Rip current is an important part of nearshore current. Affected by special beach topography, waves will form a high velocity flow moving along the offshore direction, which can quickly take people away from the shore and pose a threat to beach safety. In order to further explore the formation mechanism and hydrodynamics characteristics, three-dimensional numerical simulation of rip current was carried out. In this paper, based on the second-order Stokes wave theory, a typical sandbar model with variable cross-section is adopted and used to generate rip current. The free liquid surface is captured by volume of fluid method. The rip current flow field distribution laws of instantaneous velocity, time-averaged velocity and pressure are analyzed and made some discoveries: there is a pair of opposite water circulation systems between the bar and the shoreline. By comparing the velocity distribution of rip current a different depth, the interaction between waves and rip currents is understood. Furthermore, the influence of incident wave height on intensity and distribution of rip current is also studied, which deepens the understanding of the hydrodynamic process of rip current.

The significant wave height (SWH) is a key parameter for describing the ocean waves. In this paper, the SWH in the Taiwan Strait provided by the ERA-Interim reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) in March 2013 is compared with the buoy observations and the simulation results of the SWAN (Simulating Waves Nearshore) model. The results showed that the correlation coefficient of SWH between the buoy data and the ERA-Interim as well as the SWAN results is 0.94 and 0.98, respectively. The average SWH of the ERA-Interim data is about 51% of the buoy data and 70% of the SWAN results. The monthly averaged values of the spatial anomaly correlation coefficient (ACC) of the SWH between the ERA-Interim data and the SWAN results is 0.51. The ACC was minimal when the wind started, it boosted rapidly with increasing of the wind speed and reached the maximum before the wind speed reached the peak. Then the ACC turned to decrease at the peak wind speed. Integrated analysis imply that the ERA-Interim data can reflect the spatial distribution and the temporal variations trend of the SWH over the Taiwan Strait during this period, but it’s evidently smaller than the SWAN model data.

Tuna is an important fishing target in China’s pelagic fishery. Its morphological indexes are of great significance for the study of the growth, development and life history of tunas. Manual measurement of morphological index is a very tedious and inefficient measurement method, while computer vision is an efficient and objective automatic measurement method. Therefore, in this paper, images of three Thunnus species are preprocessed by the computer vision library (OpenCV). It mainly uses image processing techniques such as bilateral filter, gray transformation, image binarization and contour extraction to obtain the contour image of tuna. According to the pre-selected feature points, the computer vision technology is used to traversal all the pixel points on the contour image, and 17 pre-selected feature points of each contour image are automatically located. By using the computer vision technology, the pixel length of the morphological index of the three species of tuna is automatically measured and the actual length of the morphological index is calculated. The absolute error and relative error between automatic measurement and manual measurement are compared and analyzed. The results show that the computer vision technique is effective in the automatic measurement of the morphological indexes of the three Thunnus species. The absolute error ranges of 12 morphological indices of Thunnus obesus, Thunnus albacores and Thunnus alalunga are 0.00−1.46 cm, 0−1.73 cm and 0−1.32 cm, respectively, and the relative error ranges are 0.01%−5.84%, 0%−6.17% and 0%−6.89%, respectively. It is expected to provide a basis for intelligent identification of tuna and a basic reference for automatic measurement of other fish.

In order to explore the effects of low temperature stress on the expression of genes related to lipid synthesis and catabolism in cobia (Rachycentron canadum), the experiment set up a normal temperature group (30.5±1.0)°C and a low temperature group (20.0±0.5)°C, and used real-time fluorescent quantitative PCR (qRT-PCR) to analyze the expression levels of 5 target genes in liver, muscle and intraperitoneal fat (IPF). The results showed that at 1 d, the expression of carnitine palmitoyl transferase-1 and hormone-sensitive lipase genes of liver, carnitine palmitoyl transferase-1, hormone-sensitive lipase and monoacylglycerol lipase genes of muscle were up-regulated (p<0.05), acetyl-CoA carboxylase and fatty acid synthase genes of liver, muscle and 5 lipid metabolism related genes of IPF were significantly down-regulated (p<0.05); at 4 d, the expression of carnitine palmitoyl transferase-1, hormone-sensitive lipase and monoacylglycerol lipase genes of liver, and hormone-sensitive lipase, monoacylglycerol lipase, acetyl-CoA carboxylase, fatty acid synthase genes of muscle and carnitine palmitoyl transferase-1, hormone-sensitive lipase, monoacylglycerol lipase, acetyl-CoA carboxylase genes of IPF were up-regulated (p<0.05), acetyl-CoA carboxylase and fatty acid synthase gene of liver were down-regulated (p<0.05); at 7 d, the expressions of carnitine palmitoyl transferase-1, hormone-sensitive lipase, monoacylglycerol lipase, acetyl-CoA carboxylase genes of liver and IPF, and hormone-sensitive lipase, monoacylglycerol lipase, acetyl-CoA carboxylase genes of muscle were up-regulated (p<0.05), carnitine palmitoyl transferase-1 gene of muscle and fatty acid synthase genes of liver were down-regulated (p<0.05). The results showed that cobia responded to low temperature stress by inhibiting lipid synthesis and metabolism, promoting lipid hydrolysis in the liver and muscle, and inhibiting the lipid hydrolysis of IPF in the early stage of low temperature stress; in the late period of low temperature stress, cobia lipid synthesis and catabolism were significantly increased, and the main tissue that used fatty acids to provide energy was transformed from the liver and muscle to liver and IPF.

Numerous engineering projects show that beach nourishment is a common method against coastal erosion. Beach nourishment is an artificial process of adding sediment to a beach to increase beach width and protect it from erosion. In this paper, a 1D numerical model for beach profile was established and verified by the results of physical model experiment. In addition, the rates of profile change to equilibrium profile on different positions and different sand volume schemes were calculated, and the efficiency was compared and analyzed. To analyze the protection effects of beach nourishment, the profiles in nourishment schemes and no nourishment schemes after storm condition were compared. It turned out that when the nourishment volume was large the efficiency of bar nourishment under the calm condition was higher than of berm nourishment, and the nourishment effect under the storm condition was better. This study has important implications to save construction costs and raise working efficiency during the practical nourishment engineering. In the meantime, it sheds light on evaluating the effect of beach nourishment.

Ocean waves can affect the roughness of the ocean surface, and the waves generated by tropical cyclones impact the momentum and energy fluxes across the air-sea interface. In this study, the impacts of ocean waves on the momentum and energy fluxes under tropical cyclones is examined by using the tropical cyclone observation dataset IBTrACS (International Best Track Archive for Climate Stewardship) and the simulations from wave model WW III (WAVEWATCH III). It is found that the intensity of tropical cyclones increased by about 1 m/s every decade in the past 30 years, but the change of translation speed is not obvious. For the stronger tropical cyclones, the difference for momentum flux and the energy flux between the air-sea interface can be significantly increased by the waves. Owing to the asymmetry of wind and surface wave fields under tropical cyclones, momentum difference and energy difference also demonstrate asymmetric distribution: the area with larger momentum difference is behind the moving direction of tropical cyclone, while energy difference is the largest in the right-rear quadrant, and both are relatively smaller in the left front quadrant. The inverse wave age is highly correlated with momentum difference and energy difference, and the correlation coefficient is about 0.95, indicating that the younger the surface wave, the more momentum and energy absorbed and stored by surface wave field. The inverse wave age increases with the increase of tropical cyclone translation speed, and the speed is positively correlated with momentum difference and energy difference according to the correlation coefficient above 0.8. Therefore, the surface waves affect the distribution and magnitude of momentum and energy input from the atmosphere to the ocean under tropical cyclones. In the future study of ocean boundary dynamics and thermodynamics, especially the study of tropical cyclones, considering the influence of ocean wave evolution is necessary.

Using in-situ hydrographic observations from January to December 2017, 3D thermohaline structure and seasonal variation in the Zhanjiang Bay is investigated in this study. The results show that: (1) In 2017, the annual mean temperature is 23−27℃, the mean salinity is 19−27, the mean potential density is between 11−17 kg/m³, and the mean buoyancy frequency (N²) is about 7×10⁻⁵−5×10⁻³ s⁻² in the Zhanjiang Bay. The vertical structure and horizontal distribution of N² are similar to that of the temperature, while the distributions of potential density and salinity are similar. (2) The temperature has significant seasonality with the highest value in summer, followed by autumn, and the lowest in winter. The maximum temperature difference between winter and summer reaches 15℃, while the seasonal mean of the salinity varies slightly. The ebb and flood have less influence on temperature and salinity, comparing with their seasonal variations. The thermocline is the strongest in summer with the maximum gradient reaches 0.7℃/m at 10 m, whereas it shallows to 5 m in spring and fall, and the water well mixed in winter. The halocline is prominent in summer and fall, with the maximum gradient 1.1 m⁻¹. The seasonal variation of the thermohaline in the upper layer and lower layer are consistent. (3) For the horizontal distribution, the temperature decreases and the salinity increases from the bay head, the mid bay, the bank region, the shoal region to the bay mouth. The average temperature difference between the bay head and the bay mouth is 2.3℃, and the salinity difference is 2.7. The temperature-salinity (θ-S) diagram shows banding distributions with one end as the low-temperature and high-salinity water in the bay mouth, one end as the high-temperature and low-salinity water in the bay head, and the other water masses are between them. Different bands are shown in different seasons.

The community structure of scleractinian corals in the southwest seawaters the of the Weizhou Island was analyzed with the data collected in a survey conducted with the method of line intercept transect from May 14 to 22, 2019. The results showed that 38 species of scleractinian corals in 9 families were found, dominated by mass corals such as porites sp., favites abdita, goniopora stutchburyi etc. The coverage of the living scleractinian corals ranged from 5.20% to 31.20%, the average coverage were 16.66%, higher at the sites far from or close to the shore but with deeper water. The living scleractinian coral had low recruitment rate, few diseases and low mortality rate. Species diversity, dominance and evenness of the scleractinian coral communities were positively correlated one another (p<0.05). The coverage and biodiversity of the living scleractinian corals were higher at the sites where anthropogenic disturbance was less, i.e. closer to the cliff, deeper water, fewer boating and diving etc. The living scleractinian corals closer to sandy beach influenced severely by suspended sediment on eroded coast and diving had the lowest coverage, the highest dominance of the dominant species and relatively lower diversity. Human activities, southwest monsoon, storm surge, suspended sediment on eroded coast and extreme weather are the main influential factors on the coral reef ecosystem in the southwest seawaters of the Weizhou Island.

The radionuclides ⁷Be, ²¹⁰Po and ²¹⁰Pb transported by the atmosphere can be used as important tracers for studying the material deposition flux of the Arctic Ocean’s atmosphere, modern ocean sedimentation and the transport of materials into the sea ice. They have been widely used in the study of air mass movement, soil erosion, and particle circulation processes in water systems. This paper reports the activities of ⁷Be, ²¹⁰Po and ²¹⁰Pb in the surface snow of the high-latitude ice floes of the Arctic Ocean in 2018. The activity concentrations of ⁷Be, ²¹⁰Po and ²¹⁰Pb are 33.6−632.68 mBq/L, 36.2−87.5 mBq/L, and 30.9−194.49 mBq/L, respectively. The activity concentrations of ⁷Be and ²¹⁰Pb in the surface snow of the Arctic Ocean are lower than those in the mid-latitude continental areas. The results show that the activity concentrations of ⁷Be in snow increased with the increase of latitude. The activity ratio of ²¹⁰Po/²¹⁰Pb ranged from 0.70 to 1.48 (with an average of 0.93), ²¹⁰Po is almost in equilibrium with ²¹⁰Pb. It indicates that the age of the surface snow is “older”.

The seabed soil layer will gradually accumulate pore pressure under the action of wave cyclic load, reduce the stability of the soil layer, and threaten offshore engineering. In order to study the accumulation mechanism of pore water pressure, the discrete element pore density flow method was proposed, and the discrete element analysis software MatDEM was improved to realize the simulation of the accumulation process of seabed sediment pore pressure. Based on the field test device and the mechanical parameters of the soil body, a discrete element model was established. By comparing field test and numerical simulation results, it was found that after applying the wave load to the seabed sediment, a higher pore pressure was generated in the surface soil body and gradually transferred to the deep layer. Under the action of cyclic wave load, the cumulative range of pore pressure between soil particles gradually increased. When the pore pressure accumulation time was long enough, the pore pressure in the soil layer converged to the average of the maximum and minimum loads applied. As the number of load cycles increased, the pore pressure at all depths increased cumulatively until the soil body liquefied and the internal soil particles became resuspended sediments. Under the action of periodic wave loads, the soil particles moved after being liquefied and suspended, and the shallow particles had a large displacement, and the overall performance of the soil was circular arc movement.