Framboidal pyrite, a common form of authigenic pyrite in marine sediments, forms through the co-precipitation of equant, equidimensional microcrystals that can effectively sequester trace elements. Nevertheless, the relationships among key attributes of framboids (i.e., framboid size, microcrystal dimensions, and number of microcrystals) and the detailed mechanisms of trace−element enrichment within framboids are not yet well understood. To address this gap, we present a dataset encompassing framboid key attributes, sulfur isotopes, and trace−element (Ni, Mo) concentrations from two gas−hydrate−bearing drillsites (GMGS4−SC−W02B and GMGS4−SC−W03B) in the Shenhu area, Pearl River Mouth Basin, South China Sea. In this methane−seep−influenced setting, framboid size is primarily controlled by microcrystal diameter and secondarily by microcrystal abundance. Nickel enrichment in framboidal pyrite follows a two−stage mechanism. Initially, Ni is taken up into FeS precursors before being incorporated into pyrite via isomorphous substitution on {111} microcrystal surfaces during framboid growth. This results in a strong positive correlation with microcrystal size (R² = 0.73, p < 0.001) rather than with their number (R2 = 0.18, p = 0.02). In contrast, Mo content shows positive correlations with both framboid size and microcrystal abundance (R² = 0.66, p < 0.01 and R² = 0.42, p = 0.01, respectively), consistent with its incorporation as nano−inclusions or nanoparticles within the pyrite lattice. The enrichment of both elements initiates from the strong adsorption capacity of iron monosulfide precursors. In methane release environments, enhanced anaerobic oxidation of methane facilitates the conversion of molybdate to particle-reactive thiomolybdates, which are effectively captured by growing pyrite framboids. Nickel, on the other hand, benefits from the increase in microcrystalline surface area during growth, where it replaces exposed Fe2+ through isomorphic substitution, leading to enrichment on microcrystal surfaces. This study advances the mechanistic understanding of trace−element incorporation in framboidal pyrite, and these findings strengthen the reliability of nickel and molybdenum as robust proxies for reconstructing paleoenvironmental conditions and paleo-methane release activity.

Large-scale methane release events (MREs), which can trigger transient climatic hyperwarming, are associated with enhanced anaerobic oxidation of methane (AOM), generating diagnostic geochemical and petrographic signatures in authigenic pyrite. Previous studies of MREs have analyzed single proxies such as pyrite framboid size or the sulfur isotopic composition of bulk-sediment pyrite over short core intervals, providing insufficient data regarding the intensity and magnitude of such events. Here, we utilize multiple proxies (i.e., pyrite framboid content, size, and sulfur isotopic composition) to reconstruct a detailed history of paleo-MREs at Site U1329 (IODP Leg 311) on the Cascadia Margin since 1 Ma. The recovered pyrite consists mainly (>99%) of isolated framboids and framboid aggregates, some having late diagenetic overgrowths. The characteristics of these framboids reflect the intensity and magnitude of each MRE: strong events were associated with FeS2 > 1.0 wt.%, mean framboid size >20 mu m, and Delta S-34 < 0 parts per thousand (where Delta S-34 = delta S-34(CRS) - delta S-34(SMTZ)), whereas weak events were associated with FeS2 = similar to 0.5-1.0 wt.%, mean framboid size similar to 10-20 mu m, and Delta S-34 > 0 parts per thousand. The study core contains four MREs (one strong, three medium) with mean pyrite content of 1.27 wt.%, mean framboid diameter of 26 +/- 6 mu m, and mean Delta S-34 of 10.5 parts per thousand (cf. background interval values of 0.85 wt.% mean FeS2 content; 12 +/- 2 mu m mean framboid diameter; and 16.0 parts per thousand mean Delta S-34). Each MRE was associated with a glacio-eustatic lowstand, a relationship reflecting destabilization of gas hydrates through pressure release, leading to an upward flux of methane, shallowing of the sulfate-methane transition zone (SMTZ), and enhanced AOM activity. Our results indicate that the morphological and geochemical signatures of pyrite are important carriers of paleoclimate information that can be used to study the occurrence and intensity of paleo-methane events and further improve understanding of methane hydrate dynamics.

ABSTRACT Archaea, a pivotal domain in the global biosphere, serve as indispensable mediators in biogeochemical turnover of mangrove wetlands. Nonetheless, high‐resolution vertical changes of archaeal communities, function, co‐occurrence patterns, and assembly mechanisms as well as their driving factors are poorly described in the mangrove sediments. Herein, through high‐throughput analysis of archaeal communities across seven depth intervals (0–90 cm) within 8 sediment cores collected in the Zhanjiang mangrove wetlands, we provide the vertical profiles of archaeal community composition and function, co‐occurrence networks, and assembly mechanisms along the sediment depth. Our results show that archaeal abundance declined with sediment depths, while higher archaeal diversity was observed in the mangrove deep sediments. Thermoplasmatota was more abundant in surface mangrove sediments, whereas Thermoproteota (Bathyarchaeia) was remarkably enriched in deep sediments. Metabolically, surface archaeal communities are characterized by carbohydrate, amino acid, cofactor and vitamin metabolism, whereas glycan biosynthesis, xenobiotics biodegradation, and nucleotide metabolism serve as the predominant functions in deep archaeal communities. The surface network displayed greater complexity and stability than the deep counterpart, with Thermoproteota functioning as keystone taxa across all three networks. Further, stochastic processes govern archaeal community assembly in all sediment layers. Finally, sediment depth, temperature, moisture, TP, clay content, and salinity were identified as key drivers shaping archaeal communities. These findings expand our knowledge regarding the vertical distribution characteristics and key driving factors of mangrove archaea, while also underscoring their ecological importance in deep mangrove sediment habitats.

Framboidal pyrite in modern sediments occurs predominantly as isolated framboids and aggregates of a few distinct morphotypes (e.g., irregular-shaped, rod-like, and foram-fill). However, there has been little study to date of potential disparities in geochemical proxy signals among these aggregate morphotypes. Here, we present a morphotype-specific morphological and geochemical dataset comprising framboid size, delta 34S, and trace-element compositional data for framboidal pyrite aggregates recovered from IODP Expedition 311 Site U1329C on the Cascadia Margin, an area of both modern and ancient methane seepage. Our results demonstrate that there is significant geochemical variation among different co-occurring aggregate morphotypes. The observed heterogeneity reflects differences in formation microenvironments (e.g., porewater connectivity, spatial confinement, local material supply) and, more fundamentally, the polygenetic nature of pyrite populations. We demonstrate that the traditional approach of analyzing bulk pyrite consisting of a mixture of isolated framboids and aggregate morphotypes likely obscures or distorts paleo-environmental signals. Therefore, we conclude that morphotypespecific analysis is essential for accurate interpretation of pyrite-based geochemical proxies. This study provides a valuable framework for research that relies on pyrite-based geochemical indicators to reconstruct paleoenvironmental and methane seepage history.

The enrichment and accumulation of natural gas hydrates depend on sufficient gas supply and effective migration pathways. The upward migration of deep thermogenic gases through fault systems is critical for seepage-type hydrate formation. This study aims to elucidate the developmental characteristics of Cenozoic fault systems in the eastern offshore area of Dongsha Island and their influence on natural gas hydrate formation. Utilizing high-resolution 3D seismic data, this study conducted a detailed structural interpretation and seismic attribute analysis to systematically investigate the spatial distribution, developmental stages, and dynamic mechanisms of the Cenozoic fault systems in this region. In addition, this study explored the role of these fault systems in facilitating the migration of deep thermogenic gases to the shallow strata. The study area is dominated by extensional and transtensional normal faults characterized by inherited development and relatively small fault displacements. The Cenozoic strata exhibit a tectonic framework of block-faulted uplift and subsidence with alternating highs and lows. Faults on either side of the central uplift dip in opposite directions and commonly exhibit parallel, step-like patterns. Differences in fault system attitudes were observed between the southern and northern parts of the study area. In the south, fault strikes remained consistent from deep to shallow levels, predominantly trending NE and NEE. In the north, fault strikes varied significantly with depth, transitioning from predominantly NEE in deeper strata to EW and NWW in shallower strata. The study identifies two distinct phases of Cenozoic fault activity: (1) 66–10 Ma, a regional extensional tectonic regime controlled fault development, resulting in the formation of NEE-trending normal faults; (2) 10–2.6 Ma, the Dongsha Movement influenced fault activity, during which EW- and NW–W-trending transtensional faults with dextral strike-slip characteristics developed in the Miocene strata of the northern region. The Cenozoic fault system played a significant positive role in facilitating the migration of deep thermogenic gas to shallow levels, thereby enabling the formation of natural gas hydrates.

The semi-enclosed Okinawa Trough hosts hydrothermal vents and cold seep systems. The authigenic carbonate formation in the Okinawa Trough is thought to be associated with the anaerobic oxidation of methane (AOM) driven by Fe/Mn oxide reduction due to hydrothermal metal supply. However, in seep sediments near hydro- thermal vents, Fe, Mn, S and C cycles and their diagenetic interactions are disconnected. Herein, a comprehensive suite of pore water solute concentrations and isotope ratios of four gravity cores (GC02, GC04, GC05, GC07) and three drilling cores (QZ02-C1, QZ03, QZ04) were analyzed to examine the diagenetic processes in the Okinawa Trough seep sediments. The accumulation of total dissolved Fe (DFe) and total dissolved Mn (DMn) in pore water suggested that metal oxide reduction occurred commonly in the sediments. In the Manganous zones, dissimilatory Mn reduction generally increased closer to the hydrothermal field, indicating that hydrothermal Mn supplies promoted organic matter mineralization. In the Sulfidic zones of Sites QZ03 and QZ04, the DMn and HS- contents reached peaks synchronously revealed inorganic Mn reduction coupled with HS- oxidation. At 21-25 m below the seafloor (mbsf) of Site QZ02-C1 and at 0.5 and 1.1 mbsf of Site GC02, the accumulation of DFe in pore water, accompanied by the negative offset in delta 13CDIC, suggested Fe-AOM or a Fe-derived cryptic S cycle in the Sulfidic zones. In the Methanic zone of Site QZ03, high Mg2+ consumption with DFe and DMn enrichment and effectively neutralized pore water implied that Fe/Mn oxide reduction could promote dolomite and siderite precipitation. However, the upward migration of deep CO2 prevented precipitation. The results revealed that hydrothermal metal is crucial in the diagenetic processes in methane seep sediments, e.g., it promotes organic matter degradation, enhances benthic filtering of methane by promoting Fe-rich carbonate precipitation, and alters the geochemical cycles of Mg2+, HS-, total alkalinity, pH, dissolved inorganic carbon, and CH4. Overall, this research helps understand Fe, Mn, S and C cycles in back-arc basins and can be important for the CH4-rich but SO2-4-depleted Archaean ocean.

Traditional carbonate factories (e.g., Schlager’s tropical factory, cool-water factory, and mud-mound factory) primarily focus on carbonate depositional environments. In contrast, cold-seep carbonate factories highlight microbial-mediated authigenic carbonate formation within siliciclastic-dominated sedimentary settings, offering a novel paradigm for understanding marine carbon cycling. This review article systematically synthesizes the key geochemical fingerprints of cold-seep carbonates, including carbon-oxygen isotopic compositions, trace element enrichment patterns, and metal stable isotope characteristics, to establish diagnostic criteria for identifying cold-seep carbonates. These signatures not only aid in distinguishing cold-seep carbonates but also serve as critical tools for tracing paleo-seep activity and evaluating its impacts on marine carbon cycling. Research indicates that precipitation processes in cold-seep carbonate factories typically exhibit strongly negative δ13C anomalies, relatively enriched δ18O values, and anomalous enrichment of trace elements (e.g., Mo, U, REEs). Additionally, metal stable isotopes (e.g., Mo, Sr, Ca) can constrain the redox conditions and fluid sources in cold-seep environments. The formation of cold-seep carbonate factories is closely linked to modern carbon cycling, acting not only as a short-term carbon sink for methane sequestration but also potentially influencing deep-time carbonate sedimentary dynamics. Future studies should integrate high-resolution analytical techniques, geochemical numerical simulations, and interdisciplinary approaches to decode the evolution of cold-seep systems and explore their potential roles in achieving carbon neutrality.

Low-strength sediment layers within continental slope strata precondition submarine sediment for failure, potentially leading to destructive tsunamis. Using geophysical and Ocean Drilling Program well data, here we show that the glide planes of widespread submarine failures in the northern South China Sea, dated to the glacial stages following the Mid-Pleistocene Transition, have higher opal content, particle size, and porosity, which reduce the undrained shear strength. Cyclic weak-layer deposition, modulated at Milankovitch time scale, was controlled by increased ocean primary productivity and sedimentation rates linked to high-amplitude sea-level fluctuations and intensified winter monsoons. This study represents an important step forward for understanding how climate influences the formation of weak layers and the stability of continental slope globally.

The long-term burial of organic carbon in marginal seas plays a critical role in Earth’s carbon cycle and climate change. However, the mechanism of organic carbon (OC) burial in the Okinawa Trough (OT) during glacial-interglacial timescales remains unclear. In this study, we analyzed the foraminiferal carbon isotopes, total organic carbon (TOC), and δ13C-TOC over the past 200 ka in core Z1 collected in the central OT. We aimed to reveal the history of OC burial in the middle Okinawa Trough during the past 200 ka, and we combined our findings with relevant paleoenvironmental indices to reveal underlying mechanisms. We found reduced surface primary productivity during MIS 6, which may indicate changes in the pathways of the Kuroshio Current (KC). Furthermore, we observed decoupling between high TOC flux and low OC burial during glacial periods. We proposed that the dilution effect caused by the high sedimentation rate and poor OC preservation during the glacial period resulted in the low TOC content. Ventilation of the North Pacific Intermediate Water (NPIW) regulated the redox conditions of the intermediate water in the Okinawa Trough. Additionally, the intensified Kuroshio Current during interglacial phases led to water column stratification, creating reducing conditions in the bottom water and facilitating improved OC preservation. Subsequently, the enhanced water column oxygenation resulting from the oxygen carried by the intensified glacial NPIW weakened the burial of OC. This study sheds new light on our understanding of the carbon cycle in marginal seas on a glacial-interglacial timescale.

Submarine methane seepages constitute an important part of global carbon cycle and may be promoted by the dissociation of gas hydrate. The migration pattern of a seepage is commonly dominated by vertical transport of methane-rich pore fluids, and then lateral migration of these fluids probably occurred due to self-sealing effect of carbonate crust above vertical migration conduit. Some studies found the evidence of this lateral migration, but the one from the record of seep carbonate in nature is very rare. In this study, we present the results of mineralogical, isotopic, and dating analyses of a core containing seep carbonates obtained from seafloor drilling site D5 in the Middle Okinawa Trough. The core contains 0.98-m-long carbonate interval that predominantly consists of aragonite, with an average content of similar to 86.6%. The carbonate exhibits moderate depletion in C-13 (delta C-13 values: -37.2 parts per thousand to -16.3 parts per thousand Vienna Pee Dee Belemnite; VPDB) and enrichment in O-18 (delta O-18 values: 4.3 parts per thousand-5.8 parts per thousand VPDB), with relatively constant Sr-87/Sr-86 values (0.709167-0.709197). These results suggest that the precipitation of the seep carbonate was induced by the sulfate-driven anaerobic oxidation of methane close to the seabed and this methane could be from the dissociation of gas hydrates. U-Th age-depth profile shows that two carbonate intervals grew downwards coevally to coalesce into a thicker crust, and its upper segment also grew upwards. We interpret that lateral migration of the fluid flows at two levels are responsible for the formation of upper and lower segments of carbonate intervals because they have (a) the distinct clustering of delta C-13 and delta O-18 values and (b) a coeval period of fast growth. It is likely that upward migration of methane was redirected by self-sealing of overlying carbonate crust, leading to lateral migration at the flank of seabed mound Db4 during 6.2-4.6 ka. Our findings highlight the interaction between fluid flows and authigenic carbonates during Late Quaternary, which implies that more methane could be consumed by oxidation because it takes longer time for methane to bypass self-sealing of carbonate to escape into the ocean.

Subsurface karst caves provide unique opportunities to study the deep biosphere, shedding light on microbial contribution to elemental cycling. Although ammonia oxidation driven by both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) is well explored in soil and marine environments, our understanding in the subsurface biosphere still remained limited to date. To address this gap, weathered rock and sediment samples were collected from the Xincuntun Cave in Guilin City, an alkaline karst cave, and subjected to high-throughput sequencing and quantification of bacterial and archaeal amoA, along with determination of the potential nitrification rates (PNR). Results revealed that AOA dominated in ammonia oxidation, contributing 48–100% to the PNR, and AOA amoA gene copies outnumbered AOB by 2 to 6 orders. Nitrososphaera dominated in AOA communities, while Nitrosopira dominated AOB communities. AOA demonstrated significantly larger niche breadth than AOB. The development of AOA communities was influenced by deterministic processes (50.71%), while AOB communities were predominantly influenced by stochastic processes. TOC, NH4+, and Cl− played crucial roles in shaping the compositions of ammonia oxidizers at the OTU level. Cross-domain co-occurrence networks highlighted the dominance of AOA nodes in the networks and positive associations between AOA and AOB, especially in the inner zone, suggesting collaborative effort to thrive in extreme environments. Their high gene copies, dominance in the interaction with ammonia oxidizing bacteria, expansive niche breadth and substantial contribution to PNR collectively confirmed that AOA better adapted to alkaline, oligotrophic karst caves environments, and thus play a fundamental role in nitrogen cycling in subsurface biosphere.

The elemental and isotopic compositions and abundance of carbonates in marine sediments are used to recon-struct ancient climate and ocean conditions. These carbonates usually include biogenic and authigenic carbon-ates in origin, which are controlled by sedimentary and diagenetic processes, respectively. However, the specific mechanisms involved in controlling the origin of biogenic and authigenic carbonates are still unclear. To address this knowledge gap, we analyzed core CSHC-4 sediment from the Okinawa Trough to examine the elemental and isotopic compositions of carbonates and their relationship to methane seepage and sea-level changes. Our results indicate that high-Mg calcite is the dominant authigenic carbonate, indicating moderate methane seep intensity. Negative carbon isotope values as low as -4.06%o V-PDB of the bulk sediments deposited in the glacial period suggest a connection between the formation of authigenic carbonates and methane seepage. Negative oxygen isotope values as low as-2.6%o V-PDB may be attributed to the input of 18O-depleted fluids influenced by gas hydrate formation. Biogenic carbonates contribute the majority (96.3%) of the total carbonate contents in sediments. Biogenic carbonate contents are lower during glacial periods and higher during interglacial periods. The reduced carbonate content during glacial periods may be due to lower export productivity influenced by the deepening of North Pacific Intermediate Water, as well as terrestrial inputs and anoxic conditions during low sea level periods. Our findings highlight the importance of considering both biogenic and authigenic carbonates when reconstructing paleoclimate and paleoceanography based on their geochemical characteristics.

The geological storage of carbon dioxide (CO2) in offshore saline aquifers stands as a primary option for reducing CO2 emissions in coastal regions. China’s coastal regions, particularly Shandong and Jiangsu provinces, face significant challenges in CO2 reduction. Therefore, evaluating the feasibility of CO2 geological storage in the adjacent seas is critical. To assess the suitability of a CO2 storage site, understanding its structural and reservoir characteristics is essential to mitigate injection and storage risks. In this study, we analyzed the structural characteristics and potential traps of the Yantai Depression in the South Yellow Sea Basin based on seismic data interpretation. We further conducted well logging analysis and post-stack seismic inversion to obtain lithological data, including acoustic impedance and sandstone content percentages from the Cenozoic Funing Formation, Dainan–Sanduo Formation, and Yancheng Formation. Our findings highlight that the Yantai Depression in the South Yellow Sea Basin exhibits diverse structural traps and favorable reservoir–caprock combinations, suggesting promising geological conditions for CO2 storage. This area emerges as a suitable candidate for implementing CO2 geological storage initiatives.

The Dongsha area, a key region in the northern South China Sea (SCS), features both diffusive deep and seepage shallow gas hydrate reservoirs. Utilizing sediment samples from gas hydrate reservoirs and adjacent layers at sites W08 and W16 in the Dongsha area, this study aims to uncover the sediment property differences between deep and shallow gas hydrate reservoirs and their impact on gas hydrate accumulation through grain size, X-ray diffraction, and specific surface area (SSA) analyses. The findings classify the study intervals into four distinct layers: shallow non-gas hydrate layer (shallow-NGHL), shallow gas hydrate reservoir (shallow-GHR), deep non-gas hydrate layer (deep-NGHL), and deep gas hydrate reservoir (deep-GHR). In the clayey silt sediment reservoirs, grain size has a minor influence on gas hydrate reservoirs. Both shallow and deep NGHLs, characterized by high smectite content and SSA, possess a complex structure that impedes gas and fluid migration and offers limited potential reservoir space. Consequently, both shallow and deep NGHLs function as sealing beds. The deep GHR, having low smectite content and SSA, exhibits a strong capacity for gas and fluid migration and greater potential reservoir space. As a result, sediment properties significantly influence the deep GHR. Seepage primarily controls the shallow GHR.

Sediments on continental slopes, which are rich in hydrates and organic matters, may release methane into the overlying seawater and even into the atmosphere. To evaluate the impact of sediment emissions on oceanic methane cycling and greenhouse gas emissions, this study assessed the distribution of methane in surface sediments and water columns and calculated the sea-to-air methane flux in the Dongsha area of the northern South China Sea. Results show that the methane concentrations exhibited large spatio-temporal changes. In May 2019, the methane concentrations and sea-to-air methane flux (4.1 & PLUSMN; 3.7 & mu;mol m- 2 d-1) were close to the background values, indicating that in situ aerobic methane production was a weak atmospheric methane source. In contrast, in September 2020, abnormally high methane concentrations up to 26.6 nM were detected in the upper slope with water depths of 600-950 m and to the east of a seamount; the average sea-to-air methane flux increased to 11.3 & PLUSMN; 7.9 & mu;mol m- 2 d-1. The consistency of methane distribution throughout the water column and surface sediments, with a generally increasing trend with the increasing depth, indicates that in September 2020, sediment emissions were crucial methane sources in seawater and led to moderate emissions into the atmosphere. The heterogeneities of methane concentrations and sea-to-air methane fluxes were attributed to the uneven distribution of methane in the sediments. Besides, strong internal solitary waves in summer and autumn exacerbates methane release, especially around high terrain areas, such as in continental upper slopes and in the upstream side of seamounts. Our results demonstrate that methane released from the sediments, being perhaps affected by internal solitary waves induced sediments disturbance, substantially impacted the oceanic methane cycling in continental slopes. Thus, this study provides new insights into the methane budget of marginal basins.

Abstract 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.

天然气水合物地质调查中通常采用地质、地球物理、地球化学等多种调查方法获得各类地质资料,而海洋地质取样可直接获得海底实物样品,是海洋地质调查中的重要手段.浅表层天然气水合物赋存于近海底沉积物中,利用合适的地质取样方法,在勘探目标区可以直接获得水合物样品及其存在的标志.基于浅表层水合物的存在指示标志和赋存特征,结合前期调查的成功经验,总结了适用于浅表层水合物的地质取样技术方法,主要有海底表层取样、重力柱状取样、海底钻探和保温保压取芯等,不同的取样方法所取的样品类型也有差异,应根据实际地质特征做出优选.针对浅表层天然气水合物的赋存特征,建立了一套海洋天然气水合物取芯样品现场处理和分析方法.水合物采集样品回收到甲板后快速处置分析是水合物调查的重要环节,而正确的现场处理方法是保证样品测试准确的关键.

Dendritic canyon system is the most widespread type of submarine canyons along continental margins and plays important roles in sediment delivery and deep-water ecosystem. Based on high-resolution multibeam bathy-metric and seismic reflection data, this study investigates a slope-confined dendritic canyon system in the Dongsha Slope, South China Sea. The dendritic canyon system between water depths of 550-2200 m consists of one main canyon (C2) and three V-shaped tributaries (C1, C3, and C4), in association with clearly visible tectonic deformation (uplifting and faulting) at the upper segment. The main canyon is characterized by a concave-up longitudinal profile, while the tributaries show convex-up and/or linear profiles, probably indicating that they are affected by tectonic deformation to variable degrees. The alignments and locations of tributaries C3 and C4 are determined by the NE-SW trending faults, while the distribution of the tributary C1 and the upper segment of C2 is less affected by faults, which also indicates that tectonic controls on the dendritic canyon system vary spatially among tributaries. Widespread NE-SW oriented sediment waves and southeast-facing scarps and iso-lated scour depressions at canyon banks highlight the significant influence of northwestward-propagating in-ternal tide/wave on the morpho-sedimentary processes. The internal tides/waves within canyons not only flushed canyon floor, but also contributed to the asymmetric distribution of sidewall gullies and failures. The obliquely shoaling internal waves, combined with other hydrodynamics (e.g., Kuroshio Current and mesoscale eddies), could significantly intensify along-slope bottom currents and erode the NE-SW-oriented trough and tributaries. Under the significant erosion of ocean currents, some of the sidewall gullies, troughs and sub-tributaries may finally evolve into new tributaries. This study reveals the coupling relationship between slope-confined dendritic canyon system and tectonic/oceanographic processes, which can shed light on the slope/ canyon evolution of similar settings worldwide.

Submarine cold seeps and hydrothermal vents are the key agents of material and energy exchange between the marine lithosphere and outer geospheres. Moreover, they breed natural gas hydrates, massive metal sulfides, and precious genetic resources and are one of the main targets of modern marine scientific research and resource exploration. A series of cold seeps and hydrothermal systems are developed in the Okinawa Trough (OT), a typical back-arc basin in the western Pacific. Due to their geographical proximity, the two extreme environments have evident mutual exchange or influence on the geological structure, material transportation, and ecological community, resulting in a unique carbon cycle model in this region. This study presents a series of recent research results in a symbiotic zone between hydrothermal vents and cold seeps in the OT. First, the genesis, carbon source, fluxes, and carbon fixation of cold seeps in the western slope of the OT are systematically summarized. In addition, characteristics of the carbon source, genesis, and flux in the hydrothermal area, near the spreading center of the basin, are compared and described. Second, the latest discoveries on the interaction between the two extreme systems on the seabed of the OT are illustrated. Furthermore, the evidence and progress of metal reduction driven anaerobic oxidation of methane and the global significance of the Fe–C coupling cycle are presented. Finally, key scientific problems in future research on the submarine symbiotic zone between cold seeps and hydrothermal vents are discussed. This study aims to provide an accurate model for the global marine methane cycle with additional consideration for metal electron receptors to gain further insights into the evolutionary history of the global carbon cycle process.

基于AMS14C年龄和底栖有孔虫氧同位素建立的地层年代框架,重点探讨了冲绳海槽中北部CSHC-15孔MIS6期以来(约200 ka)底栖有孔虫δ13C特征及其古海洋指示意义.结果显示,冰期-间冰期表层初级生产力和有机质通量的变化是导致底栖有孔虫δ13C值在MIS4和MIS6期负偏而在MIS1、MIS3和MIS5期正偏的主要原因.MIS2期的底栖有孔虫δ13C正偏,指示了 NPIW侵入冲绳海槽,导致通风性加强,底层水呈弱氧化状态.甲烷渗漏引发的甲烷厌氧氧化作用(AOM)是导致CSHC-15孔底栖有孔虫在MIS4期碳同位素大幅负偏的原因.