In this study, hydrodynamic characteristics of transformation and breaking processes of the undular tidal bore on the uneven seabed have been numerically investigated by applying a nonhydrostatic numerical wave model (NHWAVE). Effects of tidal bore height, initial water depth and bed slope on the hydrodynamics of tidal bore are discussed in detail. Research findings indicates that the tidal bore height and initial water depth have significant effects on the transformation and breaking processes of the undular tidal bore on the uneven seabed. However, different bed slope on the undular tidal bore hydrodynamic characteristics of the influence of less. The existence of bed slope can lead to a significant increase in the height of the undular tidal bore, causing dramatic changes in the maximum water level along the range, and make the tidal bore propagation speed is reduced. The average speed of water depth tends to increase with the tidal bore height, as well as the height difference between the upstream and downstream tidal bore height. When increasing the water depth, the tidal difference between the upstream and downstream tidal bore height decreases, and the surface velocity decreases monotonically with the average velocity of water depth. The research findings drawn from this study can have certain reference significances for the accurate understanding of the hydrodynamics of tidal bore on the uneven seabed. It provides a scientific basis for the engineering design and safety assessment of wading buildings in the tidal river section.

Polar ships always collide with various types of sea ice in varying degrees during their voyages in ice-covered regions, so sufficient fatigue strength reserves are essential. This paper proposes a cumulative damage analysis method for ice-induced fatigue on polar ship structures based on field measured ice loads. Firstly, according to the statistical analysis of the field data of ice thickness and sailing speed of RV Xue Long during the China’s 8th Arctic Scientific Expedition, ice-induced fatigue conditions are constructed within the ice thickness range of 0.5−2.5 m and the sailing speed range of 2−12 kn. The joint probability distribution of the two parameters is taken as the occurrence probability of fatigue conditions. Then, the time histories of ice loads under typical conditions are identified based on the support vector machine method. The key positions and corresponding hot spot stresses are determined by dynamic analysis. The rainflow counting algorithm is adopted to count the number of stress cycles. Finally, the fatigue damage during the voyage is further calculated by S-N curve and Miner linear cumulative damage theory, which verifies the ice navigation safety of RV Xue Long. This paper has certain reference significance for the ice-resistant design and safety evaluation of polar ship structures.

Fully integrating the use of satellite remote sensing and in-situ observation information to build a high-quality underwater temperature and salinity fields is a frontier topic in the development of marine scientific research. Currently, the vast majority of assimilation systems use assimilation schemes that require the assumption that elements have some artificially predetermined relationship between the surface and underwater. As a result, the temperature and salinity analysis field was more man-made and could not objectively reflect the real state of the ocean. This paper proposed a scheme that did not make any relationship assumptions, only relied on the complementary effects of different types of observation data in time and space, and combined the satellite remote sensing and in-situ observations for spatio-temporal four-dimensional multiscale objective analysis. Compared with the experimental results of assimilating these two types of observation data separately, it was found that the method could not only obtain more accurate temperature and salinity profile structure characteristics, but also reflect the detailed information of the mesoscale changes in the sea surface, the multi-scale information in the observation data was extracted to the maximum, and the effect of “1 + 1 > 2” was realized, and constructed a completely objective temperature and salinity analysis field. The results also showed that assimilating satellite remote sensing sea surface salinity data can effectively improve the analysis of temperature and salinity, which proved that the role of satellite remote sensing sea surface salinity observation on temperature and salinity assimilation could not be ignored.

In order to quickly obtain a large-scale, quasi-real-time internal structure of the ocean, sea surface remote sensing data are widely used to construct the vertical structure of the temperature profiles, but satellite remote sensing can only obtain relatively accurate ocean surface or near-surface data. In order to improve the accuracy of temperature profile inversion, this paper takes the depth-fixed temperature as the constraint, and the nonlinear mapping between the temperature profiles and the sea surface remote sensing data such as sea surface temperature (SST) and sea level anomaly (SLA) is generated through the radial basis function (RBF) neural network, and discuss the theoretical basis for constrained depth selection. The inversion results of the temperature profiles in the South China Sea show that the first empirical orthogonal function (EOF) coefficient can characterize the vertical displacement of the thermocline. And there is a strong correlation between the temperature at the depth corresponding to the extreme point of the first EOF and the first EOF coefficient. Therefore, when the temperature at this depth is added as a constraint, the inversion accuracy of the thermocline is about 0.35℃ higher than that of only using sea surface remote sensing data, and the mean root mean square error of temperature profile inversion is about 0.33℃.

Based on the statistical data of direct economic losses of typhoon storm surge in China from 1989 to 2021, the economic losses of storm surge disasters in China during 32 years showed a significant downward trend, showing a thick-tailed distribution as a whole, and a normal distribution after logarithmic processing. The periodic changes of the direct economic losses of typhoon storm surge in China were analyzed by Morlet wavelet analysis method. According to the t-test, there were two quasi-high-frequency oscillations in the whole region, 1−2 years and 7−8 years oscillation , but the annual cycle gradually shortened to 3−5 years with the change of time. It indicated that the economic loss sequence of storm surge had high-frequency oscillation and multi-period nested low-frequency oscillation. On this basis, Daubechies wavelet decomposition was used to separate high frequency signal and low frequency signal. According to the results of root mean square error (RMSE) and signal-to-noise ratio, Daubechies wavelet base was set the vanishing moment is 7 and the number of decomposition layers is 2 for the direct economic loss time series of typhoon storm surges in China from 1989 to 2021, which had the optimal decomposition and reconstruction effect. Based on the results of stationarity test and white noise test of wavelet coefficients of each decomposition layer, the combined wavelet decomposed−ARMA model was established. The simulation accuracy and prediction accuracy were both better than that of single Autoregressive Integrated Moving Average model and Fourier series expansion model, which verified the reliability and superiority of wavelet decomposition method for rapid assessment of economic loss of typhoon storm surge in China.

Red tide is a major marine ecological disaster in China. Effectively monitoring the occurrence and spatial distribution of red tide is of great significance for their prevention and control. Traditional red tide monitoring is mainly conducted by watercolor satellites with low spatial resolution. However, there are monitoring blind areas for frequent small-scale red tides. GF-1 WFV remote sensing images, featuring high spatial resolution and a wide imaging range, can be used to monitor small-scale red tides. However, the traditional method for watercolor satellites cannot be used for GF-1 WFV satellite data as GF-1 WFV remote sensing images are characterized by low spectral resolution and few bands. And it is hard to extract the information about red tide as they differ in both shape and scale. Due to diverse shapes of the red tide distribution, this paper proposes a scale-adaptive red tide detection network (SARTNet) for GF-1 WFV sensing images. This network adopts a two-layer backbone structure to integrate the shape and detail features of red tide and introduces an attention mechanism to model the correlation between features of red tides at different scales, thereby improving its performance in detecting red tides that are complexly distributed. The experimental results show that the red tide detection performance of SARTNet is better than that of the existing methods, with an F1 score above 0.89; and it is less affected by environmental factors, with few missing and misstated pixels for red tide information at different scales.

Estuaries are the main channels for land-derived pollutants to enter the sea. Under the background of rapid global climate change and intensified human activities, the flux of river pollutants into the sea has increased sharply, resulting in serious ecological problems such as water pollution and ecological damage in estuaries, bays and their adjacent marginal seas. This paper selects the Jiulong River Estuary, which is significantly affected by strong tides, extreme events and human activities, and applied a biomarker tool−coprostanol to trace the environmental fecal pollution, explore the enter the sea behavior (“to”) of fecal pollutants (“source”) in the Jiulong River Estuary after entering the river, and reveal the spatial and temporal distribution characteristics and controlled factors (“sink”) of fecal organic matter within the estuary. The study found that the estuarine runoff process and tidal action in different seasons affect the spatial and temporal distribution of fecal organic pollutants, and the tidal process has a greater impact on the occurrence of coprostanol in the water environment of the middle and upper reaches of the estuary, showing a tidal cycle of low concentration at high tide and high concentration at low tide. The occurrence characteristics of coprostanol in the land-sea transport process in the estuarine area are also controlled by the complex water body and sediment dynamic process in the maximum turbidity zone, which has a certain purification effect on fecal organic pollutants. The study also shows that the spatiotemporal distribution characteristics of coprostanol in estuarine areas are closely related to human activities by comparing the nutrient inputs from rivers such as ammonia and nitrogen dominated by anthropogenic contributions.

Most of the small rivers in the Shandong Peninsula have clear sediment sources and relatively small mineral deposition differentiation, and their study can provide regional similarities for the analysis of the sources of large rivers into the sea, as well as the characteristics of the material sources in the Shandong Peninsula for the deposition of the Yellow Sea shelf and Bohai Sea shelf. In this paper, the distribution patterns of detrital minerals in surface sediment samples taken from riverbeds, estuaries and beaches were analysed at multiple grain levels, taking the Xin’an River, a small short-source river in the northeastern part of the Shandong Peninsula, as an example. The study shows that the Xin’an River basin and beach sediments are mostly medium and fine sands, with moderate heavy mineral content in the whole sample, ranging from 1.47% to 8.19%. Twenty-seven heavy minerals and eight light minerals occur, with the main heavy minerals hornblende (41.7%), chlorite (16.7%), actinolite (10.6%) and limonite (6.7%) and the main light minerals quartz (49.0%), plagioclase (26.5%) and potassium feldspar (20.7%), which are much more abundant than the other detrital minerals in the riverbed, estuary and beach, and the mineral assemblage remains constant, with less significant variation in relative content between them, while there is a significant non-linear correlation between non-dominant mineral species and clastic grain size. Mineral species and content in the Xin’an River are controlled by the regional lithological sources, i.e. acidic and moderately acidic intrusive rocks and regional metamorphic rocks, and the relatively stable output of amphibole group minerals across the different features of the Xin’an River is responsible for their homogeneity. The short source rivers of the Shandong Peninsula are derived from similar geological features and rock types, although the types and content of detrital minerals vary. The main controlling factors for mineral composition variation are regional sources and particle size sorting, followed by sedimentary environmental differences. In contrast, the high content of mica group and carbonate minerals in a specific grain size and the low content of amphibole group minerals are the aspects that distinguish the Huanghe River from the river source materials in the northern and southern coastal waters of the Shandong Peninsula.

Seagrass coverage ratio is an important indicator reflecting the ecological status of seagrass beds. In this paper, through the design of aerial photography scheme and flight condition test, the high-resolution seagrass image map of the Dongjiao Coconut Forest sea area was obtained by using UAV aerial photography. Combined with the image classification tools of ArcGIS software and 3D tools, a new method for calculating the coverage ratio of seagrass were obtained and the coverage of seagrass was calculated. The station location of simulating survey method of the traditional seagrass coverage ratio was compared and discussed. Seagrasses in the coastal sea bed of the Dongjiao Coconut Forest are distributed on the coral reefs within 300 m from the shore with patches and intervals. Using the new method, the concentrated distribution area of seagrass at sea bed of the Dongjiao Coconut Forest is about 23 221 m², and average concentration distribution ratio is 17.79%. The distribution area of seagrass in this study area is about 16 423 m², and the coverage ratio of seagrass is 12.58%. The coverage ratio of seagrass is higher, and the ecological condition of seagrass bed is good. Sargassum is densely distributed in the southeast area of the study area, with a distribution area of 755.6 m² and a coverage of 0.5%, and grows as a single cylinder floating. By simulating the investigation station location of the sample frame method and sample line method of traditional seagrass coverage survey, seagrass coverage ratio changes with different stations, sample frame, and sample line positions changing randomly, which is the reason for the representativeness and comparability of the traditional survey results. The research results of this project have the promotion and application value in the investigation of seagrass ecological monitoring area.

The surge process, magnitude and timing are of critical importance for accurate storm prediction and warning as well as hazard mitigation. A total of 28 tropical cyclones that most affected the head Bay of Bengal during 1991−2020 are selected and simulated with interactive forces including wind, tide, wave and river discharge. The occurrence frequencies of the maximum surge cluster in the rising tide, amounting to 89.3%, mostly 3 h and 4 h before the peak tide. The larger maximum surges are associated with phase shift of storm tide from astronomical tide. The surge processes can be classified into “(quasi-) solitary wave” and “(quasi-) periodic” oscillations. The solitary-wave-like surge may last only the rising tide or both the rising tide and the falling tide. The non-linear interactions between the storm surge and astronomical tide have the same period of a semi-diurnal tide, and their amplitudes are controlled by tidal range. The surge-tide interaction curves demonstrate two types: one is “peak in rising tide and trough in falling tide”, the other is the opposite. They are 180°out of phase, i.e. 6 h for a semi-diurnal tide. The advancing direction of cyclones relative to tidal current, the tidal phase at a cyclone landfall and the formation & propagation of trapped edge surge waves are the dominant mechanism to determine the timing of maximum surges.