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The division of freshwater into separate channels at tidal junctions plays an important role in determining the hydrodynamics and material transport in multichannel estuaries. To obtain a better understanding of the net material transport, it is essential to precisely measure the residual flow near the tidal junction. In this study, the phase-averaging method (PAM) was applied to investigate the residual current and freshwater division at the lower reaches of the Modaomen Estuary (ME), China. This is the first PAM-based quantitative evaluation of the freshwater division at the tidal junction, which controls the freshwater division between the mainstem of the ME and the Hongwan Waterway (HW). The accuracy of the PAM results was examined by comparison with the subtidal flow obtained at a moored site near the estuary mouth. The results showed that the HW received freshwater discharge from the ME during both spring and neap tides. The stratification in the HW was determined by water masses advected from the mainstem of the ME. During the spring tide, the ME had a stronger longitudinal salinity gradient. Via interaction with the vertical shear of the along-channel velocity, the tidal straining tended to enhance the vertical salinity gradient, which generated more vigorous stratification in the channel during the spring tide than during the neap tide. In accordance with the stratified and longitudinal salinity gradient, the mainstem of the ME exhibited a stronger exchange flow during the spring tide. Harmonic analysis and error estimation showed that the PAM can effectively remove the tidal signals. The accuracy of our results suggests that the PAM can be applied to survey other tidal junctions.

With the development of the Jidong oilfield,three large artificial islands have been planned in the coastal water around the Nanpu area in recent years.To well understand the character of dynamic geomorphology of the area is significant for the construction of artificial islands.Using the data of measured tide and related currents offshore,in combination with the data from side-scan sonar and offshore sampling,the authors studied the tidal dynamic geomorphology pattern around the three planned artificial islands,and discussed the possible migration of nearby sand ridges,and its impact on construction of artificial islands.The impact of the construction to the tidal dynamic system is also predicted.

The area reduction and function deterioration of the coastal wetland in the Yellow River Delta,as a response to climate change,is basically controlled by natural factors.Water and sediment from the Yellow River are the fundamental materials for the survival of the coastal wetland.The rate of increment of coastal wetland has slowed down as the water and sediment discharges of the Yellow River decreased since last seventies.The joint action of the factors,such as wave,tide,storm surges,land subsidence and sea level rise has led to area loss and the negative growth of the wetland in the last decade.Owing to water shortage,soil salinization and the drought frequently happened in the coastal wetland,the diluted water from the Yellow River is nearly disappeared.It results in the increase in salinity and decrease in surface water temperature in the offshore water,the damage of environment and the reduction in biodiversity.

The distributions of thickness of unconsolidated Quaternary sedimentary layers in Jiaozhou Bay and Qingdao offshore area were studied by using 1079-km high-resolution shallow seismic profiles and drilling core data, and the factors controlling the Quaternary evolution were discussed. The results show that such thickness distributions resulted from the coactions of geologic structures and marine hydrodynamic conditions since the Holocene. The geologic structures controlled the slope deposit, proluvial and fluvial fillings since the late Pleistocene. Holocene marine hydrodynamics eroded away sediments at the bay mouth, and tides carried these eroded materials to the sides of the bay mouth and released them there, forming channel-ridge-alternating geomorphic features. During transgressive processes, the sea level rose rapidly, and insufficient sediment supply and tidal actions yielded the relict sediments in the east of Qingdao offshore area.

With available survey data and 237 surface sediment samples, the modern sedimentation in Qingdao bays is studied. The research result shows that the east area is shallower (16.4 m) than that in the west (45.8 m). The geography was formed by a symmetric wave in a sequence of bank — offshore depression — platform — tidal channel — platform — offshore depression — foreshore from south to north. Flood sedimentary systems were formed from inlet of the Jiaozhou Bay in the west to the barrier bar in the east. Lateral sedimentation includes mainly tidal current ridges in two tidal channels. Gravel sandy sediments formed by wave lie in midland of from seashore to wave base. Dynamic functions are mainly tide and wave. Tidal current moves sediment in vertical and horizontal directions, sorting sediments and providing materials for coastwise beaches. The sources of sediment are mainly from eroded headland rocks. In general, grain sizes in this area from the inlet of the Jiaozhou Bay in the west (120°17′) to the barrier bar outside in the east (120°35′) are coarse-fine-coarse, forming gravel-gravelly sand (G-S), sand (S), gravel clay silt (G-YT), clay silt (YT), gravelly silty sand (G-TS), silty sand (TS), gravelly sandy silt (G-ST), and sandy silt (ST) in turn.

Ninety-eight clay mineral samples from the YSDP102 core were analyzed by x-ray diffractometer to study the four clay minerals: illite, chlorite, kaolinite and smectite. Twenty-eight samples had been analyzed on the laser particle-size analyzer to reveal the particle features of the sediments. Distribution of the clay minerals and the particle characteristics in the YSDP102 core show that the core experienced three different depositional periods and formed three different sedimentary intervals due to different sediment sources and different depositional environments. Features of the clay minerals and the heavy minerals in the YSDP102 core indicate that coarse-grained sediments and fine-grained sediments result from different sources. The Yellow Sea Warm Current has greatly influenced the sedimentary framework of this region since the current’s formation.

The sand-hill section in Hongguang, Pengze County, Jiangxi Province is composed of eolian sand beds interbedded with 12 weakly-pedogenetic paleosols, and this sedimentary sequence was formed from about 25 to 13 kaBP. A detailed rock-magnetic study demonstrates that the magnetic minerals in the sequence are dominated by multi-domain magnetite grains in addition to small amounts of maghemite and hematite. Compared with the eolian sand beds, the paleosols are characterized by smaller magnetic particles, higher proportion of low-coercivity minerals and markedly increase in the magnetic mineral content. In the section, various magnetic parameters (K, ARM, SIRM and S ratios) display a roughly gradual increase from eolian sand beds to the overlying paleosols but an abrupt decrease from paleosols to the overlying eolian sand beds. The content of low-coercivity magnetic minerals shows the lowest values in the second eolian sand bed from the bottom of the section, and from the bed upwards it gradually increases on the whole in the eolian sand beds. These magnetic properties reflect regional climatic changes during the last glacial maximum.

Northwest of Cheju Island in the eastern South Yellow Sea there is an arc patch of muddy deposit which coincides with an anticlokwise eddy and thus is referred to as muddy deposit of eddy. Two drilling wells, the YSDP 102 well and the YSDP 103 well, penetrated the muddy deposit and revelated the sedimentary sequence in the sea area during the last deglaciation and the Holocene. Based on shallow seismic profiles, sedimentary features and dating data, stratigraphic units formed in the eastern South Yellow Sea, documents the path, time and process of the earliest post-glacial transgression in the South Yellow Sea are presented, the formation of the Yellow Sea warm current and its control over the Yellow Sea sedimentation are discussed, and deals with the source of the muddy deposit is dealt with.

[1] Two studied sediment cores from the Korea Strait contain mud sequences (14 m and 32.62 m in thickness) that were deposited during the last 6,000 years. The sediments have uniform lithology and geochemical properties, however, marked down-core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties. An expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep-sea sediments. The studied sediments are divided into four descending intervals, based on magnetic property variations. Interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite, and the lowest solid-phase sulfur contents. Interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations, which suggest active reductive dissolution of detrital magnetic minerals. Interval 3 is marked by a progressive loss of hematite with depth, and coincides with the minimum magnetite concentration. Interval 4 has an increasing down-core enhancement of authigenic greigite, which apparently formed at depths of 3–30 m below the sediment-water interface due to arrested pyritization reactions. These results indicate delays of thousands of years for acquisition of magnetizations carried by greigite, which suggests that studies of geomagnetic field behavior from greigite-bearing continental shelf sediments should be conducted with care. Also, virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn-depositional environmental processes.