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.

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.

Under the background of global climate change, the extreme storm surge events caused by tropical cyclones in the Changjiang River Estuary and adjacent coastal area present non-stationary feature. In this study, a storm surge model for the Changjiang River Estuary was constructed using the ADCIRC model to reproduce the storm surges during 241 tropical cyclones affecting the Changjiang River Estuary from 1979 to 2019. By combining the non-stationary generalized extreme value distribution with the state space approach, a statistical model for capturing the non-stationarity of extreme storm surges was built to investigate the spatiotemporal variability of the extreme storm surges in the Changjiang River Estuary and its adjacent coastal area. The statistical model can well reproduce the non-stationary feature of extreme storm surges, which was mainly represented by the time-dependent location parameter. The time-dependent location parameters at the tidal gauge stations were stationary before 2008 and presented increasing trends afterwards, which was mainly caused by the increase of the annual second- and third-largest storm surges. The reoccurrence period of storm surge event with 100-year return period under the stationary assumption was reduced to around 40–80 years, indicating an increased flood risk in the Changjiang River Estuary. Combined with the changes in the intensity and path of the tropical cyclones that caused the annual second- and third-largest storm surges, it was concluded that the increasing trends of extreme storm surges were mainly caused by the increase in the intensity of the tropical cyclone that tracking northward to the offshore of the Changjiang River Estuary and veering eastwards.

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.

Rare earth elements (REE) and their relationships with biogenic silica (BSiO₂), magnetic susceptibility, Al₂O₃ and Fe₂O₃ in Core DC-11 were analyzed to reveal sediment provenances and transport history by iceberg-current-atmosphere since 34 ka BP in the southeastern Scotia Sea, Antarctica. Temporal variation of REE is similar to that of Al₂O₃, indicating they mainly occur in terrigenous detritus and BSiO₂ has obvious dilution effect on them. Sediments with high REE concentration, flat shale-normalized pattern, weak positive Eu anomaly, and high La_N/Yb_N ratio during the last glacial period indicated they are transferred from the Weddell Sea and eroded from the bordering lands with relatively old crust. The increases in magnetic susceptibility, ΔAl₂O₃, TFe₂O₃/Eu ratio indicated an enhanced input of dust from South America during this period. In early Deglaciation (19.6−14.1 ka BP), increasing Eu positive anomaly and lower La_N/Yb_N ratio indicated the southern branch of Antarctic Circumpolar Current (ACC) strengthened and contributed more sediments from the South Shetland Islands and Antarctic Peninsula due to the southward shifts of oceanic fronts, while decreasing magnetic susceptibility, ΔAl₂O₃, TFe₂O₃/Eu ratios showed rapid decrease in dust supply from South America. During the Antarctic Cold Reversal period (ACR, 14.1−12.9 ka BP), sediments from the South Shetland Islands and Antarctic Peninsula decreased sharply due to cold condition and weakened ACC branch, the weakest Eu positive anomaly and highest La_N/Yb_N ratio indicated that the sediments from the Weddell Sea dominated in the core again, and the peak of ice raft debris indicated ice rafting is vital or dominant agent. In the late Deglaciation (12.9−11.7 ka BP), the return of ACC branch to the South Shetland Islands and Antarctic Peninsula contributed more to the sediments in Core DC-11; in Holocene (11.7−0 ka BP), the ACC branch in the area between the South Shetland Islands and Antarctic Peninsula was generally enhanced, and its contribution to core sediments increased to be roughly equivalent to the amount of sediments from the Weddell Sea.

Occasional species are vulnerable to external threats such as environmental changes and human activities and have important values in biodiversity conservation. However, due to their limited availability of data and associated difficulties in statistical analysis, there are few studies on the spatial distribution and their relationships with environmental factors. In this study, based on the fishery resource surveys in the Haizhou Bay conducted from 2013 to 2019, we analyzed the relationships between the distribution and environmental factors for three occasional species, Coilia mystus, Odontamblyopus rubicundus and Erisphex pottii, using generalized additive model (GAM) and random forest (RF) model. The models were compared according to their goodness of fit and the predictive performances were evaluated using cross-validation. The results showed that depth was the most significant factor affecting the distribution of C. mystus and O. rubicundus in spring and autumn, the sea bottom temperature was the most important environmental factor influencing the distribution of E. pottii in autumn. The distribution model of C. mystus had the highest deviance explanation, followed by O. rubicundus, and E. pottii had the lowest deviance explanation. The deviance explanation by the distribution models of C. mystus, O. rubicundus and E. pottii were all lower in spring than in autumn. The cross-validation showed that the area under the curve (AUC) of the three species ranged from 0.70 to 0.85, and only the AUC of C. mystus reached 0.9 in autumn; meanwhile, the AUC of the GAM prediction results were larger than those of the RF model, indicating that the prediction performance of the GAM was better than that of the RF model for the occasional species. This study would provide a reference for the selection of models for future studies of occasional species, and have guiding significance for the conservation of the occasional species.

As a frontier subject of nonlinear science, wave-current interaction has been studied by many scholars. This paper will explore the wave-current interaction under the serious sea conditions in the Northwest Pacific during the influenced by No.1 super Typhoon “Nepartak” in 2016. The results indicate that wave-current coupling model can effectively improve the simulation accuracy of significant wave height (SWH) under serious sea conditions. The influence of wave-current interaction on SWH is closely related to the angle between wave direction and sea surface current direction: when wave direction is close to current direction, wave-current interaction will decrease the SWH; in those areas where the wave and the current have the opposite direction, wave-current interaction will increase the SWH; the closer the angle between the wave and the current is to 90°, the less influence wave-current interaction has on the SWH. The maximum SWH difference whether including wave-current interaction or not is about 1.5 m.

Based on the tide level data along the tidal reach of Xijiang River from 2015 to 2017, we applied the nonstationary tidal harmonic analysis model NS-TIDE to study the spatial and temporal variation characteristics of the amplitude and phase of different cycles of tidal constituent, the change of tidal dynamics composition and tidal wave deformation characteristics, and discussed the causes of tidal level deformation and the reversal of the lowest low waters along the tidal reach. The results show that, unlike the diurnal constituent and semi-diurnal constituent along the tidal reach that have amplitude decay and phase increment, the shallow water component amplitude increases and then decreases, the amplitude of MS_f is increasing, and the phase is changing alternately; the decay rate of each tidal amplitude is higher in the flood season than in the dry season, and the phase changes more in the flood season, indicating that the tidal wave propagates upstream more slowly under the top support of river discharge. Due to the influence of river discharge and topography, the amplitude of MS_f is larger in the flood season and upstream section of the river, and the tidal dynamic composition changes from the main tidal constituent to the secondary tidal constituent; the change of amplitude ratio of M₄ and M₂ indicates significant tidal deformation, and the reversal of the lowest low waters when the amplitude ratio of MS_f to M₂ and S₂ is relatively large.

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℃.

The flume experiment is commonly used to investigate the wave propagation deformation and the stability of the breakwater armor block, with the wave elements changing along the longitudinal direction of the flume while remaining unchanged in the cross direction perpendicular to the flume. However, when the wavelength has a certain relationship with the flume width, visible cross fluctuations may occur. In this paper, the analytical expressions of longitudinal wave along the flume direction and cross wave perpendicular to the flume direction on an exponential symmetric shoal are derived respectively based on the linear long wave equation. The longitudinal waves on symmetric exponential topography in the flume can be expressed as the first and second kinds of first order Bessel function, and the complete solution can be obtained by combining with the conditions of free surface and velocity continuity. Cross waves with even symmetric and odd symmetric modes in the flume with an exponential symmetric shoal can be expressed as the first kind of ν order Bessel function. The even symmetric (n, m) mode has n nodal lines along the direction of the flume and 2m nodal lines perpendicular to the direction of the flume; odd symmetric (n, m) mode has n nodal lines along the direction of the flume and 2m−1 nodal lines in the cross direction.