Based on National Oceanic and Atmospheric Administration daily optimum interpolation sea surface temperature (SST) data set from 1982 to 2019, spatial-temporal changes in marine heat wave (MHW) (frequency, duration, intensity) in the Bohai Sea and Yellow Sea and associated circulations were analyzed using various statistical methods. Results show that: (1) there are obvious regional differences in MHW. More frequency, longer duration, more intensity MHWs are all located at the most part of the Bohai Sea and northern Yellow Sea. (2) In recent 38 years, the annual frequency, annual average duration, annual average intensity and maximum intensity of the marine heat waves in the Bohai Sea and Yellow Sea have generally increased and strengthened, together with spatial heterogeneity. The trends at the coast of the Korean Peninsula coastal show insignificant trend. (3) MHWs were classified into four levels by daily SST: moderate, strong, severe and extreme. Result shows that except extreme MHWs, there are significant geographic differences in the frequency and trend of the other three MHW levels. Moderate MHWs are more frequent and have a significant increasing trend in most part of the Bohai Sea and Yellow Sea, while strong and severe marine heat waves are mainly concentrated in the Bohai Sea. However, extreme MHW in this region was hardly occurred. (4) Regional, there were 83 MHWs occurred in the Bohai Sea and Yellow Sea during 1982 to 2019, with an average of 2.2 times per year. The frequencies of MHWs appeared seasonal variation obviously. More MHWs with different levels of intensity occurred in summer. (5) Composite analysis shows that, summer MHWs in the Bohai Sea and Yellow Sea have significant relationship with atmospheric circulation. Barotropic positive geopotential height anomalies centered on Lake Baikal were favorable for anomalous descending air motion in the lower troposphere and west-northerly winds in high troposphere, there should be more clear days and hence more MHWs during the high-solar-radiation summer period.

The global climate and environment have changed significantly upon the development of the Northern Hemisphere glaciation (NHG) during the Pliocene/Pleistocene. The Pacific meridional overturning circulation (PMOC) plays an important role on the distribution of heat in the global ocean and atmospheric CO₂ sequestration in the deep ocean, however, the relationship between PMOC and the formation of NHG is poorly studied. In this paper, we collected the available Nd isotope data of seamount Fe-Mn crusts from the Pacific. By comparing the Nd isotopic records from different water depths and different regions of the Pacific, considering the influences of water mass evolution and dust input on the Nd isotope records, we discuss the evolution of the PMOC and its relationship with the global climate change. It is suggested that the stagnation of the deep water formation in the North Pacific and the increase of the Asian dust input may be the reasons for the decline of the εNd of the North Pacific deep water since 3～4 Ma, and the increase of CO₂ sequestration in the deep ocean caused by the weakening of the deep water ventilation in the North Pacific contribute to the global cooling and the formation of NHG.

The information on sediment flux (Q_s) from continental shelf islands is an important supplement to the study of accurate records interpretation of continental shelf sedimentary systems. Aiming at the scientific problem of how to estimate the Q_s of continental islands, this paper proposes a solution to calculate their Q_s based upon the empirical formula of small and medium-sized rivers in adjacent continent, taking the 8227 continental islands in Southeast China as examples. Two preconditions are set up to perform the calculation. That is, the Q_s rule of the continental islands follows the rule of the small and medium-sized rivers in adjacent continent, and a continental island can be treated as a river basin to calculate its Q_s. The results show that: (1) the Q_s calculated by empirical formula is the minimum estimated value; if the actual basins of the continental island are taking into considered, the Q_s value will slightly increase, but the increase will not exceed n^0.13 (n is the number of basins); (2) the empirical formula give the approximate magnitude information of Q_s for continent islands; the total area of the continental islands is 4418.49 km², and the corresponding order of magnitude of Q_s is 10⁶ t/a; (3) during the completion of the estuarine filling stage, the continental island sediment is one of the main source for the inner continental shelf areas. Therefore, more attentions and researches are expected to the role play by the continental shelf islands to the formation and evolution of continental shelf depositional systems.

Based on the 141 surface sediments collected from the Yazhou Bay, Hainan Island, the distribution characteristics of grain size components, grain size parameters and sediment types were analyzed. The results indicate that the samples can be classified into 6 types as argillaceous arenaceous gravel, gravelly argillaceous sand, sand, silty sand, arenaceous silt and silt in the study area. In particular, the arenaceous silt is most widely distributed. The grain size diameters increase and then decrease, showing a banding distribution from north to south. The separation coefficient is generally high, which indicates the complex sediment sources and hydrodynamic conditions in this area. Base on Flemming ternary diagram, combined with sediment sources, hydrodynamic conditions and topographic features, the study area is divided into three sedimentary districts from north to south: the nearshore zone which showing the characteristics of wave-controlled deposition is mostly impacted by wave winnowing and transport, and the grain size is relatively small; the central Yazhou Bay zone is a high-energy coarse grained sand area, mainly controlled by the combined action of runoff, wave and tidal current; relatively, the southern zone is mainly affected by tidal current load, where the wave action is weakened, the sediment is the finest and deposited in a lower energy environment. In addition, the analysis of sediment transport trend shows that the midwest part of the study area is a depositional center, the silt of coastal erosion, Ningyuan River and offshore tidal current transport are carried to this area.

The vertical distribution of rip current formed by the cross wave field near a groin is studied through the physical model experiment with regular and irregular waves and the characteristics of the distribution for transverse, longitudinal velocities and velocity vector at each measurement section are examined. The measurement is along the center line of the depth-average velocity profile in the rip channel. The influence of the position of the node and antinode point relative to the channel centerline is considered. The results of time-average and time-dependent values of rip curent velocity are analysed, and it is found that the longitudinal velocity has stable mean values for different lengths of time spans considered, but this is not the case for the transverse velocity. Due to the effect of rip current instablity, the latter has different mean values for different lengths time spans. This leads to different three-dimensional distribution characteristics of velocity vector over different time spans. However, there are some common points among the results of the different time spans, this includes, most of the velocity vectors at measurement sections deflect towards the groin, which reflects the influence of the groin; the vertical distribution of longitudinal velocity at different measurement sections all follow the power law.

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 characteristics of the maximum shear force in the boundary layer were studied based on the wave attenuation experiment of nearshore plants considering the influence of roots. The maximum shear force characteristics of the boundary layer under two plant models, root alone and combination of roots and stems, were investigated by using the formula of boundary layer velocity calculation with plant water flow under regular waves proposed by predecessors. The shear force variation along the path and the effect of plants on the shear force attenuation characteristics of the two models were analyzed, and the formulas of the attenuation coefficients were fitted. Studies have shown that when waves pass through the plant zone, the shear force increases to a certain extent and then decreases gradually. The reduction effect of plant on shear force increases with the increase of incident wave height, and the stem contributes to the reduction effect of root group on the maximum shear force of boundary layer, and the reduction coefficient ranges from 0.06 to 0.61. The fitted formula is more suitable for shallow water.

The effects of three kinds of modulation (the tilt modulation, the hydrodynamic modulation and the velocity bunching modulation) on sea wave SAR (synthetic aperture radar) image are compared and analyzed firstly. The results show that the velocity bunching modulation has the most significant effect on SAR images. In addition, due to the inherent speckle noise in the SAR image, it is difficult to filter or suppress the noise in the range of low wavenumber. And the inversion of wave spectrum by classical MPI (max-planck institute) method will result in the larger spectral value in the range of low wavenumber. Referring to the classical MPI inversion algorithm, an azimuth slope spectrum and SWH (significant wave height) inversion algorithm based on the velocity bunching modulation are proposed in this paper. Comparing the SWH obtained by the classical MPI method, the co-polarization modulation method and the algorithm proposed in this paper with the buoy data, one can find that the mean square error between the SWH retrieved by the algorithm proposed in this paper and the SWH obtained from buoy data is 0.79 m, which is the smallest among the three methods.

When performing work, underwater platforms usually need about 1-month to 3-months ocean numerical forecasts results. However, the current numerical forecasting technology is limited to the corresponding weather-driven field forecasting, and it is difficult to provide numerical forecast products for more than 10 days. Considering that the seawater itself has large inertia physically, and the inner ocean area has its own evolutionary principles, a statistical prediction method based on evolutionary operator is proposed. The method uses historical satellite remote sensing data to construct a long-term evolution matrix of ocean state variables, and then combines with the inertial prediction model. The final medium- and long-term statistical prediction model of the South China Sea is constructed, which can provide the prediction results for 1 d to 60 d of daily sea surface height anomaly in the South China Sea. We carry out the numerical experiments to show the effectiveness of the method. The results show that the correlation coefficients between the forecast results and the satellite data are all higher than 0.8 within 15 days and higher than 0.6 within 60 days after the start date of forecast.

The waterline method is an important method for remote sensing inversion of intertidal terrain. Aiming at the problems in the digital elevation model (DEM) construction with variable topography, which the waterlines intersect and lack of representation of micro-topography for the tidal creek in the conventional waterline method, an enhanced terrain remote sensing construction method was proposed in this paper. First, the waterlines with the correct trend of elevation change and spatial separation were selected through tidal level sorting. Second, the images group with similar waterlines position in the screening process were combined according to the mean of a sequence of the modified normalized difference water index values in each pixel, and the boundary line of land-sea was obtained. These two methods worked together to construct the initial intertidal DEM. Then, the tidal creek DEM was generated by using the boundary and centerline of the tidal creek in the low tide period. Through the mosaic processing, the tidal flat DEM that can express the undulating micro-topography of the beach surface was constructed. Comparing with the measured terrain, the results in the central core area of the radial sand ridges off the coast of Jiangsu showed that the mean absolute error of the 4 measured sections was 0.43 m, the root mean square error was 0.54 m, and the average correlation (r) was 0.75. The simulation results and the measured results were in good agreement with the changes in beach undulations. Furthermore, the spatial fragmentation of the simulated DEM was small and can reflect more detailed terrain features. This method can provide a new idea for constructing high-precision DEM of intertidal zone considering micro terrain changes by using multi-source remote sensing data.