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Free-spanning submarine pipelines are usually affected by vortex-induced vibration (VIV). Such vibration could influence the liquefaction of the supporting soil at both ends of the free spans and could have catastrophic consequences, including the failure of the local seabed and the displacing, sinking, or floating of pipelines. The influence of pipeline vibration on soil liquefaction has not been studied sufficiently. Therefore, we explored the influence of vortex-induced pipeline vibration on the excess pore pressure of silty soil around a pipeline using flume experiments. Our results showed that pipeline vibration could induce the buildup of excess pore-water pressure, even without wave loading. A fully liquefied zone was found close to the pipeline, where excess pore pressure reached the soil liquefaction criterion, which was surrounded by a partially liquefied zone. The extent of liquefaction depended on the vibration conditions and the weight and burial depth of the pipeline. The pipeline vibration amplitude increased after soil liquefaction. Unlike wave-induced liquefaction, pipeline-induced vibration liquefaction occurred at a critical value smaller than the initial mean normal effective stress. Considering the possibility of pipeline-vibration-induced seabed liquefaction, conventional approaches could underestimate the potential risks to pipeline stability and result in unsafe maintenance practices.

The sediments in core YS01 recovered from the South Yellow Sea mud deposit zone contain abundant benthic foraminifera, particularly shallow continental shelf species, but rare of planktonic foraminifera. The benthic foraminifera are dominated by stenohaline cold shallow-water species and euryhaline brackish-water species. In this paper, the palaeoenvironmental changes were discussed based on the grain-size compositions and benthic foraminiferal assemblages. Six different benthic foraminiferal assemblages were discriminated by species analysis from the foraminiferal fauna. According to AMS14C dating data in core YS01, we identified four main stages of marine environmental changes since the last deglaciation: a near-shore depositional stage (13.1–9.5 kyr B.P.), a transitional stage from near-shore deposition to shallow-sea deposition (9.5–5.6kyrB.P.), a high sea level stage with shallow-sea deposition (5.6–2.9kyrB.P.), and a stable shallow-sea depositional stage (2.9kyr B.P. to the present).

Through the geochemical analysis of two hundred-meters cores KD4 and ZK3 from Laizhou Bay, in this study, we determined the distribution law and controlling factors of the geochemical elements. We analyzed 24 elements with respect to their R factors and major principal components, which were combined with the source discrimination functions DFCr/Th and DFCa/Al to obtain the sediment source index and its variation with depth for this area. A comparison of the changes in climate indicators suggests a clear correlation between the source and climate changes. The results show that the Yellow River and surrounding short-term rivers are the main sediment sources in this area. The PC3 of the KD4 core and PC2 of the ZK3 core (e.g., CaO, MnO, SiO2) exhibit significant variations and reflect the relative contributions of Yellow River sources. The deposition process can be divided into six stages: in Phase I (MIS 5c-MIS 5a), the Yellow River formed, and the composition of the Yellow River had a greater influence on the sedimentary composition of the study area. In Phase II (MIS 5a-MIS 3), the sediment sources of the Yellow River and the short-term streams in this area were wavering, with the sediments derived from short-term rivers playing a more important role. In Phase III (MIS 3), with a sharp drop in temperature, the study area was in the process of retreat, and the sediment source changed from the Yellow River to short-term rivers, after which the Yellow River source material remained the main sediment source for the region. A similar process occurred three more times in Phase IV (MIS 3-MIS 2), Phase V (MIS 2-MIS 1), and Phase VI (MIS 1). With changes in climate, especially during alternating sea-land phases, the sediment source varied in marine-terrestrial-marine phases, and the changes are observed as Yellow River source-surrounding provenance-Yellow River source. However, this process of change is not synchronized with the sea-land strata alternation.

Equilibrium scour depth (S) of seabed is critical to the safety of offshore pipelines which is one of the most important topics in ocean engineering. Compared to sands, few experiments have been done for silty seabed. In the present work, scour experiments under wave-only action were performed for both sandy and silty seabeds. Together with the data from literature, the most abundant dataset at the present stage is established. Based on this, two practical formulas for S were obtained with adaptive robust regression (ARR) from a data-driven perspective. One is for sands only that is related to the Keulegan–Carpenter (KC) number, pipeline-seabed gap and grain size of sands. The other is a more generalized model for both sands and silts, which is related to the KC number and sediment type that is distinguished by introducing a dummy variable. The formulas outperform the commonly-used process-based and data-driven models while also showing good interpretations in physical meaning. For silts from the Yellow River Delta, the S in silts is generally 1.2 times of that in sands. The better performance is attributed to (1) the outliers in the dataset are effectively handled with ARR; (2) the most abundant dataset.

In situ observations of suspended sediment concentrations (SSCs), bed elevations, and concurrent hydrodynamics were conducted with an instrumented tripod on an abandoned lobe of the Yellow River Delta in the winter of 2014–2015. Four typical winter storms were recorded, but no significant local seabed erosion was observed at the observation site. Nevertheless, the sediment dynamic processes in this area were inferred from the data. The bottom sediment is eroded by the waves induced by strong northerly winds, and the erosion source area is located northwest of the observation point. Therefore, during strong wind and wave conditions, the observation point forms a horizontal SSC gradient, which generally decreases from west of to east of the observation point. The gradient mainly passes the observation site through diurnal tidal horizontal advection and is intermittently influenced by advection by the residual current driven by sea‒land wind and semidiurnal tides. Additionally, local resuspension of a “fluffy layer” on the seabed by the semidiurnal tide occurs. Flood tides transport the SSC gradient southeasterly, while ebb tides push the gradient back periodically. An asymmetry in the suspended sediment transport rate exists and is estimated to be 1.77 kg m−2 s−1 to the southeast. A new parameter, the net loss rate of suspended sediment, is defined and is estimated to be 0.0109 g L−1 h−1. These findings provide a better understanding of the erosion mechanism of the Diaokou lobe and some new ideas/methods for analysing hydrodynamics and sediment dynamics with a single-point measured dataset.

A two-month seabed-mounted observation (YSG1 area) was carried out in the western Yellow Sea Cold Water Mass (YSCWM) using an RDI-300K acoustic Doppler current profiler (ADCP) placed at a water depth of 38 m in late summer, 2012. On August 2012, Typhoon Bolaven passed east of YSG1 with a maximum wind speed of 20 m s−1. The water depth, bottom temperature, and profile current velocities (including u, v and w components) were measured, and the results showed that the typhoon could induce horizontal current with speed greater than 70 cm s−1 in the water column, which is especially rare at below 20 meters above bottom (mab). The deepening velocity shear layer had an intense shear velocity of around 10 cm s−1 m−1, which indicated the deepening of the upper mixed layer. In the upper water column (above 20 mab), westward de-tide current with velocity greater than 30 cm s−1 was generated with the typhoon’s onshore surge, and the direction of current movement shifted to become southward. In the lower water column, a possible pattern of eastward compensation current and delayed typhoon-driven current was demonstrated. During the typhoon, bottom temperature variation was changed into diurnal pattern because of the combined influence of typhoon and tidal current. The passage of Bolaven greatly intensified local sediment resuspension in the bottom layer. In addition, low-density particles constituted the suspended particulate matter (SPM) around 10 mab, which may be transported from the central South Yellow Sea by the typhoon. Overall, the intensive external force of the Typhoon Bolaven did not completely destroy the local thermocline, and most re-suspended sediments during the typhoon were restricted within the YSCWM.

Coastal dams along the Yellow River Delta are built to prevent seawater intrusion. However, land subsidence caused by significant oil, gas and brine extraction, as well as sediment compaction, could exacerbate the flooding effects of sea-level rise and storm surge. In order to evaluate the coastal dam vulnerability, we combined unmanned aerial vehicle (UAV) Light Detection and Ranging (LiDAR) with small baseline subsets (SBAS) interferometric synthetic aperture radar (InSAR) results to generate an accurate coastal dam digital elevation model (DEM) over the next 10, 30 and 80 years. Sea-level simulation was derived from the relative sea-level rise scenarios published by the Intergovernmental Panel on Climate Change (IPCC) and local long-term tide gauge records. Assuming that the current rate of dam vertical deformation and sea-level rise are linear, we then generated different inundation scenarios by the superposition of DEMs and sea-levels at different periods by way of a bathtub model. We found that the overtopping event would likely occur around Year 2050, and the northern part of the dam would lose its protective capability almost entirely by the end of this century. This article provides an alternative cost-effective method for the detection, extraction and monitoring of coastal artificial infrastructure.

We use the particle size of sediments in core YS01A to study the sedimentary environment of the mud deposit in the central South Yellow Sea of China during late Marine Isotope Stages 3 (MIS3; 40.5 kyr–31.3 kyr). In addition, the East Asian Monsoon and its relationship with the North Atlantic Ocean climate change are discussed based on the sensitive grain-size calculation and the spectrum analysis. The results show that during late MIS3, the muddy area in the central South Yellow Sea experienced the evolution of coastal facies, shallow marine facies, coastal facies, and continental facies, with weak hydrodynamic conditions. Compared with other climate indicators, we found that there were many century to millennium-scale climate signals documented in the muddy area sediments in the central South Yellow Sea. According to our particle size results, three strong winter monsoon events occurred at 37.6 kyr, 35.6 kyr and 32.2 kyr. The East Asian Winter Monsoon records in core YS01A are consistent with the Greenland ice core and the Hulu cave stalagmite δ18O. The millennial and centennial scale cycles, which are 55 yr, 72 yr, 115 yr, 262 yr respectively, correspond to solar activity cycles, while the 1049 yr and 2941 yr cycles correspond to the Dansgaard-Oeschger cycles. These cycles indicate that the paleoclimate evolution of the area was controlled by the solar activities, with the high-latitude driving thermohaline circulation as the main energy conveyor belt, followed by the sea-air-land amplification of the winter monsoon variation in the central Yellow Sea in the late MIS3.

A230Th-dated stalagmite record from Linyi, Shandong Province, provides a detailed history of the East Asian summer monsoon (EASM) in northern China during the last deglaciation. Our record reveals changes that are similar to previously published stalagmite records from the East Asian monsoon region on centennial and millennial scales, although some subtle and detail discrepancies are observed. Comparisons with other paleoclimate records show that the EASM was jointly controlled by the North Atlantic climate and low-latitude tropical processes during the last deglaciation. Ocean-atmospheric interactions, particularly sea surface temperature changes in the tropical Pacific might have contributed to the increasing trend of the EASM during the Bolling-Allerod and to the lesser weakening in the EASM during the Younger Dryas. In addition, the significantly higher growth rates of the stalagmite during the Heinrich Event 1 might have been driven by the CO2 degassing processes. Future studies with long-term monitoring of the calcite deposition rate at this site will be needed to support our arguments on the CO2 degassing processes.

Characteristics and formation of the tidal shear front off the Yellow River Mouth had been previously studied based on observations and models. However, its long-term variability and thus related mechanisms have not been investigated. In this study, a three-dimensional hydrodynamic model was used to examine the long-term evolution on the location, propagation, and magnitude (length, duration, and shear strength) of the tidal shear front from 1976 to 1996. Over the 20 years, a peninsula of about 27 km long and 7 km wide (above the high water line) was formed off the new river mouth, while the coastline retreated by 5–10 km, and the water depths increased by about 2 m in the north (the abandoned river mouth). Results also show that for the period of each flood and ebb tidal cycle, the tidal shear front originated in the north of the delta, then propagated southeastwards and finally disappeared at the south of the river mouth. During the two decades, the front had an obvious shoreward movement, and its duration within a tidal cycle increased slightly. Furthermore, the length of the front decreased, while the shear strength of the front increased. The propagation of the front was determined by flood and ebb process in the delta, where both of them were from north to south due to tidal phase distribution. Long-term characteristic variations of the front were mainly caused by morphology change, which had a significant influence on the tidal current gradient and the location of maximum bottom stress gradient area. The morphology change also had a slight impact on the tidal current phase in the front area, which may have caused the slight duration variation of the front.

We studied pore water pressure responses in silty seabed under random wave action through a series of experiments in a wide wave flume. Unlike previous experiments involving regular waves, we focus on random waves including wind-induced short waves and long waves so as to gain further insights into seabed responses and liquefaction risks posed by random waves. In particular, the study investigated how the secondary long waves that were induced by incident short wave groups affected the seabed responses. The test results revealed that these long waves could cause much larger seabed responses than the short waves (eight times larger in our flume tests). Although they had smaller wave heights than the short waves, the long waves were found to contribute much more significantly to the cumulative pore pressure than previously recognized. The likely reason is that the long waves are disproportionally effective in generating cumulative excess pore pressure, confirming qualitatively some of the earlier theoretical predictions. One of the implications from these research findings is that the existing design methods when applied to random waves could grossly underestimate liquefaction potential in silty sediment bed if either spectrum-based mean wave parameters or significant wave parameters were used.

We studied pore water pressure responses in silty seabed under random wave action through a series of experiments in a wide wave flume. Unlike previous experiments involving regular waves, we focus on random waves including wind-induced short waves and long waves so as to gain further insights into seabed responses and liquefaction risks posed by random waves. In particular, the study investigated how the secondary long waves that were induced by incident short wave groups affected the seabed responses. The test results revealed that these long waves could cause much larger seabed responses than the short waves (eight times larger in our flume tests). Although they had smaller wave heights than the short waves, the long waves were found to contribute much more significantly to the cumulative pore pressure than previously recognized. The likely reason is that the long waves are disproportionally effective in generating cumulative excess pore pressure, confirming qualitatively some of the earlier theoretical predictions. One of the implications from these research findings is that the existing design methods when applied to random waves could grossly underestimate liquefaction potential in silty sediment bed if either spectrum-based mean wave parameters or significant wave parameters were used.

Microbial communities are a large component of abyssal and hadal benthic environments, especially in deep-sea areas like Yap Trench, they provide a continuous source of nutrients and energy in their unique ecosystems. However, due to sampling difficulties, these microbial communities are relatively understudied. In the summer of 2017, sediment samples were collected from 21 stations around Yap Trench in the Western Pacific Ocean (mostly in the West Caroline Basin), at depths ranging from 3156 to 7837 m. Sediment samples from deep water depths and shallow water depths differed in organic matter content, median grain size, silt-clay content, and biodiversity. The structure of the microbial communities in the surface sediments had distinct relationships with environmental factors and their co-occurrence networks exhibited a clear spatial pattern. In addition, for both prokaryotes or eukaryotes, a combination of variables including silt-clay content, organic matter content, median grain size, and depth had the greatest impact on community structure. It was notable that fungi played important roles in the co-occurrence networks of deep water depth sediment samples while bacteria dominated those of shallow water depth samples. The differences in structure and ecological niches in the different networks were due to differences in sediment texture and organic matter content. Since clay had a positive effect on the diversity of bacteria, it had an indirect positive effect on fungi, leading to differences in biodiversity among different groups. More organic matter meant more nutrients were available for the growth and reproduction of microbes, which led to fewer niche overlaps. This study conducted an extensive and systematic sequencing survey of surface sediments around Yap Trench in the Western Pacific Ocean, providing insight into microbial responses to environmental heterogeneity in deep-sea benthic ecosystems.

The Yellow Sea Cold Water Mass (YSCWM) is an important component of the hydrodynamic system in the South Yellow Sea (SYS). However, its intricate interactions with the ambient flows over long time scales are not fully understood. This paper presents the analysis of the data set obtained from a seabed‐mounted Acoustic Doppler Current Profiler (ADCP) deployed for nearly 1 year in the western SYS. It allowed us to study the evolution of YSCWM, including the seasonal changes of tidal currents, near‐inertial oscillations (NIOs), and the wind‐driven currents due to typhoons and winter storms. Strong NIOs were found near the bottom of mixed layer and in the pycnocline with nearly opposite current directions, with maximum velocity of nearly 20 cm·s−1 in summer. The YSCWM can also inhibit the direct downward energy transport in the water column due to typhoons. Conversely, the hydrodynamic system also feeds back to influence the change of YSCWM. A large current shear (S) of 20 cm·s−1·m−1 is generated near the top of pycnocline. Generally, the intensity and depth of the pycnocline determine S's magnitude and vertical location, respectively. Based on the monthly averaged density profile data, the Richardson number and wavelet analysis, the NIOs are considered to be capable of inducing predominant shear instability around the pycnocline. However, the NIOs are not strong enough to influence the lower YSCWM. In addition, in autumn, each fortnightly spring tide corresponds with a bottom temperature increase of nearly 2°C, indicating that tidal currents are the leading hydrodynamic driving force to decline the YSCWM.

River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosystems as well as high concentrations of human population, are highly vulnerable to the effects of global climate change. In order to understand the wave climate, their potential changes and implication on coastline evolution for environment monitoring and sustainable management of the Niger Delta in the Gulf of Guinea, an investigation was carried out based on offshore wave statistics of an 110-year time series (1900–2010) dataset obtained from the ECMWF ERA-20C atmospheric reanalysis. Results of multivariate regression analyses indicate that interannual mean values of Hs and Tm trends tended to increase over time, especially in the western part of the delta coast, so that they are presently (1980 and 2010) up to 264 mm (300%) and 0.32 s (22%), respectively, higher than 80 years (1900–1930) ago. The maximum directions of the wave have become more westerly (southward) than southerly (westward) by up to 2° (33%) and the mean longshore sediment transport rate has increased by more than 8% over the last 80 years. The linear regression analysis for shoreline changes from 1987 to 2013 shows an erosional trend at the western part of the delta and accretional trends towards eastern part. The relationship between wave climate of the study area and atmospheric circulation using Pearson's correlation shows that the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), East Atlantic pattern (EA) and El-Nino/Southern Oscillation (ENSO) Index explain significant proportion of the seasonal and annual wave variabilities compared to other indices. But it is most likely that the combination of these climatic indices acting together or separately constitutes a powerful and effective mechanism responsible for much of the variability of the offshore Niger Delta wave climate. The study concludes that changing wave climate off the Niger Delta has strong implications on the delta coastline changes. However, other processes (such as fluvial discharge variability due climatic variability and anthropogenic effect) may be acting concomitantly with changes in wave regime and associated littoral transport to influence shoreline evolution along the Niger Delta coast.

Based on monthly averaged current, temperature, and salinity, we analyzed the changes of suspended sediment concentration (SSC) and the relationship with the warm current, coastal current, and cold water mass (CWM) in the East China Seas (ECSs). The result shows that the coastal current and surface diluted water are the route for transporting suspended sediment. The Kuroshio and its derived warm current branches play the important role of the continental shelf circulation system and control the diffusion of suspended sediment. High SSC has been mainly concentrated in coastal current and CWM. Two sedimentary dynamic patterns have been identified. The winter-half-year pattern lasts almost 7 months. The coastal currents off the Shandong Peninsula, northern Jiangsu, Zhejiang-Fujian coast are the main routes for diffusion and deposition of the suspended sediment from the Yellow River and Changjiang River. The summer-half-year pattern is characterized by the well-developed CWM. All CWMs have a unique function to trap suspended sediment under the thermocline due to weakening tidal current and residual current there. These CWMs in the Yellow Sea (YS) and north ECS are connected together. The layer above the thermocline is characterized by diluted water with low salinity, high temperature. Suspended sediment can be transported into the Okinawa Trough and the South Korea coast during this period. A strong eddy always occur nearby the Kuroshio bend at northeast Taiwan, which has promoted the exchange between the ECS shelf and Okinawa Trough, and the development of the shelf edge current and Taiwan warm current (TWC).

Deltaic coasts are dynamic geomorphic systems where continuous changes occur on diverse spatial and temporal scales, and these changes constitute an important aspect of their evolution. Based on three-year satellite-derived shoreline data coupled with re-analyzed wave data and hydro-meteorological data, a comprehensive analysis of the dominant processes governing the seasonal shoreline changes along the oil-rich arcuate section of the Niger Delta, in the Nigerian Shelf of the North Atlantic Ocean has been undertaken. Shoreline analysis results show that the delta coast is characterized by predominant summer erosion and maximum winter accretion. Between 2010 and 2012, erosion dominated over accretion and a total of 9.1 km2 deltaic land was lost to coastline erosion at an annual average erosion rate of 4.55±1.21 km2/yr. A greater understanding of the dominant factors responsible for the change is presented. Shoreline change interactions with cross-shore sediment exchange processes are prominent at seasonal timescale (Summer R2=−0.85 and Winter R2=0.7), and interannual timescale (R2=−0.93) with longshore sediment transport processes. Correlation analysis reveals a gradual degeneration of relationship between the suspended sediment flux and coastal hydrodynamics beginning from 2010 to 2012 (cross-shore transport, R=0.68, 0.36 and 0.2 for 2010, 2011 and 2012, respectively; longshore transport R=0.63, 0.44 and 0.2 for 2010, 2011 and 2012, respectively). The study concludes that the effect of fluvial sediment reduction to the delta coast due to capital dredging of the Lower Niger River channels between 2009 and 2012, and periodic fluctuations in the nearshore hydrodynamics processes caused the observed annual shoreline erosion that eventually forced the deltaic coastline toward a state of landward migration during the study period.

It is a question whether the suspended sediment from the China continent could enter the Kuroshio Current and Pacific Ocean. Surface suspended matter (SSM) and sea surface temperature (SST) in the East China Seas from December 2009 to November 2010 has been extracted from the satellite NOAA-19 AVHRR/3. We have monitored the change of the SSM diffusion during summer half-year and winter half-year. High SSM areas occur in the inshore of the Liaodong Bay, Bohai Bay, Yellow River Delta, Shandong Peninsula, Jiangsu Coast and Yangtze Estuary, especially blooming in winter half-year. Going by our findings, the sediment provenance influences the SSM distribution, and the current system and monsoon are important factors that drive the SSM diffusion all year round. In winter half-year, the ocean colour images show that the current system is well developed. The SSMs are transported southeastward, and a part reaching the outer continental shelf is captured by the Kuroshio Current before it finally reaches the open Pacific Ocean through the Tokara Strait. Some SSMs are transported by the Yellow Sea and Tsushima Warm Current into the Yellow Sea and Japan Sea. In summer half-year, most of the SSM could not reach the continental shelf break and only little SSM could be captured by the Kuroshio Current into the open ocean. Copyright © 2016 John Wiley & Sons, Ltd.

Typhoons are commonly occurring disastrous events in the Western Pacific and have become more severe as the result of global climate changes, increasingly affecting the ocean and seafloor throughout the Western Pacific. However, studies on the influences of typhoon processes and dynamic mechanisms on the continental shelf remain rather limited because of insufficient observational data in the area. This paper uses observational records at a water depth of 110 m on the continental shelf of the East China Sea in the periods when the No. 1323 typhoon ‘Fitow’ and No. 1324 typhoon ‘Danas’ passed the East China Sea to study changes in the water temperature, salinity, current and turbidity. Observation results show that typhoon Fitow had limited effects on the measurement site because of the long distance to the centre of the typhoon, but during typhoon Danas, the measured surface current speed reached 2.95 m/s, and the turbidity of the sea water increased rapidly due to the vertical mixing of sea water. Typhoon Danas causes both near-inertial oscillations (NIOs) and diurnal currents to increase, which is considered to be the major factor that contributes to bottom water temperature changes and the suspension of bottom sediments after the passage of the typhoon. Typhoons can also cause the Kuroshio Current to shift towards the continental shelf, which may affect the Tsushima Current. Copyright © 2016 John Wiley & Sons, Ltd.

Cold water mass (CWM) is a distinct hydrologic phenomenon in summer in worldwide continental shelf seas. CWM can significantly affect circulation patterns and biogeochemical fluxes, and thus marine ecosystems. Nonetheless, limited studies have documented the seasonal migration of the CWM thermal front and the corresponding sediment distribution in the South Yellow Sea (SYS). This study used field observations and a well-validated numerical model to investigate the evolution of the CWM in the SYS; and its potential effect on the seasonal and spatial variations of suspended sediment distribution and transport. Remarkable seasonal variation in the CWM and its thermal front were observed from spring to fall. Numerical model results indicated that the reductions in current velocities and bottom shear stresses were induced by the baroclinic effect of the thermal front. Hence, the offshore sediment transport existed near the thermal front. The variations of intensity and location of the thermal front are capable of inducing the variation of suspended sediment concentration and sediment transport without winds. Sediment transport direction was slightly adjusted by winds. Northerly wind drove sediment transport seaward from the Chengshan Cape to the central SYS as the thermal front moved seaward in fall. Besides, the seaward extension of highly turbid water near the Subei coast in fall was also caused by wind-induced currents and waves. The thermocline of the CWM restricted the sediment from efficiently dispersing upward to the surface, which promoted the formation of the central SYS mud area. The understanding about the effect of CWM with its thermal front on the sediment transport in this study should benefit further exploring other CWMs on the continental shelf seas.

Waves are fundamentally important for sediment re-suspension in estuary and coastal areas, especially for silty sediments, which can be easily suspended by waves, but the differential effects of swell and wind waves are still unclear. Integrated field observations were made from November 2012 to March 2013 including waves, currents, and suspending sediments on the offshore seabed of the Huanghe Delta to explore the mechanism of sediment re-suspension in silty coastal zones. During the five months of observation, there were more than 30 winter wind events that affected the study area and induced sediment re-suspension with varying suspended sediment concentration. The observed wave composition was separated into swell and wind waves using a bandpass filter. Results show that large swell (with significant height > 1.0 m) coming from the offshore direction (NE in our study area) dominated sediment resuspension in the coastal seabed due to the fact that this wind direction had the longest average fetch. Winds from the onshore direction usually had smaller swell due to their short fetches and caused limited sediment re-suspension. The residual currents caused by NE winds also transport larger sediment. An individual NE wind event could transport sediment 8–13.6 t/m2 and 5.1–8.2 t/m2 in directions parallel and perpendicular, respectively, to the isobaths, which is much higher than the sediment transportation during an individual NW wind event, which could transport 1.5–4 t/m2 and 0.6–5 t/m2 parallel and perpendicular, respectively, to the isobaths. Our research shows that large swell and the accompanying residual currents caused by NE winds (from offshore direction) are a vital driving force for sediment resuspension and transportation in the offshore zone.

The safety of submarine pipelines is largely influenced by free spans and corrosions. Previous studies on free spans caused by seabed scours are mainly based on the stable environment, where the background seabed scour is in equilibrium and the soil is homogeneous. To study the effects of background erosion on the free span development of subsea pipelines, a submarine pipeline located at the abandoned Yellow River subaqueous delta lobe was investigated with an integrated surveying system which included a Multibeam bathymetric system, a dual-frequency side-scan sonar, a high resolution sub-bottom profiler, and a Magnetic Flux Leakage (MFL) sensor. We found that seabed homogeneity has a great influence on the free span development of the pipeline. More specifically, for homogeneous background scours, the morphology of scour hole below the pipeline is quite similar to that without the background scour, whereas for inhomogeneous background scour, the nature of spanning is mainly dependent on the evolution of seabed morphology near the pipeline. Magnetic Flux Leakage (MFL) detection results also reveal the possible connection between long free spans and accelerated corrosion of the pipeline.

An Acoustic Doppler Current Profiler (ADCP) observation site was set up in the Western South Yellow Sea from 2012 to 2013 to study the local suspended particle matters (SPM) distribution pattern. The SPM concentration could be semi-quantitatively represented by backscatter intensity (Sv), converted by the echo intensity (EI) of ADCP. Results show two types of SPM in the water column: the quasi-biological SPM and quasi-mineral SPM. The quasi-biological SPM mainly exists in summer half year and is concentrated above the thermocline. It has periodically diurnal variations with high concentration at night and low concentration in the daytime. The quasi-mineral SPM is located in lower part of the water column, with similar relation to monthly tidal current variation all year round. However, the daily quasi-mineral SPM distribution patterns vary between summer and winter half year. The sunlight is thought to be the origin factor leading to the diurnally vertical motion of the biological features, which might cause the diurnal Sv variation. Unlike in winter half year when tidal current is relatively single driving force of the monthly SPM pattern, the high speed current near the thermocline is also responsible for the concentration of quasi-mineral SPM in summer half year. The sediment input difference between summer and winter half year contribute to the varied daily variation of quasi-mineral SPM with re-suspended SPM in winter and sediments from Yellow Sea Mud Area (YSMA) in summer. The seasonal variations in hydrodynamics, water structure and heavy-wind incidents are the primary factors influencing the differential seasonal SPM distribution patterns.

Topography around the Yellow River mouth has changed greatly in recent years, but studies on the current state of marine dynamics off the Yellow River mouth are relatively scarce. This paper uses a two-dimension numerical model (MIKE 21) to reveal the tidal and wave dynamics in 2012, and conducts comparative analysis of the changes from 1996 to 2012. The results show that M2 amphidromic point moved southeastward by 11 km. It further reveals that the tides around the Yellow River mouth are relatively stable due to the small variations in the tidal constituents. Over the study period, there is no noticeable change in the distribution of tidal types and tidal range, and the mean tidal range off the river mouth during the period studied is 0.5–1.1 m. However, the tidal currents changed greatly due to large change in topography. It is observed that the area with strong tidal currents shifted from the old river mouth (1976–1996) to the modern river mouth (1996–present). While the tidal current speeds decreased continually off the old river mouth, they increased off the modern river mouth. The Maximum Tidal Current Speed (MTCS) reached 1.4 m s−1, and the maximum current speed of 50-year return period reached 2.8 m s−1. Waves also changed greatly due to change in topography. The significant wave height (H 1/3) of 50-year return period changed proportionately with the water depth, and the ratio of H1/3 to depth being 0.4–0.6. (H 1/3) of the 50-year return period in erosion zone increased continually with increasing water depth, and the rate of change varied between 0.06 and 0.07 m yr−1. Based on the results of this study, we infer that in the future, the modern river mouth will protrude gradually northward, while the erosion zone, comprising the old river mouth and area between the modern river mouth and the old river mouth (Intermediate region) will continue to erode. As the modern river mouth protrudes towards the sea, there will be a gradual increase in the current speed and decrease in wave height. Conversely, the old river mouth will retreat, with gradual decrease in current speed and increase in wave height. As more coastal constructions spring up around the Yellow River mouth in the future, we recommend that variation in hydrodynamics over time should be taken into consideration when designing such coastal constructions.

Laizhou Bay and its adjacent waters are of great importance to China’s marine oil and gas development. It is therefore crucial to estimate return-period values of marine environmental variables in this region to ensure the safety and success of maritime engineering and maritime exploration. In this study, we used numerical simulations to estimate extreme wave height, sea current velocity and sea-level height in western Laizhou Bay. The results show that the sea-level rise starts at the mouth of the bay, increases toward west/southwest, and reaches its maximum in the deepest basin of the bay. The 100-year return-period values of sea level rise can reach 3.4–4.0 m in the western bay. The elevation of the western part of the Qingdong Oil Field would remain above the sea surface during extreme low sea level, while the rest of the oil field would be 1.6–2.4 m below the sea surface. The return-period value of wave height is strongly affected by water depth; in fact, its spatial distribution is similar to the isobath’s. The 100-year return-period values of effective wave height can be 6 m or higher in the central bay and be more than 1 m in the shallow water near shore. The 100-year return-period values of current velocity is about 1.2–1.8 m s−1 in the Qingdong Oil Field. These results provide scientific basis for ensuring construction safety and reducing construction cost.

The East China Seas (ECS) is one of the world's largest continental shelf seas. Based on the combination of global sea level change and sequence stratigraphy, we systematically investigated the evolution of sedimentary system in the ECS since the last glacial maximum (LGM). We have defined the transgressive boundary layer and constructed several sedimentary models of the ECS on the sequence stratigraphy and evolution of tidal sand ridges since the LGM, and sediment “source to sink” during the high sea level. The result shows that the ECS represent a typical case for large-scale continental shelf response to the global sea level change. Three sedimentary system tracts had been formed in the ECS since the LGM. First is the lowstand system tract corresponding to the late of last glaciation and LGM (23–15.4 cal. kyr B.P.). The progressive wedge occurred along the Okinawa Trough slope and the paleo-coastal zone (PCZ) along the continental shelf edge. Second is the transgressive system tract corresponding to the last deglaciation (15.4–7 cal. kyr B.P.). A large-scale transgressive boundary layer and tidal sand ridges were formed in this stage. Third is the highstand system tract corresponding to the high sea level since 7 cal. kyr B.P. The eddy mud, coastal current mud, present tidal sand ridge, delta, tidal flat and beach have been accumulating since then. The global sea level change after LGM can be divided into seven phases, of which four rapidly rising phases (RRP, I, II, III, IV) and three slowly rising phases (SRP, I, II, III) are distinguished. The tidal sand ridges were formed in the SRP and transgressive boundary layer in the RRP. The tidal sand ridges can be divided into three types including radicalized, channel and emanative. The modern circulation current system of the ECS had been built in the end of the last deglaciation. The effect of sediment “source to sink” in the ECS is closely correlative to the current system driven by the interaction of the East Asian monsoon and Kuroshio. The major sediment source is from the river discharge of the Huanghe and Changjiang River, and coastal resuspension. The muddy sediment in the eddy and coastal current, which cover the tidal sand ridges and transgressive boundary layer, is a major sediment sink in the modern ECS.

River channels and coastlines near the modern Yellow River mouth were identified using Landsat TM satellite remote sensing images,and the evolvement feature of the river channel,coastline and nearshore erosion/deposition pattern were studied.The stability of the large-scale artificial island in Yellow River mouth was studied from the viewpoint of dynamic evolution of the entirely new and old mouth region based on historical measured data.It is found that the downstream channel after the Qing 8 diverged twice and could be divided into three stages.The coast is entirely depositional in the new mouth,but erosional in the old mouth;the area surrounding the artificial island is effected by such seabed evolutionary pattern,i.e.erosion in south and deposition in north;the evolvement of the new and old mouth spits and uneven subsidence of the local strata threatens the stability of the artificial island.It is proposed in this paper to build protection constructions on both sides of the artificial island,and to strengthen the monitoring of the subsidence of the whole delta region.

The sediment in the Okinawa Trough (OT) preserves considerable information regarding land–ocean interactions and palaeoenvironmental evolution in the East Asian marginal seas. More specifically, the sediment provenance in the OT must be studied to recover this information. However, arguments about this remain, especially regarding the contribution of Yellow River (YR)-derived materials to middle OT depositions. To resolve this problem, we systematically investigated a gravity core (M063-05; 3.87 m in length, since the last deglaciation) collected from the middle OT by integrating environmental magnetism, diffuse reflectance spectroscopy, and transmission electron microscopy, as well as analyses of sediment grain size, clay mineralogy, and major elements. Our results indicated that sediment from the YR has contributed dominantly to this core since the last deglaciation. Limited contributions were also made from the Yangtze River and Taiwan rivers during the Holocene. Terrigenous inputs derived from the YR could be well characterized by the ratio of hematite/(hematite + goethite). Additionally, the Kuroshio Current (KC) activity since the last deglaciation, which is an important influencing factor for sediment provenance changes, was well deciphered using a new proxy RelDM (relative contribution of detrital ferrimagnetic minerals to bulk magnetic properties). Based on comprehensive analyses of our results and previously published studies, we hypothesised that, during the last deglaciation, abundant resuspended sediment from the palaeo-YR mouth was transported to the East China Sea (ECS) continental shelf edge and the northern OT through seaward bottom flow and further spread into the middle OT. Since the Middle to Late Holocene, the central mud area of the South Yellow Sea and the mud area southwest off Cheju Island may have become the main sources to provide YR-derived materials to the middle OT. However, the mud-area-derived sediment could only be restricted to a small range owing to the hindrance of the strengthened KC. This study provides a new perspective for sediment provenance evolution of the middle OT since the last deglaciation and proposes new methods and parameters for future research on palaeoenvironmental evolution in the ECS.

The hazardous exposure and self-burial of a submarine pipeline were studied based on the investigation of a submarine pipeline in the sand wave area in the South China Sea, as well as on statistical data and mathematical calculations. The results indicate that the pipeline free span in the area was mainly induced by seabed erosion, sand wave movement, and human disturbance. Extreme weather events cause severe impacts on seabed topography and the pipeline condition. The burial status of the pipe is mainly controlled by the evolution of local seabed topographical conditions, i.e., the amount of sediment load and the movement of seabed sand waves. The migration of the continuous small-scale sand waves facilitates the self-burial of pipes, while the migration of isolated large-scale sand waves creates potential hazards for pipelines because of the existing free span continues to grow on both sides of the sand wave.

A stability evaluation system for artificial islands was established using the fuzzy comprehensive evaluation method,upon the basis of the surrounding engineering geological environment.Thirteen factors were selected as the evaluation index,which were grouped into four categories,i.e.: factors of regional crustal stability(including tectonic features,seismic intensity,and ground subsidence),factors of seabed stability(including topography,liquefaction,and scouring),factors of foundation stability(including bearing strata,engineering soft strata,and buried ancient channels),and factors of marine environment stability(including storm surges,tidal current,wave height,and water depth).AHP method was adopted to weigh those factors.The research results would be useful to the construction of the artificial islands and its safety insurance.

Experiments on three types of soil ( d 50 =0.287, 0.057 and 0.034 mm) with pipeline( D =4 cm) either half buried or resting on the seabed under regular wave or combined with current actions were conducted in a large wave flume to investigate characteristics of soil responses. The pore pressures were measured through the soil depth and across the pipeline. When pipeline is present the measured pore pressures in sandy soil nearby the pipeline deviate considerably from that predicted by the poro-elasticity theory. The buried pipeline seems to provide a degree of resistance to soil liquefaction in the two finer soil seabeds. In the silt bed, a negative power relationship was found between maximum values of excess pore pressure p max and test intervals under the same wave conditions due to soil densification and dissipation of the pore pressure. In the case of wave combined with current, pore pressures in sandy soil show slightly decrease with time, whereas in silt soil, the current causes an increase in the excess pore pressure build-up, especially at the deeper depth. Comparing liquefaction depth with scour depth underneath the pipeline indicates that the occurrence of liquefaction is accompanied with larger scour depth under the same pipeline-bed configuration.

The paper presents an experimental investigation of seabed evolution behavior around a submarine pipeline and the hydrodynamic forces on the pipeline under regular waves. Unlike the previous flume tests that have largely used beds with median sands, this study focuses on fine sediments such as sandy silt and silt. The primary objective of the study was to investigate: (i) the scour process under different wave conditions and with different sediments and (ii) the influence of the bedform evolution on the hydrodynamic forces experienced by the pipeline. In terms of scour and ripple formation, four distinct regimes of the near-field bed evolution behavior are identified which are: (I) no scour, (II) scour without ripples, (III) scour with small ripples and (IV) scour with large ripples. The influence of bedform evolution on wave forces was found to vary significantly in different regimes. In regime I, the wave forces were quite stable; in regime II and III, the wave forces underwent a gradual reduction before reaching their equilibrium values at fairly early stages of the scour process; in regime IV, the wave forces were significantly affected by the migrating ripples and can be rather unsteady throughout the testing period.

The seabed scours around a submarine pipeline on cohesive seabed were studied by analyzing the field investigation data of DF1-1 submarine pipeline off the west coast of Dongfang, Hainan Island. The results show that, the tidal current in the study area can cause the seabed scours on both sides of the pipeline (side scours). The maximum scour depths agree well with that calculated according to the formulae proposed by various researches based on experimental studies with sand or silt beds. It is found that the finer sediments were transported mainly in the form of suspended load in the scour process, while the coarser sediments were mainly as bedload. This process caused a noticeable coarsening process of the local sediments. There exists a large number of scour pits under the pipeline (down scours), which are believed to be caused by hurricanes, but the onset of the scour (piping) is a progressive process, and piping occurs only when the critical piping conditions are exceeded.