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The sedimentary rhythm is well developed in the environment which is controlled by strong seasonal climate changing condition. This rhythm is important for sediment core dating purpose. In this study, we examine muddy sediments on the inner continental shelf of the East China Sea that are influenced under seasonal change of the East Asian monsoon. We use Ensemble Empirical Mode Decomposition (EEMD) method to process sediment grain size and X-radiograph negatives grayscale value data in three sediment cores from this area and use the results to analyze the patterns of sedimentary variability and the causes of cyclic variability of the sedimentary process. The variability in the grain size and grayscale values of the core sediments has three components: the high-frequency variability, low-frequency variability and a secular trend. Among these components, the high-frequency component reflects variability on annual time scale can be well recognized, we suggest that the annual variability is derived from seasonal variation in the sediment flux from the Yangtze River to the sea, as well as the East Asian monsoon's impact on the sedimentary dynamics of the East China Sea's inner continental shelf. However, the other variability is hard to identify which cycles there are. This variability may reflect decadal winter monsoon oscillation and human activity of dam construction in the Yangtze River. Each annual variability presents a varve in the sediment sequence, which can be used to determine the sediment deposition rate and accurately date the core sediment. We found that the average deposition rates of the three cores from north to south on the inner shelf were 3.1 cm/yr, 1.0 cm/yr, 0.9 cm/yr, indicating that the Yangtze-derived sediment decreased with the increasing distance from the Yangtze estuary to the shelf. The deposition rate of each core varies over time, and the maximum deposition rate can be 3–5 times greater than the minimum rate. The sediment ages obtained from varve chronology and radiometric dating are fairly consistent on a centennial scale, differing only by 2–5 years. Thus, varve counting is a useful supplementary approach to radiometric age dating for constructing chronologies for core sediment in shelf seas influenced by monsoons. [ABSTRACT FROM AUTHOR]

Abstract Seafloor hydrothermal systems and cold seeps contribute considerable amounts of dissolved carbon to ocean water. To investigate the compositional characteristics and potential sources of the dissolved carbon in the Okinawa Trough (OT), East China Sea (ECS), we measured the concentrations and distributions of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and their 13C stable isotopes in a full-depth water column in this area. Our results indicate that in the upper layer (water depth < 200 m), the dissolved carbon is mainly controlled by biological processes. In contrast, in the deeper layer, the concentration and isotopes are clearly influenced by seafloor hydrothermal and cold seep fluids in the OT. Based on our mass balance model estimation, cold seeps and hydrothermal fluids contribute up to 14.3% and 19.6%, respectively, of the seawater DIC. Our study shows that both of these extreme seafloor systems contribute considerable proportions of the local carbon budget. Moreover, they may also have an important impact on the extreme seafloor ecosystems therein. [ABSTRACT FROM AUTHOR]

The Yangtze River Basin, which has a population of 0.4 billion and an economic output accounting for 50% of China׳s Gross Domestic Product (GDP), is one of the most developed regions in China. With dramatic developments in the economy, large quantities of pollutants have entered the Yangtze River and have eventually been discharged into the East China Sea (ECS), and then most of them were preserved in the inner shelf coastal mud areas of the ECS. The inner shelf costal mud areas of the ECS, with sedimentation rate ranging from 0.8 cm/a to 1.2 cm/a, are an ideal place to obtain the high-resolution heavy metal record. In this work, two sediment cores collected in the inner shelf of the coastal mud areas of the ECS in 2009 were used to reconstruct historical records of anthropogenic heavy metal input from the Yangtze River Basin. The temporal distribution of enrichment factors (EFs) is in good accordance with social development of Yangtze River Basin. Before the 1930s, the EFs of Pb and Zn are considered as the background level of study area, according to the agricultural country of China in that time. The much higher EFs of Pb and Zn from the 1930s to 1980s were associated with significant improvement of industry of the Yangtze River Basin. After 1983, the dramatical incensement of EFs of Pb and Zn responded to the remarkable economic development of the Yangtze River Basin. Of particular interest, the construction of the Three Gorges Dam (TGD) in 2003 possibly induced a significant increase in the heavy metal levels in the coastal ECS, and the ban on leaded gasoline in China induced a remarkable decrease in Pb levels. Although heavy metal levels have increased since the 1930s, the coastal mud area of the ECS remains under low ecological risk. [ABSTRACT FROM AUTHOR]

Abstract: Biogenic silica (BSi) is an important parameter for understanding biogeochemical processes and paleoceanographic records in the ocean, but this proxy still has many challenges when used to reconstruct changes in the paleoproductivity and evolution of the environment, one of which is the grain size effect. We analyzed the BSi distribution in different size fractions from 8 surface sediments collected in the East China Sea (ECS). We observed the particulate characteristics of diatoms in the water and assessed the grain size effect of BSi. The results suggest the following conclusions: (1) the BSi content of the surface sediments in the ECS is generally below 1%, and the BSi content of different size fractions varies significantly, with largest fraction <16μm, which is approximately 1.1–1.8 times that in the bulk sediments. (2) The variation in the BSi content in different size fractions is largely controlled by the species of diatoms and their cell sizes. In the East China Sea, nano-diatoms are the dominant species, with dominant cells of 2–14μm, resulting in a high BSi content in the fraction <16μm. (3) The hydro-dynamic condition affects the diatom cell size distribution and sediment character, and, thus, has a significant influence on the BSi content of different size fractions. Our research suggests that the grain size distribution of the bulk sediment should be considered when using BSi as a proxy for diatom primary production. [Copyright &y& Elsevier]