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Simple Summary: Ecosystem processes and energy flow drive marine food web dynamics with primary food sources, trophic interactions, and functional groups are crucial for stability. In continental shelf ecosystems, seasonal benthic–pelagic coupling influences food webs and fisheries, but research on shelf fish responses to environmental shifts is limited. The Southern Sea of Korea (SSK), influenced by the Tsushima Warm Current (TWC) and Changjiang River Diluted Water (CDW), faces rapid warming and seasonal changes that affect productivity and trophic dynamics. Using carbon (δ13C) and nitrogen (δ15N) stable isotopes, we examined fish trophic structures, revealing distinct seasonal food web patterns. During stratified conditions, reduced benthic–pelagic coupling shifts TWC fish to more pelagic prey, with some species showing lower trophic positions. Benthic fish rely on detrital sources, while pelagic fish are more influenced by pelagic production, especially in spring. Seasonal isotopic shifts reflect changes in pelagic and benthic pathways, with a stronger pelagic influence in spring and reduced resources in summer. Higher productivity in the CDW region leads to more pronounced variations in pelagic consumers, while benthic consumers in TWC regions remain stable. These findings emphasize the need for monitoring warming and TWC influence, which could shift food webs toward greater benthic dependence, impacting fisheries. In seasonally stratified marine environments, the dynamics of benthic–pelagic coupling plays a crucial role in shaping food web structures and fisheries production. We examined fish food web structures across three distinct shelf areas in the Southern Sea of Korea (SSK) during both stratified (summer) and mixed (spring) water conditions using stable isotopes of carbon (δ13C) and nitrogen (δ15N). In spring, fish communities exhibited a broader range of δ13C values compared with summer, indicating more diverse feeding strategies. Seasonal variations in the proportion of benthic and pelagic prey in consumer diets highlighted shifts in benthic–pelagic coupling, illustrating how consumers adjust their reliance on benthic or pelagic resources. The relative importance of the benthic pathway varied among species groups throughout the year. During stratified conditions, reduced benthic–pelagic coupling led to increased reliance on benthic prey, particularly in the oligotrophic region influenced by the Tsushima Warm Current (TWC). The food web spanned five trophic levels, with a median of 3.6. Several species, notably benthic ones, declined in their trophic positions during the summer stratification. These results suggest that fish food webs in the SSK are shaped by temperature-driven seasonal bottom-up control. Our findings further offer insights into how increased water-column stratification could impact the trophic niches of shelf-food webs in the TWC region. [ABSTRACT FROM AUTHOR]

Observations have revealed the existence of persistent slope countercurrents (SCCs) that flow southwestward beneath the Kuroshio Current at several locations over the East China Sea (ECS) continental slope. It was not clear whether these flows are localized circulation features or segments of a trough‐scale circulation system in the Okinawa Trough (OT). We demonstrate that there indeed exists a potentially continuous trough‐scale SCC along the ECS slope that is associated with an OT‐wide cyclonic circulation using high‐resolution model simulations and physical interpretations. The detailed features of the deep OT circulation are illustrated by the trajectories of the Lagrangian drifters and the time‐varying distributions of passive tracers. The SCC in the ECS is characterized by its weak yet persistent nature, typically located in narrow sloping regions at the isopycnal layer of 26.6–27.3 kg m−3. It exhibits a characteristic speed of approximately O‐(1) cm s−1. Analyses and experiments suggest that the divergence of upwelling in the SCC layer (26.6–27.3 σθ surface) gives rise to lateral potential vorticity transport, ultimately driving the deep cyclonic circulation. Furthermore, the SCC also displays a substantial connection with the onshore intrusion of the Kuroshio Current, particularly to the northeast of Taiwan Island. The SCC may potentially play a crucial role in the transport of heat and nutrients, as well as in regulating sediment distributions within the deep OT. This mechanism offers fresh insights into explaining the presence of undercurrents in semi‐enclosed marginal seas. Plain Language Summary: The Okinawa Trough (OT) is a key link between the Pacific Ocean and the East China Sea (ECS) continental shelf. It was observed by previous studies that persistent southwestward slope countercurrents (SCCs) exist beneath the northeastward Kuroshio Current at several locations over the ECS continental slope. These countercurrents have been attributed to a variety of mechanisms based on analyses and interpretations of observations made at different locations. It is yet not clear whether these flows are localized circulation features or segments of an OT‐wide circulation system. In this study, we find that there indeed exists a trough‐scale SCC along the ECS slope that is associated with an anti‐clockwise circulation. Analyses indicate the OT experiences different vertical volume exchanges at the deep layer, which induces lateral exchanges of potential vorticity (a dynamically conserved quantity in an ideal and rotating fluid) and eventually drives the SCC. Numerical experiments are performed to show the validity of this process. The SCC may be of vital importance in transporting heat and nutrients and regulating the sediment distributions in the OT. This mechanism is potentially applicable to explain the undercurrent in similar semi‐enclosed marginal seas. Key Points: Over the entire East China Sea continental slope, the slope countercurrent beneath the surface Kuroshio Current is potentially continuousThe slope countercurrent is the western part of a deep cyclonic circulation in the Okinawa TroughThe upwelling divergence along the East China Sea continental slope is the main forcing mechanism of the slope countercurrent [ABSTRACT FROM AUTHOR]

The East China Sea (ECS) is among the most important and highly dynamic shelf seas, where the coupling of physical and biogeochemical processes is distinctive and may play a crucial role in regulating nutrient conditions and the pattern of primary production. Based on field observations during the late summer of 2019, the physical controls of nutrient supply and the subsequent influences on phytoplankton chlorophyll‐a (Chl‐a) regime were investigated in the ECS. The coastal upwelling originating from the Kuroshio Subsurface Water (KSSW) intrusion serves as a nutrient source on the inner East China Sea (ECS) shelf, and this inshore upwelling combined with the coastal water largely governs the surface Chl‐a patterns. The halocline, thermocline and nutricline exhibit a vertically synchronous fluctuating phenomenon, and the coexistence of several subsurface cold rings/patches was significantly observed on the middle‐outer ECS shelf, indicating intense vertical advection and the occurrence of upwelling. The subsurface cold rings greatly regulate the vertical hydrodynamics, constituting unique upward pathways of the onshore intruded KSSW on the middle‐outer shelf. Nutrients can be upwelled within these cold rings to support primary production, thus partially leading to the spatial variability of subsurface Chl‐a maximum in terms of intensity and depth. Our findings would considerably contribute to our understanding of the physical‐biogeochemical‐ecological processes on the ECS shelf. Plain Language Summary: The East China Sea (ECS) is one of the most important continental shelves in the world. Exploring the physical‐biogeochemical processes is of great significance for the in‐depth understanding of ecosystem in this shelf sea. Here, specific attention was paid to the physical controls on the nutrient supply and the associated influences on phytoplankton chlorophyll‐a (Chl‐a) regime in the ECS. We show that the coastal/inshore upwelling originating from the nearshore branch of the Kuroshio Subsurface Water (KSSW) intrusion serves as a nutrient source on the inner ECS shelf. The co‐occurrence of several subsurface cold rings clearly indicates the upward transport of the onshore intruded KSSW on the middle‐outer ECS shelf. The subsurface cold rings may play a role in modulating the vertical hydrodynamics and related biogeochemical‐ecological processes, leading to the upward delivery of nutrients and enhanced Chl‐a levels. Our results would provide a sound scientific basis for the studies of biogeochemical and ecological dynamics in the ECS. Key Points: The coexistence of several subsurface cold rings indicating upwelling on the middle‐outer East China Sea shelf was observedSubsurface cold rings and coastal upwelling constituted unique upward pathways of the onshore intruded Kuroshio Subsurface WaterNutrients could be upwelled within the cold rings and potentially modulated the associated biogeochemical‐ecological processes [ABSTRACT FROM AUTHOR]

Gravity and seismic tomography models of the tectonosphere, which allow greater detailing and refining of the structure of the crust and subcrustal mantle in the region are considered. In the East China Sea, the crust is considerably deconsolidated; this deconsolidation has been found to be continued within the subcrustal mantle down to a depth of 40–45 km. A wide NW-trending transform-fault-related pull-apart zone has been identified at the western boundary of the Pacific Plate. In the eastern East China Sea areas, the lower layer of the Philippine oceanic lithosphere is underthrust beneath the Ryukyu Arc with further underthrusting under a viscous subcrustal layer of the continental shelf. In the central sea areas, the oceanic lithosphere is upthrust on the continental marginal lithosphere. Evidence of a central-type structure, which is likely of plume origin, has been detected in the subasthenospheric mantle layer at the western boundary of the Philippine Sea plate, which is the middle fragment of the Ryukyu Arc. [ABSTRACT FROM AUTHOR]

The study of critical geological processes of sediments from source to sink in the East China Sea (ECS) is of great significance for further understanding the surface processes, material cycling, and sedimentary evolution in the East Asian continental margin. Based on the high-resolution clay mineralogy and REEs in fine-grained sediments of Core CSHC-15, this study has analyzed the periodic transition mechanism of sinks in fine-grained sediments in the ECS from a source-to-sink perspective. The clay mineral provenances of Core CSHC-15 exhibited distinct periodic abrupt shifts between the Changjiang and Taiwan island over the past 200 kyr, indicating the periodic transitions of sinks in fine-grained sediments between the inner shelf of the ECS and the Okinawa Trough. When the sea level rose or fell to a critical depth (around −25 m or −50 m), the changes in the accommodation space of the continental shelf and the shelf fronts were the direct factors leading to the periodic transitions of sinks in fine-grained sediments in the ECS. The intense eccentricity cycles (100-kyr) of the clay mineral parameters of Core CSHC-15 reflected the impacts of the East Asian Winter Monsoon (EAWM). This study confirms that long-term (eccentricity and longer cycles) climate signals of the source areas can be extracted from the clastic sedimentary records of the ECS. The new finding highlights the periodic transition mechanism of sedimentary sinks in the ECS that will promote the progress of sedimentary geology since the Late Quaternary. • We report high-resolution clay mineralogy and REEs in fine-grained sediments of Core CSHC-15. • The provenances exhibited periodic abrupt shifts between Changjiang and Taiwan over the past 200 kyr. • Frequent abrupt shifts in provenances indicate the periodic transitions of sinks. • The changes in accommodation space and shelf fronts are the direct factors leading to the periodic transitions of sinks. [ABSTRACT FROM AUTHOR]

The mud depositional area ("mud area") of the South Yellow Sea serves as a prominent carbon sink within the Eastern Continental Shelf of China, offering crucial insights into human activities and climate fluctuations and its relationship with carbon cycle. This study investigates variations in total organic carbon (TOC) and black carbon (BC) concentrations in South Yellow Sea sediments. By combining 210Pb isotope analysis with grain-size profiling, the study distinguishes organic carbon origins, revealing the complex interplay between human activities and environmental shifts since the Industrial Revolution. The reasons for discrepancies between TOC and BC contents are analyzed, yielding the following results: (1) Sediment core QY-2 predominantly contains terrestrial-sourced organic carbon, primarily derived from the Yellow River and the Yangtze River. (2) Temporal fluctuations of BC in core QY-2 show distinct trends, periodic responses to human activities, particularly peaks in 1937 and 1945, linked to large-scale wars in China. (3) Relaxed carbon emission regulations in China, coupled with industrial growth spurred by the "reform and opening up" policy, led to a continuous rise in BC content from the mid-1960s to the 1980s, peaking in 1980. Subsequently, reduced BC values during the 1990s correlated with emission control policies and the shift from highly polluting domestic coal stoves to cleaner alternatives like liquefied petroleum gas or natural gas stoves. (4) BC content was influenced by the East Asian monsoon and Pacific Decadal Oscillation (PDO), with higher BC accumulation rates occurring in summer and depletion in winter. (5) Interestingly, changes in BC and TOC content exhibited a negative correlation. While grain size and material sources minimally influenced these discrepancies, the primary driver lay in the water's redox environment, impacting other TOC components and thereby causing variations in both TOC and BC content. This study of black carbon sources to sinks in the South Yellow Sea Mud Area holds significant implications for the broader Yellow Sea sedimentary system and provides support for understanding carbon cycle and marine environments. • South Yellow Sea's mud area acts as a significant carbon sink in East China Sea. • Our records show the terrestrial sources (Yellow River and Yangtze River) dominate organic carbon in sediment core QY-2. • Peaks in black carbon contents coincide with the major historical events during the last century. • The East Asian monsoon and PDO could have an impact on black carbon content in South Yellow Sea. • Redox environment can influence organic carbon variations, impacting TOC and BC contents. [ABSTRACT FROM AUTHOR]

Near-inertial waves (NIWs) play an important role in diapycnal processes and energy dissipation. A mooring observation deployed on the continental shelf in the East China Sea captured anomalously intensified subsurface near-inertial kinetic energy (NIKE) during the passage of Typhoon Danas (2013). An early study has investigated the role of Parametric Subharmonic Instability (PSI) induced by internal tides in the intensification of the subsurface intensified near-inertial velocity. However, results based on regional numerical simulations reveal that strong subsurface near-inertial velocity persists even in the absence of tidal effects, implying the existence of additional sources of NIWs. Our analyses showed that after excluding the effect of PSI, approximately 30% of the remaining subsurface NIKE can be attributed to another Typhoon Fitow (2013), which occurred a week prior to Typhoon Danas. Constrained by the Kuroshio current and the continental shelf, the NIKE generated by Typhoon Fitow propagates northward and reaches the mooring location, leading to the intensified subsurface NIW signal. Our simulation, together with the observations, suggests complicated NIW dynamics in continental shelf regions, involving interactions between successive typhoons, topography and background current, and differing from the open ocean. These interactions will further influence vertical mixing on the continental shelf along the pathway of NIW. • Subsurface near-inertial kinetic energy on the continental shelf increased significantly after the passage of Typhoon Danas. • Numerical simulations suggested the enhanced subsurface near-inertial kinetic energy are caused by two successive typhoons. • The propagating NIWs may cause a remote influence on the mixing along its pathway. [ABSTRACT FROM AUTHOR]

The East China Sea (ECS) is located between the Eurasian continent and the Pacific Ocean with a wide continental shelf, which acts as a potential source of reactive iron in the Western Pacific. However, the source and fate of reactive iron in continental shelf sediments of the ECS remain poorly constrained. Here, we examined the influence of the depositional environment on the fate of reactive iron on the continental shelf of the ECS since the last deglaciation. The contents of redox-sensitive elements (U and Mo) indicate that the sediments in the ECS inner shelf have primarily deposited in oxic and suboxic environments since 18.5 ka. The ratio of reactive iron to total iron (Fe HR /Fe T) ranges from 0.24 to 0.41, and the ratio of total iron to aluminum (Fe T /Al) is approximately 0.55 ± 0.11. These ratios suggest that the majority of reactive iron is derived from fine-grained terrestrial sediments discharged by the Changjiang River. The contents of Fe py and Fe carb exhibit opposite trends with depth in the core, indicating competition between carbonate (bicarbonate) ions and sulfide ions for ferrous ions. This competition is primarily controlled by the depositional environment and redox state since 18.5 ka. The Fe carb is the dominant iron speciation throughout the core sediments, but its abundance declined since 13.2 ka when the ECS inner shelf was influenced by seawater transgression due to deglacial sea-level rise. The Fe py content reached its maximum when the ECS inner shelf was fully flooded. Our study highlights the depositional control on the source-sink processes of reactive iron, providing new insights into the fate of reactive iron on continental shelves in response to environmental evolution. • Redox-sensitive elements indicate oxic and suboxic environments since 18.5 ka. • Particulate iron originates from fine-grained sediments of the Changjiang River. • Fe py and Fe carb are primarily influenced by the depositional and redox conditions. [ABSTRACT FROM AUTHOR]

The distribution pattern and flux variation of POC in the continental shelf seas are essential for understanding the carbon cycle in marginal seas. The hydrodynamic environment and complicated estuarine processes in the East China Sea result in challenging estimates and substantial spatio-temporal variability in terms of POC concentrations. A hybrid retrieval model based on the mutual combination of the color index algorithm (CIPOC) and the empirical band ratio algorithm was applied in this study to effectively and dynamically monitor the surface POC concentration in the East China Sea in a long-term series for the first time using MODIS/Aqua remote sensing satellite data from 2003 to 2020. A hybrid retrieval model based on the mutual combination of the color index algorithm (CIPOC) and the empirical band ratio algorithm was applied in this study. The MODIS/Aqua remote sensing satellite data from 2003 to 2020 were employed for the first time to dynamically monitor the surface POC concentrations in the East China Sea for a long time series. The results demonstrated that the performance (R2 = 0.84, RMSE = 156.14 mg/m3, MAPE = 43.30%, bias = −64.79 mg/m3) exhibited by this hybrid retrieval algorithm confirms the usability of inversion studies of surface POC in the East China Sea. Different drivers such as river discharge, phytoplankton, wind, and the sea surface current field jointly influence the spatial and temporal distribution of POC concentrations in the East China Sea. This paper also verifies that the hybrid algorithm can be applied to retrieval tasks for POC in different seas with similar optical properties to the waters of the East China Sea. In conclusion, the long-term series East China Sea POC data record, which was established based on MODIS/Aqua, provides supplementary information for in-situ sampling, which will aid the long-term monitoring of POC fluxes in shelf seas. At the same time, it has also improved our understanding of the transport and spatio-temporal variability of POC in the East China Sea, enhancing our comprehension of the impact of POC on environmental changes and carbon cycling in marginal seas. [ABSTRACT FROM AUTHOR]

As the expiration date of the Japan-Korea joint development of the continental shelf in the East China Sea comes closer, the joint development agreement is becoming a hot issue between Korea and Japan. The Joint Development Zone (JDZ), established under the joint development agreement, is set to expire in 2028 unless the two countries agree otherwise. Despite not having any commercially significant discovery of oil and gas in the JDZ, it has served as a provisional arrangement to manage peacefully the disputed continental shelf in the tri-junction where China also claims jurisdiction. Given its significant role in the peaceful management of overlapping marine resources and jurisdiction claims over decades, the two countries need to engage in negotiations to come up with a solution to the pending issues concerning the development of the JDZ. The JDZ area has the potential to become a flashpoint of conflicts in the strained relations between the two countries, if the agreement expires without any provisional or permanent arrangements. [ABSTRACT FROM AUTHOR]

In this study, we investigate spatial and temporal variabilities of particulate organic carbon (POC) in the East China Sea (ECS) and explore the dominant influencing factors for its three subregions—coastal, continental shelf and open sea—by analyzing satellite derived POC from 2001 to 2011 after calibration against in situ samplings. The analysis reveals that the largest POC occurs in spring at the coastal region with a value of 297.5 mg m−3, and the smallest in summer at the open sea region with a value of 108.9 mg m−3. POC in the coastal region is dominated by biological activity related to river discharge of nutrients and organic matter, and is regulated by sediment discharge variation due to the Three Gorge Project and chemical fertilizer application along the Changjiang River watershed; the open sea region is dominated by water exchange with the Kuroshio current, which results in the highest sea surface temperature and the lowest chlorophyll and POC among the three subregions; POC in the continental shelf region is driven by the seasonal competition between the influence of the coastal ocean and the Kuroshio current through biological activity and water exchange. A method to estimate the organic matter reserve in the ECS was developed based on satellite data and in situ samplings. Organic carbon storage was estimated at 4.08 × 1013 g, which could be used as a baseline for future estimates. An improved estimation could be found with additional in situ data and with the use of a more sophisticated algorithm for satellite POC analysis. [ABSTRACT FROM AUTHOR]

The UNCLOS prescribes basic principles on maritime boundary delimitations, but interpretation and application of the relevant provisions differ, and the views expressed on them still leave ample room to be unilaterally interpreted and applied. So, it is undeniable that conflicts over ocean waters among the concerned countries are serious and difficult to overcome. To solve these problems, the UNCLOS calls for the countries concerned to make every effort to enter into provisional arrangements of a practical nature. Korea and Japan have maritime boundary problems in the waters surrounding the Korean peninsula, and so, in order to solve those problems, both nations established a joint development zone (JDZ) in the East China Sea in 1974. The zone can be terminated in 2028. Therefore, this study examines and analyzes the impact of the JDZ agreement between Korea and Japan over the East China Sea as to the delimitations of the continental shelf/EEZ. [ABSTRACT FROM AUTHOR]

Coastal offshore currents transport terrestrial materials from coastal areas to continental shelf areas in the upper layer; these currents are regarded as unimportant in winter when wind‐driven onshore currents are dominant. In this paper, both long‐term observations and high‐resolution simulations in the East China Sea reveal unique wintertime offshore currents in the upper layer that are widespread in the 30–70‐m isobath area and even overcome the wind‐driven onshore currents at the 50–70‐m isobaths. The mixed layer instabilities, frontogenesis and turbulent thermal wind, which constitute a mechanism in the generation of submesoscale offshore currents, have a growth rate that is fast enough to compete with the wind‐driven dynamics when the winter monsoon is relatively weak (<10 m/s). The alternation of the weak‐wind and strong‐wind modes during the winter monsoons provides a general condition for the repeated occurrence of remarkable submesoscale cross‐shore transport and carbon sequestration in coastal seas. Plain Language Summary: The mechanism by which wintertime cross‐shore currents occur in coastal seas is re‐examined together with wind‐driven mesoscale currents and submesoscale processes. Submesoscale currents, which is shaped like filaments or eddies with a horizontal scale of approximately O(1) km, have frequently been reported in the upper ocean. These submesoscale currents are dynamically defined by conditions where the relative vertical vorticity equals or exceeds the planetary vorticity, where the Rossby number is O(1). Both long‐term observations and high‐resolution simulations in the East China Sea reveal unique wintertime offshore currents in the upper layer that can prevail over wind‐driven onshore currents. The synoptic winter monsoons provide the general conditions for the repeated occurrence of remarkable submesoscale cross‐shore transport and carbon sequestration in coastal seas. Key Points: Significant wintertime offshore currents that overcome wind‐driven onshore currents are investigated in the East China SeaThe submesoscale dynamics are fast enough to compete with the wind‐driven dynamicsThe synoptic winter monsoon provides a general condition for submesoscale cross‐shore events in coastal seas [ABSTRACT FROM AUTHOR]

This study investigates the presence of plastic and non-plastic microparticles in the gastrointestinal tracts of two deep-sea sharks, Etmopterus molleri (n = 118) and Squalus mitsukurii (n = 6), bycatch from the East China Sea continental shelf. We found a total of 117 microparticles, predominantly fibres (67.52 %), with blue (31.62 %) and black (23.94 %) being the most prevalent colours. E. molleri contained 70 microparticles (0.63 ± 0.93 items/shark), 61.42 % non-plastics like viscose and cotton, while plastics included polyethylene, polyethylene terephthalate, and acrylic. Despite S. mitsukurii's limited sample size, the results show that it takes in a lot of microparticles (47 microparticles, 7.83 ± 2.64 items/shark), 57.44 % non-plastics (viscose, cotton, and ethyl cellulose), and 42.56 % plastics. A positive correlation between microparticle presence and total length was observed for E. molleri. These results provide initial data on microparticle ingestion by these species, highlighting potential ecological risks and trophic transfer implications in deep-sea ecosystems. [Display omitted] • E. molleri & S. mitsukurii , deep-sea sharks, ingest plastic & non-plastic microparticles • Predominance of viscose & cotton microparticles highlights textile fibre contamination in deep-sea. • Findings suggest species-specific microparticle ingestion rates/exposure in deep-sea sharks. [ABSTRACT FROM AUTHOR]

The dissolved (d) and total dissolvable (td) trace metals were determined in seawater samples collected from the East China Sea (ECS). Labile particulate (lp) species was calculated as td minus d, and the sectional and vertical distributions of d and lp trace metals were evaluated. The surface concentrations of dAl, dCo, dNi, dCu, and dPb were higher in the continental shelf region than in the Kuroshio region. lpAl and lpFe were the dominant species below a depth of 400 m, and a strong positive correlation was observed between them in the Kuroshio region. The enrichment factor (EF) against crustal abundance was calculated for the purpose of estimating the origin of dMs in the ECS. The EF(dFe) was close to unity. These results suggest that both lpFe and dFe are dominated by crustal sources. The other elements had high EF, indicating significant contributions from other sources. EF(dPb) was close to the enrichment factor in aerosol, suggesting atmospheric input from anthropogenic sources. The dM/P ratios were calculated to investigate the validity of the extended Redfield ratio in the ECS. The Mn/P, Co/P, Cu/P, Zn/P, and Cd/P ratios in shallow water (< 200 m) were within the same order of magnitude as those in phytoplankton. In contrast, the Al/P and Fe/P ratios were, respectively, 27 and 213 times higher in phytoplankton compared to those in shallow water. These results suggest that dFe is a potential limiting factor for biological production, although it is not exhausted in surface water. [ABSTRACT FROM AUTHOR]

Fronts in coastal oceans are important mesoscale processes that relate to regional dynamics and can impact ecosystems. The daily distribution of a sea surface temperature (SST) front is obtained in the East China Sea (ECS) using 15 years of satellite observations. High frontal activities are mainly found near the coast. The spatial and temporal variability of the monthly frontal probability is subsequently investigated using an empirical orthogonal function (EOF). Seasonal variability in frontal activities is predominant for the majority of the ECS, with the highest and lowest values occurring during winter and summer, respectively. Some major fronts have been identified, such as coastal and shelf fronts. The coastal fronts can be further divided into three separate sections: near Hangzhou Bay and along the Jiangsu and Zhejiang coasts, respectively. The shelf fronts have two sections: north and south of the Changjiang River. All fronts are characterized by a prominent seasonal cycle, though their seasonalities differ. The underlying driving forces, e.g., alongshore wind, SST, and river discharge, are further analyzed for the individual fronts. River discharge is the driving factor of fronts to the south of the Hangzhou Bay along the Zhejiang coasts while wind is the main reason for the frontogenesis near and north of Hangzhou Bay. The SST largely influences the frontal dynamics for the shelf and coastal fronts to the north. This study comprehensively describes the frontal activities in the ECS and leads to a better understanding of frontogenesis in the coastal region. It is fundamentally helpful for fisheries management and has great potential for oceanic pollution control. [ABSTRACT FROM AUTHOR]

Shelf mud is an important sink for fluvial sediment, and it is sensitive to variations in river discharge and ocean circulation, which are significantly influenced by climate change. However, the evolution of shelf mud in response to climate change during the Holocene is poorly understood. Here, we present high‐resolution sedimentary records of heavy minerals and mass accumulation rates (MARs) from the East China Sea shelf to study the response mechanisms of the Holocene shelf mud supply, transport, and sedimentation to the climate‐driven variations in fluvial discharge and ocean currents. The results indicate that the shelf mud primarily originates from the Changjiang (Yangtze) River and has been mainly transported by wind‐driven longshore currents in suspension since approximately 8.0 ka. A comparison of the MARs with several shelf mud sedimentation‐rate records and climate changes during the Holocene on millennial timescales showed that strong (weak) precipitation in the river basin, which is positively linked with Asian summer monsoon and El Niño‐driven storms, could intensify (weaken) the fluvial sediment supply, thereby increasing (decreasing) the shelf mud deposition flux. On multicentennial timescales, changes in the relative intensities of different ocean currents due to climate oscillations during the Holocene could generate frequent migrations of the current shear front (a hydrodynamic barrier), which has trapped an abundance of suspended materials on the shoreward side and resulted in rapid mud sedimentation (~2.3 g/cm2/year) at different sites during different periods. Therefore, our study highlights that the Holocene shelf mud evolution responds sensitively to climate changes on different timescales. Key Points: The Changjiang River mud has been mainly carried southward by wind‐driven longshore currents since 8.0 kaHolocene shelf mud supply is modulated by precipitation from summer monsoons and El Niño‐related stormsHolocene rapid shelf mud sedimentation is directly linked with climate‐driven migrations of ocean currents [ABSTRACT FROM AUTHOR]

Due to the ubiquitous steep continental shelf slope in the East China Sea, topographic Rossby waves are very common when the Kuroshio Current flows along the slope, and of great importance in the water and energy exchange between the open ocean and coastal sea. To examine the structural characteristics of topographic Rossby wave, we use stretching transform of time and space and perturbation method to get the analytic solution of potential vorticity equation with topography. For a given background flow v = v0 + δx, the effect of background flow shear is discussed. The main conclusions are drawn that background flow shear is required for the existence of solitary Rossby waves; for flow shear δ < 0 (δ > 0), anticyclonic (cyclonic) solitary Rossby waves exist and their zonal structure tilts eastward (westward); the phase speed of solitary Rossby waves is related to the amplitude and flow shear intensity; solitary Rossby waves are non-dispersive waves, and the width of solitary waves is inversely proportional to the intensity of the flow shear. Furthermore, these theoretical results are used to explain the propagation speeds and distributions of eddies along the Kuroshio Current in the East China Sea. In addition, these results could be applied to other areas with similar meridional current and topography. [ABSTRACT FROM AUTHOR]

The possibility of oil reserves under the seabed of the East China Sea created competition between Japan, South Korea, and Taiwan to claim ownership of these natural resources. The dispute marked the start of international cooperation in maritime East Asia and introduced the United States into this power game due to its exploration techniques and financial power. While Taibei, Tokyo, and Seoul put sovereignty-related disputes aside in an attempt to explore resources jointly, the change in international politics in East Asia and Washington's perception of the western Pacific rim led to the failure of cooperation. This article argues that this international power game over natural resources management epitomized the dynamic politics between the United States and its East Asian allies. The roles of sovereignty, local interests, and U.S. international security created a dynamic scenario revealing how oil reserves were never the issue, but instead the embodiment of the actual concerns of these players behind their diplomatic language. Situating the 1970s oil exploration in the context of the Cold War, this article provides a historical lens to understand the contours of the shifting geopolitical structure in maritime East Asia. [ABSTRACT FROM AUTHOR]

A meteo-tsunami is a tsunami-like phenomenon excited by a traveling atmospheric disturbance. In Japan, meteo-tsunamis are frequently observed along the western coast of Kyushu Island during winter–spring. One of the largest meteo-tsunamis occurred on March 3, 2010, where the maximum amplitude of water level oscillations exceeded 1 m in various bays on the western coast of Kyushu Island including Nagasaki Bay and Makurazaki Bay. Simultaneously, a sequence of rapid atmospheric pressure changes with amplitudes of ~ 1 hPa was recorded at various meteorological stations along the western coast of Kyushu Island. We numerically reproduce large sea level oscillations in both bays assuming that a simple atmospheric pressure disturbance consisting of a sequence of triangular-shaped pressure changes in 10–20 min propagates east-southeastward at a speed of ~ 30 m/s over the East China Sea. Over a wide area of the shallow continental shelf in the East China Sea, oceanic waves are amplified through a resonant coupling (Proudman resonance) to the traveling atmospheric disturbance. Oceanic waves propagate eastward while being further amplified through reflection and refraction owing to the complicated topographic and configuration constraints in the coastal area and excite meteo-tsunamis along the western coast of Kyushu Island. In particular, the reflection of oceanic waves (edge waves) from the end of the elongated continental shelf running east–west off Makurazaki Bay plays a key role in amplifying water level oscillations; the eigen-oscillations are excited on the continental shelf, which continue to supply water waves that are resonant with eigen-oscillations in Makurazaki Bay. [ABSTRACT FROM AUTHOR]

Typhoon Soulik decayed rapidly via two‐way interaction with the northern East China Sea, the extratropical shelf region, before landing on the Korean Peninsula on 23 August 2018. In the northern East China Sea, where the water column is strongly stratified with warm surface and cold subsurface waters, a large cold wake emerged with intense sea surface cooling, which is primarily caused by vertical mixing in the water column. This abrupt sea surface cooling rapidly increased the downward enthalpy flux, mostly in the form of latent heat flux. The slow translation speed of Typhoon Soulik and strong thermal stratification in the region transferred its energy into the ocean, as the typhoon had a long residence time over the wake, and consequently led to rapid decay with energy loss to typhoon intensity ratio of −4.4 ± 1.0 hPa (kJ cm−2)−1. Plain Language Summary: Understanding and predicting tropical cyclones, including typhoons, are very important for reducing and preventing damages to life and property. In August of 2018, Typhoon Soulik was predicted to make landfall on the Korean Peninsula as a strong cyclone with high winds. However, the typhoon rapidly weakened over the northern East China Sea before making landfall—a failed prediction. This study reveals that the rapid decay was caused by two‐way interactions between the typhoon and the ocean on the continental shelf. Strong mixing with cold subsurface water due to the high winds associated with the slowly moving typhoon significantly lowered the sea surface temperature, leading to energy loss into the ocean for a sufficiently long period of time to cause rapid decay. These results provide quantitative evidence of energy exchange between the typhoon and the ocean, which can help to improve forecasts of tropical cyclone intensity particularly in the stratified shelf region. Key Points: Two‐way interactions between stratified ocean and a slowly translating (~2 m s−1) tropical cyclone yields rapid decaySevere (>8 °C) sea surface cooling is primarily caused by vertical mixing with cold subsurface water on the extratropical shelfRapid decay is driven by downward energy transfer enhanced by Soulik's long (~15‐hr) residence time over a large cold wake [ABSTRACT FROM AUTHOR]

The present analysis has revealed that both the altimetry and tide gauge records show a prominent sea level rise from 1993 to 2016 in the coastal seas east of China, including Bohai, Yellow Sea, and East China Sea (BYECS). The regional mean sea level rise rate for the BYECS continental shelf area is ~ 3.2 mm/year, which is close to the global mean (2.9 mm/year). Besides the rising trend, the BYECS sea level anomaly (SLA) also shows obvious interannual and decadal oscillation. It is found that the mid-latitude westerlies, rather than the steric height variability, are responsible for these oscillations. By analyzing the 67-year (1950–2016) hindcast outputs from an eddy-resolving ocean general circulation model, a 14.2 years decadal period is found to dominate the BYECS SLA variability, and the decadal oscillation is positively correlated with the North Pacific Gyre Oscillation (NPGO). The composite analysis and causality analysis demonstrate that during the positive phase of the NPGO, the mid-latitude westerlies decrease and a positive wind stress curl anomaly at the same latitude of the East China Sea's Kuroshio occurs to the south of the westerlies. Consequently, the Kuroshio Current volume transport and sea surface height difference between the two sides of the Kuroshio decrease, that is, the sea level in the BYECS rises. [ABSTRACT FROM AUTHOR]

This paper presents review of dissolved Rare Earth Elements (REE) and methane anomalies distribution in the East China Sea water column. In general, the REE concentrations of the shelf water are markedly higher than those of Okinawa Trough water in the East China Sea. Rare earth elemental concentrations in the Okinawa Trough water mainly governed by the Kuroshio Current, along with particle scavenging processes and REE released from lateral transport. Hydrothermal vent activities also have their influence at some sites in the Okinawa Trough intermediate water. The result of comparison between dissolved REE in the East China Sea water with the South China Sea (known as Bien Dong or East Vietnam Sea) water shows that the dissolved REE contents of the South China Sea water are relatively similar to those of the slope water and the Okinawa Trough water and significantly lower than those of the continental shelf water in the East China Sea, except for the case of Ce. The South China Sea surface water may have the effects of fluvial and aeolian input, and coastal water masses at the deep-sea basin but less influenced than at the continental shelf. Both the East China Sea and the South China Sea contain methane gas emission sites, indicating deep fluid input into the seawater that influences the chemical composition of water masses, especially near the bottom water layer. [ABSTRACT FROM AUTHOR]

Abstract Sedimentary responses to the cross-shelf transport on the East China Sea continental shelf are ascertained based on analyses of the sediment grain size and detrital mineral components of surficial sediments. Sedimentological data show that fine-grained sediments can be transported across the continental shelf and have formed a tongue-shaped zone with an axis located near 29°N that extends from the coast to 124°40′E or beyond. The sediments in this tongue-shaped zone are rich in very fine silt and clay, as are the dominant sediment fractions discharged by the modern Yangtze River indicating a modern terrigenous source. Sediment with grain sizes 7–9 Φ is the main fraction that is transported across the continental shelf. In contrast to the regions in the same longitude, in the tongue-shaped zone the relatively low heavy mineral content, high schistose mineral content and high dolomite content and the mixture of fresh and weathered minerals show that modern Yangtze River sediment has been widely transported to this region. Meanwhile, the simultaneous existence of the fine-grained tongue and a coarse-grained area immediately south of the base of the tongue coincident with the nearshore Kuroshio branch current intrusion area indicate that the Kuroshio intrusion plays an important role in triggering the cross-shelf flows. Graphical abstract Unlabelled Image Highlights • Sedimentological data demonstrate cross-shelf transport in the East China Sea. • Sediment grain size and mineral distributions show apparent cross-shelf transport. • Cross-shelf transport occurs in a relatively fixed location near 29°N. • Fine-grained sediment can be transported cross-shelf to 124°40′E or even farther. • Kuroshio intrusion is an important factor that triggers the cross-shelf flows. [ABSTRACT FROM AUTHOR]

Horizontal resolutions of regional ocean models are often inadequate to resolve submesoscale vertical advection (SVA) in the continental shelf seas. This study aims to compare the SVA in two similar model setups in the East China Sea with different horizontal resolutions. A novel method to parameterise the impact of SVA on temperature (SVA-T) has also been proposed, which can significantly improve the low-resolution model (LRM) results. In particular, we focus on the time frame wherein this method can be applied. The suggested method primarily improves the representation of an internal warming process, which is significant in both the observations and high-resolution model (HRM) but is absent in the original LRM. Combined with the observations, we found that the internal warming, which occurred in the barrier layer of the water column during early autumn, is accompanied by submesoscale oscillations of isothermals in the HRM. SVA dominates the internal warming process and increases the total vertical advection by up to an order of magnitude in the HRM compared with the LRM. Therefore, we parameterised SVA-T by increasing the vertical thermal diffusion coefficient in the LRM. To further specify the time frame wherein the parameterisation can be applied, we introduced two empirical conditions related to the major generation mechanisms of frontogenesis, mixed-layer instabilities and turbulent thermal wind in the mixed layer: a deep mixed-layer depth >20 m and a large surface-bottom temperature difference (∆T >2 °C). Finally, we successfully simulated the internal warming in the LRM during early autumn by applying the proposed method. Nevertheless, the parameterisation of the horizontal distribution of SVA-T needs to be considered in the future to achieve better three-dimensional model results. • SVA-T generates internal warming in the barrier layer in the southern East China Sea. • This warming occurs in early autumn owing to submesoscale oscillations of isothermals. • The timing of the internal warming is expected under conditions of MLD >20 m and ∆T >2 °C. • SVA-T parameterization results in a larger thermal vertical diffusion coefficient. [ABSTRACT FROM AUTHOR]

Abstract The bottom branches of the Kuroshio Current in the East China Sea were recently discovered from physical and chemical oceanographic perspectives. To examine the diversity and distribution of demersal fish community in the East China Sea and to assess the impact of the bottom branches of the Kuroshio Current, we investigated the demersal fish community with an Agassiz trawl in the East China Sea shelf in the summer of 2015. A total of 72 species were collected in 40 sampling sites with Amblychaeturichthys hexanema , Champsodon snyderi , Odontamblyopus rubicundus , Cynoglossus interruptus , and Coelorinchus multispinulosus being the top 5 most abundant species. Three ecological groups of demersal fish—the Coastal group (CG), Transitional group (TG) and Kuroshio group (KG)—were identified through multivariate analyses, and significant differences in species composition among the three ecological groups were detected. The dominant species varied among the groups: gobies in CG; Neobythites sivicola , Cynoglossus interruptus and Aseraggodes kobensis in TG; and Champsodon snyderi , Callionymus beniteguri and Ostorhinchus fasciatus in KG. Most diversity indices, including the number of species (S), Margalef's index (d), Shannon-Wiener's index (H '(log 2)), Simpson's index (1- λ '), rarefaction index (ES (100)), Hill's number (N ∞), average taxonomic diversity (Δ), total taxonomic distinctness (SΔ +), variation in taxonomic distinctness (Λ +) and total phylogenetic diversity (SΦ +) increased from inshore to offshore, whereas abundance and biomass increased from south to north. K -dominance curves suggested diversity rankings of offshore region > inshore region and southern region > northern region for regional comparisons. A diversity ranking of KG > TG > CG for group comparisons was also detected. The funnel and ellipse plots of taxonomic measures indicated that diversity was approximately equal to the expected range in KG (healthy), whereas it was significantly lower in CG (unhealthy). CCA (canonical correspondence analysis) revealed that turbidity, fine silt sediment, fluorescence, dissolved oxygen and salinity were the most active environmental variables influencing demersal fish community. RDA (redundancy analysis) found turbidity and temperature showed significant associations with the biodiversity matrix. Highlights • Three demersal fish groups—the Coastal group (CG), Transitional group (TG) and Kuroshio group (KG)—were identified. • The spatial pattern of KG could reflect the impact of Nearshore Kuroshio Branch Current. • A diversity ranking of KG > TG > CG was revealed. • Turbidity was the most active environmental variable influencing demersal fish community and diversity. [ABSTRACT FROM AUTHOR]

Both tropical and extratropical cyclones can affect the East China Sea (ECS) shelf in summer. Based on a current mooring deployed in 2014, near-inertial waves (NIWs) triggered by both extratropical and tropical cyclones were examined. During the observation period, three tropical cyclones (i.e., NEOGURI, MATMO, and NAKRI) passed by the mooring site. MATMO and NAKRI led to obvious near-inertial responses. The weakest tropical cyclone (MATMO) caused the strongest NIWs due to its large translation speed and favorable position relative to the mooring site. Mode 1 dominates the vertical structure of the NIWs caused by tropical cyclones. Due to the modulation of the background vorticity, the NIWs show a significant blueshift. However, the NIWs caused by extratropical cyclones are mainly concentrated near the surface layer with a higher proportion of mode-2 NIWs. The highest value of the near-inertial kinetic energy generated by extratropical cyclones is about half of that generated by tropical cyclones. In addition, both two kinds of cyclones can lead to an enhancement of sub-inertial current in the ECS shelf. The nonlinear interactions between NIWs and semidiurnal internal tides (D 2) are also evidenced, with the NIWs being a potential trigger for D 2 - f waves. This study highlights the important role of NIW on the nonlinear interactions and energy transfer within the internal wave spectral continuum in the continental shelf region. • Near-inertial wave (NIW) in the East China Sea shelf was captured by a mooring. • Besides tropical cyclone (TC), extratropical cyclone is another driver for NIWs. • Nonlinear interactions between NIWs induced by TC and D 2 trigger D 2 - f waves. [ABSTRACT FROM AUTHOR]

Abstract The sea-level curve during the last deglaciation is characterized by two episodes of rapid sea-level rise, termed Meltwater Pulses (MWPs) 1A (14.6–14.3 kyr BP) and 1B (11.45–11.1 kyr BP), as well as an episode of relatively slow sea-level rise during the Younger Dryas stadial (YD; 12.85–11.65 kyr BP). However, the relative sea-level changes during the YD and MWP-1B periods are still not well defined. Here, we use precisely dated intertidal sediments derived from 6 sediment cores on the tectonically stable continental shelf of the East China Sea (ECS) to reconstruct a high-resolution sea-level curve between 14.0 kyr BP and 10.0 kyr BP. Although linear regression analysis suggests that the sea level rose continuously, with an average rate of 10.6 ± 0.6 mm/yr (r = −0.87, p(a) < 0.01, n = 95), the mode of sea-level rise differs before, during, and after the YD stadial. A rapid sea-level rise of 30.5 ± 4.9 mm/yr (r = −0.79, p(a) < 0.05, n = 25) occurred during 14.0–12.85 kyr BP. Subsequently, the rate of sea-level rise decreased significantly in response to the YD stadial, and it increased smoothly to 12.0 ± 1.4 mm/yr (r = −0.86, p(a) < 0.01, n = 29) from 11.65–10.0 kyr BP, indicating that MWP-1B was absent on the ECS shelf. Furthermore, based on comparisons of these data with other high-resolution curves of sea level or elevation at different latitudes, we suggest that the poleward seawater migration from intertropical broad oceans occurred because glacial isostatic adjustment could have generated a relatively consistent global sea-level height during the last deglaciation, especially during the YD, when the rate of sea-level rise was slowed. Highlights • Sea-level rise is constrained by East China Sea intertidal sediments. • A possible rapid sea-level rise occurred during 13.6–13.0 kyr BP. • Sea-level rise slowed remarkably in response to the Younger Dryas. • Meltwater Pulse 1B is not recorded on the East China Sea shelf. • The poleward migration of seawater can lead to global sea levels remaining the same. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the late Quaternary sedimentary evolution of the outer shelf of the East China Sea (ECS) using borehole core data (DH02). Three unconformity-bounded sedimentary facies, namely, prodelta facies of marine isotopic stage (MIS) 3, intertidal to subtidal flat facies of the deglacial period, and offshore tidal sand ridge facies of the Holocene, were identified from the base upward according to combined evidence of lithology, microfossil assemblages, and geochronology. Through comparative analysis with other neighboring borehole cores, these three facies, along with the MIS 3 nearshore facies and the last glacial maximum (LGM) river facies, were found to constitute the late Quaternary sediment strata. Sedimentary processes of these five facies were interpreted based on a synthetic consideration of sea-level change, climate variation, paleotopographic setting, and paleoriver-sea interactions. In particular, the development of the delta was attributable to integration of the slow sea-level decline during the later stage of the MIS 3 and abundant sediment supply resulting from the warm-wet climate. The gentle shelf topography suggests the presence of shallow and wide rivers in the delta, and the lateral shift of river channels might have induced the local formation of nearshore facies at the abandoned river mouth. The LGM river facies, which was rarely observed (presumably due to marine erosion with deglacial transgression), was inferred to have been deposited during the latter half of the LGM in response to the rise in river base level. Occurrences of tidal flat facies imply the formation of a tide-dominated estuary with the deglacial transgression. Furthermore, tidal flat sediments were reworked by enhanced tidal currents in the estuary front environment, forming mud ridges during subsequent deglacial transgression. Formation of tidal sand ridges in offshore environments of the Holocene was attributable to the uneven base caused by the underlying estuarine erosion mud ridges, and this promoted the occurrence of tidal depositional processes. The sedimentary evolution in association with sea-level change was constructed using the above-mentioned results. Overall, this study systematically elucidates the late Quaternary sedimentary processes and evolution of the outer ECS shelf, and provides an insight into the sedimentary development of analogous shelves around the world. [ABSTRACT FROM AUTHOR]

The current shear fronts (CSFs) in the East China Sea have been observed during winter in previous studies. In this research, we systematically study characteristics and variation mechanism of the CSFs and its potential effects on the transport of water and suspended sediment and on the inner shelf mud area (ISMA), using the methods of observation data analysis and numerical simulation. The spatial structures, shear intensities, and sea‐land locations of the CSFs are obviously affected by wind, temperature and salinity. The CSFs curve seaward due to the nonuniformity of topography, and the tide causes its periodic and sea‐land shift. The landward U component near the CSFs indicate little cross‐CSF transport (i.e., the barrier effect). The CSFs are important hydrodynamic factors that affect the formation of the ISMA. The periodic shift of the CSFs in the longitudinal direction and its variations in spatial structure are the main mechanisms affecting the spatial distribution and thickness of the ISMA. However, the barrier effect of the CSFs can be interrupted, and both the strong wind in the northeast direction and baroclinic conditions are beneficial for cross‐CSF transport. Furthermore, cross‐CSF transports occur in the upper layers under northwest wind condition, in areas with nonuniformity of topography and during the spring tide period. Three cross‐shelf channels are identified in areas where the CSFs curve seaward resulting from nonuniformity of topography. Plain Language Summary: Variation in the current shear front (CSF) and its potential effect on sediment transport over the inner shelf of the East China Sea (ECS) in winter were studied in this paper. Wind, temperature, and salinity affect CSFs in the ECS; topography induces its seaward curve; tide causes its periodic and sea‐land shift. The barrier effect of the CSFs affects the formation of the inner shelf mud area. But three cross‐shelf channels are identified during winter in areas where the CSFs curve seaward resulting from nonuniformity of topography. This study will provide reference for other sea areas where the CSFs have been found and corresponding suspended sediment transport process. Key Points: Wind, temperature, salinity, topography, and tide affect current shear fronts in the East China Sea during winterThe barrier effect of current shear fronts controls the spatial distribution and thickness of the inner shelf mud area in the East China SeaThree cross‐shelf channels are identified in areas where the current shear fronts curve seaward resulting from nonuniformity of topography [ABSTRACT FROM AUTHOR]

We studied the behavior of chemical substances in the upper 300 m of the water column across the continental shelf-slope interface in the East China Sea off the Okinawa Trough. The behaviors of iron, inorganic nutrients, and humic-like fluorescent dissolved organic matter were strongly influenced by the extensive water exchange between the East China Sea and the Kuroshio Current across the shelf break and slope via upwelling and frontal processes. We attributed the high humic-like fluorescent intensity at the subsurface of the shelf break and slope regions to the lateral supply of humic-like fluorescent dissolved organic matter from the shelf sediments to the outer shelf region due to the intrusion of shelf water into Kuroshio subsurface water. We found that the behavior of iron at the continental shelf-slope was remarkably different from the conservative mixing of inorganic nutrients and humic-like fluorescent dissolved organic matter. In deep and bottom waters at the shelf-slope, high total iron concentrations, which were closely related to water transmittance, possibly resulted from the swept transport of iron-rich resuspended sediments over the shelf floor from the slope by the invading Kuroshio Intermediate Water close to the bottom. [ABSTRACT FROM AUTHOR]

The wintertime variations and distributions of sea surface temperature (SST) and thermal fronts associated with the spatial distribution of ichthyoplankton were investigated in the continental shelf waters of the southern East China Sea (ECS) by using 10 year (2005-2015) satellite SST images with an entropy-based edge detection method. The Mainland China Coastal Front and Kuroshio Front (KF) in winter (December to March) were examined with SST gradient magnitudes (GMs) of 0.20-0.40 and 0.30-0.45°C Km−1, respectively, along the 50 m and 100-200 m isobaths in the southern ECS. These two fronts coincided with isotherms of 14-16°C and 21-22°C, respectively. The Mainland China Coastal Front pattern remained fairly stable along the 50 m isobaths, and the coexisting SST front and upwelling were shifted seaward or shoreward with the recession or intrusion of the KF during the winters. Notably, the SST GMs of the KF showed a significant strengthening that was higher than those of the past two decades. Moreover, the total abundance of the nearshore waters of the KF (which was occupied by approximately 75% neritic species) was 23 times higher than that of the offshore waters (which was occupied by approximately 63.60% oceanic species). We suggest that the generation of the KF in winter may act as the biological barrier of oceanic organisms and larval fishes in the study area. [ABSTRACT FROM AUTHOR]

Sea surface concentrations of [nitrite + nitrate], [N + N], have been assessed successfully by remote sensing in the open oceans by utilizing its relationship to sea surface temperature (SST). A similar approach was not met with similar success in the river-influenced shelf waters in the northern South China Sea Shelf-sea (NoSoCS) where riverine inputs, in which the relationship between the concentration of [N + N] and SST was not straight forward, are significant. By considering river-influenced shelf waters as a mixture of open ocean water and riverine inputs and then combining SST with the absorption coefficient of colored dissolved organic matter (CDOM) at 412 nm, a g (412), which serves as an indicator of the riverine influence, an algorithm has been developed for remotely sensing the surface concentration of [N + N] in the NoSoCS. This satellite-derived concentration of [N + N] was validated by direct observations. In 16 match-up comparisons within a time window of ±24 h and concentrations of [N + N] ranging between 0.2 and 74 μM, the uncertainty was ±40%. The climatological distributions of the derived concentration of [N + N] in the NoSoCS and surrounding waters between 2002 and 2014 are consistent with the reported distributions based on ship-board observations. Thus, as a result of riverine inputs, the concentration of [N + N] generally increases towards the coasts, varying by more than two orders of magnitude from about 0.5 μM and near zero in the open northern South China Sea (NSCS) in January and July respectively to about 50 and 100 μM at the mouth of the Pearl River. In the open NSCS where nutrient availability is controlled primarily by the enhanced winter convective overturn, the intra-annual variations in the concentration of [N + N] follow a distinct seasonal cycle, reaching a minimum close to zero in the summer and a maximum, 0.7 μM, in the winter. In the NoSoCS, as a result of the high riverine input of nutrients in the summer, in addition to the maximum in the winter, there is a secondary summer maximum, which becomes increasingly prominent towards the coast. This work represents a first attempt to characterize the distributions of the surface concentration of [N + N] in river-influenced shelf-seas from space. With appropriate regional tuning, a similar approach may be applicable to other river-influenced shelf-seas such as the Texas-Louisiana Shelf. [ABSTRACT FROM AUTHOR]

The absorption properties of chromophoric dissolved organic matter (CDOM) in the East China Sea (ECS) and the waters off eastern Taiwan (WET) were studied during May 2014. CDOM absorption coefficient ( a 280 ) and spectral slope ( S 275–295 ) revealed considerable spatial variations. In the ECS, the values of a 280 and S 275–295 presented a reverse distribution pattern. In the WET, a 280 values were generally low while S 275–295 values were generally high. Vertical distributions of a 280 and S 275–295 also varied in different regions. Terrestrial input, phytoplankton production, sediment release or photobleaching may be responsible for the dynamics of CDOM. Relationships among CDOM related parameters could partly support this conclusion. a 280 were also used to trace different water masses and the result showed that the influence of Changjiang Diluted Water could reach the outer shelf of the northern ECS, and that the Kuroshio Current had a strong influence on the middle shelf of the southern ECS. [ABSTRACT FROM AUTHOR]

Comprehensive carbon chemistry data were measured from the mainstream of Kuroshio, off eastern Taiwan, in May 2014. Results indicated that variations of pH@25 °C, POC, ΩCa, DIC, pCO2 and RF were closely related to the characteristics of various water types. Phytoplankton photosynthesis played important roles in DIC variation in Kuroshio SurfaceWater (KSW), whereas the DIC variation in Kuroshio Subsurface Water (KSSW) was probably influenced by the external transport of DIC-enriched water from the South China Sea. Vertical profiles of hydrological parameters and carbonate species indicated that the Kuroshio Current off eastern Taiwan could intrude into the ECS shelf as far as 27.9° E, 125.5° N in spring. What is more, the KSW, KSSW and Kuroshio Intermediate Water (KIW) could convey DIC into the East China Sea (ECS) with flux of 285, 305 and 112 Tg C/half year (1 Tg = 1012 g), respectively. The relevant flux of POC was 0.16, 2.93 and 0.04 Tg C/half year, respectively. Consequently, the intrusion of Kuroshio could probably exert a counteracting influence on the potential of CO2 uptake in the ECS, which needs further study. [ABSTRACT FROM AUTHOR]

Euphausiids are commercial fishery targets and one of the primary preys of an important component of marine food webs. However, knowledge about the natural life history of euphausiids in the East China Sea is limited. To describe the seasonal variation of euphausiids abundance, diversity, life stage, and taxonomic composition, we visited a site northeast of Taiwan (25.5°N, 121.9°E) in 21 cruises from May 2010 to September 2016. This site is known for an all-year-round upwelling due to the impingement of Kuroshio onto the continental shelf break. We found that the overall euphausiids abundance and diversity tended to be higher in summer to autumn (June to November) compared with spring. In terms of life stages, we found that larval stages (furcilia and calyptopis) predominated in spring when upwelling was prominent, while post-larval stages (juvenile and adult) dominated in summer and autumn when upwelling was weak, and stratification was strong. Moreover, we found that, in spring and summer, Euphausia nana was the dominant species accounting for 90% of total euphausiid abundance, whereas in autumn, Pseudeuphausia latifrons was the dominant species occupying 36% of total abundance. This study provides the foundation to better understand the ecological roles of euphausiids under the influences of upwelling northeast of Taiwan. • The euphausiid abundance and diversity tended to be higher in summer to autumn. • The euphausiids larval stages predominated in the winter/spring season. • The euphausiids post-larval stages predominated in the summer and autumn season. • Euphausia nana account for 90% of total euphausiid abundance in spring and summer. • Pseudeuphausia latifrons occupied 36% of abundance in autumn. [ABSTRACT FROM AUTHOR]

The sedimentary rhythm is well developed in the environment which is controlled by strong seasonal climate changing condition. This rhythm is important for sediment core dating purpose. In this study, we examine muddy sediments on the inner continental shelf of the East China Sea that are influenced under seasonal change of the East Asian monsoon. We use Ensemble Empirical Mode Decomposition (EEMD) method to process sediment grain size and X-radiograph negatives grayscale value data in three sediment cores from this area and use the results to analyze the patterns of sedimentary variability and the causes of cyclic variability of the sedimentary process. The variability in the grain size and grayscale values of the core sediments has three components: the high-frequency variability, low-frequency variability and a secular trend. Among these components, the high-frequency component reflects variability on annual time scale can be well recognized, we suggest that the annual variability is derived from seasonal variation in the sediment flux from the Yangtze River to the sea, as well as the East Asian monsoon's impact on the sedimentary dynamics of the East China Sea's inner continental shelf. However, the other variability is hard to identify which cycles there are. This variability may reflect decadal winter monsoon oscillation and human activity of dam construction in the Yangtze River. Each annual variability presents a varve in the sediment sequence, which can be used to determine the sediment deposition rate and accurately date the core sediment. We found that the average deposition rates of the three cores from north to south on the inner shelf were 3.1 cm/yr, 1.0 cm/yr, 0.9 cm/yr, indicating that the Yangtze-derived sediment decreased with the increasing distance from the Yangtze estuary to the shelf. The deposition rate of each core varies over time, and the maximum deposition rate can be 3–5 times greater than the minimum rate. The sediment ages obtained from varve chronology and radiometric dating are fairly consistent on a centennial scale, differing only by 2–5 years. Thus, varve counting is a useful supplementary approach to radiometric age dating for constructing chronologies for core sediment in shelf seas influenced by monsoons. [ABSTRACT FROM AUTHOR]

The heavy metals in surface sediments of the continental shelf of the South Yellow Sea (SYS) and the East China Sea (ECS) collected in 2016 were analyzed to assess the heavy metal distributions, contamination status, and likely sources. The metal concentrations generally met the China Marine Sediment Quality criteria. However, the enrichment factor and geoaccumulation index values clearly showed elevated Cd and Pb concentrations in the region. Cd and Pb contamination occurred mostly to the southwest of the Changjiang River mouth and to the east of the Shandong Peninsula because of rapid economic and industrial development. The results are likely to be useful for authorities responsible for sustainable coastal zone management. [ABSTRACT FROM AUTHOR]

The Kuroshio has an important influence on the circulation systems and ecological environment of the East China Sea (ECS), but the intrusion pattern of the Kuroshio on the ECS continental shelf and its seasonal variability are still debated. Our study shows that evidence from both hydrographic data and dissolved inorganic iodine species (DIIS) suggest that a cold (< 19 °C), saline (> 34.4 PSU), dense (> 24.5 kg/m 3 ), R-iodate-rich (> 0.35 μM) and R-iodide-poor (< 0.10 μM) water (R-iodate and R-iodide are represented by iodate and iodide concentrations normalized to a salinity of 35) occurs at the bottom of the ECS continental shelf (depth < 100 m). The characteristics of this water are similar to those of the Kuroshio Subsurface Water (KSSW), and the intrusion pattern of the KSSW onto the ECS shelf consists of an intrusion from the northeast of Taiwan and another intrusion at ∼ 28.5°N along the 100-m isobaths. In the spring of 2014, the KSSW intrusion northeast of Taiwan flowed northwestward then bifurcated into a nearshore branch and an offshore branch at ∼ 27.5°N. The nearshore branch flowed approximately northward and finally appeared in the subsurface layer within the 50-m isobath off the Zhejiang coast (∼ 29.5°N). In addition, the offshore branch flowed along the 100-m isobath and reached ∼ 29.5°N. The KSSW intrusion northeast of Taiwan was obviously weaker in autumn than in spring. In autumn, the nearshore branch was not observed, and the offshore branch reached only ∼ 28°N. In addition to the main intrusion center northeast of Taiwan, the DIIS concentrations indicate that another weaker intrusion from the KSSW occurs at ∼ 28.5°N along the 100-m isobaths. However, this phenomenon could not be observed via hydrographic data alone. Moreover, seasonal fluctuation in this additional KSSW intrusion was observed. In spring, this water flowed northwestward and reached 29.5°N, whereas this water was confined along the 100-m isobath in autumn. Overall, DIIS can be used as complementary tracers of the KSSW intrusion, and more details of the intrusion pattern of the KSSW were well revealed. [ABSTRACT FROM AUTHOR]

In this study, we investigated the CO 2 system in two distinct continental shelf systems in the Northwest Pacific in the summer of 2014. The East China Sea (ECS) is a river-dominated shelf system, and the Peter the Great Bay (PGB) of the Japan/East Sea represents an ocean-dominated shelf system. The results show that the PGB acted as a source of atmospheric CO 2 , while the ECS was a sink. We suggest that the observed divergent behavior, in terms of CO 2 absorption, may result from differences in the river runoff received. Under the influence of the Changjiang River, the nutrient discharge into the ECS is much higher than that into the PGB, where only a few small rivers act as inputs. The high nutrient discharge may stimulate high biological production, which may consume CO 2 , driving the ECS to act as a CO 2 sink despite its high temperature in summer. The temperature effect may dominate the effect of biological production in the PGB because of its limited riverine nutrient inputs. We found that external CO 2 sources from the adjacent open ocean could explain the source status of the PGB. This finding agrees with the “Ocean-dominated Margin” (OceMar) hypothesis, which has only been tested using data from tropical marginal seas. The present data set from the PGB, thus, provides the first example to support that the “OceMar” hypothesis may also be applicable in high latitude shelf systems. [ABSTRACT FROM AUTHOR]

Lead-210 and 210 Po have been widely used as tracers for quantifying particulate scavenging in the upper layer of the oceanic water column. In this study, we investigated the 210 Po/ 210 Pb disequilibrium in the water column of the PN section in the East China Sea (ECS) during autumn 2013. In most of the water column, a deficiency of 210 Po was observed with respect to its parent nuclide 210 Pb (i.e., a 210 Po/ 210 Pb activity ratio < 1.0). The ( 210 Po/ 210 Pb) dissolved , ( 210 Po/ 210 Pb) particulate and ( 210 Po/ 210 Pb) total activity ratios ranged from 0.29 to 0.71 (average: 0.53 ± 0.13, n = 27), 0.31 to 1.42 (average: 0.70 ± 0.27, n = 27) and 0.22 to 0.62 (average: 0.50 ± 0.12, n = 27), respectively. The distribution coefficients ( K d ) of 210 Po and 210 Pb were 12.1× 10 4 ml g −1 and 8.8× 10 4 ml g −1 , with an average ( 210 Po/ 210 Pb) total activity ratio of (0.50 ± 0.12, n = 27). However, over the continental shelf, planktonic detritus and fecal pellets appear to be the main carriers for 210 Po, which preferentially scavenges 210 Po and produces a lower ( 210 Po/ 210 Pb) total activity ratio (0.49 ± 0.12, n = 22) with a K d for 210 Po of 13.8× 10 4 ml g −1 in the water column. The variations in the fractionation factor (1.48 ± 0.66) of 210 Po/ 210 Pb reveal distinct differences between the distribution and scavenging of 210 Po and 210 Pb by particulate matter in different marine environments: in the estuarine zone (a high turbidity area), terrigenous suspended particulate matter scavenges 210 Pb from the water column, while in areas dominated by biogenic particular matter, 210 Po is preferentially scavenged from the water column. Using the 210 Po/ 210 Pb disequilibrium in the water column, we estimated the removal fluxes of POC from the upper waters downward to be 25.0 mg C m −2 d −1 , comparable to those in other marginal seas. Moreover, a decreasing trend of POC removal fluxes was observed with increasing distance offshore. [ABSTRACT FROM AUTHOR]

In summer, Changjiang Diluted Water (CDW) expands over the shelf region of the northern East China Sea. Dilution of the low salinity water could be caused by vertical mixing through the halocline. Vertical mixing through the pycnocline can transport not only saline water, but also high nutrient water from deeper layers to the surface euphotic zone. It is therefore very important to quantitatively evaluate the vertical mixing to understand the process of primary production in the CDW region. We conducted extensive measurements in the region during the period 2009–2011. Detailed investigations of the relative relationship between the subsurface chlorophyll maximum (SCM) and the nitracline suggested that there were two patterns relating to the N/P ratio. Comparing the depths of the nitracline and SCM, it was found that the SCM was usually located from 20 to 40 m and just above the nitracline, where the N/P ratio within the nitracline was below 15, whereas it was located from 10 to 30 m and within the nitracline, where the N/P ratio was above 20. The large value of the N/P ratio in the latter case suggests the influence of CDW. Turbulence measurements showed that the vertical flux of nutrients with vertical mixing was large (small) where the N/P ratio was small (large). A comparison with a time series of primary production revealed a consistency with the pattern of snapshot measurements, suggesting that the nutrient supply from the lower layer contributes considerably to the maintenance of SCM. [ABSTRACT FROM AUTHOR]

Contradicting findings were observed when decadal changes of primary productivity in the eastern Chinese shelf sea were learnt through examination of sediment cores (Lv, 2007; Zhou, 2007; Jin, 2009; Zhao, 2010; Yang et al., 2012). This inconformity may imply the regional differences of decadal environmental changes in different types of seas. To verify the possible regional differences, we examined sediment cores collected in different types of seas in the eastern Chinese shelf sea. 210 Pb activity in the sediment was used to estimate sediment rate, while biogenic silica (BSi) was applied to indicate diatom paleoproductivity. And then the decadal change trends of diatom primary productivities (DPP) over the past 100 years in different areas were achieved. Subsequently, the differences in these DPP changes and the possible controlling mechanism were also discussed. Results reveal the presence of regional differences in DPP decadal changes in the eastern Chinese shelf sea. In all coastal seas, DPP followed similar trends before the 1980s; after the 1980s, DPP increased obviously in Shandong coastal waters where no large river mouth exists nearby, but decreased in the Yangtze River estuary. By contrast, in open waters, DPP in the past 100 years followed almost opposite trends against that in Shandong coastal waters. The differences in DPP changes between coastal and open sea areas before the 1980s could be attributed to the distinct influence mechanism of Pacific Decadal Oscillation (PDO) on DPP variation. However, the regional differences of DPP changes after the 1980s were probably attributed to the differences in influence type and intensity of human activities. Summarily, the disproportion of the influence of human activities and PDO could induce regional differences in DPP decadal changes in the Chinese shelf sea. These actual and probably general existences of regional differences prompt us to comprehensively assess long-term environmental changes in the complex shelf seas, rather than rebuild paleoenvironmental change patterns by using only one or limited sediment cores. [ABSTRACT FROM AUTHOR]

In this work, we examined the carbonate parameters, i.e. total alkalinity (TA), pH, and partial pressure of CO ( pCO), and the air-sea CO flux ( FCO) in the continental shelves of the southern Yellow Sea (SYS) and East China Sea (ECS), based on two field surveys conducted in April and August of 2011. Surface pCO showed significant spatial variations, ranging from 246 to 686 µatm in spring (average ± standard deviation = 379 ± 95 µatm) and from 178 to 680 µatm in summer (384 ± 114 µatm). During the spring cruise, the central SYS ( pCO < 240 µatm) and the Changjiang estuary ( pCO < 300 µatm) were under-saturated with CO, while the southern SYS and the southwestern ECS were supersaturated ( pCO = 420-680 µatm). In summer, however, the CO-supersaturated waters ( pCO = 380-680 µatm) occupied a relatively wide area, including the nearshore of the SYS and the Changjiang estuary, whereas pCO-deficient water ( pCO = 220-380 µatm) was observed only at the offshore ECS. In general, the entire SYS and ECS area behaved as a sustained CO sink, with average FCO of −3.9 and −2.1 mmol m d in spring and summer, respectively. Phytoplankton production was the driving force for CO absorption, especially during the spring cruise. In addition, we found that typical water mixing processes and decomposition of terrestrial material were responsible for the release of CO in three turbidity maximum regions. [ABSTRACT FROM AUTHOR]

Onshore and offshore currents and the associated volume transport across three isobaths (50, 100, and 200 m) over the continental shelf of the East China Sea were examined using daily reanalysis data in 1993-2012. After being averaged along the isobaths, the velocities across 100 and 50 m are onshore in the bottom layer but offshore in the surface layer. In contrast, those across the 200-m isobath are onshore in the surface and bottom layers but without a clear direction in the midlayer, suggesting a three-layer structure. The surface offshore current across the 100-m isobath mainly arises from the Taiwan Strait Current, while the surface onshore current across the 200-m isobath mainly arises from the Kuroshio, both of which converge in the area between the 100- and 200-m isobaths and flow toward the Tsushima Strait. The control of bottom Ekman dynamics on the onshore bottom currents is important at the 100-m isobath, partly important at the 200-m isobath, and slightly important at the 50-m isobath. The seasonal variations of onshore and offshore currents in the surface layers across the three isobaths are likely caused by local winds, the Taiwan Strait Current, and the Changjiang discharge, while those in midlayer across the 200-m isobath demonstrate a strong geostrophic control and can be interpreted from a traditional viewpoint on the Kuroshio intrusion over the entire water column across the shelf slope. The close connection of bottom onshore currents across the three isobaths suggests that the bottom layer is an important pathway for water exchange of shelf water and the open sea. [ABSTRACT FROM AUTHOR]

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The East China Sea (ECS) is one of the most important fish spawning and nursery grounds in the north Pacific. Even though summer is an important spawning season for many fishes in the region, large-scale molecular identification studies on ichthyoplankton during this season are few. In this study, we sampled 8,933 fish eggs and 12,161 fish larvae from 25 stations during the summer of 2009. Using DNA barcoding, a number of the fish eggs and larvae were identified and classified into 45 and 124 taxa, respectively. Principal component analysis (PCA) categorized the inshore stations of the Changjiang Diluted Water area as having the hydrographic features of low sea surface temperature (SST), salinity (SSS) and high chlorophyll a (SSC) contents, whereas the continental shelf and offshore stations under the influence of the Kuroshio Current displayed the opposite results. Ichthyoplankton was more abundant at the inshore stations than the offshore stations, but species diversity was lower at the former locations. Species compositions of both fish eggs and fish larvae at the 25 stations were categorized into three different assemblages based on a non-metric multidimensional scaling analysis. Combining the assemblage patterns of ichthyoplankton with the results of the PCA and satellite images of SST and SSC showed that the assemblage patterns of fish eggs were correlated with water mass, while those of the fish larvae were not. [ABSTRACT FROM AUTHOR]

The temporal evolution of suspended sediment concentration (SSC) in a river debouching into the ocean provides vital insights into erosion processes in the watershed and dictates the evolution of the inner continental shelf. While the delivery of sediment from rivers to the ocean has received special attention in the recent past, few studies focused on the variability and dynamics of river SSC, especially in the Changjiang (Yangtze) river, China, the longest river in Asia. Here, variations in SSC delivered by the Changjiang River to the East China Sea and possible causes of its variability were detected based on a long-term time series of daily SSC and monthly water discharge measured at the Datong gauging station. The SSC data are further compared to a hydrological analysis of yearly precipitation covering the entire catchment. The results indicate the presence of a decline in SSC in the period 1956–2013, which can be divided into three phases: (i) high SSC (0.69 kg/m 3 ) in the wet season and low SSC (0.2 kg/m 3 ) in the dry season from 1956 to 1970; (ii) relative high SSC (0.58 kg/m 3 ) in the wet season and low SSC (0.15 kg/m 3 ) in the dry season from 1971 to 2002; and (iii) low SSC (0.19 kg/m 3 ) in the wet season and very low SSC (0.09 kg/m 3 ) in the dry season after 2002. These three periods have a mean yearly SSC values of 0.62, 0.42, and 0.18 kg/m 3 , respectively. Compared with 1956–1970, the slope of the rating curve between SSC and water discharge decreased, respectively, by 2% and 30% during the period 1971–2002 and 2002–2013. Soil erosion, dam construction, and banks reinforcement along the Changjiang River are the main causes of SSC variations. Fluctuations in water discharge are also controlling the SSC long-term variations. Specifically, from 1956 to 1970, the effect of soil erosion overrules that of dam impoundment, which is likely responsible for the high SSC; during the period 1970–2002, the influence of dam impoundment increases while that of soil erosion decreases, which together produce a small reduction in SSC. Since 2002, the impact of soil erosion further decreases and large-scale sediment trapping behind the Three Gorges Dam is responsible for the occurrence of extremely low SSC. The results presented herein for the Changjiang River can inform a better management strategy of sediment resources and water quality for both the river and the coast. Our conclusions can be well applied to other rivers discharging in the ocean subject to similar human activities. [ABSTRACT FROM AUTHOR]