Coastal wetland ecosystems have important carbon sink function. Human life, industrial and agricultural production will input heavy metals into wetlands, however, the impacts of heavy metals on various soil carbon components are still unclear. Based on the comparison of the soil carbon component content in the different types of coastal wetlands in Yueqing Bay of southern Zhejiang Province, it was found that the contents of soil organic carbon (SOC), easily oxidizing organic carbon (EOC) and dissolved organic carbon (DOC) in the adult mangroves, young mangroves, Spartina alterniflora salt marshes and mudflats presented the significant regional and inter-habitat differences. Soil total carbon (STC) and microbial biomass carbon (MBC) presented the significant regional differences. By monitoring the spatial distribution of heavy metals, the results showed that the contents of Cd, Pb and Hg in the coastal wetlands adjacent to industrial/agricultural lands and residential area were higher than those in the non-disturbed areas. Correspondingly, the contents of STC, SOC and EOC of the high-disturbed wetlands were lower than those of the non-disturbed wetlands. Furthermore, the results of redundancy analyses (RDA) showed that the STC, SOC and EOC contents were significantly negatively correlated with the Hg and Cd content in the S. alterniflora salt marshes; the SOC and EOC contents were significantly negatively correlated with the Pb and Zn contents in the adult mangroves; the STC, SOC and EOC contents were significantly negatively correlated with the Pb and Cr contents in the young mangroves; and the STC, SOC and EOC contents were significantly negatively correlated with the Cd and Cr contents in the mudflats. This reflects that the increased heavy metals might cause a negative impact on the soil carbon pool. However, the RDA analysis indicated that the MBC content was positively correlated with some heavy metals, probably reflecting the adaptability of the microbial community in the coastal wetland to the low content of heavy metals. The results of this study can provide scientific basis and data support for the environmental quality assessment and natural carbon sink management of coastal wetlands in Zhejiang Province.

The Western Pacific is characterised by high species diversity. However, limited studies have been carried out in the past, particularly in terms of biology in the Western Pacific seamount region owing to its unique geography. Therefore, it is important and necessary to carry out zooplankton species diversity study in this region. In this study, 15 dominant zooplankton species (Pleuromamma robusta, Nannocalanus minor, Haloptilus longicornis, Corycaeus speciosus, Scolecithrix danae, Euchaeta rimana, Chelophyes appendiculata, Bassia bassensis, Eudoxoides mitra, Abylopsis eschscholtzi, Abylopsis tetragona, Sagitta enflata, Sagitta pacifica, Paraconchoecia oblonga, Thalia democratica) collected by macroplankton net from eight stations in the Western Pacific seamount region were microscopically photographed, morphologically described, and their geographical distribution and ecological habits were analysed. This study provides a scientific basis and reference for more in-depth future studies on the composition, distribution, origin, dispersal, zonation and geographic characteristics of marine zooplankton species in the Western Pacific.

Deep-sea seamounts are known as hot spots of marine biodiversity, supporting a high richness of deep-sea biological communities. However, a key question in deep-sea ecology remains: how do benthic communities on these seamounts thrive despite the limited availability of food sources? To explore the food sources of the megabenthic communities from a deep seamount (the Weijia Guyot) in the oligotrophic open ocean, we measured the stable isotope values (δ¹³C and δ¹⁵N) of eight representative benthic groups (Porifera, Anthozoa, Gammaridea, Asteroidea, Crinoidea, Ophiuroidea, Holothuroidea and Tunicate) as well as two potential food sources (zooplankton and surface sediments). The results showed that the δ¹⁵N values of zooplankton increased with water depth. The δ¹⁵N value of surface sediments were 7.7‰. The δ¹³C and δ¹⁵N values of benthos exhibited a wide range of variation (δ¹³C: -22.9‰ to -15.1‰, δ¹⁵N: 8.3‰ to 19.2‰). The differences in δ¹⁵N values between zooplankton, surface sediments, and some benthic species were approximately equivalent to one trophic level, suggesting that they might serve as direct food sources for some megabenthos. However, the substantial variation in δ¹³C and δ¹⁵N values among different megabenthic species indicated that additional, unidentified food sources also likely contribute to their diets. This study provides a preliminary analysis of carbon and nitrogen isotope variations among the major benthic communities of deep-sea seamounts and explores their possible food sources. Our findings offer valuable insights into the food web and trophic structure of deep-sea seamount ecosystems, make contributions to a better understanding of the function of this unique environment.

Oyster reefs are one of the important coastal habitats. Over the past century, oyster reefs have been severely degraded worldwide. However, with the gradual recognition of the irreplaceable ecosystem service functions of oyster reefs, the significance of oyster reef conservation and restoration has become prominent in the global efforts to restore and protect degraded coastal ecosystems. This study systematically collects and collates the distribution information of natural oyster reefs and artificially restored oyster reefs in China, summarizes the main work and achievements in the field of oyster reef conservation and restoration in China since the beginning of this century. Combined with the author’s practical experience in the Wenzhou coastal zone protection and restoration project (oyster reef), the technical process of restoration is described in detail, with emphasis on the design and structure of the inclined support composite oyster reef and the artificial seedling attachment technology used in the restoration project. Corresponding suggestions are put forward, which can provide references for future oyster reef conservation and restoration work.

Given the underutilization of elemental geochemistry in paleoenvironmental and sea-level studies during the Late Pleistocene in southern Hangzhou Bay, this research employs an integrated approach using core NZD01. Combining sedimentological analysis, grain-size distributions, and key geochemical proxies (Sr/Cu, CIA, CIW, Sr/Ba, 100×(MgO/Al₂O₃), U/Th, Ni/Co) with AMS ¹⁴C dating and correlation of magnetic susceptibility with speleothem δ¹⁸O records, we aim to reconstruct the sedimentary evolution sequence and its responses to climate-sea level interactions. Five sedimentary facies were identified: fluvial channel, floodplain, estuarine, shallow marine and modern estuary. Grain-size characteristics indicate a hydrodynamic evolution process: from strong to relatively weak, then to stronger and more complex, followed by weak and stable, and finally to moderate conditions. Geochemical indicators reveal: (1) Sr/Cu ratios document a distinct paleoclimatic transition from arid to warm-humid and finally to semi-arid conditions with frequent humidity-aridity oscillations since the Late Pleistocene; (2)CIA and CIW values indicate weathering intensity variations: moderate weathering phase, moderate-dominated phase with localized intense weathering,moderate weathering recurrence, generally moderate phase with intermittent primary weathering, and transition from moderate to primary weathering(frequent fluctuations); (3) Sr/Ba and 100×(MgO/Al₂O₃) demonstrate rising paleosalinity responding to Last Deglaciation transgression; (4) U/Th and Ni/Co ratios suggest overall oxidizing conditions, with Ni/Co peaks in Unit I potentially marking extreme marine events. This study demonstrates that element geochemical approaches effectively reveal the evolutionary sequence from continental to marginal marine environments and their responses to climate-sea level fluctuations in this region.

The new seawall ecological armour block is a type of face protection structure with both excellent wave dissipation performance and ecological function. In order to systematically evaluate its wave dissipation performance, this study carried out a two-dimensional wave flume physical modeling test using Zhoujiayuanshan Island in Zhoushan as the engineering background. The test systematically investigated the effects of wave period, wave height, relative water depth, wave steepness, breaking parameter, and block geometry (outer diameter and height), as well as model materials on the reflection coefficients under the action of regular waves. The results show that: firstly, the feasibility of using polypropylene random copolymer (PP-R) instead of foamed concrete in the physical modeling test is verified through the comparison experiments of nine working conditions, and the average difference in their reflection coefficient is only 1.17%. Secondly, for its wave dissipation performance, the reflection coefficient increases with increasing wave period, relative water depth and breaking parameter, and decreases with increasing wave height and wave steepness. Among all the tested conditions, the two types of blocks with outer diameter 7.5 cm-height 10 cm and outer diameter 10 cm-height 6.5 cm have the best wave dissipation performance, with average reflection coefficients of 0.395 and 0.382, respectively. Finally, the reflection coefficient formula for the six types of blocks is fitted based on the experimental data in this study. The formula has a root mean square error (RMSE) of 0.106 9, which is of high accuracy and our study can provide a certain reference for related engineering design.

Accurate assessment of tidal flat erosion and deposition dynamics is very important for coastal zone resource management and disaster prevention and mitigation. However, due to the solidification of artificial shorelines and the time-lag effect of tidal flat profile evolution, the methods based on shoreline transition often have great uncertainty in evaluating tidal flat morphology and dynamics, and the analysis of the internal mechanism is also relatively insufficient. In this study, synchronous hydrological-sedimentary-geomorphological dynamic measurements were carried out for 19 consecutive tidal cycles in the upper, middle and lower intertidal zones on the Dafeng tidal flat on the coast of Jiangsu in May 2021. A sediment conservation model was constructed to quantitatively analyze the transport process of sediments during the observation period and its relationship with the dynamic changes of tidal flat landforms. The results show that the erosion and deposition changes estimated based on sediment budget are basically consistent with the measured elevation changes, which verifies the effectiveness of this method in describing the tidal flat landform dynamics. In addition, the analysis also shows that high energy dynamics (such as spring tide and strong wind wave) are the main driving forces of tidal flat erosion. This study can provide a new empirical basis and method support for the research and scientific management of tidal flat landform process.

Optical survey and evaluation of deep-sea polymetallic nodules face challenges such as low contrast, small object detection, and boundary ambiguity. This study proposes an improved Mask R-CNN model incorporating dynamic sparse convolution (DSConv) and simple parameter-free attention module (SimAM) for nodule image segmentation. SimAM effectively suppresses sediment background interference, while DSConv alleviates boundary blurring. The combined model achieves an accuracy of 91.5%, precision of 78.0%, recall of 75.1%, and IoU of 69.4%. When applying the improved model and the original model to the actual survey lines, it was found that in the identification results of the seabed nodules coverage rate, the proportion of data with an error less than 5%, increased from 57% of the original model to 77% of the improved model. This research can provide a reliable technical solution for the calculation of deep-sea polymetallic nodule coverage rate, and its modular design can also be extended to other fields of target recognition and image segmentation.

To assess the potential impact of plumes generated by deep-sea mining on the midwater ocean, this study systematically analyzed the flow field characteristics of the intermediate currents at the 1 000 m and 2 000 m in deep-sea mining areas of the Pacific Ocean (Western Pacific: Block C, Block M, Block CW, Block WJ; Eastern Pacific: Block A5, Block KW, Block EK, Block A12678, Block A3, Block A4) and predicted the zonal movement trend of midwater plumes. The analysis was based on the global Argo float trajectory and mid-depth current dataset from the China Argo Real-Time Data Center covering the period from August 1997 to October 2024, combined with data from 3 moored observation stations. The results show that: (1)The currents at the 1 000 m layer in the Pacific mining areas are mainly controlled by zonal currents, with the velocity of eastward jets being greater than that of westward jets. The velocity and direction of currents in the mining areas are sensitive to changes in latitude. (2)The eastward jets that affect the 1 000 m flow field in the Western Pacific mining area have the center located at 14°N (weak) and 18°N (strong). Under their influence, in the southern part of the Block M, the midwater plumes move eastward. In other areas, the midwater plumes move slowly westward.(3) The eastward jets that affect the 1 000 m layer of the Eastern Pacific mining areas have the centers located at 7°N and 9°N. They are stronger in summer and autumn, and weaker in winter and spring. (4)The flow field directional characteristics in the 2 000 m area of Block M, Block A5, Block KW and Block EK are the same as those in the 1 000 m layer, indicating that the depth affected by jets can reach 2 000 m.

Ocean waves are a fundamental component of marine dynamics, exerting significant impacts on maritime navigation and offshore operations. The wave spectrum provides an effective representation of the statistical distribution of wave energy across the frequency domain. In this study, observational data from 70 NDBC buoy stations were used to retrieve significant wave heights based on both the JONSWAP spectrum and the third-order Stokes nonlinear spectrum. Results show that, compared with the JONSWAP-based retrievals, the nonlinear spectrum achieves average improvements degree exceeding 10% in both absolute and relative errors, with maximum improvements degree of 28.54% and 22.29%, respectively, demonstrating the nonlinear spectrum’s clear advantages. Further analysis indicates that the performance degrees of the nonlinear spectrum are closely related to significant wave height, wind speed, the angle between wind and wave directions, and water depth. Specifically, the improvement degree increases with larger wave heights and stronger winds; smaller directional angle between wind and waves yields greater benefits, though wind speed exerts a much stronger influence than directional angle. In water depths shallower than 500 m, the inversion accuracies of both wave spectras are higher than those in depths deeper than 500 m. However, within the depth range of 500-5 500 m, the improvement degree in the nonlinear spectrum exceeds that in the shallow-water region, showing a linear increasing trend.

In 1988, the tropical Pacific experienced a strong La Niña event, during which significant equatorial Pacific easterly wind surges were observed. Analysis based on reanalysis data indicates that the intensity of the 1988 surges reached the highest level during 1982-2020. Linear regression results show that the equatorial Pacific SST gradient contributed 70.59% to the surge intensity index in 1988. Further examination of wind field characteristics after removing the influence of the SST gradient reveals that, apart from the enhanced spatial extent of the surge event in late February, both the frequency and magnitude of surges decreased significantly from mid-March onward. To gain deeper insight into the specific causes of the easterly wind surges, a typical case analysis was then conducted to investigate the triggering mechanism of a representative event. Composite analysis confirms that the strong easterly wind surge at the end of March 1988 was closely linked to the convectively active phase of a Madden-Julian Oscillation (MJO) event over the Maritime Continent, which contributed approximately 42.96% to the surge’s formation.

The carbon sink capacity of muddy tidal flat plays a significant role in coastal blue carbon ecosystems. Microalgae, as the main primary producers in these habitats, are key contributors to carbon sequestration and storage. However, the community composition and carbon stock of microalgae in China’s muddy tidal flats remain poorly understanding. Here, microalgae samples were collected from muddy tidal flat of Aiwan Bay, Wenling, Zhejiang Province in August 2021. The microalgae were identified using an inverted microscope, and their carbon stock was estimated based on cellular biovolume measurements. A total of 59 species from 4 phyla were identified, with diatom being the overwhelmingly dominant group. The most abundant genera included Coscinodiscus, Nitzschia, Gyrosigma, and Synedra. The abundance and biomass of microalgae showed pronounced spatial heterogeneity across sampling sites, likely influenced by terrestrial inputs. In addition, tidal creeks caused by strong outflow from water gates might have affected the settlement and resuspension of microalgae. Based on biomass calculations, the regional microalgal carbon stock in muddy tidal flat of Aiwan Bay was estimated at approximately 2 134 t, with approximately 60% derived from settled planktonic microalgae. This study underscores the significant impact of phytoplankton on microalgal community composition and carbon storage. These findings provide valuable insights for assessing carbon sinks in muddy tidal flats and contribute to a better understanding of blue carbon dynamics in coastal ecosystems.

Mangroves are among the most effective carbon sequestration ecosystems on earth, which is crucial in addressing global climate change and achieving China’s “dual carbon” goals. This research focused on the Yanpu Bay mangroves in Zhejiang, where surface (0-25 cm)sediment samples were collected in the spring and autumn of 2018-2019 to analyze organic carbon, total nitrogen, total phosphorus, and sediment particle size. The findings revealed that the sediment organic carbon content ranged from 6.50 to 11.90 g/kg, the total nitrogen content ranged from 1.08 to 1.36 g/kg, and the total phosphorus content ranged from 0.57 to 0.74 g/kg. Correlation analysis revealed a significant positive correlation between sediment organic carbon and total nitrogen (p<0.05), indicating their potential sources shared similarities. The sediment organic carbon also showed a highly significant positive correlation with clay content (p<0.01), indicating that fine-grained sediments were more conducive to organic carbon sequestration. Conversely, it exhibited a highly significant negative correlation with total phosphorus, mean particle size, sand and silt content (p<0.01). Hierarchical segmentation analysis suggested that the sand and silt content in the sediment were key environmental factors affecting the distribution of organic carbon in the surface of mangroves. Additionally, mangrove species composition, stand age, surface runoff distribution, typhoon impacts, and pond dredging in aquaculture areas were also identified as driving factors influencing sediment organic carbon distribution.

Total nitrogen (TN)is an important indicator for measuring water eutrophication, and understanding its spatiotemporal variation is crucial for marine ecological protection. This study selected the Pearl River Estuary-Jiangmen sea area as the research area and utilized TN measurement data from 2021 to 2023, as well as the MODIS data from 2003 to 2023 and the Sentinel-3 remote sensing images from 2017 to 2023. By selecting high-correlation band combinations and constructing random forest regression models to invert TN mass concentration, the spatiotemporal variation characteristics of TN mass concentration in the region from 2003 to 2023 were analyzed. The results indicated that the inversion model achieved good fitting accuracy (R²=0.797-0.931). From 2003 to 2023, the TN mass concentration in the Pearl River Estuary-Jiangmen sea area showed an overall decreasing trend, with relatively high mass concentrations from 2003 to 2015, followed by a significant decline after 2016. TN showed obvious dry/wet seasonal variations, and the variations within the year in the estuary and shallow water areas were also significant. This study revealed the trend and distribution characteristics of TN in the study area through remote sensing inversion, which can provide a basis and reference for the formulation of pollution control measures in the coastal waters.

The response coefficient method is one of the widely used methods for controlling the total amount of pollutants from land-based sources in harbors and gulfs. However, the current popular ocean models do not have a tracer module that simultaneously calculates the response coefficient field of multiple release points without interfering with each other. Aiming at the characteristics of the response coefficient method, this study improves the tracer module (DYE)of the three-dimensional hydrodynamic ocean numerical model FVCOM (Finite-Volume Community Ocean Model)by adding independent modules with the same functions as the original DYE module to DYE modules in parallel, so that FVCOM can simultaneously calculate the response coefficient fields of multiple release points without interfering with each other. The improved DYE algorithm was tested with one case of ideal rectangle grid and one case of ideal Xiangshan Bay grid. The results show that the advection-diffusion process of multiple point source tracers simulated by the improved algorithm does not interfere with each other, and the simulation results are the same as those of the traditional algorithm; at the same time, the computation process of the improved algorithm takes less time, and the computation efficiency of the ideal rectangle case is increased by up to 85% and that of the Xiangshan Bay case is increased by up to 78% compared to the traditional algorithm; and the improved algorithm has a higher utilization rate of the CPU process under the condition of parallel computation than those of the traditional algorithm. The use of the improved DYE to calculate the response coefficient field can shorten the total time for marine environmental capacity assessment.

The global ionospheric model based on the global navigation satellite systems (GNSS)reference stations is currently the most widely used global ionospheric product. The analysis and evaluation of the reliability and accuracy of the global ionospheric model during magnetic storms is a necessary prerequisite for the rational use of the model. In this study, the data of the reference stations near the South China Sea were used to verify the reliability of the ionospheric vertial total electron content (VTEC)calculated from shipboard GNSS data, and the accuracy of the global ionospheric model in the South China Sea during magnetic storms was preliminarily analyzed and evaluated using the shipboard GNSS observation data and reference stations data. The results show that the ionospheric VTEC calculated from the shipboard data and the reference stations data have the same trend of change. During the magnetic storm, the error between the global ionospheric model value in the South China Sea region of China and the shipboard observation data and the reference stations (HKSL, PIMO)data increases, and the daily average RMSE values are 41.21, 27.40 and 30.86 TECU, respectively, which indicates that the disturbance of the ionosphere by the magnetic storm activity has led to a significant decrease in the accuracy of the global ionospheric model.

Island ecosystems are characterized by resource specificity and ecosystem vulnerability, thus, the scientific assessment of the impact of land use change on the carbon sequestration and other ecosystem service functions of island ecosystems is of great significance to the sustainability management of islands. The Dongtou Islands in Zhejiang Province represents a typical island ecosystem that has undergone developmental utilization such as land reclamation and conservation-restoration initiatives like the Blue Bay Project. It serves as an ideal case study for establishing assessment methods of how land use changes affecting the carbon sequestration service function of island coastal ecosystems and others, and for exploring the effectiveness of management measures. In this study, a land classification model based on XGBoost algorithm was used to obtain land use classification data of the Dongtou Islands in 12 phases (3 years as a phase)from 1988 to 2023 (with accuracy of 91.52%). On this basis, the changes in carbon sequestration amounts of major ecosystems, including woodland, salt marshes, and tidal flats, in the Dongtou Islands were calculated. A coupling coordination degree model of “economic development-land use-carbon sequestration function” was constructed by combining the socio-economic statistical data, and the degree of coupling coordination between the economy and ecosystem of the Dongtou Islands for more than 30 years was explored. The study found that from 1988 to 2023, the total land area of the Dongtou Islands increased by 34.97% due to natural silt deposition and sea reclamation efforts. The cumulative total of ecosystem carbon sequestration amount and net carbon sequestration amount for the main ecosystems amounted to 49.45×10⁴ t and 46.13×10⁴ t, respectively, basically showing an oscillating upward trend. Carbon sequestration mainly resulted from woodland and coastal wetlands (including tidal flats and salt marshes), with cumulative carbon sequestration amount of 25.44×10⁴ t and 24.01×10⁴ t, respectively. The “economic development-land use-carbon sequestration function” coupling coordination degrees of the Dongtou Islands were in a coordinated state from 2006 to 2023. Overall, the coupling coordination degree is greatly affected by the land use changes. Ecological restoration projects can enhance the comprehensive evaluation index of the land use and carbon sequestration function system, and then improve the coupling coordination degree. This study can provide a scientific theories and data foundation for the socio-economic development and ecological environmental protection planning of the Dongtou Islands.

During satellite operation, sensor malfunctions can lead to irregular strip-like missing areas in imagery, which compromises the integrity of observed information. To address this issue in geostationary satellite remote sensing imagery, a reconstruction model based on convolutional neural networks (CNN)is proposed. The model’s performance is evaluated under different combinations of temporal input data to identify the optimal configuration of consecutive temporal auxiliary data. In the auxiliary data combination, (taking the generation time of the image to be restored as the current time t), when the model takes the previous four phases (t-4, t-3, t-2, t-1)and the previous and subsequent three phases (t-3, t-2, t-1, t+1, t+2, t+3)as inputs respectively, the restoration effect is excellent and can be used for data restoration and reconstruction in real-time and delayed scenarios respectively. Compared with models that use only a single time point as auxiliary data, the proposed model utilizing multi-temporal inputs demonstrates better reconstruction results and higher accuracy. The model is also applicable to the restoration of missing information in other geostationary satellite images.

Tidal flats are influenced by tides, experiencing periodic inundation and exposure, thus the inundation frequency reflects the elevation of tidal flats. This study utilizes time-series SAR satellite remote sensing data to conduct research on the remote sensing inversion method of tidal flat topography based on tidal level complementary cumulative distribution function. The key lies in proposing a new method for inundation frequency correction based on the weighting scale of remote sensing observation counts. And, based on the mathematical definition of inundation frequency, the functional relationship between inundation frequency and tidal flat elevation was explored, leading to the construction of a tidal flat topography inversion model based on the tidal level complementary cumulative distribution function. Then, the validation of the method was conducted in the Yueqing Bay. Based on the time-series Sentinel-1 satellite SAR remote sensing data, the tidal flat topographies for the periods 2019-2020 and 2021-2022 were successfully inverted. The accuracy assessment was conducted based on the corresponding period’s ICESat-2 satellite laser altimetry data. The root mean square errors (RMSE)of the tidal flat topographies for the periods 2019-2020 and 2021-2022 were 0.41 m and 0.51 m, respectively. Additionally, the RMSE of topography for the period of 2019-2020 using in-situ data was 0.48 m. The accuracy assessment suggest that the proposed method in this study can achieve high-precision tidal flat topography without field-measured topographic data. It is expected to be applicable to the monitoring of tidal flat topography in more regions.

Using the measured data of extreme waves causing by 6 typhoons and 2 cold waves (caused by typhoon is called typhoon wave, caused by cold wave is called cold wave)during a one-year wave observation process in the Cangnan sea area of Zhejiang Province, the distribution and variation characteristics of wave parameters for each extreme wave as well as the typical characteristics of typhoon waves during Typhoon “Lekima” and “Mitag” were analyzed. The results show that the typhoon waves in the study sea area were significantly affected by the typhoon track and intensity, the stronger the typhoon intensity and the closer its proximity to the study area, the more significant and intense the process of typhoon waves, the higher the wave height and spectral peak density of typhoon waves. Both summer and autumn could be affected by extreme typhoons and lead to extreme typhoon waves. Extreme waves caused by cold wave occured both in winter and spring, of which intensity were directly affected by the intensity of cold waves, overall, extreme waves caused by cold wave were not as severe as typhoon waves. The duration of the impact of typhoon waves was two to three days, and the duration of the impact of extreme waves caused by cold wave was about 1 day; the maximum wave height and spectral peak density during extreme waves exhibited a synchronous development process of initially increasing and then decreasing. During the impact of Typhoon “Lekima”, the maximum wave height in the studied sea area was 10.80 m, with a maximum spectral peak density of 55.10 m²/Hz, the development and change process of wave spectrum was bimodal spectrum-unimodal spectrum-bimodal spectrum, and the development and change process of wave types was mixed waves dominated by swell-wind wave-mixed waves dominated by wind wave. During the impact of Typhoon “Mitag”, the maximum wave height in the studied sea area was 8.89 m, with a maximum spectral peak density of 36.37 m²/Hz, the wave spectrum was mainly composed of unimodal spectrum, with occasional bimodal spectrum. The wave type was mainly swell, with occasional mixed waves dominated by swell.

The interaction between deep-ocean geostrophic current and seamounts can generate near-inertial internal waves (NIWs). While the intensity of these waves relates to the seamount height, its dependence on seamount width remains elusive. This study employs a two-dimensional, non-hydrostatic numerical model based on MITgcm to investigate the interaction of geostrophic current with deep-sea seamounts and examine how differing seamount widths influence the generation and dissipation of NIWs. Our results demonstrate that topographic forcing triggers robust nonlinear wave-wave interactions along the summit edges on the downstream flank of the seamount. This process generates energetic near-inertial internal waves that radiate away and develop, facilitating energy transfer from the geostrophic mean flow to the NIWs. For a fixed seamount height, narrower seamounts induce stronger near-inertial waves, characterized by more rapid wave development and decay. Moreover, the downstream flank exhibits significantly enhanced vertical shears within the near-inertial internal waves, driving greater turbulent dissipation compared to the upstream flank. Therefore, our findings highlight that, in addition to seamount height, seamount width is also a critical factor governing the generation and subsequent evolution of near-inertial internal waves.

This study was conducted to explore the contribution of silicon dissolution from beach sediments to the dissolved silicon budget in the coastal waters. From March to September in 2017, six field surveying cruises were conducted in the Muping offshore area (Yantai, China), the southern North Yellow Sea. By investigating monthly distributions and the averaged values of dissolved inorganic nutrients, monthly accumulation of dissolved silicate anomaly (ΔSi, as defined with the difference between dissolved inorganic nitrogen and silicate concentrations)of 1.5 μmol·L^-1 was observed in this offshore area with weak circulation from May to August. Further combining laboratory incubation experiments, theoretical calculation and field data analyses, It was found that the permeable particles in beaches could be dissolved, leaching active silicate to seawater, and increasing the offshore silicate concentration by 0.7~2.0 μmol·L^-1 every month, roughly consistent with the monthly accumulation rate of field ΔSi. Extrapolating the beach silicate-leaching flux to the length of the coastline rounding the Yellow Sea, the previously reported imbalance in silicate budget in this coastal sea could roughly be bridged. This study indicated again that the dissolving of permeable particles might contribute significantly to coastal silicate budget.

Global warming has led to rising sea levels and weakened the ability of natural barriers such as coral reefs to withstand extreme disasters like hurricanes and tsunamis. Therefore, artificial barriers, such as seawalls or submerged structures, need to be deployed near coasts to effectively protect shoreline areas. This study aims to investigate the hydrodynamic effects of submerged artificial structures on the propagation and deformation of solitary waves over reefs through numerical simulation. A high-precision wave numerical flume was established using the non-hydrostatic model NHWAVE, and the model was validated with experimental data. The study focused on analyzing the impacts of factors such as incident wave height, reef flat water depth, slope of artificial structure, peak width of artificial structures, and slope of the fore reef on hydrodynamic characteristics of solitary waves. Results show that the presence of submerged artificial structure increases wave reflection coefficients and induces vortex formation between waves and water, and the complex flow field can effectively dissipate part of the incident wave energy, which has a mitigating effect on the amplitude and climbing height of the solitary wave. The results of this study can provide a valuable reference for the design of submerged artificial structures.

Based on the field survey in May 2023 along with data obtained from indoor culture experiments, the distribution characteristics of seawater partial pressure of carbon dioxide (pCO₂) and its main control mechanisms in Daao Bay (coral reefs region) in spring were explored. The pCO₂ in Daao Bay ranged from 412.9 to 555.7 μatm in spring, and the study area acted as a source for atmospheric CO₂ with the average efflux of 0.53±0.90 mmol·m^-2·d^-1. During the survey period, the horizontal distribution of pCO₂ was generally higher in nearshore area than that in offshore zone, which was mainly controlled by biological activities (net respiration) and coastal terrestrial input. In addition, pCO₂ showed significant diurnal variation with a maximum difference of 168 μatm. Diurnal differences in biological activities (photosynthesis and respiration) were the main factors leading to changes in pCO₂, contributing 89.4% and 66.4% of pCO₂ in the reef and non-reef areas, respectively. In comparison, physical processes (temperature and tidal effects) had a weak effect on the pCO₂ dynamic, and the temperature effect contributed 12.7% and 21.5% of pCO₂, which was much lower than that of biological processes. Furthermore, the metabolic activity of corals might increase the pCO₂ in the local (reef area) of Daao Bay and enhance the CO₂ source properties of the sea area.

Coastal estuaries are influenced by terrestrial inputs and usually act as sources of atmospheric carbon dioxide (CO₂), whereas mangrove ecosystems generally serve as sinks of atmospheric CO₂. Therefore, accurately measuring the CO₂ emissions at mangrove estuaries is of great significance for constructing regional and global carbon budgets. Dongzhai Harbor locates in the northeastern of Hainan Island, and connects to the Qiongzhou Strait outward, surrounding by 5 major small rivers. Mangroves are mainly distributed in the west and south of Dongzhai Harbor. This study conducted four field surveys in Dongzhaigang, the surrounding major rivers and the adjacent sea areas in December 2022 (dry season), December 2023 (dry season), May 2022 (wet season) and August 2023 (wet season) respectively. The results show that the surface water partial pressure of CO₂ (pCO₂) presents a decreasing trend from rivers to inner and outer harbor. Temperature, river-sea mixing, and biological respiration jointly affect the spatial distributions of pCO₂ in the dry and wet seasons. The CO₂ flux in wet season (8.8±8.2 mmol·m^-2·d^-1) is greater than that in dry season (3.4±3.6 mmol·m^-2·d^-1), and the annual CO₂ flux (6.1±6.3 mmol·m^-2·d^-1) is lower than that in other tropical mangrove estuaries around the world. This study estimates that the estuarine CO₂ emission could offset about 10.4%~21.9% of the carbon sequestration by plants in Dongzhai Harbor.

Based on the satellite altimeter data from January 1993 to December 2021, the least squares method and the ensemble empirical mode decomposition (EEMD) were used to analyze the long-term changes of the sea level in Zhoushan and the adjacent East China Sea and its influencing factors. The study found that the sea level in the study area was generally on an upward trend, and the upward trend was more obvious in the coastal waters on the east side of the Zhoushan Islands. The average linear rate was 0.36±0.10 cm/a, and the upward trend had been somewhat mitigated since 2018. The sea level in the study area showed obvious seasonal differences. Its linear rate was the largest in autumn (0.37±0.12 cm/a), followed by in winter, and slightly smaller in spring and summer (approximately 0.34±0.10 cm/a). The nonlinear change trend over the past 30 years showed that the upward rates in summer and autumn had almost remained unchanged, the upward rate in winter had shown a slowdown trend, and the upward trend in spring had been accelerating. There was a trend of increasing annual amplitude of the sea level in the study area. The long-term changes of the sea level were closely related to the seawater thermal expansion effect caused by temperature and the water increase-decrease effect caused by changes in wind stress.

The construction of artificial island will inevitably cause damage to the marine ecological environment while satisfying the land demand. Therefore, evaluating the effects of marine ecological restoration around artificial islands is a key and challenging aspect of island and coastal ecological restoration work. Based on pressure-state-response (PSR) model, the evaluation index system of ecological restoration effect in the sea area around artificial islands was constructed, and the best-worst method (BWM) was used to assign weights to the evaluation indexes, and combined with Bayesian network (BN) to evaluate the ecological restoration effect of the sea area around Riyue Island in Hainan. The results indicated that from 2016 to 2019, under the restoration strategy “natural recovery as the main and artificial restoration as the auxiliary”, the marine ecological environment around Riyue Island had shown some restoration effectiveness. The expected values of the ecological environment quality in the tourism and leisure area, agriculture and fisheries area, and reserve area increased by 32.6%, 31.7%, and 22.7% respectively. Although water environmental pressure and sediment environmental pressure significantly decreased, there was no improvement in the biological conditions. The results of sensitivity analysis showed that the ecological environment quality of the three marine functional zones was less sensitive to sediment indicators, while it was most sensitive to the density of benthic organisms. Therefore, future restoration measures should focus on improving biological ecological indicators. This study provides valuable insights for the evaluation of marine ecological restoration effects.

The Zengmu-Beikang Basin, located in the southern South China Sea, was formed under a complex geological background, with a large number of oil and gas reservoirs developed, and various types of fluid flow structures widely distributed. Seismic data indicate that the fluid flow system composed of gas chimneys, faults, tubular channels, mud volcanoes, and mud diapirs in the southern South China Sea may be related to the accumulation of gas hydrates. Seabed seepage and bottom simulating reflection (BSR) indicate the possible existence of gas hydrates. The formation of gas chimneys originates from hydraulic fracturing caused by deep oil-gas accumulation, which transports fluids to shallow areas. The gas chimneys are related to BSR, indicating the enrichment of gas hydrates. Faults developed in deep and were connected to potential source rocks or reservoirs, thus accumulating a large amount of shallow gas and gas hydrates around the faults. Pockmark is also an indicative structure for seabed seepage and an area where cold seepage gas hydrates are usually enriched. The formation of mud volcanoes and mud diapirs not only leads to vertical fluid migration, but also triggers the shallow strata deformation and fault development. Therefore, the development areas of mud volcanoes and mud diapirs are also potential areas for gas hydrate enrichment. In addition, this article uses the volume method to estimate the gas hydrate resources in the Zengmu-Beikang Basin in the southern South China Sea. The results show that the gas hydrate resources in the Zengmu-Beikang Basin are approximately 1.62×10¹³ m³. The Zengmu-Beikang Basin has strong potential for gas hydrate resources and is a region worthy of attention for future gas hydrate exploration activities.

Deep-sea sediments and polymetallic nodules are rich habitats for microorganisms. Exploring their community structure and functionality is crucial for understanding microbial genetic resources and their role in mineral formation. Current research on the bacterial diversity and structure within the nodules and surrounding sediments is limited, especially regarding microbial contributions to nodule formation. Using full-length 16S rRNA sequencing, we analyzed the bacterial composition of various nodule types and surrounding sediments in the Pacific Ocean. Scanning electron microscopy and energy dispersive spectroscopy revealed bacterial-like microsphere structures and metal element distribution on their surfaces. The bacterial community composition varied among different nodules and sediments, with Proteobacteria and Bacteroidetes dominating. Functional groups like Shewanella and Colwellia, known for metal oxidation-reduction and biofilm formation, may contribute to nodule formation. These microsphere structures promoted metal aggregation, potentially serving as mineral precipitation sites. This study enhanced our understanding of microbial functions and mineral interactions, crucial for insights into deep-sea biogeochemical cycles and microbial mineralization.