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The Landsat TM/OLI remote sensing images from 1973 to 2018 were obtained as the data source by using the remote sensing and GIS technology. Based on the geographical background information, the spatial and temporal evolutions of the coastline in the Pearl River Delta region over 45 years were analyzed. The results show that the Pearl River Delta changed significantly, a large number of muddy coast changed into urban industrial coast and port coast. The artificialization index of Pearl River Delta coastline was rising, the types of coastline were developed in a diversified direction, the total length and fractal dimension of shoreline were increasing continuously, the main factors of increase shoreline length and fractal dimension were port construction, coastal industrial zone and reclamation.The evolution of the coastline had obvious regional characteristics, and the regions with large changes were mainly concentrated in Shenzhen Mirs Bay, Guangzhou Nansha and Zhuhai Doumen. From the perspective of the main structure of shoreline, each region presented different type changing tendency, substituted the natural shoreline, the industrial and port shorelines became the main type in each region. The intensity of development and utilization was increasing in various regions, among which the intensity of development in Shenzhen was growing the fastest. Social activities and location policies were the main driving factors for the evolution of shoreline.

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.

The river-estuary-coastal ocean continuum (referred to as the continuum hereinafter) is a transition zone connecting lands and oceans. The carbon budgets in the continuum are dynamic and uncertain components in global carbon budgets. This complex landocean interactive ecosystem can absorb atmospheric CO2 through photosynthesis and dissolution of CO2. Also, the carbon fixed by photosynthesis or chemical weathering in land and watershed can be transported horizontally to the shelf waters and open oceans. In this paper, the progress of carbon cycles in the continuum is reviewed by taking the famous Chesapeake Bay and Changjiang Estuary-East China Sea continuum as typical examples. It is concluded that systematic observation characterized with land-sea coordination, sea-space integration, point-line combination, should be combined with physicalecological numerical simulation to reveal the multiple time-space scale processes. The strategy is generally operable, and the historical retrospective of results is also achievable. Thus, it can be used to clarify the evolution of carbon exchange along the river-estuary-coastal ocean continuum and their influences on carbon budgets under the combined pressures of climate change and anthropogenic activities.

Mangroves, coastal salt marshes and seagrass beds, as the typical coastal blue carbon ecosystems, have been widely recognized for their remarkable capacity in carbon storage. Vegetation carbon pool and sediment (or soil) carbon pool were considered to be the major carbon pools within the coastal blue ecosystems and their variations determined the overall carbon sequestration of the ecosystems. From a perspective of carbon pool interactions, this study summarized the previous research work based on literature review, including the interactions within various vegetation carbon pools and within various sediment carbon pools, as well as the interactions between vegetation and sediment carbon pools. Interspecific competition, allochthonous carbon input and biogeomorphology were found to be the key to understand the carbon pool interactions. Finally, a perspective on the current state-of-the-art of blue carbon pool study is offered, with challenges and suggestions for future directions.

Sea surface salinity is an important physical quantity for studying ocean changes and its climate effects. In this study, it was compared the monthly and daily average sea surface salinity products of the SMAP satellite in 2018 with the monthly average grid products and real-time scattered salinity data of Argo respectively, its accuracy was assessed and the global sea surface salinity distribution characteristics were analyzed. The results show that the average monthly product RMSE of SMAP satellite is 0.17, BIAS is 0.11, STD is 0.17, R is 0.98, and the t-test shows a significant correlation; the average daily product RMSE of SMAP satellite is 0.28, BIAS is 0.23, STD is 0.26, and R is 0.81. Compared with the monthly average product, the accuracy of average daily product is lower. The monthly average product deviation of SMAP satellites is small in mid-latitude seas and larger in high-latitude seas; the average daily product deviation of SMAP satellites is -0.6~0.6 in the Pacific Ocean and exceeds 1.0 in the Mediterranean Sea. The global sea surface salinity is between 25.0 and 40.0, among which the Atlantic sea surface salinity is generally higher than those of the Pacific and Indian Oceans, and the global sea surface salinity has an obvious zonal distribution pattern in the latitude direction.

The polymetallic nodule samples were analyzed for their mineralogical and geochemical features, which were acquired on the northeastern slope of the South China Sea using the ROV named as Sea Dragon III. The results showed that the nodules in the study area were predominantly by rod-shaped with a two-layer structure. The outer layer of the polymetallic nodules was mineralogically and geochemically similar to hydrogenic nodules. While the inner layer was porously and composed of goethite with residual minor pyrite. Geochemically, the inner layer was characterized by high concentration of Fe and As but extremely low concentration of Mn, REE and other elements. The inner layer carbon isotopes ( δ¹³C ) of sample NH-2 was -30.91‰. The study presented that the early forming process of the nodules was related to the activities of cold seep, but the pyrite was oxidized following the extinction of cold seep. Under the influences of contour current in the area, the ferromanganese oxides continued to grow in the outer layer of the nodules.

The UK Met Office EN4 analyses product revealed that the surface area and the volume of the North Pacific subtropical high-salinity center, namely North Pacific Tropical Water (NPTW), decreased in the period of 2000-2008 and 2014—2017, and grew in 2008—2014. The changing period of NPTW was highly correlated with Pacific Decadal Oscillation (PDO). Using the ECCO2 reanalyzing data, the fresh water flux was calculated through the NPTW surface. Our results show that the fresh water flux has less contribution to changes of NPTW, while the horizontal advection contributes significantly to the surface area and volume changes of NPTW, which is related to the northward(southward) swing of North Equatorial Current (NEC) during the PDO positive(negative) phase.

The climatology distribution of isopycnal layer in the Indian Ocean were analyzed based on the WOA18 (World Ocean Atlas 2018) dataset firstly. And then three time periods were defined as 1985-1994, 1995-2004 and 2005-2017 to research the decadal variation. The results show the climatology distributions of 11 isopycnal layers. As far as σ₀=26.00kg/m³ (reference pressure as 0 dbar) isopycnal layer was concerned, the layer was outcropping at roughly 40°S. As the potential density increased, the outcrop area of the isopycnal layer gradually moved southward until it disappeared. When the potential density was greater than σ₀=26.95 kg/m³ and less than or equal to σ₂=37.00kg/m³, the deepest part of the isopycnal layers were located in southern Madagascar, and the depth of the North Indian Ocean was almost the same. Furthermore, present study investigates the decadal variances of depth and salinity of isopycnal layers, where the three layers include σ₀=26.00 kg/m³, σ₁=31.87 kg/m³ (reference pressure as 1 000 dbar) and σ₂=36.805kg/m³ (reference pressure as 2 000 dbar). Studies show that the depth and salinity of the isopycnal layer had significant decadal changes in the three periods from 1985 to 2017. For the isopycnal layer of σ₀=26.00kg/m³, the depth decreased first and then increased during the three periods. And the decadal variation of the isopycnal depth was mainly located in 30°S-40°S(the rapid change area of the isopycnal depth). The difference of salinity between 1995-2004 and 1985-1994 was basically opposite to the difference between 2005-2017 and 1995-2004 when the isopycnal layer was σ₀=26.00kg/m³. For the isopycnal layer of σ₁=31.87kg/m³ and σ₂=36.805kg/m³, the decadal variations of the depth were concentrated on 40°S-50°S. Overall, the salinity of σ₁=31.87kg/m³ show a decreasing trend but σ₂=36.805kg/m³ show an increase trend.

To investigate monochromatic wave nonlinear characteristics around coral reefs with large surface roughness, laboratory experiments were carried out in a wave flume. A cylinder array was used to model the reef roughness and a series of monochromatic wave conditions were tested. Results show that magnitudes of the wave skewness, the wave asymmetry and the Ursell Number reach their peaks at the endpoint, in the interior and at the stating location of the reef surf zone, respectively. All the three parameters increase with the increasing wave height. Meanwhile, the skewness decreases with the increase of wave period while both the asymmetry and the Ursell Number increase with the increase of wave period. Moreover, the skewness increases with the increase of reef-flat water level while both the asymmetry and the Ursell Number decrease with the increase of reef-flat water level. The deep-water Ursell Number is able to describe the variations of the three examined parameters on the reef flat, and the empirical formulas are finally proposed in this study to predict these parameters.

In the past two decades, large scale blooms Prorocentrum donghaiense Lu (P. donghaiense) have frequently occurred in the coastal water of the East China Sea (ECS). Previous studies have shown that P. donghaiense blooms in the ECS originated from the front of Taiwan Warm Current (TWC) and expanded with its invading inshore. However, little is known about the location where the P. donghaiense blooms firstly occur, as it is limited by the investigation section of previous studies. In this research, four surveys in the East China Sea (24 °N-30 °N) in spring and summer of 2013 were conducted. Results clearly showed that P. donghaiense blooms occurred firstly at the northern end of the Taiwan Strait and spread northward and inshore with the invading of the front of TWC. It was not only confirmed again that the TWC played a seed bank role for P. donghaiense blooms in the ECS, but also confirmed the location where P. donghaiense blooms firstly occurred in the ECS. This research was useful to monitor P. donghaiense blooms and similar algal blooms.

There are abundant mesoscale phenomena in the Bay of Bengal and near the mouth of the bay. In this study, a 2.0 version of the Chelton's data set was used, which can distinguish mesoscale eddies in low-latitude regions, and obtain the genesis distribution of mesoscale eddies by tracing. The northwest sea off Sumatra (the area with 5 °N,94 °E as the core) is an important origin of mesoscale eddies. The eddy tracking of Lagrangian method shows that there were 57 cyclonic and 40 anticyclonic mesoscale eddies in the origin (3°N—6°N, 92°E—95°E) during 19932017. Spectrum analysis indicates that there are two significant periods of 180-day and 360-day in sea surface height anomalies. The dynamic mechanism of mesoscale eddies in this origin is the combined effect of topography and wind field, the Rossby wave propagating westward along 5°N increases instability and triggers the mesoscale eddy generation under the action of the ridge topography. The equatorial wind field is an important source of energy in the origin, and the local wind field can induce the polarity of the mesoscale eddy. This study also reveals the reason why the previous literatures described the northwest sea area off Sumatra as a high eddy kinetic area, but failed to identify many mesoscale eddies.

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.

The Pearl River Estuary (PRE) is one of the coastal areas with serious land subsidence, which forms a serious threat to the quality and safety of human life and production. In response to the problems associated with the lack of man-made targets of traditional time-series Interferometric Synthetic Aperture Radar (InSAR) in estuaries and other coastal areas, a distributed scatterers InSAR (DS-InSAR) method based on a spatially adaptive filter and an eigendecomposition algorithm to estimating the optimal phase of statistically homogeneous DS was applied to obtain the deformation information in PRE between 2015 and 2018. High-density and high-coherence points were extracted in asphalt pavement, bare soil and other non-urban areas, to improve the inversion accuracy. The results suggest that land subsidence in the PRE was widespread and unevenly distributed. The northwest and southeast are the main subsidence areas, with a maximum subsidence rate greater than 25 mm/a.

In order to evaluate the ecological environment quality of the estuarine coastal zone, based on remote sensing information technology in land, a remote sensing assessment system of the ecological environment of the estuarine coastal zone was established.Through the analytic hierarchy process and the Delphi Method, the area of 5 km land forward along the coastline of Baoshan District was taken as an example to evaluate. The results show that the estuarine coastal zone of Baoshan District is dominated by industrial and mining warehousing land, and the ecological environment quality in this area gradually decreases from west to east, reaches the lowest point in the area between the Lianqi River and the Malu River, and starts to rebound to the east,the overall situation is poor.

The island is one of the core contents of the value of marine resources development and utilization. In order to reasonably develop, utilize and protect island resources in Guangdong-Hong Kong-Macao Greater Bay Area and optimize the industry structures and arrangement on islands, from the perspective of the spatial distribution of island resources, the role of islands in the development of the key platforms in Guangdong-Hong Kong-Macao Greater Bay Area was explored. The spatial distribution characteristics of islands in Guangdong-Hong Kong-Macao Greater Bay Area were investigated by application of ArcGIS software platform, Nuclear Density Estimation Method, Lorenz Curve and Gini Coefficient calculation based on the statistical data of 850 islands coordinates and land areas, which have been listed in the China Seas Island Standards Directory. The results show that the distribution type of islands in Guangdong-Hong Kong-Macao Greater Bay Area tends to be concentrated and presents the overall band distribution, the characteristics of local group distribution in space. The islands in Guangdong-Hong Kong-Macao Greater Bay Area have shaped the western part of the bay area and 4 obvious gathering areas,Including Dapeng Bay-Daya Bay Area, Kyushu Islands Area, Wanshan-Jia Peng Islands Area, Chuanshan Islands Area. The islands in Guangdong-Hong Kong-Macao Greater Bay Area are mainly coastal islands and the area distribution of islands is characterized by an imbalance, with a Gini coefficient of 0.58.

Artificial intelligence in oceanography has demonstrated a great potential with the explosive growth of ocean observation data and numerical model products. This article first reviews the history of ocean big data development, and then introduces in detail the current status of artificial intelligence in oceanography applications including identifying ocean phenomenon, forecasting ocean variables and phenomenon, estimating dynamic parameters, correcting forecast errors, and solving dynamic equations. Specifically, this article elaborates the research on the intelligent identification of ocean eddies, internal waves and sea ice, the intelligent prediction of sea surface temperatures, El Ni?o-Southern Oscillation, storm surges, waves and currents, the intelligent estimation of ocean turbulence parameterization for numerical models, and the intelligent correction of waves and current forecast errors. In addition, it discusses the recent progress of applying physical mechanism fusion and Fourier neural operator for solving ocean dynamic equations. This article is based on the current status of artificial intelligence in oceanography and aims to provide a comprehensive demonstration of the advantages and potential of applying artificial intelligence methods in the field of oceanography. With the two emerging research hotspots: digital twin oceans and artificial intelligence large models, the future development direction of artificial intelligence provides enlightenment and reference for interested scientists and researchers.

Abstract: The impact of the flood event on the distribution and source of particulate organic carbon(POC) in Changjiang (Yangtze River) Estuary and adjacent waters was analyzed based on the data of temperature, salinity, total suspended matter(TSM), POC and δ13CPOC ,which were collected during the July 2020 flood. The results show that POC is negatively correlated with salinity (r2=0.41, p＜0.01), and positively correlated with TSM (r2 =0.92, p＜0.01). The mixing of salt and fresh water is an important factor affecting the distribution of POC. The distribution of δ13CPOC values in the surface water indicates that the phytoplankton production is another important factor affecting the distribution of POC in the northeastern part of the study area. Flood events reduce the concentration of terrigenous POC due to the dilution of high runoff, meanwhile, light δ13CPOC values in the southeastern part of the study area indicate that flood events could expand the influence range of terrigenous POC in the East China Sea.

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.

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.