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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

 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.

 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. 

Coastal bays are greatly affected by human activities and natural changes, and the influence mechanism of variation in seawater carbon source and sink patterns is extremely complex. Due to the small spatial scale of the bay, it is necessary to use wide-bands high-spatial resolution satellite remote sensing for monitoring the air-sea CO₂ flux. Compared with the traditional kilometer-level ocean color satellite data, the retrieval of the sea surface partial pressure of CO₂ (pCO₂), the key parameter to calculate air-sea CO₂ flux, is extremely challenging in small-scale bays. Taking Xiangshan Bay in Zhejiang Province in autumn as an example, a satellite retrieval algorithm for sea surface pCO₂ was proposed based on the in situ pCO₂ data and Sentinel-2 satellite images in the past five years, using the machine learning method of support vector machine (SVM). The algorithm validation results showed a good performance with R² of 0.92 and RMSE of 23.23 μatm, and the satellite-derived results were consistent with the in situ values. On this basis, the satellite products of pCO₂ in Xiangshan Bay in autumn from 2017 to 2021 (September to November) were produced. The results revealed that the pCO₂ of Xiangshan Bay showed a decreasing trend from the top of the bay to the mouth of the bay, with an average value of 514.56 μatm, of which the average pCO₂ in the inner bay was 551.94 μatm and the average pCO₂ in the outer bay was 477.19 μatm, which implied that Xiangshan Bay was a source of atmospheric CO₂ as a whole. There was no significant trend change of pCO₂ in autumn in the past five years. Combined with the analysis of in situ data of multiple parameters, it was found that the sea surface pCO₂ of autumn in Xiangshan Bay in 2021 was jointly regulated by physical mixing and biological activities. Sea surface temperature (SST) had a good positive correlation with pCO₂, which was mainly reflected by the thermodynamic equilibrium of carbonate system. In addition, the normalized pCO₂(NpCO₂) with average temperature had a good negative correlation with seawater salinity and dissolved oxygen saturation. The relationship between NpCO₂ and salinity resulted from the exchange of sea water inside the bay and offshore coastal water under tidal effect. Long-time series satellite data analysis also confirmed that sea surface pCO₂ had a relatively consistent trend with the average tide height inside and outside the bay, and this trend was stronger in the outside bay than that in the inner bay. In this study, a set of pCO₂ remote sensing retrieval methods in the small-scale bay was constructed, which laid a good foundation for the subsequent long-time series satellite monitoring of sea-air CO₂ fluxes.

Marine gas hydrate deposits are significant temporal reservoirs for hydrocarbons migrating from deep sources. This is crucial to our understanding of ocean carbon cycling. The cold seep, a geological process regarding gas leakage from deep or shallow sources, is usually linked with gas hydrate decomposition. In this thesis, we reviewed the latest applications of in situ monitoring and detecting methods regarding the leakage plumes, migration pathways, and seafloor geomorphologies associated with gas hydrate and cold seep systems, primarily including vessel-and land-based gas plume measurements, surface ocean-lower atmosphere hydrocarbon emission detections, seafloor visualization techniques, and in situ observation networks. The integrated applications of these in situ observation methods provide a nuanced view of the temporal and spatial variability of hydrate and cold seep systems, facilitate understanding of the fate of hydrocarbons, and expand our knowledge of cold-seep biota in a watery desert.