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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.

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.

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 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 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.

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 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.

Based on the mesoscale atmospheric model WRF and the regional ocean model ROMS, a two-way coupled WRF-ROMS air-sea model was constructed to simulate the super typhoon Mangkhut in 2018. The results showed that the simulation results of the coupled air-sea model were better than those of the only atmospheric or ocean model, and the error of the typhoon track obtained from the coupled model was within 60 km, which was in good agreement with the best track. Compared with the observation results, the simulation results of wind speed and sea level pressure in the coupled model were better than others model. Based on the simulation results of the coupled air-sea model, the spatial and temporal distribution of the wind field, pressure field, sea surface flow field, and storm surge under the super typhoon Mangkhut were further analyzed. The results showed that: (1) In terms of spatial distribution, after the typhoon entered the South China Sea, the radius of the seven-level wind circle was larger behind the right side of the typhoon; the cyclonic flow field showed a significant Ekman effect with the typhoon wind field, and the flow direction was 45° from the wind direction. The wind field, pressure field, wind-generated flow field and water gain distribution all had obvious asymmetry, and the typhoon intensity, flow velocity and water gain were greater on the right side of the typhoon path than on the left side. (2) In terms of time distribution, the distribution of the wind field and the pressure field were similar and synchronized with the typhoon center, while the wind-driven flow field and storm surge were three hours behind the typhoon track.

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.

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.

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.

Carbon stock variation observation forms the basis for coastal saltmarsh blue carbon sink accounting. In order to accurately estimate the carbon sequestration rate of coastal saltmarshes over a short-term scale (seasonal to annual), this study carried out field observations and sample collections within a coastal saltmarsh on the south bank of Hangzhou Bay, covering different seasons of 2022. This study was primarily based on high-resolution surface monitoring by Surface Elevation Table (SET) systems. The results revealed a seasonal plant growth pattern between March and September for both the native species Scirpus mariqueter and the exotic species Spartina alterniflora. In terms of belowground biotic carbon stock changes, over the growing season, the carbon stock increase for Scirpus mariqueter reached 11 g C·m^-2 whilst this value was 56 g C·m^-2 for Spartina alterniflora. The SET data indicated a sedimentation rate of 13.02 cm·a^-1 within the Spartina alterniflora saltmarsh, higher than that of the Scirpus mariqueter saltmarsh, 12.30 cm·a^-1. Calculating the sedimentation rate data with sediment bulk density and organic carbon content, the sediment carbon accumulation rate of Scirpus mariqueter saltmarsh was estimated to be 460 g C·m^-2·a^-1, lower than 588 g C·m^-2·a^-1 of the Spartina alterniflora saltmarsh. Combining the biotic carbon stock increase and sediment carbon stock increase, the carbon sequestration rate for the Spartina alterniflora saltmarsh was found to be 644 g C·m^-2·a^-1, higher than the value of Scirpus mariqueter saltmarsh, 471 g C·m^-2·a^-1. Thus, the difference in carbon sequestration abilities of native and exotic species should be considered for future coastal blue carbon management.

Costal ocean receives a bunch of carbon materials and nutrients from terrestrial sources, relates a lot of carbon-involving interactions. Meanwhile, it is normal that sedimentary reservoir-cap systems with good trap conditions beneath coastal ocean, these entrapments have potentials to storage CO₂. This review focuses on the coastal ocean as the research object, and introduces the carbon cycle processes in coastal ocean, their factors which could influence CO₂ fluxes in the carbon cycle processes, and the potential carbon storage mechanisms of the coastal marine sedimentary basins. From the perspective of “carbon peaking and carbon neutrality”, the significance of coastal oceans for “Ocean Negative Carbon Emission (ONCE)”, its potential promotion paths, carbon storage potentials in sedimentary basins and the problems faced by coastal oceans are discussed. Overall, the costal ocean is one of the important blue carbon sink areas. In the coastal marine seawater system, improving the reaction efficiency of microbial carbon pump and carbonate carbon pump have positive significance for CO₂ negative emissions; The suitable reservoir-cap systems for CO₂ storage beneath coastal ocean can not only provide extra spaces, but also guarantee the safety for CO₂ storage. In the future, the main research directions should be to inhibit the conversion process of carbon materials to CO₂ in coastal oceans and ensure the safety of CO₂ storage in sedimentary reservoirs, these could provide theoretical basis and technical guarantee for CO₂ negative emissions.

The annual greatest tidal bore in the Qiantang River almost occurs during typhoons. Based on the measured tidal data and combined with the harmonic analysis of astronomical tides, the influence of typhoon on tide downstream of the tidal bore formation section in the Qiantang River Estuary was studied, and then the tidal bore changes indirectly caused by tidal changes was discussed. The results show that typhoons cause the changes in low tide level, tidal range, tidal bore arrival time and duration of flood tide, and indirectly affect tidal bore through typhoons, resulting in the changes in tidal bore height, steepness, propagation speed, arrival time and flow velocity. In general, during a typhoon, the tidal bore height at Yanguan increases by 0.18 m on average, and the time of tidal bore arrives 37 min earlier on average, the propagation speed of tidal bore from Ganpu to Yanguan increases by 8.9% on average, the steepness of tidal bore increases, and the velocity of tidal bore increases or decreases, but the unit width flow rate increases.

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.