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Recent advances in ocean-circulation research on the Yellow Sea and East China Sea shelves are summarized. Observations using acoustic Doppler current profilers (ADCPs) suggest that the connectivity of mean-volume-transports is incomplete between the Tsushima (2.6 Sverdrups; 1 Sv = 10 6 m 3 /s) and Taiwan Straits (1.2 Sv). The remaining 1.4-Sv transport must be supplied by onshore Kuroshio intrusion across the East China Sea shelf break. The Yellow Sea Warm Current is not a persistent ocean current, but an episodic event forced by northerly winter monsoon winds. Nevertheless, the Cheju Warm Current is detected clearly regardless of season. In addition, the throughflow in the Taiwan Strait may be episodic in winter when northeasterly winds prevail. The throughflow strengthens (vanishes) under moderate (severe) northeasterly wind conditions. Using all published ADCP-derived estimates, the throughflow transport ( V ) in the Taiwan Strait is approximated as where V 0 , V 1 , K are 1.2 Sv, 1.3 Sv, and 157 days, respectively, t is yearday, and T is 365.2422 days (i.e., 1 year). The difference between the throughflow transports in the Tsushima and Taiwan Straits suggests that the onshore Kuroshio intrusion across the shelf break increases from autumn to winter. The China Coastal Current has been observed in winter, but shelf currents are obscure in summer.

Penetrating fronts are frequently observed off the Zhejiang-Fujian coast, but their life cycles are poorly understood because of the lack of time series data. In this study, Geostationary Ocean Color Imager data are used to describe the complete evolutionary process of a penetrating front, and the impacts of wind and circulation on evolution are explored. Based on the horizontal coverage and the front of the penetrating water, the evolutionary process is divided into three stages of development, maturation and decay. During the development stage, the area of the penetrating water increases rapidly with eastward extension, and the penetrating front is well connected to the Zhejiang-Fujian coastal front in the southwestern area. During the maturation stage, the penetrating water continues to extend eastward at a low speed and finally arrives at the Kuroshio area on the continental slope. Moreover, the southwestern part of the penetrating front is gradually separated from the coastal front. During the decay stage, the coverage of the penetrating water decreases rapidly, and the penetrating front disappears first in the south. In this stage, the penetrating front is rarely moves east but completely separated from the coastal front south of 30°N. Dynamic analysis suggests that the typhoon-induced southward extension of the Changjiang Diluted Water off the Zhejiang-Fujian coast is an important precondition for the generation of the penetrating front. The eastward extension of the penetrating front during the development stage is mainly driven by a southwesterly wind, while in the maturation stage, it is affected by both the wind and the offshore branch of the Taiwan Warm Current. The detachment of penetrating water from coastal water is caused by the inshore branch of the Taiwan Warm Current. Numerical tracer experiments confirm the wind and Taiwan Warm Current impacts on the eastward extension and detachment of penetrating water. In addition, the Kuroshio frontal eddy may play an important role in the dissipation of the penetrating front during the decay stage.

The volume transport of the Tsugaru warm current (TWC), defined as the branch current of the western boundary current of the North Pacific subtropical gyre flowing through the Tsugaru Strait, is a critical factor affecting the acidification in the strait as well as the surrounding coastal regions by promoting the enhancement of the vertical mixing of the deep water rich in dissolved inorganic carbon. The in-phase sea-level variation along the coast of mainland Japan with a gap at the Tsugaru Strait permits the discharge of the sea surface water from the Sea of Japan to the Pacific Ocean, which is significantly correlated to the variation in the sea-level difference across the Tsugaru Strait, being possibly related to that in the TWC volume transport. Furthermore, by averaging the wind-driven Sverdrup streamfunction along the eastern coast of mainland Japan—from the southern end of Kyushu (30 ∘ N) to the separation latitude of the Kuroshio (36 ∘ N)—and scaling by a factor of the ratio between the depths of the Tsushima Strait and the East China Sea, we obtained the volume transport varying similarly with the sea-level difference across the Tsugaru Strait. As obtained, the interannual wind stress variation in this latitude band to the east of mainland Japan on the North Pacific is suggested to altered the strength of the TWC.

This review covers the discovery and studies of the year-round northeastward currents off the southeastern China coast, paying special attention to its upwind characteristic in winter, mainly focusing on work by Chinese oceanographers. This current system is a prominent and unique phenomenon in the shelf circulation of the world ocean. The general features of the current system are summarized. The evidence for the existence and the variation of the three parts of the currents—the South China Sea Warm Current, the Taiwan Strait Warm Current and the Taiwan Warm Current—are separately elucidated. The formation mechanisms of the current as a whole are explained using dynamic analysis and numerical simulation results. Some suggestions for further studies are also made.

This study investigated microplastic distribution characteristics by collecting surface seawater from sea areas to the south of Jeju Island in August 2020. The average microplastic abundance was 0.46 ± 0.27 particles/L (n = 23), and PE had a high ratio, averaging 53%. The levels of fragments and fibers were observed to be 69% and 31% on average, respectively. The most common size of the microplastics was on average 0.02–0.30 mm at a level of 69%. We found a higher abundance of microplastics in the study area than in other open waters such as the Arctic Central Basin and the Atlantic Ocean, whereas the abundance was lower than that in previous studies on coastal areas. We studied an area of open sea connecting China, Japan, and the Pacific Ocean, and, in this region, the microplastic distribution varies depending on sea currents in the surrounding areas. In the summer, the western and central regions of the study sea area have low salinity levels due to discharge from China’s Yangtze River. This generally indicates that high-density plastic deposits are found in the Yangtze River estuary, and low-density plastics are found in the study area. Furthermore, this implies that low- and high-density plastics are transported in water for long periods of time due to the Taiwan Warm Current and because the eastern sea area has high salinity.

This study investigated the summer subsurface marine heatwaves (SSMHWs) in the East/Japan Sea (EJS) using the Japan Coastal Ocean Predictability Experiment 2 ocean reanalysis datasets during 1993–2023. Climatologically, the cumulative (maximum) intensity area-averaged over the EJS ranges from 20°C days (2.5°C) at surface to its maximum of 36°C days (4°C) at approximately 70 m, confirming significant subsurface intensification of summer MHWs. Compared with the almost uniform spatial patterns at surface, the intensities of MHWs at subsurface layers show substantial spatial variations. The SSMHWs in the EJS are caused not by surface atmospheric forcings, but primarily by internal oceanic processes. During summer, the strong stratification in the EJS inhibits the vertical mixing and traps more heat fluxes at surface. As the main heat sources of the upper ocean, the Tsushima Warm Current (TWC) plays a crucial role in triggering SSMHWs in the EJS. Anomalous increased volume transport of TWC carries more warm water into the EJS, favoring the basin-scale intense SSMHWs. This warm water is redistributed by the East Korean Warm Current and mesoscale eddies, leading to regional features of SSMHWs in the EJS. Our results highlighted the roles of oceanic circulation in forming intense SSMHWs in the EJS.

Advances in reconstructing the East Asian monsoon have provided important insights into the natural climate variability in Asia during the pre-instrumental period. However, there are still unresolved paleoclimate issues that necessitate the use of geological proxy data to further our understanding of past climate changes. This study focused on core B13, located in the muddy area of the North Yellow Sea (NYS), to investigate the evolutionary history over the past 1500 years and reconstruct the records of the East Asian summer monsoon (EASM) and Yellow Sea warm current (YSWC). The mean grain size of sediment ranged from 4.2 Φ to 5.6 Φ, with the sorting coefficient ranging from 1.9 to 2.2, indicating poor sorting. The C–M pattern showed a limited range of values, with the M values being between 33 and 83 μm and the C values being between 165 and 287 μm, suggesting uniform-suspension transport. The L* index ranged from 40.41 to 44.12, while the a* and b* indexes ranged from 0.55 to 1.78 and 2.86 to 5.94, respectively. A stable and relatively strong sedimentary environment is indicated through a comprehensive analysis of the C–M plot, triangular plot, the relationship between the mean grain size and sorting, and the changes in grain-size and color parameters. The sedimentary evolution in the muddy area of the NYS over the past 1500 years can be categorized into three distinct stages. In this study, proxies for the EASM and YSWC were extracted using the VPCA method from the sediment grain size and diffuse spectral reflectance (DSR) data, respectively. The reliability of these proxies has been confirmed through comparison with other validated proxies. The results indicated that the strength of the EASM and YSWC also exhibited three stages, corresponding to the Dark Ages Cold Period (DACP), Medieval Warm Period (MWP), and Little Ice Age (LIA), respectively. On a centennial scale, the correlation between the EASM and YSWC was predominantly negative. This research validates the reliability of the VPCA method for paleoclimate reconstruction, contributes important climate records in a special muddy area, and provides a new perspective on how to eliminate temporal errors in verifying the correlation between the two climate systems.

Recent silicoflagellate distributions have been examined in 195 surface sediment samples from the North Pacific to establish the silicoflagellate assemblage dataset from surface sediments across the North Pacific for paleo sea surface temperature (SST) reconstruction. The relative abundance data of all seven silicoflagellate taxa identified in this study were used for the modern analog method to reconstruct past SST. The SST reconstruction based on the silicoflagellate modern analog technique was applied to the two sediment cores from the Japan Sea. With the development of ice sheets, the Japan Sea experienced a low salinity isolation event during the Last Glacial Maximum (LGM: 19 ka–26.5 ka), which hampers the SST reconstruction employing geochemical proxies such as alkenone and Mg/Ca thermometry. The reconstructed glacial SST between 25 and 15 ka was ~ 5 °C in the northern and southern Japan Sea, indicating significant southward migration of the glacial subpolar front. The timings of the deglacial SST rises were ~ 14 ka at the south core site and ~ 10 ka at the north core site, indicating a latitudinal lag. This lag likely reflects a gradual increase in the fluxes of the Tsushima Warm Current from the East China Sea through the Tsushima Strait. Compilation of the silicoflagellate assemblages in the North Pacific surface sediments used for the modern analog technique to reconstruct past sea surface temperature (SST), revealing the Japan Sea SST during the last glacial maximum ~20 ka ago.

An individual-based model of Scomber japonicus in the East China Sea (ECS) was developed to simulate the effects of physical environment on the transport and distribution of eggs, larvae and juveniles of S. japonicus from 1978 to 2013. The results showed that there were interannual differences in the transport and distribution of eggs, larvae and juveniles of S. japonicus in the ECS due to different physical environments from 1978 to 2013, and this difference was extremely obvious in some specific years. The current in the drift path of eggs and juveniles controlled and affected the transport process and distribution characteristics. In April, the distribution of eggs and larvae was mainly controlled by the Taiwan Warm Current (TWC). The number of eggs and larvae transported into the northeastern waters of the ECS was positively correlated with the intensity of TWC. In May, it was mainly regulated by the TWC and the Tsushima Strait Warm Current (TSWC). In June, the number of larvae and juveniles entering the Tsushima Strait and the Pacific Ocean was determined by the TSWC. In general, in the years with high number of larvae and juveniles into the Tsushima Strait, the catch of 0-year-old S. japonicus was also higher. In addition, the number of larvae and juveniles entering the Tsushima Strait in El Niño years was less than that in La Niña years. In July, the transport was mainly controlled by the Kuroshio Current (KC), and the eddy within the KC strongly affected its distribution.

Based on the historical observed data and the modeling results, this paper investigated the seasonal variations in the Taiwan Warm Current Water (TWCW) using a cluster analysis method and examined the contributions of the Kuroshio onshore intrusion and the Taiwan Strait Warm Current (TSWC) to the TWCW on seasonal time scales. The TWCW has obviously seasonal variation in its horizontal distribution, T-S characteristics and volume. The volume of TWCW is maximum (13 746 km3) in winter and minimum (11 397 km3) in autumn. As to the contributions to the TWCW, the TSWC is greatest in summer and smallest in winter, while the Kuroshio onshore intrusion northeast of Taiwan Island is strongest in winter and weakest in summer. By comparison, the Kuroshio onshore intrusion make greater contributions to the Taiwan Warm Current Surface Water (TWCSW) than the TSWC for most of the year, except for in the summertime (from June to August), while the Kuroshio Subsurface Water (KSSW) dominate the Taiwan Warm Current Deep Water (TWCDW). The analysis results demonstrate that the local monsoon winds is the dominant factor controlling the seasonal variation in the TWCW volume via Ekman dynamics, while the surface heat flux can play a secondary role via the joint effect of baroclinicity and relief.