Liaodong Bay is the most severely ice-covered sea waters in China during winter. The large area of sea ice on the sea surface has significant impacts on maritime economic activities. This study focuses on reconstructing a time series of sea ice extent from 2001 to 2021 for Liaodong Bay based on MODIS satellite images. Meanwhile, a nonlinear relation between the floe ice distance and sea ice extent in Liaodong Bay is figured out, which is used to extend the historical maximum sea ice extent of Liaodong Bay back to 1953. Then, the interannual variation of the maximum sea ice extent is researched to obtain the sea ice extent in Liaodong Bay in the return period of engineering design. The impact factors of the maximum sea ice extent in Liaodong Bay are analyzed, and the results show that the correlation coefficient between the maximum sea ice extent and the freezing degree-days, as well as northerly wind component, reached 0.96. Furthermore, the correlation between the sea ice concentration in some regions of the Arctic during autumn and the winter sea ice extent in the Liaodong Bay is analyzed. Our results provide valuable insights for understanding the trend of sea ice extent in Liaodong Bay and formulating measures for sea ice disaster prevention.

The Zhujiang River Estuary is located in the northern South China Sea. It has a wide intertidal zone and a high diversity of intertidal macrobenthos. However, most of the previous intertidal-related studies and intertidal species records were carried out on the east coast of the Zhujiang River Estuary, while studies on the west coast of the Zhujiang River Estuary were relatively scarce. From 2021 to 2023, a comprehensive survey focus on Brachyura (crabs), one of the main groups of intertidal macrobenthos, was conducted in the intertidal zone of Qi’ao Island, Zhuhai City, western Zhujiang River Estuary. Combined with the collection and revision of species recorded in previous studies, an updated checklist of intertidal crabs in Qi’ao Island was created, and the ecological and geographical distribution of these crab species were described. A total of 90 specimens were colleted and 31 species from 10 families and 21 genera were identified. Seventeen species (e.g. Orisarma patshuni and Anomalifrons lightana) were new to the Qi’ao Island, and one species (Hemigrapsus takanoi) were new to the Zhujiang River Estuary. The updated checklist includes 48 intertidal crab species belonging to 13 families and 29 genera, among which Sesarmidae (10 species), Varunidae (10) and Ocypodidae (8) are the three most species-rich families. The crab fauna composition of the island is mainly composed of East Asian endemic taxa and Indo-West Pacific/West Pacific widespread taxa, showing overwhelming East Asian warm water characteristics. Mudflats and mangroves are the most abundant habitat types for crab species on the island. Our results has increased the number of intertidal crab species on the west coast of the Zhujiang River Estuary from 31 to 55 species, which is the same as the number of species recorded in Shenzhen Bay on the east coast of the Zhujiang River Estuary. The total number of intertidal crab species recorded in the Zhujiang River Estuary has reached 77 species in 14 families and 38 genera, of which 33 species (42.9%) has been reported on both the east and west coasts.

The ocean contains various spatiotemporal scales of motion processes, and ocean striations are a newly discovered form of flow in recent years. This flow phenomenon lies between geostrophic turbulence and quasi-steady flow. Due to the dominance of large-scale motion in the upper ocean, ocean striations are masked and need to be extracted using filtering methods. In this study, the three-dimensional structure of ocean striations in the North Pacific was extracted based on zonal velocity data using Chebyshev high-pass filtering. The “flow stability” index was defined to quantitatively analyze the barotropic feature of ocean striations in the North Pacific, thereby deepening the understanding of the structural characteristics of ocean striations in the North Pacific.

Combining satellite altimetry and drifter data, the method of sea surface height to discover and track an anticyclonic eddy merger event that occurred near the southeastern Gulf of Mexico was used in this study. By studying this typical anticyclonic eddy merger process, the mode of eddy merging is preliminarily revealed, which helps to further understand the complex eddy mechanism. The Eulerian eddy results show that pairs of anticyclonic eddies attract each other and propagate together for more than three weeks before merging into a unified eddy structure and continuing to propagate westward. The Lagrangian vortex trajectories captured by drifters provide evidence of water exchange between the vortices before the merger, as one drifter exchanged its original anticyclonic eddy on November 15, indicating significant water exchange between the vortices before being observed by the altimeter. Before and after the merger, the radii of the Eulerian and Lagrangian vortices both increased significantly with the Eulerian radius improving by 96.2% and the Lagrangian radius of the drifting buoys pulled by two anticyclonic eddies improving by 49.1% and 115.6%, respectively. The sea surface temperature field also exhibited different environmental responses due to the merging effect, further verifying the occurrence of the merger process. Finally, the analysis of the dynamic evolution of kinematics such as kinetic energy, vorticity, and divergence before and after the merger, as well as the morphological changes such as radius, amplitude, and shape, showes that the merger roughly experienced processes such as vortex asymptote, water exchange, contour compression and deformation, elongated elliptical vortex generation, and boundary reshaping. The vertical structure of the plane where the vortex is located mainly shows evolution from bimodal to unimodal. After the vortex merger, energy is transferred to the mesoscale through inverse cascade. Due to the single-core vortex structure, some statistical properties are biased during the merging process, which may have led to abrupt changes before and after the event.

The composition and texture characteristics of plagioclase in basalt from the 26°S hydrothermal field of the Southern Mid-Atlantic Ridge provide an important basis for the study of magmatic evolution characteristics. On the basis of observing the petrography of basalt and analyzing the composition of plagioclase, the structure and composition of plagioclase at different stages are compared to explore the process of magma evolution. The results show that the study area is mainly composed of porphyritic basalt, and plagioclase porphyries are commonly characterized by glomerocryst structures, oscillatory-zoned, dissolved and resorbed rim, and growth structures. The plagioclase in the matrix is mainly acicular and swallow-tailed crystals; the basalts in the SMAR-26°S hydrothermal zone are mainly sodium tholeiitic basalts. In the early stage of magma evolution, bytownite was mainly formed, while in the late stage, labradorite was mainly formed. Throughout the entire evolution process, the content of CaO and Al₂O₃ decreases, while the content of SiO₂, Na₂O, FeO, and MgO increases; from the core to rim of plagioclase phenocrysts and then to plagioclase microcrystalline in the matrix, the An values decreases overall. The An values in the rim of plagioclase phenocryst partially overlaps with the An values of plagioclase microlites in the matrix, resulting in a gradual decrease in temperature. These represent the changes from the magma origin area to magma eruption. After the formation of mantle magma, it rapidly rises and erupts to form basalt. During the upwelling process, it may undergo the process of decompression accompanied by volatiles escaping, dissolving in the deep, supersaturated crystallizing of the melt, mixing of low-Si same sourced magma, and syn-eruptive fast decompression of degassed magma.

It has been an important research topic in oceanography and climatology to understand the evolution of marine environment in the context of anathroprogenic warming. In the geological past, the Earth has experienced several warming periods (including the early Holocene), which provide natural analogs for future climate. The global climate experienced rapid warming during the early Holocene, accompanied by ice sheet melting and rapid sea level rise, which have significantly impacted sedimentary processes and marine environment in high-latitude marginal seas, including the Bering Sea. The Bering Sea consists of a broad continental shelf, adjacent to the North American continent, and receives material supplies from the Yukon River, Anadyr River and Kuskokwim River. There are still significant gaps in our understanding of how the Bering Sea responds to the early Holocene climate. In this study, high-resolution analysis of major and minor elements in bulk sediments of Core LV63-19-3 retrieved from the northern slope of the Bering Sea, in combination with a well-constrained sedimentary age model to investigate the sedimentary environment changes on the northern Bering Sea slope during the early to middle Holocene (11.7–5.5 ka BP). The results show that the sedimentation rate on the northern continental slope of Bering Sea was as high as 392.9 cm/ka during 11.5–11 ka BP, and decreased rapidly to 17.2 cm/ka after 9.7 ka BP. At 11–10.7 ka BP, a dark laminated sediment layer about of 40 cm thick was found. In the period of high sedimentation rate, the average grain size of sediments was finer, and increased gradually after 9 kaBP. Both major and minor element concentrations indicate that the lithological properties of terrigenous clastic sediments were mainly felsic sediments with a small amount of pyroclastic contributions. The high sediment rate corresponds to the Meltwater Pulse-1B event (11.4–11.1 ka BP) and resulted in a blooming of siliceous productivity on the Bering Sea continental slope. In the study area from 11 ka BP to 10.7 ka BP, the increase in seasonal sea ice coverage inhibited the oxygen supply from the atmosphere to surface water and subsequent transport to the bottom water, while the glacial meltwater and the persistent high productivity in summer and autumn further exacerbated the surface water stratification and ocean interior oxygen consumption on the continental slope of the Bering Sea, both of which together triggered the formation of laminated sediment. After 9 ka BP, the seasonal sea ice activity in the Bering Sea increased gradually, but the mass accumulation rate of terrigenous detrital materials decreased, indicateing a decrease in the supply of terrigenous materials to the study area along with sea level rise. We suggest that the rapid shift in early Holocene sedimentary environment on the northern Bering Sea continental slope is the result of a combination of sea level, Meltwater Pulse 1B event and seasonal sea ice activity, which is actually controlled by high-latitude solar insolation, North American ice sheet melting, and global climate.

Empirical Orthogonal Functions (EOFs) are usually used for sparse representation of the sound speed profile (SSP). However, due to the restriction of data completeness and measurement time, the representative error of the EOF will lead to limited accuracy of SSP reconstruction. In order to improve the reconstruction accuracy of SSP, the fuzzy C-means clustering algorithm is used to analyze the BOA_Argo historical data set and the reconstruction accuracy of the measured SSP based on different clustering spaces of data samples is discussed. The results shows that the SSPs are significant temporal-spatial clustering. The EOF and mean SSP generated by the clustered historical SSPs have the best reconstruction performance. The results of this paper are helpful to provide practical guidance for the selection of historical SSP training data and can improve the accuracy of SSP reconstruction.

The phenomenon of seabed liquefaction is widely distributed in the underwater delta of the Huanghe River, which poses a great threat to submarine engineering facilities. The determination of liquefaction depth can provide a reference for offshore engineering construction, which has great theoretical significance and application value. The columnar sediments were obtained by drilling in the liquefaction disturbance area of Chengdao sea area in the north of the Huanghe River Delta, and the profile image scanning, radionuclide and particle size composition testing were carried out to obtain the image stratification characteristics, ²¹⁰Pb, ¹³⁷Cs activity and particle size profile, and the deposition rate was calculated on this basis. The results show that the Chengdao sea area was significantly affected by the change of the Huanghe River from the Diaokou channel in 1976, and the sedimentation rate decreased significantly during this period and showed a phased character. During the rapid deposition period, the sand layer produced by frequent liquefaction of surface sediments accumulated continuously, thus forming the dense sand layer. By analyzing ²¹⁰Pb_ex and ¹³⁷Cs activity profiles, the sedimentary records of liquefaction history in the study area were obtained, and the historical liquefaction depth was determined to be at least 5 m, which is similar to previous studies. It is feasible to use the activity of ²¹⁰Pb and ¹³⁷Cs as tools to judge the history and depth of sediment liquefaction, which has great development potential.

The bioturbation structure is an important indicator of the state of the seabed environment and the main basis for the reconstruction of the paleosedimentary environment; moreover, it affects the early diagenesis of sediments and the redistribution of materials, and becomes the interference factor for the interpretation of the 100-year scale sedimentary records. In this article, sediment cores from 21 stations in the Changjiang River Estuary and its adjacent areas were characterized qualitatively and quantitatively by using high-resolution X-ray computed tomography technology, and the main factors affecting the bioturbation structures were analyzed. The result shows that the bioturbation structures in the Changjiang River Estuary and its adjacent areas are relatively developed, which can be divided into four types: biodiffusor structures, conveyor structures, regenerator structures and gallery-diffusor structures. Conveyor structures and gallery-diffusor structures are common. The bioturbation structure is distributed in various forms in the core, including exponential attenuation type, wave attenuation type, uniform distribution type, pulse distribution type and other vertical distribution forms. The depth of disturbance varies, most of which are within 20 cm, but some are more than 40 cm. The bioturbation structures are spatially uneven. The Changjiang River Estuary and the inner shelf are relatively developed, with a disturbance inventory of 0–13 972 mm³, while the northern Jiangsu coast and the middle continental shelf are less, with a disturbance inventory of 351–3 212 mm³. The bioturbation structures from the coast to the outside have a decreasing trend. The development degree of bioturbation structure is mainly restricted by the type of bottom material and sedimentation rate. Clay silt and suitable sedimentation rate (0.52–1.34 cm/a) are conducive to the development and preservation of bioturbation structures.

The observation and exploration of the seabed urgently requires the appearance of large-scale and long-term observation platforms. The subsea AUV has three main points: a structure that suitable for the mobility in the seabed, an intelligent motion performance that adapts to the complex environment of the seabed, and the underwater acoustic communication and positioning technology that adapts to the seabed. In this paper, the development and evolution of subsea AUV is analyzed, the key technical challenges of underwater AUVs are summarized, and corresponding solutions for underwater AUV hydrodynamic shape optimization technology, intelligent motion control technology, underwater acoustic communication and positioning navigation technology, and underwater connection and charging technology are provided. Finally, a study case of Autonomous Underwater Helicopter is given, to provide a solution for subsea AUV. This paper provides guidance for the development of subsea AUV, as well as ocean observation and exploration technology.