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.

This study focuses on the physical process of a sea fog event during Typhoon “Lekima” (1909) in the northern Yellow Sea by using observation data, reanalysis data and backward trajectory model. The analysis indicates that the typhoon circulation was the decisive factor determining whether fog formed offshore and developed inland. The warm and humid southerlies from the South Yellow Sea condensed into fog on the colder sea surface besides the typhoon center, which not only provided sufficient moisture for the formation and development of the sea fog but also formed a significant inversion layer over the fog area with the downdraft in the center of the typhoon. The “stable up and turbulent down” structure in the atmospheric boundary layer improved the development of sea fog on the coast and inland area. However, the horizontal wind steering and the strengthening wind speed behind the typhoon strengthened the wind shear in the atmospheric boundary layer, resulting in the enhanced turbulent mixing and the decrease of the stability in the bottom atmospheric boundary layer, which was the main cause of the fog dissipation.

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.

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.

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.

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.

Investigating the potential for application of environmental DNA to identify benthic organisms for evaluating ecological quality status collection of 17 benthic samples from the Yalu River Estuary, environmental DNA and morphological identification and comparative analyses of the resulting ecological quality assessment indices (AMBI, BENTIX, Shannon-Wiener H', M-AMBI) were used, respectively. The results show: environmental DNA identification of organisms belonging to 10 class, 16 orders, 19 families, 20 genera and 22 species, morphological identification of organisms belonging to 9 class, 27 orders, 43 families, 55 genera and 57 species, with a total of 10 organisms; the two methods of identification yielded AMBI inter-index (R = 0.428, p = 0.043, y = 0.32x + 1.08), BENTIX inter-exponential (R = 0.430, p = 0.043, y = 0.28x + 3.59) significant consistency exists, while there was significant difference between the Shannon-Wiener H' indices; the two methods of identification yielded AMBI intergrade, M-AMBI intergrade higher similarity, 51.02%, 44.90%, respectively; the AMBI and M-AMBI grades from the two identification methods were more in line with the actual situation and evaluated the overall ecological quality status of the Yalu River Estuary as good. This study demonstrates that the identification of benthic organisms based on environmental DNA to evaluate the ecological quality status has a high potential for application in marine environmental monitoring surveys.

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.

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.

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.