In the real sea state, the differences in directions of component waves result in three-dimensional short-crested waves, which have many different characteristics compared to two-dimensional long-crested waves. Therefore, in present study, the whole generation and evolution processes of short-crested freak waves are experimentally simulated by dispersive and directional focusing of component waves, in order to examine the external features and relationship of the abnormal large waves occurring during the processes. The results indicate that the abnormal large wave evolves symmetrically along the peak wave direction and undergoes a three- or four-stage process, each stage is indicated by the characteristic parameters of the abnormal large wave, it implies that the characteristic parameters can be used to identify the stage which the large abnormal wave is in and predict the variation tendency; and that compared to the two-dimensional cases, the “wave group” and “deep trough” stages are likely to be skipped, as a result, the spatio-temporal spans of the generation and evolution processes are smaller for the three-dimensional cases, it implies that in three-dimensional wave fields, the deep troughs and successive large waves (wave group) associated with freak waves may have a low probability of occurrence.

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.

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.

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.

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.

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.

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.

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.

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.

When the wharf project of Tieshan Port in Beibu Gulf was constructed, nearby mangrove plants were damaged. A coupled model of hydrodynamic force and sedimentation in the gulf including mangrove intertidal zone based on remote sensing enhancement was built. Impacts of the wharf on the tide, sediment transport, erosion and deposition in the mangrove zone were evaluated. Results showed that the model can make full use of the tidal simulation information in the South China Sea and can finely simulate the sediment transport principle nearby the wharf. In association with information fusion technology of remote sensing inversion of the cover probability of global surface water and local tidal levels, elevation data in mangrove zone were reliably obtained. The tides mainly in the southern of the mangrove zone were influenced by the wharf. The velocity decreased at the most rising tide, and that in the tidal channel increased at the most ebb tide. When the way to the wharf was transferred using a steel trestle, the velocity in the southeast of the mangrove zone increased slightly. During the construction period of the wharf, the increase of suspended sediment concentration varied from 20 mg/L to 50 mg/L in the range of 69% and 72% of the mangrove zone. Before the wharf construction, the average sediment deposition in the mangrove zone accounted for 0.27 cm/a. For two designed ways to the wharf, i.e. the road isolating tide and the steel trestle allowing tide passing, the average deposition accounted for 0.45 cm/a and 0.36 cm/a with the range of 96.6% and 89.3% in the mangrove zone respectively. Provided that the steel trestle to the wharf would be selected, the average increment of the deposition in the mangrove zone decreased by 50%. The conclusions can provide the scientific basis for the simulation of tide and sedimentation in intertidal zone and the decision of the mangrove protection.