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Abstract Flocculation plays an important role in sedimentation of estuaries and continental shelves. The process of flocculation in estuary or shelf is extremely complicated. In this paper, the flocs observed at five sections that include 36 stations within the Yangtze Estuary of the East China Sea were studied systematically using scanning electron microscopy and energy dispersive X-ray spectrometry. The characteristics and spatial distributions of the flocs were obtained, and the factors about the spatial distributions of the flocs were discussed. The flocs were divided into 6 types according to their components: mineral flocs, bio-detritus flocs, mineral-biological flocs, organic-mineral flocs, organic-biological flocs and complex flocs. The percent of the mineral flocs is the highest. The mean particle size of the flocs ranges from 4.00 to 5.00 Ф. The sizes of the mineral flocs are the finest, while the sizes of the complex flocs are the coarsest. The percent of mineral flocs is high near the coastal areas and decreases toward the open sea; this trend is similar to those of organic-mineral flocs and complex flocs. High percentage of bio-detritus flocs and organic-biological flocs is observed to the east of the Taiwan Warm Current. The types and spatial distributions of the flocs are restricted by the properties of the water masses, and they are affected by the interactions of electrolytes, organic matter, biological processes and estuarine authigenesis process. The formation of flocs increases the settling velocity of suspended particles and has an important effect on the formation of mud areas on the continental shelf of the East China Sea. Highlights • Approximate 6 types of flocs within Yangtze River Estuary and its adjacent seas were discerned. • The characteristics of grain-size patterns and spatial distributions of the flocs were obtained. • Spatial distributions of flocs are mainly controlled by electrolytes interactions, biological and authigenesis processes. [ABSTRACT FROM AUTHOR]

Abstract: The summer behavior of Changjiang diluted water (CDW) toward the East/Japan Sea (EJS) is investigated by using a numerical ocean model. The present study focuses on the summer 2003, in which significant low salinity water is observed in the southwestern EJS in spite of similar amount of Changjiang discharge to the normal year. This paper mainly compares two experimental results for the summer 2003 (Exp. Y2003) and the normal year (Exp. NML). The simulated CDW in summer 2003 reveals remarkable changes in the pathway toward the Tsushima/Korea (T/K) Strait. The northeastward CDW behavior to the Jeju Strait, a major pathway in the normal year, is significantly reduced, while an intense southeastward extension to the along-shelf current (i.e., Taiwan–Tsushima Warm Current System) is dominant, similar to the field observation in July 2003. It is suggested that the Ekman dynamics plays an active role in remarkable changes of the CDW behavior. Namely, the reduction of northeastward behavior is associated with the dominance of strong northerly wind anomaly where the fresher bulge develops. On the other hand, the strengthened southwesterly wind over the southern region off the river mouth reinforces the extension to the along-shelf current. In consequence, the CDW below 28.0psu joins the along-shelf current in the central East China Sea, and a passage of significant low salinity water is resulted at the T/K Strait in August 2003 due to the advection by along-shelf current. The additional experiment also exhibits that the strength of along-shelf current has an impact on the passage of CDW via the T/K Strait. [Copyright &y& Elsevier]

Abstract: This paper reports the initial result of the flux of submarine groundwater discharge (SGD) into the Changjiang effluent plume (CEP). A radium mass balance model and a 224Ra/223Ra activity ratio (AR) apparent age model were applied to estimate the residence time of water above the pycnocline in the CEP. These two approaches gave similar results, yielding residence times of 5.4d and 7.0d, respectively, in the inner and outer plume zones. The nonconservative inventory of 226Ra was established in the CEP, and converted to a 226Ra flux by dividing by the water residence time and assuming steady state conditions. After subtracting the desorption of 226Ra from suspended sediment and the diffusion from the bottom sediment, the 226Ra flux from SGD was converted to a total SGD flux by dividing by the measured activity of 226Ra in local groundwater. The SGD flux in the CEP is estimated to be 0.2–1.0×109 m3 d−1, which is equivalent to 6–30% of the Changjiang water discharge during flood season. This large flux indicates that SGD may be another important nutrient source to the East China Sea. [Copyright &y& Elsevier]

Abstract: In this paper we discuss the links between saltwater intrusion and subtidal circulation in the Changjiang Estuary based on a 3D numerical model. We restricted our study mainly to the three major outlets of the estuary: the South Passage, the North Passage, and the North Channel. Subtidal transport is landward in the South Passage and NNW- or NW-ward on the shoals, whereas it is mainly seaward in the North Passage and North Channel. Such a residual characteristic is caused by the interaction between tide and shallow water depth. Decomposing analysis indicated that Stokes transport is the major mechanism causing this particular residual transport pattern. Under its influence, the South Passage is the most saline outlet and the North Channel is the major route discharging the Changjiang runoff. Results of a tracer experiment indicated that active water mass exchange occurs from the South Passage to the North Passage and finally to the North Channel. Thus, the salinity in each outlet is determined not only by the tidal-averaged diversion ratio around the bifurcation of the South and North Channels but also by the subtidal circulation in the waterways and on the shoals. The northerly wind produces a horizontal circulation around the river mouth, which flows into the estuary in the North Channel and out of the estuary in the South Channel and South Passage. This circulation increases the salinity in the North Channel and decreases it in the South Passage. Recent engineering projects have intensified the landward residual in the South Passage, thereby increasing the salinity in the South Passage and decreasing the salinity in the North Channel. [ABSTRACT FROM AUTHOR]

Abstract: X-ray diffraction (XRD) mineralogical and grain-size analyses indicate that inner continental shelf sediments in the East China Sea (ECS) represent a unique mixing of clays derived from the Yangtze River and silts/sands from small western Taiwanese rivers. Taiwanese (e.g., Choshui) clays (<2μm) display no smectite but the best illite crystallinity and are only distributed along southeastern Taiwan Strait. Both Yangtze and Taiwanese river clays are illite-dominated, but the poor illite crystallinity and the presence of smectite and kaolinite indicate that Taiwan Strait clays are mainly Yangtze-dominated. In contrast, medium silts (20–35μm) and very fine sands (63–90μm) in the Taiwan Strait are characterized by low feldspar/quartz, low K-feldspar/plagioclase and high kaolinite/quartz, indicating their provenance from Taiwanese rivers. Taiwanese silts and sands are introduced primarily by the way of typhoon-derived floods and transported northward by the Taiwan Warm Current during summer–fall months. Yangtze clays, in contrast, are widely dispersed southward about 1000km to the western Taiwan Strait, transported by the China Coastal Current during winter–spring months. Since most Taiwan Strait samples were collected in May 2006, clay results in this paper might only represent the winter–spring pattern of the dispersal of Yangtze sediments. [Copyright &y& Elsevier]