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River‐dominated marginal seas are important carbon sinks on Earth. However, their carbon sequestration capacities are changing due to increased anthropogenic perturbations. Herein, we employ substantial datasets to study the characteristics of organic carbon (OC) from the East China Sea (ECS) in 2006 and 2018 and reveal the impacts of reservoir construction on the OC deposition in this region. We show that the distribution of sedimentary OC in the ECS is primarily controlled by riverine input and seabed erosion processes. Hydrodynamic processes influence the OC deposition due to both the scouring of fine‐grained sediments and selective degradation of OC associated with the sediment mobilization. The deposition flux of OC in the ECS decreased by 48% after reservoir construction. These findings demonstrate that reservoir construction seriously affected the OC deposition in the ECS and may be applicable to river‐dominated continental shelves worldwide. Key Points: Reservoir construction changed the transport process and deposition pattern of organic carbon in the East China SeaThe deposition flux of organic carbon in the East China Sea decreased by 48% due to reservoir constructionDeposition flux reduction threatens river‐dominated margins worldwide and should be taken seriously [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]

In coastal regions, typhoons are one of the most frequent natural disasters, and instrumental data indicate that they can greatly boost marine primary productivity. Typhoons' long-term ecological repercussions, however, are still little understood. To investigate the ecological effects of typhoons since the mid-Holocene, we focused on the sediment cores in the East China Sea, with key parameters of organic C N and Bio-Si to reveal the paleo-productivity variation. Over a millennium, the occurrence of El Niño-Southern Oscillation (ENSO) has had a substantial impact on primary productivity in the southern East China Sea. The primary productivity in the southern East China Sea was risen by humid climate conditions in ∼3.0–2.0 ka and frequent typhoons in 1.5–0 ka. With a millennial period, ENSO frequency has been significantly influencing primary productivity in the southern East China Sea since the mid-Holocene. During 1.5–0 ka, frequent ENSO events have led to more frequent typhoons, which caused terrestrial materials input and water vertically mix in the southern East China Sea, ultimately increasing primary productivity. Particularly on a centennial time scale, ENSO phases determined how much primary productivity was increased, and this magnitude was bigger during the La Niña-like periods than it was during the El Niño-like periods since La Niña is when typhoons occur more frequently. During the Little Ice Age, the cold climate hindered the reproduction of phytoplankton, but increased human activities in Taiwan resulted in more soil erosion and the supply of terrestrial-derived nutrients into the sea, then amplified the typhoon-induced increase in primary productivity. As a result, this stage showed the highest primary productivity since the mid-Holocene. This study reveals that frequent typhoons promote marine primary productivity on centennial-millennial timescales and emphasizes that human activities amplify the ecological effect of typhoons in recent centuries. [Display omitted] • Frequent typhoons caused by ENSO led to higher primary productivity in the southern East China Sea during 1.5–0 ka. • The La Niña periods exhibited higher primary productivity than the El Niño periods in the southern East China Sea. • The anthropogenic activity amplified the typhoon-induced rise in primary productivity during the Little Ice Age. [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]

The Changjiang (i.e., Yangtze River) distal mud is a typical region for studying source-to-sink systems in the world. The coupling between climate change and the sedimentary system evolution of the Changjiang distal mud since the Holocene is widely debated. In this study, based on a 14C chronological framework, we investigated the sedimentary system evolution of the Changjiang distal mud since 8 ka. The provenance identification and climate conditions indicated that the climate oscillation largely determined the sediment source-to-sink processes. The sedimentary system was controlled by monsoon system oscillation from 8 to 3 ka. Specifically, during 8–5.4 ka, the prevailing Indian and east Asian summer monsoons increased the sediment flux to the Changjiang distal mud, and the proportion of the Changjiang sediments increased across the entire Changjiang distal mud. Notably, the southern regions were significantly influenced by western Taiwan rivers. Additionally, the prevailing east Asian winter monsoon enhanced the Zhejiang-Fujian coastal current, resulting in the deposition rates increased in south while declined in north. During 5.4–3.0 ka, the summer monsoon systems attenuated, causing decreased sediment discharges from the Changjiang and Taiwan, and the deposition rates declined across the entire Changjiang distal mud. In the southern regions, the intensified Taiwan warm current increased the proportion of Taiwan sediments. Since 3 ka, the monsoon system has become stable, and anthropogenic activities in south China have increased remarkably. The anthropogenic activities resulted in increased Changjiang sediments and rose deposition rates across the entire Changjiang distal mud. During 1.2–0 ka, the frequent floods in the Changjiang basins and typhoons in Taiwan, caused by increased El Niño–Southern Oscillation (ENSO) frequency, resulted in provenance fluctuation at the Changjiang distal mud. In addition, the attenuated east Asian winter monsoon caused a northward depocenter shift, which was reflected in spatially different deposition rates, i.e., retained high values in the north but declined in the south. Our findings emphasized the dominant roles of different climatic factors in different stages, and enhance our understanding of the east Asia land-ocean interactions and the relationships among the Earth's spheres since the mid-Holocene. • Sedimentary system of Changjiang distal mud displayed spatiotemporal difference. • The monsoons controlled sedimentary system of Changjiang distal mud before 3 ka. • Human activity has led to increased sediment supply from Yangtze River since 3 ka. • The frequent ENSO resulted in fluctuant provenance in the Changjiang distal mud. [ABSTRACT FROM AUTHOR]

Growing evidence has suggested that human activities could cause significant changes in marine sedimentation processes. The spatio-temporal response of sedimentary environment to human activities, however, remains unclear. Here, we present new evidence of sedimentary changes in the East China Sea over the past three decades (i.e., 1984–2016 CE) by using the mean grain size of sensitive components and geochemical parameters (i.e., Si/Ti and Fe/Al) from two sedimentary records from the Zhejiang-Fujian mud belt (ZFMB). Comparison with a compilation of published data shows that natural climate oscillations were the dominant factors that controlled the sedimentation processes before 2005 CE. Variations in the mean grain size of sensitive components over the ZFMB were mainly controlled by the East Asian Winter Monsoon before 2005 CE. The Si/Ti and Fe/Al ratios in the northern and southern of the ZFMB before 2005 CE were controlled by the Pacific Decadal Oscillation/Kuroshio Current and the East Asian Summer Monsoon, respectively. However, our synthesis shows a significant shift in the sedimentation processes between the north and south of the ZFMB since 2005 CE, i.e., after acceleration of the human imprint on sedimentation (e.g., dam construction). The mean grain size of sensitive components and the Si/Ti and Fe/Al records in the north and south of the ZFMB since 2005 CE are mainly controlled by human activities (e.g., human-induced catchment changes in the Changjiang River) and natural climate oscillations (e.g., the East Asian Winter Monsoon and Pacific Decadal Oscillation/Kuroshio Current), respectively. Our study reveals a human-induced asynchronous sedimentary signal in the East China Sea since 2005 CE, and may be applicable to river-dominated marginal seas worldwide during the human-impacted period, providing new evidence to better characterize the Anthropocene epoch. • Natural climate oscillations control the sedimentation processes of the Zhejiang-Fujian mud belt before 2005 CE. •Asynchronous sedimentation processes exist between the north and south of the Zhejiang-Fujian mud belt since 2005 CE. •Human activities cause this asynchronous sedimentary response in space since that time. [ABSTRACT FROM AUTHOR]