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• Clay mineral and elemental compositions of surface sediments were analyzed. • The old Yellow River and Yangtze River are the main sediment sources. • The influence of Yangtze sediments reaches up 35°N west of the study area. • Yangtze sediments are transported in different ways during summer and winter. The southwestern South Yellow Sea (SYS) is influenced by tremendous sediment loads derived from the Yellow River (Huanghe) and the Yangtze River (Changjiang). However, the influence of Yangtze River sediments and their transport mechanism in this area remain unresolved. In this study, we present the grain size, clay minerals, and elemental compositions of surface sediments from the southwestern SYS, together with an analysis of field observation seawater salinity and suspended sediment data, to investigate the provenance and transport mechanism of the sediments. Discrimination diagrams of clay minerals, Cr/Th vs. Sc/Al, and rare earth elements (REEs) indicate that the southwestern SYS sediments are mainly derived from the old Yellow River subaqueous delta and the Yangtze River. Interestingly, Yangtze sediments enter the SYS in ways that differ seasonally. In summer, Yangtze sediments may be transported into the central SYS by the dispersion of Changjiang Diluted Water (CDW) and may also be transported northwestward by the Subei Coastal Current (SCC) to the area off the Jiangsu coast. In winter, the Yangtze-derived sediments deposited off the Jiangsu coast in summer are transported into the central and/or even north SYS under the combined effects of the SCC, Yellow Sea Coastal Current (YSCC), and Yellow Sea Warm Current (YSWC). Throughout the transport processes, there is an alternation between a source and sink of Yangtze sediments off the Jiangsu coast; the coast serves as a sink of Yangtze sediments in summer but as a source of SYS sedimentation in winter. The depositional and transport mechanisms of Yangtze-derived sediments are closely associated with seasonal variations in the circulation system of the SYS. [ABSTRACT FROM AUTHOR]

In the past decade, the 800 km elongated mud belt off Zhejiang-Fujian coast, East China Sea (ECS), has been extensively studied for understanding the source to sink processes on the East Asian continental margin in the context of the Asian monsoon. However, to better understand the sediment source and dispersal pattern, the existing mineralogical and geochemical data of adjacent river systems, including the Changjiang River (CJR) and local rivers in Zhejiang, Fujian and Taiwan, need to be systematically reviewed. Therefore, various indicators from published literatures for the provenance discrimination in the mud belt have been summarised in this article. The results show that high diversity of clay mineral assemblages in fluvial sediments being supplied into the mud belt, e.g., dominant illite and chlorite in the CJR, absence of smectite in Taiwan rivers, similar amounts of the four clay mineral species in Zhejiang rivers, and dominant kaolinite in Fujian rivers. On heavy mineralogy, the CJR is dominated by dolomite, hornblende, and flaky minerals; and among of them, dolomite is distinctive for the CJR. For geochemical approaches, elemental compositions, combined with strontium and neodymium isotopes, reflect strong provenance control. However, geochemical and mineralogical compositions are found to vary with grain size, and thus extra caution should be taken when using these parameters as provenance indicator to discriminate the marine sediments with variety of grain-size fractions. In addition, pyrrhotite, occurred in fluvial sediments from western Taiwan, has not been found in sediments derived from mainland China, indicating that magnetic parameters could be used to discriminate sediment provenance. The mud belt formed during sea-level highstand, when modern current system in the ECS has been established, resulting in sediments derived from the CJR have been transported southward since 8 ka. In addition, sediment provenances have not been constant since initiation of the mud belt in response to climatic and oceanographic changes during the Holocene, which has been documented by mineral and geochemical signals. Nevertheless significant studies have been carried out, to better understand the formation mechanism for the mud belt and its implications for environmental changes, further studies on sediment provenance throughout the Holocene, in situ observation, and sedimentation dynamical modelling are required. [ABSTRACT FROM AUTHOR]

Surface sediment samples collected from the South Yellow Sea and northern part of the East China Sea during spring and autumn, respectively, were analyzed for grain size, aluminum, and heavy metals (Cr, Ni, Cu, Zn, and Pb) to evaluate heavy metal levels and the contamination status. The results showed that all of the heavy metal concentrations met the standard criteria of the Chinese National Standard Criteria for Marine Sediment Quality. Both the EFs and a multivariate analysis (PCA) indicated that Cr, Ni, Cu, and Zn were mainly from natural contributions, while Pb was influenced by anthropogenic inputs, especially during autumn. The geoaccumulation index of Pb near the mouth of the Yangtze River suggested that the pollution degree in autumn was heavier than that in spring, which might be caused by the greater river discharge in summer and more heavy metal adsorption with finer grain sizes. [ABSTRACT FROM AUTHOR]

Selected trace elements (As, Cr, Zn, Cu, Cd, Co, Pb and Ni) in 76 surface sediment samples collected from the rivers and the intertidal zone of Jiaozhou Bay (JZB) were evaluated to assess their environmental background values in the JZB catchment. Overall, the sediment quality in the area meets the China Marine Sediment Quality criteria. The background values (ranges) of the elements As, Cr, Zn, Cu, Cd, Co, Pb and Ni were, respectively, 8.28 (4.10–12.46), 67.96 (38.40–97.52), 56.80 (16.42–196.51), 19.13 (5.71–64.06), 0.10 (0.02–0.42), 6.51 (2.08–20.40), 17.97 (12.26–55.84) and 20.69 (10.43–30.95) mg/kg. The background values of most of the trace elements were lower than those in Chinese soil, the upper continental crust, global shales and global preindustrial sediments. The results may assist in defining future coastal and river management measures specifically targeted at monitoring trace element contamination in the JZB catchment. [ABSTRACT FROM AUTHOR]

The major (Al) and trace metal (Cu, Pb, Zn, Cr, Cd, and As) concentrations in 29 surface sediment samples from the intertidal Jiaozhou Bay (JZB) are evaluated to assess the contamination level. The results show that the overall sediment quality in the area has been obviously impacted by trace metal contamination. The geoaccumulation index and the enrichment factor values indicate that no Cr or Cu contamination has occurred on the whole, only a few stations have been polluted by As, and some areas have been polluted by Cd, Pb, and Zn. Principal component analysis suggests that the Cu, Pb, Zn, and Cd are derived from anthropogenic inputs and that Cr, As, Cu, and Zn are influenced by natural weathering processes. Cu and Zn may originate from both natural and anthropogenic sources. The contamination in the northeastern JZB is higher than that in other areas of the bay. [ABSTRACT FROM AUTHOR]

Okinawa Trough receives a large amount of fluvial sediment transported by complex oceanographic circulations, and is an ideal location for the study of paleoceanography and paleoenvironment changes. However, our knowledge of the sediment provenance and paleoenvironment evolution in the Trough during the past 17 ka is still limited. Based on high-resolution grain size, clay minerals and AMS 14 C data of the Core OKI04, we present new evidences of the provenances and paleoenvironment evolution in the middle Okinawa Trough during the last 17 ka. Our results indicate that clay-sized terrigenous sediment deposited in the middle Okinawa Trough is mainly from those rivers flowing into East China Sea and Yellow Sea (e.g., Yangtze and Yellow Rivers) and Taiwanese Rivers. Their contributions varied greatly in space and time during the past 17 ka. From 16.5 to 13.8 ka, sediment was mainly derived from the Yangtze and Yellow Rivers, with little contribution from Taiwan. From 13.8 to 5.4 ka, the contributions from the Yangtze and Yellow Rivers oscillated multiple times: low in 13.8–11.6 ka, high in 11.6–7.6 ka, and back to low in 7.6–5.4 ka, whereas the pattern of Taiwanese contribution was opposite. After 5.4 ka when the sea level was high and shoreline was far away from the Okinawa Trough, the Yangtze River and eastern Taiwanese Rivers became the main provenances. The contribution from the Yellow River decreased, which is probably because Yellow River mouth was far away from the middle Trough. Sediment grain size data show that two environmentally sensitive populations are 71–7 μm and 7–0.5 μm. The variation of the populations' mean grain size and content shows that the strength of Kuroshio Current was weak during 16.5–11.6 ka, and became strong in 11.6–5.4 ka, in which Tsushima Warm Current and Yellow Sea Warm Current formed around 8.5 and 6.5 ka, respectively. The strength of Kuroshio Current decreased in 5.4 ka and increased since 3.2 ka. Based on clay mineralogical analysis, we find that the kaolinite/chlorite could be used as a new effective indicator for the East Asian Winter Monsoon's evolution in the Trough since 17 ka. [ABSTRACT FROM AUTHOR]

Forty-three surface sediment samples and one gravity core obtained from the offshore area of the Changjiang River were analyzed for selected heavy metals (Cu, Pb, Zn, Cd, As, Hg) to evaluate the spatial distribution and potential ecological risk during the last century. The results indicated that the sediments are composed of silty sand, sandy silt and silt and were deposited in a relatively stable environment over the last century. The studied marine sediments are fine and easily adsorb heavy metals from aquatic systems. The heavy metal concentrations were found to be enriched in the sediments and were generally closely related to anthropogenic activities. However, the data analysis demonstrated that the levels of heavy metal contamination were below background values during the last century, indicating low ecological risk. Spatially, a higher concentration was found at the entrance to the Changjiang River, while it decreased to the northeast. The vertical distribution of contamination levels and ecological risk can be divided into four periods based on the downcore variation in heavy metals: pre-1940s, 1940s–1970s, 1970s–1990s and the late 1990s to the present. These conclusions form the basis for implementing appropriate policies to protect marine sediment quality. [ABSTRACT FROM AUTHOR]

Surface sediment and box core samples collected from the East China Sea (ECS) inner shelf mud area before and after Typhoon Talim (2017) were analyzed for grain size, chemical elements, and heavy metals (Cr, Ni, Cu, Zn, and Pb). By comparing the results of the survey in May with those in September, we distinguished the possible sources of heavy metals, assessed heavy metal contamination status, and elucidated the impacts of summer typhoons on the distribution of heavy metals. The results of the enrichment factor (EF) and geoaccumulation index (I geo) showed that Cr, Ni, Zn and Pb were mainly derived from natural sources, while Cu was partly influenced by anthropogenic activities and showed minor to moderate pollution. The difference between the minimum and maximum values of heavy metals became larger after the typhoon. The distribution of heavy metals in surface sediments was positively correlated with grain sizes of 11–18 μm, while the distribution in box cores was positively correlated with grain sizes of 0.8–12 μm. Additionally, the correlation between heavy metals (except Cu in box cores) and specific grain sizes increased after the typhoon passage. The thickness of the storm layer caused by Typhoon Talim was 16 cm, and the erosion depth was 4 cm. The stations with high and low values of the enrichment factor of typhoons (EF t) were separated from each other, indicating that heavy metal pollution increased at some stations and decreased at others after Typhoon Talim. The impact of typhoons on heavy metal pollution is related to seabed erosion and deposition. Summer typhoons can play a great role in the redistribution and burial of heavy metals, which is significant in the marine environment of the ECS. ● Grain size and heavy metals were analyzed before and after Typhoon Talim. ● Copper was partly influenced by anthropogenic activities. ● The thickness of the storm layer caused by Typhoon Talim was 16 cm. ● The typhoon impact on heavy metals was related to seabed erosion and deposition. [ABSTRACT FROM AUTHOR]

Abstract: Major and trace elements, loss on ignition (LOI), and grain-size distributions were determined on 190 surface sediment samples collected from the continental shelf, slope and the north Okinawa Trough in the East China Sea, at water depths of 100–200, 200–600 and more than 600m respectively. The sediments are composed mainly of sand and silt, generally low clay contents (average 10.5%), increasing over the range of 0.12–53.6% from the shelf and slope to the trough. Sediments were sandier on the continental shelf, particularly in the northern shelf sector. Spatial distributions in chemical compositions show that the contents of SiO2, CaO, Sr, and LOI values were relatively high on the sandy continental shelf. By contrast, the contents of Al2O3, MgO, Na2O, MnO, FeO, TiO2, Cu, Zn, Co, Ni and Cr were relatively high in the trough and along the central western shelf margin, where the sediments were composed mainly of silt. Fe2O3, P2O5 and Zr enrichment was highest in the slope sediments. Three factors were extracted by means of an R-mode factor analysis of chemical composition. Factor 1 has two inversely correlated elemental assemblages: (1) SiO2, K2O, TiO2, Al2O3 and Zr, which can be associated with terrigenous debris input and show high positive factor scores in the southern sector of the shelf; and (2) CaO, Sr, and LOI, which can be related with biogenic debris enrichment and show high negative factor scores in the northern shelf sector as well as in a more restricted area along the slope. CaO, SiO2, K2O and Sr represent the element assemblage of the shelf. Factor 2 comprises Na2O, FeO, Al2O3, TiO2, Cu, Zn and Ni, and shows high scores in the trough sediments. Na2O, Cu, Zn and Ni represent the elemental assemblage of the Okinawa Trough, and can be associated with volcanic matter. Factor 3 comprises Fe2O3, MgO, Cr and Co, with high factor scores on the slope and along the central western shelf margin of the study area, due to upwelling-induced enrichments in nutrients and biogenic shells. Fe2O3 and MgO are the slope elements. Based on the results of the distribution of the chemical compositions and the elemental assemblage of the surface sediment in the source-to-sink system, the influence of the Yellow River on the continental shelf is stronger than that of the Yangtze River. From the continental shelf and slope to the trough, the influence of the Yellow River decreased. From north to south in the Okinawa Trough, the sediment from the Yellow River decreases and from the Yangtze River increases, and the chemical compositions changed. [Copyright &y& Elsevier]

Abstract: Samples of one core in the Bohai Sea mud area (BSMA) were analyzed in grain size, magnetic susceptibility (MS), major minerals, foraminifera, ostracod, stable isotopes, and 14C dating to reconstruct sedimentary environment and impact of the Yellow River sediments on deposition in the Bohai Sea during the last deglaciation. The central Bohai Sea was river mouth or swamp environment before 12.9ka BP, when sediments with low MS values had high sand content. Appearance of two peat layers at 11.2 and 12.9ka BP at Core M7-6 showed that seawater had not yet entered the central Bohai Sea, where the limnetic ostracod was frequently existed and foraminifera were hardly seen. Abundance and diversity of foraminifera began to increase sharply, while their oxygen and carbon isotopes became heavier from ∼9.3ka BP due to seawater entrance into the central Bohai Sea. Related to intrusion of the Yellow Sea Warm Current (YSWC) extension into the central Bohai Sea, oxygen and carbon isotopes reached the maximum at ∼6.5ka BP. MS values between 2.4 and 8.3ka BP increased continually together with slow sedimentation rate, revealing that the impact of the Yellow River sediments was limited because of strong hydrodynamic condition and small sediment discharge. At the last 2.4ka, the influence of the Yellow River reached the maximum due to large sediment discharge into the Bohai Sea. However, the BSMA had slow sedimentation rate compared with other mud areas in the Chinese marginal seas despite of its close distance from the Yellow River mouth, indicating that although the BSMA was the primary sink of the Yellow River sediments, most of the Yellow River sediments were deposited at other areas (e.g. deltaic areas and Shandong mud wedge). [Copyright &y& Elsevier]

The heavy mineral composition and sensitive grain size changes from core SS4 retrieved from the mud wedge on the East China Sea inner shelf have been studied for better understanding provenance variations in the sediment and climate changes during the last ~1500 yr. High dolomite content and occurrence of ubiquitous polysynthetic mica indicate that the sediments in core SS4 were mainly derived from the Yangtze River, while the relatively high epidote content represent the contribution of small local rivers from Zhejiang and Fujian provinces. The substantial decrease in the epidote/hornblende ratio since ~730 yr BP manifests a decline in the relative contribution of sediment from the small local rivers to the core. We propose that the changes in drought/flood conditions in response to the East Asian winter monsoon (EAWM) and human activities might have been mainly responsible for changes in sedimentary characteristics. During 1400–730 yr BP, the core sediments were characterized by relatively finer sensitive grain size and high epidote/hornblende ratio, due to a possibly weaker EAWM (i.e., less Yangtze River-derived sediment transported by the southward coast current). This time interval coincides with the Sui-Tang Warm Period (1400–1130 yr BP) in China and the Medieval Warm Period (1000–730 yr BP) on a broader regional scale. The prolonged warm periods were, however, interrupted by three short cold phases at 1350–1280 yr BP, 1130–1000 yr BP and 870–750 yr BP, characterized by coarse sensitive grain size and decreased epidote/hornblende ratio. Between 360 and 150 yr BP, the sensitive grain size significantly coarsened, which corresponded to the Little Ice Age. Our new findings suggest that sedimentation processes of mud wedge formation are responsive to natural environmental change and human activity. ∙ Provenance and climate changes have been detected in the East China Sea ∙Significant changes in the ratio of epidote/hornblende indicate source variations ∙The contribution of small local rivers has declined since 730 yr BP ∙Climate-driven drought/flood conditions and human activities are the main causes ∙The alternation of the warm and cold period is well recorded by heavy minerals [ABSTRACT FROM AUTHOR]