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Based on a substantial number of seabed sediment samples and corresponding acoustic characteristic and physical property test data collected in the continental shelf area of the northwestern South China Sea, this study employed a sound speed ratio correction model to analyze the correlation between the sound speed ratio of seabed sediments and parameters such as porosity, density, mean grain size, and water content. This study resulted in the development of both single-parameter and double-parameter empirical formulas for the sound speed ratio of seabed sediments in this marine region. The determination coefficients (r2) for the single-parameter empirical formulas based on physical properties, excluding the mean grain size (r2 ≤ 0.75), were all above 0.78, indicating a strong correlation. Additionally, the fitting curve at 100 kHz was slightly greater than that at 50 kHz, consistent with the acoustic dispersion characteristics of sediments. To assess the applicability of the empirical formulas to different maritime areas, the formulas derived from the South Yellow Sea, East China Sea, and South China Sea were compared with those of the study area. The results indicated that the empirical formulas for the sound speed ratio established in this study have general applicability, especially for sediments with low porosity, high density, and low mean grain size. In addition, the determination coefficient of the dual-parameter empirical formula for the sound speed ratio–porosity–mean grain size is superior to that of the single-parameter empirical formula for the sound speed ratio–mean grain size. Through comparative studies with other marine areas, it was found that there are certain differences in the relationships between porosity and mean grain size established in different marine areas. Therefore, based on the rough sphere model, this study transforms the GS model into a single-parameter model built on either porosity or mean grain size. The error analysis results indicate that the single-parameter GS model has a smaller error than the measured data. However, the GS model controlled by a single parameter performs poorly compared to the predicted curves of the sound speed ratio–porosity and the sound speed ratio–mean grain size fitted in this study. This discrepancy may be attributed to the fact that the input parameters of the GS model are reference values, emphasizing the need for further research to determine suitable input parameters for the GS model in this marine area. • The empirical equations for the sound speed ratio were developed in this study in different marine regions. • The established empirical equations for the study area were compared with those for the South Yellow Sea, East China Sea, and other marine regions. • This study compared the empirical equations with the grain shearing (GS) theoretical model. [ABSTRACT FROM AUTHOR]

Two new free-living marine nematode species of the genus Antomicron Cobb, 1920 belonging to the family Leptolaimidae are described from the seabed sediment of Jiaozhou Bay of the Yellow Sea. Antomicron holovachovi sp. nov. is characterised by loop-shaped amphideal fovea; male with five straight tubular and 41 alveolar supplements; short cephalic setae; slightly curved slender spicule with cephalated proximal end and tapered distal end; and rectangular gubernaculum with a short dorsal caudal apophysis. Antomicron chinensis sp. nov. is particularly characterised by loop-shaped amphideal fovea; male with only alveolar supplements, without tubular supplement; slender and slightly inverted S-shaped spicule with cephalated proximal end and tapered distal end; and rectangular gubernaculum with a slender dorsal caudal apophysis. An updated identification key to species of the genus Antomicron is also provided. [ABSTRACT FROM AUTHOR]

In this study, shear wave speed and related physical properties were measured for 21 seafloor sediment cores collected in the northern South China Sea. Results reveal that the shear wave speed in this study area ranges between 15.57 and 75.55 m/s and demonstrates a pattern of regional distribution. The sediment in the continental shelf area shows characteristics of high shear wave speed, high wet bulk density, low porosity, and large grain size. Contrarily, the sediment in the continental slope area exhibits characteristics of low shear wave speed, low wet bulk density, high porosity, and fine particles. Accordingly, the correlation between shear wave speed and physical properties such as porosity, wet bulk density, water content, and average grain size was studied. Prediction formulas of shear wave speed of sediments in this study area containing single and double physical parameters were established via regression analysis. The comparison between single‐parameter and double‐parameter prediction formulas indicates that the determined coefficient of the double‐parameter prediction formulas based on porosity and average grain size is higher than that of single‐parameter prediction formulas. It indicates that the double‐parameter prediction formulas based on porosity and average grain size have better prediction performance. Moreover, the prediction formulas established in this study were further compared with those of other study areas, and their differences were analyzed accordingly. Plain Language Summary: The shear wave speed of seafloor sediments is the velocity of shear wave propagating in seafloor sediments. Shear wave speed is one of the critical acoustic properties of seabed sediments, which is very useful in many fields such as exploration and exploitation of seabed resources, precise prediction of the acoustic field, and prediction of stability with regard to engineering geology. In view of the importance of shear wave speed, the correlation between shear wave speed and physical properties such as porosity, wet bulk density, water content, and average grain size were analyzed, and the prediction formulas of shear wave speed were established in this study. Key Points: Shear wave speed and physical properties of sediments in the continental shelf were compared with those in the continental slopePrediction formulas of shear wave speed based on porosity, density, water content, average grain size were establishedThe prediction formulas established in this study were compared with those of other study areas, and their differences were analyzed [ABSTRACT FROM AUTHOR]

Seabed sediment classification has important applications in ocean engineering and submarine pipeline design. This paper proposed the dimension-invariant residual network to improve the seabed sediments classification accuracy. The dimension of each channel of the feature extracted from the dimension-invariant residual block is the same as the original image. Compared with down-sampling, each feature vector has more feature parameters, which can improve the accuracy of seabed sediments classification. Shortcut connections were introduced in the proposed network, which can make the network easier to optimize and achieve good performance by using only a not very deep network. It also has a lower complexity compared to powerful classifiers like Transformer and has a better performance in small-scale seabed sediment classification. And to improve the accuracy of seabed sediment classification without consuming too much time for training the classifier, the network parameters optimization method was proposed in this paper. Recording the classification accuracy and training time of the network with these different parameters. Determining the parameters of the network by the proposed optimization method. The proposed classification model and optimization method were validated by using the side-scan sonar images, acquired from the area around the Shandong Peninsula of China. The layers and convolutional kernel sizes were determined to be 8 and 3, respectively. The classification accuracy of overall, rock, sand, and mud of the dimension-invariant residual network model were 97.83%, 94.04%, 97.80%, and 98.02% respectively. In comparison with state-of-the-art classifiers, the experimental results demonstrated that the proposed classification model achieved better performance, and the network parameters optimization method enables the network to achieve satisfactory classification accuracy while spending less time. The proposed classification model and network parameters optimization method show great potential in seabed sediments classification, which can also be extended to the task of underwater target recognition in future research. • The dimension-invariant residual network identifies seabed sediments more accurately. • The dimension-invariant residual block can retain more features than the traditional. • Network parameter optimization methods can balance the training time and performance. [ABSTRACT FROM AUTHOR]

Kelp aquaculture activities occupy large nearshore areas with significant effects on sediment properties, primarily caused by the influence of the suspended kelp on local hydrodynamics. Changes in sediment composition and grain-size distributions were investigated prior to and following the commencement of kelp aquaculture activities in Heini Bay in eastern China. Seabed sediment types and the particulate matter in suspension during the kelp seeding and harvesting periods, and in sediment cores, were analyzed. While suspended sediment in the kelp aquaculture area was up to 20% organic material, sediment organic content on the seabed remained at similar levels as areas lacking aquaculture. The composition of the seabed sediment in the kelp aquaculture area became finer-grained by the capture of fine particles. Within the kelp aquaculture area, the sediments are poorly sorted and positively skewed, whereas at the shoreward and seaward of the aquaculture area the sediments are relatively coarse-grained, well-sorted and nearly symmetrically distributed. Therefore, the kelp aquaculture activities not only increase the fine particulate fraction in the sediments within the aquaculture area, but also result in similar deposits seaward of it, indicating that seabed erosion and accretion is also controlled by the sediment source and the hydrodynamic conditions. The analysis of sediment cores showed that kelp culturing refines the sediment by preferentially capturing particles in the 38–40 μm size class, while having no effect on the <32 μm fractions, as evidenced by the positive skew of the surficial sediments. The captured particle size class became well mixed into the sediment, thereby changing the composition of the sediment in the uppermost layer of the core, indicating the existence of continuous and stable hydrodynamic conditions within the kelp aquaculture area. The same effect was observed in the seabed sediments seaward of the aquaculture area. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an experimental study in which the occurrence and evolution of inhomogeneity in the strength of a uniform-originated silty seabed were investigated. The pore pressure and penetration strength at different depths inside the seabed were observed during the experimental process under the weight of the soil and under the action of waves of different heights (H=5cm, 10cm, 15cm). We found that a well-mixed silty seabed consolidates under the stress of its own weight, and its strength gradually increases as a result. Small wave action consolidates and strengthens the seabed and sediment. When the seabed is exposed to progressively higher waves, a fluidised response characterised by an arc-shaped boundary surface occurs on the seabed, and this response further controls the occurrence and evolution of the strength inhomogeneity of a uniform-origin seabed. The analyses clearly illustrate that features of seabed erosion and mass-transportation activity previously ascribed to increasing wave-current bed shear stress are controlled primarily by the process of wave-induced inhomogeneity in the strength of seabed sediments originating in the preceding period. In addition, the implications of the mechanism are explored. [Copyright &y& Elsevier]

Abstract: Through a large-scale examination of the morpho-sedimentary features on sea floors in the Taiwan–Luzon convergent margin, we determined the main sediment dispersal system which stretches from 23°N to 20°N and displays as an aligned linear sediment pathway, consisting of the Penghu Canyon, the deep-sea Penghu Channel and northern Manila Trench. The seafloor of South China Sea north of 21°N are underlain by a triangle-shaped collision marine basin, resulting from oblique collision between the Luzon Arc and Chinese margin, and are mainly occupied by two juxtaposed slopes, the South China Sea and Kaoping Slopes, and a southward tilting basin axis located along the Penghu Canyon. Two major tributary canyons of the Formosa and Kaoping and small channels and gullies on both slopes join into the axial Penghu Canyon and form a dendritic canyon drainage system in this collision marine basin. The canyon drainage system is characteristic of lateral sediment supply from flank slopes and axial sediment transport down-canyon following the tilting basin axis. The significance of the collision marine basin in term of source to sink is that sediments derived from nearby orogen and continental margins are transported to and accumulated in the collision basin, serving as a temporary sediment sink and major marine transport route along the basin axis. The comparison of the Taiwan–South China Sea collision zone with the Papua New Guinea collision zone of the western Solomon Sea reveals remarkable similarities in tectonic settings and sedimentary processes that have resulted in similar sediment dispersal systems consisting of (1) a canyon drainage network mainly in the collision basin and (2) a longitudinal sediment transport system comprising a linear connection of submarine canyon, deep-sea channel and oceanic trench beyond the collision marine basin. [Copyright &y& Elsevier]

Based on a data base of multi-channel seismic profiles covered over Dongsha plateau of the northern South China Sea margin, we found that the sea bed morphology of northern South China Sea margin had been changed dramatically after Dongsha uplifting, that sedimentary layer since Miocene age had been eroded with maximum eroded thickness more than 1000 m, and that an erosive channel had been formed of 20 km in width and 200 km in length and several hundreds meters in depth on the outer shelf of northern South China Sea. The erosive channel is parallel to the 600 m isobath line, stretching from northeast to the southwest north of Dongsha uplift. The Kuroshio intrudes the South China Sea through Luzon Strait both in winter time and summer time, and in the northern South China Sea margin area, the intruded Kuroshio Branch takes the form of Pacific-Indian Ocean Through Flow (PITH) in winter time, while the Luzon Strait Subsurface Inflow (LSSIF) in summer time, the routes of both PITH and LSSIF coincide well with the distribution of the erosive channel. After climbing from the northern slope up to the northern shelf, and after joined by the southward flow from the middle northern shelf of South China Sea, the Kuroshio Branch is strengthened and thus is able to erode the sea floor, and the shape of the erosive channel is a result of the long-term interaction between the Kuroshio South China Sea Branch and the Dongsha outer shelf sea floor. [ABSTRACT FROM AUTHOR]

Abstract: Radioisotopes from dry and wet atmospheric deposition (i.e., 7Be, 210Pb and 137Cs) can be used to determine the sources, fluxes and rates of internal processes in sedimentary compartments such as rivers, estuaries and oceans. The activities of 7Be, excess 210Pb (210Pbex) and 137Cs in surface sediments collected in the Changjiang Estuary during May and June of 2007 were measured to elucidate the routes and budgets of these radionuclides and the sediment transport. The ranges of the activities of 7Be, 210Pbex and 137Cs were 0.0–34.6, 0.39–2.90 and 8.0–214.0Bqkg−1, with averages of 9.8, 1.56 and 43.5Bqkg−1, respectively. Based on the material balance of inputs (riverine loading, atmospheric deposition) and outputs (decay, burial into sea bed) of 7Be, 210Pb and 137Cs, the calculated results indicate that around 35% of both the 210Pbex and 7Be total inputs in the Changjiang Estuary should be exported out of this area. However, the evaluated results showed that 83% of the 137Cs total input into the Changjiang Estuary should be from offshore and/or the south. These phenomena can be explained by the current structure of the water mass around this region. Changjiang Dilute Water (CDW), with sediment, is first moved to the south and northeast. Then, the Zhejiang–Fujian Coast Current (ZFCC), with sediment, can travel farther south. Moreover, the Jiangsu Coast Current (JCC), with sediment from the Yellow Sea, can approach the Changjiang Estuary. However, both the Taiwan Warm Current/upwelling and the ZFCC can carry fine sediment with 137Cs to the Changjiang Estuary. [ABSTRACT FROM AUTHOR]

This article preliminarily reports and analyses the transmission characteristics and behaviors of shear wave in the offshore seafloor surface sediments in China, discusses the relationships between the physical and mechanical features of the shear wave and the compression wave, and compares the testing results with that of Hamilton and Chen et al. The result shows that the shear wave can be tested if the seafloor surface sediment has tangent modulus. The shear wave velocity ranges from 50–600 m/s and the measuring frequency from 50–200 kHz. The sound velocity rate of shear wave and compression wave can be used to appraise the stress-strain feature of seafloor surface sediments. This study provides a basis for further describing and appraising the seafloor sedimentary acoustic-mechanical feature and building a geological-acoustic model on China's offshore sea area. [ABSTRACT FROM AUTHOR]

Seabed erosion is a vital process for sediment transport in estuaries and coasts. In this study, we investigated the seabed erosion process and its spatiotemporal variability in the Pearl River Estuary, China, via in-situ observations and laboratory experiments. It is found that the seabed was more erodible in the channel than at the shoal in most cases due to the difference in sediment size. In a neap-spring-neap tidal cycle, a laminated seabed with different sediment ages was inferred to form due to deposition on flood tides and erosion on ebb tides. The seabed was more erodible during spring tides than neap tides because of the difference in sediment availability at the unconsolidated fresh layer. Furthermore, the erosion curve showed evident flood-ebb asymmetry, which was found to be related to the variations of sediment availability and bottom stress. Besides, erosion experiments with different sediment consolidations revealed that sediment erodibility decreased with the growth of consolidation. This study promotes our understanding on the spatiotemporal variability of sediment erodibility, and has significant implications for simulation and prediction of estuarine sediment transport and morphological evolution. • The seabed was found more resistant to erode with the growth of sediment age. • The flood-ebb asymmetry in erodibility in the Pearl River Estuary was noted. • Seabed experiencing frequent erosion-deposition processes was prevented from further consolidation and became more erodible. [ABSTRACT FROM AUTHOR]