Accurate inversion of shallow water depth is essential for marine space management and ecological environment protection. Lingyang Reef of Xisha Islands in the South China Sea is taken as a typical study area. The single-band model, multi-band model and band-ratio model are established based on GeoEye-1 and WorldView-2 high-resolution multi-spectral remote sensing data and measured points. The results show that the correlation of the inversion model established with the participation of green band is generally high, while the multi-band model established by four bands combination has the highest accuracy and the correlation coefficient reaches 0.870 and 0.853, respectively. Comparing with the inversion accuracy of GeoEye-1 and WorldView-2 data in different depth ranges based on the above model, the conclusion is that the inversion errors of the two kinds of data in different depth ranges have the same trend, with the maximum value of the average relative errors occurring in the range of 0−5 m and the minimum value occurring in the range of 20−25 m. In general, the inversion accuracy of WorldView-2 image is higher than that of GeoEye-1 image. This study has a certain reference significance for the inversion of water depth in shallow tropical sea.

The stable acquisition of large-scale and continuous coastline data through remote sensing is an important basis for the development of coastal zone research. Aiming at the problems of noise sensitivity and threshold instability in the traditional edge detection algorithm for high-resolution remote sensing images, the strected forests edge detection algorithm based on the structured random forest model is introduced to identify the sandy shoreline of the west coast of Haikou City, and proposed based on the Bruun-Dean balanced profile model, a new method of tide level correction is established to fit the profile model, and finally the fine coastline data is extracted. Based on the measured data, the precision evaluation and error analysis of the extraction results are carried out, and the prospects for method improvement and popularization and application are put forward. The research show that: (1) the result of the water edge line detected by the strected forests edge detection algorithm is clear and delicate, which is more accurate and efficient than the traditional edge detection operator methods such as Roberts operator, Canny operator, and LoG operator, and is suitable for the study of coastline extraction from high-resolution remote sensing images; (2) aiming at the tide level correction of the sandy coastline, the fitted profile model established based on the RTK measured data and the fitted profile model overcomes the large error of the traditional linear model and improves the accuracy and feasibility of the coastline correction; (3) based on actual measurement for the shoreline, the results are quantitatively analyzed using the section method, and it is verified that the positioning accuracy of the extracted shoreline is better than 2.5 m.

Remote sensing retrieval of phytoplankton group can provide important data for a comprehensive understanding of the role of phytoplankton in marine ecosystem. However, due to the complex optical characteristics, there are still great challenges in the remote sensing retrieval of phytoplankton group in offshore waters. In this study, the eastern China seas region, a complex optical class II water body, is taken as the research area. By using three modeling methods, namely band combination method, multiple linear regression method based on singular value decomposition (SVD+MLR) and XGBoost regression method based on singular value decomposition (SVD+XGBoost), the phytoplankton group is retrieved from remote sensing reflectance (R_rs) data. Verified by the in-situ measured data set, the chlorophyll a (Chl a) concentration retrieval model of eight phytoplankton groups by SVD+XGBoost has the highest accuracy, and the determination coefficient (R²) of Chl a concentration inversion model of diatoms and dinoflagellates in the validation set is greater than 0.7. In contrast, the accuracy of Chl a concentration of chlorophytes, cyanobacteria and chrysophytes estimated by the three modeling methods is low (the R² of the validation results is less than 0.45). At the same time, the applicability of three atmospheric correction methods of OLCI images (C2RCC, POLYMER and MUMM) in the eastern China seas is evaluated. The results show that compared with the other two atmospheric correction algorithms, C2RCC has better performance in each band (root mean square error is less than 0.0048 sr⁻¹). Finally, the performance of the retrieval model on satellite images is verified by the in-situ data. The validation results show that the diatoms Chl a concentration model established by SVD+MLR has better accuracy (the R² is 0.56), while the Chl a concentration inversion models of other phytoplankton groups have poor results.

Eddies in the Southern Ocean play a critical role in transporting material and heat across fronts. Scotia Sea is located downstream of the Drake Passage and is an important economic fishery area, hence study on the distribution and role of eddies in this region is of urgent importance. Based on satellite remote sensing data from 2005 to 2019, the characteristics of eddies are statistically calculated, including radius, propagation distance, and lifespan. Their spatial distribution, cross-front movement, and movement characteristics are also analyzed. Meanwhile, the internal hydrographic characteristics of eddies are analyzed based on profile data. Results show that about 92% of eddies have a lifespan shorter than 30 d, with an average radius between 10 km and 30 km. The generating location of eddies are mainly near Polar Front (PF), Southern ACC Front (SACCF), and Sub-antarctic Front (SAF), corresponding to the bottom depth ranging 3 000 m to 5 000 m. Large values of eddy kinetic energy (EKE) concentrate between PF and SAF due to the obstruction of the submarine ridges, and EKE reaches a significant positive anomaly after 2016. The number of equator-ward eddies is dominant in the eddies across PF and SACCF, with most being cyclonic eddies. Anticyclonic eddies are dominant in poleward eddies. The internal hydrographic structures of eddies show that temperature and salinity are relatively low in the subsurface layer of the cold eddies, consistent with the characteristics of water masses at high latitudes. While they are relatively high in the subsurface layer of the warm eddies. It suggests that cold eddies may carry water from high latitudes to low latitudes and warm eddies may carry seawater from low latitudes to high latitudes. This study provides a basis for further understanding of the characteristics of eddies in the Scotia Sea and their effects on the distribution of biological populations and material and energy transport.

In this paper, using the equatorial beta-plane approximation of the linear barotropic perturbation equations and introducing the reduced gravitational acceleration, we obtain the analytical solutions of anomalous equatorial ocean stationary wave and give the calculation results of the solutions. Then we compare the results with the modes of complex EOF analysis about abnormal circulation of the real tropical Pacific Ocean and Indian Ocean. The main conclusions are: in the first mode of anomalous equatorial ocean stationary wave, the current disturbance throughout the whole ocean is the half wave, which appears as the consistent zonal flow. The maximum disturbance appears at the middle of the tropical ocean and decays rapidly from equator to north and south, which is restricted in about 2 degree range on both sides of the equator. In the second mode, the current disturbance throughout the whole ocean is the full wave and has the opposite flow direction at east and west of the ocean. The degree of the attenuation of the current disturbance from equator to north and south is as that of the first mode. Anomalous equatorial ocean stationary wave meets the boundary conditions of the east and west coast directing along the longitude. The coefficient is inversely proportional to the square root of the product of the reduced gravity acceleration and the upper water standard depth, which determines the decay rate of anomalous equatorial ocean stationary wave on both sides of the equator. If the square root values take the same, the decay rates are the same. The oscillation frequency of anomalous stationary wave is proportional to the modal number and the square root values, which is inversely proportional to the width of tropical ocean. The modal number is lower and the width is larger, the frequency is lower and the corresponding oscillation period is longer; the first mode of the oscillation period is the longest. Taking every parameters as the typical values and the modal number as one, then taking the width of the equatorial Pacific Ocean and Indian Ocean respectively, the calculation results show that the spatial distribution and interannual variability of the first mode are the same as the corresponding mode of the real abnormal circulation obtaining from the complex EOF analysis; this means that the nature of the first mode above is the anomalous equatorial ocean stationary wave and the anomalous stationary wave is one of the generating mechanism of ENSO and IOD.

Three monthly altimeter datasets of the Arctic Ocean are compared in this paper. The datasets provided by the Centre for Polar Observation and Modelling (CPOM) and Technical University of Denmark (DTU) are found to be consistent with each other and due to their high spapce coverage, are more suitable for the study of the sea level variation in the Arctic Ocean, the former is better in terms of spatial resolution, smoothness, and consistency with the tide gauge observation. Based on the data of both altimeter and tide gauge, the temporal and spatial characteristics of sea level in the Arctic Ocean are analyzed and the results show that the climatological sea level in the Arctic Ocean is represented by the striking contrast between the high values in the Canadian Basin and low values in the Eurasian basin. The variation of sea level in the Arctic Ocean is dominated by the seasonal variability and low-frequency variability associated with the Arctic Oscillation, large amplitudes of both the seasonal and inter-annual sea level variability are found in the Canadian Basin, and large seasonal variability occurs along the coast of Russia. During the period 2003−2014, the mean sea level of the Arctic Ocean is rising with the largest rising rate is found in the Canadian Basin, while the sea level in the Russian coastal area is declining slightly. It is also found that large uncertainty exists in the altimetry products of the Canadian Basin and the coast of Russia, as the difference both between altimetry products and between altimeter and tide gauge data cannot be ignored, data in these areas should be used with caution.

Based on the Typhoon Hato in 2017, the Himawari-8 AHI infrared radiance data are assimilated under the clear-sky condition in WRFDA system to investigate its impact on the typhoon forecast. The structure, strength, as well as the track forecasts are also studied for the Typhoon Hato. The results show that the clear-sky assimilation of Himawari-8 infrared radiance data provides obvious increment of cyclonic winds in the typhoon core and an obvious increase of typhoon in background field. Compared with the control experiment without assimilating Himawari-8 AHI infrared radiance data, the experiment that assimilates Himawari-8 AHI data strengthens the wind field of Typhoon Hato, 500 hPa pressure field analysis, and typhoon cyclonic circulation. In addition, the AHI radiance assimilation further improves the forecast of track, minimum sea level pressure, and the maximum wind speed of the Typhoon Hato. The average track error, the precipitation distribution, the root mean square error against the conventional data are also improved.

Based on the data of Philippine shallow strata profile, combined with the sample data and borehole data in this area, this paper has a preliminary understanding of the shallow sediment characteristics of Kyushu-Palau Ridge and the West Philippine Basin and Parisi Vera Basin adjacent to the ridge. There are generally three wave impedance interfaces below the seabed, and the reflection characteristics of the shallow stratum profile are divided into four basic types. The causes of the profile characteristics are preliminarily discussed. It is believed that the sediment supply, tectonic activities, topography and hydrodynamic conditions play an important role in the deep-water sedimentation during the sedimentation process. Besides being influenced by the main control factors, most of them are also superimposed with the transformation effects of various factors in the later period. In this paper, the sedimentary characteristics and controlling factors of shallow strata in Philippine Sea are analyzed, which can provide useful reference for further study of deep shallow sediments in Philippine Sea.

Morphodynamic relationships between fringing reefs and back-reef beach play key roles in understanding the evolution of coral coasts. The fringing reef coasts of Leizhou Peninsula, in Xiluo Port, Xuwen, are taken as the research object in this paper. RTK-GPS and unmanned-surface-vessel are used to measure and analyze the topography of the beach profile and reef as well as the sediment sampling in beach. FUNWAVE-TVD is used to simulate and analyze the hydrodynamic process of short wave and infragravity wave cross the different reef. The results show that the reef topography in the study area has significant effects on the morphology of back-reef beach. Whether the nearshore wave energy dominated by the short wave band or the infragravity band is controlled by the topography. In the narrow reef, there is a predominance of infragravity energy near the back-reef beach. The dominated wave band in the nearshore wave energy is the main factor shape the back-reef beach equilibrium profile. However, the beach equilibrium profile model of coral coast proposed by Muñóz-Pérez did not take this factor into account, it need to further research.

We presented an optimized and purification procedure as well as an analytical method for Cu and Zn isotopes measurement in marine sediments. We reported Cu and Zn isotope of 5 samples in a sediment cores and 20 surface sediment samples in the northern and southern Okinawa Trough. Anion exchange resin (AG MP-1M) was applied to separate matrix elements of sediment samples from Cu, Fe and Zn using 8.2 mol/L HCl+0.01% HF+0.001% H₂O₂, 2 mol/L HCl+0.001% H₂O₂ and 0.5 mol/L HNO₃ as eluents. The recoveries of Cu and Zn were both close to 100%. Cu and Zn isotopes were measured on a Nu Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Instrumental mass bias was corrected using a combination of sample-standard bracketing and internal spiking. The long-term reproducibilities were 0.11‰ (2SD) for Cu isotopes and 0.09‰ (2SD) for Zn isotopes. The δ⁶⁶Zn of surface sediments varies from 0.07‰ to 0.67‰, with an average of 0.31‰ ± 0.32‰ (2SD); the δ⁶⁵Cu of surface sediments ranges from −2.26‰ to −0.52‰, with an average of −1.21‰ ± 0.55‰ (2SD). The results show that Cu and Zn isotopes of surface sediments in the Okinawa Trough varies widely, meanwhile, Cu and Zn isotopes in sediment core varies with depth.