The full-length cDNA of glutathione S-transferase (Sc-GSTσ) and heat shock protein 90 (Sc-HSP90) genes were cloned from Sinonovacula constricta and their expression characteristics under ammonia nitrogen stress were analyzed. The results show that the full-length cDNA of Sc-GSTσ was 1 414 bp, and containing 639 bp open reading frame (ORF), encoding 212 amino acid polypeptides. The homology of amino acid sequence of Sc-GSTσ with other species’ GST amino acid sequence was 31.88%−43.40%. The full-length cDNA of Sc-HSP90 was 2 752 bp, ORF was 2 181 bp, encoding 726 amino acids. The amino acid sequence was 76.77%−87.05% homology with other species. Quantitative analysis showed that Sc-GSTσ and Sc-HSP90 genes were expressed in all tested tissues, the strongest expression being in the digestive gland. After exposure to ammonia, the mRNA expression of Sc-GSTσ and Sc-HSP90 were significantly up-regulated (p<0.05) in the digestive gland, indicating that ammonia stress induced stress response, both GST and HSP90 may be participate the process of detoxification or defense. However, the decrease of expression in the later period of stress is presumed to be due to the organism have limited ability to defense, which is not enough to protect the host from stress-induced cell damage.

This study investigated the oxidative stress and energy utilization responses of juvenile cobia (Rachycentron canadum) to environmental hypoxia stress, and provided reference for the healthy cultivation of cobia. Through the hypoxia stress-reoxygenation test, the oxidative stress and energy utilization indexes of liver and muscle tissues were measured after hypoxia ((2.64±0.25)mg/L) stress for 3 h and reoxygenation ((6.34±0.15)mg/L) stress for 8 h, 24 h and 48 h. The results showed that after hypoxia stress, the activity of malondialdehyde (MDA), catalase (CAT) and glutathione reductase (GR) in the liver were significantly lower than that in the control group (p<0.05), and the activity of lactate dehydrogenase (LDH) was significantly higher than that in the control group (p<0.05). MDA and lipid peroxidase (LPO) activities in muscle were significantly lower than those in control group (p<0.05), and superoxide dismutase (SOD) and LDH activities were significantly higher than those in control group (p<0.05). The contents of muscle glycogen and liver glycogen were significantly lower than those of control group (p<0.01). During reoxygenation, the contents of MDA, LPO, SOD, CAT, glutathione peroxidase (GPx) and GR in liver and muscle all increased differentially. Liver glycogen content was significantly higher than that of the control group 24 h after reoxygenation (p<0.05), and significantly lower than that of the control group 48 h after reoxygenation (p<0.05). Muscle glycogen content was significantly lower than that of control group after reoxygenation for 8 h, 24 h and 48 h (p<0.05). In conclusion, hypoxia stress can cause some oxidative damage to the body of cobia, and the enzyme activity and energy supply of liver and muscle tissues change. The reoxygenation environment after hypoxia stress causes more severe oxidative damage to the body, which can be gradually restored to the normal level through physiological regulation.

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.

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.

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.

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.

Jason-3 satellite was successfully launched on January 17, 2016, and was put on its nominal orbit on February 12, 2016. Jason-3 was flying in formation with Jason-2 only 1 minute 20 seconds, and was about 560 km from Jason-2. Jason-2 was moved to its new interleaved orbit on September 1, 2016. Two orbits were parallel to increase the spatial coverage of satellite observations. The objectives of this paper are to assess Jason-3 data quality and to estimate the altimetry system performance includes validation of Jason-3 data availability and data quality monitoring of Jason-3 and radiometer parameters. The objectives focused on comprehensive comparison of the parameters of the Jason-2 and Jason-3, accurately evaluated the consistency of the two altimeter parameters using the opportunity that the missions were on the same ground track during the formation flight phase, analyzed the ability and stability of the Jason-3 from the perspective of global data, verified Jason-3 data accuracy by self-crossover analysis and dual crossover analysis with Jason-2. From the results presented here, it is demonstrated that the Jason-3 mission fulfils the requirements of high precision altimetry. It allows continuing the observation of the sea surface height variations at the same or higher accuracy as Jason-1, Jason-2 and T/P. In addition, significant wave height quality of Jason-3 data is significantly better than the Jason-2.

Resuspension and its distribution of sediment depend upon three interacting components namely the characteristics of the mobile sediment, the bed forms and the forcing hydrodynamics. A good understanding of the process of sediment resuspension is important in sediment transport. In this paper, in-situ measurements of wave, current, and suspended sediment concentration profiles in the marine ranching of Xiangyun Bay were carried out. The vertical distribution characteristics of suspended sediment in the bottom boundary layer under the wave-current action were analyzed. The results show that the resuspension of seabed sediments in the study area is controlled by storm-waves. The bottom shear stress under storm wave is 10−15 times of the critical shear stress of sediment, resuspension of sediment lags behind storm-wave for 2−3 hours. The type of vertical distribution of suspended sediment is "I" under small wave load, the vertical distribution of suspended sediment in the bottom boundary layer presents a power exponential function, which is "L" type under storm-wave. Bedforms evolved with wave and current action, and which affected the resuspension process of sediments. ${u_{*w}}{\rm{/}}{u_{*c}} = 1.00$ can be used as a criterion to distinguish the bedfroms under the dominant control of wave or current. The value of ${u_{*w}}{\rm{/}}{u_{*c}}$ under wave load is higher than that under the dominant control of wave, and the cutoff value between them increased with the increase of wave load.

Due to the influence of runoff and estuarine morphology, asymmetrical phenomena of hydrodynamics, suspended sediment concentration (SSC) and salinity occurs between the flooding and ebbing stage in the estuary. Such a phenomena also shows significant regional and seasonal differences. Based on hydrological survey in July 2013 and January 2014 in the Changjiang River Estuary, it is found that suspended sediment concentration in the branched channels of the Changjiang River Estuary has asymmetric characteristics, which varies with flood and dry season as well as spring and neap tide. In terms of spatial variability, there exists along channel difference, inter-channel difference as well as water colume difference. The evolution of the estuary controlls the overall SSC difference between the North Branch and South Branch. The flood and dry seasons affect the redistribution process of SSC in the estuary. Spring tides has a stronger impact on SSC asymmetry than that of neap tides. Theseasonal wave condition affect the SSC asymmetric distribution in the turbidity maximum zone of the estuary along the north-south direction. The high sediment concentration near the bottom contributes significantly to the SSC asymmetry between flooding and ebbing stages at the river mouth.