The coastal plain of Jiangsu Province is a fragile zone of water resources in Jiangsu Province, and groundwater salinization has become a serious ecological problem. In order to analyze the groundwater recharge and its salinity sources in the north flank of the Changjiang River Delta since Pleistocene, a 275 m deep well HYRD1 was deployed and the whole hole was continuously collected with easily soluble salt samples, geotechnical samples and water samples. Surface water, shallow and deep groundwater, and seawater samples were collected in the area. The hydrochemical characteristics of Well HYRD1 high-precision porewater were obtained by using soluble salt index combined with geotechnical index (water content, wet density, specific gravity). In order to analyze the groundwater recharge and its salt source since Pleistocene, Piper trilinear diagram, Gibbs diagram and ion ratio method were used in combination with δD and δ¹⁸O data and ¹⁴C data. The results show that the salinity of Well HYRD1 soil is mainly NaCl, and the percentage of saline soil is 25%. The saline soils are mainly distributed in the Q_p3 aquitard, Q_p2 stratum and the upper part of Q_p1 stratum. The water chemistry type of porewater is Cl-Na type (only the lower section of Q_p1 is HCO$_3^- $-Ca·Na at individual points), 7% of brackish water, 49% of saline water and 44% of haline water. The brackish water is mainly distributed in the sand layer of the lower section of Q_p1. The δ¹⁸O and δD of diving indicate that the source of diving is atmospheric precipitation and is subject to a relatively strong evaporation effect. The δ¹⁸O and δD of the aquitard pore water and pressurized water are located near the standard seawater dilution line, and the trend of δ¹⁸O and δD decreases with the increase of depth, which indicates that the porewater is subjected to the mixing effect of seawater decreases with the increase of depth. Calcareous nodules are mostly seen in the Q_p1 aquitard, indicating that the Q_p1 aquitard was subjected to strong evaporation after soil formation. The salinity of the upper part of Well HYRD1 Q_p1 and the overlying strata is mainly from the 5th stage sea erosion, evaporite and silicate weathering dissolution. The salinity of the lower part of Q_p1 is mainly from the crustal source. The groundwater chemistry is influenced by water-rock action, evaporation concentration and human activities.

Investigating the potential for application of environmental DNA to identify benthic organisms for evaluating ecological quality status collection of 17 benthic samples from the Yalu River Estuary, environmental DNA and morphological identification and comparative analyses of the resulting ecological quality assessment indices (AMBI, BENTIX, Shannon-Wiener H', M-AMBI) were used, respectively. The results show: environmental DNA identification of organisms belonging to 10 class, 16 orders, 19 families, 20 genera and 22 species, morphological identification of organisms belonging to 9 class, 27 orders, 43 families, 55 genera and 57 species, with a total of 10 organisms; the two methods of identification yielded AMBI inter-index (R = 0.428, p = 0.043, y = 0.32x + 1.08), BENTIX inter-exponential (R = 0.430, p = 0.043, y = 0.28x + 3.59) significant consistency exists, while there was significant difference between the Shannon-Wiener H' indices; the two methods of identification yielded AMBI intergrade, M-AMBI intergrade higher similarity, 51.02%, 44.90%, respectively; the AMBI and M-AMBI grades from the two identification methods were more in line with the actual situation and evaluated the overall ecological quality status of the Yalu River Estuary as good. This study demonstrates that the identification of benthic organisms based on environmental DNA to evaluate the ecological quality status has a high potential for application in marine environmental monitoring surveys.

Reliable assessment of the impact and risk of typhoons on coastal areas is very important for scientific resistance to typhoon disasters. China has a detailed typhoon observation record with a history of only 60 years, which makes it limited in estimating extreme wind speed with a long recurrence period and corresponding extreme wave height and tide level. The insufficient records also limits the application of data-driven models in typhoon disaster prediction. Therefore, it is necessary to construct synthetic typhoons based on the actual typhoon travel law to overcome the problem of insufficient historical observations. In this paper, 18 671 synthetic typhoons were constructed in the Northwest Pacific Ocean by using the Empirical Path Model based on kernel density estimation, and the parameters such as the start and end position, frequency of occurrence, travel speed and direction of the synthetic typhoons were statistically compared and analyzed with historical typhoons. The results show that the synthetic typhoon constructed based on the proposed method is generally consistent with the traveling characteristics of historical typhoons in the Northwest Pacific Ocean. Through the construction of these synthetic typhoons, a synthetic typhoon database with sufficient data and reliable performance can be provided for the study of extreme wave and storm surge along the coast of China.

Based on the satellite altimeter observation data from 1993 to 2022, this paper analyzes the temporal and spatial characteristics of the multi frequency seasonal variation signal of sea surface height in the Sulawesi sea, and gives the dynamic interpretation by using Rossby standard mode theory. The spectral analysis shows that there is a strong intra-seasonal signal of 30–90 days in the sea surface height variation of Sulawesi sea, and its average power spectral density is 13 times of the average power spectral density of the signal in half a year. These seasonal signals have discrete and discontinuous spectral peak periods, and the peaks of 54.0 d and 64.4 d are the largest, which are 28 times and 23 times of the signal of 30–90 days, respectively. The theoretical analysis shows that the existence of Rossby standard modes in the nearly closed Sulawesi deep-sea basin. The seasonal variation observed by satellite altimeter is consistent with the two-dimensional spatial structure evolution, period and westward propagation velocity of Rossby standard mode results, the superposition of Rossby standard mode solutions presents a variance distribution similar to the sea surface height variation field. This shows that the inherent oscillation of Sulawesi Sea basin is one of the important mechanisms that contribute to its intra-seasonal variation.

As a national key construction sea area, the trend of offshore wind power construction in the Jiangsu sea area towards the open sea is the main trend of future development. The open sea areas have more surge components, and the wave spectrum often appears in the form of bimodal spectrum. Therefore, the wave characteristics of bimodal spectrum waves need further in-depth research to provide reference basis for offshore construction. Based on the observation data of the buoy station throughout 2018, 1223 bimodal spectral data were obtained through outlier testing and bimodal spectral identification. The bimodal spectral characteristics of waves in the Jiangsu sea area were studied, and different typical bimodal spectral types were compared. The fitting of the measured bimodal spectra was carried out, and the corrected spectral width parameters were proposed. The dependency relationship between the correction coefficient, peak rise factor, and spectral width parameters was explored, and the bimodal spectral fitting expression was obtained. The results indicate that the Ochi–Hubble spectrum proposed based on the North Atlantic sea area and the Torsethaugen spectrum proposed based on the Norwegian sea area are not applicable to the bimodal spectrum type in the Jiangsu sea area. The bimodal JONSWAP fitting spectrum proposed in this paper has adaptability and can scientifically and reasonably describe the bimodal spectrum in the Jiangsu sea area, and is widely applied to different wind and terrain conditions in the sea area.

As potential mineral resources, rare earth elements (REY) and yttrium enriched sediments in the deep sea have attracted a lot of attention in recent years. It has been shown by studies that the enrichment process of REY is most likely to occur at the sediment-water interface (SWI), however studies on the early diagenetic processes in REY-enriched sediments are in general lacking. In this paper, we collected two short sediment cores in REY-enriched sediments in the Southeast Pacific Ocean, then we had conducted an in-depth analysis on the early diagenesis process of REY at SWI and its influence on the enrichment mechanism of REY in deep-sea sediment. The low Fe, Mn concentration and high Mo, U and V concentration in pore-water indicated that the sediment cores were in oxic environment. Compared to the REY in overlying water column, the dissolved REY in pore-water characterized by a middle rare earth elements (MREE). In sediment, phosphate phase is the main phase of REY, while the distribution pattern of REY in pore-water may be controlled by the phosphate content in sediments. Our results show that during the early diagenetic processes, the REY initially combined with Fe/Mn phase and other phases re-released into the pore-water, which is subsequently adsorbed by and eventually buried with the phosphate phase. Therefore, the early diagenetic process is an important mechanism of REY enrichment in deep sea sediments.

Wastewater is usually discharged into the sea in the form of jet, and its dilution process is the result of the interaction of jet, wave and tidal current. In this study, based on the reasonable assumptions, the governing equations are integrated to the form of ordinary differential equations. According to the hydrodynamic characteristics of the jet in the wavy current environment, the entrainment and drag force functions of the jet are introduced to close the governing equations, thus the integral model for the turbulent jet under the combined action of waves and currents is established. Through comparison and verification, it is confirmed that the integral model can accurately simulate the time average movement and dilution process of the near-field jet under the wavy current environment. It is found that compared with a pure current environment, the influence range of jet on the surrounding water is larger than that in a wavy current environment, and the dilution capacity of jet can be remarkably enhanced by the wave effect. Based on the momentum integral simulation results, the empirical fitting formulas for the position of the jet cross-sectional trajectory line and the minimum dilution in the wavy current environment are established. The developed model could be served as an efficient and accurate tool to assess the environmental impacts of submarine outfalls on the surrounding waters.

Beach nourishment, as a widely-adopted soft solution to coastal erosion, can effectively alleviate the beach erosion induced by the construction of artificial islands. This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example. Based on the bimonthly surveys of beach profiles and shorelines since nourishment, the characteristics of beach erosion and accretion and the associated driving factors were analyzed by using empirical orthogonal function (EOF) and digital shoreline analysis system methods. The EOF results showed that the first two eigenvalues accounted for more than 90% of the total variance, which could reflect the main spatio-temporal changes of the beaches. The area with conspicuous changes, corresponding to the first spatial mode, was located between the outer edge of the beach berm to the mean sea level, in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone. The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment, followed by mild profile changes. The second spatial mode demonstrated the impact of typhoons on the beaches, resulting in the accumulation and leveling of some low-lying sites on the beach berms in the wave shadow zone. This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages. The first stage was the adaptation period, during which the artificially designed beach profile adjusted to the equilibrium state for adapting to the local hydrodynamics. The equilibrium time of nourished profiles was approximately 4 months, during which beach changes were dominated by cross-shore sediment transport. The second stage was dominated by the longshore sediment transport induced by the artificial island, resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone. At that time, the nourished beach shoreline in Haikou Bay had not reached the equilibrium state. The beaches on both sides of the wave shadow zone would continue to retreat in the future, while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium. This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.

Based on the non-hydrostatic model SWASH, a numerical wave flume was established to systematically investigate the hydrodynamic characteristics of the interaction between waves, mangroves, and vertical sea dikes through a comparative experiment with and without mangroves. The study analyzed the influence of factors such as wave steepness, relative water depth, Ursell number, mangrove length, density, and characteristic diameter on the wave height in front of the sea dike and the maximum wave pressure on the windward side of the sea dike. The results indicate that in the absence of mangroves, the Goda formula cannot accurately estimate the impact load on the vertical sea dike. In a numerical experiment with a model scale of 1∶10, a 2 m-wide mangrove in front of the dike was observed to reduce wave height by 6% to 45% and wave pressure by 11% to 74%. However, in conditions with relatively large wave heights and smaller characteristic parameters of the mangrove, an increase in the wave height in front of the dike by approximately 4% to 26% was noted. In the hydraulic conditions considered in this study, the maximum wave pressure decreased by 58% to 93% with a decrease in wave steepness, by 42% to 72% with an increase in relative water depth, and by 87% to 96% with a decrease in the Ursell number. The attenuation rates of wave height and wave pressure in front of the dike non-linearly increased with the increase in the width, density, and characteristic diameter of the mangroves. These findings provide a scientific basis for a deeper understanding of the wave-damping effects of mangroves, as well as for the design and planning of coastal protection projects combining mangrove ecosystems with sea dikes.

Tidal flats maintain a complex ecosystem, while its formation is driven by multi-factor interaction, including hydrodynamics, sediment transport, and biological processes. In particular, investigating tidal flat biological processes and elucidating their biological-physical effects are current research hotspots and challenges in the field of marine science. This study focused on intertidal biofilms, constructed a two-dimensional biomorphodynamic model which coupled biofilms with hydrodynamics, sediment transport, and bed level change, to explore the role of biofilms in sediment transport and geomorphological evolution. The biomorphodynamic model was validated using literature data, indicating that the constructed model can simulate the growth pattern and interannual variation of biofilms well. Model results show that tidal creeks with biofilm attachment are more fully extended towards the landward side, showing a branching distribution when hydrodynamics are weak, and biofilms were distributed on both sides of the intertidal zone. Through quantitative analysis of tidal creek morphology, it is found that the presence of biofilms promoted an increase in the number of tidal creek and their development in the vertical direction, while limiting the increase in their width. Compared to tidal flats without the influence of biofilms, the average depth of tidal creeks increases, the total area decreases, the total length increases, the average width decreases, and the overall volume increases. The research outcome of this study deepens the understanding of the role of biofilms on tidal flat evolution and provides a scientific basis for coastal zone protection and ecological restoration projects.