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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...
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... current ellipses of the four dominant constituents that were derived from the tidal current analysis ( Pawlowicz et al., 2002) are shown in Figure 5, and these results are in excellent accordance with that of pre- vious models ( Bao et al., 2001;Chough et al., 2004;Luo, 2015). ...
Citations
... The model used in this study was based on the MIKE 3 hydrodynamic module by the Danish Hydraulic Institute (DHI), which is developed for a wide range of applications in areas such as oceans, coastal regions, estuaries, and lakes (DHI, 2012;Liu et al., 2018). The model domain covered the area between 37°-41°N and 117.5°-122.5°E, ...
Since the 1970s, extensive land reclamation has been carried out in the Bohai Sea. However, reclamation activities were prohibited in 2018. Using the MIKE3 numerical model, this study selected 1976 and 2018 as representative years before and after reclamation, respectively, and developed a highly accurate three‐dimensional hydrodynamic and sediment transport model for the Bohai Sea. The model was employed to access the effects of reclamation on tidal waves, tidal prism, residual current, tidal flux (TF), and suspended sediment flux (SSF). The results revealed that after reclamation, the amphidromic points of M2 and S2 shifted southward near Qinhuangdao, and eastward near the Yellow River estuary. The M2 amplitude in the Bohai Bay exhibited a maximum increase of 30 cm. In the Bohai Sea, the tidal prism decreased by 3.95%, suggesting a decrease in water exchange capacity. The TF in the Bohai Sea and Laizhou Bay decreased by 0.7% and 12%, respectively, while increasing by 16% in Bohai Bay and 12% in Liaodong Bay, primarily due to the variations in tidal waves. Furthermore, SSF decreased by 6% in the Bohai Sea, but increased by 125% in Bohai Bay and 114% in Laizhou Bay. The significant increase in SSF in Bohai Bay and Laizhou Bay was mainly attributed to the higher suspended sediment concentrations and the stronger residual current velocities near the Yellow River estuary. This study provides comprehensive insights into the impacts of reclamation on TF and SSF in the Bohai Sea, which could contribute to marine resource development and the planning of environmental restoration projects.
... The Northern Taiwan (NTW) Sea is in the southern East China Sea (ECS) and is one of five cross-shelf transport paths in the ECSS (Yang and Liu, 2007;Yuan et al., 2005;Ren et al., 2015;Qiao et al., 2017;Shi et al., 2019;Liu et al., 2018b)) (near 27.5 N, Fig. 1a) and is significantly influenced by the monsoon climate and submesoscale activity. In winter, northerly or northeasterly winds prevail with a mean wind speed of approximately 9-10 m s − 1 (Fig. 1c), and in summer, southerly winds prevail with a wind speed of approximately 5-6 m s − 1 . ...
... Atmospheric forcing weakens, causing the temperature front to shift but remain at shallow water depths of 80 m (Fig. 1c, 2b-2, 2c-2). Factors such as potential energy relaxation superimposed on a topographic slope may contribute to offshore transport (Liu et al., 2018b;Yao et al., 2021). Additionally, there is a widespread distribution of shear fronts at the offshore transport channel. ...
... The coastal front of Zhejiang and Fujian Provinces, China, forms a significant part of the complex current system on the inner shelf of the ECS. It is controlled by either current shear or tidal mixing with apparent seasonal variations in location, width and intensity (Lü et al., 2006;Zeng et al., 2012;Liu et al., 2015Liu et al., , 2018. As impacted by the coastal front, the riverine sediments are transported by the longshore current and eventually accumulate to form an elongated muddy belt on the inner shelf (Fig. 1b;Liu et al., 2006Liu et al., , 2007Li et al., 2013). ...
... Since the 1980s, the coastal fronts in the ECS have been intensively investigated by the approaches of in-situ observations, remote sensing analysis and numerical modeling (Tang, 1995;Park and Chu, 2006;Chen, 2009;Lee et al., 2015), which mainly focused on the front identifications (Lou et al., 2005;Belkin and O'Reilly, 2009), front dynamics and variations on a variety of spatio-temporal scales Cao et al., 2021), mechanisms for frontogenesis (Wu, 2015;He et al., 2016), and the environmental effects Hung et al., 2014). Generally, the current shear front in the ECS is evident in winter and disappears in summer (Hickox et al., 2000;Liu et al., 2018). Additionally, previous works reported that wave and tidal mixing could produce mixing fronts in the ECS in summer as characterized by the discontinuity in vertical stratification of water column (Lü et al., 2006;Qiao et al., 2006;Wu and Wu, 2018). ...
... The TWC flows northward throughout the year and can be further intensified by the southeast monsoon in summer (Su and Yuan, 2005). As a result, current shear fronts may arise in winter between the cold, fresh ZFCC and the warmer, saline offshore TWC (Zeng et al., 2012;Liu et al., 2018). However, with the alternative direction of ZFCC, increased solar radiation and intensified TWC, the current shear front gradually weakens or even disappears in summer (Lee et al., 2015). ...
Mixing fronts on the inner shelf of the East China Sea (ECS) are common under normal summer conditions, yet its migration during extreme weather events, such as typhoons, has been poorly understood due to limited availability of observational data. In this study, we used a well-validated Finite-Volume Community Ocean Model (FVCOM) to investigate the intermittent migration of mixing fronts on the inner shelf of the ECS during the passage of Typhoon Chan-hom in July 2015. The sedimentary and ecological effects of the front migration were also revealed. Results suggested that the potential energy anomaly (PEA) of 10 J/m3 could be a critical value to determine the location of the mixing front, which was consistent with that derived from the Simpson-Hunter (SH) parameter. Accordingly, the mixing front showed a rapid seaward migration from 15-m isobaths to 60-m isobaths under the drastic ocean turbulence during the typhoon and recovered shortly after its passage. This intermittent migration of the mixing front had the potential to facilitate cross-shelf material transport during the typhoon. On the one hand, the front migration could not only open the access for the seaward transport of nearshore resuspended sediments but also trap them within a certain area, causing an offshore deposition between 20 and 60 m isobaths south of the typhoon track. The mixing fronts had a boundary effect constraining the typhoon- induced sedimentation. On the other hand, unlike sediments that would settle down with weakened ocean dynamics, the offshore movement of coastal diluted water triggered by the typhoon remained after the front recovery. These nutrient-rich waters could be transported to the middle or even outer shelf of the ECS by the subsequent southwest summer monsoon, enhancing local primary production and potentially trigering significant algal blooms.
... High dissolved PCB concentration in the narrow zone could be derived from the cross-shelf transport at current shear fronts (CSFs), which is a front between two water masses. The cross-CSF transport occurs in the upper layers of the ECS continent shelf, in association with the nonuniformity of topography (Liu et al., 2018). Bottom water from Zhejiang-Fujian coast expands seaward due to the downwelling of coastal water under the northerly monsoon in winter and lateral Ekman transport ( Figure S10 in Supporting Information S1), which could bring PCBs in bottom water and sediments along the Zhejiang-Fujian coast to the outer continental shelf Liu et al., 2006Liu et al., , 2018. ...
... The cross-CSF transport occurs in the upper layers of the ECS continent shelf, in association with the nonuniformity of topography (Liu et al., 2018). Bottom water from Zhejiang-Fujian coast expands seaward due to the downwelling of coastal water under the northerly monsoon in winter and lateral Ekman transport ( Figure S10 in Supporting Information S1), which could bring PCBs in bottom water and sediments along the Zhejiang-Fujian coast to the outer continental shelf Liu et al., 2006Liu et al., , 2018. Another possible source of PCBs could be derived from the suspended sediments in the Okinawa Trough due to the strong eddy at northeastern Taiwan, where high suspended sediment concentration was discovered (Li et al., 2016). ...
Continental marginal seas are key reservoirs of anthropogenic pollutants. Understanding the physical processes controlling the air–sea exchange dynamics of polychlorinated biphenyls (PCBs) in the continental margin seas is crucial to constrain the contribution of PCBs from land and rivers to the ocean; however, the transport and fate of PCBs, and their controlling factors of air–sea exchange in the continental marginal seas still remain poorly understood. Here, we collected atmospheric and surface water samples from the Yellow Sea (YS) and East China Sea (ECS) in summer 2018 and winter 2019, and examined the PCB concentrations. The PCB air–sea gas exchange fluxes showed higher net volatilization in winter, largely due to southward movement of the strengthened Yellow Sea Coastal Current and Yangtze River Diluted Water with high PCB concentrations. Both the dissolved PCB concentrations in seawater and wind speed were the primary factors influencing the PCB air–sea exchange fluxes in winter. By contrast, weak PCB volatilization fluxes occurred when the Taiwan Warm Current with low PCB concentrations dominated in the ECS in summer. In comparison, the accumulation and release of some PCB homologues caused by a green tide in the coastal YS could lead to increased volatilization flux in summer. Our results suggest the transfer of air–sea exchange dynamics of PCBs from a water concentration‐dominated pattern to an environmental parameter‐controlled one due to their decreased land‐based input, and highlight the impact of water mass‐triggered changes (environmental parameters and algal blooms) on the air–sea exchange behavior of PCBs in the continental marginal sea.
... After a comprehensive analysis, we conclude that cross-shore winds dominate cross-shore sediment transport in winter, in a mainly offshore direction. These sediment transport processes can provide a reference for other researches on the inner-shelf that are also affected by the storm, e.g., the Middle Atlantic Bight, (Wright et al., 1994), the East China Sea (Liu et al., 2018b) We attempted to use statistical analysis to generate the annual accumulation rate. By combining the in situ observational data and cruise data, we determined that the average SSC b was about 20 mg/l in winter and 10 mg/l in summer. ...
The long-distance transport of Yellow River sediments has formed an omega-shaped (‘Ω’) distal muddy deposit in the Yellow Sea. Numerous studies have investigated the sediment dynamics and sedimentary evolution of the deposit, but several key questions remain unanswered due to insufficient observations. To reveal the mechanisms of sediment dynamics and quantify sediment transport and deposition processes, this study collected field datasets in the depocenter of the muddy deposit off the Shandong Peninsula. Bottom mounted tripods were deployed from August 18 to 27, 2017, and from February 23 to March 2, 2018, during which two strong wind events with speeds of over 10.8 m/s occurred. The results showed that near-bed suspended sediment concentration responded directly to varying hydrodynamic conditions, and significant differences in suspended sediment concentration between two wind events could be ascribed to a number of factors (e.g., tidal current, wave periods, wind stress, turbulence). The harmonic analysis demonstrated that suspended sediment variations during the spring tide were directed mainly by resuspension, while resuspension and advection contributed equally at neap tide. The variations in background suspended sediment concentration can be ascribed to the residual current. Furthermore, the sediment transport pattern is similar to the pattern of water circulation. Generally, the along-shore suspended sediment flux is about one order of magnitude higher than the cross-shore flux. In summer, the suspended sediment was transported mainly downcoast. In winter, sediment was transported downcoast during wavy periods and upcoast during calm periods. Advection dominated sediment flux in most cases, except during wavy periods when local resuspension increased significantly, and the contribution of resuspension term to along-shore flux was up to 87%. Meanwhile, cross-shore flux also increased significantly under strong winds, which was simultaneously modulated by downcoast and offshore winds. After statistical analysis, we found that offshore winds controlled the cross-shore sediment transport in winter. Using parameterized calculation and statistical analysis, the average accumulation rate of the study site was estimated to be 0.6 cm/yr. During calm periods, lower background sediment concentration in summer led to lower deposition rates than in winter. In addition, the frequent strong wind events in winter cause extremely high erosion rates. This study provides new perspectives on quantitative variations in suspended sediment transport and regional erosion/deposition from synoptic to seasonal variations in the distal mud deposit.
... Moreover, climate change can affect the intensity and location of oceanic circulation patterns (Hu et al., 2015;Wang & Oey, 2016), which are closely linked with shelf mud transport and sedimentation (Hanebuth et al., 2015;Walsh & Nittrouer, 2009). This phenomenon is particularly obvious in the western Pacific because multiple large rivers in Asia (e.g., the Changjiang [Yangtze] River) discharge abundant suspended materials (Milliman & Farnsworth, 2013), which can be transported or trapped by well-developed ocean currents (Hu et al., 2015;Li et al., 2016;Liu, Qiao, et al., 2018). Because of the remarkable influence of the Asian summer and winter monsoons, precipitation in the river basin and the current circulations display distinct seasonal changes (Chen & Sheu, 2006;Liu, Gu, et al., 2019;Wu et al., 2003). ...
... Perennial observations indicate that the mud is from Changjiang River-suspended material, which is predominantly transported southward by the Min-Zhe longshore current on the ECS shelf (Li et al., 2013Pang et al., 2016). This wind-driven longshore current , main locations of current shear fronts (colored dots) at different water depths (Liu, Qiao, et al., 2018), and Changjiang River-dominated Holocene mud wedge (in meters, gray areas) (Liu et al., 2007) on the low-gradient ECS continental shelf. The triangles represent the river sediment samples. ...
... Additionally, the Kuroshio onshore intrusion current is a shoreward-intruding branch of the Kuroshio Water from the northeast corner of Taiwan and subsequently flows northward along the ECS coastal areas to 30.5°N, although it behaves contrary to the Kuroshio Current, that is, stronger in winter and weaker in summer, resulting from the influences of the Asian monsoon Liu, Dong, et al., 2014;Yang et al., 2012). Because of the interactions among these currents, observations show that well-developed ocean current shear fronts are widely distributed on the western Pacific continental shelf, especially during wintertime (Hickox et al., 2000;Liu, Qiao, et al., 2018) (Figure 1b). This current shear front is a hydrodynamic interface between two different bodies of water where the flow velocity is very small (~0 m/s), the flow directions are opposite on the different sides, and the velocity gradients on both sides are significant (Cromwell & Reid, 1956;Liu, Qiao, et al., 2018;Wang et al., 2007). ...
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.
... Clarification of the sediment distribution, transport pathways and seasonal variations on the continental shelf is critical to further understanding marine environmental changes over geological time and recent impacts on coastal morphology and ecosystems ). The East China Sea continental shelf (ECSCS), one of the world's widest shelves, features seasonally variable hydrodynamic and river inputs and receives large amounts of terrigenous sediments supplied by coastal rivers (Liu et al. 2018a). On the ECSCS, various sedimentary systems shaped by complex hydrodynamic conditions are preserved (Xiao et al. 2005). ...
This study discusses the seasonal variations in surficial sediment grain size and their implications for sediment transport driven by the hydrodynamics in the East China Sea, based on grain size analysis of surficial sediments and salinity data collected from the East China Sea continental shelf during two cruises in 2011. The results show that the grain size distribution on the East China Sea continental shelf presents apparent spatial and seasonal variations. The mud area exhibits more variation than the sand area, which indicates that the sediment supply is the main factor controlling the surficial sediment grain size distribution on the East China Sea continental shelf. The grain size near the Yangtze River Estuary is relatively coarse in summer, because of the inherited characteristics from the previous winter, whereas it is much finer in autumn, due to the input of fine-grained materials during the flood period of the Yangtze River. A high fine-grained sediment concentration was found along the Zhejiang-Fujian coast in autumn when the Zhejiang-Fujian Coastal Current forms. The sediments in the northeast of the study region (the mud patch southwest of Cheju Island) are much coarser, and the fine-grained area is narrower in autumn than in summer because of seasonal variations in the Yellow Sea Coastal Current and the frequency of storms. Simultaneously, the tongue-shaped fine-grained cross shelf front located along the Zhejiang-Fujian coast occurs farther to the south in autumn than in summer. However, the surficial grain size distribution patterns on the middle and outer shelf are similar in the two seasons.
