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A large scale mud deposit associated with the Changjiang (Yangtze River) has been formed over the inner shelf waters of the East China Sea. It serves as both source and sink for finegrained sediment and organic matter. Three scientific problems in regional sediment dynamics have been identified, i.e., the processproduct relationships of the mud deposit, the role played by the mud in ecosystem dynamics, and the potential of future magnitude of the carbon reservoir contained in the sedimentary system. The research topics include the future evolution of the Changjiang mud deposit, the generation of sediment gravity flows, organic matter content in the deposit in relation to water column primary production and hypoxia, wave energy attenuation over the mud bed, the decay of particulate organic matter in response to resuspension, and the carbon reservoir pattern in relation to the evolution of the mud deposit. Such research requires an enhanced ability to collect longterm, continuous, highresolution data associated with the benthic boundary layer, the water column and some new sources (e.g., data derived from in situ imagery analysis). The bottom boundary layer data are useful to the studies on sediment gravity flow, wave energy dissipation over the mud area, and the turbulenceinfluenced sediment initiation conditions. The water column data will help to establish the delay curves of organic matter, which is critical to deal with the organic matter burial rate, the formation of shallow gas, and the carbon reservoir issues. Furthermore, there is a demand to collect innovative types of data, to obtain additional information on material source and mud deposit evolution, which awaits technological breakthroughs from the observation systems.

The river-estuary-coastal ocean continuum (referred to as the continuum hereinafter) is a transition zone connecting lands and oceans. The carbon budgets in the continuum are dynamic and uncertain components in global carbon budgets. This complex landocean interactive ecosystem can absorb atmospheric CO2 through photosynthesis and dissolution of CO2. Also, the carbon fixed by photosynthesis or chemical weathering in land and watershed can be transported horizontally to the shelf waters and open oceans. In this paper, the progress of carbon cycles in the continuum is reviewed by taking the famous Chesapeake Bay and Changjiang Estuary-East China Sea continuum as typical examples. It is concluded that systematic observation characterized with land-sea coordination, sea-space integration, point-line combination, should be combined with physicalecological numerical simulation to reveal the multiple time-space scale processes. The strategy is generally operable, and the historical retrospective of results is also achievable. Thus, it can be used to clarify the evolution of carbon exchange along the river-estuary-coastal ocean continuum and their influences on carbon budgets under the combined pressures of climate change and anthropogenic activities.

The combination of human activities and natural factors has formed the eutrophication of the Changjiang (Yangtze River) Estuary and its adjacent waters, leading to increased hypoxic condition in the bottom water in summer, which has become an important signal of the deterioration of ecosystem health. This paper combs the important understandings gained from the recent studies of hypoxia in this area, analyzes multiscale temporal changes of dissolved oxygen, e.g., focusing on the tidalscale, eventscale, and interannual scale, and factors relevant to stratification and material transport. The relevant mechanisms analyzed includes processes such as the diluted water extension, Taiwan Warm Current, fronts, wind field and tides that affect oxygen consumption or transport process. It is also revealed that the main hypoxia phenomena were separated in the Changjiang Estuary and the coastal waters of Zhejiang Province. The similarities and differences in the formation and evolution of the two hypoxic zones were presented. At present, a solid foundation has been laid for the understanding of the hypoxia occurrence, however due to its multiscale temporal variations, field experiments and quantitative studies should be strengthened from a multidisciplinary perspective, and the longterm evolution trend of hypoxia in this area should also be clarified based on longterm time series monitoring.

The acquisition of seawater carbonate system parameters is essential to understand the carbon cycle in coastal ocean, the pattern of CO2 sources and sinks and assess the potential of carbon sinks. Based on the data obtained by 4 seasonal cruises conducted off Changjiang (Yangtze River) Estuary and adjacent East China Sea in March, July, November and December in 2011, we discuss the seasonal and spatial distributions of dissolved inorganic carbon (DIC) and total alkalinity (TA) and their influencing factors. The results showed that the averaged DIC and TA concentrations in inner shelf were increased from summer to autumn, then winter to spring; In cross-section distribution, DIC and TA in summer and autumn showed stratification pattern due to the influence of Changjiang Diluted Water, while in spring and winter, DIC and TA were vertically uniform due to mixing. In inner East China Sea shelf, transect DIC showed a significant negative correlation with temperature and dissolved oxygen, while TA was less regulated by temperature and dissolved oxygen changes, but positively correlated with salinity. DIC was significantly positively correlated with apparent oxygen consumption (AOU), while pH was significantly negatively correlated with AOU. The slope of pH/AOU in the outer East China Sea shelf was -0.002 7 pH/(μmol·kg-1), which was much higher compared with that of -0.001 8 pH/(μmol·kg-1) in the inner shelf. The inner East China Sea shelf seawater (water depth is less than 200 meters) was affected by seasonal ventilation and had stronger carbonate system buffer capacity, which alleviated the seasonal acidification in the subsurface water induced by organic matter decomposition.

Controlling mechanism of air-sea carbon flux in estuary-shelf continuum is important for understanding the role of ocean in “carbon neutrality” goal of China. Based on underway sea surface partial pressure of CO2 (pCO2), temperature and salinity in the Changjiang (Yangtze River) Estuary-East China Sea in spring of 2017, the spatial variations of pCO2 in four domains of the Changjiang Estuary-East China Sea continuum were presented. The roles of water mass sources, organic matter production and decomposition in controlling pCO2 were discussed semi-quantitatively. The results indicated that water mass sources were key factors in determining pCO2 and air-sea carbon flux in the Changjiang Estuary-East China Sea continuum. In addition, production and decomposition of organic matters also influenced pCO2 significantly. Influenced by Changjiang discharge, surface waters in the inner Changjiang Estuary and Zhejiang coast had relatively high pCO2, served as source of CO2 to atmosphere, with magnitude of 5.36 mmol·m-2·d-1. The north and east of study area were influenced by the Changjiang Diluted Water, and Kuroshio Surface Water, respectively. While, they were both carbon sinks with magnitude of -15.44 mmol·m-2·d-1 in the north study area. The average air-sea carbon flux in study area in spring of 2017 was -6.73 mmol·m-2·d-1. End-member mixing model revealed that decomposition of organic matter increased pCO2 of the inner estuary by about 200 μatm, which transferred the inner estuary from carbon sink to carbon source in spring; the shelf waters were carbon sink if water mass sources were considered only, while biological production decreased pCO2(decreased 144 μatm) further, and enhanced the carbon sink.

Base on underway surface CO2 data obtained from Changjiang (Yangtze River) Estuary and adjacent area in August 2019, combined with the temperature, salinity, dissolved oxygen and other parameters, the spatial variation of pCO2 and its controls during late summer were discussed briefly. The results show that the pCO2 generally decreases with distance offshore, and is the lowest in the mesohaline zone of river plume. After removing temperature effect, the good negative correlation between temperaturenormalized pCO2 and DO% indicates that biological processes are the main reason for the spatial variation, and the strong sink for atmospheric CO2 just results from high biological production. Moreover, the section distributions of temperature, salinity and DO% in the riverocean mixing zone show that the influence from vertical mixing on pCO2 is minor due to the water stratification. On the whole, the airsea CO2 fluxes for the study area are -2.0±5.2 mmol·m-2·d-1, showing a carbon sink with respect to atmospheric CO2. However, with environment changes and human perturbation such as the decrease of Changjiang runoff, Changjiang Estuary and its adjacent area may gradually shift from a sink to a source, which is necessary for us to pay more attention and further study.

Abstract: The impact of the flood event on the distribution and source of particulate organic carbon(POC) in Changjiang (Yangtze River) Estuary and adjacent waters was analyzed based on the data of temperature, salinity, total suspended matter(TSM), POC and δ13CPOC ,which were collected during the July 2020 flood. The results show that POC is negatively correlated with salinity (r2=0.41, p＜0.01), and positively correlated with TSM (r2 =0.92, p＜0.01). The mixing of salt and fresh water is an important factor affecting the distribution of POC. The distribution of δ13CPOC values in the surface water indicates that the phytoplankton production is another important factor affecting the distribution of POC in the northeastern part of the study area. Flood events reduce the concentration of terrigenous POC due to the dilution of high runoff, meanwhile, light δ13CPOC values in the southeastern part of the study area indicate that flood events could expand the influence range of terrigenous POC in the East China Sea.

The Changjiang (Yangtze River) Estuary has been subject to the double pressure of human activities and natural changes for a long time. As a result, the change of environmental factors may lead to a great alteration of phytoplankton community composition in this area. To explore the composition and variation of phytoplankton community in the Changjiang Estuary and compared with historical data, phytoplankton samples were collected vertically using net trawl method during “LORCE” cruise in August of 2017. Among all the samples collected, 7 phyla, 86 genera, and 205 species were identified, their total abundance was 1.47×105 cells/L. The results showed that diatoms and dinoflagellates accounted for 95.8% and 1.2% of the total phytoplankton abundance, respectively. Warmwater species, including Pseudonitzschia delicatissima (56.35×103 cells/L), Trichodesmium thiebautii (3.30×103 cells/L), Pseudosolenia calcaravis (3.05×103 cells/L), Chaetoceros lorenzianus (2.64×103 cells/L), Proboscia alata (1.89×103 cells/L) and Coscinodiscus gigas (1.71×103 cells/L), were dominant in the phytoplankton community. Their total abundance was 68.94×103 cells/L, which accounted for 47.00% of the total abundance of netcollected phytoplankton. High abundances of these warmwater species were observed near the front formed by the convergence of the Changjiang Diluted Water and Taiwan Warm Current. Spearman’s rank correlation showed that C. lorenzianus and P. calcaravis were negatively correlated with phosphorus, C. gigas were positively correlated with the concentrations of dissolved inorganic nitrogen, and P. calcaravis was positively correlated with salinity, C. lorenzianus and C. gigas were negatively correlated with salinity. Compared with the summer dominant phytoplankton species during the past 30 years, it was found that warmwater species of phytoplankton in the Changjiang Estuary increased significantly and their distribution area expanded northward. It was speculated that this phenomenon was highly associated with sea temperature elevation and the enhancement of warm current.

 In summer, large areas of low dissolved oxygen or hypoxia are prone to occur in the bottom waters of Changjiang (Yangtze River) Estuary. The zooplankton community (＞160 μm) in hypoxic area (DO＜2 mg/L), low dissolved oxygen area (2 mg/L＜DO＜3 mg/L) and normal area (DO＞3 mg/L) of the Changjiang Estuary in summer of 2016 and 2017 were compared. The results showed that the abundance and biomass of zooplankton in hypoxic area were significantly higher than those in the low dissolved oxygen area and normal area in 2016. The abundance of small mediumsized copepods and gelatinous zooplankton in hypoxic area and the low dissolved oxygen area were all higher than those in the normal area. It was dominated by filterfeeding of the class Thaliacea and Appendiculata in the summer of 2016 when the degree of hypxia was more serious, but in the summer of 2017, it was dominated by carnivorous Chaetognaths of the class Sagitta.

As the pilot of constructing HighFrequency(HF) ground wave radar observation network in LORCE plan, a pair of OSMARS50 HF ground wave radar was set up in Guojushan and Baimajiao of Liuheng Island, facing the Niubishan Channel of Xiangshangang Bay. To verify the accuracy of the synthesis surface current from HF ground wave radars, 25 hcontinuous observations were carried out using the Valeport Propeller Current Profiler and ADCP in the core of the effective area of this pair of HF ground wave radar. Comparison of currents shows a good correlation between data from the fixedpoint current and the HF ground wave radars, which suggests that currents obtained by the HF surfacewave radars at this point have a relatively high accuracy. At the same time, the availability of the HF ground wave radar data in large region is also tested by simulated results using a regional model established by SCHISM. Results show that the observation and simulation are consistent in the general trend: the Niubishan Channel is a regular semidiurnal tidal area, and M2 is the main tidal component, while the semidiurnal tidal component M2 and full diurnal tidal component K1 are mainly reciprocating currents. During flood tide, the sea water flows to the interior of Xiangshangang Bay first through the Niubishan Channel, and then to the Fodu Channel after a period of time. During ebb tide, the sea water in Xiangshangan Bay first flows out to the sea through the Niubishan Channel, and then the sea water from Fodu Channel gradually flows into the Niubishan Channel.

 The temporal and spatial change characters of coastline and tidal flat in the islands with different principle functions in the Zhoushan Archipelago were analyzed, using a coastal remote sensing monitoring dataset with 30 m spatial resolutions at annual interval from 1986 to 2017. The results suggested that the coastlines in Zhoushan Archipelago advanced toward the sea, with many water areas(152 km2) and tidal flats(18 km2) reclaimed into lands and the government policies were the main driven factors. The change characters were various among the islands with different principle functions. In particular, the land reclamation was significant in the islands with the principle functions of comprehensive development, coastal industry, coastal tourism, and harbor and logistics, accounting for 96% of the archipelagos new lands. The land reclamation was slight in the islands with marine science and education and scientific fishery functions, accounting for 4% of the archipelagos total new lands. Meanwhile, the coast was stable and well protected in the islands with ecological conversation and clean energy functions. The results could provide scientific basis for coastal zones ecological protection and restoration projects, as well as the marine principle functional zoning.