The ocean acidification effect is increasing with the large amount of CO₂ emissions. To investigate the effects of future seawater acidification on Ruditapes philippinarum, a control group (pH = 8.1) and acidification group (pH = 7.7, 7.1 and 6.4) were set up for 42 days. The changes in tissue structure, immune and antioxidant enzyme activities of Ruditapes philippinarum under acidification conditions were measured, as well as the effects produced at the molecular level. The results show that when Ruditapes philippinarum are placed in an acidified seawater environment, gill filament spacing expands with decreasing pH, gill filament cilia adhere, and the pipes and outer epidermal folds of the mantle gradually deepen. The activities of acid phosphatase (ACP) and superoxide dismutase (SOD) in gill tissues show a pattern of decreasing followed by increasing. Alkaline phosphatase (AKP) activities exhibit different trends in each group. Total antioxidant capacity (T-AOC), catalase (CAT), and lysozyme (LZM) activities show a pattern of increasing followed by decreasing. Glutathione peroxidase (GSH-Px) activities in gill and visceral masses show a continuous increase. LZM activity in the viscera group displays varying trends, while ACP activity shows a decreasing and then increasing pattern. AKP, SOD, and CAT activities exhibited an increasing and then decreasing pattern, while T-AOC activity shows a continuous decrease. Analysis of the transcriptome reveals that the GO functions in gill tissue are mainly enriched in DNA integration, integral components of the membrane, and RNA-directed DNA polymerase activity, among others. The KEGG pathway analysis shows enrichment in the phagosome pathway and pathways related to protein processing in the endoplasmic reticulum. The acidification of seawater caused varying degrees of damage to the tissues of Ruditapes philippinarum, disrupting its internal environmental homeostasis and altering metabolic levels and immune-related gene expression, and led to an increased risk of disease and even death in Ruditapes philippinarum.

To study the hydrodynamic performance of an oscillating-water-column (OWC) wave energy converter in a real sea, a two-dimensional nonlinear numerical model of the interaction between irregular waves and a land-based OWC device is developed based on the potential flow theory and the high-order boundary element method (HOBEM) in this paper. The irregular waves are generated based on the JONSWAP spectrum. The viscous damping is introduced on the water surface boundary conditions inside the air chamber to consider the energy dissipation due to water viscosity. And physical modeling experiments are carried out in the wave-current flume at Dalian University of Technology to validate the numerical model. It is found that the OWC hydrodynamic efficiency under irregular waves is reduced in comparison with that under regular waves, especially in the low-frequency wave region where the efficiency difference is the largest. The frequency corresponding to the peak efficiency under the action of irregular waves is larger than that under regular waves. The dimensionless surface elevation inside the chamber decreases, while the dimensionless air pressure inside the chamber increases with the significant wave heights. The OWC hydrodynamic efficiency is less affected by the significant wave height. The frequency corresponding to the peak efficiency is not dependent on wave nonlinearity. This work can provide a reference for the design of OWCs.

Manganese (Mn) is an essential trace element for the marine ecosystem. As the transitional zone between rivers and oceans, estuaries have a significant effect on dissolved Mn and its terrigenous input. In this study, the distribution of dissolved Mn, investigated in the surface water of Changjiang River Estuary and its adjacent area during September 2019 (autumn), March 2021 (spring) and July 2021 (summer), was analyzed by automatic solid phase extraction and inductively coupled plasma mass spectrometry. The results indicated that the average concentration and estuarine behaviors of dissolved Mn showed seasonal variations between the three cruises: the maximum average concentration occurred in summer and dissolved Mn was removed firstly and then added with the increase of salinity; the medium average concentration occurred in autumn and dissolved Mn was mainly removed with the increase of salinity; the minimum average concentration occurred in spring and dissloved Mn was mainly conservative with the increase of salinity. The results of significance test indicated that only in the season when the fresh water had high concentrations, dissloved Mn carried by the Changjiang River had significant influence on the distribution of dissolved Mn in the Changjiang River Estuary and its adjacent area; the distribution of dissolved Mn was co-dominated by a variety of biogeochemical processes in the season when the concentrations were low in the fresh water. The high suspended particulate matter concentrations were the important factor of the removal of dissolved Mn in the Changjiang Estuary’s water with medium-low salinity. And the addition mechanism of dissolved Mn in water with high salinity needs further vestigation.

Based on the comprehensive fishery survey in the Chongming Island adjacent waters in November 2020, January 2021, April 2021, and August 2021, we used an open-source program Rpath to build a mass balance model containing 22 functional groups for this area. The ecosystem structure and characteristics in this sea area were then studied. Results showed that the trophic level for these 18 functional groups ranged from 1 to 4.32, with the highest trophic level of bottom carnivorous fish. The ecological transfer efficiency of small benthic organisms is the lowest (0.01), suggesting a bottleneck in their energy transfer to higher trophic levels and indicated it was the bottleneck to limit the energy transfer in the benthic food chain. The analysis of the overall characteristics of the ecosystem shows that the total system throughput of the Chongming Island adjacent waters ecosystem was 2 909.42 t/(km²·a), which was lower than that of the nearby marine ecosystem. Phytoplankton contributes 60% of the energy to the total primary productivity of the ecosystem and was the main nutrient source of this ecosystem. The total primary production/total respiration is 1.99 and the system omnivorous index is 0.18. This indicate that the Chongming Island adjacent waters ecosystem has low maturity, simple trophic interaction, and low recovery ability after disturbance. Sensitivity analysis showed that functional group biomass was the main index that affected the accuracy of ecosystem model output. The results of this study can provide a reference for the evaluation of the effect of the Changjiang River fishing ban.

The intraseasonal variability (ISV) associated with mesoscale eddies in the northern South China Sea has been significant. Comparing the intraseasonal variability of flow at different times helps to elucidate the influence of mesoscale eddies with various dynamic instability, therefore, this study analyzed the dynamic instability of mesoscale eddies in the spring of 2009 and 2020 in the northern South China Sea, to figure out the characteristics of intraseasonal variability. Based on mooring velocity data, it conducted kinetic spectral analysis, and the results demonstrated that the ISV with period of 10‒60 days in 2009 and the ISV with period of 30‒90 days in 2020 displayed a similar vertical feature, with strong intraseasonal signals primarily occurring in the upper layer above 200 m. Moreover, the ISV with period of 30‒90 days was the main intraseasonal component during the corresponding observation period. Lag-regression analysis and calculation of dynamic instability showed that the intraseasonal variation of spring 2009 was affected by fast-moving but weak surface mesoscale eddies, and the dynamic instability was modulated by baroclinic instability and barotropic instability. On the other hand, the intraseasonal variability in the spring of 2020 was influenced by strong baroclinic mesoscale eddies, which might trigger the occurrence of intraseasonal variability in the flow fields more rapidly through enhanced vertical shear of velocity. The findings of this study contribute to a deeper understanding of the impact mechanisms of mesoscale eddies on intraseasonal activities in the northern South China Sea, providing important references and a theoretical basis for ocean dynamics and climate research.

This paper investigates the characteristics of turbulent structures in combined wave-current boundary layers based on the standard $ k $-$ \varepsilon $ model. Good agreements were found between the numerical results and experimental data of the time-averaged mean velocity profiles. Periodic variations of turbulence parameters within a wave cycle (i.e. vorticity magnitudes, TKE and TKE dissipation rates etc.) were observed. The vorticity magnitudes, TKE and TKE dissipation rates all decrease during the deceleration phase, reach their minimum values during the wave trough, increase during the acceleration phase and reach their maximum values during the wave crest. The variations of turbulent structures are very high in the near-wall regions (53% for TKE dissipation rates), and are quite low in the outer regions (3% for TKE dissipation rates). The wave-current boundary layer thickness increases (decreases) during the deceleration phase (acceleration phase). The model developed in this study has solved the existing issue of low accuracy in the near-bed region by previous models based on the “high Reynolds number methods”. The present model performs well in describing the physical process of turbulence variations under the effects of wave-current interaction. This can provide some guidance for the sediment transport in coastal areas, beach erosion prediction and developments of marine renewable energy.

The Zhujiang River Mouth Basin is located in the northern shelf of the South China Sea, and its tectonic evolution is very complicated. At the same time, as one of the hydrocarbon-rich basins in offshore China, Zhujiang River Mouth Basin ranks the top in oil and gas production among the offshore basins. With the deepening of exploration, the boundary of the Zhujiang River Mouth Basin has been changing, and the southern boundary of the basin is disputed. In this paper, based on satellite gravity and magnetic anomaly data, the fault distribution of Zhujiang River Mouth Basin is re-studied and the plane location of igneous rocks is identified. The Cenozoic thickness of the study area is retrieved with high-precision seismic data, and the tectonic units of the study area are adjusted according to the processing results. The results show that the fault distribution in the study area is mainly NEE, NE and NW trending. In this study, four new faults were identified based on the satellite gravity data. The overall strike of the igneous rocks in the plane is NEE strike, but there are differences among different regional strikes. There are nearly EW trending igneous rocks in the western basin, NWW trending igneous rocks in the central basin, and no other strike in the eastern basin. According to gravity data and Cenozoic characteristics, Yangjiang Sag is divided into Yangjiang West Sag and Yangjiang East Sag, and Wenchang D Sag and Wenchang E Sag are deleted. The Beiweitan Fault is the same as the Yangjiang-Yitong Fault, which divides the basin into three parts: the west, the middle and the east. The fault strike, the plane position of igneous rock, the thickness of Cenozoic and the tectonic units of the three parts are different. The study of faults, igneous rocks and tectonic units in Zhujiang River Mouth Basin aims to provide geophysical support for subsequent basin research and oil and gas breakthrough.

The tectonic evolution of the northwestern continental margin of the South China Sea were controlled by many factors, such as the Red River Fault, the Hainan mantle plume and the formation and evolution of the South China Sea. The Yinggehai Basin is located in the northwest of the South China Sea, where thick Cenozoic sediments were deposited. The Cenozoic evolution history of the northwestern continental margin of the South China Sea was recorded in detail in the Yinggehai Basin. However, which factor has mainly controlled the evolution of the Yinggehai Basin since the Cenozoic is still ambiguous. In this paper, 7 drilling wells and 23 simulated wells were selected in the Yinggehai Basin, and the sedimentation rate and subsidence rate of the Yinggehai Basin were reconstructed by empty basin tectonic subsidence analysis method. The deep structure of the Yinggehai Basin was simulated by gravity inversion method based on previous study. The results show that during the rift period, the subsidence rate of the Yinggehai Basin in the north and middle sections is larger than in the south section. There are two stages of “step acceleration subsidence” in the north and middle sections, which are 23–11.7 Ma BP and 11.7 Ma BP–present, respectively. The maximum tectonic subsidence rate can be up to 80 m/Ma in the post rift stage in the north section and about 110 m/Ma in the middle section. The maximum tectonic subsidence rate of the Southern Graben and Uplift is both close to 70 m/Ma during the periods of 11.7–5.7 Ma BP and 15.9–11.7 Ma BP, respectively. The Cenozoic subsidence of the Yinggehai Basin is consistent with the change of sedimentary rate, indicates that tectonic subsidence plays a significant role on sedimentary evolution. According to the results of gravity inversion, it may be lower crust high density anomaly intrusion underlying the Yinggehai Basin. We suggested it may be basic rock according to the drilling basalts in the sediments. By comparing with the subsidence rate of surrounding basins in the South China Sea, the acceleration subsidence in the 15.9–11.7 Ma BP may be related to the disappearance of secondary mantle convection due to the ceasing of the seafloor spreading of the South China Sea. The 5.7 Ma BP–present accelerated subsidence of the Yinggehai Basin may be related to the dextral strike-slip activity of the Red River Fault.

Sediment source is a key issue in sedimentology. Although sediment geochemistry is an important tool in sedimentology, the explorations and applications of radionuclides in sediment geochemistry are still limited. In this study, naturally occurring radionuclides (²³⁸U, ²²⁶Ra, ²²⁸Ra, and ⁴⁰K) in sediments were simultaneously measured using a high-purity germanium γ-spectrometer in three typical ecosystems of mangrove, seagrass, and coral reefs. The distribution characteristics of radionuclides in sediments from the these ecosystems were discussed in one-dimensional view of activity level, two-dimensional view of radionuclide pairs and activity ratio, and three-dimensional view of ternary diagram of radionuclides to identify distinct sources of sediments. Ternary diagram of ²³⁸U-²³²Th(²²⁸Ra)-⁴⁰K/10 in sediments was applied in the China different seas for tracking distinct sediment sources. This study emphasized that the three-dimensional view of ternary diagram of ²³⁸U-²³²Th(²²⁸Ra)-⁴⁰K/10 comprehensively exhibited the information of activity level, composition, and spatial distribution area of radionuclides. In conclusion, ternary diagram of ²³⁸U-²³²Th(²²⁸Ra)-⁴⁰K/10 may be an optimized method for source identification in sediments and provide a supplement to the existing tools of geochemical proxies.

Previous research has conducted extensive work on sediment grain size testing, data analysis, and information extraction. However, studies on whether the collected sediment samples are representative are still relatively rare. Based on indicators such as the mode, median grain size, particle size distribution, sediment type, and grain size parameters, this study compared and analyzed the quantitative and qualitative results of the grain size distribution parameters of 30 parallel sediment samples collected from beaches in the southern part of Leizhou Peninsula, China. The study examined the differences, correlations, and consistencies of these parameters. The results showed that: (1) the mode, median grain size, and particle size distribution of parallel samples exhibited a certain degree of variability; (2) the skewness and kurtosis of parallel samples showed significant differences, with average values of P1 ranging from –2.90 to –1.53 and 11.23 to 21.59, P2 ranging from –2.55 to –1.52 and 11.23 to 21.59, and P3 ranging from –2.81 to –1.86 and 13.41 to 27.69; (3) about two-thirds of the combinations of grain size parameters had no correlation (R² ≤ 0.29); (4) qualitative results of sorting coefficients, skewness, and kurtosis showed differences in 1/3, 1/2, and 4/15 of the cases, respectively. The spatial heterogeneity of sediment grain size distribution information and the randomness of sample collection are the main reasons for these differences. To minimize the randomness of sample collection and characterize the spatiotemporal heterogeneity of grain size distribution information, parallel samples are recommended for future sample collection. This study provides a typical case of comparing the results of parallel sample grain size parameters for beach sediment, which can improve our understanding of effective sediment sample collection strategies.