Using multiple observational subsurface temperature and salinity datasets based on Argo, we analyze the trend of 0–1 500 m ocean heat content in the Pacific between 2004 and 2020. It was found that the long-term trend of the Pacific ocean heat content showed a shift in 2013. The ocean heat content in 2013–2020 increased rapidly compared with that in 2004–2012. The linear trend of the former reaches about 0.50 × 10²² J/a, which is significantly higher than that of the latter. The Pacific has recently experienced rapid warming. During 2013–2020, the largest linear trend of the ocean heat content in the Pacific appeared in the western North Pacific, followed by the Tropical Pacific and eastern North Pacific. While the ocean heat content in the entire South Pacific showed a slightly decreasing trend. In the western North Pacific, the rapid increase of ocean heat content was concentrated in the Kuroshio Extension areas, and this warming trend is likely to be caused by the northward shift of the Kuroshio Extension main axis. It is worth mentioning that there was a local decreasing trend of ocean heat content in the sea south of Japan, and this cooling trend is associated with the strengthening of the Kuroshio large meander. In the Tropical Pacific where the warming trend is the second largest, the rapid increase of ocean heat content is likely to be induced by the thermocline deepening. In addition, we point out that the rapid warming in the Pacific is reflected by the rapid rise of sea level. The linear trend of sea level per 1 cm/a corresponds to the linear trend of ocean heat content of 0.11 × 10⁹ J/(m²·a). This study elucidates the rapid warming of the Pacific since the end of the global warming hiatus, deepening our understanding of recent thermal conditions in the Pacific.

Quantitative studies on the spatial distribution of geometric parameters of complex submarine sand waves in the developmental area are rare, and the correlation between the complex geometric parameters of sand waves and environmental variables has not been clarified. Based on measured data of water depth, sediment grain size and flow velocity in the western area of Hainan Island, the environmental variables of the study area were quantified and extracted. The morphological parameters of complex submarine sand waves were calculated using an automated extraction and analysis method, and the correlation between sand wave geometric parameters and environmental variables was analyzed. The results show that the morphological characteristics of submarine sand waves in the study area are complex and variable, with an average wavelength ranging from 64 to 340 m and an average wave height ranging from 0.39 to 4.13 m. There is a strong positive correlation between wave height and steepness, as well as between wave height and the average angle of the lee side. There is also a strong positive correlation between wavelength and symmetry, and a strong positive correlation between median sediment grain size and the average angle of the lee side and wave height. The development of submarine sand waves in the study area is less influenced by water depth. Under the action of tidal currents, sediment transport is mainly by traction, and the erosion of submarine sand waves is relatively weak. The evolution of sand waves is mainly characterized by vertical growth and migration, with wave height growth prioritized over wavelength increase. Under stable tidal flow conditions, regional sediment supply and sediment grain size can both affect the scale of submarine sand waves.

In recent years, natural processes and human activities have significantly altered the Huanghe River channel and the coastal geomorphic pattern, while the impact of the dramatic geomorphic evolution on the coastal hydrodynamics has not been fully studied. Based on series images captured by the Landsat satellites and bathymetric measurements, this paper analyzed the shorelines and topography changes of the Huanghe River Delta from 1992 to 2020. Several sets of numerical models covering the entire Bohai Sea were established by TELEMAC-2D to investigate the response of tidal dynamics to geomorphic evolution and its depositional effects in the Huanghe River Delta. The results show that the erosion and deposition had significant spatial and temporal heterogeneity, and there were multiple siltation and erosion centers. The erosion center outside the old Qingshuigou Estuary moved 9.6 km to the south during 2000–2020, and the one outside the Diaokou Estuary moved 6.4 km to the east during 1992–2015. The tidal dynamics were dominated by the coastline and terrain changes on the medium and long time scales. The tidal range of the Diaokou estuary decreased, while the old and the new estuary increased. And the tidal range at 5 m depth had a maximum variation of 0.27 m. The K₁ tidal amplitude increased significantly, while the M₂ tidal amplitude was considerably reduced, and the amphidromic point near Dongying port eastward migration of 3.8 km. The high velocity outside the Diaokou Estuary and the old estuary continued to weaken, and another high velocity area gradually developed outside the current estuary. The continuous and stable high velocity area caused the erosion of the subaqueous delta and the coarsening of sediment.

Based on the high-resolution oceanic numerical model product of MITgcm with a resolution of (1/48)°, the geostrophic balanced motion and unbalanced wave motion are decomposed via the frequency-wavenumber spectrum analysis method to analyze the distribution of submesoscale characteristics and diagnose the main factors affecting their seasonal variations in the Agulhas current system. The results show that the submesoscale processes in the Agulhas current system have a significant seasonal distribution with strong features in winter but weak features in summer. The mixed layer baroclinic instability is the main reason affecting the submesoscale seasonal differences in the area. In addition, the geostrophic balanced motions are predominant in the submesoscale process in the regions with stronger eddy kinetic energy (EKE) and have no obvious seasonality. For the regions with weaker EKE, the balanced and unbalanced geostrophic motions show significant seasonality, where the local mixing layer shallowness is responsible for the increase of the unbalanced kinetic energy in summer. Our analysis helps to further clarify the characteristics of submesoscale seasonal variation and its primary factors in the Agulhas current system. The effective separation of geostrophic balanced and unbalanced motion enhances our understanding of energy transformation between multiscale processes in the ocean.

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.

Study on the coral reef canopy hydrodynamics not only provides guidance for the health of coral reef ecosystem and the ecological restoration project, but also supports the decision-making process for the reef coast hazard prevention and mitigation under extreme wave events such as the typhoons. Meanwhile, it also has significant value for predicting the sediment transport over the reef and the reef coast evolution. This paper reviews the state-of-the-art research on reef canopy hydrodynamics, and systematically summarize the research progress from three aspects: the flows inside and outside of reef canopy, the characteristics of canopy resistance as well as the simulation of canopy resistance. This paper finally proposes the further research directions as follows: future study can focus on the hydrodynamics under more severe wave condition or under combined action of wave and current. It should also fully consider the anisotropy of canopy skeleton. Moreover, it can solve the Navier-Stokes equations directly to reproduce the finer flow field at the canopy scale.

The concept of ecosystem-based fisheries management has been widely recognized, but it’s application in the construction of marine ranch is still very rare. In this study, based on the data from a bottom trawl survey of fishery resources conducted in the waters of Wuzhizhou Island from 2020 to 2021, a marine ranch fish community size-spectrum model (SSM) was built, which reflects the complex structure of food webs and interspecies interactions in marine ranch, to assess the impacts of fishing on the fish community in marine ranch. The study analyzed the effects of changes in species-specific fishing death coefficient on fish community by simulating two management strategies (single-species management and multispecies management) and monitored the state of fish community characteristics using five community ecological indicators: the total biomass of the community, the slope of size spectrum, the mean maximum weight, the mean weight, and the large fish index. The results of the single-species management strategy showed that the marine ranch ecosystem of Wuzhizhou Island showed top-down control, and there was a strong regulatory effect of carnivorous fish on plankton-feeding fish. Complex interactions such as competitive predation among different species produce trophic cascade effects after changes in fishing death coefficient. The results of the multispecies management strategy showed that fishing death coefficient of Muraenesox cinereus had the greatest effect on the slope of size spectrum, and that fishing death coefficient of Trachiocephalus myops and Muraenesox cinereus had the greatest effect on fish community biomass and community structure and function. The results of this study have important implications for the conservation and stabilization of fish community, and can help managers to better understand the potential impacts of changes in fishing death coefficient rates on fish communities, so that viable and effective conservation and management strategies can be developed based on the importance of the species to the fishery.

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.

Beach is a common and vulnerable coastal ecosystem with huge ecological service functions. Due to the multiple impacts of climate change and human activities, beach ecosystem has been seriously damaged. Beach nourishment is an effective approach to prevent coastal erosion and improve the beach environment by using sand replenishment to restore beach morphology. Previous nourishments have often neglected the impacts on beach ecosystem. Many studies show that beach nourishment have multifaceted, multi-scale and complex impacts on beach ecosystem. Based on reviewing previous researches, the compositions, characteristics and functions of beach ecosystem are summarized. The basic characteristics of beach ecological damage, the impact process and mechanism of beach nourishment on beach ecosystem at various scales are analyzed. Then, some adaptive measures for beach nourishment are suggested from the perspective of reducing negative ecological impacts, which would support coastal management and sustainable utilization of beach.

The Sardinops melanostictus and the Scomber japonicus are important economic species in the northwestn Pacific Ocean, and exploring the correlation between their habitat changes is conducive to the rational development and management of fishery resources. This study utilizes fishery data of Sardinops melanostictus and Scomber japonicus in the northwestern Pacific Ocean from June to November between 2017 and 2021. By incorporating three key environmental variables, namely sea surface temperature, sea surface height, and chlorophyll a mass concentration, habitat models with different weights are constructed. The models are then validated using fishery data from 2021. The optimal models are selected to predict the most suitable habitat distribution of Sardinops melanostictus and Scomber japonicus under different El Niño-Southern Oscillation (ENSO) events. The study analyzes the differences and synchronicity in the spatial and temporal distribution of the most suitable habitat between the two species under different ENSO events. The results indicate that the suitable habitat area of Sardinops melanostictus (above 15%) was higher than that of Scomber japonicus (less than 6%) under different ENSO events; however, the growth rate of the most suitable habitat area for Sardinops melanostictus under La Niña events is higher than that of El Niño events. The former has a growth rate of 0.197 and the latter has a growth rate of 0.123, on the contrary, the growth rate of Scomber japonicus under the La Niña event is lower than that of El Niño event, the former has a growth rate of 1.114 and the latter has a growth rate of 2.082; additionally, when the distribution locations of Sardinops melanostictus and Scomber japonicus are close to each other, it promotes favorable conditions for their habitats. On the other hand, when the distribution locations are far apart, it somewhat inhibits the increase in the suitable habitat area for Scomber japonicus. The co-variation of suitable habitat areas for Sardinops melanostictus and Scomber japonicus under different ENSO events may be related to their interspecies relationship (competition/predation-prey) and the distribution of ocean currents in the northwestern Pacific Ocean.