activities are a crucial emission source of organic pollutants, posing potential risks to the surrounding environment and human health. To understand the potential impact related to diverse e-waste dismantling activities, we investigated two categories of popular flame retardants (i.e., organophosphate esters (OPEs) and chlorinated paraffins (CPs) and their resultant possible ecological risk in 53 surface soil samples from Qingyuan, a well-known e-waste recycling region in South China. Varied concentrations of ΣOPEs (20.5-8720 ng/g) and ΣCPs (920-16800 ng/g) were observed at diverse dismantling sites, while relatively low levels of ΣOPEs (6.13-1240 ng/g) and ΣCPs (14.8-2870 ng/g) were found in surrounding soils. These results indicated that primitive e-waste dismantling processes were the primary emission source of OPEs and CPs in the studied area, with e-waste dumping and manual dismantling being the most important emission sources for OPEs and CPs. More importantly, CPs could be degraded/transformed into more toxic intermediates via dechlorination and decarbonization during the burning of e-waste. Furthermore, our results indicated the potential ecological risks posed by OPEs and CPs related to e-waste recycling., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Cold seeps on the continental margins are characterized by intense microbial activities that consume a large portion of methane by anaerobic methanotrophic archaea (ANME) through anaerobic oxidation of methane (AOM). Although ANMEs are known to contain unique ether lipids that may have an important function in marine carbon cycling, their full lipidomic profiles and functional distribution in particular cold-seep settings are still poorly characterized. Here, we combined the 16S rRNA gene sequencing and lipidomic approaches to analyze archaeal communities and their lipids in cold seep sediments with distinct methane supplies from the South China Sea. The archaeal community was dominated by ANME-1 in the moderate seepage area with strong methane emission. Low seepage area presented higher archaeal diversity covering Lokiarchaeia, Bathyarchaeia, and Thermoplasmata. A total of 55 core lipids (CLs) and intact polar lipids (IPLs) of archaea were identified, which included glycerol dialkyl glycerol tetraethers (GDGTs), hydroxy-GDGTs (OH-GDGTs), archaeol (AR), hydroxyarchaeol (OH-AR), and dihydroxyarchaeol (2OH-AR). Diverse polar headgroups constituted the archaeal IPLs. High concentrations of dissolved inorganic carbon (DIC) with depleted δ 13 C DIC and high methane index (MI) values based on both CLs (MI CL ) and IPLs (MI IPL ) indicate that ANMEs were active in the moderate seepage area. The ANME-2 and ANME-3 clades were characterized by enhanced glycosidic and phosphoric diether lipids production, indicating their potential role in coupling carbon and phosphurus cycling in cold seep ecosystems. ANME-1, though representing a smaller proportion of total archaea than ANME-2 and ANME-3 in the low seepage area, showed a positive correlation with MI IPL , indicating a different mechanism contributing to the IPL-GDGT pool. This also suggests that MI IPL could be a sensitive index to trace AOM activities performed by ANME-1. Overall, our study expands the understanding of the archaeal lipid composition in the cold seep and improves the application of MI using intact polar lipids that potentially link to extent ANME activities., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Zhang, He, Liang, Zheng, Xiao, Zeng, Zhou, Yao, Chen, Zhu, Zhao, Zheng and Zhang.)

Anaerobic oxidation of methane (AOM) coupled with reduction of metal oxides is supposed to be a globally important bioprocess in marine sediments. However, the responsible microorganisms and their contributions to methane budget are not clear in deep sea cold seep sediments. Here, we combined geochemistry, muti-omics, and numerical modeling to study metal-dependent AOM in methanic cold seep sediments in the northern continental slope of the South China Sea. Geochemical data based on methane concentrations, carbon stable isotope, solid-phase sediment analysis, and pore water measurements indicate the occurrence of anaerobic methane oxidation coupled to metal oxides reduction in the methanic zone. The 16S rRNA gene and transcript amplicons, along with metagenomic and metatranscriptomic data suggest that diverse anaerobic methanotrophic archaea (ANME) groups actively mediated methane oxidation in the methanic zone either independently or in syntrophy with, e.g., ETH-SRB1, as potential metal reducers. Modeling results suggest that the estimated rates of methane consumption via Fe-AOM and Mn-AOM were both 0.3 μmol cm -2  year -1 , which account for ~3% of total CH 4 removal in sediments. Overall, our results highlight metal-driven anaerobic oxidation of methane as an important methane sink in methanic cold seep sediments. IMPORTANCE Anaerobic oxidation of methane (AOM) coupled with reduction of metal oxides is supposed to be a globally important bioprocess in marine sediments. However, the responsible microorganisms and their contributions to methane budget are not clear in deep sea cold seep sediments. Our findings provide a comprehensive view of metal-dependent AOM in the methanic cold seep sediments and uncovered the potential mechanisms for involved microorganisms. High amounts of buried reactive Fe(III)/Mn(IV) minerals could be an important available electron acceptors for AOM. It is estimated that metal-AOM at least contributes 3% of total methane consumption from methanic sediments to the seep. Therefore, this research paper advances our understanding of the role of metal reduction to the global carbon cycle, especially the methane sink.