In this study, the activity range and distribution patterns of radium and radon isotopes in the coast sea of the Hongyanhe Nuclear Power Plant were investigated in autumn, 2017. The water ages were calculated by "Apparent Radium Age Model", which distribution was then used to assess the major direction of water transport in the study area. We also discussed the relationship between jellyfish abundance distribution and water transport direction. The results indicate that: (1) the activity ranges of ²²⁴Ra, ²²⁶Ra and ²²²Rn were 2.9−62.4 dpm/(100 L), 11.9−57.4 dpm/(100 L), and 0.1−1.3 dpm/L in the study area in autumn, respectively. (2) Based on the “Apparent Radium Age Model”, the so-calculated water ages were ranged from 0 to 16 d, with an average of (10.9±3.6) d. The major water transport direction was towards northeast with the velocity of 7.2 cm/s. (3) There was clear correlation between the distribution of jellyfish abundance and the major water transport direction. The higher jellyfish abundance was found in main water transport direction with older water ages.

Based on the data from the zooplankton survey in the waters around the Ningde nuclear power plant in January (winter), April (spring), July (summer) and November (autumn) 2018, the structure and seasonal changes of jellyfish communities in the area were analyzed. The potential risks of jellyfish to the safe production of nuclear power in Ningde were discussed. The results showed that there were seasonal changes in the species composition, abundance distribution and dominant species succession of jellyfish in the Ningde nuclear power plant area. The numbers of jellyfish species in the spring, summer, autumn and winter were 7, 16, 9 and 3, respectively. The mean abundances were (45.48±8.24) ind./m³, (50.26±12.13) ind./m³, (3.68±1.91) ind./m³, and (0.18±0.07) ind./m³, respectively. The main dominant species were Laodicea indica, Pleurobrachia globosa, Diphyes chamissonis and Euphysa aurata. The seasonal succession of dominant species was obvious. The correlation analysis between the change of jellyfish abundance and environmental factors showed that the abundance of jellyfish in spring and summer was significantly related to the total abundance of zooplankton, and its number was significantly related to the number of copepods in zooplankton in summer（p<0.05, R=0.363). The abundance of jellyfish communities in autumn and winter was mainly affected by salinity. The salinity of the sea area was relatively low in autumn and winter, and the temperature is also low, so the abundance of jellyfish was also low. According to the distribution characteristics of jellyfish in Ningde, the jellyfish abundance of 50 ind./m³ was considered as the risk threshold value, and summer was the potentially high-risk season for ecological disasters. It was necessary to focus on the 5−20 km away from the intake area in summer; followed by the spring, the focus was on the 2.5−5 km away from the intake area; in autumn and winter, the safety of nuclear power sources was basically not caused by jellyfish.

Based on the direct turbulence observations in the Bohai Sea during September 2017, this study investigates the spatial distribution of turbulent mixing in the Bohai Sea and the associated influencing factors. The water column was weakly stratified during the observation period. As influenced by the freshwater input from Yellow River, relatively warm and fresh water was found in the Laizhou Bay. The typical south-north dual-core cold bottom water structure still exited in the central Bohai Sea during the observation period. The observed turbulent kinetic energy (TKE) dissipation rate ε ranged from 10⁻⁹ to 10⁻⁵ W/kg and statistically satisfied the lognormal distribution. Intensified mixing was found at the nearshore region of the Liaodong Bay and the Bohai Bay. The corresponding vertical eddy diffusivity was about 10⁻⁶～10⁻² m²/s. In the vertical direct direction, strong mixing occurred near the sea surface and bottom layers. Further analysis shows that the station-averaged TKE dissipation rate are positively related to the wind speed and barotropic tidal velocity. On the other hand, the dissipation rate and buoyancy frequency N satisfied the power function relationship of $\varepsilon = 2.0 \times {10^{ - 8}} + 3.0 \times {10^{ - 7}}{({N^2}/N_0^2)^{ - 5}}$ indicating that inhibition effect of stratification on turbulent mixing.

As a new type of coastal ecological protection measure, ecological buffer zone formed by woody plants in coastal areas has attracted more and more attention in coastal engineering projects. It is an urgent problem to be solved that how to carry out the research on the protection effect of woody plants. The numerical simulation method is used in this paper. Firstly, a theoretical model of surface wave attenuation for wave climbing along a slope under the protection of woody vegetation is proposed by including the drag forces of branches and trunks in the N-S equation. Next, the MAC method is used to track the trajectories of water particles on the free surface. Then, taking the wave climbing along a slope of 1/30 as an example, the wave propagation process along an inclined beach with or without vegetation is discussed. The validity of the numerical model is verified by comparing the numerical result and those of the previous experiments. Finally, influences of the vegetation characteristics, such as height, density and tilt angle of plant branches and those of wave factors on wave dissipation are discussed and analyzed, respectively. Additionally, the rules of wave dissipation are summarized. The calculation results of this model can also be applicable to the design of revetment structures and ecological landscape.

As tidal waves propagate into the estuary, they are featured by significant longitudinal variation in seasonal scale due to the nonlinear interactions between tide and river discharge. In this study, the variations of tide-river dynamics in terms of tidal damping rate, wave celerity and residual water level slope were explored based on long-term time series of tidal water levels from 2002 to 2014 along the tidal reach of the Changjiang River (including the Tianshenggang, Jiangyin, Zhenjiang, Nanjing, Maanshan and Wuhu stations) in together with the monthly averaged river discharge observed at Datong hydrological stations. Subsequently, the underlying controlled factors that influence the tidal wave propagation were discussed. It was shown that the seasonal difference in tide-river dynamics was gradually reduced in the seaward direction. We identified a transitional zone located between the Tianshenggang and Jiangyin stations, where the seasonal differences in tidal range are 0.01 m and −0.04 m, respectively. Generally, upstream from Jiangyin Station the dynamics character was river-dominated, while in the lower reaches it was mainly controlled by the tidal forcing. In addition, we show that there exists a threshold in river discharge in the upper reaches of the tidal reach of the Changjiang River due to the increase of residual water level and hence water depth caused by the residual water level slope. This phenomenon was particularly true in the upstream reach between Maanshan to Wuhu stations, where the threshold of river discharge was approximately 33 000 m³/s. The results obtained from this study can enhance our understanding of tide-river interaction, and will, hopefully, provide guidelines for water resources management in the tidal reach of the Changjiang River.

Using the ECMWF ORAS4 reconstruction data, the different response characteristics of the South China Sea Sea Level Anomaly (SLA) to the Eastern Pacific (EP) El Niño and the Central Pacific (CP) El Niño were analyzed. The South China Sea SLA showed different spatial and temporal evolution during the two types of El Niño. For the EP El Niño, the average SLA in the South China Sea decreased significantly in the autumn and winter of the developing year, with a minimum of −2 cm, and began to rise in the following year, up to 2 cm in the following winter. In terms of spatial distribution, in the autumn and winter of developing year, except for the existence of a positive anomaly to the southeast of Vietnam, in most of the South China Sea, SLAs are characterized by significant negative anomalies; from the spring of the following year, SLA negatively weakens, while the southeastern part of Vietnam was beginning to develop abnormally until the majority of the South China Sea is dominated by positive anomalies. For the CP El Niño, the South China Sea SLA showed significant negative anomalies throughout the El Niño development and decline, the outliers were always maintained at around −2 cm, and spatially represented as a consistent negative anomaly of the whole basin. Compared with the traditional empirical orthogonal decomposition (EOF), the seasonal EOF (S-EOF) can better characterize the temporal and spatial evolution of the South China Sea SLA during the two types of El Niño. The first mode of the S-EOF is CP El Niño mode, while the second mode is more characterized by the evolution of the South China Sea SLA during the EP El Niño. The different variations of the South China Sea SLA during the two types of El Niño are mainly due to the thermal specific volume effect caused by the thermal advection transport anomaly at the channel, but the contribution of the thermosteric sea level is mainly concentrated in the interior South China Sea. While in the coastal regions, such as the western South China Sea, the mechanism of sea level change needs further study.

Salinity linear trends and their contributed dynamics processes in the tropical Pacific Ocean were investigated with the Argo salinity and temperature fields, current assimilations and atmospheric reanalysis datasets. The robust salinity anomaly event (SAE) occurred in the tropical Pacific Ocean during 2015−2017, which resulted possibly in the reversing of Argo salinity long-term trends. Such SAE was characterized as distinct regional discrepancies and vertical structures. Significant surface freshening occurred in the northern tropical Pacific (NTP) and Southern Ocean Convergence Zone (SPCZ), whose remarkable freshening maximum could reach 0.71−0.92 and covered the upper mixed layer. Another subsurface salinification in the southern tropical Pacific (STP) with the maximum of 0.46 was found around thermocline layer. Moreover, the salinity anomalies in SAE can expand from west to east along the isopycnal layers. Salinity advection and entrainment were exhibited as the fundamental dynamic processes to the SAE event in the tropical Pacific Ocean, while advection term acted as the major contribution to salinity variability. Both of the dynamic factors played important role on SAE features during the whole event in the NTP and later period in the SPCZ and STP. The surface freshwater flux and subsurface mixing induce by density compensation were also supplements to the SAE events in the NTP freshening and STP salinification respectively.

To recognize the environmental effects on underwater acoustic localization in deep sea and improve the measurement system performance against environmental variations, an simulation method for localization performance evaluation under different oceanographic conditions was presented, in which the sound filed calculation, error propagation and crossing solution were integrated by modelling, and the effects of seasonal environmental variation on localization performance were discussed in the case of Western Pacific. According to simulation results, when the receiving depth was near the surface, the sound channel showed different models in summer and winter, such that the accuracy was worse in summer influnced by seasonal thermocline and better in winter influnced by surface duct, the difference of root mean square error (RMSE) beyond 50 m; when the receiving depth was in the upper ocean, the localization performance had an obviously seasonal change caused by the active range of direct wave, and the accuracy was better in winter than that in summer, the difference of RMSE was 15−20 m; when the receiving depth was near the bottom, the better accuracy was obtained using reliable acoustic path, and the localization performance had little change with season. This work indicates that the seasonal environmental variation induces differences in the sound channel as well as the arrival acoustic information, the error propagation and crossing solution for the localization in the half convergence zone area of deep sea, then exert significant effects on localization performance as the receiving depth in the upper ocean.

Sub-bottom profile is based on the acoustic signal (frequency in hundreds to thousands Hz) in the sediment propagation to reflect the sedimentary formation structure. The seabed reflection coefficient is closely related to the sediments physical properties. The Biot-Stoll theoretical model can predict the physical properties of seabed sediments and establish the relationship between acoustic parameters such as reflection coefficient and physical parameters, but the results obtained by using different parameters in different sea areas are different. For this, this article is based on the measured sediments physical parameters in the northern slope of the South China Sea to establish the relationship between the reflection coefficient and the sediments physical parameters based on Biot-Stoll model. The results show that the calculated value of the model is in good agreement with the measured value of the sample, and the equation for the relationship between the bottom reflection coefficient and the porosity, density, mean grain size of sediments at a frequency of 3.5 kHz is established. The equation has a high fitting degree, and the determination coefficient R² is all greater than 0.99. On the basis of calculating the seabed reflection coefficient by the typical Chirp profile data, the porosity, density and mean grain size of the sub-bottom sediments are inversed. The relative errors of the inversion porosity, density, mean grain size and the measured porosity, density, mean grain size are all less than 5%, and the results are basically consistent with the measured values, indicating that the inversion method is feasible in the northern continental slope area of the South China Sea.

The horizontal suspended and bed-load sediment transport in the bottom boundary layer were computed by applying a one-dimensional parameterized scheme to the in-situ data obtained from two stations in the Bohai Strait during a winter field investigation in 2018. In the parameterized scheme, a simplified one-dimensional advection-diffusion equation was used to calculate the vertical suspended sediment concentration in the bottom boundary layer. Aiming at verifying the reliability of the parameterization scheme, two models of bed shear stress calculation, four critical bed-shear stress methods and two advection-diffusion solutions were compared based on the observations. It showed that: (1) bed shear stress calculated by different models are fairly consistent; (2) the critical bed-shear stress is affected by sediment cohesive effects; (3) stratification effect of sediment concentration and the difference of critical bed-shear stress with different particle size fractions need to be considered solving the one-dimensional advection-diffusion equation. Based on the optimal parameterization obtained from the comparisons, sediment transport of the two stations was further calculated: (1) during resuspension events, the ratio of the horizontal suspended sediment flux within 5 meters above bottom accounting for the suspended sediment flux throughout the entire water column which is about 21% in T01 and 17% in T02 is significantly higher than the ratio of the water flux within the same layers; (2) the mean suspended sediment flux estimated by the parameterization scheme in winter is about 16% higher than the result estimated from the conventional method which ignores the vertical variation of suspended sediment concentration in the bottom boundary layer; (3) bed-load transport is generally 2 orders of magnitude smaller than the suspended load transport.