Search Results (319)

Soil microbial biogeography on nearshore islands remains less well understood than that on remote archipelagos, particularly when bacterial and fungal diversity, community composition, and co-occurrence associations are evaluated together. We characterized bacterial 16S rRNA gene and fungal ITS communities in 36 topsoil samples collected from five nearshore islands in the northern South China Sea and examined their associations with plant diversity, soil physicochemical properties, and climatic and geographic conditions. Bacterial Shannon diversity, ACE richness, and Simpson diversity differed significantly among islands, as did fungal ACE richness, whereas fungal Shannon and Simpson diversity showed no significant differences. Bray–Curtis-based analyses revealed island-associated differentiation in bacterial community composition and fungal community composition, although multivariate dispersion also differed among islands. Sample-level subnetworks derived from an integrated co-occurrence network showed that the number of bacteria–bacteria edges differed significantly among islands, whereas the numbers of bacteria–fungi and fungi–fungi edges did not. Exploratory Spearman correlation analyses and variation partitioning indicated that microbial properties were more broadly associated with soil physicochemical properties and climatic–geographic conditions than with plant diversity. By evaluating both microbial kingdoms within the same field campaign, this study identifies partly distinct bacterial and fungal biogeographic and co-occurrence patterns and provides a baseline for future microbial biodiversity monitoring on nearshore islands. Full article

Bottom currents and their associated sedimentary structures are key agents in shaping deep-sea morphodynamics, among which the genesis of seafloor undulations is still debated, restricting engineering risk assessment and resource development safety. Based on high-resolution multibeam bathymetry, sub-bottom profiles, and near-bottom current observations, this study analyzes morphological characteristics, internal reflection structures, and near-bottom current dynamic processes of seafloor undulations in the Shenhu canyon area. The results indicate that undulations occur at canyon heads, canyon interfluve, and east side of canyon. The undulations are generally characterized by vertical aggradation, with some sediment waves exhibiting directional crestline migration accompanied by wave merging, indicating the existence of persistent sediment transport processes. Within the canyon, the flow is concentrated and exhibits significant vertical deflection, reflecting the pronounced flow-guiding effect of the confined topography on near-bottom currents, which consequently controls the lateral migration of crestlines on both sides of the canyon and the shaping of seafloor undulations at canyon heads by internal tides. In contrast, in the relatively open canyon interfluve, flow directions are more dispersed, predominantly characterized by weaker currents. These findings contribute to the understanding of deep-water sedimentary dynamic processes and provide a reference for interpreting the genesis of similar deep-water seafloor undulations. Full article

The Pearl River Mouth Basin (PRMB) is a significant offshore petroleum basin located in the northern South China Sea, characterized by its complex structural features and well-developed boundary faults. Despite its importance, several critical questions regarding fault growth, evolution models, and genesis mechanisms remain unresolved. This study aims to address these gaps by discussing the evolution of the boundary fault system and its associated stratigraphic record. This study utilizes high-resolution 3D seismic reflection data interpretation and fault displacement profiles to investigate the Zhu I depression, the largest hydrocarbon-bearing depression in the northern rifted zone of the PRMB. The findings indicate that the syn-rift growth of boundary faults within the Zhu I depression exhibits three distinct patterns, along-strike linkage, transverse linkage, and oblique linkage, which are formed under the action of the pre-existing basement fault systems. These patterns describe how individual fault segments connect and evolve during the rifting process, influencing the overall structural development of the basin and hydrocarbon accumulation. Although transverse linkage includes three development stages, consistent with previous studies, these stages are isolated normal faults, overlapping faults, and hard linkage. The study reveals a unique example of how transfer faults within a relay ramp connect the normal boundary faults on both sides. The break progression of the relay ramp can also be classified into three stages, similar to the transverse linkage. This study proposes a new approach, through the inversion of fault evolution by sequence migration, for the reconstruction of fault connection processes and complex fault linkage models developed in southern China and similar areas worldwide. Full article

Submesoscale processes in marginal seas are central to the ocean’s energy cascade, mixed-layer dynamics, and biogeochemical exchanges and are typically driven by complex mechanisms influenced by local background currents as well as external forcings such as winds, tides, and topography. Among these drivers, however, the role of surface gravity waves has received comparatively little attention. In this study, we investigate the influence of surface waves on nearshore submesoscale processes in the northern South China Sea using high-resolution nested simulations with the Coastal and Regional Ocean COmmunity model (CROCO). The model implements the Eulerian wave-averaged current equations based on the vortex-force formalism, accounting for wave-induced effects. Our results reveal that onshore Stokes drift induces an onshore transport of water masses, thereby raising the nearshore sea level and intensifying nearshore currents. The strengthened currents, in turn, enhance convergence- and strain-induced frontogenesis, leading to the intensification of nearshore submesoscale fronts. These findings elucidate a specific mechanistic link between wave-induced sea-level changes and submesoscale dynamics, contributing to a better understanding of the role of surface waves in shaping coastal circulation. Full article

Accurate daily three-dimensional (3D) ocean sound speed prediction is essential for underwater acoustic applications. Existing data-driven studies often focus on global field errors, leaving localized thermocline-related errors insufficiently addressed. Using ten years of daily GLORYS12 reanalysis data from an equatorial Pacific region, we developed a 3D ConvLSTM predictor for background spatiotemporal evolution. We then proposed the Full-Depth Dynamic Gradient-Guided Residual Correction Network (FDGRC-Net), which derives a continuous mask from the previous-day regional temperature gradient profile to guide residual learning and output gating. On the 2009 test set, FDGRC-Net reduced the overall RMSE from $0.4209$ to $0.3916$ m/s and the MAE from $0.2302$ to $0.2180 \mathrm{m}/\mathrm{s}$. It also demonstrated improved prediction performance in the northern South China Sea cross-region evaluation and achieved annual RMSE reductions of $5.12$–$7.90\%$ in frozen 2010–2015 tests. Against 521 collocated Argo profiles, it slightly but consistently improved the observational agreement. In a controlled Bellhop diagnostic, the transmission loss MAE decreased from $2.825$ to $2.489 \mathrm{dB}$ and the mean arrival time error from $4.099$ to $3.653 \mathrm{ms}$. These results demonstrate that FDGRC-Net provides an effective and physically interpretable approach to thermocline-aware daily 3D sound speed prediction. Full article

The basement lithology in the northern South China Sea remains poorly constrained because of the lack of drilling data, which creates major challenges for predicting bedrock buried-hill reservoirs. This study is based on 2D and 3D seismic data, together with gravity and magnetic data, and is constrained by previous studies on the regional tectonic framework and lithologic distribution of the northern South China Sea. We investigated the basement lithologic composition of the XS area, established an integrated gravity–magnetic–seismic interpretation framework for basement lithology, and discussed the possible geological controls on basement lithologic distribution. The results show the following: (1) The basement in the study area is mainly composed of granite intrusive bodies, metamorphic rocks, and volcanic rocks. Granite bodies are characterized by irregular to intrusive seismic geometries, strong double-peak reflections at the upper boundary, and weak-amplitude, medium- to low-frequency internal reflections, reflecting their intrusive characteristics. Metamorphic rocks show diverse external seismic geometries, single-peak or weak reflections at the upper boundary, and medium- to strong-amplitude parallel internal reflections that intersect the upper boundary at high angles. Their gravity and magnetic responses show considerable overlap with those of granitic rocks. Volcanic rocks commonly show mound-shaped or lenticular seismic geometries and medium- to strong-amplitude, moderately continuous internal reflections. Intermediate–mafic volcanic rocks are associated with relatively stronger gravity and magnetic anomaly responses, whereas felsic volcanic rocks generally exhibit weak to moderate gravity and magnetic responses. These characteristics provide an integrated seismic–gravity–magnetic constraint framework for basement lithology interpretation in the South China Sea. (2) Integrated gravity–magnetic–seismic interpretation indicates that, near the present top of the pre-Cenozoic basement in the XS area, granite intrusive bodies are the dominant lithology. Metamorphic rocks mainly occur as discontinuous basement remnants in local structural lows or erosional windows, whereas volcanic rocks are mainly distributed near fault intersections or occur as bead-like bodies along fault zones. (3) The distribution of granite intrusive bodies and metamorphic basement is interpreted to be related to Indosinian–Yanshanian magmatic activity, tectonic deformation, and subsequent denudation. Faults formed during Early Yanshanian compression were later reactivated during the Himalayan period and may have acted as magma conduits, promoting the development of volcanic edifices along fault zones. Full article

Ship weather routing in regional seas under severe seasonal weather systems, such as typhoons, poses a critical operational challenge for maritime safety and efficiency. Traditional single-agent reinforcement learning (RL) methods frequently suffer from training instabilities and erratic trajectory adjustments when exposed to the highly non-stationary, multi-scale dynamics of coupled wind–wave–current fields. To address these limitations, this study proposes a dual-agent hierarchical reinforcement learning framework (HRL-MOO) featuring a built-in dynamic risk-weight adaptation mechanism. The proposed global agent discerns large-scale environmental evolutions and adaptively updates the relative weights of wind-, wave-, and current-induced risks at a strategic level, while the local agent translates this macro-level guidance into short-term tactical heading and speed adjustments within realistic vessel motion boundaries. The framework incorporates bathymetric constraints through a high-resolution navigable domain mask derived from ETOPO topography to guarantee practical navigability. Simulated experiments are executed using hourly environmental reanalysis data and best-track records corresponding to the passage of Typhoon Yagi (2024) through the northern South China Sea and Taiwan Strait. The empirical results demonstrate that the cooperative dual-agent structure establishes a superior global Pareto frontier compared to conventional standard single-agent Proximal Policy Optimization (PPO) and metaheuristic baselines. Under extreme typhoon conditions, the HRL-MOO model effectively decreases the cumulative environment-induced risk from approximately 0.17 to 0.12, improves path smoothness by achieving a higher index of 0.842, and accelerates policy convergence to within 3000 training episodes, all while maintaining a highly efficient voyage distance with minimal detour overhead. Ablation studies further validate that the synergy between macro-level stream field recognition and adaptive multi-objective optimization significantly enhances decision-making stability. This framework offers a robust and interpretable computational tool for autonomous ship weather routing in fast-changing, high-risk ocean environments. Full article

The Miocene Sanya, Meishan, and Huangliu formations in the Qiongdongnan Basin (QDNB) record a complete evolutionary history of submarine fan systems, yet a continuous Miocene-scale depositional framework has not been established for the Northern Lingshui Sag. Using 3D seismic data, this study investigates the paleogeomorphological reconstruction, channel system architecture, channel-sink correspondence, and controlling factors of Miocene submarine fans within the Northern Lingshui Sag, QDNB. Paleogeomorphological reconstruction reveals three fundamentally different slope configurations. The Sanya Formation is characterized by a gentle ramp-like slope (1–2°) with high accommodation. The Meishan Formation exhibits a steep structurally partitioned slope (eastern part ~9°, western part 8° decreasing to 2°) with a confined trough in the east. The Huangliu Formation shows a mature moderate slope (3–4°) with reduced structural confinement. Channel system architecture shows fifteen NW-SE oriented channels in the Sanya, six N-S oriented channels in the Meishan, and seven bidirectional channels in the Huangliu. Channel-sink correspondence is strong in the Sanya, localized in the Meishan, and weak in the Huangliu. Fan evolution was driven by three controlling factors: relative sea-level fluctuations, sediment supply and provenance, and paleogeomorphology. Global eustatic falls at 23.0 Ma (T60), 15.5 Ma (T50), and 10.5 Ma (T40) facilitated fan development within lowstand systems tracts. The Ningyuan River supplied sand-rich sediment to the Sanya, the Lingshui River supplied mud-rich sediment to the Meishan, and dual Ningyuan and Lingshui rivers supplied low-flux mud-dominated sediment to the Huangliu. Two major transitions are identified: the Sanya-to-Meishan transition (ca. 15.5 Ma) represents channel reorientation from NW-SE to N-S, reduction from fifteen to six channels, and shift from sand-rich to mud-rich supply; the Meishan-to-Huangliu transition (ca. 10.5 Ma) represents channel reorientation from N-S to bidirectional, increase from six to seven channels, and shift from mud-rich to low-flux mud-dominated supply. Full article

This study develops a MATLAB-based (MathWorks, Natick, MA, USA; version R2024b) first-order probabilistic screening framework for the Shenhu gas hydrate production area, northern South China Sea, to separate the roles of bottom-water warming, geothermal and fluid perturbation, hydrate saturation, excess pore pressure, and slope geometry. The framework integrates methane hydrate phase equilibrium, geothermal profiles, transient heat diffusion, base of gas hydrate stability zone (BGHSZ) migration, conceptual reservoir phase layering, and infinite-slope factor-of-safety (FoS) analysis. The modeled present-day BGHSZ (~271 mbsf) is broadly consistent with reported bottom-simulating-reflector depths. At the baseline thermal diffusivity, conductive potential dissociation thickness stays below 4 m even for +3.0 °C over 1000 years; across the full tested diffusivity–warming–time matrix it ranges 0–19.5 m; geological tests, reported as equilibrium BGHSZ offsets, give larger responses. Monte Carlo analysis under three parallel slope-angle assumptions shows that absolute FoS depends strongly on the slope distribution. Conductive warming reduces the median FoS by about 5.5%, with about 9% of realizations exceeding a 10% reduction, yet low-FoS outcomes remain absent within the tested ranges. Within the adopted parameterization, modeled FoS variability is controlled primarily by slope angle, friction angle, and the prescribed excess pore-pressure ratio, while conductive thermal forcing produces a comparatively modest reduction in relative stability margin. Full article

To characterize the fish community composition and seasonal variation in the coastal waters of Sanya, a tropical coastal region on Hainan Island in the northern South China Sea, and to evaluate the applicability of environmental DNA (eDNA) metabarcoding for biodiversity monitoring, water samples were collected from 16 nearshore sampling sites in June 2024 and January 2025. Fish community structure was analyzed using eDNA metabarcoding, combined with diversity indices and multivariate statistical analyses. A total of 488 marine fish species were detected, including 426 species in summer and 205 species in winter, with higher species richness observed in summer. Perciformes was the dominant order in both seasons. Dominant species composition varied seasonally, with a relatively dispersed pattern in summer and a dominance concentration structure in winter. The Chao1 and Shannon indices were significantly higher in summer than in winter, whereas evenness showed no significant seasonal difference. NMDS and ANOSIM analyses revealed significant seasonal differences in community structure, and low Sørensen similarity coefficients indicated substantial species variation between seasons. These results indicate that fish communities in the coastal waters of Sanya exhibit clear seasonal variation. eDNA metabarcoding provides an effective complementary approach for monitoring fish diversity in complex coastal habitats, although its results may be influenced by eDNA transport, degradation, and reference database limitations. Full article

Isolated drowned carbonate platforms in the Xisha Area represent critical research archives for deciphering the evolutionary mechanisms of carbonate systems and paleoenvironmental changes within the marginal sea of the northern South China Sea. Nevertheless, existing academic research lacks comprehensive investigations into the sedimentary processes and episodic demise signatures of typical drowned platforms in this region. This study targets the Ganquan Isolated Drowned Carbonate Platform—the largest and best-preserved drowned carbonate platform in the Xisha area. Based on high-resolution 2D multi-channel seismic data and multibeam bathymetric data, this research systematically characterizes the stratigraphic architecture and sedimentary differentiation of the Ganquan Carbonate Platform, and reconstructs its complete Cenozoic evolutionary history via interval velocity inversion, seismic sequence stratigraphic interpretation, sedimentary facies identification, and geomorphological feature analysis. The results reveal that the carbonate succession of the Ganquan Carbonate Platform exhibits prominent vertically zoned interval velocity variations, with two sharp velocity discontinuities identified at the seabed surface and the contact boundary between carbonate rocks and metamorphic basement. Four stratigraphic units are distinguished from top to bottom: seawater column, loose Upper Miocene carbonate deposits, compact Lower–Middle Miocene carbonate strata, and metamorphic basement. Five key Cenozoic seismic boundaries are recognized within the study area, which divide the evolutionary history of the Ganquan Carbonate Platform into four successive episodes: incipient initiation during the Early Miocene, vigorous expansion in the Early–Middle Miocene, transitional decline in the late Middle Miocene, and drowning reworking since the Late Miocene. This study establishes a comprehensive evolutionary model for isolated drowned carbonate platforms in the Xisha region, and advances the theoretical framework governing carbonate platform evolution in marginal seas. Full article

Microseisms, as the most energetic component of the Earth’s background noise field, represent a forefront area of research where precise location of their sources is paramount. This study systematically investigates the spatiotemporal characteristics of 50 mHz Rayleigh wave microseisms using the dense Shandong array deployed in eastern China, through beamforming and a multi-array combined analysis. The results reveal that the incident direction of the Rayleigh waves exhibits distinct temporal and seasonal variations, primarily originating from four back-azimuth sectors. To further constrain the source regions, we integrate background noise data from the Alaska array and the Venezuela array (supplemented by the Indonesia array). The multi-array product back-projection, by cross-constraining back-azimuths from geographically separated arrays, mitigates the inherent ambiguity of single-array analyses and enables robust global source localization. This approach not only improves the reliability of source attribution but also demonstrates the potential of using microseismic noise as a passive tool for monitoring ocean wave activity and investigating solid-Earth structure. The combined analysis identifies four microseism source regions (M1–M4): the Bering Sea–Gulf of Alaska–Aleutian Islands, the central South Pacific, the southwestern Indian Ocean off southern Africa, and the northeastern North Atlantic–Northern Europe. These source regions fundamentally correspond to areas of elevated significant wave height, confirming the coupled ocean–solid Earth excitation mechanism. These findings provide a methodological basis for future applications of multi-array microseismic monitoring in ocean-climate studies and seismic imaging. Full article

Located in the northern South China Sea (SCS), the Guangdong Sea areas exhibit a highly complex hydrodynamic structure driven by the combined effects of tides, monsoons, and offshore current systems, serving as a core region for China’s marine economy and offshore engineering. Although the Regional Ocean Modeling System (ROMS) is widely applied in current simulations, its accuracy is often constrained by the inadequate adaptability of its parameterization schemes to the regional environment. Furthermore, systematic parameter optimization tailored to this specific domain remains scarce. To address these limitations, this study conducts an observation-driven parameter optimization for surface current simulations in the western Guangdong Sea areas, aiming to enhance the reliability of hydrodynamic simulations and forecasting. A three-dimensional ROMS hydrodynamic model was employed to systematically design 18 physical parameterization experiments. The model’s performance was rigorously evaluated against 26 h continuous in situ current measurements from four observation stations, utilizing statistical metrics including the correlation coefficient (R), root mean square error (RMSE), Taylor diagrams, and the MMS standardized evaluation. The results indicate that the Mellor–Yamada vertical mixing scheme yields the optimal regional adaptability. For horizontal diffusion, the biharmonic scheme outperforms the Laplacian approach. Regarding bottom friction, the logarithmic formulation demonstrates superior accuracy compared to the quadratic and linear schemes, with the latter proven unsuitable for this region. A comprehensive evaluation identifies the ‘MY–Biharmonic–Logarithmic’ combination as the optimal parameterization configuration for the western Guangdong Sea areas. This study establishes an adaptable ROMS parameterization framework for the western Guangdong Sea areas and elucidates the influence mechanisms of key physical parameters on simulation outcomes. These findings not only provide high-precision hydrodynamic support for short-term pollutant dispersion forecasting, and disaster mitigation in this region but also offer valuable methodological references for numerical modeling in the broader SCS and analogous complex coastal environments. Full article

Malabar red snapper (Lutjanus malabaricus) is widely farmed across Asia (e.g., China, Malaysia, Singapore, Taiwan) and is highly valued in regional markets. Despite its importance to fisheries and aquaculture, population structure and genetic connectivity between wild and farmed populations across the South China Sea remain poorly understood. We analyzed 594 individuals retained after quality filtering from an initial dataset of 930 samples, representing eight wild and farmed populations spanning north-eastern Australia (Queensland) and the South China Sea region (Hong Kong, Malaysia, Singapore, Taiwan), using 18,177 SNPs to quantify genetic diversity, population structure, and effective population size (Ne). Genetic differentiation was low but significant. Wild populations from Australia were differentiated from all other populations, indicating regional genetic isolation. In contrast, farmed populations from Malaysia and Singapore clustered closely with wild populations from Hong Kong and Singapore, indicating regional connectivity. Effective population size (Ne) in farmed populations was low (Ne = 49.1–138.6). Farmed populations from Malaysia and Singapore formed a genetically connected cluster, whereas the Taiwan farm population was genetically distinct. Low Ne was observed in farmed populations from Singapore and Taiwan. These findings support aquaculture management by identifying Australian populations as a distinct unit and enabling biosecure broodstock exchange within the Malaysia–Singapore cluster to minimize inbreeding and strengthen sustainable selective breeding programs. Full article

Coastal waters of eastern Guangdong are important fishing grounds and ecologically sensitive areas in the northern South China Sea, where nekton communities are increasingly affected by environmental heterogeneity and human activities. However, systematic studies on the spatial differentiation and driving mechanisms of nekton communities in this region remain insufficient. This study aimed to clarify the community structure, diversity distribution characteristics, and key driving environmental factors of nekton in the coastal waters of eastern Guangdong, and thereby provide scientific support for an ecological health assessment and sustainable utilization of fishery resources in this region. Based on bottom-trawl survey data from 19 stations in the coastal waters of eastern Guangdong, northern South China Sea, this study systematically analyzed the species composition, dominant species, and diversity distribution pattern of nekton and their correlations with environmental factors using methods including the Index of Relative Importance, Alpha diversity indices, Beta diversity indices, and redundancy analysis. A total of 119 nekton species belonging to three phyla, four classes, 14 orders, and 56 families were collected. Among them, there were 79 fish species (accounting for 66.39%), 36 crustacean species (30.25%), and four cephalopod species (3.36%). The dominant species were Trachypenaeus curvirostris and Portunus sanguinolentus (IRI ≥ 1000). Wilcoxon’s test showed that there were significant differences in the Shannon–Wiener index, Gini–Simpson index, and Pielou’s evenness between the nearshore and offshore groups, while no significant regional difference was observed in the richness index. Cluster analysis, based on the Bray–Curtis distance, divided the 19 stations into five clusters, with significant differentiation in species composition and functional structure within the nearshore group. RDA results indicated that environmental factors collectively explained 99.66% of the variation in community structure. Particulate Inorganic Carbon (PIC), Phosphate (PO₄³⁻), Distance to Port, Summer Maximum Chlorophyll-a (Chl-a), and Total Suspended Matter (TSM) were identified as the key driving factors. The coastal waters of eastern Guangdong boast rich nekton species, with significant differences in community structure between nearshore and offshore areas. The heterogeneity of the natural environment and human activity disturbances jointly shape the nekton diversity pattern in this region. The research results can provide a theoretical basis for regional marine ecological protection and fishery resource management. Full article