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As a pivotal intertidal blue-carbon ecosystem, the seagrass-mangrove continuum is a focal point of contemporary blue-carbon research. In contrast to individual ecosystems, the continuum facilitates lateral carbon transport and redistribution between systems via tidal forcing—a process that profoundly influences regional and even global assessments of blue carbon budgets. However, the internal carbon cycling within the continuum and the multi-interface, multi-process coupling mechanisms of carbon sequestration remain a black box, representing one of the hot topics in blue carbon research. Here we systematically synthesize current understanding of carbon cycling in the seagrass-mangrove continuum, mapping key processes—from plant photosynthetic carbon sequestration, sediment carbon accumulation to aquatic carbon transformation, and gas exchange—within a novel, dual perspective of “vertical sequestration vs. lateral transport”. Special emphasis is placed on tide-driven lateral carbon fluxes (e.g., litter fall, DOC, POC, DIC), highlighting their central role in the continuum’s carbon dynamics. Given the complexity of intertidal habitats, future research on the coupled carbon cycling mechanisms within the seagrass-mangrove continuum remains a critical and underexplored field. In particular, key processes such as plant carbon fixation mechanisms, sediment carbon accumulation, and elemental exchange urgently require further investigation.

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.

The sediment source-to-sink system serves as a critical link connecting active carbon pools (e.g., atmosphere, biosphere, hydrosphere) with the stable lithospheric carbon pool, playing a core buffering role in the global carbon cycle. As the core area of marine sedimentary carbon sinks, delta-shelf regions account for over 80% of the global marine sedimentary organic carbon flux while occupying less than 8% of the global ocean area. The processes and mechanisms of carbon burial in these regions are crucial for global carbon balance. This paper systematically reviews the source composition and sedimentary flux characteristics of terrestrial organic carbon in delta-shelf sedimentary systems, focuses on elaborating organic carbon source-to-sink tracing technologies, remineralization processes and their dominant mechanisms, analyzes the impacts of human activities on sedimentary carbon sinks, and discusses marine negative emission and carbon sequestration enhancement schemes based on sediment management. Studies show that the heterogeneity of terrestrial organic carbon, physicochemical conditions of the sedimentary environment, and human disturbance collectively regulate the migration, transformation, and burial efficiency of organic carbon. Currently, the potential of sedimentary carbon sinks has not been fully exploited; thus, it is urgent to promote the integration of sedimentary carbon sinks into the global climate governance system through methodological innovation, mechanism deepening, and technological development, so as to provide scientific support and feasible paths for achieving the temperature control goals of the Paris Agreement.

To investigate how tidal dynamics influence the composition of dissolved metabolites in seawater, we collected seawater samples across a semidiurnal tidal cycle, spanning both the salinity and turbidity fronts of the Changjiang River Estuary in March 2023. Using high-resolution mass spectrometry-based untargeted metabolomics, a total of 1 379 metabolite molecules were annotated (annotation rate of 6.8%), covering 14 super classes. Among these, organoheterocyclic compounds, benzenoids, lipids and lipid-like molecules were dominant (accounting for 59.1%). The results indicated that the composition of metabolites was significantly influenced by tidal forces, with greater heterogeneity during ebb tide than flood tide, revealing a temporal asynchrony between tidal movement and metabolite compositional variation. Statistical analyses further demonstrated that metabolite compositions were significantly negatively correlated with salinity, and that non-conservative nutrients (nitrate, phosphate, and silicate) exerted strong influences on metabolite variations. These results suggested that terrestrial dissolved organic matter inputs were a primary driver, with their influence further modified by brackish water mixing. In addition, the correlation between turbidity and most metabolites was relatively week. However, substantial percentage changes in lipids and lipid-like substances were observed within the suspended sediment front, indicating that the transformation of dissolved organic matter driven by resuspension processes primarily occurs under strong hydrodynamic conditions. Analysis of differential metabolite during flood and ebb phases further showed that these substances were dominated by secondary metabolites, such as lipids and heterocyclic compounds. These substances might reflect regulation by microbial community interactions. Overall, this study highlights the short-term tidal influence on dissolved organic matter composition and provides new insights into how multi-scale physical processes regulate organic matter cycling in estuarine environments.

Deep-water sedimentary processes are key drivers that shape seafloor topography and actively participate in marine material cycles, thereby playing a crucial role in the formation of depositional systems and material cycling along continental margins and within deep-sea basins. The transport and transformation of carbon elements and carbon-containing substances are essential for sustaining organic life and maintaining climate stability. As an important end-member reservoir in this cycle, deep-sea sediments act as efficient sinks for atmospheric greenhouse gases, exerting significant regulatory effects on climate evolution over geological timescales. This study aims to elucidate the coupling mechanisms between distinctive deep-water sedimentary processes and organic carbon burial, providing a theoretical basis for establishing the “Shelf edge-slope-deep sea basin organic matter continuous transport system” and the “Deep-water organic carbon burial pyramid model”. By comprehensively analyzing representative deep-water organic carbon burial systems in global ocean basins, this research demonstrates that turbidity currents and bottom currents are the main dynamic mechanisms enabling the continuous transport of deep-water organic matter. The (micro)biological carbon pump, turbidity current carbon pump, bottom current carbon pump, and deep stratigraphic carbon pump together form the core framework for deep-water sedimentary carbon burial. Furthermore, the factors influencing deep-water organic carbon burial outcomes exhibit hierarchical characteristics. However, current research on deep-water organic carbon burial is still in its early stages, with limited case studies and mechanistic understanding, underscoring the urgent need to strengthen research on carbon burial processes in deep-water environments.

Submarine cable and pipeline hold multifaceted strategic significance for national security, socio-economic development, and marine ecological environmental protection. This paper systematically reviews the evolution of China’s management policies for submarine cable and pipeline, traces the development trajectory of both the international legal framework and the domestic policy system. It analyzes the main existing issues such as administrative approval, protection management, spatial regulation, and national security. The study argues that with increasingly frequent marine development activities, lagging management mechanisms, and a complex and volatile international geopolitical landscape, submarine cable and pipeline face challenges including intensified competition for spatial resources and heightened security risks. The article proposes optimizing management policies across four dimensions: institutional restructuring, systematic protection, spatial governance, and security safeguarding. This approach aims to promote the construction of a forward-looking, efficient, and resilient governance system for submarine cable and pipeline. Such a system is essential to safeguard the implementation of China’s maritime strategy and ensure sustainable development.

The United Nations Decade of Ocean Science for Sustainable Development (2021-2030) (hereinafter referred to as the “UN Ocean Decade”) is a global scientific initiative aimed at transforming and advancing the global ocean governance system through enhanced marine scientific research and innovation. By establishing a collaborative framework that spans disciplines, regions, and institutions, the initiative seeks to improve ocean observation capabilities, promote data and knowledge sharing, and strengthen the translation of scientific findings into policy and practice. As one of the participating countries in this initiative, China has systematically advanced related actions through the establishment of a national committee, the leadership of major scientific programs and construct Decade Collaborative Center. In this process, scientific research institutions have played a critical role in the implementation of scientific programs, technological innovation, and international cooperation. For instance, the Second Institute of Oceanography, Ministry of Natural Resources has led or deeply involved in several endorsed UN Ocean Decade actions that have established internationally recognized research and collaboration systems in areas such as conducting cutting-edge science and technology, and promoting capacity-building. Although significant progress has been made in the implementation of the UN Ocean Decade, global ocean governance still faces numerous challenges. These include disparities in technological capabilities and resource investments among countries, inadequacies in data-sharing mechanisms, and inefficiencies in translating scientific outcomes into policy. Additionally, geopolitical factors may also impact international cooperation. To achieve the goals set for 2030, further efforts are needed to deepen scientific innovation, improve open-sharing mechanisms, and strengthen inclusive collaboration, thereby promoting the establishment of a more equitable and effective global ocean governance system. In this process, research institutions worldwide can contribute to the realization of the UN Ocean Decade vision by continuing to participate in global observation networks, advancing digital and intelligent technologies, and supporting regional cooperation and capacity-building.

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.

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.

Black carbon (BC), a refractory organic carbon, is produced during the incomplete combustion of biomass and fossil fuels. Globally, an estimated 3%-10% of the annual BC production ultimately buried in marine sediments. As a critical component of the inert carbon pool, its spatiotemporal distribution and source-to-sink processes are essential for understanding global carbon cycling and climate evolution. Based on published BC data from nearly 1 000 marine sediment samples worldwide, this study reveals that BC contents vary widely, from 0.02 to 9.72 mg/g, with averaging 1.06 mg/g and accounting for an average of 15.1% of total sedimentary organic carbon. Spatial patterns are controlled by sediment grain size, organic carbon content, and depositional environments while temporal variations reflect the combined influence of climate change and human activities. Current knowledge of marine sedimentary BC sources predominantly assumes terrestrial dominance, with riverine transport, atmospheric deposition, and coastal erosion as primary input pathways. However, emerging evidence indicates that BC sinking fluxes in mid- to deep-ocean layers substantially exceed known terrestrial supply. This raises the possibility of potential unidentified sources. In addition, BC degradation and recycling processes within the marine systems remain poorly understood. Future research must prioritize source-to-sink dynamics in key areas (e.g., deep-sea environment) by integrating geochemical and organic molecular isotopic techniques to resolve BC cycling mechanisms and address current budget imbalances.

The estuarine turbidity maximum (ETM) is a critical hub for the transport of particulate organic carbon (POC) from estuaries to ocean. To investigate the provenance and transport patterns of POC within the ETM, the Jiulong River ETM was selected as a research site. Hourly-resolved hydrological parameters, horizontally transported POC (collected via filtration), and vertically settling POC (collected using sediment traps) were systematically sampled. POC was analyzed for organic carbon isotopes, and the Monte Carlo end-member model was employed to analyze the relative contribution of different endmembers. Then the empirical orthogonal function (EOF) analysis was applied to examine and discuss the transport patterns and their driving mechanisms of POC within the ETM. The results revealed significant spatiotemporal variations in POC sources: surface POC was primarily of riverine sources (35.5%), while bottom POC was dominated by sedimentary sources (35.1%). Settling POC was also mainly derived from sedimentary sources, reaching up to 65% in high-flow flood tide periods. The bottom POC mass concentrations (0.8-8.4 mg·L^-1) showed a significant positive correlation with the magnitude of bottom tidal current velocity (absolute range: 0-0.5 m·s^-1). The peak settling flux of particles (227.1 mg·cm^-2·h^-1) occurred during low-flow periods (profile-averaged velocity <0.2 m·s^-1). Based on the results, it is find that tidal current velocity is a key factor regulating the sources and transport of POC within the Jiulong River Estuary’s ETM. It influences the horizontal transport, resuspension, and vertical mixing processes of POC through its magnitude, direction, and duration, thereby governing the provenance composition and mass concentration of POC. This control manifests specifically in three ways: a significant positive correlation exists between tidal current velocity and POC mass concentration, where high-velocity currents primarily drive the resuspension of sediments, making this process the main source of sedimentary POC; the alternating flow patterns of flood and ebb tides are the dominant control for the shifting predominance between river and marine POC; and velocity stratification (especially during the ebb tide stage) governs the vertical mixing intensity of POC from different sources. Moreover, from the perspective of how tidal current velocity regulates POC sources and transport processes within the ETM, this study summarizes the POC transport models for different tidal stages: During the flood tide, currents drive the input of marine POC. However, the high flow velocities cause significant sediment resuspension, resulting in the overall dominance of sedimentary POC. During the high slack tide, characterized by low flow velocities, particle settlement predominates, and sediment resuspension diminishes. This leads to a relative increase in the proportions of river or marine POC. Although the contribution of sedimentary POC decreases, it remains the dominant source overall. During the ebb tide, the outgoing currents facilitate the input of river POC. Meanwhile, the high flow velocities in the surface layer have a limited effect on adding sedimentary POC. The proportional distribution among the three POC sources is closely linked to the duration of the preceding high-velocity flood tide; generally, a longer duration leads to more pronounced dominance of sedimentary POC. During the low slack tide, which also features low flow velocities, settlement is again the primary process. The contributions of the three POC sources are generally comparable during this stage. These findings provide a valuable reference for a deeper understanding of the source-to-sink processes of POC within the ETM.

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.

Coastal wetlands have a strong capacity for carbon capture and storage, playing a significant role in mitigating climate warming. Vegetation type is an important factor influencing the carbon storage. In this study, we measured the soil organic carbon (SOC), lignin, stable carbon isotope (δ¹³C), grain size, and iron content in the surface soil of three typical vegetation habitats (Phragmites australis, Phragmites australis-Tamarix chinensis, and Suaeda salsa) in the Yellow River Estuary wetland, and analyzed the content, source, and degradation characteristics of organic carbon. The results showed that the SOC content in the three vegetation habitats of the Yellow River estuary wetland ranged from 0.34% to 1.85%, with the highest in P. australis, which had an average value of 0.94%. The SOC content was jointly affected by vegetation type and clay content. The three-end-member Monte Carlo model calculation found that the soil organic carbon in the three vegetation habitats was mainly from terrestrial (47.7%±13.2%) and plant sources (36.3%±15.0%), with a relatively low marine source (16.0%±14.2%) (S. salsa>P. australis-T. chinensis>P. australis). The soil lignin in the three vegetation habitats all showed a mixture or single source of woody and herbaceous tissues, indicating that part of the soil organic carbon in the P. australis and S. salsa habitats originated from the upstream Loess Plateau. Iron oxides and water in the soil might reduce the degradation of lignin due to their protective effect on organic carbon and their inhibitory effect on aerobic respiration of microorganisms. This study showed that there were significant differences in the distribution, source, and degradation characteristics of soil organic carbon among different vegetation habitats.

Spaceborne synthetic aperture radar (SAR), with its all-weather and day-and-night imaging capability, has demonstrated tremendous value in ocean monitoring. This paper provides a systematic review of the current research status of spaceborne SAR technology in the field of marine monitoring, from the perspectives of ocean dynamic environmental parameters and maritime targets. For the former, we summarize mainstream SAR-based techniques and algorithms for monitoring ocean environmental parameters such as waves, internal waves, eddies, winds, currents, and seafloor topography, and further discuss the roles of multi-frequency, multi-polarization, and multi-mode SAR data in improving inversion accuracy. For the latter, we review SAR-based methods for the detection of maritime targets including sea ice, oil spills, vessels, and offshore infrastructures, highlight the importance of multi-polarization information in characterizing target scattering properties. In addition, this paper reviews and evaluates recent advances in applying artificial intelligence to SAR-based ocean monitoring and discusses future development directions for SAR ocean remote sensing technologies.

The continental shelf regime under the United Nations Convention on the Law of the Sea (UNCLOS) marked the first time that the scope of coastal states’ sovereignty rights was extended to the deep-sea areas beyond 200 nautical miles. This provision not only endows coastal states with legal standing for the exploitation of deep-sea resources, but also fosters an institutional linkage between geoscience and international law. To date, a total of 109 submissions have been formally lodged with the Commission on the Limits of the Continental Shelf (CLCS), signifying that global continental shelf delineation has entered a new phase characterized by the high integration of scientific practice and legal procedures. Nevertheless, driven by the rapid advancement of science and technology and the sensitive impacts of geopolitics, continental shelf delineation is confronted with unprecedented challenges, which will exert a major influence on global ocean governance. Based on the 109 submissions received and 44 recommendations issued by the CLCS, this paper systematically sorts out the major progress and challenges in the delineation of continental shelves beyond 200 nautical miles from three dimensions: legal regimes, geoscientific theories, and practices. It aims to reveal how continental shelf delineation has evolved into a crucial driving force reshaping the global marine spatial order within the international deep-sea governance system where scientific evidence and legal institutions intersect, and further looks ahead to the development direction of continental shelf delineation in the context of scientific and technological progress, international cooperation, and global ocean governance.

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.

Under the dual pressures of global change and human activities, the impact of extreme storm events on estuarine sedimentary processes and carbon sink capacity has become increasingly prominent. However, traditional single-core methods face challenges in quantitatively characterizing the erosion-deposition processes and net carbon burial effects induced by storm events. In this study, we conducted repetitive coring at a fixed station near the Dayushan Island in the Hangzhou Bay, China in 2021 (before Typhoon Chanthu) and 2022. Through analysis of sedimentary structures, grain size and radionuclides, we identified an intense erosion-deposition event triggered by Typhoon Chanthu. Combined with elemental composition and organic geochemical indicators, we further quantitatively assessed its net impact on carbon burial. The results demonstrate that despite the efficient organic carbon preservation within the storm layer, the related intense erosion resulted in a net organic carbon deficit of 1 950±523 g·m^-2. This finding highlights a preservation bias of the storm layers in sedimentary records, leading to a systematic overestimation of the storm contribution to estuarine carbon burial in studies relying on single cores. The “repetitive coring-radionuclides tracing” methodology developed in this study provides a new paradigm for accurately assessing estuarine sedimentary processes and carbon cycling under non-steady-state conditions.

River deltas are critical global sinks for organic carbon (OC). To elucidate their evolutionary patterns under natural and anthropogenic influences, this study systematically reconstructs the OC burial history of the Changjiang Delta since the mid-to-late Holocene (8 ka BP), based on chronological, sedimentological, and organic geochemical data from 50 boreholes. The results revealed that the sediment accumulation rate was the core driver controlling the OC burial flux, with the two showing a strong positive correlation (r²=0.87). However, a significant decoupling existed between the OC burial flux and the total OC content, with the latter remaining stable within a low range of 0.41%-0.52% throughout the study period. This was primarily constrained by the dual effects of clastic dilution and particle size sorting. The provenance of OC showed a distinct phased evolution: from 8 to 2 ka BP, source variations were mainly driven by natural factors, with sea-level rise (8-5 ka BP) and the weakening of the East Asian Summer Monsoon (5-4 ka BP) successively leading to a decrease in the terrestrial OC fraction. Since 2 ka BP, human activities had become the dominant factor, profoundly reshaping the delta’s geochemical signals by altering sediment provenance zones within the catchment. This study unveils the complete process of the Changjiang Delta’s carbon sink function transitioning from a dynamic equilibrium under a natural background to being intensely disturbed in the Anthropocene, providing crucial scientific insights for understanding and predicting the vulnerability of deltaic carbon reservoirs in the context of global change.

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.