Submarine fans developed in the middle Miocene Meishan Formation possess significant potential for natural gas exploration. Most of scholars believed that these Miocene submarine fans were formed primarily by turbidity currents. However, drilling cores revealed the presence of pebbles with a particle size of up to 5 cm in the sandy conglomerates. These sandy conglomerates exhibited good roundness and poor sorting, indicating that the traditional turbidity formation mechanism cannot fully explain the origin of this type of sandy conglomerates. Furthermore, the classic submarine fan model has limitations in predicting the distribution of sand bodies. Through a comprehensive study involving core, thin section observation, and grain size analysis, we have conducted a systematic investigation of the petrological characteristics and sedimentary structures of submarine fan in the study area. Our findings suggest that submarine fans in the study area resulted from the interaction of turbidity and hyperpycnal flow deposits. We have identified distinct sequences of turbidites and hyperpycnalites within the submarine fan. Based on the paleogeomorphlogy of the study area, we have established a genetic evolution model for the submarine fan in Meishan Formation. This model reveals that the hyperpycnites dominated by feldspathic litharenite, exhibit low compositional maturity. Poor sorting and subangular-circular of the rocks indicate middle-to-high structural maturity. Typical features of hyperpycnal flow include orientated gravel within block sandy conglomerates, reverse-to-normal grain order bedding, parallel bedding, carbonaceous debris, and biological fossil fragments. Multi stage superimposed turbidite sequence and hyperpycnites sequence developed in submarine fan in the study area. The early Meishan period is primarily composed of turbidite submarine fan lobes, while the middle Meishan period is dominated by hyperpycnites submarine fan channels. The late Meishan period, on the other hand, is mainly composed of turbidite submarine fan channels. We predict that more favorable submarine fan sand bodies could be found in the southern part of the study area. The results can serve as a basis for predicting the distribution of favorable submarine fan reservoirs of the Qiongdongnan Basin, and they hold significance for selecting exploration and development targets for hydrocarbon exploration.

The buried hill oil and gas reservoirs have become an important exploration field in China’s marine basins. The northwestern area of Shaleitian area of Bohai Bay Basin is a typical carbonate buried hill zone. Due to the lack of research on the reservoir control effect of multiple stage fractures and their related karstification, the oil and gas exploration of carbonate buried hills is restricted. This paper conducts a detailed analysis of the development characteristics of the fracture-cave system in carbonate buried hill reservoirs in the northwestern Shaleitian Uplift, and studies the reservoir control effects of fractures and karst. The results indicate that the lower Paleozoic carbonate buried hills in the northwestern area of Shaleitian Uplift belong to fracture related karst reservoirs. The reservoir space includes dissolution pores, structural fractures, and expansion pores along the structural fractures. High quality reservoirs have lithological selectivity, and fractures and dissolution pores developed in microlite crystalline dolomite and fine crystalline dolomite are better. The reservoir mainly develops three sets of fractures, with E−W and NE oriented shear fractures mainly related to two tectonic compressions during the Indosinian and Late Yanshanian. The third set of NW oriented tensile fractures is related to the intracratonic movement during the Himalayan orogeny, and compression is the main mechanism for forming high-density fractures. The later stage of extension is a necessary condition for the relaxation of fractures to form reservoir spaces. The Lower Paleozoic carbonate buried hill reservoirs have undergone three stages of karstification, which are karstification in the steady Caledonian tectonic background, karstification in the Indosinian compressive background, and fault block-horst karstification in the Yanshanian-Himalayan extensional background. In summary, the carbonate buried hill reservoirs in the northwestern Shaleitian Uplift are formed by multiple stages and multiple types of tectonic-karst processes, and the analysis of the differences in the degree of recombination in different structural parts is an important factor in understanding the reservoir formation mechanism.

In real ocean environments, natural reefs typically exhibit complex topography, with reef platforms presenting non-uniform characteristics. Previous extensive research has mainly focused on simplified stepped reef models and has not conducted in-depth studies on the impact of non-uniform reef platforms on the propagation and evolution characteristics of waves. To address the shortcomings of previous research, this paper conducted physical model experiments to systematically study the propagation and evolution characteristics of tsunami-like waves over complex reef platforms. Previous studies did not consider the impact of the non-uniformity of reef platform topography on solitary waves, therefore, this paper also analyzed the effects of incident wave height and reef platform water depth. To investigate the impact of non-uniform reef platform geometric characteristics on the propagation and evolution of tsunami-like waves and the load characteristics of sea walls under different incident wave conditions, this paper further carried out a series of high-resolution numerical calculations. First, physical experiments were used to verify the accuracy of the numerical simulation method, and then numerical calculations were used to study the effects of two wave parameters, incident wave height and reef platform submergence depth, and three complex reef topography factors—the height of the second reef platform, the position of the reef platform steps, and the slope of the reef front slope—on the maximum wave height along the path, reflection coefficient, maximum run-up height, distribution of the maximum impact pressure on the sea wall, and the variation of the maximum total force and total moment on the sea wall. The research results indicate that the reflection coefficient of solitary waves decreases with increasing incident wave height and increases with increasing reef platform water depth. The maximum run-up height increases with increasing incident wave height and decreases with increasing cot α of the reef front slope. The maximum total force and maximum total moment on the sea wall increase with increasing incident wave height and reef platform water depth, and decrease with increasing height of the second reef platform. The position of the maximum impact pressure on the sea wall rises with increasing incident wave height, increasing reef platform water depth, and decreasing distance between the reef platform steps and the sea wall. The research results can provide a reference for further protecting coastal facilities from the impact of extreme marine environments.

In response to contingencies that arise during the underwater coverage missions of multiple autonomous underwater vehicles (AUVs), this study addresses the problem of coverage path replanning for multiple AUVs. A multi-robot multi-regional coverage path planning (M²CPP) method is proposed to reassign uncovered areas to available AUVs and plan their coverage paths. Initially, the lawnmower algorithm is employed to determine the internal paths and candidate entry points within each region. Subsequently, a coevolutionary approach is utilized to solve for the optimal region allocation, region sequence, and the best entry points for each region. Three populations coevolve collaboratively to determine the complete paths for all AUVs, ensuring population diversity and preventing convergence into local optima. Simulation results demonstrate that the proposed method not only replans shorter paths for multiple AUVs based on their initial positions and remaining energy but also optimizes the path structure to ensure a balanced workload among the AUVs, effectively resolving the replanning issue under such scenarios.

Iron oxides play a significant role in the global soil (sediment) organic carbon (OC) storage. Mangrove wetlands, receiving both terrestrial and marine inputs, provide a unique habitat for the preservation of organic carbon by reactive iron oxides (Fe_R). However, the impact of Fe_R in the surface sediments of mangroves on the preservation process of OC, as well as the selectivity of Fe_R towards different OC components, is still unclear. The surface sediments in the present work was collected in the natural mangrove areas around the estuaries of the Dafeng River and Maowei Sea in Guangxi, which are highly influenced by tides and rivers. The research was focused on the changes in the content and composition of iron-bound organic carbon (Fe-OC) in sediments. The results indicated that the average content of Fe-OC in surface sediments in the estuaries of Dafeng River and Maowei Sea was 0.16% ± 0.07% and 0.17% ± 0.07%, respectively. These values represented 16.2 ± 5.04% and 10.9 ± 5.63% of the total organic carbon (TOC) content in the respective sediments, which were primarily preserved through adsorption. Furthermore, the preservation of OC by Fe_R was influenced by the sediment particle size, the content and form of Fe_R, and the source and composition of TOC. TOC, Fe_R and Fe-OC were mainly distributed in the smaller grain size sediment fractions. The predominant form of iron in surface sediments was Fe³⁺, accounting for 87.42% of the total iron, and was relatively higher in high salinity sediments. Fe_R selectively preserved OC with higher δ¹³C (stable carbon isotope natural abundance) and aromatic OC. Compared with the Maowei Sea, the proportion of protein-like fluorescent components in Fe-OC of surface sediments from the Dafeng River estuary was higher and the proportion of protein-like fluorescent components increased as the molar ratio of Fe-OC∶Fe increased. This study helps to clarify the selective preservation mechanism of OC by Fe_R in mangrove surface sediments in Guangxi, and deepen our understanding of the preservation process of OC in land-sea interface sediments.

Seagrass meadows play a vital role in protecting marine biodiversity, mitigating ocean acidification, and preventing soil erosion in the coastal ecosystem. However, global climate change and human activities seriously affect the life of seagrass, which cause the widespread degradation of the seagrass and threaten the safety of coastal ecosystems. Recently, the vital value of microorganisms in promoting the energy flow of seagrass meadows and their growth and development has gradually gained attention. Plant growth-promoting microorganisms(PGPM) will play their value in seedling cultivation, plant transplantation, seed planting and other techniques of seagrass meadow restoration. This paper reviewed the research on how microorganisms interacts with seagrass to promote the growth of plants and increase the resistance to abiotic stress. We introduced the mechanism of PGPM to enhance plant stress tolerance under high temperature, high salt, and low light. We propsoed that modern molecular biological technique should be used to screen seagrass PGPM, clarify the colonization site of PGPM, and explore the molecular interaction mechanism between PGPM and seagrass in different environmental conditions. This paper is some advice for promoting the application of PGPM in seagrass meadow restoration and seagrass protection.

Sargassum horneri has good economic traits and value, and its culture is gradually being emphasized. However, the suitable water depth for culture is still unclear, and the physiological characteristics and ecological functions of S. horneri in different water depths are also unclear. In this paper, we compared the primary productivity, nutrient uptake capacity, and algal trophic composition of S. horneri at different water depths (0.5 m and 2 m) based on light intensity in different water depths. The results showed that light intensity varied significantly (P < 0.05) with water depths and that the difference in light intensity due to water depth was significantly correlated with the primary productivity of S. horneri. The total productivity of S. horneri grown at 0.5 m water depth (upper layer) was significantly higher than that of S. horneri grown at 2 m water depth (lower layer) (P < 0.05), and S. horneri in the upper layer showed higher primary productivity and carbon sequestration capacity. The uptake of ${{\rm {NH}}_4^+} $ and ${{\rm {PO}}_4^{3-}} $ by the upper layer of S. horneri was significantly better than that of the lower layer of S. horneri under the light conditions (P<0.05), which has good potential in purifying the eutrophic water and regulating the ecological balance of the waters. However, the uptake of ${{\rm {NO}}_3^-} $ and ${{\rm {NO}}_2^-} $ by the upper layer of S. horneri is significantly lower than the lower layer of S. horneri (P>0.05), and it indicates that some strong light inhibition phenomenon occurs in S. horneri which affects the uptake of ${{\rm {NO}}_3^-} $ and ${{\rm {NO}}_2^-} $ by S. horneri. The moisture content of S. horneri at different water depths ranged from 71% to 75%, the ash content from 20% to 23%, the total lipids content from 6% to 8%, and the crude protein content from 8% to 10%. Nutrient composition did not differ significantly (P > 0.05) between the two water depth treatment groups. Studies have shown that by appropriately raising the culture layer, S. horneri can achieve higher productivity and nutrient uptake capacity, while the nutrient composition of S. horneri in the different water layers would remain relatively stable. This study has great significance for the technological development and upgrading of the artificial culture of S. horneri in natural sea areas as well as for the ecological environmental protection of sea areas.

To analysis the suitability of using wind field data for forecasting Pacific saury habitat in the northwest Pacific, this paper use the generalized additive model to fit the habitat suitability index (HSI) for Pacific saury in summer and autumn, based on the Chinese fishery data, environmental data and four types of wind field data included the China-France oceanography satellite (CFOSAT) during June to November in 2019−2020. The result indicates that: (1) Weighted analysis shows distinct seasonal variation of environmental variables on catch per unit effort, with chlorophyll concentration and sea surface temperature having the highest weights in summer and autumn respectively, while wind speed had the lowest weight and direct proportionality to the weight. (2) The average accuracy of the four data in summer and autumn is 68.37% and 76.65% respectively, and CFOSAT reaching the highest accuracy of 80.94% in autumn. (3) The high-HSI areas are consistent with the fishing grounds of Pacific saury, while the HSI high-value regions of scatter meter in autumn seems more robust. There are advantages of using wind speed on the forecast model in autumn, as this model can reflect the influence of transient variation factors on the migration and aggregation of Pacific saury.

The tidal creek system is an active geomorphic unit in coastal wetlands, and the water environment of different level tidal creeks changes significantly, leading to spatial distribution differences of biological communities. This study selected a typical tidal creek unit in the Huanghe River Delta and used environmental DNA metabarcoding (eDNA) technique to detect the diversity of invertebrates. The biological co-occurrence network analysis and redundancy analysis (RDA) were respectively used to reveal the keystone species and driving factors of the invertebrate community in the typical tidal creek. The results showed that a total of 127 operational taxonomic units (OTUs) of invertebrates were detected in the tidal creek unit, belonging to 9 phyla, 24 classes, 53 orders, 103 families, 87 genera, and 90 species; among them, the class level was dominated by the Arthropoda (43.9%), and the genus level was dominated by the Perinereis (25.2%). The comprehensive diversity index (CD) analysis showed that the comprehensive diversity of invertebrates in the third-level tidal creek was the highest, and the comprehensive diversity of invertebrates in the first-level tidal creek was the lowest. The biological co-occurrence network analysis showed that the Perinereis linea and the Obelia dichotoma were the keystone species, which played a key role in maintaining the stability of the invertebrate community structure in the tidal creek. The RDA showed that the silicate content of the water body, temperature, and the proportion of fine sand and clay in the sediment were the main environmental factors affecting the invertebrate community characteristics in the tidal creek. Correlation network analysis showed that the keystone species were significantly affected by silicate content, clay, and nitrogen content in water (P < 0.05). The research results are helpful for understanding the community structure of typical tidal creek invertebrates, revealing the keystone species of typical tidal ditch invertebrates, and providing data support and theoretical reference for the monitoring and protection of invertebrate diversity.

The phenomenon of marine phytoplankton bloom in ocean refers to the annual cycle increase in biomass caused by rapid reproduction, which plays an important role in the biochemical cycles of marine organisms. However, the spatiotemporal variation characteristics of global phytoplankton blooms and their response mechanisms to the environment still require further exploration. Based on the chlorophyll a products of the MODIS-Aqua (Moderate Resolution Imaging Spectroradiometer) from 2003 to 2022, we extracted the bloom indexes of global ocean phytoplankton (the ratio of bloom duration and bloom intensity). Then, we analyzed their spatiotemporal characteristics, trends, and correlations with environmental factors. The results indicated that there are significant seasonal and latitudinal difference in the distribution of the bloom indexes. Blooms in high latitudes of the Northern Hemisphere mainly occur from April to October, while in mid-low latitudes, blooms mainly occur from November to March of the following year. In the Southern Hemisphere, blooms develop in the month of November and persist until March of the following year in high latitudes, while those in low and middle latitudes occur from May to September. The ratio of bloom duration and bloom intensity show decreasing trends mainly in the mid-low latitude regions of the North Pacific, while increasing trends are observed in mid-high latitude regions of the Southern Hemisphere. The distribution and trends of bloom indices are both regulated by environmental factors. Sea surface temperature and photosynthetically active radiation promote blooms intensity in high latitude waters, but inhibit them in low latitude waters. Meanwhile, the wind speed plays a restraining role in the high latitude sea area and a promoting role in the low latitude sea area.