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The concentration of dissolved silicic acid (DSi) and its isotopic composition (δ30Si(OH)4) were determined for the East China Sea (ECS) shelf in the spring season with high spatial resolution. DSi concentrations and δ30Si(OH)4 values ranged from 1.3 to 116.5 μM and +0.85‰ to +2.53‰, respectively. An enrichment of 30Si was observed in most surface‐water samples compared with bottom waters. Several shallow‐water stations at water depths of <20 m reflected the overall control of biological utilization of DSi and regeneration of DSi from biogenic silica (BSi) on the distribution of δ30Si(OH)4 values. A seasonal difference in δ30Si(OH)4 values was observed in the euphotic zone of shelf waters, which is attributed mainly to continuous consumption of DSi in enhanced diatom blooms. The major water masses influencing the ECS shelf were characterized with distinct DSi concentrations and isotopic compositions. Using Si isotopic constraints, modeling of δ30Si(OH)4 values implied that utilization of DSi in the ECS occurred as if in a steady‐state mode. Riverine input was the major DSi source for the surface waters of inner‐shelf areas, as well as part of the middle‐ and outer‐shelf surface waters near the Changjiang River estuary. Upwelled Kuroshio Subsurface Water from the shelf break supported diatom growth in middle‐shelf surface waters. Taiwan Strait Warm Water and Kuroshio Surface Water were relatively oligotrophic, and their influence was confined to waters near the Taiwan Strait and the outer shelf and slope areas. Plain Language Summary: The continental shelf is characterized with spring diatom blooms, which are fed by a complex sources of dissolved silicic acid (DSi). The East China Sea (ECS) is a productive marginal sea, with active mixing among the freshwater and pelagic seawaters. The significant changes in the riverine nutrients (reduced DSi and elevated nitrogen and phosphorus loadings) due to human disturbance may impact the growth of diatoms in the ECS. In this scenario, we investigated the DSi concentration and silicon isotopic composition (δ30Si(OH)4) in the ECS with wide coverage and high spatial resolution. Based on the recognition of hydrological properties, DSi concentration and δ30Si(OH)4 of the major end‐members, we reproduced the distribution of δ30Si(OH)4 in the shelf surface waters by applying a steady‐state fractionation model under different mixing scenarios. The modeling calculation suggests that DSi‐rich riverine input is important to support the diatom growth in the inner shelf, while in the middle shelf, the DSi for the diatom's growth is mainly from the upwelled Kuroshio Subsurface Water. Our study in the ECS demonstrates the usefulness of δ30Si(OH)4 in discriminating the DSi source in a dynamic marginal sea environment and may have implications in the study of silicon cycle in river‐influenced coastal areas. Key Points: High‐spatial‐resolution study of DSi concentration and δ30Si(OH)4 are carried out in the East China Sea in springMajor end‐members influencing the East China Sea are characterized with distinct DSi concentration and silicon isotopic featuresRiverine‐DSi support diatoms growth in the inner shelf and upwelled Kuroshio Subsurface Water support the diatoms growth in the middle shelf [ABSTRACT FROM AUTHOR]

Living coccolithophore assemblages collected at discrete depths (0–490 m) from eleven stations across the shelf and slope regions of the Yellow and East China Seas (YECS) during fall 2013 were analyzed using a scanning electron microscope. A total of 32 taxa were recorded, and the predominant taxa were Emiliania huxleyi , Gephyrocapsa spp., Syracosphaera spp. and Algirosphaera robusta . The body coccoliths of A. robusta exhibited an unusual morphology with incomplete hoods, which were recorded in nearly half of the samples and may represent a new variety. In addition, an agglutination relationship was observed between Gephyrocapsa coccoliths and the tintinnid Dictyocysta lepida in oligotrophic waters. Total coccolithophores reached a maximum cell abundance of 252 × 10 3 cells/l (on average 27.8 × 10 3 cells/l), with the contribution of Gephyrocapsa ericsonii , E. huxleyi and Gephyrocapsa oceanica accounting for 36.4%, 29.6% and 15.3%, respectively, of the total abundance. Coccolithophore assemblages in the YECS were a mixture of coastal, shelf and subtropical taxa, with the diversity decreasing in a radial direction from the Okinawa Trough to the inner shelves. Distinct deep-water flora existed in the Kuroshio slope waters (100–490 m), which was precisely reflected by the cluster analysis, illustrating very low percent similarity (48.1%) with the other groups. The occurrence of subtropical taxa in the coccolithophore assemblages can be used as benign warmer water signals. In the bottom turbid layers, the coccolithophore assemblages were largely composed of free coccoliths (84.3%), implying complex processes, such as cell death, resuspension and lateral advection, in the sandy and detrital waters. To clarify the relationship between the species distribution and ambient environments, a redundancy analysis (RDA) was applied to distinguish how much the variation in the taxon composition could be attributed to changes in the environmental conditions. Conclusively, salinity and temperature, which to some extent could reflect the physical properties of water stability and stratification, were key factors in driving the distribution patterns of living coccolithophores in the study areas. [ABSTRACT FROM AUTHOR]

Sediment oxygen consumption (SOC) rates on the shelves of the East China Sea (ECS) and the Yellow Sea (YS) were measured during five field studies in the period April 2010 to May 2011, using the batch intact core incubation technique. The measured SOC rates ranged from 1.73 to 17.56 mmol O 2 m −2 d −1 , which are comparable to values reported for other typical continental shelves worldwide. For the shelves of both the ECS and the YS there was a remarkable spatial and temporal variation in SOC rates. SOC was used as a proxy to assess the benthic organic carbon mineralization in the ECS and the YS, and to prepare simple organic carbon budget. For the YS it was found that on average approximately 90% of the organic carbon derived from primary productivity was decomposed in the water column and 8% was decomposed in the sediment, resulting in <4% being permanently buried in the YS sediment. In contrast, approximately 70% of the organic carbon derived from primary productivity was decomposed in the water column in the ECS and 17% was decomposed in the sediment, suggesting that the permanently buried percentage (14%, relative to the primary productivity) was higher in the ECS. The contrasting contributions of benthic mineralization to the organic carbon cycle in the ECS and the YS indicated that there is tight coupling between pelagic and benthic biogeochemical processes in the ECS, but in the YS, the regenerated production and external non-marine nutrients regulated pelagic primary production. [ABSTRACT FROM AUTHOR]

The metal elements (Al, Fe, Mn, Cr, Co, Ni, Cu, Zn, As, Pb and Ca) in the bottom sediment of the Changjiang Estuary and its adjacent continental shelf of the East China Sea were studied to map their spatial distribution and to assess their potential risk to the marine biota. These metal concentrations except Ca were generally higher in the inner shelf and northeastern part, and were found to decrease from the coast to the offshore of the Changjiang Estuary. Sedimentary Ca was most abundant in the outer shelf sediments and decreased in inner shelf. Arsenic (As) appeared to be contaminated due to economic development from 1980s in the inner shelf overall, but the potential ecological risk from the selected metals was low in the coastal sea off the Changjiang. [ABSTRACT FROM AUTHOR]

The 454 sequencing method was used to detect bacterial diversity and community structure in the East China Sea. Overall, 149 067 optimized reads with an average length of 454 nucleotides were obtained from 17 seawater samples and five sediment samples sourced in May 2011. A total of 22 phyla, 34 classes, 74 orders, 146 families, and 333 genera were identified in this study. Some of them were detected for the first time from the East China Sea. The estimated richness and diversity indices were both higher in the sediment samples compared with in the seawater samples. All the samples were divided by their diversity indices into four regions. Similarity analysis showed that the seawater samples could be classified into six groups. The groups differed from each other and had unique community structure characteristics. It was found that different water masses in the sampling areas may have had some influence on the bacterial community structure. A canonical correspondence analysis revealed that seawater samples in different areas and at different depths were affected by different environmental parameters. This study will lay the foundation for future research on microbiology in the East China Sea. [ABSTRACT FROM AUTHOR]

Anammox (anaerobic ammonium oxidation) is an important process in many suboxic to anoxic marine environments for converting fixed nitrogen to N, and has a major impact on the marine nitrogen cycle. Ladderane core lipids have been utilized as an indicator of the contribution of anammox to the marine nitrogen cycles. However, such studies have not been reported for the China seas and little is known about the importance of anammox within the nitrogen cycle of these marginal seas. In the research reported here, the ladderane core lipid contents of 17 surface sediment samples from the East China Sea are reported, and their spatial distribution is investigated. C -[5]-ladderane FAME, C-[5]-ladderane FAME and C-[3]-ladderane FAME have all been detected, suggesting that the anammox bacteria are widely present within the study area. The total contents of the three ladderane lipids (ΣFAMEs) range from 24-355 ng/g (weight of dry sediments), with higher contents occurring in the Minzhe Mud Zone and broadly coincident with the spatial distribution of hypoxia. It is suggested that the sedimentary ladderane core lipids are mainly produced in the water column and their sedimentary contents can be used as indicators of water column hypoxia. [ABSTRACT FROM AUTHOR]

To investigate the atmospheric deposition of nutrients into the coastal and shelf regions of the northwest Pacific Ocean, observation sites were established upon Qianliyan Island (within the Yellow Sea) and the Shengsi Archipelago (within the East China Sea), respectively. Nutrient concentrations, including $$ {\text{NH}}^{ + }_{4} ,{\text{NO}}^{ - }_{3} ,{\text{NO}}^{ - }_{2} ,{\text{PO}}^{{3 - }}_{4} {\text{ and SiO}}^{{2 - }}_{3} $$ , were determined in both aerosols and rainwater samples. The analytical results contain clear seasonal signatures, with high values during the dry season and low values during the rainy season. Similar trends are observed for deposition fluxes. The amount of wet deposition is greater than that of dry deposition for the studied nutrient species. The influence of meteorological factors such as rainfall means that samples from Qianliyan Island record higher nutrient values than those from Shengsi. Along with riverine inputs, atmospheric deposition plays an important role in determining the biogeochemistry of nutrient species in coastal and shelf oceans. [ABSTRACT FROM AUTHOR]

Dissolved nitrous oxide (N 2 O) at different depths of 73 stations in the Changjiang (Yangtze River) Estuary and the East China Sea (ECS) were determined from August 4 to 31 of 2013, and the sea-to-air fluxes of N 2 O were also estimated in this study. N 2 O concentrations in the surface waters ranged from 6.33 to 44.40 nmol L −1 with an average of (9.27±4.30) nmol L −1 and the values in the bottom waters ranged from 5.19 to 26.98 nmol L −1 with an average of (11.87±3.71) nmol L −1 . The concentrations of N 2 O decreased with distance from the Changjiang Estuary to the open sea. The vertical distributions of N 2 O indicated great spatial variations. A region of significant bottom-water hypoxia, with oxygen concentration less than 1.5 mg L −1 , occurred at the north of the ECS, and increased bottom N 2 O concentrations was observed. Frequent vertical mixing may enhance the emission of N 2 O from this hypoxic area. N 2 O in the surface waters of all stations were over-saturated, and the N 2 O saturations ranged from 106% to 658%, with an average of (149±62)%. We estimated the sea-to-air fluxes of N 2 O as (30.6±59.1) μmol m −2 d −1 from the Changjiang Estuary, (9.8±8.8) μmol m −2 d −1 from the coastal and shelf, and (21.0±12.7) μmol m −2 d −1 from the continental slope using the Wanninkhof 1992 equation, (24.9±47.2) μmol m −2 d −1 , (8.0±6.7) μmol m −2 d −1 and (16.5±9.6) μmol m −2 d −1 using the Nightingale 2000 equation, respectively. N 2 O emission from the ECS was estimated to be about (8.2-16.0)×10 −2 Tg-N 2 O yr −1 , suggesting that the ECS was a significant net source of atmospheric N 2 O. [ABSTRACT FROM AUTHOR]

The picoplankton distribution in the East China Sea was investigated during bloom events occurred in spring (June) and summer (August) 2011. In spring, there was no significant difference in picoplankton abundances between areas where bloom conditions were or were not established. In the bloom area, Synechococcus , picoeukaryotes and heterotrophic prokaryotes exhibited at only some stations that abundances were higher than those within the non-bloom area. In summer, the abundances of Synechococcus and picoeukaryotes were significantly higher inside the bloom area than outside. Among the picoplankton components, heterotrophic prokaryotes represented the highest carbon biomass. Factors that most influenced picoplankton distribution under bloom conditions in the East China Sea varied with season. In spring, ciliates and salinity tended to be the main factors, whereas in summer, this role was played by temperature and chlorophyll a concentration. [ABSTRACT FROM AUTHOR]