Volume articles

The Pacific Ocean is the main region occurring the interannual and interdecadal variabilities of sea surface temperature. Comparing to the sea surface temperature, the variabilities of ocean heat content in the Pacific Ocean were less studied. Therefore, this paper studied the variabilities of ocean heat content (at depth of 0300 m) in the Pacific Ocean during the period from 1980 to 2020. The Ensemble Empirical Mode Decomposition method (EEMD) was applied to the Institute of Atmospheric Physics (IAP) heat content data to extract the signals at different time scales, and then the Empirical Orthogonal Function (EOF) was applied to analyze the temporal and spatial characteristics of the ocean heat content at different time scales. The results showed that besides the interannual variation, there were also evident interdecadal variations and longterm warming trends of heat content at depth of 0~300 m in the tropical northwest Pacific. In the eastern Pacific and the highlatitude western Pacific, the interdecadal variability of heat content was not prominent. In the tropical northwest Pacific, the heat content was higher during 19801988 and 19992013 than those during 19891998 and 20142020. Our analysis showed that the interdecadal variability was mostly occurred at 5°N—20°N, 120°E—180°E, and at depth of 50200 m in the tropical northwestern Pacific. The interdecadal variation of ocean heat content in the tropical northwestern Pacific played an important role in the interdecadal variation of global sea surface temperature.

There is strong tide in the Changjiang (Yangtze River) Estuary and its adjacent area. Except for the coast area, there is a lack of longterm tide level and tidal current data in the offshore area. Long time series of water level observation data was used in this study, and the results reveal that the tidal type in the Changjiang Estuary is a regular semidiurnal tide, with a significant shallow water division in the nearshore area; the M2 division is the most significant semidiurnal tide, and the amplitude tends to increase from the open sea in the east to the shallow water or island group at the mouth of Hangzhou Bay in the west. The M2 tidal current is the most significant semidiurnal tidal current, and the rotating tide is the most significant semidiurnal tide. The two stations to the south of the Changjiang mouth are rotating counterclockwise, while the stations to the east of the mouth are rotating clockwise. The vertical structure of the tide has significant spatial differences, the ellipticity of the M2 tidal current is mostly negative, the ellipticity of the M2 tidal current, the direction and the arrival time of maximum velocity all vary significantly with depth.

As a key parameter in hydrodynamic and sediment transport models, bottom shear stress is very important to study the initiation and erosion rates of bottom sediment. At present, there are six theoretical methods for calculating bottom shear stress based on field measured flow velocity data: LPmean method, LPmax method, TKE method, TKEW method, RS method and ID method, all of which have their specific applicable conditions. It is very important to select an appropriate method to calculate the bottom shear stress in the shallow water area of estuarine and coastal areas where the actions of current and wave are complex. In this study, one observation site at Dafeng Doulong Port, Jiangsu Province (median particle size: 68.56 μm) and two observation sites at Eastern Chongming Shoal, Shanghai (median particle size: 12.89 μm and 45.02 μm) were taken as examples. Field data were collected using Acoustic Doppler Velocimetry and wave measurement instrument (RBRwave), and the bottom shear stress was calculated by six theoretical methods. The results show that: (1) The LPmean method is affected by the average velocity, the distance from the probe to bed and the strength of waves, which underestimates the bottom shear stress and is not suitable for shallow water environment in intertidal flat; (2) LPmax method and TKE method can overestimate shear stress in shallow water environment of intertidal flat where flow velocity varies greatly and wave action is obvious; (3) TKEW method was modified on the basis of TKE method, which is more suitable for solving the bottom shear stress under strong wave action; (4) The results of RS method are affected by waves, and the results of ID method are more reliable than those of RS method when large waves exist, but ID method will overestimate the bottom shear stress when water depth is insufficient.

In this study, Particle Image Velocimetry (PIV) and Wave Gauge (WG) were used to measure the wave height, wave velocity and other hydrodynamic parameters within inner surf and swash zones under three slopes. Based on the second-order spectrum method, the probability density distribution of wave height and velocity between different sections, as well as high-order nonlinear statistical variables such as skewness, asymmetry and kurtosis were analyzed. The results show that the wave height and velocity deviate from the normal distribution, the skewness and kurtosis of wave height decrease first and then increase during the nearshore propagation, the asymmetry increase first and then decrease, and the nonlinear characteristics of wave height are not affected by the slope. The velocity in the three cases shows different nonlinear distribution characteristics. In the steep slope and composite slope, section distribution of velocity skewness characteristics are not obvious. Only the vertical distribution of velocity skewness at each section of gentle slope increases first and then decreases. The velocity asymmetry of the three cases increases first and then decreases with the increase of the distance from the bed.

As an ecological buffer zone, the salt marsh plants growing in the coastal zone play an important role in reducing the current velocity, weakening wave energy and preventing coastal erosion, it is of great significance to investigate the mechanism of wave attenuation by salt marsh plants in estuaries and coastal zones. Based on the open source CFD software package of OpenFOAM software, a 3D numerical model considering the effect of vegetation on flow and wave was established in this study. Firstly, the model was applied to investigate the propagation processes of dambreak wave over the triangle obstacle and the solitary wave climbing on the sloping beach, the results show that the OpenFOAM model can accurately capture the propagation of dambreak waves and free water movement of solitary waves. Then this model was also used to simulate the formation, development and attenuation of solitary waves in a vegetated wave flume, where the wave height of solitary waves decreases obviously through the vegetation zone, the vegetation can effectively attenuate wave energy on a coastal beach. Lastly, the propagation process of sine waves on the vegetated beach was numerically studied, the obtained numerical results show that the attenuation of wave height is directly proportional to the incident wave height, plant density, the drag force coefficient of plant and the steepness of the coast.

Orbital data are important parameters involved in the satellite data processing and HY1C satellite products with high quality are inseparable from the accurate calculation of the orbit. In this study, data were extracted from the TLE (TwoLine Orbital Element) and used to accurately simulate satellite orbit based on STK (Satellite Tool Kit) software. The ephemeris was outputted to compare the accuracy of two satellite orbit algorithms of HY1C and evaluate the influence of perturbation factors on orbit calculation. Method one uses an algorithm which does not consider perturbation factors and extrapolates the ephemeris parameters of the observation time based on the orbit elements of the reference time, and then calculates the satellite orbit data. Method two adopts the SGP4 model which considers perturbation to calculate the orbit data. The results show that perturbation has a significant impact on the orbit calculation. The algorithm error without considering the perturbation increases significantly with the passage of time, and the position errors are less than 10 km with the speed errors less than 10 m/s in half an hour. While SGP4 model algorithm runs fast with high calculation accuracy and good stability, the position and speed errors within 24 hours are less than 68 m and 0.051 m/s respectively. Therefore, SGP4 model algorithm can be used for the highprecision orbit calculation of the loworbit satellite HY1C.

 Suspended sediment concentration (SSC) is one of the important water quality parameters in estuarine water research. Remote sensing determination of SSC is an important method. In order to study the quantitative gradient relationship between remote sensing spectral data and surface suspended sediment concentration(SSSC), the surface sediments near the Nanhuizui of the Changjiang (Yangtze River) Estuary were collected, the gradient changes of SSSC were designed quantitatively, and the optical characteristics of sediment laden water with different concentrations were measured by ASD hyperspectral spectrometer. The results show that with the increase of SSSC, the spectral reflectance curve of water has similar morphology, but there are also some differences. When SSSC<36.59 mg/L, the spectral curve has only one reflection peak at 560-580 nm. When SSSC>52.69 mg/L, the first reflection peak of the spectral curve is at 570-710 nm, and the second reflection peak appears at 780-820 nm in the near infrared band. There is an obvious “red shift” phenomenon in the first peak interval of the spectral curve, and the linear fitting R2 between the “red shift” change of wavelength and SSSC reaches 0.91, indicating a strong linear correlation between them. In the spectral range of 400~900 nm, 600-860 nm band is sensitive and stable to the change of SSSC in the range of 0~200 mg/L, and 740900 nm band has stronger response to the change of SSSC>200 mg/L.

Aiming at the problem of low inversion accuracy and time resolution in single-system GNSS-MR tide level monitoring, a multi-system fusion tide level inversion method based on LS-SVM was proposed. Using GPS, BDS, Galileo and GLONASS satellite data from Hong Kong's HKQT station for 30 consecutive days, experiments were conducted to compare three multi-system fusion methods based on sliding window least square, SVR, and LS-SVM. The results show that compared with the BDS system with the smallest RMSE for single-system GNSS-MR tide level inversion, the RMSE value of multi-system fusion tide level inversion based on LS-SVM reduced by 55.8% and the correlation coefficient increased by 4.1%. Compared with the GLONASS system with the highest time resolution, the time resolution increased by 59.3%; Compared with the multi-system fusion tide level inversion based on the SVR model, the RMSE value reduced by 52.3%, and the correlation coefficient increased by 2.2%; Compared with the multi-system fusion tide level inversion of the sliding window least square method, the RMSE value reduced by 41.1%, and the correlation coefficient is increased by 1.2%. Multi-system fusion tide level inversion based on LS-SVM has better tide level inversion performance than that of sliding window least square method and SVR algorithm.

Optical dissolved oxygen sensor based on fluorescence quenching principle can obtain spatiotemporal data of dissolved oxygen in seawater, which is widely used in long-term monitoring of marine environment. However, due to the “storage drift” and “measurement drift” occurring during storage and distribution, it is necessary to calibrate and correct the data drift of the instrument. Existing calibration methods have long cycle and complex operation. In this project, the response characteristics of optical dissolved oxygen sensor in air and water medium were studied, and a field calibration method of optical dissolved oxygen sensor using air medium was proposed, and a two-point calibration model of the instrument was established. Experimental results show that the calibration method can effectively correct the data drift of the dissolved oxygen sensor, and the deviation between the measured value of the sensor and the standard value of Winkler titration is within  ±6 μmol·L-1. This method can realize the convenient and rapid correction of optical dissolved oxygen sensor, avoid the tedious steps of laboratory maintenance, improve the quality of monitoring data, maintain the continuity of monitoring data, and has important application value.

A bibliometric method was employed to evaluate the global scientific production of tidal bore research and seek the characteristics of publication outputs including countries, institutions, authors, journals and keywords from papers related to tidal bore. The basic data were obtained from CNKI and Web of Science core collection database. The 652 papers published by 632 authors from 433 research institutions in 239 publications were retrieved from CNKI. “Qiantang River Estuary” and “North branch of the Yangtze River Mouth” were areas of high concern in China. “tidal bore pattern”, “river bed evolution”, “tidal bore pressure” and “tidal bore height” were hot keywords in the researchs. “numerical modelling” and “physical modelling” had become important means of tidal bore research. A total of 277 articles published in 143 journals by 447 authors from 224 institutions in 34 countries were retrieved by Web of Science. The literatures payed high attention to Qiantang River in China, Seine and Garonne River in France, Amazon River in Brazil and other estuaries. “turbulence”, “sediment transport”, “hydraulic jump”, “wave”, and “environmental impact” were hot issues on tidal bore, and “physical modelling”, “field measurements” and “numerical modelling” had become important means of research on tidal bore. Although the number of research papers published at home and abroad fluctuated in different years, it showed a rapid growth trend and rich research results. Due to the limitation of specific estuarine area, the research institutions were relatively concentrated and the total amounts of papers published were not much. This study objectively analyzed the current status of tidal bore research at home and abroad to provide data reference for researchers and decision makers.

Based on the Acoustic Doppler Current Profiler (ADCP) data of buoy and mooring during Typhoon Kalmaegi (1415) in the northern South China Sea, a set of algorithms were proposed to calculate the spatial variation, data bias and correction. On buoys, the maximum horizontal displacement of ADCP can reach 2.61 km, the maximum horizontal velocity bias can reach 0.27 m/s, but the maximum vertical velocity bias is only 5×10-4 m/s after the typhoon. The velocity in thermocline of horizontal correction after typhoon is prominently larger than the observed velocity, indicating the horizontal correction is necessary for the quality control of the thermocline velocity. On moorings, the maximum displacement increments on the mooring are closed to 179 m, the maximum rope tilt angle can reach 35°, the maximum horizontal displacement of ADCP can reach 1.5 km. The horizontal velocity bias and tilt bias of ADCP are small to be ignored,the vertical correction can not be ignored for velocity of middle layer after typhoon.

The foot of the continental slope is an important topographical feature of the continental margin. Its the basis for coastal states to extend its continental shelf rights and to delimit the outer limit of the continental shelf beyond 200 nautical miles. Its also an important technical parameter that the Commission on the Limits of the Continental Shelf pays special attention to when considering the submissions of coastal states. The formulation of the continental shelf regime in Article 76 of the United Nations Convention on the Law of the Sea originates from the typical passive continental margin. However, due to the diversity and complexity of the global continental margin, especially the transformation and influence of late tectonic activities and sedimentation on the continental margin, the seabed topography is extremely complex and changeable, which makes it very difficult to identify the foot of the continental slope. In addition, in order to obtain the largest extent of the outer continental shelf, each coastal state has interpreted the relevant provisions of the foot of the continental slope in their own favor, making the foot of the continental slope a hot and controversial issue in the delimitation of the outer continental shelf. Based on the provisions of the United Nations Convention on the Law of the Sea and the "Scientific and Technical Guidelines of the Commission on the Limits of the Continental Shelf" on the foot of the continental slope, combined with the geological characteristics of different types of continental margins and the delimitation practice of various coastal states, the determination of the base of the continental slope, the selection of the point of greatest change and the application of the evidence to the contrary are discussed.

Sea surface temperature (SST) is the critical factor for depicting the marine thermal distribution. Daily global SST data sets support the typhoon elaborated monitoring and other marine disasters forecast. SST products retrieved by the visible infrared radiometers and mediumresolution imagers have high spatial resolution, while the SST products retrieved by infrared remote sensing are affected by clouds, fog and haze, and therefore a large areas under the clouds are lack of value. SST products retrieved by the microwave radiometer have low spatial resolution, while the microwave could penetrate the cloud layer to achieve all-weather sea surface observation. The data interpolation empirical orthogonal function method (DINEOF) was used to reconstructed the global SST products, and FY-3 (Fengyun 3) SST data sets were applied in this study, which included the SST data sets from the FY-3B/FY-3C Visible and Infra-Red Radiometer, FY-3D Medium Resolution Spectral Imager and FY-3D Micro-Wave Radiation Imager. Accuracy of the reconstructed data sets was verified using OISST measurements to demonstrate the validity and reliability of the DINEOF method. The results show that DINEOF reconstructed sea surface temperature (DSST) data are validated reliable. Root mean square error of the original data is ranging from 0.59 ℃ to 0.70 ℃, while the reconstructed data is relatively stable, ranging from 0.10 ℃ to 0.34 ℃. Correlation coefficient obvious raises from 0.33-0.48 to 0.78-0.98. Multi-sensors reconstructed SST products is continuous and credible in spatial distribution and monitor the variation of warm pool from spring to winter. Addition of FY-3D microwave SST products has significantly improved the spatial continuous distribution and temporal resolution of reconstructed SST.

Based on the sea surface wind data at 10 m during 1979 to 2018 from European Center for MediumRange Weather Forecasts (ECMWF), the Growing Hierarchical Self-Organizing Map (GHSOM) method were used to analyze the seasonal variation and interannual anomaly variation characteristics of near-surface wind field over the South China Sea (SCS). Four feature patterns are extracted in the first-layer GHSOM from original wind field data, which highly summarize the seasonal variation characteristics, and the second-layer results reveal the monthly variation characteristics. Four anomaly feature patterns also are extracted in the first-layer GHSOM network and they are anticyclonic wind anomaly, cyclonic wind anomaly, southwest wind anomaly and northeast wind anomaly patterns, respectively. Anticyclonic and cyclonic wind anomaly patterns are closely related to ENSO events with time lags by three months and five months comparing with Niño3.4 index. Anticyclonic and cyclonic wind anomalies also show asymmetry, that is, the amplitude of anticyclonic wind anomaly is obviously larger than that of cyclonic wind anomaly. The occurrence frequency of the northeast wind anomaly pattern is greater than that of the southwest wind anomaly pattern. The more SOM patterns in the second layer expose particulars of anomaly wind.

The seafloor is characterised by active sand bodies of different scales, and  a large number of small-scale sand waves (ripples) is often superimposed on the large active sand bodies. The analysis of the small-scale sand waves (ripples) can reveal the genetic mechanism of these active sand bodies. However, their scales are small, and conventional analysis methods often filter them out as high-frequency noise, making it difficult to separate and quantify sand waves on the seafloor at this scale. To address this problem, a method was designed and implemented for decomposing small-scale submarine sand wave topography based on wavelet analysis, and achieved the decomposition and quantitative analysis of small-scale submarine sand wave topography: background topography, small sand waves and sand ripples (wavelength less than 0.6 m) by using high-precision bottommoored in situ observation data from a typical area of the Taiwan Banks. A quantitative method for decomposition of small-scale submarine sandwave topography was proposed, which can be widely applied to the study of the development and evolution of highly active landforms in shallow seas and the sediment dynamics of submarine boundary layer, and also has practical value for assessing the stability of marine engineering.

In order to study the deep resistivity structure of intraplate volcanoes and their formation processes, a marine magnetotelluric survey at Suda Seamount in the western Pacific Ocean was conducted. The mainstream data processing method SSMT2000 was used for data processing. The measured data after rotation and the two groups of rotation invariants obtained from the measured data were tested for magnetotelluric response under the assumption of one-dimensional structure, and one-dimensional inversion was conducted for the YX direction data with the best response. Combined with one-dimensional forward modeling and other geological data, the inversion results were comprehensively interpreted. The inversion results show that the thickness of the crust at Suda Seamount is about 21.5 km. The thick volcanic clastic rocks indicate that the formation of Suda Seamount is mainly eruptive and weakly intrusive.

Rapid land subsidence is a kind of geological disaster, which is related to the sustainable development of society and even threatens the safety of human life and property. InSAR technology can obtain long-term and large-scale surface deformation data, analyze potential land subsidence problems, and then provide reliable means for preventing geological disasters. How to predict land subsidence based on InSAR data has always been the key direction and problem that researchers focus on. Thus, on the basis of previous research on land subsidence prediction, a land subsidence prediction method was proposed, which combines the Auto Regressive Integrated Moving Average (ARIMA) model with the Long Short-Term Memory (LSTM) model in deep learning. The difference between the deformation data and the prediction result of the ARIMA model was obtained and then LSTM was used to train and predict the difference. Taking the InSAR monitoring data of Hangzhou Bay from 2017 to 2019 as an example, the method was verified. The result shows that compared with the traditional single prediction algorithm, the root mean square error of the method is reduced by at least 2.23 mm, and the mean absolute error is reduced by at least 0.98 mm, and the average prediction accuracy is improved by at least 15.19%, which verifies the feasibility of this method and provides some ideas and methods for early warning of ground subsidence.

Wave diffraction will happen when it encounters the island in the wave propagation process. Based on the modified slope equation, the hybrid element method was introduced to solve the equation, and the analytical solutions proposed by KUO et al was used to verify the present numerical solutions. Wave diffraction from a 3D circular island for engineering scale was conducted. The ratio of the wave height to the incident wave height (defined as the relative wave height) along the section of the wave propagation direction and around the island coastline was calculated for different incident wave periods, shoal shape parameters and island sizes. The results indicate that with the decrease in the incident wave period and the size of island, as well as the increase in the shoal shape parameters, the oscillation amplitude of the relative wave height at the head wave side of the circular island, the value of the relative wave height at the back wave side of the circular island, and both the oscillation amplitude and the value of the relative wave height around the island coastline all increase. However, for the different cases, the majority of the maximal relative wave heights happen at the head wave point, and several maximal relative wave heights happen at about 20-25 degrees on the both sides of the head wave point. The minimum relative wave heights are located about 30 degrees on the both sides of the back wave point.

Based on the measured hydrological and water quality data of Xincun lagoon in December 2020, the characteristics of tide in Xincun lagoon were studied, and the effects of tidal elevation changes on nutrients in Xincun lagoon were discussed. The results show that the tide of Xincun lagoon is irregular diurnal. The tidal current at the inlet of the lagoon is a reciprocating current, lasting 15 h for flood tide and 10 h for ebb tide. The concentration of dissolved inorganic nitrogen (DIN), phosphate (PO3-4) and silicate (SiO2-3) vary from 0.91 to 20.87 μmol/L, 0.11 to 5.92 μmol/L and 2.36 to 134.75 μmol/L respectively. The concentrations of DIN, PO3-4 and SiO2-3 at the observation sites in the lagoons changed with the flood and ebb of the tidal process. The flow velocity at the inlet of the lagoon has an important influence on the change of tidal elevation at the observation sites, and the tidal flux basically determines the change of tidal elevation at the observation sites. There is a significant negative correlation between the nutrient concentration at the inlet of the lagoon and at the mariculture area and the tidal elevation, and the tidal current velocity has an important effect on the nutrient concentration at the inlet of the lagoon and the mariculture area. The results will provide scientific basis for pollution control and ecological restoration of Xincun lagoon.

Based on the measured water level data of Xiuying Station from 1980 to 2017, the distributional characteristics and influencing factors of storm surge in Haikou were studied by using the methods of statistical analysis and numerical model. It is found that Haikou is frequently affected by typhoon storm surge, with an annual average of 2.79 times, which usually occurs from July to October, and the probability of tidal disaster caused by storm surge is high. The horizontal distribution of storm surge shows that the storm surge intensity of Dongzhai Port ranks first, followed by Xiuying Port, Haidian Island and South Port. Influencing factors show that the weight of topography is usually greater than the moving path of tropical cyclone storm surge in Haikou; when the moving speed of tropical cyclone is 14-19 km/h, the storm surge in Haikou is usually the largest.

Hyperspectral remote sensing water depth inversion which has many advantages such as convenience, quickness, and economy is a supplement to traditional measurement methods of water depth, and is worth studying. The research area of this study is located in Hengsha, Shanghai, which is a typical shallow water area of tidal flats. The research data was obtained from GF5-AHSI hyperspectral remote sensing and measurement of water depth at the same time. The modeling parameters were extracted through data transformation and correlation analysis. The single-band ratio model, multivariate linear regression model, optimal scale regression model and BP neural network model were used for water depth inversion in this area. By comparing and verifying the accuracy of the four models, it is found that the optimal scale regression model is better than the other three models, with R2 reaching 0.972 and RMSE of 0.47 m, which is suitable for inversion of shallow water depth in Hengsha.

The meiofaunal abundance and biomass in the Changjiang (Yangtze River) Estuary and adjacent waters was evaluated based on samples collected from July 13 to August 30, 2006. The group composition, the horizontal and vertical distribution of abundance and biomass, environmental factor were analyzed. A total of 11 meiofauna groups and Naupius were found from the surveyed area, including Nematodes, Copepods, Polychaetes, Oligochaetes, Ostracoda, Acari, Bivalves, Gastrotricha, Kinorhyncha, Amphipods and Isopods. The results showed that average abundance was 453.22±355.34 ind/10 cm2. Nematode accounted for 81.37% of the total abundance of all meiofauna, followed by Copepod (10.13%) and Polychaetes (2.96%). The average biomass of the meiofauna was 622.65±505.07 μg/10 cm2. Polychaetes accounted for 30.21% of the total biomass of all meiofauna, followed by Nematode (23.69%) and Oligochaetes (19.44%). The horizontal distribution showed that the meiofaunal abundance increased from the estuary to the East China Sea Shelf. The average abundance in the Hangzhou Bay was 240.96±223.47 ind/10 cm2. The average abundance in the Changjiang Estuary was 442.91±304.16 ind/10 cm2. The average abundance in the East China Sea was 865.42±553.88 ind/10 cm2. The analysis of vertical distribution showed that the abundance of meiofauna decreased with the depth in the sediment. The highest abundance of meiofauna was 290.28±250.03 ind/10 cm2 in 0-2 cm layer. The second highest abundance of meiofauna was 132.81±128.74 ind/10 cm2 in 2-5 cm layer. The lowest abundance was 30.14±31.91 ind/10 cm2 in 5-10 cm layer. The Nematodes, Polychaetes, Oligochaetes, Copepods had the same vertical distribution trend. The correlation analysis of environmental factors indicated that dissolved oxygen, depth and salinity were the main factors to influence the meiofaunal abundance in the surveyed area. Result of BIOENV analysis showed that the best combination of environmental factor was dissolved oxygen and salinity.

 Land-ocean interface has been a challenge in determining the boundary conditions for earth system modelling. Due to the uncertainty of material fluxes, the localization effect on counter gradient convergence, and the existence of self-adapted structures, land-ocean interface is unable to be monitored ergodically under the framework of classic linear theory. There is a great difficulty in quantifying real parameters for this interface, which is the key connection between linear and nonlinear systems under harmonic conditions, to better improve the simulation and prediction capability of earth system modelling. In a previous work, based on a two-dimensional multi-constituent tidal model and its adjoint model, together with assimilation using satellite altimeter data and tidal gauge array data, the spatial and temporal variation in bottom friction coefficient was estimated in an improved way. Inspired by the abovementioned study, this contribution proposed a suggestion of complex parameterization for land-ocean interface, in combination with remote sensing observation and numerical modelling.

Since a diagram depicting "The Great Ocean Conveyor" was first appeared as a logo by Wally Broecker in 1987, how the warmed upper ocean circulation ran through the Indonesian Seas with their complex coastline geometry and narrow passages, known as the Indonesian through-flow, becomes one of the difficult settings in boundary conditions of climate change model. With strong nonlinear effect, a shallow narrow passage forms vertical mixed hotspots on the one hand, and on other hand, it becomes a self-adapted low-pass filter if the tidal resonance units are introduced. Qiongzhou Strait, a sufficient sediment supply and shallow narrow passage for the northern shelf of the South China Sea, is reported with strong tidal current and westward through-flow. And its tidal channel and tidal deltas are maintained by the tidal resonance units introduced themself. Strong disturbances such as typhoon and cold wave can cause storm jet flow through the strait, triggering different high nutrition, algal bloom and hypoxia events over the adjacent Beibu Gulf. Qiongzhou Strait seems to be a noteworthy case of studying how the self-adapted low-pass filter introduced and whether human activities can affect the through-flow on the shallow narrow passages.

Marine sands are important submarine mineral resources. The marine sand resources of Hainan Island are widely distributed in coastal zones and continental shelf areas, with large scale, good quality and rich in heavy minerals. The basic distribution characteristics of marine sand resources around Hainan Island are described, and the progress and main achievements of marine sand exploration around Hainan Island are reviewed with emphasis on heavy mineral sand and aggregate sand. Through the exploration, 15 abnormal areas of heavy mineral placer have been delineated in the sea area around Hainan Island, and one large zirconiumtitanium placer deposit has been proved. However, due to the low level of investigation and research, the resource potential of heavy mineral placer is not clear. The scale of sediment survey around Hainan Island has basically reached 1∶250 000, which provides a solid foundation for the exploration of aggregate sand resources. In recent years, billions of cubic meters of aggregate sand resources have been discovered in the east entrance of Qiongzhou Strait and tidal sand ridge area of the western Hainan, and the resource potential is predicted to reach tens of billions of cubic meters. According to the comprehensive analysis, 8 potential exploration areas of marine sand resources can be delineated around Hainan Island. Except the east mouth of Qiongzhou Strait and the tidal sand ridge area of the western Hainan, the northeast continental shelf of Hainan, the southwest continental shelf of Hainan and Beibu Gulf area are all favorable enrichment areas of marine sand resources, and may contain heavy mineral resources potential. According to the specific sedimentary environment, the exploration objectives and tasks of each prospective area are discussed respectively. Combined with the current work progress and existing problems, the suggestions for the future marine sand exploration are put forward.

Climate reconstructions for the last millennium are essential for understanding climate change and will provide an important basis for predicting future climate change. However, there are spatial differences in monsoonal precipitation, and the hydrothermal configurations of two important characteristic periods of the past millennium, the Medieval Warm Period and the Little Ice Age, are highly controversial, especially in southern China. Therefore, the Core BBG-02 taken from the northeastern Beibu Gulf were analyzed for chronology, grain size, major elements and trace elements to understand the physical source of the Core BBG-02 and the climate and environmental changes in its source area. The analysis of chondrite-normalized distribution patterns of rare earth element and geochemical indicators reveal that the Red River may be the main source of the Core BBG-02, and the changes in geochemical indicators of the core reflect changes in the intensity of Indian Summer Monsoon. The results indicate that the climate was warm and humid during the Medieval Warm Period and cold and arid during the Little Ice Age, which is consistent with the results of previous studies on the variation of Indian Summer Monsoon and precipitation. The variation of solar radiation intensity is the essential reason of the variation of Indian Summer Monsoon, which is also influenced by ENSO activity and Indian Ocean Dipole.

Based on remote sensing images and geographic information system technology, the coastline and reclamation information of Fangcheng Bay in China and Haiphong Port in Vietnam from 1980s to 2010s were compared. The results showed that in the past 30 years or so, the coastline of the two places mainly migrated to the sea, of which the average end point rate of Fangcheng Bay was 6.49 m/a, and that of Haiphong Port was 6.21 m/a, showing a trend of rising first then falling and falling first then rising, respectively. In the 1980s and 1990s, the average end point rate of Fangcheng Bay was higher than that of Haiphong Port, while in the 2000s and 2010s, it was the opposite. In the past 30 years or so, the average new reclamation area of the two bays was 122.48 hm ²/a and 164.24 hm ²/a, respectively, and the reclamation intensity index of the two places showed a rising trend. In the 1980s and 1990s, the reclamation intensity index of Fangcheng Bay was smaller than that of Haiphong Port, while in the 2000s and 2010s, it was the opposite. From 1980s to 2010s, the reclamation area and the average spatial expansion rate per year increased first in Fangcheng Bay and then decreased, while Haiphong Port continued to fluctuate. Reclamation was the main factor for the change of the coastline of the two places, and port construction was the main driving force.

 Hydrological observations were carried out in the northeastern of Beibu Gulf in July and October 2018, February 2019 to reveal its seasonal variations. Sectional measurements of temperature, salinity and current velocity were deployed to the north of 18°N and east of 108°E. The results show that there is obvious seasonal disparities on the character of water masses in this region: the sea water temperature in summer decreases from northern shallow water to southern deep region and the onshore brackish water dominates the area shallower than 30 m, and a occlusive cold water mass appears in deep layer to the west of Hainan Island; while in winter the water temperature increases from north to south, the brackish water shrinks to the northern coast shallower than 10 m, the area is occupied mainly by the mixed water, and a warm tongue appears in upper layer on the west of Hainan Island. The circulation in the research region is mainly counterclockwise in all three seasons, though the strength of current varies in different seasons, and is significantly influenced by wind. The water exchange between the northeastern gulf and outer ocean is not active, since the observed salinity is entirely less than 34. The water mass is generally shear instable, and static instability appears in winter. This suggests that the diapycnal mixing in this region might be strong. 

Based on the runoff, the chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) data in the Maolingjiang River Estuary section from 2014 to 2020, the inflow fluxes of COD, TN and TP were calculated by the LOADEST model. Results showed that: (1) The regression equation of COD, TN and TP fluxes into the sea from the Maolingjiang River was well fitted by the LOADEST model, there were consistencies between the simulated and measured values. (2) The simulated multi-year average COD, TN and TP inflow fluxes were 34 537 t/a, 3 302 t/a and 235 t/a, and the monthly average inflow fluxes were 2 878 t/month, 275 t/month and 19.58 t/month, respectively. COD, TN and TP inflow fluxes in the wet season accounted for 77%, 80% and 71% of the total annual inflow fluxes, respectively. The multi-year average inflow fluxes of COD, TN and TP were 21 059~25 271 t/a, 1 775~2 130 t/a and 70~84 t/a from non-point sources, respectively. COD and TN were mainly controlled by non-point sources. TP was controlled not only by non-point sources but also by point sources. (3) Comparatively, the multi-year average inflow fluxes of COD, TN and TP of the Qinjiang River were about 1.16, 2.15 and 2.37 times those of the Maolingjiang River, respectively. The difference of inflow fluxes of COD, TN and TP from the Qinjiang River and Maolingjiang River were mainly affected by the number of people living along the river.

Taking Beibu Gulf, South China Sea as a case, the occurrence, source, and ecological risks of 12 organophosphate esters (OPEs) were investigated in 34 surface sediment samples. The Σ12OPEs in the sediments ranged from <LOQ to 35.1 ng·g ^-1. Triphenyl phosphate (TPHP), tri-n-butyl phosphate (TNBP), tris (2-chloro-propyl) phosphate (TCIPP) and tris (2-chloroethyl) phosphate (TCEP) were the dominant OPEs in the surface sediments. Generally, the total mass fraction of OPEs detected in sediments from the offshore was higher than that in the near shore, and the mass fraction for major OPEs were also different between the above two areas. On the one hand, the main reason might be related to their physiochemical properties. TPHP and TNBP compounds with higher lipophilicity might be more likely to accumulate in the sediments. On the other hand, it might be related to the source. For example, the OPEs detected in the offshore might be related to the oil exploitation and transportation, submarine optical cable and oil pipeline laying, shipping activities and the transportation of circulation in Beibu Gulf, while the discharge of life and industrial sewage as well as marine aquaculture might be the major sources for OPEs detected in the inshore area. Risk assessment revealed that most individual OPE could pose low ecological risks, but medium ecological risks of TPHP and the mixture of OPEs on aquatic organisms were found, which requires more attention. Therefore, the OPEs pollution situation in Beibu Gulf needs to be paid attention to, especially the pollution emission and control TCIPP and TCEP from inshore area, as well as TPHP and TNBP from offshore area, so as to reduce OPEs pollution from the source.

²¹⁰Po is a typical natural particle active radionuclide, which can be used as a tracer for the study of atmospheric aerosol deposition dynamics and particle dynamics in marine environment. In this study, the water quality parameters and the specific activities distributions and behavior of different phases for ²¹⁰Po in six offshore sections of the north coastal Beibu Gulf were investigated. Results showed that the specific activities of dissolved, particulate and total ²¹⁰Po were 0.16-2.78 mBq/L, 0.14-2.43 mBq/L and 0.51-3.94 mBq/L, respectively. There was no significant correlation between the specific activities of dissolved ²¹⁰Po and the water quality parameters, but the specific activities of particulate ²¹⁰Po showed significant correlation with water temperature, salinity and mass concentrations of TSM, respectively. At the same time, the specific activities of total ²¹⁰Po were significantly correlated with water temperature and mass concentrations of TSM, respectively. The distribution trends of ²¹⁰Po in different sections were not consistent, but in general, the particulate phase was the main existence form of ²¹⁰Po in the nearshore water, and the offshore ²¹⁰Po was confirmed mainly in the form of dissolved phase. Further analysis showed a negative correlation between the distribution coefficients of ²¹⁰Po in the solid-liquid phase and the mass concentrations of total suspended particulate matter. Based on the one-dimensional steady-state irreversible removal model, a longer residence time of dissolved ²¹⁰Po relative to particulate ²¹⁰Po was obtained, indicating that the atmospheric deposition and riverine input of ²¹⁰Po into the coastal Beibu Gulf would partially enter the dissolved phase after entering the seawater, so that its residence time in the water was prolonged.

Understanding the spatial evolution of mangrove patches is important to comprehensively and accurately evaluate the results of protection and restoration efforts in regional mangroves. In this study, the recent 30-year changes in area and number of mangrove patches in Maowei Sea and their driving factors were analyzed. The 1990, 2000, 2010 and 2019 Landsat remote sensing images were used as the main data sources, whereas the landscape dynamic analysis, spatial overlay analysis and main transformation route counting were adopted as the analytical approaches. The results demonstrated that: (1) The area of mangrove in Maowei Sea increased from 479.7 hm ² to 1 477.5 hm ² between 1990 and 2019 with the centroid shifting northward and westward. (2) Anthropogenic and natural factors were identified as the main driving force leading the changes in mangrove patch quantity in Maowei Sea from 1990 to 2010 and 2010 to 2019, respectively. (3) The number of mangrove patches increased from 204 in 1990 to 405 in 2019. However, the simultaneous occurrence of declining patch density and increasing mean patch size indicated that the patch fragmentation had been alleviated caused by the driving of natural factors. The artificial plantation of mangroves, especially using Sonneratia apetala, had contributed to the overall increase in mangrove area in Maowei Sea. Nevertheless, research on the artificial forestation process, expansion mechanism of mangrove patches and their ecological effects should be emphasized in future.

Chlorophyll a (Chl a), as the main pigment of phytoplankton photosynthesis, is often used to indicate the existing amount of phytoplankton in water column. The concentration of Chl a in Beibu Gulf from August to September 2021 was analyzed and its spatial distribution characteristics and influencing factors were discussed based on the summer cruise of the Shiptime Sharing Program on 2020 Beibu Gulf Scientific Research Expedition. The results showed that the mass concentration of Chl a ranged from 0.03 to 10.59 μg/L with an average value of 0.84 μg/L, among which the surface layer mass concentration ranged from 0.08 to 10.59 μg/L (average 0.97 μg/L) and the bottom layer mass concentration ranged from 0.03 to 4.69 μg/L (average 0.99 μg/L). Combined with the analysis of remote sensing data, the spatial distribution of Chl a mass concentration in Beibu Gulf was generally high in the nearshore and low in the offshore area. The high value area was mostly distributed in the nearshore area of Guangxi, namely the northern part of Beibu Gulf, while the mass concentration in the central and southern part of Beibu Gulf was relatively low. The correlation analysis between water environmental parameters and Chl a indicated that water nitrogen limitation was an important factor affecting the mass concentration of Chl a in Beibu Gulf from August to September.

In order to explore the distribution, formation mechanism and motion law of eddy around Kuroshio in East China Sea, firstly, the eddy distribution around the Kuroshio in the East China Sea during the past 27 years was analyzed by using the mesoscale eddy data set of the AVISO(Archiving, Validation and Interpretation of Satellite Oceanographic Data). The results show that there are 650 eddies generated in the meander of the Kuroshio, and 271 eddies in the middle part of the Kuroshio. The diameters of the most these eddies were between 100 to 150 km, and the amplitudes were between 2 to 6 cm. Secondly, the motion path and eddy motion process of the Kuroshio in the East China Sea are also analyzed. The results show these the cyclonic eddies are easy to be generated in the inner side of the Kuroshio cyclonic bend, with a long path. For example, at the cyclone bend of the Kuroshio axis in the northeast of Taiwan, the average length of the path was 87.6 km. Otherwise, when these anticyclonic eddies are generated, these eddies usually are wandered. In the middle part of the Kuroshio, the eddy showed the polar symmetric distribution characteristics of these cyclonic eddies in the west side of the Kuroshio main axis and these anticyclonic eddies in the east side of the Kuroshio main axis. Both types of eddies moved northeastward along the Kuroshio main axis. Finally, combined with reanalysis data sets of ocean current and sea surface height, the eddy motion law and generation mechanism were discussed. It is concluded that these eddies generation at the curve of the Kuroshio are related to the separation of the boundary layer of the Kuroshio fluid. The Kuroshio countercurrent from the south of Yanmei Island to the west of Okinawa Island played a key role in the polar symmetric distribution of these eddies in the middle part of the Kuroshio. These eddies usually experience three stages of growth, maturation and decay in the process of movement.

The East China Sea Shelf Basin is a Mesozoic and Cenozoic superimposed basin with high oil and gas potential. At present, the discovery of oil and gas in the basin comes from the Cenozoic reservoirs, and various aspects of the Mesozoic residual strata are less known. Furthermore, previous qualitative or semi-quantitative studies are usually spatially limited within specific structural units in the western part of the basin and mainly involves Cretaceous and Jurassic. This study collects and sorts out the latest reflection seismic data and well data penetrated into the Mesozoic in the entire study area. Based on seismic sequences of the Cretaceous, Jurassic and Pre-Jurassic, our results show that the Mesozoic residual strata in the East China Sea Shelf Basin suffered from severe denudation in the later period. The Mesozoic residual strata generally thicken to the east and south, and the range of residual strata expanded eastward over time. Comparing the distribution characteristics of the residual strata between different periods, it is further supported that the East China Sea Shelf Basin was a passive continental margin depression basin in the Triassic, and an active continental margin fore-arc basin in the Early-Middle Jurassic, and a continental margin back-arc extensional basin in the late Jurassic to late Cretaceous. Correspondingly, the subduction of the paleo-Pacific plate began in the Late Triassic-Early-Middle Jurassic, and the retreat of the plate began in the Late Jurassic. The east boundary of the Mesozoic proto of the East China Sea Shelf Basin was located on the east side of the Diaoyu Island uplift.

Alkaline phosphatase activity (APA) is an important indicator of phytoplankton phosphorus limitation status in the marine science study. In the “nitrogen-excess” areas such as the Changjiang Estuary (CJE), phosphorus is a major factor controlling the primary productivity in the sea. However, the extent of phosphorus limitation is often difficult to define and little is known about the effect of phosphorus limitation on phytoplankton at different sizes. In this study, the spatial distribution of phytoplankton (Net: ≥20 μm; Nano: 2~20 μm; Pico: 0.8~2 μm) APA, bacterioplankton APA (0.2~0.8 μm) and dissolved APA (<0.2 μm) in the surface layer of the CJE in the summer of 2020 were given, and the correlation between APA and environmental factors were analyzed. The results showed that size-fractionated phytoplankton APA was negatively correlated with dissolved inorganic phosphate (DIP), indicating that DIP concentration was the main factor affecting the distribution of size-fractionated phytoplankton APA. In the spatial distribution, phytoplankton APA was lower in the light-limitation zone near the mouth, and showed an increasing trend from the mouth to the east, contrary to the distribution of DIP. Net and Nano phytoplankton APA (mean values of (40.28±32.35) nmol/(L·h) and (52.38±34.78) nmol/(L·h), respectively) were significantly higher than Pico phytoplankton APA (mean values of (28.43±20.23) nmol/(L·h)) in the CJE, implying that large size phytoplankton were more susceptible to DIP decline. In this study, the DIP concentration for inducing a rapid increase in phytoplankton APA was 0.159 μmol/L, which was close to the empirical threshold for nearshore phosphorus limitation. This study revealed the characteristics of phytoplankton response to phosphorus distribution in the CJE at different grain levels in summer, and also contributed to the understanding of the environmental regulatory mechanisms of primary production processes in the CJE.

Based on the unsupervised pixel-based Spectral Rule-based Classifier (SRC) algorithm, an effective Modified Spectral Rule-based Classifier (MSRC) was proposed considering the influence of atmospheric correction on spectral reflectances of remote sensing images. MSRC modifies rule sets according to ground object spectrum curves and spectral indices, optimizes spectral categories through refined and supplementary rules as well as modified thresholds. The Landsat 8 remote sensing images of islands (Jiapeng, Qi'ao) and coastal zones (Quanwan, Huidong) in the Pearl River Delta were chosen as the experimental data. The band reflectances and ground object spectrum curves before and after atmospheric correction process were contrasted. Classification results and accuracy of the MSRC algorithm were analyzed and compared with those of other six classification algorithms: the original SRC algorithm, Minimum Distance Classification (MDC) algorithm, Maximum Likelihood Classification (MLC) algorithm, Support Vector Machine (SVM) algorithm, Neural Network Classification (NNC) algorithm and spectral indices-based classification methods. The overall accuracy (OA) of MSRC algorithm using experimental data were respectively 87.66%, 82.38%, 77.67% and 80.05%, which were all higher than those of the original SRC algorithm, MDC, MLC and spectral indices-based classification methods, and closed to the accuracy of supervised algorithms (SVM and NNC) without the requirement of manually labelling the training dataset. MSRC performs well in land-cover type scenarios of islands and coastal zones on Landsat 8 multispectral remote sensing images.

The variation characteristics of water and sediment in the Pearl River Basin over the past about 70 years were analyzed by using the runoff and sediment discharge data at three major hydrological stations in the Pearl River Basin, Gaoyao Station (Xijiang River), Shijiao Station (Beijiang River) and Boluo Station (Dongjiang River) from 1954 to 2019, and applying the Mann-Kendall nonparametric test and accumulative anomaly curves. The results showed that the change of the runoff in the Pearl River from 1954 to 2019 was not obvious while the sediment discharge was decrease, among which the sediment discharge at Gaoyao and Boluo Stations changed abruptly in 2003 and 1991, decreasing by 71.3% and 48.88%, respectively, compared with before the abrupt change, while the sediment discharge at Shijiao Station did not change abruptly. On this basis, the change of vegetation cover in the basin and its relationship with the change of water and sediment were studied by using the precipitation data and Normalized Difference Vegetation Index (NDVI) in the basin from 2000 to 2019. The NDVI in the Pearl River Basin showed an overall increasing trend from 2000 to 2019, and the improvement area of vegetations cover accounted for 89.27% of the total basin area. Among which NDVI in the Pearl River Basin was poorly correlated with sediment discharge from 2000 to 2008, NDVI in the Xijiang River Basin and Dongjiang River Basin were positively correlated with precipitation in the basin but not with sediment discharge form 2009 to 2019, and only in the Beijiang River Basin, NDVI was insignificantly negatively correlated with sediment discharge. The influence of human activities on sediment discharge in the Pearl River at different periods was discussed using the double cumulative curve method. Since the 1980s, human activities such as deforestation, reservoir construction, and soil and water conservation had a significant impact on sediment discharge. After 2000, the construction of Longtan Reservoir was the main reason for the decline of sediment discharge in the Xijiang River, but the improvement of vegetation coverage had no significant impact on the sediment discharge in the Pearl River Basin.