Taiwan Strait is the largest strait in China and the main channel for material and energy exchange between the East China Sea and the South China Sea. The topography changes dramatically and the tidal environment is complex in the Strait. In addition, many mountainous streams on both sides carry a large amount of sediment into the strait. It is an ideal place to study dynamic sedimentation processes. Currently, due to a lack of high-resolution bathymetry and relevant data for the entire Taiwan Strait, there are few studies on modeling the tide and sediment behaviors of the Taiwan Strait as a whole. In this study, based on high-resolution bathymetric and relevant hydrological data, a two-dimensional tidal current numerical model of the Taiwan Strait has been established, and a sediment transport module has been coupled to simulate the sediment transport in the Taiwan Strait. The dynamic simulation results indicate that the tidal current field in the Taiwan Strait is governed by two tidal waves from the south and north, exhibiting distinct temporal and spatial characteristics. The tidal flow velocity is higher in summer than in winter, and it is lower in the central part of the strait compared to the southern and northern sides, with the northern side being less than the southern side. Based on the deposition and erosion simulation results, the Taiwan Strait is categorized into three main types and a total of seven sedimentary subdivisions: deposition zones, erosion zones, and deposition-erosion equilibrium zones. The maximum sedimentation rate in the accumulation zones can reach 5 cm/a, primarily concentrated in the northern part of the Taiwan Bank, with erosion rates ranging from 2 cm/a to 5 cm/a in the erosion zones. Leveraging these simulation outcomes, this study constructs a sediment transport model and a ‘source-to-sink’ pattern model for the Taiwan Strait, elucidating the dynamic mechanisms behind the strait’s deposition and erosion changes and the ‘source-to-sink’ process.

The Japan Sea is the largest marginal sea in the northwestern Pacific Ocean. For a long time, it has been widely believed that the sediments are deposited in strongly reducing environment, which results in extremely weak magnetic signals and then restricts the application of frequently-used magnetic method in this region. To investigate deeply the availability of magnetic indicators in paleoenvironmental and paleoceanographic studiesin the Japan Sea, we conducted systematic rock magnetic analyses, high-resolution accelerator mass spectrometer (AMS) ¹⁴C dating, and grain-size analysis on a 626-cm-long sediment core (LV87-2-3, water depth 740 m) recovered from the northern Japan Sea that has been studied in relatively low level. The results indicate that the studied core corresponds to a sedimentary record since approximately 48.3 ka BP. The majority of primary ferrimagnetic minerals, mainly magnetite, in the sediments below 55 cm, had been reduced into pyrite, which caused weakly magnetic intensity. This is associated closely with the intensified stratification of water body and the increase in surface productivity during interstadials in the Dansgaard-Oeschger (D-O) cycles. Nevertheless, there are still four strong magneticlayers characterized by elevated percentages of high-coercivity minerals (i.e., hematite and goethite), which are termed as ‘hard-magnetic abnormal’ layers and correspond well with the Heinrich Events. This indicatesrelatively weak reducing conditions that were resulted from the enhanced East Asian Winter Monsoon (EAWM) and injection of high salinity Tsushima Warm Current (TWC). These changes, however, are not reflected by the grain-size of sediment. Our study therefore not only indicates that the role of magnetic parameters in the paleoenvironmental and palaeoceanographic reconstructions of the Japan Sea during the last glacial, but also provides new perspectives and ideasfor relevant investigations in the future.

The double-row perforated cylinder breakwater is a new type of environment-friendly breakwater, and the research on its wave absorbing characteristics is of great engineering significance. With the development of artificial intelligence, solving the water dynamics problem of breakwater based on machine learning technology has become a new research paradigm. This paper proposes a Convolutional Neural Network (CNN) model based on Sparrow Search Algorithm (SSA) to achieve intelligent optimization prediction of transmission coefficient of double-row perforated cylindrical breakwater. The results show that: (1) wave height, wave period, wavelength, wave velocity, row spacing, hole rate and water depth are identified as the key factors affecting the transmission coefficient. (2) When the population size of the SSA-CNN model is 10, the R² value of the wave transmission coefficient prediction reaches 0.9909, and the average relative error is reduced by 22.24% compared with the single CNN model. The research results provide a new optimal prediction model for the study of wave transmission by using neural networks.

Sea surface gusts are important marine dynamic environmental information required for the development of marine resources, marine disaster prevention and reduction, and marine scientific research. However, so far, there has been a serious lack of observational data on sea surface gusts, which has hindered the development of gust forecasting, application research, and other aspects. This article uses the backscatter coefficients in the C and Ku bands of the dual frequency HY-2B satellite altimeter to correct the existing sea surface wind speed ($ {U}_{10} $) and gust wind speed ($ {U}_{{\mathrm{g}}} $) inversion algorithm. The inversion results were verified for authenticity with the buoy data from the National Buoy Data Center (NDBC) of the United States from 2018 to 2022. The correlation coefficient (R) was 0.91, and the root mean square error (RMSE) was 1.82 m/s; based on the inversion results of this method and the NDBC station data from 2018 to 2022, the RMSE of similar foreign satellites Jason-3 is superior to the conventional 2 m/s accuracy requirement; the inversion results were verified with individual cases of offshore and oceanic stations at different latitudes, and the RMSE was better than 2 m/s. Therefore, based on the existing HY-2B satellite altimeter sea surface wind speed observation data, this article uses different band information to achieve observation of sea surface gusts, which has high observation accuracy. Meanwhile, this method is also applicable to foreign satellite altimeters with the same observation system.

Reliable assessment of the impact and risk of typhoons on coastal areas is very important for scientific resistance to typhoon disasters. China has a detailed typhoon observation record with a history of only 60 years, which makes it limited in estimating extreme wind speed with a long recurrence period and corresponding extreme wave height and tide level. The insufficient records also limits the application of data-driven models in typhoon disaster prediction. Therefore, it is necessary to construct synthetic typhoons based on the actual typhoon travel law to overcome the problem of insufficient historical observations. In this paper, 18 671 synthetic typhoons were constructed in the Northwest Pacific Ocean by using the Empirical Path Model based on kernel density estimation, and the parameters such as the start and end position, frequency of occurrence, travel speed and direction of the synthetic typhoons were statistically compared and analyzed with historical typhoons. The results show that the synthetic typhoon constructed based on the proposed method is generally consistent with the traveling characteristics of historical typhoons in the Northwest Pacific Ocean. Through the construction of these synthetic typhoons, a synthetic typhoon database with sufficient data and reliable performance can be provided for the study of extreme wave and storm surge along the coast of China.

There are also obvious inter-annual variations of the North Equatorial Countercurrent (NECC) during the occurrence and development of the El Niño-Southern Oscillation (ENSO), but its changing process in hydroecological conditions and response mechanism influenced by ENSO cycle are still unclear. Taking the NECC affected area in the tropical western Pacific as the study area, this paper analyzes the characteristics of the changes of hydroecoclimatic conditions at different stages during the ENSO cycle during autumn and winter transition period from 2006 to 2022. Results reveal that there are high chlorophyll concentration bands in the NECC source area and its path, which are formed by the combined influence of nutrients carried by the NECC from its source area and the New Guinea Coastal Undercurrent. The upwelling of the Mindanao Dome also has a great influence on the nutrient supply. When El Niño events occurred, the westerly wind events in the tropical western Pacific increased, the NECC strengthened, a large amount of surface water moved eastward, the sea level in the study area decreased, the deep water recharge to the shallow layer increased, and the deep cold water rose. The jointly enhanced NECC, New Guinea Coastal Current, New Guinea Coastal Undercurrent and Mindanao Dome upwelling transport more nutrients to the sea surface from both horizontal and vertical levels, resulting in significant increases in surface chlorophyll concentration and primary organic carbon production by all types of phytoplankton. When La Niña events occurred, the changes of ecohydroclimatic conditions in the NECC affected area are almost opposite to those during El Niño events, but the degree of change is weaker than that during El Nino events. The combined weakening of the NECC, the New Guinea Coastal Undercurrent and the Mindanao Dome upwelling significantly reduce the nutrients delivered to the sea surface from the horizontal and vertical levels. The chlorophyll concentration and primary organic carbon production by all types of phytoplankton decreased significantly. This paper proposes a model of the response mechanism of the evolution of hydroecoclimatic conditions in the NECC affected area to El Niño and La Niña events, which is conducive to further analysis of the role of ENSO cycle in local ecological effects and hydroclimatic evolution. It has important significance for understanding the impact of global climate change on the material cycle.

Natural gas hydrates have received widespread attention due to their enormous resource potential, but previous researches have focused mostly on the passive continental margin in the northern South China Sea, while rarely on the active continental margin in the eastern South China Sea. Based on the analysis of multi-channel seismic profiles in the active continental margin area of the Manila Trench in northeast of the South China Sea, this paper identified typical gas hydrate indicators such as bottom simulating reflector, blanking zone, polarity-reversal, and fluid migration channels, such as reverse fault and mud diapir are identified in this paper. The Orogenic Belt in southwestern Taiwan is an extension of the accretionary wedge of the Manila Trench. The associated gas of mud volcano is mainly CH₄ and minorly showing high nitrogen anomaly. The geochemical characteristics of the associated gas show that natural gas in this area is mainly mature hydrocarbon gas of pyrolysis origin, and is mainly the contribution of Neogene thick marine sedimentary source rock. According to the analysis, the cause is that the plate subduction brought deep hydrocarbon into the accretionary wedge and formed a high-pressure environment. The thermally generated hydrocarbon gas migrated upward along mud diapir and reverse fault. During the migration, some natural gas was gradually transformed by decomposition of microorganisms and mixed with in-situ microbial gas. The thermogenic and biogenic methane eventually mixed in the suitable stable zone to form a mixed gas hydrate reservoir dominated by thermogenic and partly biogenic. In addition, with the change of external environment and the continuous activities of subduction movement, the stability of natural gas hydrate is damaged and decomposition leakage occurs, which may cause landslide. In the further exploration and development of natural gas hydrate resources in this area, we must pay attention to the potential geological disaster risk.

The coastal plain of Jiangsu Province is a fragile zone of water resources in Jiangsu Province, and groundwater salinization has become a serious ecological problem. In order to analyze the groundwater recharge and its salinity sources in the north flank of the Changjiang River Delta since Pleistocene, a 275 m deep well HYRD1 was deployed and the whole hole was continuously collected with easily soluble salt samples, geotechnical samples and water samples. Surface water, shallow and deep groundwater, and seawater samples were collected in the area. The hydrochemical characteristics of Well HYRD1 high-precision porewater were obtained by using soluble salt index combined with geotechnical index (water content, wet density, specific gravity). In order to analyze the groundwater recharge and its salt source since Pleistocene, Piper trilinear diagram, Gibbs diagram and ion ratio method were used in combination with δD and δ¹⁸O data and ¹⁴C data. The results show that the salinity of Well HYRD1 soil is mainly NaCl, and the percentage of saline soil is 25%. The saline soils are mainly distributed in the Q_p3 aquitard, Q_p2 stratum and the upper part of Q_p1 stratum. The water chemistry type of porewater is Cl-Na type (only the lower section of Q_p1 is HCO$_3^- $-Ca·Na at individual points), 7% of brackish water, 49% of saline water and 44% of haline water. The brackish water is mainly distributed in the sand layer of the lower section of Q_p1. The δ¹⁸O and δD of diving indicate that the source of diving is atmospheric precipitation and is subject to a relatively strong evaporation effect. The δ¹⁸O and δD of the aquitard pore water and pressurized water are located near the standard seawater dilution line, and the trend of δ¹⁸O and δD decreases with the increase of depth, which indicates that the porewater is subjected to the mixing effect of seawater decreases with the increase of depth. Calcareous nodules are mostly seen in the Q_p1 aquitard, indicating that the Q_p1 aquitard was subjected to strong evaporation after soil formation. The salinity of the upper part of Well HYRD1 Q_p1 and the overlying strata is mainly from the 5th stage sea erosion, evaporite and silicate weathering dissolution. The salinity of the lower part of Q_p1 is mainly from the crustal source. The groundwater chemistry is influenced by water-rock action, evaporation concentration and human activities.

To understand the characteristics and distribution of benthic shellfish communities in the vicinity of the Nanji Islands, we conducted bottom trawl surveys in the surrounding waters during October 2022 (autumn) and March 2023 (spring). The findings reveal that a total of 49 benthic shellfish species were captured, spanning 2 classes, 6 orders, and 17 families. During spring, the average abundance of benthic shellfish was (2 429 ± 2 038) ind./Agt, with an average biomass of (4 849.79 ± 2 513.84) g/Agt. In autumn, the average abundance was (1 149 ± 1 589) ind./Agt, with an average biomass of (4 985.30 ± 2 159.23) g/Agt. The primary dominant species comprised Turritella bacillum, Murex trapa, Tegillarca nodifera, Inquisitor jeffreysii, Bufonaria rana, Cancellaria sinensis and Trigonaphera bocageana. Notably, Turritella bacillum emerged as a dominant species in both spring and autumn, with dominance significantly surpassing that of other species. The dominance of benthic shellfish communities in this marine area appears relatively stable, with the community’s functionality and nature being primarily governed by a select few species. This study provides a reference basis for the dynamic changes in the marine ecosystem of the Nanji Islands and offers foundational data for the protection of marine ecological environments.

Based on the survey data of fishery resources and environment of four voyages from April 2021 to January 2022, the spatial and temporal distribution of Portunus trituberculatus and its relationship with influencing factors in the Ruian sea area were studied, including its marine dominance, community structure and resource density distribution. At the same time, generalized additive model (GAM) is used to analyze the relationship between resource density and influencing factors. The results showed that: in the Ruian sea area, P. trituberculatus is an important species (100 ≤ IRI < 1 000) in spring and summer and a dominant species (IRI ≥ 1 000) in autumn and winter. The average carapace length and body weight of P. trituberculatus ranged from 33.9 mm to 60.4 mm, and 22.9 g to 126.1 g. The carapace length and body weight of P. trituberculatus were the highest in summer and the lowest in autumn. There were significant differences between different seasons. P. trituberculatus showed negative allometric growth in spring, summer and winter (b < 3), and positive allometric growth in autumn (b > 3). The average resource density of P. trituberculatus ranged from 16.57 kg/km² to 422.60 kg/km², with the highest in autumn and the lowest in spring, and the average resource density in autumn was 25.5 times of that in spring. GAM analysis showed that the interpretation rate of the model was 80.2%. Season, surface water temperature, bottom water temperature, bottom salinity and surface chlorophyll a concentration had significant effects on the resource density of P. trituberculatus (p < 0.05), among which season had the greatest effect. Through this study, it provides reference for grasping the dynamic change law of P. trituberculatus resources in Ruian sea area, and further provides theoretical support for the proliferation and release of P. trituberculatus.