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Two sediment cores from the Changjiang (Yangtze) River estuary and its adjacent East China Sea were collected and studied for eutrophication history using paleoecological records of environmental changes over the last century. A multiproxy approach by using biological and geochemical analyses revealed changes in diatom assemblages, total organic carbon (TOC), total nitrogen (TN) and biogenic silica (BSi) and give an indication of nutrient in status and trends in Changjiang River estuary and its adjacent East China Sea. The diatom assemblages in the two cores generally increased gradually from the 1970s, and accelerated from the 1990s until now, reflecting the increased eutrophication and causing large algae blooms/red tides. The TOC, TN and BSi showing the similar trends, supported the interpretation of the eutrophication process indicated by diatom analyses. The two cores were located in different sea areas of the East China Sea, and we discuss their relative changes based on their environment characteristics. We also discuss the potential effect of anthropogenic influences and ongoing projects on eutrophication in the Changjiang River and its adjacent East China Sea. [ABSTRACT FROM AUTHOR]

Limited observations exist for reliable assessment of annual CO2 uptake that takes into consideration the strong seasonal variation in the river-dominated East China Sea (ECS). Here we explore seasonally representative CO2 uptakes by the whole East China Sea derived from observations over a 14yr period. We firstly identified the biological sequestration of CO2 taking place in the highly productive, nutrient-enriched Changjiang river plume, dictated by the Changjiang river discharge in warm seasons. We have therefore established an empirical algorithm as a function of sea surface temperature (SST) and Changjiang river discharge (CRD) for predicting sea surface pCO2. Synthesis based on both observation and model show that the annually averaged CO2 uptake from atmosphere during 1998-2011 was constrained to about 1.9mol C m-2yr-1. This assessment of annual CO2 uptake is more reliable and representative, compared to previous estimates, in terms of temporal and spatial coverage. Additionally, the CO2 time-series, exhibiting distinct seasonal pattern, gives mean fluxes of -3.0, -1.0, -0.9 and -2.5molC m-2yr-1 in spring, summer, fall and winter, respectively, and also reveals apparent inter-annual variations. The flux seasonality shows a strong sink in spring and a weak source in late summer-early fall. The weak sink status during warm periods in summer-fall is fairly sensitive to changes of pCO2 and may easily shift from a sink to a source altered by environmental changes under climate change and anthropogenic forcing. [ABSTRACT FROM AUTHOR]

To investigate the influence of fresh water on phytoplankton absorption properties, the phytoplankton absorption coefficient and pigments identified by high-performance liquid chromatography (HPLC) were measured at the surface and subsurface chlorophyll a maximum (SCM) in the East China Sea (ECS), which is highly influenced by river discharge from the Changjiang during summer. For comparison, data were also collected in the Tsushima Strait (TS) at the surface and SCM. The majority of ECS surface samples taken from the low-salinity Changjiang diluted water (CDW), and even most of SCM samples taken from waters beneath the CDW, displayed significant freshwater influences. The specific absorption coefficient normalized by total chlorophyll a concentration (Tchl a), aph*(λ), of these samples was substantially higher than values derived from global regressions between aph*(λ) and the Tchl a. Using the pigment data derived from HPLC, the increase of aph*(λ) was found to be mainly caused by the phytoplankton size structure, which indicated that both surface and SCM samples in the ECS still incorporated considerable portions of picophytoplankton (cyanobacteria), even though the Tchl a was high. When water from the surface and the SCM were merged, variations in the phytoplankton size-fractions and aph*λ) vs. Tchl a that were consistent with values for the global ocean were found in the TS but not in the ECS. Data for the ECS indicated that there was no correlation between Tchl a and the size-fraction or total pigment absorption. As a consequence, aph*(λ) was poorly correlated with Tchl a and displayed large variability within a small Tchl a range. These findings suggest the need for care when considering the changing patterns of size-fractions vs. Tchl a and the relationship between aph*(λ) and Tchl a in coastal regions that are significantly influenced by fresh water. [ABSTRACT FROM AUTHOR]

This review paper provides a brief review on the development of ideas in the fields of the sea level change of the ECS (East China Sea), the history of the Yangtze River entering the sea and paleochannels in the shelf of the ECS since the Last Glacial Maximum (LGM). The paper summarizes two opposite theories about the Yangtze River entering the sea during the LGM. One theory is that the Yangtze River input a lacustrine in the north of Jiangsu province which was defunct in middle Holocene, and the river was once dry. The other was that the Yangtze River still existed and entered into the Okinawa Trough during the LGM, but scholars share different opinions on which course the river ran across and which place the river input the trough. This paper concludes future work is to study the evolution of the Yangtze River and the paleoclimate and the corresponding events as a whole from the view of regional and even global change, and more attention should be paid to the study on mud sediment, the Yangtze River's response to the changes in climate and sea-level, and the channel metamorphosis. [ABSTRACT FROM AUTHOR]

This study presents the spatial distribution of total dissolved Cu, Zn, Co, and V during an autumn survey in the East China Sea (ECS). Dissolved Fe and its organic complexation were also investigated. The present study aimed to evaluate the relationship between Cu, Zn, Co, V, D-Fe and its organic ligands and total dissolved phosphate (TDP) in the coastal waters of the ECS. A correlation analysis shows that Cu, Zn and D-Fe were nutrient-like metals, whereas Co and V were non-nutrient-like metals. A multivariate statistical analysis showed that TDP was associated with D-Fe, Cu, Zn and Co, but was not associated with V. Furthermore, TDP was observed to be positively related with D-Fe, while negatively with Fe′, which indicated that the limitation of TDP decreased the uptake of Fe′. This paper improves our understanding of the association among trace metals, TDP and phytoplankton biomass in the ECS. [ABSTRACT FROM AUTHOR]

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: Matrix bound phosphine (MBP) is commonly considered an important phosphorus form in the natural environment. This paper presents an investigation of the spatial distribution of MBP and its relationship with the environmental factors in the Changjiang Estuary and its adjacent shelf areas (29.5–32°N, 122–124°E). A total of 32 surface sediment samples were collected from April 24 to 30, 2008. MBP was detected in all samples from the Changjiang Estuary and its adjacent shelf surface sediments (0.1–29.7 ng kg−1). The concentration of MBP decreased from the Changjiang Estuary to the East China Sea shelf. Environmental factors such as organic matter, type of sediments, and redox conditions were found to affect the concentration and distribution of MBP in the marine sediments. Although the MBP levels were low in the marine sediments, the marine biogeochemical cycles of MBP in sediments were established and the information presented here will contribute to the understanding of the biogeochemical cycle of phosphorus. [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]

Dissolved inorganic carbon (DIC) in the East China Sea (ECS) is physically and chemically affected by the northward intrusion of the Kuroshio Branch Current (KBC) and the Changjiang River (CR) outflow. We trace these processes using dual DIC isotopic compositions (Δ14C and δ13C) along transects that begin in the CR and estuary, and extend out into middle shelf waters of the ECS. We especially focus on frequently occurred nearshore hypoxia, as they appeared in the summer of 2017. The Δ14C values (28.8‰--35.3‰) from the ECS mid-shelf water were comparable to the reported value from the Kuroshio Current (KC) at the continental slope (34.4‰ ± 7.4‰), but Δ14C values in the CR (-173.6‰ & -162.3‰) were substantially lower than observations made in 2014. We also found that the Δ14C of DIC in the bottom waters along the inner shelf, including hypoxic area, decreased from 25.0‰ to 18.5‰, from south to north. Water masses mixing between the CR and the ECS mid-shelf waters with and without organic carbon degradation can be identified in plots of Δ14C versus DIC-1. With simple mixing calculations, we show that the northward decreasing Δ14C of inner shelf bottom water is caused by downward transport of DIC with low Δ14C value mediated by biological process from the surface, as opposed to simple physical mixing. [ABSTRACT FROM AUTHOR]

Sediment settling velocity ( w) patterns are well established at the Huanghe and Changjiang river mouths, but no w results have been reported for the Yellow Sea and the East China Sea (YSECS) shelves due to the labor-intensive and time-consuming aspect of traditional w measurement approaches (e.g., settling column method). This disadvantage can be overcome by the acoustic Doppler velocimeter (ADV). In this study, ten ADV-based field campaigns were conducted over various seasons of the years 2011 and 2013 at six YSECS sites, five on the East China Sea shelf (28 to 87 m depth) and one on the Yellow Sea shelf (74 m depth). The results demonstrate that ADV backscatter was a reliable proxy of suspended sediment concentration over a measurement range of 1 to 1,000 mg/L. The ADV-estimated w was highest (1.43-1.88 mm/s) in summer in the southern East China Sea, and lowest (0.07 mm/s) in spring in the northern Yellow Sea. This can plausibly be explained by the hydrodynamic environment and bottom sediment type at the campaign sites. More importantly, the data reveal evidence of marked seasonal variations of w in the middle sector of the East China Sea, as well as intra-tidal variations at all campaign sites. However, these variations of w are not directly regulated by current velocity or suspended sediment concentration. This aspect represents a major challenge in future research in this shelf region and, for that matter, in similar settings worldwide. Evidently, expanding on the well-resolved continuous time series provided by the ADV approach is a key step in this direction. [ABSTRACT FROM AUTHOR]

Spatial and temporal variations in the abundance and biomass of heterotrophic protists and of their grazing impact were investigated during five cruises between July 2006 and February 2009 in the continental shelf waters of the northern East China Sea (ECS). Strongly patchy distributions were observed on all cruises, generally with a higher biomass in the western areas affected by the Changjiang River discharge. An opposite pattern was observed in February when the Kuroshio onshore transport is greatest, with a greater biomass in the eastern area. Small heterotrophic dinoflagellates (<20 µm) were most abundant numerically, whereas ciliates contributed the most to the biomass, accounting for 28–58% of the total heterotrophic protist biomass. Small heterotrophic dinoflagellates were more strongly correlated with phytoplankton biomass than were other types of protists. The total protist biomass was often most strongly related to amounts of particulate organic carbon of non-phytoplankton origin, suggesting that their abundance distribution often depended on prey other than phytoplankton, such as heterotrophic bacteria. Heterotrophic protists consumed 30.1–91.5% of Chl a production (mean 68.2%), with grazing rates increasing with the phytoplankton biomass. The results suggest that heterotrophic protists were the major consumers of primary production, and that their grazing is one of the most important losses affecting the phytoplankton biomass in the northern ECS. [ABSTRACT FROM AUTHOR]

A patchlike structure of low-salinity water detached from the Chanjiang “Diluted Water” (CDW) is frequently observed in the East China Sea (ECS). In this study, the offshore detachment process of CDW into the ECS is examined using a three-dimensional numerical model. The model results show that low-salinity water is detached from the CDW plume by the intense tide-induced vertical mixing during the spring tide period when the tidal current becomes stronger. During the spring tide, thickness of the bottom mixed layer in the sloping bottom around Changjiang Bank reaches the mean water depth, implying that the stratification is completely destroyed in the entire water column. As a result, the offshore detachment of CDW occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period. On the other hand, the surface stratification is retrieved during the neap tide period, because the tidal current becomes substantially weaker than that in the spring tide. Wind forcing over the ECS as well as tidal mixing is a critical factor for the detachment process because the surface wind primarily induces a northeastward CDW transport across the shelf region where tide-induced vertical mixing is strong. Moreover, the wind-enhanced cross-isobath transport of CDW causes a larger offshore low-salinity patch, indicating that the freshwater volume of the low-salinity patch closely depends on the wind magnitude. [ABSTRACT FROM AUTHOR]

Aerobic anoxygenic phototrophic bacteria (AAPB) are a group of heterotrophic bacteria capable of photosynthesis. The dynamics of AAPB in the East China Sea, a typical marginal sea characterized by diverse physical-chemical and ecological conditions, were investigated from April 2002 to September 2003. The results showed that the abundance of AAPB varied from 0.16 to 7.9 × 104 cells mL−1 and the percentage of AAPB (AAPB%) in the total heterotrophic bacterial abundance varied from 0.5% to 11.6% over a gradient of environmental conditions. The abundance of AAPB and AAPB% was higher in coastal and continental shelf waters than in oceanic waters. An interesting seasonal pattern was observed in the Yangtze River estuary: the abundance of AAPB was highest in summer and lowest in winter; however, AAPB% was higher in winter than in the other seasons. Throughout the investigation period, variation of AAPB abundance with temperature was much less than that of nonAAPB abundance, suggesting that low temperature was not a limiting factor for AAPB in this case. Close correlation between AAPB and chlorophyll a was observed in each season, suggesting that dependence of AAPB on dissolved organic carbon produced by phytoplankton (PDOC) may be one key factor controlling AAPB distribution. [ABSTRACT FROM AUTHOR]