The annual, seasonal, monthly and diurnal variations of sea surface wind field over the Taiwan Strait were analyzed based on the new version of Cross-Calibrated Multi-Platform Version 3.1 (CCMP V3.1) wind data from 1993 to 2022. The results showed that the wind field in the Taiwan Strait and the water around Taiwan Island had obvious spatial distribution characteristics, the topographic effect leads to the maximum and minimum wind speed regions in different sea areas. Because the central Taiwan Strait was affected by the “narrow tube effect”, the wind speed was the highest and the wind direction was basically parallel to the strait in winter; the wind speed in summer was lower than the speed outside the channel, and there was no “narrow tube effect”. In addition, the sea surface wind field also had obvious seasonal and monthly variation characteristics. The northeast wind prevailed in winter, and in this season the wind speed was the highest in the whole year; the southwest wind prevailed in summer with the lowest wind speed; the characteristics of spring and autumn monsoon fields were similar, both prevailing northeast wind; winter monsoon last longer than summer monsoon, accounting for about three quarters of the year. The analysis of the inter-annual variation of wind field showed that the wind direction tended to deflect at a large angle in summer. The annual mean wind speed maintained a basically flat linear trend, and the abnormal high or low in some years was related to the occurrence of El Niño-Southern Oscillation (ENSO). When the diurnal variation characteristics were studied, it was found that the wind speed and direction fluctuated most at 20 PM. The wind speed varied periodically within a day. The diurnal variation of wind direction deflection was most obvious in summer.

The impact of the El Niño-Southern Oscillation (ENSO) on the climate of the low-latitude tropical region of the Malay Peninsula, particularly with regard to precipitation, remains a topic of debate. This study focuses on the NTT-3 drill core from Setiu Lagoon in Terengganu, northeastern Malay Peninsula. By employing analyses such as grain size, total organic carbon/nitrogen content, C/N ratio, and XRF core scanning, this research investigates the sedimentary environmental changes in the drill core and their response to ENSO. The results reveal two distinct trends in the drill core record, appearing around 1970 (at 84 cm depth). Sediment characteristics such as grain size and geochemical features of both organic and inorganic components suggest the possible occurrence of episodic sedimentation or sedimentary interruptions, with exceptionally slow sedimentation rates observed in the lower part of the core before 1970. Since 1970, the organic components in the lagoon sediment primarily originate from mangroves, accompanied by contributions from freshwater phytoplankton associated with river inputs. Spectral analysis indicates a pronounced ENSO periodic variation in the upper part of the drill core since 1970. The variations in Zr/Rb and Zr/Ti ratios correlate well with the occurrences of strong El Niño and La Niña events. This conclusion not only supports contemporary observations of climate change in the eastern coastal region of the Malay Peninsula but also provides direct geological evidence of ENSO variations in the sedimentary record. This discovery holds significant practical implications for a comprehensive understanding of the impact of ENSO on climate change in Asia, regional land-sea interaction processes, and environmental responses.

Near-inertial motion is a type of motion in the ocean that is ubiquitous and has a frequency close to the local inertial frequency. Tropical cyclones are one of the mainmechanisms that generate near-inertial motion. This study established a three-dimensional hydrodynamic model based on COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) numerical model system, which couples waves and currents, covers the northern shelf of the South China Sea, and was fully verified. The model was used to simulate the near-inertial motion triggered by Typhoon “Cempaka”, the No.7 typhoon of 2021, on the shelf of western Guangdong. The results indicate that there are spatially two peaks of near-inertial kinetic energy, one in the coastal area with the highest typhoon wind speed, and the other at 130 km offshore, with the second energy peak lasting longer. In the coastal area with water depth shallower than 40 m, the near-inertial motion is mainly in a barotropic mode. As the water depth gradually increases offshore, we found that the near-inertial motions exhibit a clear two-layer structure inthe regions with depths ranging from 70−100 m, with opposite directions of near-inertial flow in the surface and bottom layers, and two energy peaks in the vertical direction, showing the characteristics of the first baroclinic mode. Through dynamic modedecomposition, we found that some areas with obvious two-layer structures are composed of the first and secondbaroclinic modes. As the water depth continues to increase, higher modes of near-inertial flow account for an increasing proportion of the total near-inertial kinetic energy. Momentum balance analysis shows that in the coastal area with shallow water depth and high wind speed, the balance of momentum equation in the entire water layer is dominated by the vertical turbulent viscous force and pressure gradient force. In offshore areas with deeper water depths and lower wind speeds, vertical turbulent viscous forces are concentrated in the surface and bottom layers, and the balance of momentum equation in the intermediate water body is mainly dominated by the pressure gradient forces, Coriolis forces, and local acceleration. This indicates that the near-inertialmotion in the coastal area is mainly driven by barotropicwave caused bywind stress, while in the continental shelf area, the near-inertial motion in the uppermixed layer is driven by wind stress, and the near-inertial motion below the mixed layeris driven by barotropic pressure gradient force.

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.

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.

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.

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.

In order to explore the relationship between zooplankton community structure and environmental factors in the Oujiang River Estuary, four voyages were conducted in March (winter), May (spring), August (summer) and November (autumn) in 2021 to investigate the zooplankton and other environmental factors such as sea temperature, salinity and chlorophyll a concentration in the Oujiang River Estuary sea area. The results show that 78 species of zooplankton are identified, including 16 species of larva, it belongs to 8 classes and 14 categories , with the highest number of species in summer (47 species) and the lowest number in winter (23 species). The dominant species (Y ≥ 0.02) include Calanus sinicus, Sinocalanus sinensis, Acartia pacifica, and Centropages dorsispinatus, 17 species. The average annual abundance of zooplankton is (162.95 ± 310.96) ind./m³, and the average annual biomass is (118.85 ± 62.80) mg/m³. The abundance and biomass of zooplankton are the highest in spring and the lowest in autumn. The abundance in winter is higher than that in summer, and the biomass is lower than that in summer. The average annual Shannon-Wiener diversity index (H'), Pielou evenness index (J') and Margalef richness index (D) are 1.500 ± 0.702, 0.656 ± 0.270 and 2.301 ± 1.087, respectively. Spearman correlation analysis and canonical correspondence analysis show that sea temperature, salinity, Chl a concentration and phytoplankton abundance are important environmental factors affecting the dominant abundance of zooplankton in the Oujiang River Estuary. It provides scientific reference for the study on the influence of seasonal environmental changes on zooplankton in the Oujiang River Estuary, and provides basic data and theoretical basis for the sustainable development of biological resources in the Oujiang River Estuary.

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.

Planktonic copepods is an important group of zooplankton. It is of great significance to study the distribution characteristics of planktonic copepods abundance and its correlation with various environmental indicators. In this study, we analyzed environmental monitoring data of Haizhou Bay, Lianyungang, Jiangsu Province, from 2003 to 2022 using generalized additive model (GAM), to investigate the spatiotemporal variation of planktonic copepods and its correlation with other sea water indicators. The results showed that the abundance of planktonic copepods varied significantly different between seasons (p < 0.01), and the mean value of copepods was greater in spring than in summer than in autumn. The spatial distribution of abundance was generally low in the artificial reef area and high in the southern coastal area. GAM analysis showed that the main influencing factors were different between seasons. The main influencing factors in spring were dissolved oxygen, chlorophyll a concentration, ${\mathrm{SiO}}_3^- $-Si concentration and ${\mathrm{NO}}_3^- $-N concentration. The main influencing factors in summer were biochemical oxygen demand, temperature, ${\mathrm{SiO}}_3^- $-Si concentration and ${\mathrm{NH}}_4^+ $-N concentration. The main influencing factors in autumn were dissolved oxygen, salinity, suspended solids content and ${\mathrm{PO}}_4^{3-} $-P concentration. This study can provide a reference for further study of zooplankton structure and habitat suitability evaluation in artificial reef waters.