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Although extreme weather events make a strong impact in shallow marine sedimentary environments, there is still a paucity of past records for the Holocene period. Estuarine-inner shelf mud regions deposited from rivers that transport a large amount of suspended sediment represent an important archive of the Holocene. Two cores (S5-2 and JC07) retrieved from the estuarine-inner shelf regions of the East China Sea provided an opportunity to use sensitive grain size and 210Pb dating to reconstruct a history of extreme weather events in the Yangtze River basin. Here, we show that the average sedimentation rates of the two cores, S5-2 (1930–2013) and JC07 (1910–2013), were estimated to be 3.11 and 1.56 cm/yr, respectively. The results indicated that sediment supply played an important role in sedimentation of the estuarine-inner shelf mud region of the East China Sea. Sand content strongly increased in the late 1980s, a result of downstream riverbed erosion of the Yangtze River and submerged deltas. The grain size versus the standard deviation method was used to identify grain-size intervals with the highest variability along a sedimentary sequence. The Yangtze estuary mud area coarse population correlated well with historical literature on Yangtze River floods since AD 1930. Extreme storm events corresponded well with historical literature on the Zhe-Min mud region of the East China Sea. The spectral analyses of the sample core coastal population demonstrated that flood and storm events were consistent with a ~3–8 a periodic change of El Niño Southern Oscillation (ENSO), suggesting that the flood events usually follow ENSO years in the Yangtze River. Consequently, sediment records preserved in the two cores demonstrated different sedimentary responses to Yangtze River floods and storms, which is important to recover centennial scale flood events, to infer extreme precipitation, and to understand climate change in the estuarine-inner shelf of the East China Sea. Nevertheless, more efforts are still needed to simulate paleo-flood and predict future flood events in the context of global warming. [ABSTRACT FROM AUTHOR]

A hydrographic-sedimentological investigation was conducted in May 2001, aimed at assessing dynamic sedimentation patterns near and off the Changjiang River mouth, East China Sea. Current speed/direction, suspended sediment concentration (SSC), and turbidity were measured at eight nearshore and offshore sites, spanning a distance of ca. 150 km. The results identified a high-speed current ranging from 0.9 to 1.6 m/s at lower low water in the front of the turbidity maximum zone. This anomalous current, lasting about 4 h, was the fastest recorded over two semi-diurnal tidal cycles. Simultaneous measurements showed a high SSC (0.5 g/l) and high turbidity (>230 ppm) near the seafloor. This phenomenon would help explain periodic enhancement of sediment resuspension in the area, and an associated southward transport route from the Changjiang River mouth. [ABSTRACT FROM AUTHOR]

We examined the source-to-sink sediment transport processes from the Changjiang River to the estuarine coastal shelf area by analyzing the clay mineral assemblages in suspended sediment samples from the Changjiang River catchment and surface samples from the estuarine coastal shelf area following the impoundment of the Three Gorges Dam (TGD) in 2003. The results indicate that the clay mineral compositions throughout the study area are dominated by illite, with less abundant kaolinite and chlorite and scarce smectite. The clay minerals display distinct differences in the tributaries and exhibit obvious changes in the trunk stream compared with the periods before 2003, and the source of sediment has largely shifted to the mid- to lower reaches of the river after 2003. Spatially, the clay mineral assemblages in the estuarine area define two compositionally distinct provinces. Province I covers the mud area of the Changjiang River estuary and the Zhe-Min coastal region, where sediment is primarily supplied by the Changjiang River. Province II includes part of the Changjiang River estuary and the southeastern portion of the study area, where the sediment is composed of terrestrial material from the Changjiang River and re-suspended material from the Huanghe River carried by the Jiangsu coastal current. Moreover, the other smaller rivers in China (including the Oujiang and Minjiang rivers of mainland China and the rivers of West Taiwan) also contribut sediments to the estuarine and inner shelf areas. In general, the clay mineral assemblages in the Changjiang River estuarine area are have mainly been controlled by sediment supplied from upstream of the Changjiang River tributaries. However, since the completion of the TGD in 2003, the mid- to downstream tributaries have become the main source of sediments from the Changjiang catchment into the East China Sea. These analyses further demonstrate that the coastal currents and the decrease in the sediment load of the river have the greatest impacts on the distribution and transport of clay minerals assemblages in the sediments. [ABSTRACT FROM AUTHOR]

Abstract This study analyzes the distribution and transportation of heavy metals in surface sediments by determining the concentrations of 6 heavy metals (Cr, Zn, Ni, Pb, Cu, and Cd) based on 164 surface sediments collected from the East China Sea (ECS). The results indicated that concentrations of heavy metals were higher in the south than the north with a clear boundary near 30° N. The distributions of the six heavy metals could be divided into four groups that corresponded well with different sediment components, suggesting that hydrodynamic sorting processes play an important role in the selective transportation of sedimentary heavy metals. In addition, the spatial distributions of heavy metals were more consistent with fine-grained sediments having a grain size lower than 32 μm. Heavy metal concentrations were slightly higher than found in previous studies conducted from 2002 to 2010. In addition, their spatial patterns have changed drastically compared to data from 2006, suggesting that intensive inland human activities have had a profound impact on heavy metal transportation and distribution in the estuarine & inner-shelf regions of the ECS. Graphical abstract Unlabelled Image Highlights • Distribution patterns of heavy metals in the East China Sea are depicted. • Hydrodynamics and sediment properties are the main factors affecting heavy metal distribution. • Spatial patterns have drastically changed in the context of intensive human activities. [ABSTRACT FROM AUTHOR]