Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

We consider the sea level, air–sea heat flux, and wind stresses and use an ocean model to investigate the evolution of the Kuroshio path and intensity during the last 35,000 years. Relative to the present, the Kuroshio during the last glacial period traveled the same path albeit with higher surface velocity in the East China Sea, while it migrated northward south of Japan and southward at the Kuroshio Extension (KE). The southward migrations of the KE axis were closely related to the positions of zero wind-stress curl. To a certain extent, stronger glacial trade winds enhanced the North Equatorial Current. Consequently, Kuroshio transport increased in the southern and middle Okinawa Trough. Regarding Kuroshio strength, we suggest that the horizontal gradient of the subsurface temperature would be a better indicator than the upper-ocean vertical thermal gradient, which is a commonly used index in paleoceanography.

DOI： 10.1029/2021GL097250

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Field observations of persistent organic pollutants (POPs) in shelf seas presented abnormal phenomena such as high-concentration patches in offshore areas and different vertical profiles of POPs at the same location. We assumed that these phenomena were associated with the presence of bottom cold water mass (BCWM) in shelf seas and used a hydrodynamic-ecosystem-POP coupled model to confirm this hypothesis. Based on model results, with the formation of BCWM during summer, POPs accumulated inside BCWM due to their transport across the thermocline by the sorption to sinking particles. With the intensification of vertical mixing during winter, the release of POPs from BCWM induced high-concentration patches of POPs on the surface layer. Meanwhile, the low water temperature in winter was favorable for the gas deposition of POPs, which led to high surface concentrations of POPs. Because the accumulation of POPs in BCWM depended on the sorption of dissolved POPs by particles, not all types of POPs accumulated in BCWM. Some POPs even accumulated at the sea surface above the BCWM due to large gaseous deposition and weak sorption by particles. Using this feature, we proposed a prediction function for the accumulation of POPs in BCWM.

DOI： 10.1016/j.jhazmat.2024.136422

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Sea surface temperature cooling (SSTC) is an important indicator of the ocean response to typhoons and is a factor in the evolution of typhoons. Understanding the intricate mechanisms underlying the SSTC induced by different typhoons is important. Based on the numerical simulation, we investigated the SSTC induced by typhoons Megi (2010), Linfa (2015), and Sarika (2011), which had relatively similar tracks in the South China Sea. As the strongest (weakest) typhoon, Megi (Sarika) induced the largest (smallest) SSTC, which is consistent with the traditional understanding that stronger typhoons usually induce larger SSTC than weaker typhoons. However, the SSTC induced by the moderate typhoon Linfa was nearly comparable to that induced by Megi, while Linfa had a wind power input an order of magnitude smaller. A comparison of near-inertial waves (NIWs) induced by Linfa and Megi showed that the former contained a larger proportion of high modes, substantially contributing to vertical shear. Consequently, the vertical mixing coefficient during Linfa reached one third of that during Megi. Because the SSTC is primarily influenced by vertical mixing, which is dominated by vertical diffusion at the mixed layer depth, the relatively strong vertical mixing coefficient and large temperature gradient during Linfa ultimately resulted in the SSTC nearly comparable to that induced by Megi. The results of this study enhance the understanding of typhoon-induced SSTC.

DOI： 10.1016/j.ocemod.2024.102452

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Ocean boundary currents are complex and highly variable systems that play key roles in connecting the open and coastal ocean through cross-slope circulation and upwelling of nutrient-rich water. The structure, strength, and variability of boundary currents are associated with a broad range of spatial and temporal scales. For that reason, long-term boundary current monitoring is challenging and requires the use of complementary observing platforms and sensors coupled with numerical simulations. The Ocean Observations Physics and Climate Panel Boundary Systems Task Team recently held a virtual dialogue series to discuss six mature boundary current monitoring systems. The goal of the series was to examine strategies for developing a conceptual design for sustained observing activities applicable to a wide range of boundary current systems. This article provides a brief overview of the six systems, including users and the observational and modeling components needed to achieve scientific, operational, and societal goals. Ocean observing best practices and recommendations are shared to provide guidance for the coordination and sustainability of observing systems at ocean boundaries and to strengthen and integrate partnerships across and within the global observing networks.

DOI： 10.5670/oceanog.2024.504

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Copernicus GmbH  

Abstract. The Seto Inland Sea (SIS) is a critical semi-enclosed coastal sea in Japan, characterized by intricate coastlines and narrow straits that give rise to various fronts. Despite extensive research on tidal fronts, knowledge gaps persist regarding their spatiotemporal dynamics, particularly in certain poorly documented regions. Additionally, the understanding of thermohaline fronts, which emerge during winter, requires further investigation. We aimed to enhance our understanding of tidal and thermohaline fronts in the SIS by analyzing their dynamic processes, including intra-tidal and spring–neap tidal cycles, seasonal variations, and anomalous frontal variability. Using a gradient-based algorithm with an advanced contextual feature-preserving median filter, we processed the high-resolution sea surface temperature dataset to detect and quantify tidal and thermohaline fronts. Our analysis revealed the presence of numerous tidal fronts, predominantly influenced by the M2 tide, across the SIS, with substantial spatial variations in amplitude due to complex coastlines and narrow straits. Intra-tidal movements of tidal fronts corresponded to ebb and flood currents, while spring–neap tidal cycles and seasonal shifts influenced frontal positions and intensities. Additionally, thermohaline fronts were identified in certain regions during winter, characterized by large horizontal temperature and salinity gradients. This study enhances the understanding of tidal and thermohaline fronts in the SIS, emphasizing the importance of intra-tidal and wind-driven influences on frontal dynamics. However, limited observational coverage and resolution emphasize the need for further research to explore long-term temporal changes and better grasp the influences of ambient currents and wind patterns. Such insights are vital for effective coastal management and environmental monitoring in the SIS region.

DOI： 10.5194/os-20-1527-2024

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

The Tokara Strait is a mixing hotspot due to the coexistence of complex bottom topographies and strong composite flow including both the Kuroshio and tidal currents. Although previous studies have revealed several mechanisms from the view of Kuroshio-Topography interaction, the role of tides in driving mixing is still not clear. Given that it is located at the M2 critical latitude (29°N), parametric subharmonic instability (PSI) is expected as an important process responsible for the mixing. Here, we study PSI of the M2 internal tides in the Tokara Strait based on a high-resolution model. Our model results indicate that intense near-inertial waves are generated via PSI, which exhibit a horizontally layered structure and have much larger vertical wavenumbers than the M2 internal tides. Energy is transferred from the M2 internal tides to the near-inertial waves around the generation sites, and most of the near-inertial energy is dissipated locally. The dissipation rates of near-inertial waves are comparable to those of the M2 internal tides. Simulations with and without the Kuroshio Current revealed the suppression of PSI along the Kuroshio path, which could be attributed to two mechanisms. First, the Kuroshio Current modifies the local minimum internal wave frequency by its horizontal and vertical shear, making the condition for PSI not satisfied. Second, the Kuroshio Current advects the near-inertial waves downstream in the Okinawa Trough, which inhibits the accumulation of near-inertial energy there. However, in most of the areas outside the Kuroshio path, PSI majorly contributes to mixing in and around the Tokara Strait.

DOI： 10.1029/2022JC019622

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Nutrient exchange with the East China Sea plays an important role in primary production in the Yellow Sea. Owing to lack of simultaneous observations, the spatiotemporal nutrient exchanges across the boundary between the Yellow Sea and East China Sea (Section YE) remain unclear. In this study, a three-dimensional physical-biogeochemical coupled model was used to determine the flux of dissolved inorganic nitrogen (DIN) across Section YE. The results showed that DIN was transported from the East China Sea to the Yellow Sea throughout the year and was highest in summer, accounting for 38 % of the total annual amount. Seasonal variations in the DIN flux were attributed to seasonal variations in the ocean currents across Section YE. In the Yellow Sea, the annual amount of DIN from lateral boundaries was larger than the river input and was comparable to the atmospheric deposition.

DOI： 10.1016/j.marpolbul.2024.116992

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Publisher：Copernicus GmbH  

Abstract. We constructed a coupled physical-ecosystem model with a tracking module to evaluate the influence of submarine groundwater discharge (SGD) and river water on nutrient distribution and phytoplankton growth in Toyama Bay, a deep bay in the Japan Sea. The tracking technique allows us to distinguish SGD- and river-derived nutrients in the bay and evaluate their contributions to the nutrient inventory and phytoplankton growth. Horizontally, SGD-derived nutrients were primarily distributed within a narrow band from the coastline (< 3 km), and vertically, they were abundant in the middle and bottom layers. Because of the buoyancy of SGD, SGD-derived nutrients were transported upward to the surface layer and used by the phytoplankton growth. On the other hand, river water exerted a greater effect on phytoplankton growth than SGD did, on both the spatial range and the amount of phytoplankton biomass. Due to the different distributions of river- and SGD-derived nutrients, their proportions used by phytoplankton differed from coastal to offshore areas. These findings enhance our understanding of the coastal ecosystems affected by land water.

DOI： 10.5194/egusphere-2024-2581

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To assess the potential effects of future climate change on Undaria pinnatifida cultivation in the Seto Inland Sea, Japan, we developed an individual-based growth model for the U. pinnatifida sporophyte. Initially, we validated the model’s performance using field observation data. The simulation results replicated temporal variations in the total lengths of sporophytes at two stations with differing oceanographic conditions. Subsequently, we conducted numerical simulations of sporophyte growth in the Seto Inland Sea during the 1990s and projected outcomes for the 2090s under four emission scenarios of the Representative Concentration Pathway (RCP 2.6, 4.5, 6.0, and 8.5). The majority of areas exhibited decreased sporophyte growth in the 2090s compared to the 1990s, except for the eastern area under the RCP 2.6 scenario. This decline was attributed to delayed cultivation start times associated with ocean warming and reduced dissolved inorganic nitrogen concentrations. Interestingly, the impacts of ocean warming on U. pinnatifida cultivation were not uniformly negative. In addition to adverse effects, there were positive effects that accelerated growth rates in low-temperature winter areas. Sensitivity analyses revealed that the balance between positive and negative impacts varied geographically; moreover, the contrasts were enhanced with higher RCP scenarios. Simulations for climate change adaptation using a high-temperature tolerant cultivar indicated that yield losses could be mitigated, even under the RCP 8.5 scenario. Despite uncertainties in the simulation results, such as future management of nutrient loads and herbivore feeding damages, our projections underscore the potential sustainability and future viability of U. pinnatifida aquaculture in the Seto Inland Sea.

DOI： 10.1007/s10811-024-03291-1

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

The deep-water environment and its ecosystem are becoming the ultimate sinks for Polychlorinated Biphenyls (PCBs). A three-dimensional hydrodynamic-ecosystem-PCB coupled model was applied to the Sea of Japan (SoJ), where deep water is isolated from the surrounding oceans, to elucidate the accumulation processes of CB153 and assess the contributions of physical and biological processes to the accumulation. We suggest that the dissolved CB153 concentration formed a three-layer vertical structure in the SoJ: the highest concentration is in the intermediate layer (100–600 m), followed by those in the deep (600 m to the bottom) and surface layers (0–100 m). Different accumulation mechanisms in the northern and southern SoJ were discovered. The oceanic biological pump enhances the accumulation in the northern SoJ by taking CB153 out of the thermocline in summer and contributes 70 % to the accumulation in the intermediate layer; while the vertical advection contributes 70 % to the accumulation in the intermediate and deep layer in the southern SoJ.

DOI： 10.1016/j.scitotenv.2024.173599

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The distribution of polycyclic aromatic hydrocarbons (PAHs) in the ocean is affected by the sorption-desorption process of sediment particles. This process is determined by the concentration of PAHs in seawater, water temperature, and organic matter content of sediment particles. Quantitative relationships between the net sorption rates (=the difference of sorption and desorption rates) and these factors have not been established yet and used in PAH transport models. In this study, phenanthrene was chosen as the representative of PAHs. Three groups of experimental data were collected to address the dependence of the net sorption processes on the initial concentration, water temperature, and organic carbon content representing organic matter content. One-site and two-compartment mass-transfer models were tested to represent the experimental data using various parameters. The results showed that the two-compartment mass-transfer model performed better than the one-site mass-transfer model. The parameters of the two-compartment mass-transfer model include the sorption rate coefficients kafand kas (L g−1 min−1), and the desorption rate coefficients kdf and kds (min−1). The parameters at different temperatures and organic carbon contents were obtained by numerical simulations. Linear relationships were obtained between the parameters and water temperature, as well as organic carbon content. kaf, kas and kdf decreased linearly, while kds increased linearly with temperature. kaf, kas and kdf increased linearly, while kds decreased linearly with organic carbon content. The r2 values between the simulation results based on the relationships and the experimental results reached 0.96–0.99, which supports the application of the model to simulate sorption-desorption processes at different water temperatures and organic carbon contents in a realistic ocean.

DOI： 10.1016/j.ecoenv.2024.116440

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The nutrients from the East China Sea (ECS) through the Tsushima/Korea Strait (TS) strongly impact the ecosystem of the Japan Sea (JS). The complex origins of the Tsushima Warm Current and the various nutrient sources in the ECS result in complex spatial-temporal variations in nutrients in the TS. Using a physical-biological model with a tracking technique, we studied the effects of nutrient sources from the ECS on the TS. Among all the nutrient sources, the Kuroshio has the highest nutrient concentrations in the TS. Its maximum concentration occurs at the bottom, while those of rivers and atmospheric deposition occur at the surface, and that of the Taiwan Strait occurs in the middle layer. The nutrient transport through the TS exhibits similar seasonal variations, as does the volume transport. The transport of nutrients from the Kuroshio accounts for more than 85% of the total. The transport of nutrients from the Taiwan Strait is greater during autumn and winter. The transport of dissolved inorganic nitrogen (DIN) from both rivers and atmospheric deposition through the TS peak in August. Nutrient transport cannot be equated with volume transport. The DIN in the less saline zone originates not only from rivers but also from atmospheric deposition and the Kuroshio. The transport of nutrients from the Taiwan Strait is not as significant as its volume transport in the TS.

DOI： 10.1007/s13131-024-2372-1

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Internal tides (ITs) radiated from the Luzon Strait (LS) to the South China Sea (SCS) exhibit variability closely related to changes of stratification. Based on the CanESM5 simulation from the sixth phase of Coupled Model Intercomparison Project, the stratification within the LS will increase in the following century due to climate change resulting from human activities. Here we conduct numerical experiments to investigate changes of the M2 ITs under different shared socioeconomic pathway (SSP) scenarios. Results show that the cumulative generation of ITs within the LS weakens with strengthening stratification. The amount of ITs generated in the LS will decrease by 22.7% (2.7%) and that propagating into the SCS will decrease by 27.9% (4.4%) in a century under the SSP5-8.5 (SSP1-2.6) scenario that represents the high (low) end of future emissions. The changes are attributed to the interference of the M2 ITs within the double ridges, which weakens as the stratification strengthens and finally reduces the IT generation. Considering that ITs are one of the most important energy sources for diapycnal mixing, the decrease in ITs would have significant physical and biogeochemical implications in the LS and the SCS.

DOI： 10.1007/s00382-024-07148-8

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Coastal seas are important pools of persistent organic pollutants (POPs) discharged from land. Considering the complex conditions in coastal seas and various biochemical features of POPs, special temporal-spatial variations in POPs have been reported. To understand these variations, we developed a three-dimensional hydrodynamic–ecosystem–POP coupled model and applied it to the Yellow Sea. We selected two POP species (polychlorinated biphenyl congener 153 (PCB-153) and decabromodiphenyl ether (BDE-209)), which have different biochemical properties, as target materials. The dissolved PCB-153 simulated concentration was high in late spring and low in autumn, whereas that of BDE-209 was high in summer and low in winter. Both PCB-153 and BDE-209 showed high particle-bound concentrations in early spring. In summer, dissolved PCB-153 accumulated at the sea bottom, whereas dissolved BDE-209 accumulated at the sea surface. Seasonal and spatial variation differences in the two POPs are likely caused by greater Henry's Law Constant (H′) and bioconcentration factor (BCF) of PCB-153 than that of BDE-209, which leads to higher volatilization and stronger absorption by the particles for PCB-153 than BDE-209. As a component of such differences, the “biological pump” of PCB-153 in the central Yellow Sea is more apparent than that of BDE-209.

DOI： 10.1016/j.jhazmat.2024.134051

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Authorship：Last author   Publishing type：Research paper (scientific journal)  

Study area: The Chao Phraya Estuary (CPE) (100° 28'−100° 36'E, 13° 30'−14° 15'N) in the central part of Thailand. Study focus: To systematically study characters of the CPE, saltwater intrusion and its responses to natural and water regulation and abstraction using high resolution 3D hydrodynamic model with along-the-river measurements. New hydrological insights for the region: Findings show that: (i) the CPE is a partially mixed estuary regulated by the tide, river discharge, local and remote winds, and seasonal sea level that is substantially influenced by the Asian-Australian monsoon and human factors. (ii) Low freshwater discharge, prevailing down-estuary winds, and the highest annual sea level are the natural causes for the enhancement of estuarine circulation and the greatest saltwater intrusion distance, which both occur in January. (iii) Geometry of the CPE (long, narrow and meandering) enhances the tidal wave energy dissipation through horizontal turbulence and riverbank roughness which should be considered when modelling any similar estuary elsewhere. (iv) Water regulation and abstraction are likely to be responsible for severe intrusion events during 2020 and 2021, which adversely affected more than 14 million people in and around Bangkok. The freshwater discharge rate and saltwater intrusion distance from the river mouth have a negative relation (R = - 0.72, p-value = 0). Improvement of freshwater allocation within the river basin are primary ways to effectively manage the saltwater intrusion problem.

DOI： 10.1016/j.ejrh.2024.101686

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Tidal mixing in a shelf sea south of Japan (Bungo Channel) plays an important role in modulating the water exchange between the Seto Inland Sea and Pacific Ocean. In this study, based on moored observations and model results from the Japan Coastal Ocean Predictability Experiment—Tides (JCOPE-T), the generation, propagation, and dissipation of semidiurnal internal tides in the Bungo Channel are investigated. Observational results indicate that semidiurnal internal tides induce strong baroclinic currents reaching 0.3 m/s. Their energy shows obvious spring-neap tidal cycles, generally coinciding with the local barotropic tidal forcing. By conducting the empirical orthogonal function analysis, we find that the observed semidiurnal internal tides are mainly dominated by the first two baroclinic modes. The JCOPE-T results suggest two main generation sites for semidiurnal internal tides in the region: one is located at a narrow strait north of the Bungo Channel, while the other is at the shelf break south of the Bungo Channel. The latter makes a major contribution to the observed semidiurnal internal tides. Northward internal tides generated at the shelf break are superposed with those generated at the narrow strait, causing a complex interference pattern in the channel. The temporal variation of semidiurnal internal tides in the Bungo Channel is affected by several factors. The intraseasonal variation of semidiurnal internal tides can be modulated by the Kuroshio warm water intrusion (Kyucho) because the occurrence of Kyucho changes the stratification in the channel and hence affects the energy conversion. The seasonal variation of semidiurnal internal tides in the Bungo Channel is determined mainly by the seasonally varying stratification; while those generated at the shelf break are under the combined influence of seasonal stratification and background currents. Southward internal tides from the shelf break are refracted due to the spatially varying stratification and background currents. The varying Kuroshio path and strength modulate the refraction of internal tides.

DOI： 10.1016/j.pocean.2024.103229

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

Export production, which is defined as the export of organic matter fixed by photosynthesis, is crucial for sustaining oceanic carbon uptake. The export route in the open ocean is the sinking of biogenic particles through the bottom of the euphotic layer. In contrast, the export routes in the shelf seas are the sinking of biogenic particles to the sediment and the horizontal transport of biogenic particles across the boundary of the shelf seas to the open ocean. The biogenic particles in the shelf seas are supported by multisource nutrients including riverine and oceanic ones. Their exports depend on the hydrodynamic conditions and biogeochemical processes responsible for different sources of nutrients. Here, a unique physical-biological coupled model with a tracking approach is applied to evaluate the export production supported by multisource dissolved inorganic nitrogen (DIN) over the East China Sea. The total export production is 6.83 kmol N s^-1 (=17.16 Tg C yr^-1), which is slightly lower than the reported atmospheric CO₂ absorption. Approximately 80% of particulate organic nitrogen (PON) is exported via off-shelf transport, and the remaining 20% is buried in the sediment. The PON supported by DIN from rivers accounts for 8% of export production, with an e-ratio (export production/primary production) of 0.09. In comparison, that from the Kuroshio accounts for 64%, with an e-ratio of 0.22. This suggests that offshore areas here are more efficient in exporting local production than nearshore ones, largely supported by oceanic nutrients.

DOI： 10.3389/fmars.2024.1338835

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The occurrence of abnormal phytoplankton blooms is one of the significant changes in coastal ecosystems due to climate change. However, the underlying mechanism of such blooms remains poorly understood due to the complexity of the system. In this study, the data from numerous observations was used to elucidate the unprecedented phytoplankton blooms in the autumn and winter of 2021 in Laizhou Bay, a typical aquaculture bay in the southern Bohai Sea of China. The abundance of phytoplankton cells increased by more than tenfold in the southern waters compared to that in the same period from 2019 to 2020. The phytoplankton bloom was first observed in winter in the Bohai Sea, with the cell abundance in the southern bay exceeding 108 cells L−1 in December 2021. The diversity and evenness of phytoplankton communities decreased in the southern area. Cerataulina pelagica was the dominant algae, comprising 69 % of the total phytoplankton in October and 99 % in December. In autumn 2021, the largest flood of the Yellow River in recent decades occurred. This was attributed to extreme rainfall events within the river basin. The input of substantial riverine nutrients played a significant role in promoting phytoplankton blooms. Correlation analysis indicated the important cumulative impact of the Yellow River on phytoplankton blooms rather than a direct short-term effect. Numerical modeling results indicated that exceptionally high Yellow River discharge in autumn could significantly affect the entire bay from autumn to the following spring. This study may contribute to understanding the abnormal phytoplankton blooms in coastal waters and provide valuable insights for environmental management in river basins and coastal waters.

DOI： 10.1016/j.jenvman.2023.119901

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ocemod.2023.102243

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

Visible Infrared Imaging Radiometer Suite (VIIRS) Boat Detection (VBD) data have been widely used to study the patterns of fishing grounds and their linking to fishery targets, particularly species mainly caught by jiggers. In line with most species in the Ommastrephidae family, the population of Todarodes pacificus is made up of various splinter cohorts concerning the timing and location of hatching. Therefore, the satellite‐recorded fishing grounds consist of groups with complex age structures and different migration directions within cohorts. This study examined the age composition of harvestable stocks (age spectrum) of T. pacificus in the Japan Sea based on an early life history individual‐based model of T. pacificus and VBD data. Using the age spectrum, we analysed the relationship between fishery effort and the age of the target group. It was found that jiggers most prefer individuals around 310 ± 20 days. Furthermore, the correlation between ambient water temperature and fishing effort revealed that T. pacificus migrated to colder waters, reaching the coldest waters at 250 ± 7.5 days before moving back towards warmer waters. We discussed a possible way to use the age‐temperature relationship to analyse the flow of VBD distributions to record the movements related to the migration of the fishing target. The results show migration‐like trajectories, which are initially parallel to the isotherm, gradually deflect towards lower temperature sides over several months, sharply turn for about a month and then move back with a slight angle to the isotherms. The method provides a potential framework to improve our understanding of the active migration of oceanic squid.

DOI： 10.1002/rse2.368

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10872-023-00702-8

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Other Link： https://link.springer.com/article/10.1007/s10872-023-00702-8/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：American Meteorological Society  

Abstract

With the development of ocean observation technology, data from specially designed mobile profiling floats have been used to study the internal tides (ITs). However, the accuracy of IT characteristics extracted from such observations has not been fully evaluated. Based on numerical simulations of ITs and background circulation with hundreds of free-moving floats near the Luzon Strait, this study examines the IT characteristics extracted from the float observations based on statistics. For the case in which only the M₂ constituent is considered, the lowest error level of extracted M₂ temperature fluctuation amplitudes (TFAs) is 40%–50%, which appears at 200–1500 m depth. Increasing the sampling frequency of the float from daily to hourly does not decrease the lowest error level. The quasi-daily sampling and other tidal constituents also have an impact on the extracted M₂ TFAs and increase their errors. The different patterns of background currents mainly influence the errors of extracted M₂ TFAs in the upper 200 m. The relation between TFA and vertical displacement of ITs and the two error sources of the TFA extracted from float observations are discussed in this study.

DOI： 10.1175/jtech-d-22-0116.1

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.csr.2023.105055

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.dsr.2023.104005

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

In July 2020, a stationary atmospheric front over Japan caused persistent, nearly continuous rain for most of the month that resulted in new historical highest rainfall records in several areas and caused serious river floods, landslides, and debris-flow events. An existing hindcast and forecast ocean circulation model that includes climatological discharge information of major rivers failed to represent the extreme river discharge under heavy rainfall. New experiments were conducted using real-time river discharge information based on Today's Earth CaMa-Flood simulation that includes 368 rivers in Japan. The inclusion of real-time river discharge improved the salinity bias in the near-surface waters. The differences were significant compared to the observations in the heavy rain region (i.e., Ariake Bay and Tosa Bay), and insignificant at offshore stations. The ensemble experiments of real-time river discharge cases suggested the difference between the climatological and the real-time river discharge experiments was not random, but was robust. The freshening water changed the shelf circulation, and its far-reaching effect appeared hundreds of kilometers away from the shore. Passive particle tracking was conducted for examining the cross-shelf exchange. More particles released from Bungo Channel went offshore in near-surface water when the real-time river discharge was used compared to using the climatology discharge. Particles released in Tosa Bay, Seto Inland Sea, and Kii Channel showed the opposite tendency. The real-time river discharge not only changed the modeled coastal salinity distribution, but also the coastal and offshore currents. The role of the real-time river discharge on modeling normal flow periods or drought events, and its influence on a longer time scale model simulation remain to be explored.

DOI： 10.1007/s10236-023-01551-1

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Other Link： https://link.springer.com/article/10.1007/s10236-023-01551-1/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

The East China Sea (ECS) is a marginal sea with high productivity, especially in summer. In the Zhejiang coastal region of ECS, the large phytoplankton biomass in summer is attributed to the nutrients pumped up by Zhejiang coastal upwelling (ZCU), and oceanic nutrients supplied by the Kuroshio intrusion (KI) onto continental ECS. However, the yearly variations in these two processes are not consistent, which complicates coastal nutrient supplies. In this study, to understand the contributions of ZCU and KI to the nutrient supplies, nutrient concentrations, and phytoplankton biomass in ECS as well as their yearly variations, a physical‐biochemical coupled model was applied. According to model results and observations, the years 2013 and 2018 were identified as strong and weak ZCU years during 2010–2018 period, respectively. In 2013, nutrient and chlorophyll‐a concentrations were higher than 2018 in nearshore areas, but nutrient concentrations were lower than 2018 at the bottom of wide offshore areas. Strong wind stress in 2013 induced strong ZCU and shoreward net nutrient flux along the 60‐m isobath, which was seaward in 2018. The fewer nutrient supplies from KI in the spring of 2013 decreased the nutrient concentrations at the bottom of offshore areas, but its influence on nearshore nutrient concentrations was not as obvious as that caused by ZCU. Phytoplankton biomass in the nearshore and offshore areas reflected different mechanisms of nutrient supplies. In conclusion, the intensity of ZCU, rather than KI, is the principal factor influencing the coastal primary productivity of ECS in summer.

DOI： 10.1029/2022jc019216

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Publishing type：Research paper (scientific journal)  

Based on moored observations from the Beaufort Gyre Exploration Project, seven burst events of near-inertial waves (NIWs) during September 2017-September 2018 are investigated in this study. These NIW events are divided into two groups. Four NIW events in group I are dominated by downgoing components associated with near-inertial currents in the magnitude of about 0.1 m/s. The plane-wave fitting results indicate that these NIWs have much smaller vertical wavelengths and energy fluxes than those in the mid-latitude oceans. By performing simulations with the slab model and analyzing sea ice conditions, we find that one NIW event is directly excited by the wind in the ice-free summer of 2018. Whereas, the other three NIW events are likely induced by the ice motion. For NIWs in group II, the downgoing and upgoing components are comparable in strength. The downgoing NIWs could be directly forced by the wind; whereas the upgoing ones may be related to the eddy events.The occurrence of the NIW events caused strong shears and hence smaller Richardson number, further resulting in the elevation of the energy dissipation rate. Results of this study can improve our understanding on the NIW dynamics and their influence on the mixing in the Arctic Ocean.

DOI： 10.1016/j.pocean.2023.102986

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Mesoscale eddies (MEs) are active in the northern South China Sea, yet it is hard to separate their impacts on the internal tides (ITs) from those of other subtidal circulation. This study examines the role of an anticyclonic eddy and a cyclonic eddy in modulating the M2 ITs based on numerical simulations. In idealized experiments, MEs that differ only in polarity are located on the main beam of the M2 ITs in the northern South China Sea. Results show that the anticyclonic eddy and cyclonic eddy cause northward and southward refractions of the M2 ITs, respectively, which echoes the realistic simulation. The most dramatic changes in the M2 IT energy fluxes occur on the continental slope to the west of the MEs. Theoretical analysis based on the ray-tracing model and the empirical model for estimating wave front locations reveals that the MEs cause refraction of the M2 ITs by changing the phase speeds. Further investigation shows that the currents related to the MEs make a greater contribution to the IT refraction than the ME-associated stratification. These results have important implications for investigation of spatial and temporal variations in the magnitude and direction of the M2 IT energy fluxes.

DOI： 10.1016/j.dsr.2022.103946

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.chemosphere.2022.137620

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022pa004486

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022PA004486

Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

Coastal upwelling around Hainan Island has a significant impact on the physical environment, ecological environment, and fishery resources of the surrounding waters. Based on the satellite-observed sea surface temperature (SST) from 2003 to 2021, this study analyzed the interannual variations of SST around Hainan Island and the influence of the sea surface forcing on them, with special attention to the upwelling regions in Qiongdong and Qiongxi. The results show that satellite-observed SST can identify three upwelling regions located in the west (WS), east (ES), and northeast (NES) sides of the Hainan Island. The SSTs in the WS, ES, and NES showed warming trends of 0.045 °C/y, 0.010 °C/y, and 0.036 °C/y, respectively. The range of low-temperature water around Hainan Island has gradually shrunk over the past two decades, and this shrinkage trend was more prominent in the WS upwelling region than in the ES and NES upwelling regions. Both the EOF analysis and the SST difference between upwelling regions and non-upwelling regions suggests that the upwelling becomes stronger after 2013. However, it seems not to compete with the overall SST warming in the northwest area of the South China Sea. The interannual SST variations in the ES upwelling region were affected by the local wind stress curl in summer. Except for the wind stress curl, the interannual SST variations in NES upwelling are influenced by the stratification associated with local precipitation and wind direction, especially in 2018. In addition, the interannual SST variation in the WS upwelling region is closely related to the bottom cold water in the central Gulf of Tonkin, which was preserved from the previous winter and is influenced by winter atmospheric conditions. These results are helpful for understanding the variations in SST and ecosystem in the upwelling regions around Hainan Island.

DOI： 10.3389/fmars.2023.1054669

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.oceano.2022.12.001

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Publishing type：Research paper (scientific journal)  

Assessing the coastal water export rate is important for better solving the coastal environmental problems and developing environmental management strategies. To investigate the water export rate and its spatiotemporal variation in the Subei coastal water (SCW), a subregion of the Yellow Sea, this study applied water residence time (RT) as an indicator and studied the roles of tides, wind, and river discharge on the water export rate using numerical modeling and the RT adjoint method. RT had an annual and spatial mean of ∼80 days but presented highly spatial and seasonal heterogeneity. Spatially, high RT (∼100–300 days) occurred in the nearshore region, and its location varied in seasons. Temporally, RT was the shortest in the spring (∼55 days), longest in the summer (∼91 days), and median (∼81 days) in autumn and winter. Furthermore, the seasonal RT mismatched the strength of residual transport velocity (RTV) at the current season but instead relied on the combined effects of RTVs in the current and next seasons. Additional sensitivity experiments revealed that tides greatly increased the RT, the Changjiang River runoff slightly decreased the RT, while monsoon wind dominated the RT seasonal variation. As highlighted by an idealized analytical framework, increasing the magnitude ratio of the wind- and tidal-induced RTVs could amplify the RT seasonal variability. Ecologically, the shortest RT in spring might promote the rapid expansion of macroalgal blooms originating from the SCW into offshore waters, thereby contributing to green tide occurrence in the Yellow Sea. Therefore, the seasonality of RT should be considered in coastal management and scientific planning.

DOI： 10.1016/j.ocemod.2022.102137

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Publishing type：Research paper (scientific journal)  

Rivers carry large amounts of freshwater and terrestrial material into shelf seas, which is an important part of the global water and biogeochemical cycles. The earth system model or climate model is an important instrument for simulating and projecting the global water cycle and climate change, in which tides however are commonly removed. For a better understanding of the potential effect of the absence of tides in the simulation of the water cycle, this study compared the results of a regional model with and without considering tides, and evaluated the effect of tides on the behavior of three major rivers (i.e., the Yellow, Yalujiang, and Changjiang rivers) water in the eastern shelf seas of China from the perspectives of transport pathways, timescales, and water concentration. The results showed that the tides induced more dispersed transport for the water of the Yellow and Yalujiang rivers, but more concentrated transport for the Changjiang River water. The effect of tides on the transit areas of the Yellow, Yalujiang, and Changjiang rivers was 13 %, 40 %, and 21 %, respectively. The annual mean water age and transit time of the three rivers in the model with tides were several (∼ 2-10) times higher than those in the no-tide model, suggesting that tides dramatically slow the river water transport and export rate over the shelf. By slowing the river water export, tides induced a three-fold increase in river water concentration and a decrease in shelf seawater salinity by > 1. Moreover, the effect of tides on river behavior was stronger in relatively enclosed seas (i.e., the Bohai and Yellow seas) than in relatively open seas (i.e., the East China Sea). The change in the shelf currents induced by tides is the main cause of the difference in the river water behavior between the two model runs. Tides can increase bottom stress and thus weaken shelf currents and decrease the water transport timescales. The improvement in tidal parameterization in the no-tide model in the simulation of river water behavior was very limited. Given the important role of river runoff on the global water cycle and the effect of changes in river water behavior on ocean carbon cycling, it is important to include the tidal effect in earth system models to improve their projection accuracy. Copyright:

DOI： 10.5194/hess-26-5207-2022

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The long-term trend and interannual variation of ocean heat content (OHC) in the Bohai Sea, Yellow Sea, and East China Sea (BYECS) were examined using 27 years (1993–2019) of daily reanalysis data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M). The annual mean OHC was 4.25 × 1021 J, with a linear warming rate of 0.13 W m−2 with a confidence level of 95%. The spatial distributions for the annual and linear trends of OHC in the BYECS were inhomogeneous, and a considerable quantity of heat was stored on the outer shelf. The warming rate was considerably elevated in the areas northeast of Taiwan and southwest of Kyushu, showing a rate greater than that of the Pacific and global oceans by a factor of 4–5. Heat budget analysis indicated that the Taiwan Strait (TAS) is the dominant source of heat for the BYECS. The mechanisms of the OHC interannual variation in the outer and inner shelves varied. On the outer shelf, the OHC interannual variation was dependent on the Kuroshio onshore intrusion, while on the inner shelf, the OHC interannual variation was related to the variation in air-sea heat flux. The rapid warming in the outer shelf corresponded to the increasing trends of heat transport across northeast Taiwan and southwest Kyushu, which were dominated by the temporal variation of current velocity.

DOI： 10.3390/w14172763

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Meteorological Society  

Abstract

Complex small-scale processes and energetic turbulence are observed at a sill located on the I-Lan Ridge that spans across the strong Kuroshio off Taiwan. The current speed above the sill is strong (1.5 m s⁻¹) and unsteady (±0.5 m s⁻¹) due to the Kuroshio modulated by the semidiurnal tide. Above the sill crest, isothermal domes, with vertical scales of ∼20 m and ∼50 m during the low and high tides, respectively, are generated by turbulent mixing as a result of shear instability in the bottom boundary layer. Tidally modulated hydraulic character modifies the small-scale processes occurring on the leeward side of the sill. Criticality analysis, performed by solving the Taylor-Goldstein equation, suggests that the observed lee waves and intermediate layer sandwiched by two free shear layers are related to the mode-1 and mode-2 critical control between the sill crest and immediate lee, respectively. Around high tide, lee waves are advected further downstream, and only mode-1 critical control can occur, leading to a warm water depression. The shear instabilities ensuing from the hydraulic transition processes continuously mediate flow kinetic energy to turbulence such that the status of marginal instability where Richardson number converges at approximately 0.25 is reached. The resultant eddy diffusivity K_p is concentrated at O(10⁻⁴) to O(10⁻³) m² s⁻¹ and has a maximum value of 10 m² s⁻¹. The sill on the western flank of the Kuroshio is a hot spot for energetic mixing of Kuroshio waters and South China Sea waters.

DOI： 10.1175/jpo-d-21-0245.1

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Other Link： https://journals.ametsoc.org/downloadpdf/journals/phoc/aop/JPO-D-21-0245.1/JPO-D-21-0245.1.xml

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The Kuroshio in different paths is considered to have different impacts on the generation, propagation and energetics of internal tides (ITs) originated from the Luzon Strait (LS). However, its influence on the incoherence of ITs remains unknown. Based on a regional model simultaneously simulating ITs and background circulations, this study examines the incoherence of the M2 and K1 ITs radiated from the LS under the influence of looping and leaping Kuroshio. The looping Kuroshio causes stronger incoherence of the M2 and K1 ITs than the leaping Kuroshio. The reason is that the looping Kuroshio causes a larger variation of eigenspeed, which results in stronger incoherence of ITs than the leaping Kuroshio does. For both the looping and leaping Kuroshio, the low-frequency background currents play a more important role than the stratification in changing the eigenspeed. We believe that the results of this study can deepen our understanding of the incoherent nature of ITs near the LS.

DOI： 10.1016/j.pocean.2022.102850

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.pocean.2022.102860

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Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

A heavy rain event occurred in early July 2018 near the Seto Inland Sea. Despite clear weather after the heavy rain, the water temperature at 5 m depth on the eastern coast of the Bungo Channel decreased by approximately 3°C. Postulating that the water temperature decrease was related to the heavy rain event, we analyzed observed data during and after the heavy rain and conducted numerical experiments. We found that the surface water temperature decrease was caused by vertical mixing of cold water supplied from the Pacific Ocean in the bottom layer. Numerical experiments revealed that the bottom cold water from the Pacific Ocean was not controlled by the heavy rain event but was intensified by the heavy rain event. The lower salinity (lower water density) due to the heavy rain lasted until the end of August. This lower density intensified the gravitational circulation in the Bungo Channel for 2 months, which led to a 17.5% increase in inflow from the Pacific Ocean in the bottom layer and a 20% increase in the dissolved inorganic nitrogen flux to the Bungo Channel.

DOI： 10.3389/fmars.2022.869285

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

Seventeen years of satellite observational data are used to describe the variability in sea surface temperature (SST) fronts and associated features, e.g., frontal intensity and probability, in the northwestern Pacific Ocean. Compared with the SST gradient and frontal probability, the frontal intensity is less impacted by background noise in satellite observations and precisely represents the variability in frontal patterns. The seasonal variability in frontal intensity is prominent, and the corresponding seasonality varies spatially. Fronts are more common during winter in the northern region around the Oyashio Current but are most common during spring in the Kuroshio Current and to the south of the Kuroshio Extension. The meridional migration of fronts is associated with the seasonal movement of the North Pacific subtropical gyre. Though overall averaged frontal intensity along the Kuroshio Extension is most prominent in the northwestern Pacific Ocean, the associated variability in fronts is highly complex. The current study reveals that seasonality itself cannot capture the whole picture of frontal features because eddy-induced intraseasonal variability and basin-scale signal-induced interannual variability can modulate frontal dynamics. In particular, the monthly frontal intensity in regions where the seasonal cycle is not significant depends on the Pacific Decadal Oscillation and North Pacific Gyre Oscillation. Furthermore, the oscillation of the Kuroshio Extension and associated mesoscale eddies can impact its intraseasonal variability. The comprehensive analysis of frontal intensity in the Kuroshio Extension is helpful for delineating regional dynamics and has the potential to improve our understanding of controls on marine primary production.

DOI： 10.3389/FMARS.2022.836469

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/J.POCEAN.2022.102756

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/S00343-021-0440-3

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Other Link： https://link.springer.com/article/10.1007/s00343-021-0440-3/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Subsurface chlorophyll maxima (SCMs), commonly occurring beneath the surface mixed layer in coastal seas and open oceans, account for main changes in depth-integrated primary production and hence significantly contribute to the global carbon cycle. To fill the gap of previous methods (in situ measurement, remote sensing, and the extrapolating function based on surface-ocean data) for obtaining SCM characteristics (intensity, depth, and thickness), we developed an improved deep neural network (IDNN) model using a Gaussian radial basis activation function to retrieve the vertical profile of chlorophyll a concentration (Chl a) and associated SCM characteristics from surface-ocean data. The annually averaged SCM depth was further incorporated into the bias term and the Gaussian activation function to improve the estimation accuracy of the IDNN model. Based on the Biogeochemical-Argo (BGC-Argo) data acquired for three regions in the northwestern Pacific Ocean, vertical Chl a profiles produced by our improved DNN model using sea surface Chl a and sea surface temperature (SST) were in good agreement with the observations, especially in regions with low surface Chl a. Compared to other neural-network-based models with one hidden layer and a sigmoid activation function, the IDNN model retrieved vertical Chl a profiles well in more eutrophic subpolar regions. Furthermore, the application of the IDNN model to infer vertical Chl a profiles from remote-sensing information was validated in the northwestern Pacific Ocean.

DOI： 10.3390/rs14030632

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Publishing type：Research paper (scientific journal)   Publisher：American Meteorological Society  

<title>Abstract</title>The responses of surface wind stress to the mesoscale sea surface temperature (SST) anomalies associated with the SST front in the northern South China Sea (NSCS) are studied using satellite observations and reanalysis data. Both satellite and reanalysis data explicitly show the linear relationships between the spatial-high-pass filtered wind stress perturbation derivatives and the underlying SST gradient field. However, the noise in the linear relationships is much smaller in the reanalysis data than in the satellite observations. This result is rarely reported in other frontal areas. The wavelet analysis shows that the satellite scatterometer observed numerous high wavenumber perturbations within 100 km in the NSCS, but these perturbations were absent in the reanalysis data. The linear relationship between the perturbation SST gradient and derivative wind stress fields is not significant at this scale, which enhances the noise in the linear relationship. The spatial bandpass-filtered perturbation between 100 and 300 km can give reasonable estimates of the coupling coefficients between the wind stress divergence and downwind SST gradient (<italic>α</italic>_{<italic>d</italic>}) and between the wind stress curl and crosswind SST gradient (<italic>α</italic>_{<italic>c</italic>}) in the NSCS, with values of 1.33 × 10⁻² and 0.95 × 10⁻² N m⁻² °C⁻¹, respectively.

DOI： 10.1175/jcli-d-21-0498.1

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Other Link： https://journals.ametsoc.org/downloadpdf/journals/clim/35/1/JCLI-D-21-0498.1.xml

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

The Bohai Sea is a typical semi-enclosed sea in the northwest Pacific, which is subject to serious eutrophication due to human activities. Similar to hydrographic variables such as water temperature and salinity, the nutrient concentrations and ratios in the Bohai Sea also exhibit seasonal variations. However, the effects of external inputs, biological processes, and benthic processes on these seasonal variations have not been quantified to date. To address this issue, a physical–biological coupled model was developed to capture the seasonal nutrient cycling in the central Bohai Sea. The simulation results revealed apparent seasonal variations in the concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi). The N/P ratio (as the molar ratio of DIN/DIP) also exhibited an apparent seasonal variation, with the maximum and minimum values in surface water occurring in summer (>100) and winter (<30), respectively. The Si/N ratio (as the molar ratio of DSi/DIN) was slightly higher in summer than in other seasons. The budget for three types of nutrient indicated that the biological processes determined the seasonal variations in nutrient concentrations and the N/P ratio. The external inputs of nutrients via river input, atmospheric deposition, and sediment release were probably important in summer when they could alleviate the reduced nutrient concentrations due to biological processes. To maintain a reasonable nitrogen budget, it was necessary to include benthic nitrogen loss, which removed a large amount of inorganic nitrogen in summer and autumn. In addition, the variation of N/P ratio of phytoplankton uptake can reduce the ratio of DIN to DIP in surface water by ~20 in summer as compared to the calculation with a fixed N/P ratio (16:1) in phytoplankton uptake.

DOI： 10.1016/j.scitotenv.2021.149416

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>The Kuroshio—literally “the Black Stream”—is the most substantial current in the Pacific Ocean. It was called the Black Stream because this oligotrophic current is so nutrient-poor in its euphotic zone that the water appears black without the influence of phytoplankton and the associated, often colored dissolved organic matter. Yet, below the euphotic layer, nutrient concentrations increase with depth while current speed declines. Consequently, a core of maximum nutrient flux, the so-called nutrient stream, develops at a depth of roughly between 200 and 800 m. This poorly studied nutrient stream transports nutrients to and supports high productivity and fisheries on the East China Sea continental shelf; it also transports nutrients to and promotes increased productivity and fisheries in the Kuroshio Extension and the subarctic Pacific Ocean. Three modes of the Kuroshio nutrient stream are detected off SE Taiwan for the first time: one has a single-core; one has two cores that are apparently separated by the ridge at 120.6–122° E, and one has two cores that are separated by a southward flow above the ridge. More importantly, northward nutrient transports seem to have been increasing since 2015 as a result of a 30% increase in subsurface water transport, which began in 2013. Such a nutrient stream supports the Kuroshio's high productivity, such as on the East China Sea continental shelf and in the Kuroshio Extension SE of Japan.

DOI： 10.1038/s41598-021-84420-5

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Other Link： http://www.nature.com/articles/s41598-021-84420-5

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10872-021-00616-3

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Other Link： https://link.springer.com/article/10.1007/s10872-021-00616-3/fulltext.html

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Riverine nitrogen loading to the continental shelf sea is important for terrestrial–marine linkage and global nitrogen cycling and leads to serious marine environmental problems. The budget and cycle of riverine nitrogen over the continental shelf in the East China Sea (ECS) are unknown. Using the tracking technique within a physical–biological coupled model, we quantified the nitrogen budgets of riverine dissolved inorganic nitrogen (DIN) and particulate organic nitrogen (PON) over seasonal to annual scales in the ECS, especially from the Changjiang River, which plays a dominant role in riverine nitrogen input. The horizontal distributions of the Changjiang DIN and PON generally followed the Changjiang diluted water and coastal currents and were affected by stratification in the vertical direction. Their inventory variations were dominated by biological fluxes and modulated by physical ones, and changed most dramatically in the inner shelf among three subregions. Less than half of DIN were converted to PON with most of the rest leaving the ECS through lateral transport pathways, among which the flux through the Tsushima Strait was dominant. With the increasing loading of the Changjiang DIN flux from the 1980s–2010s, lateral transports rather than PON production increased due to limited primary production. Approximately 60 % of the produced PON exported to the sediment and 34 % went to the Tsushima Strait. According to the export production, the DIN from the Changjiang River contributed 12–42 % to the ECS carbon sequestration.

DOI： 10.1016/j.envpol.2021.117915

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

A three-dimensional hydrodynamic-antibiotic model is developed to investigate the transport and dilution of sulfamethoxazole (SMX) in the Upper Gulf of Thailand (UGoT). The simulation produced a spatially averaged annual mean SMX concentration of 0.58 μgm−3, which varied slightly between seasons assuming a temporally constant river SMX loading observed in August. In contrast, the horizontal distribution of SMX concentrations strongly varied with season because of the changing residual currents. In addition, SMX is diluted to concentrations lower than 10% of those in river waters a short distance offshore of the estuaries. To better understand this behavior, we examined the relationship between salinity and SMX concentrations in the UGoT. The annual budget demonstrates that 98% of SMX in the UGoT is removed by natural decomposition. As the concentrations of fluvial pollutants in the UGoT depend on their river loading and decomposition rates, functions were derived to predict pollutant concentrations and flushing times based on the river input flux and half-life.

DOI： 10.1016/j.envpol.2021.117779

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Publishing type：Research paper (scientific journal)  

Riverine and oceanic nutrients co-influence the estuarine and coastal phytoplankton production and subsequent organic carbon (OC) dynamics, which contribute significantly to the global carbon cycle. However, it is difficult to quantify the contributions of nutrients from different sources. Based on in situ observations made in July 2017, a three end-member model was developed to estimate the nutrients consumed and OC produced by biological activities in the Changjiang Estuary and its adjacent coastal region. In this way, the contributions of nutrients from different sources to phytoplankton production were quantified. In onshore water with salinity less than 20, the nutrients consumed and OC produced were mainly controlled by the mixing of various water masses and turbidity maximum zones. In offshore water with salinity larger than 20, the model results suggested that the biogeochemical processes regulating nutrients and OC dynamics were mainly impacted by the Changjiang River plume and Taiwan Warm Current deep water (TWCDW). In the stratified river plume region, nutrient uptake and OC production were controlled by the contributions of three end-members (Changjiang fresh water, Taiwan Warm Current surface water and TWCDW), while in the upwelling-influenced region, OC production was strongly regulated by the nutrients supplied by the TWCDW. This study will also shed light on the influence of multi-sourced nutrient compositions and structures on the in situ biological OC production process in similar dynamic estuarine regions.

DOI： 10.1016/j.ecss.2021.107491

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Long-term variations in ocean acidification indices in the Northwest Pacific were examined using observational data and a biogeochemical model with an operational ocean model product for the period 1993–2018. The model and observational data for the surface ocean (< 100-m depth) exhibit consistent patterns of ocean acidification in the subtropical and Kuroshio Extension regions and relative alkalinization (i.e., reduced acidification) in the subarctic region of the Northwest Pacific. Below 100-m depth, acidification dominated in the subtropical regions and alkalinization in the subarctic regions. We attribute the excess acidification in the subtropical and Kuroshio regions to the vertical mixing of dissolved inorganic carbon (DIC) exceeding the DIC release by air–sea exchange. These regional differences in acidification and alkalinization are attributed to spatially variable biological processes in the upper ocean and horizontal and vertical physical redistribution of DIC. Our model and observational results have implications for the spatial extent and pattern of ocean acidification, along with the strength of the ocean carbon sink, which are key aspects of global climate change.

DOI： 10.1007/s10584-021-03239-1

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Other Link： https://link.springer.com/article/10.1007/s10584-021-03239-1/fulltext.html

Authorship：Last author   Publishing type：Research paper (scientific journal)  

We developed a dimethylsulfide (DMS) module coupled to an ecological dynamics model studying the annual DMS cycle of the Yellow and East China seas (YECS). The model results showed that surface DMS concentrations ([DMS]) peaked in August along the coast, and there exhibited several DMS peaks offshore annually. In addition, surface [DMS] were higher in the Yellow Sea than that in the East China Sea. The annual mean surface [DMS] of the YECS reached to 4.55 nmol/L, and oceanic DMS emissions from this sea area was 6.78 μmol/(m2 day). Several sensitivity experiments demonstrated that phytoplankton community and sea water temperature exerted crucial effects on seasonal variations of surface [DMS]; and phytoplankton community or temperature changed the timing of surface DMS peak while photolysis affected the magnitude of [DMS]. Moreover, the effect size of phytoplankton community or water temperature varied spatially.

DOI： 10.1016/j.marpolbul.2021.112517

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Authorship：Last author   Publishing type：Research paper (scientific journal)  

Relative dispersion ratio (RDR) can be used to quantify the deviation behavior of a water parcel’s trajectory caused by a disturbance in a hydrodynamic system. It can be calculated by using a standard method for determining relative dispersion (RD), which accounts for the growth of the deviation of a cluster of particles from a specific initial time. However, the standard method for computing RD is time consuming. It involves numerous computations on tracing many water parcels. In this study, a new method based on the adjoint method is proposed to acquire a series of RDR fields in one round of tracing. Through this method, the continuous variation in the RDR corresponding to a time series of the disturbance time t can be obtained. The consistency and efficiency of the new method are compared with those of the standard method by applying it to a double-gyre flow and an unsteady Arnold-Beltrami-Childress flow field. Results show that the two methods have good consistency in a finite time span. The new method has a notable speedup for evaluating the RDR at multiple t.

DOI： 10.1007/s11802-021-4493-x

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Hydrographic surveys have revealed that the Yellow River plume propagates in the direction opposite to that of a Kelvin wave (upstream) under a low river discharge condition, but turns downstream as the river discharge increases. A numerical model reproduced the upstream extension of the plume under the low river discharge condition and the transition to the downstream direction under the high river discharge condition, and confirmed that the summer wind is not the necessary condition for upstream extension of the plume. With the condition of low river discharge, the model also indicated the dependence of the upstream extension of the plume on the tidal range: extending upstream in spring tide but turning downstream in neap tide. The upstream movement of the plume results from the upstream transport of freshwater that depends on the upstream tide-induced residual current around the river mouth and the downstream density-driven current around the off-shore plume front. With the condition of high river discharge, the upstream tide-induced residual current cannot compete with the downstream density-driven current and the plume turns downstream. Momentum analysis confirms the important roles of ad-vection term and viscosity term in the condition of low river discharge and the shift to a Coriolis force–dominated system under high river discharge condition. An idealized model study suggests a dimensionless number for the river discharge changing the river plume extension from upstream to downstream under a specific upstream ambient current around the river mouth.

DOI： 10.1175/JPO-D-20-0235.1

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Publishing type：Research paper (scientific journal)  

The Kuroshio in the Luzon Strait (KLS) has long been a focus of research for its complex ocean dynamics; however, it is poorly understood owing to a lack of long-term in situ observations. Empirical orthogonal function (EOF) analyses were applied to quarterly expendable bathythermograph data (XBT, with a spatial resolution of 10–20 km in the Kuroshio region and 33 km in the other regions) and sea-level anomaly (SLA) data, to examine the variations of the KLS. The first EOF modes of water temperature and SLA represent seasonal variations. The volume transport of the KLS referring to a 700 m depth reaches its maximum in warm months (19.4 Sv, July–September) and its minimum in cold months (17 Sv, January–March). This variation is similar to that east of Taiwan but is opposite to that east of Luzon, although the Luzon Strait is only 2° distant from the area east of Luzon. The outflow (1.3 Sv) from the South China Sea (SCS) to the Kuroshio in the warm months and the Kuroshio intrusion into the SCS in the cold months are responsible for this seasonal contrast. The second EOF modes of water temperature and SLA are related to the latitudinal movement of the Kuroshio recirculation on a time scale of 2–24 months. Lag correlation and wavelet analysis demonstrate that this mode is triggered by the westward-propagating SLA along 21°–24°N and is affected by the downstream propagation of low-frequency variation (mostly annual to biennial) from the North Equatorial Current bifurcation area.

DOI： 10.1029/2020JC016849

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

The intra-tidal variations of a tidal front in Bungo Channel, Japan and their dependence on the spring–neap tidal cycle and month were analyzed utilizing high-resolution (~2 km) hourly sea surface temperature (SST) data obtained from a Himawari-8 geostationary satellite from April 2016 to August 2020. A gradient-based front detection method was utilized to define the position and intensity of the front. Similar to previous ship-based studies, SST data were utilized to identify tidal fronts between a well-mixed strait and its surrounding stratified area. The hourly SST data confirmed the theoretical intra-tidal movement of the tidal front, which is mainly controlled by tidal current advection. Notably, the intensity of the front increases during the ebb current phase, which carries the front toward the stratified area, but decreases during the flood current phase that drives the front in the opposite direction. Due to a strong dependence on tidal currents, the intra-tidal variations appear in a fortnight cycle, and the fortnightly variations of the front are dependent on the month in which the background stratification and residual current changes occur. Additionally, tidal current convergence and divergence are posited to cause tidal front intensification and weakening.

DOI： 10.3390/rs13091840

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Vertical nitrate fluxes associated with turbulent mixing and upwelling around a small reef in the Kuroshio are quantified by continuously deploying a turbulence microstructure profiler with an attached submersible ultraviolet nitrate analyzer while drifting from the upstream to the downstream of the reef. Flow separations and trains of Kelvin-Helmholtz billows (thickness = 60 m) are identified using a shipboard ADCP and an echo-sounder. The turbulence diffusivity associated with the vigorous turbulent mixing reaches up to O(10−1 m2 s−1), resulting in strong nitrate fluxes of O(1–103 mmol m−2 day−1). In addition, large differences between the upstream and downstream density profiles suggest a strong upwelling velocity of O(10−3 m s−1), as well as an upwelling nitrate flux of O(102 mmol m−2 day−1) in the entire subsurface layer.

DOI： 10.1029/2020gl092063

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

The Bohai Sea is a large, semi-enclosed bay of China with a transport timescale of more than 1 year. Residence time (RT) is an important indicator used to determine the water exchange rate of coastal oceans, and it has a significant influence on coastal ecosystems and the environment. In this study, the RT and its seasonal variability within the Bohai Sea were investigated using a 3-D hydrodynamic model and the adjoint method of the RT. The model results show that the annual mean RT in the Bohai Sea is 3.43 years, and the RT increases from the Bohai Strait to the northwestern coast. The seasonal variability of the RT averaged over the entire Bohai Sea is not obvious; however, the regional RT has a significant seasonal variation, which could be more than 290% on average. When the monsoon winds were removed from the model, the sensitivity experiment showed an annual mean RT increase of ~ 90% with negligible seasonal variations in most areas of the Bohai Sea. The wind-induced residual current controls the seasonal variation in ocean circulation and induces the seasonal variability in RT; thus, monsoon winds play a dominant role in the seasonal variations of the water exchange rate in the Bohai Sea. Sensitivity experiments also suggest that tides can slow the water exchange rate, whereas the baroclinic processes and river runoff can accelerate the water exchange rate in the region near the Yellow River estuary. This study highlights the critical role of monsoon winds in affecting seasonal variabilities in the coastal transport timescale and exchange rate.

DOI： 10.1007/s10236-020-01438-5

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Other Link： http://link.springer.com/article/10.1007/s10236-020-01438-5/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

Organophosphate esters (OPEs) are man-made organic pollutants that are used in flame retardants (FRs), plasticizers, antifoaming and hydraulic agents, and extractants. The demand for FRs in China has increased, thereby rapidly increasing the use of OPEs and hence resulted in its high levels in the environment. In this study, we measured the concentrations of seven OPE congeners in the seawaters of the Bohai Sea (BS), the Yellow Sea (YS), and the East China Sea (ECS). The horizontal and vertical spatial distributions were then analyzed to assess the OPE pollution. The total concentrations of the seven OPE congeners (COPEs) in the three seas ranged from 7.31 to 100 ng L-1. The main OPE compounds were tris-(1-chloro-2-propyl) phosphate (TCPP, 3.97-35.6 ng L-1), tris(2-chloroethyl) phosphate (TCEP, 0.59-19.8 ng L-1), and triphenylphosphine oxide (TPPO, from below the detection limit to 43.5 ng L-1). The inventory of the COPEs in the BS, YS, and ECS was estimated as 54.2, 513, and 3950 tons, respectively. Horizontally, the COPE concentration was ranked as BS > YS > ECS. In the vertical direction, the OPE concentrations in the surface water were higher than those in the bottom water. Ocean currents and riverine inputs might be the main factors influencing the distributions of the OPEs in these seas. Moreover, a seasonal variation (summer 2015 versus winter 2016) in the OPEs was observed in the YS, which was probably due to anthropogenic influences and hydrological, meteorological, and biological factors. (c) 2020 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.scitotenv.2020.140434

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© 2020 Elsevier B.V. Dust deposition can supply nutrients that affect marine phytoplankton, but changing trophic statuses of the surface ocean increase the complexity of interpreting the process. In this study, four onboard incubation experiments amended with various nutrients and dust were performed in the Kuroshio Extension (KE) and Kuroshio–Oyashio transition (TR) of the northwest Pacific (NWP), which are characterised by lower and higher trophic statuses, respectively. According to the nutrient-addition experiments, phytoplankton were limited by nitrogen (N) in the KE, and limited by iron (Fe) or co-limited by Fe and phosphorus (P) in the TR. Dust additions supplied a considerable amount of N and Fe but negligible amount of P to stimulate phytoplankton growth, as indicated by chlorophyll a (Chl a) concentration. In the KE incubations, dust additions enhanced the shift of phytoplankton size structure towards larger cells from dominantly pico-sized (0.2–2 μm) Chl a to comparable contributions from each size class (i.e. pico-, nano-: 2–20 μm, micro-: >20 μm). On the basis of the large shift of size structure towards nano- or micro-phytoplankton in the unamended control treatments in the TR, dust additions furtherly promoted the shift towards micro-phytoplankton becoming the dominant contributor to the total Chl a. The collective analysis of the data from experiments in both regions revealed that, the extent of phytoplankton growth stimulation and the shift towards larger cells were enhanced gradually with increasing amounts of nutrient uptake (including N, P, and silicon). The nutrient uptake ratios of phytoplankton converged towards the Redfield ratio in comparison to the wider range of nutrient ratios in the dust-amended seawater. This study suggested consistencies in the dynamic of phytoplankton growth, shift of size structure, and nutrient uptake following dust additions in the KE and TR, although the trophic status and limiting nutrient varied between these two regions.

DOI： 10.1016/j.scitotenv.2020.139999

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Historical hydrographic data reveal that low-salinity water can detach from the Yellow River plume in summer. In this study, the mechanism of this detachment is examined using a three-dimensional numerical model that reproduced the observed detachment, including the position and size of the detached low-salinity water patch. Sensitivity experiments showed that tide-induced residual currents and tidal mixing around the Yellow River mouth played key roles in the detachment during spring tide. During the transition from neap tide to spring tide, the intensification of the northward tide-induced residual current and the weakening of the southward density-driven current lead to a net northward residual current (0.03 m/s), transporting high-salinity water to the southern area of low-salinity water. Meanwhile, the gradually strengthened tidal mixing also increased surface salinity, which was apparent in the central area of low-salinity water. With the combination of these two effects, the low-salinity water was separated into two parts during spring tide; that is, detachment of low-salinity water occurred. The above scenario works with a condition of no wind. With the prevailing southeasterly winds during summer, the northeastward wind-induced surface current promoted detachment by moving the detached low-salinity water northeastward and enlarging its size. In contrast, the northerly wind that prevails in the other seasons drove low-salinity water southward, which then flowed along the coast and hindered detachment. Consequently, the detachment of low-salinity water from the Yellow River plume occurs only in summer.

DOI： 10.1029/2020jc016344

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© 2020 Elsevier Ltd The Water Sediment Regulation Scheme (WSRS) is a unique engineering measure that has been regularly performed to reduce reservoir sedimentation and increase the flood capacity of the Yellow River in China since 2002. As a side effect, the WSRS greatly increases the monthly input flux of nutrients to the Bohai Sea (BHS) in summer, potentially exacerbating eutrophication levels therein and subsequently affecting the growth of phytoplankton. However, its influence on the Chlorophyll-a (Chl-a) dynamics over the BHS is still poorly understood. In this study, two approaches were adopted to investigate it: 1) long-term in-situ observations and satellite-derived data of surface Chl-a were used to study its seasonal variations before and since 2002, and 2) one 1D physical-biological coupled model was developed to evaluate the impact of WSRS on seasonal Chl-a. The results showed that the surface Chl-a exhibited two peaks in spring and autumn until 2002, but has exhibited only one peak in spring-summer since 2002. Satellite-derived Chl-a concentrations in spring-summer since 2002 have increased by 56% compared to those until 2002. The simulated results showed that the change in Yellow River discharge induced by the WSRS has resulted in the appearance of high concentrations of Chl-a in summer over the Central Bohai Sea since 2002. The WSRS increased the ratio of added Chl-a owing to the riverine nutrients to total Chl-a by 19% compared to that until 2002. Overall, WSRS greatly affects the seasonal cycling of Chl-a in the Bohai Sea, and the side effect needs to be considered.

DOI： 10.1016/j.chemosphere.2020.126846

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Publishing type：Research paper (scientific journal)   Publisher：Copernicus GmbH  

© 2020 Author(s). The Kuroshio Current has been thought to be biologically unproductive because of its oligotrophic conditions and low plankton standing stocks. Even though vulnerable life stages of major foraging fishes risk being entrapped by frontal eddies and meanders and encountering low food availability, they have life cycle strategies that include growing and recruiting around the Kuroshio Current. Here we report that phytoplankton growth and consumption by microzooplankton are stimulated by turbulent nitrate flux amplified by the Kuroshio Current. Oceanographic observations demonstrate that the Kuroshio Current topographically enhances significant turbulent mixing and nitrate influx to the euphotic zone. Graduated nutrient enrichment experiments show that growth rates of phytoplankton and microheterotroph communities were stimulated within the range of the turbulent nitrate flux. Results of dilution experiments imply significant microzooplankton grazing on phytoplankton. We propose that these rapid and systematic trophodynamics enhance biological productivity in the Kuroshio.

DOI： 10.5194/bg-17-2441-2020

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©2020. American Geophysical Union. All Rights Reserved. Water export rate of shelf seas is a pivotal factor impacting the global carbon cycle. Tides have important impacts on shelf hydrodynamics but are excluded in many climate models. To assess the effect of tides on export rates of shelf water, this study used a regional hydrodynamic model and a water residence time (WRT) adjoint model and examined model runs with and without tides for the eastern shelf seas of China. The results show that the average WRTs in the Bohai, Yellow, and East China seas were 11.60, 4.95, and 0.39 years, respectively. When tides were excluded, the WRTs decreased by >70% in the Bohai and Yellow seas and by ~10% in the East China Sea, indicating a significant acceleration in the shelf water export due to the absence of tides. The tidal effect has spatial variability associated with the water depth. Sensitivity experiments suggest that the tidal effect on the mean WRT was stronger than the effect of other dynamical factors (winds, rivers, and boundary currents). In the model with tides, tides weakened the wind-driven coastal current by intensifying the bottom resistance and thus slowed water export in the inner and middle portions of the shelf, compared to the model without tides. Parameterization of the tidal bottom friction in the model without tides could significantly improve the WRT result. This study highlights the crucial role of tides on the long-term transport of shelf seas and the significance of parameterizing the effect of tidal friction in climate models.

DOI： 10.1029/2019JC015863

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/S10584-020-02689-3

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© 2020 by the authors. A marine ecosystem box model was developed to reproduce the seasonal variations nutrient concentrations and phytoplankton biomasses in Jiaozhou Bay (JZB) of China. Then, by removing each of the external sources of nutrients (river input, aquaculture, wastewater discharge, and atmospheric deposition) in the model calculation, we quantitatively estimated its influences on nutrient structure and the phytoplankton community. Removing the river input of nutrients enhanced silicate (SIL) limitation to diatoms (DIA) and decreased the ratio of DIA to flagellates (FLA); removing the aquaculture input of nutrients decreased FLA biomass because it provided less dissolved inorganic nitrogen (DIN) but more dissolved inorganic phosphate (DIP) as compared to the Redfield ratio; removing the wastewater input of nutrients changed the DIN concentration dramatically, but had a relatively weaker impact on the phytoplankton community than removing the aquaculture input; removing atmospheric deposition had a negligible influence on the model results. Based on these results, we suppose that the change in the external nutrients sources in the past several decades can explain the long-term variations in nutrient structure and phytoplankton community. Actually, the simulations for the 1960s, 1980s, and 2000s in JZB demonstrated the shift of limiting nutrients from DIP to SIL. A reasonable scenario for this is the decrease in riverine SIL and increase in DIP from aquaculture that has reduced DIA biomass, promoted the growth of FLA, and led to the miniaturization of the phytoplankton.

DOI： 10.3390/su12062224

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© 2020 American Meteorological Society. The impacts of diurnal atmospheric forcing on the summer salinity change in the East China Sea are investigated using the Regional Ocean Modeling System, forced by the hourly and daily reanalysis of wind and insolation. The differences between the forcing of these two frequencies reveal a dipole pattern of salinity change with a positive salinity deviation (1–2 psu) offshore of the Yangtze River estuary, and a negative deviation (from-1 to-0.5 psu) along the Jiangsu Coast. Further dye tracking experiments confirm that diurnal forcing strengthened the northwestward longshore freshwater transport (NLFT) of the Yangtze River by 5.2 x 109 m3 and reduced the mean water age of 7 days. Sensitivity experiments using different forcing combinations suggest that the diurnal wind, that is, the land–sea breeze, is the key to developing the dipole pattern of salinity change and the NLFT. Through the experiment, the land–sea breeze induced a mean clockwise circulation offshore of the Yangtze River estuary. The above changes resulted from both the nonlinearity of wind stress averaging (i.e., the square nature of wind stress) and the baroclinic adjustment related to the diurnal salinity variation, which is directly connected to the diurnal swing of the Yangtze River front. The baroclinic adjustment generated a dipole pattern of vorticity changes offshore of the Yangtze River estuary and a coherent northwestward jet current strengthening the NLFT. These processes developed the summer dipole pattern of the salinity change.

DOI： 10.1175/JPO-D-19-0200.1

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© 2020, The Author(s). Here, we investigate the seasonal variability in the dissolved inorganic carbon (DIC) cycle in the Northwest Pacific using a high-resolution biogeochemical and carbon model coupled with an operational ocean model. Results show that the contribution to DIC from air–sea CO2 exchange is generally offset by vertical mixing at the surface at all latitudes, with some seasonal variation. Biological processes in subarctic regions are evident at the surface, whereas in the subtropical region these processes take place within the euphotic layer and then DIC consumption deepens southward with latitude. Such latitudinal differences in biological processes lead to marked horizontal and vertical contrasts in the distribution of DIC, with modulation by horizontal and vertical advection–diffusion processes.

DOI： 10.1007/s10584-020-02779-2

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© 2019 Elsevier Ltd The snow crab Chionoecetes opilio is an important fishery species in Japan. Hydrodynamics are vital to the distribution, recruitment and settlement of crab larvae in nursery areas. In this study, we developed a survival and transport model of snow crab larvae to investigate the interannual variability in larval settlement in three fishing areas: west of Toyama (region A), west of Niigata (region B) and west of Hokkaido (region C). We found that the female crab stock abundance determined the modeled number of zoea in regions A and B, whereas water temperature played a major role in the initial number of zoea in region C. As for larval settlement, the ocean current impacted settlement in region B, and water temperature was vital to settlement in region C. Both female crab abundance and hydrodynamics contributed to variability in settlement in region A. The results revealed contrasting recruitment patterns in the three fishing areas. Self-recruitment was the primary form in regions A and C, whereas both self-recruitment and recruitment from upstream sources were important in region B.

DOI： 10.1016/j.pocean.2019.102204

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© 2019 Elsevier Ltd Based on a three dimensional low-trophic ecosystem model, we revaluated budgets of nutrients and biogenic particles (phytoplankton and detritus) in the East China Sea (ECS), a continental shelf sea with high productivity that is affected by a large river (Changjiang River) and a western boundary current (Kuroshio). Following careful comparison of model results with available observation data, we calculated the monthly inventories of the nutrients and biogenic particles in the ECS and the fluxes of the nutrients and biogenic particles through the lateral and vertical interfaces of the ECS. As an improvement over previous nutrient budget calculations that treated the ECS as one box, we divided the water column into two layers: upper and lower layers corresponding to different light condition. Seasonal variations in inventories of nutrients and biogenic particles in both upper and lower layers are apparent but present different features, which are related to opposite contributions of biological processes and physical processes in the two layers. Our calculation shows the necessity of evaluating not only the horizontal fluxes of nutrients and biogenic particles into and out of the ECS through lateral boundaries with adjacent seas but also the exchange fluxes of nutrients and biogenic particles between the upper and lower layers because the latter is larger than the former. Our calculation also reveals two major export pathways of biogenic particles generated locally in the ECS: from the ECS to the Japan/East Sea through the Tsushima Strait and from the ECS to the Kuroshio region through the shelf break (200 m isobath). The export amount of biogenic particles is larger through the Tsushima Strait than through the shelf break in the water column. The depth for the biogenic particles exporting through the shelf break of the ECS is the middle layer (from ~60 m to ~160 m).

DOI： 10.1016/j.pocean.2019.102138

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© 2019 Elsevier Ltd Nutrients (dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP)) in the East China Sea (ECS) have four external sources, namely the Kuroshio, Taiwan Strait, rivers, and the atmosphere. In order to evaluate the contribution of each source of nutrients to the nutrient inventory and primary production over the ECS shelf, a tracking technique was applied to all the state variables in a low-trophic ecosystem model. Each source of nutrients has strong seasonal variations in the spatial distribution that depends closely on circulation, mixing, and stratification. The primary production supported by each source of nutrient is under the control of a combination of nutrients, temperature, and light. As a mean state over the entire ECS shelf, the Kuroshio contributes 72% of DIN input and 84% of DIP input, 57% of DIN inventory and 78% of DIP inventory, 50% DIN-based primary production and 61% DIP-based primary production and therefore is the dominant one among four sources. However, the contributions of four external nutrients have strong spatial dependence: the riverine nutrients and the atmospheric DIN dominate the inner shelf (0–50 m), the nutrients from the Taiwan Strait dominate the southern part of the middle shelf (50–100 m), and the nutrients from the Kuroshio dominate the outer shelf (100–200 m). The production efficiencies of the nutrients from the Kuroshio are low, while those from the atmosphere and Taiwan Strait are high. The riverine DIN is inefficient but DIP is efficient. The nutrient limitation, light and water temperature at the location of the nutrients determine the production efficiency of each specific sources.

DOI： 10.1016/j.pocean.2019.102122

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©2019. American Geophysical Union. All Rights Reserved. Transverse-vertical structure and temporal variability of the Kuroshio current across the Tokara Strait during 2003–2012 measured by a ferryboat acoustic Doppler current profiler with a 2-km horizontal resolution and a two-day interval are presented. The Kuroshio passing through the Tokara Strait exhibits a multicore velocity structure. Its seasonal volume transport variation is biannual for baroclinic components relative to 700 m, peaking in July and December–January. However, the barotropic transport component exhibits an annual cycle with a maximum in December. Empirical orthogonal function analysis of the cross-sectional velocity is performed. The first two empirical orthogonal function modes reveal the north-south shift of the Kuroshio current axis and the change in Kuroshio volume transport, respectively. Temporal variabilities of the leading two modes correspond to those of the Kuroshio Position Index and the sea level difference across the strait, respectively. The third empirical orthogonal function mode, with a relatively smaller horizontal scale, was examined in terms of turbulent mixing. The banded structure captured by this mode is likely induced by flow-topography interaction because islands in the Kuroshio route could cause horizontal and vertical flow separation. Additional analysis based on high-resolution reanalysis data suggested that (1) inertial instability, which is expected in the areas with negative Ertel's potential vorticity, arises to enhance vertical mixing around the islands in the Tokara Strait, and (2) when the Kuroshio directly impinges the islands, flow divergence in the lee of the islands drives upwelling and leads to uplift of isotherms.

DOI： 10.1029/2018JC014771

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©2019. American Geophysical Union. All Rights Reserved. To assess the influences of carbon sources and transport processes on the 14C age of organic matter (OM) in continental margin sediments, we examined a suite of samples collected along a river-shelf-deep ocean transect in the East China Sea (ECS). Ramped pyrolysis-oxidiation was conducted on suspended particulate matter in the Yangtze River and on surface sediments from the ECS shelf and northern Okinawa Trough. 14C ages were determined on OM decomposition products within different temperature windows. These measurements suggest that extensive amounts of pre-old (i.e., millennial age) organic carbon (OC) are subject to degradation within and beyond the Yangtze River Delta, and this process is accompanied by an exchange of terrestrial and marine OM. These results, combined with fatty acid concentration data, suggest that both the nature and extent of OM preservation/degradation as well as the modes of transport influence the 14C ages of sedimentary OM. Additionally, we find that the age of (thermally) refractory OC increases during across-shelf transport and that the age offset between the lowest and highest temperature OC decomposition fractions also increases along the shelf-to-trough transect. Amplified interfraction spread or 14C heterogeneity is the greatest in the Okinawa Trough. Aged sedimentary OM across the transect may be a consequence of several reasons including fossil OC input, selective degradation of younger OC, hydrodynamic sorting processes, and aging during lateral transport. Consequently, each of them should be considered in assessing the 14C results of sedimentary OM and its implications for the carbon cycle and interpretation of sedimentary records.

DOI： 10.1029/2019JG005107

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© 2019, The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. We found a good linear relation between the mean volume backscattering strength measured using a scientific echo sounder and the distribution density of moon jellyfish recorded simultaneously by an underwater video camera in small bays (Hokezu Bay and Mikame Bay) in Japan. This relation held in all of the surveys carried out in recent years (2013–2016), although the regression coefficient varied slightly from year to year due to the existence of ambient organisms. Using this relation and high-resolution echo sounder scan surveys across the bay, we obtained the spatial structures of moon jellyfish aggregations and categorized them into either patchy, layered, or wavy aggregations. We also examined possible physical mechanisms responsible for the moon jellyfish aggregations. In particular, passive particle tracking simulations of several idealized internal wave fields suggest that the formation of wavy aggregations is closely related to the presence of internal waves. However, internal waves alone cannot induce patchy and layered aggregations, indicating that particular biological processes (e.g., swimming behavior) are also necessary for such aggregations to form.

DOI： 10.1007/s10872-019-00507-8

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© 2019 Elsevier B.V. A three-dimensional transport-ecosystem-POP coupled model is configured to simulate the seasonal variation and budget of decabromodiphenyl ether (BDE-209) in a semi-enclosed bay adjacent to the Yellow Sea. The model includes five types of BDE-209 (gaseous, dissolved, phytoplankton-bound, detritus-bound, and suspended particulate matter (SPM)-bound) and related physical and biogeochemical processes, such as advection and diffusion due to seawater motion, input from rivers, air-sea exchange, decomposition of dissolved BDE-209, uptake and depuration between dissolved and phytoplankton-bound BDE-209, mortality of phytoplankton-bound BDE-209, remineralization and sinking of detritus-bound BDE-209, and sinking of SPM-bound BDE-209. Model results show that the dissolved and particulate BDE-209 in the bay are higher in the nearshore area than in offshore area and are higher in summer than in other seasons; these results are consistent with field data. SPM-bound BDE-209 is dominant among the five types due to its large supplying from rivers. Dissolved BDE-209 concentrations are around 5-fold that of phytoplankton-bound BDE-209, which depends on uptake and depuration rate constants between dissolved and phytoplankton-bound BDE-209 and biomass of phytoplankton. Evaluation of mass balance indicates that the input from rivers is major source of BDE-209, while the exchange with the Yellow Sea is major sink. Sensitivity experiments demonstrate that the input of BDE-209 from rivers plays the most significant role in the seasonal variation of dissolved and particulate BDE-209 concentrations, and the change in water temperature is a secondary factor.

DOI： 10.1016/j.scitotenv.2019.01.385

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© 2019 by the authors. We developed a biogeochemical and carbon model (JCOPE_EC) coupled with an operational ocean model for the North Western Pacific. JCOPE_EC represents ocean acidification indices on the background of the risks due to ocean acidification and our model experiences. It is an off-line tracer model driven by a high-resolution regional ocean general circulation model (JCOPE2M). The results showed that the model adequately reproduced the general patterns in the observed data, including the seasonal variability of chlorophyll-a, dissolved inorganic nitrogen/phosphorus, dissolved inorganic carbon, and total alkalinity. We provide an overview of this system and the results of the model validation based on the available observed data. Sensitivity analysis using fixed values for temperature, salinity, dissolved inorganic carbon and total alkalinity helped us identify which variables contributed most to seasonal variations in the ocean acidification indices, pH and Ωarg. The seasonal variation in the pHinsitu was governed mainly by balances of the change in temperature and dissolved inorganic carbon. The seasonal increase in Warg from winter to summer was governed mainly by dissolved inorganic carbon levels.

DOI： 10.3390/su11092677

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© 2019 by the authors. The snow crab (Chionoecetes opilio) sustains an important bottom trawling fishery in the Sea of Japan. Its response to global warming is attracting the attention of the public. Using a transport and survival model for crab larvae in the Sea of Japan, we examined the spatial-temporal variations of crab spawning and larval settlement in the past (mid-20th century), present (early 21st century), and future (mid- and late 21st century) under the low and high radiative forcing scenarios. It was found that the variations in spawning differed between the regions south of and north of 41.5° N, on both seasonal and long-term scales. Larval settlement in the Sea of Japan was projected to increase in the future, which is mainly attributed to a reduction in mortality due to the low water temperature. Moreover, the aggregating location of the settled megalopae will likely shift northward, with increasing settlement off Hokkaido Island. With additional sensitivity experiments, we confirmed that the change in water temperature has a stronger impact on larval settlement than that in the current field. The change in water temperature controlled both the amount and distribution of crab larval settlement, while a change in current field only affected the distribution to some extent.

DOI： 10.3390/su11082198

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Riverine input is an important source of contaminants in the marine environments. Based on a hydrodynamic model, the dilution characteristics of riverine contaminants in the Seto Inland Sea and their controlling factors were studied. Results showed that contaminant concentration was high in summer and low in winter. Contaminant concentration decreased with the reduction of its half-life period, and the relationship between them followed power functions. Sensitivity experiments suggested that the horizontal current and vertical stratification associated with air-sea heat flux controlled the seasonal cycle of contaminant concentration in the water column; however, surface wind velocity was the dominant factor affecting the surface contaminant concentration. In addition, contaminant concentration in a sub-region was likely controlled by the variations in river discharges close to the sub-region. These results are helpful for predicting contaminant concentrations in the sea and are expected to contribute to assessing the potential ecological risks to aquatic organisms.

DOI： 10.1016/j.marpolbul.2019.02.029

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©2019. American Geophysical Union. All Rights Reserved. The modulation of coastal rainfall at Hainan by large-scale circulation and coastal upwelling is studied using observations and numerical modeling. Tropical Rainfall Measuring Mission data show that the monthly mean rainfall off southern Hainan was considerably higher in August 2010 than in August 2011. The main cause of this difference is an intensification of offshore rainfall from midnight to early morning. Compared with the multiyear (2000–2017) average field, reanalysis data show that there is an apparent increase in atmospheric humidity in August 2010. During this time, a moderate El Niño was decaying and a new La Niña event was developing, so a significant adjustment of the large-scale circulation was observed in the western Pacific. The resulting anomalous onshore wind depresses the development of upwelling, leading to a relatively warm sea surface temperature off the south coast of Hainan, which in turn enhances the land-sea thermal contrast and land breeze at night. Decreases in upwelling intensity and asymmetric intensification of nocturnal and daytime offshore rainfall are confirmed not only in the summer of 2010 but also in the summer of 2003. Numerical simulations using the Weather Research and Forecasting model verify that the enhanced land breeze ultimately leads to pronounced coastal rainfall off southern Hainan at night. The results indicate that localized surface convergence associated with the sea and land breezes may be more important than the atmospheric humidity and convective instability in modulating the diurnal cycle of rainfall for tropical islands.

DOI： 10.1029/2018JD029528

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© 2019, Science Press. All right reserved. Based on a hydrodynamic model (JCOPE-T model: Japan Coastal Ocean Predictability Experiment-Tides) in 3-km horizontal resolution, we studied the internal tides in the Tokara Strait, Japan. The strait features complex topography and stable stratification, in which significant isopycnal movement (up to 30 m) is generated. Internal tides in the strait could form up near the seamounts and islands where topography changes drastically. After an internal tide is generated, it would propagate outwards perpendicular to the isobaths in two directions: one goes northwestward and finally enters the shelf of the East China Sea; another moves southeastward and finally enters the Pacific Ocean. Therefore, the strait is abundant in tidal energy. The model data averaged over-14 diurnal tidal periods show that the barotropic energy propagated into the region is 13.92 GW of which 3.73 GW is converted into internal tidal energy. About 77.2% of the internal tidal energy is dissipated locally, while the remaining part transmits mainly through the northwestern and southeastern boundaries. Both the input of the barotropic tidal energy and the conversion rate (from barotropic tides to baroclinic tides) during spring tide roughly doubled those during neap tide. Even though, the main generation area and the propagation direction remain largely unchanged, namely, internal tides transmit mainly through the northwestern and southeastern boundaries. The dissipation rate of internal tidal energy is between 76%-79% in both neap and spring tides. Therefore, the spring-neap tidal cycle affects only the amount of internal tidal energy generated in the Tokara Strait but does not affect the generation area, the propagation direction, and the dissipation rate.

DOI： 10.11693/hyhz20181000251

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© 2018 Elsevier B.V. The age of Yodo River water, the largest river flowing in the Seto Inland Sea (SIS), was calculated using the constituent-oriented age and residence time theory (CART) in order to understand the long-term material transport and environmental issues in this semi-enclosed sea. The Yodo River water was found to have a mean age of 152 days for the entire SIS. Inside the SIS, the age of Yodo River water shows spatial variation ranging from 97 days in Osaka Bay, 199 days in the Harima-Nada, and 450 days in other areas. The age of Yodo River water shows an apparent seasonal variation in the SIS. Tracing water from the Yodo River reveals two pathways for its movement around Osaka Bay: one brings ~5/8 river water directly into the Kii Channel through the Kitan Strait; the other brings ~3/8 river water into the Harima-Nada through the Akashi Strait that eventually enters the Kii Channel through the Naruto Strait. The mean age of Yodo River water is 128 days at the Kitan Strait, 125 days at the Akashi Strait, 203 days at the Naruto Strait, and 271 days at the Bisan Strait. The above estimation considers the return of old Yodo River water into Osaka Bay that does not change the spatial distribution of Yodo River water age inside Osaka Bay but increases the value of water age by ~80%. Without tidal forcing, the mean ages of Yodo River water in Osaka Bay and the Harima-Nada increase by 6% and 51%, respectively, and nearly all the Yodo River water flows directly into the Kii Channel through the Kitan Strait. Without considering baroclinic forcing, the mean ages of Yodo River water in Osaka Bay and the Harima-Nada increases by 52% and 51%, respectively, while the influence of local winds and the Yodo River discharge on the age of Yodo River water are negligible.

DOI： 10.1016/j.jmarsys.2018.12.001

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©2019. American Geophysical Union. All Rights Reserved. The Oyashio, a subarctic western boundary current in the North Pacific, transports cool, fresh, and nutrient-rich water equatorward. The Oyashio nutrient stream was assessed using long-term mean hydrographic observation data. Its nitrate transport (about 350 kmol/s) is comparable to that of the Kuroshio but has a much shallower subsurface core at 250-m depth. In the layer ranging from 26.6 to 27.4 σ θ , the Oyashio nitrate transport to the mixed water region is about 110 kmol/s. This corresponds to the nitrate transport of the Oyashio to the North Pacific Intermediate Water in the mixed water region. Along with this process, the subarctic gyre nitrate export to the subtropic gyre reaches 24 kmol/s. This work first quantifies the Oyashio nutrient transport and its intrusion into the mixed water region and suggests its importance in local/basin-scale nutrient cycles.

DOI： 10.1029/2018GL081497

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© 2019 Elsevier Inc. All rights reserved. The Environment Research and Technology Development Fund of the Ministry of the Environment, Japan S-13 was started from FY2014, aiming to develop a coastal environmental management methodology for sustainable coastal areas. This project selected three target sea areas, namely, the coastal area of the Sanriku region, the Seto Inland Sea and the Japan Sea to verify the developed management methodology. Among the three areas, our group focused on the Japan Sea.

DOI： 10.1016/B978-0-12-813060-5.00004-3

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Language：Japanese   Publisher：Coastal Oceanography Research Committee, the Oceanographic Society of Japan  

Under the Grants-in-Aid for Scientific Research in Innovative Areas（MEXT）project “Ocean Mixing Study（OMIX）”, we
established a system to measure the turbulent nitrate flux by attaching a small nitrate sensor on a turbulence profiler. In this
paper, we explain the instrument setup, the data processing method considering measurement errors, and then demonstrate the
capability of the developed observational system.

DOI： 10.32142/engankaiyo.2019.8.008

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17H01860/

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DOI： 10.1016/B978-0-12-813060-5.00006-7

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DOI： 10.1016/B978-0-12-813060-5.00006-7

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DOI： 10.1002/9781119428428.ch6

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©2018. American Geophysical Union. All Rights Reserved. The temporal variation of the Kuroshio nutrient stream south of Japan was examined using quarterly hydrographic data at section 137E from 2000 to 2013. During the seasonal cycle, nitrate flux and transport reach the maximum (minimum) in autumn (winter). The Kuroshio recirculation contributes about 60% to the mean eastward nitrate transport and the seasonal variations thereof. Empirical orthogonal function analysis showed two dominant modes in nitrate flux, nitrate concentration, and velocity at section 137E; these were associated with Kuroshio path meander and the Kuroshio Extension decadal oscillation. The Kuroshio large meander induced a significant increase in the eastward nitrate transport, from 609 to 1,723 kmol/s, at the section. Due to the modulation of the Kuroshio Extension decadal oscillation, both the eastward nitrate transport and the Kuroshio recirculation were stronger in an unstable state compared to when in a stable state. The variation in the eastward nitrate transport in these dynamic patterns can be attributed to the strength, location, and spatial expansion of the Kuroshio recirculation south of Japan. Nitrate transport from the south of Japan to the Kuroshio Extension was relatively stable at 400 kmol/s. There was a strong seasonal variation in the surface chlorophyll concentration over the subtropical gyre including Kuroshio recirculation region, whereas variations in the Kuroshio region was controlled by the Kuroshio path shift. The velocity-weighted nitrate concentration in the dense layer along the Kuroshio path increased throughout the year while that in the light layer decreased in spring and autumn and increased in summer and winter.

DOI： 10.1029/2017JC013635

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©2018. The Authors. Understanding the effects of hydrodynamic forcing on organic matter (OM) composition is important for assessment of organic carbon (OC) burial in marginal seas on regional and global scales. Here we examine the relationships between regional oceanographic conditions (bottom shear stress), and the physical characteristics (mineral surface area and grain size) and geochemical properties (OC content [OC%] and carbon isotope compositions [13C, 14C]) of a large suite of surface sediments from the Chinese marginal seas to assess the influence of hydrodynamic processes on the fate of OM on shallow continental shelves. Our results suggest that 14C content is primarily controlled by organo-mineral interactions and hydrodynamically driven resuspension processes, highlighted by (i) positive correlations between 14C content and OC% (and surface area) and (ii) negative correlations between 14C content and grain size (and bottom shear stress). Hydrodynamic processes influence 14C content due to both OC aging during lateral transport and accompanying selective degradation of OM associated with sediment (re) mobilization, these effects being superimposed on the original 14C characteristics of carbon source. Our observations support the hypotheses of Blair and Aller (2012, https://doi.org/10.1146/annurev-marine-120709-142717) and Leithold et al. (2016, https://doi.org/10.1016/j.earscirev.2015.10.011) that hydrodynamically driven sediment translocation results in greater OC 14C depletion in broad, shallow marginal seas common to passive margin settings than on active margins. On a global scale, this may influence the extent to which continental margins act as net carbon sources and sinks. Our findings thus suggest that hydrodynamic processes are important in shaping the nature, dynamics, and magnitude of OC export and burial in passive marginal seas.

DOI： 10.1029/2018GB005921

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

© 2018 Elsevier Ltd Bottom cold water (BCW) is widely reported to occur in many coastal areas in summer. Some BCW masses have an increase in temperature of only 1 °C from early spring to summer (e.g., North Sea, Yellow Sea), while the others have a 4–10 °C increase (e.g., Irish Sea, Seto Inland Sea). A model of heat transport with vertical diffusion alone gave good approximation of the temperature increase in the North Sea type BCW masses, while additional heat input from other processes was required to simulate the large temperature increases in Irish Sea type BCWs. BCWs in the Yellow Sea and the Seto Inland Sea are then taken as examples to compare heat transport into the two types of BCWs through three-dimensional numerical modeling. The small warming range of the BCW in the Yellow Sea results mainly from downward heat input by vertical diffusion. In contrast, the large temperature range of warming in the BCW in the Seto Inland Sea is a result of both advection of heat from the surrounding water and vertical diffusion. We therefore infer that advection of heat into the BCW is a necessary condition for the high temperature increase range in Irish Sea type BCWs. Moreover, advection of heat into one BCW in the Seto Inland Sea intensifies from April to July, which is induced by gradually intensified bottom currents. This example supports the importance of heat transport by advection for BCWs where the temporal change in advection of heat is capable of altering the temperature increase rate inside the BCW.

DOI： 10.1016/j.csr.2018.06.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OCEAN UNIV CHINA  

In order to examine the seasonal and spatial distributions of benthic animals in the intertidal mudflat of the southern Yellow River Delta, field investigations were carried out in 2007 and 2008 and multiple methods were applied. Results showed that, the biomass of macro benthos ranged at 0.75-1151.00 g wet m(-2) and averaged at 156.31 g wet m(-2), in which Mactra veneriformis accounted for 75.6%-93.4% of the total macro benthic biomass. More than 90% of macro benthos inhabited in the middle and low tide lines, and higher biomass occurred in early summer and lower in winter. Statistical analysis showed that: 1) M. veneriformis growth was primarily favored at higher temperature and lower salinity; 2) after long time interaction, benthic bivalve grazers led to patching distributions of Chlorophyll a (Chl a); 3) macro benthic biomass positively related with Chl a when the concentration of Chl a was low, but they were negatively related when Chl a concentration was high; and 4) furthermore, the biomass of benthic bivalves peaked in the sediment with median grain size about 0.55 mm, but decreased gradually in coarse or fine sediments. The secondary productivity ranged at 0.37-283.68 g m(-2)yr(-1) and averaged at 47.88 g m(-2) yr(-1), in which 69.7% was contributed by M. veneriformis It was estimated that primary production was transformed to secondary production at a rate of 6.87% approximately, which implies that there is a local sustainability of high bivalve production.

DOI： 10.1007/s11802-018-3313-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

©2018. American Geophysical Union. All Rights Reserved. Dust deposition is an important nutrient source to the South China Sea (SCS), but few in situ experiments were conducted on phytoplankton response to the deposition. We conducted onboard incubation experiments at three stations near Luzon Strait in the SCS, with addition of multiple dissolved inorganic nutrients, Asian dust, and rainwater. From our results, nitrogen and phosphorus were both urgently needed for phytoplankton growth in the SCS, indicated by the evident Chl a response to the addition of nitrogen and phosphorus together. Almost no evident response was observed by adding phosphorus or iron alone to incubation waters, although a delayed response of Chl a in mass concentration was observed by adding nitrogen alone. The latter implied a possible utilization of dissolved organic phosphorus because of insufficient dissolved inorganic phosphorus in incubation waters. Under such nutrient condition, Asian dust showed an apparent promotion effect on phytoplankton growth by providing sufficient amounts of nitrogen but low phosphorus. Meanwhile, it was found that large sized (> 5 μm) phytoplankton community showed different responses to dust addition at different stations. At stations A3 and A6, Chaetoceros spp. became the dominant species during the bloom period, while at station WG2, Nitzschia spp. became dominant. In combination with different initial nutrients and Chl a levels at the three stations, the different phytoplankton community evolution implied the response difference to external inputs between oligotrophic (stations A3 and A6) and ultraoligotrophic (station WG2) conditions in the SCS.

DOI： 10.1002/2017JG004088

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Copernicus GmbH  

© 2018 Author. In this study, five on-board microcosm experiments were performed in the subtropical gyre, the Kuroshio Extension region of the northwest Pacific Ocean (NWPO), and the Yellow Sea (YS) in order to investigate phytoplankton growth following the addition of artificially modified mineral dust (AM dust) and various nutrients (nitrogen (N), phosphorus (P), iron (Fe), NCP, and NCPCFe). The two experiments carried out with AM-dust addition in the subtropical gyre showed a maximum chlorophyll a (Chl a/concentration increase of 1.7- A nd 2.8-fold, while the cell abundance of large-sized phytoplankton (<5μm) showed a 1.8- A nd 3.9-fold increase, respectively, relative to the controls. However, in the Kuroshio Extension region and the YS, the increases in maximum Chl a and cell abundance of largesized phytoplankton following AM-dust addition were at most 1.3-fold and 1.7-fold larger than those in the controls, respectively. A net conversion efficiency index (NCEI) newly proposed in this study, size-fractionated Chl a, and the abundance of large-sized phytoplankton were analysed to determine which nutrients contribute to supporting phytoplankton growth. Our results demonstrate that a combination of nutrients, N.P or NCPCFe, is responsible for phytoplankton growth in the subtropical gyre following AM-dust addition. Single nutrient addition, i.e., N in the Kuroshio Extension region and P or N in the YS, controls the phytoplankton growth following AM-dust addition. In the AM-dust-addition experiments, in which the increased N.P or P was identified to determine phytoplankton growth, the dissolved inorganic P from AM dust (8.6 nmol L-1/was much lower than the theoretically estimated minimum P demand (∼20 nmol L-1/for phytoplankton growth. These observations suggest that additional supply augments the bioavailable P stock in incubated seawater with AM-dust addition, most likely due to an enhanced solubility of P from AM dust or the remineralization of the dissolved organic P.

DOI： 10.5194/bg-15-749-2018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

© 2017 Elsevier Ltd River plumes are a general phenomenon in coastal regions. Most previous studies focus on river plumes in middle and high latitudes with few studies examining those in low latitude regions. Here, we apply a numerical model to the Upper Gulf of Thailand (UGoT) to examine a river plume in low latitudes. Consistent with observational data, the modeled plume has seasonal variation dependent on monsoon conditions. During southwesterly monsoons, the plume extends northeastward to the head of the gulf; during northeasterly monsoons, it extends southwestward to the mouth of the gulf. To examine the effects of latitude, wind and river discharge on the river plume, we designed several numerical experiments. Using a middle latitude for the UGoT, the bulge close to the river mouth becomes smaller, the downstream current flows closer to the coast, and the salinity in the northern UGoT becomes lower. The reduction in the size of the bulge is consistent with the relationship between the offshore distance of a bulge and the Coriolis parameter. Momentum balance of the coastal current is maintained by advection, the Coriolis force, pressure gradient and internal stresses in both low and middle latitudes, with the Coriolis force and pressure gradient enlarged in the middle latitude. The larger pressure gradient in the middle latitude is induced by more offshore freshwater flowing with the coastal current, which induces lower salinity. The influence of wind on the river plume not only has the advection effects of changing the surface current direction and increasing the surface current speed, but also decreases the current speed due to enhanced vertical mixing. Changes in river discharge influence stratification in the UGoT but have little effect on the behavior of the river plume.

DOI： 10.1016/j.csr.2017.12.007

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© 2018, Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature. Using a three-dimensional coupled biophysical model, we simulated the responses of a lowtrophic ecosystem in the East China Sea (ECS) to long-term changes in nutrient load from the Changjiang (Yangtze) River over the period of 1960–2005. Two major factors affected changes in nutrient load: changes in river discharge and the concentration of nutrients in the river water. Increasing or decreasing Changjiang discharge induced different responses in the concentrations of nutrients, phytoplankton, and detritus in the ECS. Changes in dissolved inorganic nitrogen (DIN), silicate (SIL), phytoplankton, and detritus could be identified over a large area of the ECS shelf, but changes in dissolved inorganic phosphate (DIP) were limited to a small area close to the river mouth. The high DIN:DIP and SIL:DIP ratios in the river water were likely associated with the different responses in DIN, DIP, and SIL. As DIP is a candidate limiting nutrient, perturbations in DIP resulting from changes in the Changjiang discharge are quickly consumed through primary production. It is interesting that an increase in the Changjiang discharge did not always lead to an increase in phytoplankton levels in the ECS. Phytoplankton decreases could be found in some areas close to the river mouth. A likely cause of the reduction in phytoplankton was a change in the hydrodynamic field associated with the river plume, although the present model is not suitable for examining the possibility in detail. Increases in DIN and DIP concentrations in the river water primarily led to increases in DIN, DIP, phytoplankton, and detritus levels in the ECS, whereas decreases in the SIL concentration in river water led to lower SIL concentrations in the ECS, indicating that SIL is not a limiting nutrient for photosynthesis, based on our model results from 1960 to 2005. In both of the above-mentioned cases, the sediment accumulation rate of detritus exhibited a large spatial variation near the river mouth, suggesting that core sample data should be carefully interpreted.

DOI： 10.1007/s00343-017-6233-z

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© 2018, Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature. Long-term datasets of water temperature, salinity, dissolved oxygen, phosphate and nitrate from 1973 to 2013 were used to study interannual variations of these parameters along a transect (section PN) across the Kuroshio and shelf area in the East China Sea. Water temperature and salinity at depths of 0–200 m showed a low-high-low-high pattern over the 40-year period. Water temperature and salinity at 500 m were relatively high from 1985 to 1990 and decreased continuously thereafter. Salinity at 800 m was lowest around 1993 and increased thereafter. Nutrients were highest between 1980 and 1985. After 1985, nutrients at 500 m were increasing. The range of variation in nutrients was large before 1985 and the magnitude increased with greater depths. Apparent oxygen utilization at 500 m depth was decreasing before 1990 and started to increase after 1992. Significant changes after 1990 at 500 m depth may be due to the upward trend of the upper boundary of Kuroshio intermediate water. Interannual variation of water temperature, salinity, dissolved oxygen, phosphate and nitrate along section PN has a significant correlation with the Pacific Decadal Oscillation index.

DOI： 10.1007/s00343-017-6234-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The Yellow Sea Cold Water Mass (YSCWM), which occurs during summer in the central Yellow Sea, plays an important role in the hydrodynamic field, nutrient cycle and biological species. Based on water temperature observations during the summer from 1978 to 1998 in the western Yellow Sea, five specific YSCWM years were identified, including two strong years (1984 and 1985), two weak years (1989 and 1995) and one normal year (1992). Using a three-dimensional hydrodynamic model, the YSCWM formation processes in these five years were simulated and compared with observations. In general, the YSCWM began forming in spring, matured in summer and gradually disappeared in autumn of every year. The 8 degrees C isotherm was used to indicate the YSCWM boundary. The modelled YSCWM areas in the two strong years were approximately two times larger than those in the two weak years. Based on the simulations in the weak year of 1995, ten numerical experiments were performed to quantify the key factors influencing the YSCWM intensity by changing the initial water condition in the previous autumn, air-sea heat flux, wind, evaporation, precipitation and sea level pressure to those in the strong year of 1984, respectively. The results showed that the air-sea heat flux was the dominant factor influencing the YSCWM intensity, which contributed about 80% of the differences of the YSCWM average water temperature at a depth of 50 m. In addition, the air-sea heat flux in the previous winter had a determining effect, contributing more than 50% of the differences between the strong and weak YSCWM years. Finally, a simple formula for predicting the YSCWM intensity was established by using the key influencing factors, i.e., the sea surface temperature before the cooling season and the air-sea heat flux during the cooling season from the previous December to the current February. With this formula, instead of a complicated numerical model, we were able to roughly predict the YSCWM intensity for the following summer by using the data available online in winter.

DOI： 10.1016/j.csr.2017.10.006

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Language：Japanese   Publisher：Coastal Oceanography Research Committee, the Oceanographic Society of Japan  

Japan Sea is a semi-enclosed international sea area. The East China Sea is located in the upstream area of the Japan Sea, and various substances, sea water, and heat are transported through the Tsushima Strait. In recent years, the Japan Sea has faced environmental changes. The sea surface temperature in the Japan Sea has increased with global warming. The rapid economic growth in the Northwest Pacific area influences the environment in the Japan Sea and surrounding sea areas. In order to propose an effective coastal environmental management method for Japanese coastal areas of the Japan Sea, the impacts and its influences of global warming and environmental changes in the East China Sea on the environment and ecosystem in the Japan Sea were studied using ecosystem numerical models. Our study clarified that the Japanese coastal area of the Japan Sea is strongly influenced by the East China Sea, and it is necessary to have a large-scale perspective for its management. Then, we proposed a three-layer management for the Japan Sea. The outputs of the project and the idea of the three-layer management are introduced in this paper.

DOI： 10.32142/engankaiyo.56.1_31

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

© 2017. American Geophysical Union. All Rights Reserved. This study investigates the seasonal variation in temperature induced by diurnal forcing in the eastern shelf seas of China (ESSC) using a high-resolution Regional Ocean Modeling System model forced by the National Center for Environmental Prediction and the National Center for Atmospheric Research re-analysis data for surface fluxes with both 6 h and daily frequencies, respectively. The comparison between two experiments revealed a ±0:4ºC modification of the variation in seasonal temperature by diurnal forcing, which also increases the mixed-layer depth (MLD) in August by 26% and reduces the volume of the Yellow Sea Cold Water Mass (YSCWM) by 25%. Sensitivity experiments using different forcing variables indicated that diurnal wind can explain over 80% of the variability in seasonal temperature induced by diurnal forcing. Diurnal wind led to an increase in the net heat flux into the ocean by about 13 W/m2 in summer and a decrease by about 15 W/m2 in winter. Diurnal wind also generated an additional downward heat transport of 21 W/m2 over the ESSC that contributed to variability in the mean MLD and YSCWM in August. Experiments changing the temporal interval of wind forcing suggested that the increase in the forcing temporal interval gradually enhanced the reproduction of the variability in seasonal temperature generated by diurnal wind; a 6 h wind forcing can capture 70% of this type of variability given by 1 h wind forcing, while a 3 h or shorter wind forcing can capture 90%.

DOI： 10.1002/2017JC013473

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OCEAN UNIV CHINA  

© 2017, Science Press, Ocean University of China and Springer-Verlag GmbH Germany. Abrupt changes in freshwater inputs from large rivers usually imply regime shifts in coastal water environments. The influence of a water regulation event on the age of the Yellow River water in the Bohai was modeled using constituent-oriented age and residence time theory to better understand the change in the environmental function of the hydrodynamic field owing to human activities. The water ages in Laizhou Bay, the central basin, and the Bohai strait are sensitive to water regulation. The surface ages in those areas can decrease by about 300 days, particularly in July, and the age stratification is also strengthened. A water regulation event can result in declines in the water age in early July ahead of declines in the water age under climatological conditions (without the regulation event) by about 1 and 5 months in the central basin and Laizhou Bay, respectively. The change in the coastal circulation due to the water regulation event is the primary reason for the change in the Yellow River water age. The high Yellow River flow rate can enhance the density flow and, therefore, reduce the age of the Yellow River water. The subsequent impact of a single water regulation event can last about 1.0 to 4.0 years in different subregions.

DOI： 10.1007/s11802-017-3210-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

© 2017. American Geophysical Union. All Rights Reserved. Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ∼ O(10−3)–O(10−2) m2 s−1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10−1) m2 s−1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10−3) m2 s−1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.

DOI： 10.1002/2017JC013049

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

For the first time, we present the application of an unstructured triangular grid to the Finite-Volume Community Ocean Model using the ensemble Kalman filter scheme, to assimilate coastal acoustic tomography (CAT) data. The fine horizontal and vertical current field structures around the island inside the observation region were both reproduced well. The assimilated depth-averaged velocities had better agreement with the independent acoustic Doppler current profiler (ADCP) data than the velocities obtained by inversion and simulation. The root-mean-square difference (RMSD) between depth-averaged current velocities obtained by data assimilation and those obtained by ADCPs was 0.07 m s(-1), which was less than the corresponding difference obtained by inversion and simulation (0.12 and 0.17 m s(-1), respectively). The assimilated vertical layer velocities also exhibited better agreement with ADCP than the velocities obtained by simulation. RMSDs between assimilated and ADCP data in vertical layers ranged from 0.02 to 0.14 m s(-1), while RMSDs between simulation and ADCP data ranged from 0.08 to 0.27 m s(-1). These results indicate that assimilation had the highest accuracy. Sensitivity experiments involving the elimination of sound transmission lines showed that missing data had less impact on assimilation than on inversion. Sensitivity experiments involving the elimination of CAT stations showed that the assimilation with four CAT stations was the relatively economical and reasonable procedure in this experiment. These results indicate that, compared with inversion and simulation, data assimilation of CAT data with an unstructured triangular grid is more effective in reconstructing the current field.

DOI： 10.1002/2017JC012715

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

© 2016 Elsevier Ltd The interannual variations of the start timing, magnitude and duration of the spring phytoplankton bloom (SPB) in the central southern Yellow Sea (SYS) were studied using the satellite-derived surface chlorophyll-a concentrations (Chl-a) from 2000 to 2014. The correlations between the characteristics of SPB and the generation rate of turbulent kinetic energy (TKERT) supplied from the atmosphere to the ocean were examined. The start timing of SPB was delayed in years with high TKERT supplied to the ocean before SPB. The TKERT during SPB had no relationship with the magnitude of SPB, but had positive correlation with the duration. A 1-D physical-biological model was used to examine the influencing mechanisms of the TKERT on the characteristics of SPB quantitatively. The wind speeds and related TKERT before the start of SPB were stronger in 2010 than in 2008. Comparison of the model results forced by winds in the two years suggested that the enhanced physical dilution of phytoplankton caused by the stronger TKERT in 2010 induced a later start timing of SPB. When increasing the winds during SPB period, more phytoplankton was taken downward from the surface layer by the enhanced vertical mixing. Meanwhile, more nutrients were pumped upward to the surface layer and supported more net growth of phytoplankton. These two contrary processes led to the independence of the magnitude of SPB on the TKERT during the SPB period. However, larger TKERT along with stronger wind resulted in a longer duration of SPB because of more nutrients supply by stronger vertical mixing.

DOI： 10.1016/j.csr.2016.06.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We deployed 5 pressure-recording inverted echo sounders (PIES) along a section in the northern South China Sea (NSCS), and estimated well the distributions of temperature, salinity and velocity across the section. Applying the empirical orthogonal function (EOF) method, we found that variability of the estimates is dominated by two modes: one named the seasonal mode affecting strongly on the hydrographic distribution with explained variability of temperature/salinity by 62.9/72.2%; the other named the eddy mode, corresponding to the arrival of mesoscale eddies, affecting strongly on the circulation pattern with explained variability of velocity by 63.2%. Temporal variation of the seasonal mode is highly correlated with the monsoon winds southeast of Vietnam, suggesting a nonlocal forcing mechanism. Case studies looking at the structures and evolutions of three captured eddies, whose impacts were well quantified by the eddy mode. The monsoon (eddies) significantly affects temperature, salinity and velocity shallower than 635 m (860 m), 160 m (150 m) and 1055 m (920 m), respectively. The monsoon (eddies) can induce maximum temperature, salinity and velocity anomalies up to -1.6 to 2.1 degrees C (-2.5 to 2.2 degrees C), -0.11 to 0.14 psu (-0.13 to 0.27 psu) and -0.31 to 0.46 m/s (-0.40 to 0.38 m/s), respectively. Mean volume transport (VT) across the section is 1.0 Sv (1 Sv=1 x 10(6) m(3) s(-1), positive to the northeast). Seasonal VT (with eddy impacts removed) is -4.6 Sv, 11.4 Sv, -5.1 Sv and -4.1 Sv for spring, summer, autumn and winter, respectively.

DOI： 10.1016/j.csr.2016.06.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Depth-averaged current data, which were obtained by coastal acoustic tomography (CAT) July 12-13, 2009 in Zhitouyang Bay on the western side of the East China Sea, are used to estimate the semidiurnal tidal current (M-2) as well as its first two overtide currents (M-4 and M-6). Spatial mean amplitude ratios M-2:M-4:M-6 in the bay are 1.00:0.15:0.11. The shallow-water equations are used to analyze the generation mechanisms of M-4 and M-6, In the deep area, where water depths are larger than 60 m, M-4 velocity amplitudes measured by CAT agree well with those predicted by the advection terms in the shallow water equations, indicating that M-4 in the deep area is predominantly generated by the advection terms. M-6 measured by CAT and M-6 predicted by the nonlinear quadratic bottom friction terms agree well in the area where water depths are less than 20 m, indicating that friction mechanisms are predominant for generating M-6 in the shallow area. In addition, dynamic analysis of the residual currents using the tidally averaged momentum equation shows that spatial mean values of the horizontal pressure gradient due to residual sea level and of the advection of residual currents together contribute about 75% of the spatial mean values of the advection by the tidal currents, indicating that residual currents in this bay are induced mainly by the nonlinear effects of tidal currents. This is the first ever nonlinear tidal current study by CAT.

DOI： 10.1016/j.csr.2016.06.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

© 2017, The Author(s). A multi-scale three-dimensional variational (MS-3DVAR) scheme is developed to assimilate high-resolution Himawari-8 sea surface temperature (SST) data for the first time into an operational ocean nowcast/forecast system targeting the North Western Pacific, JCOPE2. MS-3DVAR improves representation of the Kuroshio path south of Japan, its associated sea level variations, and temperature/salinity profiles south of Japan, the Kuroshio/Oyashio mixed water region, and the Japan Sea as compared to those of the products by the traditional single-scale 3DVAR. Validation results demonstrate that MS-3DVAR well assimilates the sparsely distributed in situ temperature and salinity profiles data by spreading the information over the large scale and by representing the detailed information near the measurement points. MS-3DVAR succeeds to assimilate the Himawari-8 SST product without noisy features caused by the cloud effects. We also find that MS-3DVAR is more effective for estimating oceanic conditions in regions with smaller mesoscale variability including the mixed water region and Japan Sea than in south of Japan.

DOI： 10.1007/s10236-017-1056-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

© 2016, The Oceanographic Society of Japan and Springer Japan. We examined fossil pigments in a 210Pb-dated sediment core to document the temporal variations in phytoplankton biomass over the past 150 years in a semi-enclosed bay, Beppu Bay, in the western Seto Inland Sea, Japan. The flux of fossil pigments was used as an index of phytoplankton biomass, which we reconstructed after removing the effect of post-burial degradation on the concentrations of fossil pigments. The flux doubled from the 1960s to the early 1970s, decreased or remained stable in the early 1980s, and increased again from the late 1980s to the early 1990s. The first increase in phytoplankton biomass during the 1960s was likely caused by eutrophication due to an increase in terrestrial nutrient fluxes from watersheds. The decreasing phytoplankton biomass in the early 1980s was likely related to the establishment of a sewage treatment system that reduced the terrestrial nutrient fluxes to the sea. However, the terrestrial nutrient fluxes could not explain the second increase from the late 1980s to the early 1990s. Intensification of the influx of nutrients from the shelf slope to the sea was likely the cause of the second increase in phytoplankton biomass. This is supported by the inverse relationship between phytoplankton biomass and sea level at the shelf slope, the latter being an index of the intensity of the influx of oceanic nutrients from the shelf slope to the sea. The supply of oceanic nutrients may be therefore a critical factor in the determination of primary production in the western Seto Inland Sea.

DOI： 10.1007/s10872-016-0404-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

© 2017 American Meteorological Society. 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.

DOI： 10.1175/JPO-D-16-0231.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The response of the marine atmospheric boundary layer (MABL) structure to an oceanic front is analyzed using Global Positioning System (GPS) sounding data obtained during a survey in the northwestern South China Sea (NSCS) over a period of about 1week in April 2013. The Weather Research and Forecasting (WRF) model is used to further examine the thermodynamical mechanisms of the MABL's response to the front. The WRF model successfully simulates the change in the MABL structure across the front, which agrees well with the observations. The spatially high-pass-filtered fields of sea surface temperature (SST) and 10m neutral equivalent wind from the WRF model simulation show a tight, positive coupling between the SST and surface winds near the front. Meanwhile, the SST front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer. Analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient. It is found that the front in the NSCS is wide enough for slowly moving air parcels to be affected by the change in underlying SST. The different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the MABL, which dominates the change in the wind profile across the front.

DOI： 10.1002/2016JD026071

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In this study, a one-dimensional physical-biogeochemical coupled model was established to investigate the responses of the upper ocean to Typhoon Damrey in the basin area of the South China Sea. The surface chlorophyll a concentration (Chl a) increased rapidly from 0.07 to 0.17mgm(-3) when the typhoon arrived and then gradually reached a peak of 0.61mgm(-3) after the typhoon's passage. The subsurface Chl a decreased from 0.34 to 0.17mgm(-3) as the typhoon arrived and then increased gradually to 0.71mgm(-3). Analyses of model results indicated that the initial rapid increase in the surface Chl a and the decrease in the subsurface Chl a were caused mainly by physical process (vertical mixing), whereas the subsequent gradual increases in the Chl a in both the surface and subsurface layers were due mainly to biogeochemical processes (net growth of phytoplankton). The gradual increase in the Chl a lasted for longer in the subsurface layer than in the surface layer. Typhoon Damrey yielded an integrated primary production (IPP) of 6.5x10(3)mg C m(-2) (similar to 14% of the annual IPP in this region).

DOI： 10.1002/2016JG003331

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-Blackwell  

The response of the marine atmospheric boundary layer (MABL) structure to an oceanic front is analyzed using Global Positioning System (GPS) sounding data obtained during a survey in the northwestern South China Sea (NSCS) over a period of about 1 week in April 2013. The Weather Research and Forecasting (WRF) model is used to further examine the thermodynamical mechanisms of the MABL’s response to the front. The WRF model successfully simulates the change in the MABL structure across the front, which agrees well with the observations. The spatially high-pass-filtered fields of sea surface temperature (SST) and 10m neutral equivalent wind from the WRF model simulation show a tight, positive coupling between the SST and surface winds near the front. Meanwhile, the SST front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer. Analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient. It is found that the front in the NSCS is wide enough for slowly moving air parcels to be affected by the change in underlying SST. The different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the MABL, which dominates the change in the wind profile across the front.

DOI： 10.1002/2016JD026071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The climatology and linear trend of seasonal water temperature and heat budget in a semienclosed sea connected to the Kuroshio region (Seto Inland Sea: SIS) are investigated by constructing and analyzing a gridded data set of water temperature, salinity, and air-sea heat fluxes. In the SIS, winter-time water temperature and ocean heat content (OHC) showed a significant increasing trend while those in summer-time exhibited no significant change. By analyzing the heat budget between the tendency of ocean heat content OHC/t and air-sea net heat flux Q(net), the driving factor of the winter-time warming trend in the SIS was identified as autumn Q(net), while the unchanged summer-time OHC is mainly due to decreased spring-time oceanic heat transport to the SIS from the Kuroshio region. In addition, we showed that the decreased spring-time heat transport could have been induced by upwelling due to wind curl and wind speed in the shelf-slope region, heat transport by the Kuroshio south of Shikoku Island, and freshwater input to the SIS from rivers. The importance of both oceanic and atmospheric forcing mechanisms for explaining variation in the water temperature in coastal areas is demonstrated.

DOI： 10.1002/2016JC011748

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The long-distance transport potential of toxic lead (Pb) by plastic marine debris was examined by pure water leaching experiments using plastic fishery floats containing high level of additive-Pb such as 5100 74.3 mg kg(-1). The leaching of Pb ended after sequential 480-h leaching experiments, and the total leaching amount is equivalent to approximately 0.1% of total Pb in a float. But it recovered when the float was scratched using sandpaper. We propose that a "low-Pb layer," in which Pb concentration is negligibly small, be generated on the float surface by the initial leaching process. Thickness of the layer is estimated at 2.5 +/- 1.2 mu m, much shallower than flaws on floats scratched by sandpaper and floats littering beaches. The result suggests that the low-Pb layer is broken by physical abrasion when floats are washed ashore, and that Pb inside the floats can thereafter leach into beaches. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2016.03.038

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

This article reviews progress in our understanding of oceanic fronts around Japan and their roles in air–sea interaction. Fronts associated with the Kuroshio and its extension, fronts within the area of the Kuroshio-Oyashio confluence, and the subtropical fronts are described with particular emphasis on their structure, variability, and role in air–sea interaction. The discussion also extends to the fronts in the coastal and marginal seas, the Seto Inland Sea and Japan Sea. Studies on oceanic fronts have progressed significantly during the past decade, but many of these studies focus on processes at individual fronts and do not provide a comprehensive view. Hence, one of the goals of this article is to review the oceanic fronts around Japan by describing the processes based on common metrics. These metrics focus primarily on surface properties to obtain insights into air–sea interactions that occur along oceanic fronts. The basic characteristics derived for each front (i.e., metrics) are then presented as a table. We envision that many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.

DOI： 10.1007/978-4-431-56053-1_1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

Summer hydrographic data from 1971 to 2000 demonstrate the presence of bottom cold water (BCW) and a bottom thermal front around the BCW in a semienclosed sea in the Seto Inland Sea of Japan. The horizontal gradient of water temperature across the bottom front was larger in neap tide than in spring tide, which is the opposite the pattern observed in the fortnightly variations in other areas (e.g., the Irish Sea). A numerical model for the Inland Sea reproduced the presence of BCW and a bottom front as well as the same fortnightly variation in the horizontal gradient of water temperature across the bottom front as in observational data. Being the same BCW as those in other areas, the presence of BCW in the Inland Sea is also caused by spatial variation in tidal mixing. The intensification of the bottom front in neap tide in the Inland Sea results from a combination of tidal mixing and horizontal advection of warm water to the BCW. The presence of a bottom residual current in the direction across the bottom front results in the horizontal advection of warm water to the BCW, and its fortnightly variation is responsible for the fortnightly variation of the bottom front in the Inland Sea. The presence of the BCW induces a surface cyclonic circulation in the direction approximately along the bottom front; the intensification and weakening of the bottom front with the spring-neap tidal cycle, combined with the fortnightly variation in the bottom boundary layer thickness, produce a slightly stronger surface cyclonic circulation in neap tide than in spring tide.

DOI： 10.1175/JPO-D-15-0071.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Monthly field surveys conducted from April to November 2009 in a tidal front in the Seto Inland Sea, Japan provided a spatial and temporal dataset for investigating seasonal variations in nutrient supply and the formation of a chlorophyll a (Chl-a) maximum. The upward diffusive flux of nutrients is estimated from observational data but it accounted for less than 5% of the nutrients needed to support the primary production of phytoplankton in the front area of the stratification region when the density difference between the surface layer and bottom layer is greater than 0.5 kg m(-3). Instead of vertical diffusion, the lateral intrusion of water with high nutrient concentration from the mixed area represented the major nutrient supply in the front area. The depth of the lateral intrusion changed with the month: the surface layer in July became the middle layer in August. According to the calculation of numerical model, an anticlockwise circulation is intensified by removing river runoff (i.e., low precipitation) in this study area, and the change of lateral intrusion is likely caused by the change of anti-clockwise circulation along with the temporal variation in river runoff. Consequently, the Chl-a peak appeared in the vicinity of the surface front (up to 3 mu g L-1) in July, but was in the subsurface (up to 9 mu g L-1) in August. Diatom species were a relatively minor taxa of the phytoplankton community up to July, although a relatively high Si(OH)(4)-Si concentration (up to 20 mu mol L-1) was confirmed. In contrast, the subsurface Chl-a maximum (SCM) in August was mainly comprised of diatoms as evidenced by the reduction of both Si(OH)(4)-Si and SUN from the surface to subsurface layer (0-20 m depth). Therefore, the supply of both nutrients and the seed population necessary for the formation of the SCM results from the tidal frontal system and phytoplankton assemblages within the tidal front system should be varied on a monthly basis. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2015.10.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：World Scientific Publishing Co. Pte Ltd  

This article focuses on the physical and dynamical processes of the marginal seas of the Western Pacific. The nature of the circulation regimes and their interconnectivity are discussed in detail, with emphasis on individual basins. In addition to the Kuroshio and its variability in the North Pacific, the circulation regimes in the South China Sea and Indonesian Seas are presented for an overall view of the circulation system. These circulations play important roles in regional ocean dynamics and global climate variations such as the El Niño/Southern Oscillation.

DOI： 10.1142/9789814696623_0006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

At the present time, ocean current is being operationally monitored mainly by combined use of numerical ocean nowcast/forecast models and satellite remote sensing data. Improvement in the accuracy of the ocean current nowcast/forecast requires additional measurements with higher spatial and temporal resolution as expected from the current observation network. Here we show feasibility of assimilating high-resolution seabird and ship drift data into an operational ocean forecast system. Data assimilation of geostrophic current contained in the observed drift leads to refinement in the gyre mode events of the Tsugaru warm current in the north-eastern sea of Japan represented by the model. Fitting the observed drift to the model depends on ability of the drift representing geostrophic current compared to that representing directly wind driven components. A preferable horizontal scale of 50 km indicated for the seabird drift data assimilation implies their capability of capturing eddies with smaller horizontal scale than the minimum scale of 100 km resolved by the satellite altimetry. The present study actually demonstrates that transdisciplinary approaches combining bio-/ship- logging and numerical modeling could be effective for enhancement in monitoring the ocean current.

DOI： 10.1038/srep17672

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We deployed five pressure-recording inverted echo sounders (PIES) along a satellite altimeter track across the continental slope of the northern South China Sea (NSCS) from October 2012 to July 2014, and obtained a time series of volume transport (VTPIES) across the section from their records. Applying the empirical relationship between VTPIES and the satellite altimeter sea surface height anomaly difference across the section, we obtained a time series of volume transport (VTNSCS) over 22 years from 1992 to 2014. The VTNSCS shows a small mean value of -1.6 Sv (1 Sv = 10(6) m(3) s(-1)) (i.e., toward the southwest), but a significant seasonal reversal and mesoscale eddy induced fluctuations (-11.8 to 19.7 Sv). The monthly mean of VTNSCS over 22 years shows a maximum (3.6 Sv) in July and a minimum (-7.3 Sv) in December. This is the first long time series of volume transport for the NSCS based on in situ data.

DOI： 10.1007/s10872-015-0305-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Quantifying the tidal current and volume transport through the Qiongzhou Strait (QS) is vital to understanding the circulation in the northern South China Sea. To measure the tidal current in the strait, a 15-day coastal acoustic tomography (CAT) experiment was carried out at four acoustic stations in March 2013. The horizontal distributions of the tidal currents were calculated by inverse analysis of CAT data. The diurnal tidal current constituents were found to dominate: the ratio of the amplitudes O-1, K-1, M-2, S-2, and MSF was 1.00:0.60:0.47;0.21:0.11. The residual currents were found to flow westward in the northern QS and turn southward in the southern Q. The residual current velocities were larger in the northern area than in the southern area, with a maximum westward velocity of 12.4 cm s(-1) the northern QS. Volume transport estimated using the CAT data varied between -0.710 Sv and 0.859 Sv, with residual current transport of -0.044 Sv, where negative values indicate westward. We conducted a dynamic analysis of the observations made during the study, which suggested that tidal rectification and sea level difference between the two entrances of the QS are important in maintaining the residual current through the strait. This is the first estimation, from synchronous measurements, of major tidal current constituents, residual currents, and volume transport in this strait. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2015.08.016

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Language：English   Publisher：SPRINGER  

This article reviews progress in our understanding of oceanic fronts around Japan and their roles in air-sea interaction. Fronts associated with the Kuroshio and its extension, fronts within the area of the Kuroshio-Oyashio confluence, and the subtropical fronts are described with particular emphasis on their structure, variability, and role in air-sea interaction. The discussion also extends to the fronts in the coastal and marginal seas, the Seto Inland Sea and Japan Sea. Studies on oceanic fronts have progressed significantly during the past decade, but many of these studies focus on processes at individual fronts and do not provide a comprehensive view. Hence, one of the goals of this article is to review the oceanic fronts around Japan by describing the processes based on common metrics. These metrics focus primarily on surface properties to obtain insights into air-sea interactions that occur along oceanic fronts. The basic characteristics derived for each front (i.e., metrics) are then presented as a table. We envision that many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.

DOI： 10.1007/s10872-015-0283-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

Coastal environments are a key location for transport, commercial, residential and defence infrastructure, and have provided conditions suitable for economic growth. They also fulfil important cultural, recreational and aesthetic needs; have intrinsic ecosystem service values; and provide essential biogeochemical functions such as primary productivity, nutrient cycling and water filtration. The rapid expansion in economic development and anticipated growth of the population in the coastal zones along the Yellow and East China Sea basin has placed this region under intense multiple stresses. Here we aim to: 1) synthesize the new knowledge/science in coastal oceanography since 2010 within the context of the scientific literature published in English; 2) report on a citation analysis that assesses whether new research topics have emerged and integrated over time, indicate the location of modelling and field-based studies; and 3) suggest where the new research should develop for heavily impacted estuaries and coastal seas of East Asia. The conclusions of the synthesis include: 1) China has emerged as a dominant force in the region in producing scientific literature in coastal oceanography, although the area of publications has shifted from its traditional fields such as physical oceanography; 2) there has been an increasing number of publications with cross-disciplinary themes between physical oceanography and other fields of the biological, chemical, and geological disciplines, but vigorous and systematic funding mechanisms are still lacking to ensure the viability of large scale multi-disciplinary teams and projects in order to support trans-disciplinary research and newly emerging fields; 3) coastal oceanography is responding to new challenges, with many papers studying the impacts of human activities on marine environment and ecology, but so far very few studying management and conservation strategies or offering policy solutions. (c) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ecss.2015.05.039

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

High-resolution reanalysis data of Sea Surface Temperature (SST) show pronounced seasonal variations in oceanic fronts in the coastal area of the Northern South China Sea (NSCS), which are accompanied by the seasonality of monsoons. The NSCS oceanic fronts cover a wider area of the coastal sea in winter than in summer as strong winter monsoons progress. Nonetheless, the average SST gradients of the frontal area in both seasons are comparable. The response of surface wind to SST perturbations attributed to oceanic fronts in the NSCS coastal area has also been investigated by the observation data of satellite borne scatterometers and the simulation data of the Weather Research and Forecasting (WRF) model. Both the satellite observations and the simulations of the WRF model show apparent positive linear SST-wind coupling for most months in 2008, indicating the local influence of coastal SST fronts on the sea surface wind in the NSCS. The SST-wind coupling coefficients in the NSCS coastal sea are larger than those observed at mid-latitude oceans but smaller than those observed near equatorial oceans. It is also found that the influence of topography on the sea surface wind could be more important than that of the SST front at the southern end of the Taiwan Strait in winter. The transition of the monsoon could also affect the SST-wind coupling in the NSCS. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.dsr2.2013.12.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

This study shows that mesoscale eddies can alter the Taiwan Strait Current. The 20-yr data-assimilated Japan Coastal Ocean Predictability Experiment 2 (JCOPE2) reanalysis data are analyzed, and the results are confirmed with idealized experiments. The leading wind-forced seasonal cycle is excluded to focus on the effect of the eddy. The warm eddy southwest of Taiwan is shown to generate a northward flow, whereas the cold eddy produces a southward current. The effect of the eddy penetrates onto the shelf through the joint effect of baroclinicity and relief (JEBAR). The cross-isobath fluxes lead to shelfward convergence and divergence, setting up the modulation of the sea level slope. The resulting along-strait current anomaly eventually affects a wide area of the Taiwan Strait. The stronger eddy leads to larger modification of the cross-shelf flows and sea level slope, producing a greater transport anomaly. The composite Sea-Viewing Wide Field-of-View Sensor chlorophyll-a (Chl-a) serves as an indicator to show the change in Chl-a concentration in the strait in response to the eddy-induced current. During the warm eddy period, the current carries the southern water of lower concentration northward, reducing Chl-a concentration in the strait. In contrast, Chl-a is enhanced because the cold eddy-induced southward current carries the northern water of higher concentration southward into the strait.

DOI： 10.1175/JPO-D-14-0248.1

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In this study, 20 years of model reanalysis data are analyzed to study the effects of the subtropical countercurrent (STCC) eddies on the upstream Kuroshio, from east of Luzon to east of Taiwan. The effects are assessed from individual events to interannual time scales. The wind-driven Kuroshio is modified by the STCC eddies, with high spatiotemporal variations. The mass balance in the composite eddy events indicates that the strengthening and weakening of the Kuroshio transport are locally caused by the mass convergence and divergence produced by the eddies. The same analogy applies to the interannual time scale. In the eddy-rich years, the upstream Kuroshio is generally stronger because of wind forcing, yet the strengthening is nonuniform because of modification by the eddies. The larger number of warm eddies to the east of Taiwan and Luzon Island further strengthen the jet, whereas the larger number of cold eddies to the east of the Luzon Strait weaken the Kuroshio in the Luzon Strait. Drifter trajectories show larger Luzon Strait intrusion during the occurrence of cold eddies. The local weakening of the Kuroshio by cold eddies leads to a weaker potential vorticity jump, producing favorable conditions for the intrusion of a water mass into the South China Sea. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pocean.2015.04.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We analyze a concurrent simulation result of the ocean circulation and tidal currents using a data-assimilative ocean general circulation model covering the Western North Pacific with horizontal resolution of 1/36 degrees to investigate possible interactions between them. Four sites of active M-2 internal tide variability in open ocean (hot spots), such as Tokara Strait, Izu Ridge, Luzon Strait, and Ogasawara Ridge, are detected from both the satellite observation and the simulation. Energy cycle analysis of the simulated M-2 baroclinic tide indicates two types of the hot spots: dissipation (Tokara Strait and Izu Ridge) and radiation (Luzon Strait and Ogasawara Ridge) dominant sites. Energy conversion from barotropic to baroclinic M-2 tides at the hot spots is modulated considerably by the lower-frequency changes in the density field. Modulation at the two spots (Tokara Strait and Izu Ridge) is affected by the Kuroshio path variation together with the seasonal variation of the shallow thermocline. At the other two sites, influence from changes in the relatively deep stratification through the Kuroshio intrusion into South China Sea (Luzon Strat) and mesoscale eddy activity (Ogasawara Ridge) is dominant in the modulation.

DOI： 10.1002/2015JC010739

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Language：Japanese  

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J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OCEAN UNIV CHINA  

CART (Constituent-oriented age and residence time theory) and PTM (Particle-tracking method) are two widely used numerical methods to calculate water age. These two methods are essentially equivalent in theory but their results may be different in practice. The difference of the two methods was evaluated by applying them to calculate water age in an idealized one-dimensional domain. The model results by the two methods are consistent with each other in the case with either spatially uniform flow field or spatially uniform diffusion coefficient. If we allow the spatial variation in horizontal diffusion, a term called pseudo displacement arising from the spatial variation of diffusion coefficient likely plays an important role for the PTM to obtain accurate water age. In particular, if the water particle is released at a place where the diffusion is not the weakest, the water age calculated by the PTM without pseudo displacement is much larger than that by the CART. This suggests that the pseudo displacement cannot be neglected in the PTM to calculate water age in a realistic ocean. As an example, we present its potential importance in the Bohai Sea where the diffusion coefficient varies spatially and greatly.

DOI： 10.1007/s11802-015-2393-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The Great East Japan Earthquake on 11 March 2011, followed by the tsunami and fire, resulted in serious environmental problems in and around Japan. A huge amount of material was discharged into the ocean after the tremendous flood damage of the tsunami. A monitoring survey of the perfluoroalkyl substances (PFAs) found evidence showing an abrupt increase in the PFA concentration in the ocean east of Japan in 2011 after the earthquake. To confirm the anomalous input of two typical PFAs, perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), from the Japanese coast into the ocean, associated with the earthquake, we conducted a series of chemical tracer simulations using an eddy-resolving ocean reanalysis product: JCOPE2. The simulation model involves processes representing the emission of PFAs from the land triggered by the tsunami flood, advection of the polluted waters, and decay of the concentration by the background oceanic turbulence. Comparison of the PFOA simulation results with the observation confirms a spike-like input of PFOA into the Western North Pacific after the earthquake. Advection and diffusion by the Kuroshio Extension and the mesoscale eddies play a key role in the dilution of the concentration. Optimization of unknown simulation parameters leads to an estimation of the total amount of the anomalous PFOA emission. In contrast, the PFOS simulations are not able to explain the observed distribution, suggesting possible differences in the oceanic transport processes between PFOS and PFOA.

DOI： 10.1007/s10872-014-0250-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In spring 2013, 33 repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K-1, O-1, M-2, S-2, and MSf). The ratio of the amplitudes of O-1, K-1, M-2, S-2, and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.02.1 cm s(-1); the associated volume transport through the section is -0.0650.046 Sv (Sv=10(6) x m(3) s(-1)), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.

DOI： 10.1002/2014JC009855

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Results of a data-assimilative ocean model (JCOPE2) from 1993 to 2012 were used to examine the correlation between the Pacific Decadal Oscillation (PDO) index and interannual variations of the Kuroshio transport in the East China Sea (ECS) and the influences of mesoscale eddies on this correlation. In a period from 1993 to 2002, the Kuroshio transport estimated from the JCOPE2 reanalysis has a positive correlation with the PDO index. This well-known correlation became weak or even disappeared when the analysis period was extended from 1993-2002 to 1993-2012. This occurs because the variation range of the PDO index became small during enhanced mesoscale eddy activity southeast of Taiwan in years after 2002. The eddies caused a larger variation in the Kuroshio transport in the years after 2002 than before 2002, and therefore, changed the correlation between the PDO index and Kuroshio transport in the ECS. The influence of mesoscale eddies on the Kuroshio transport has strong regional dependence: the Kuroshio transport from the area east of Taiwan to the midway along the shelf break in the East China Sea depends mainly on eddies arriving from southeast of Taiwan, while transport from the midway along the shelf break to the Tokara Strait depends mainly on the eddies arriving from northeast of Okinawa Island. The combination of PDO-related signals and eddy-related signals determines the interannual variations of the Kuroshio transport in the ECS and sufficient attention must be paid to the spatial dependence of the Kuroshio transport in the ECS on eddies.

DOI： 10.1002/2013JC009529

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Using synchronous observational water temperature and salinity data collected simultaneously by 21 ships in summer and a three-dimensional robust diagnostic model, we calculated the density-driven current in Jiaozhou Bay (JZB), a semienclosed bay in the Yellow Sea. Special attention was paid to the influences of intratidal variations in temperature and salinity on the density-driven current. The density-driven current in JZB has a maximum speed of similar to 0.1 m s(-1) and is stronger than the tide-induced residual current in some places. The density-driven current is characterized by the intrusion of high-density (low-density) water in deep (shallow) areas. The results of the diagnostic model depend heavily on the observational data. For example, the density-driven current calculated from nonsynchronous data obtained by one ship at the same 21 stations is not consistent with that calculated from synchronous data because the nonsynchronous data correspond to different tidal phases at different stations. The intratidal variations of the density field result in a false spatial variation of density in the nonsynchronous data, which induces a false density-driven current that is of the same order as that calculated from the synchronous data. In contrast, the tidally averaged water temperature and salinity, which were used to remove intratidal variations from the synchronous data, diagnosed a density-driven current consistent with that from synchronous data. We, therefore, conclude that it is not necessary to explicitly resolve the intratidal variations in density in the calculation of density-driven current, but it is necessary to remove intratidal variations in the density field before the calculation.

DOI： 10.1002/2013JC009262

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Results of a data-assimilative ocean model (JCOPE2) from 1993 to 2012 were used to examine the correlation between the Pacific Decadal Oscillation (PDO) index and interannual variations of the Kuroshio transport in the East China Sea (ECS) and the influences of mesoscale eddies on this correlation. In a period from 1993 to 2002, the Kuroshio transport estimated from the JCOPE2 reanalysis has a positive correlation with the PDO index. This well-known correlation became weak or even disappeared when the analysis period was extended from 1993-2002 to 1993-2012. This occurs because the variation range of the PDO index became small during enhanced mesoscale eddy activity southeast of Taiwan in years after 2002. The eddies caused a larger variation in the Kuroshio transport in the years after 2002 than before 2002, and therefore, changed the correlation between the PDO index and Kuroshio transport in the ECS. The influence of mesoscale eddies on the Kuroshio transport has strong regional dependence: the Kuroshio transport from the area east of Taiwan to the midway along the shelf break in the East China Sea depends mainly on eddies arriving from southeast of Taiwan, while transport from the midway along the shelf break to the Tokara Strait depends mainly on the eddies arriving from northeast of Okinawa Island. The combination of PDO-related signals and eddy-related signals determines the interannual variations of the Kuroshio transport in the ECS and sufficient attention must be paid to the spatial dependence of the Kuroshio transport in the ECS on eddies. 2003 © 2014. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/2013JC009529

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Using synchronous observational water temperature and salinity data collected simultaneously by 21 ships in summer and a three-dimensional robust diagnostic model, we calculated the density-driven current in Jiaozhou Bay (JZB), a semienclosed bay in the Yellow Sea. Special attention was paid to the influences of intratidal variations in temperature and salinity on the density-driven current. The density-driven current in JZB has a maximum speed of ∼0.1 m s-1 and is stronger than the tide-induced residual current in some places. The density-driven current is characterized by the intrusion of high-density (low-density) water in deep (shallow) areas. The results of the diagnostic model depend heavily on the observational data. For example, the density-driven current calculated from nonsynchronous data obtained by one ship at the same 21 stations is not consistent with that calculated from synchronous data because the nonsynchronous data correspond to different tidal phases at different stations. The intratidal variations of the density field result in a false spatial variation of density in the nonsynchronous data, which induces a false density-driven current that is of the same order as that calculated from the synchronous data. In contrast, the tidally averaged water temperature and salinity, which were used to remove intratidal variations from the synchronous data, diagnosed a density-driven current consistent with that from synchronous data. We, therefore, conclude that it is not necessary to explicitly resolve the intratidal variations in density in the calculation of density-driven current, but it is necessary to remove intratidal variations in the density field before the calculation. © 2014. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/2013JC009262

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

To confirm Spatial variations of Kuroshio nutrient transport from the East China Sea to South of Japan, we apply an inverse method to hydrographic data from sections across the Kuroshio path from the East China Sea (Sections PN and TK) to south of Japan (Sections ASUKA and 137E) to get absolute geostrophic velocity, then the nutrient flux (velocity times concentration) and nutrient transport (integration of flux over a section) were calculated. In addition, Section OK east of the Ryukyu Islands was also examined. The nitrate flux during winter of 2009 shows a subsurface maximum core with a value of 11, 15, 7, 19, and 10 mol m(-2)s(-1) at Sections PN, TK, OK, ASUKA and 137E, respectively. The depth of subsurface maximum core is about 280, 470, 800, 200, and 470 m at Sections PN, TK, OK, ASUKA and 137E, respectively. The eastward nitrate transport is 248.6, 213.3, 97.7, 804.3, 879.0 k mol s(-1) at Sections PN, TK, OK, ASUKA and 137E respectively. Comparisons between nitrate transport through Section ASUKA and the sum of transports through Sections TK and OK and nitrate transport of Section 137E, suggest that the Kuroshio recirculation south of Shikoku can significantly intensify the eastward nitrate transport by the Kuroshio and therefore plays an important role in the nitrate transport in the Kuroshio region.

DOI： 10.4028/www.scientific.net/AMR.838-841.2361

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Language：English   Publisher：Research Institute for Applied Mechanics, Kyushu University  

DOI： 10.15017/1526096

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We develop an assimilation method of high horizontal resolution sea surface temperature data, provided from the Moderate Resolution Imaging Spectroradiometer (MODIS-SST) sensors boarded on the Aqua and Terra satellites operated by National Aeronautics and Space Administration (NASA), focusing on the reproducibility of the Kuroshio front variations south of Japan in February 2010. Major concerns associated with the development are (1) negative temperature bias due to the cloud effects, and (2) the representation of error covariance for detection of highly variable phenomena. We treat them by utilizing an advanced data assimilation method allowing use of spatiotemporally varying error covariance: the Local Ensemble Transformation Kalman Filter (LETKF). It is found that the quality control, by comparing the model forecast variable with the MODIS-SST data, is useful to remove the negative temperature bias and results in the mean negative bias within -0.4 °C. The additional assimilation of MODIS-SST enhances spatial variability of analysis SST over 50 km to 25 km scales. The ensemble spread variance is effectively utilized for excluding the erroneous temperature data from the assimilation process. © 2013 by the authors.

DOI： 10.3390/rs5063123

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Based on absolute geostrophic velocity, which was calculated using repeated hydrographic data of 39 cruises from 2000 to 2009 and nitrate concentrations measured in the same areas from 1964 to 2009, we obtained the temporally averaged nitrate flux (the product of velocity and nitrate concentration) and nitrate transport (integration of flux over one section) of four sections across the Kuroshio from the East China Sea (sections PN and TK) to an area south of Japan (sections ASUKA and 137E). In addition, we examined section OK east of the Ryukyu Islands in order to understand how the Ryukyu Current contributes to the transport of nutrients by the Kuroshio south of Japan. The mean nitrate flux shows a subsurface maximum core with values of 9.6, 10.6, 11.2, 10.5, and 5.7 mol m-2 s-1 at sections PN, TK, ASUKA, 137E, and OK, respectively. The depth of the subsurface maximum core changes among these five sections and is approximately 400, 500, 500, 400, and 800 m at sections PN, TK, ASUKA, 137E, and OK, respectively. The mean downstream nitrate transport is 204.8, 165.8, 879.3, 1230.4, and 338.6 kmol s-1 at sections PN, TK, ASUKA, 137E, and OK, respectively. The transport of nutrients in these sections suggests the presence of the Kuroshio nutrient stream from its upstream to downstream regions. The deep current structure of the Ryukyu Current (section OK) contributes to the same order of nitrate transport as does the Kuroshio from the East China Sea (section TK) to the area south of Japan
however, the former only has one-fifth the volume transport of the latter. A budget calculation suggests that the downstream increase of transported nitrate along the Kuroshio is mainly caused by the recirculation of nitrate into the Kuroshio. This conclusion, however, depends on water depth. In the upper layers (&lt
26.5&amp
sigma
&amp
theta
), the downstream change of nitrate concentration along the Kuroshio and that from the recirculation of nitrate has a significant contribution to the downstream increase of nitrate transport along the Kuroshio. In the deep layers (&gt
26.5&amp
sigma
&amp
theta
), the change in nitrate concentration is small and the Kuroshio recirculation dominates the downstream increase of nitrate transport. © 2013 Author(s) .

DOI： 10.5194/bg-10-6403-2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

To quantitatively understand the transport timescales of dissolved material discharged from large rivers into a semienclosed sea, the age of Yellow River water in the Bohai Sea was calculated with the constituent-oriented age and residence time theory (CART) and particle-tracking method. Yellow River water has a mean age of 3.0 years for the entire Bohai Sea. The spatial variation of the water age is significant: 1.2 years near the Yellow River estuary but 3.9 years in the Liaodong Bay. However, the temporal variation in water age is insignificant. The water particles released at the river mouth need only several days to reach the estuary area. The great water age (1.2 years) near the Yellow River estuary is caused by the presence of old water particles that initially left this area but returned to this area again. Without the reentry of Yellow River water from the Yellow Sea to the Bohai Sea, the mean age of Yellow River water in the entire Bohai Sea decreases to 1.2 years. Calculations without tidal forcing give a reduction in water age by more than 50%, suggesting that tidal forcing plays the most dominant role in controlling the age of Yellow River water in the Bohai Sea. Calculations without winds give an increase in water age by 20-30%, suggesting that wind forcing is secondary factor to the age of Yellow River water. Changes in discharge of the Yellow River and in thermal stratification have limited influence on the age of Yellow River water.

DOI： 10.1029/2012JC008263

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A three-dimensional/high-resolution transport model for persistent organic pollutants (POPs) has been developed for the East China Sea (ECS). The POPs model has four compartments (gaseous, dissolved, phytoplankton-bound, and detritus-bound phases) and includes processes for diffusive air-water exchange, phytoplankton uptake/depuration to POPs, decomposition of dissolved phase, vertical sinking of phytoplankton, detritus production by phytoplankton mortality, and vertical sinking and decomposition of detritus. The POPs model is coupled with an ocean circulation model that can reproduce the seasonal variation in physical variables to represent the advection and diffusion of POPs. We applied the POPs model to the polychlorinated biphenyl congener 153 (PCB 153) from the atmosphere and examined the behavior of PCB 153 in the ocean. The model showed a remarkable seasonal variability of PCB 153. Concentrations in the dissolved and particulate phases are high in winter (January-March) and low in summer (July-September). In coastal regions, where chlorophyll a concentration is high, horizontal and vertical distributions in the dissolved and particulate PCB 153 concentrations are strongly affected by phytoplankton uptake. The sensitivity experiments on the dynamics of PCB 153 suggested that a change of Henry's law constant associated with water temperature is the major factor controlling the seasonal variability of PCB 153. The model-based yearly mass balance of PCB 153 in the ECS indicated that most of the atmospheric input (35.5 kg year(-1)) is removed by the horizontal advection outside the ECS (19.0 kg year(-1)) and accumulates to the sea bottom by vertical sinking (15.7 kg year(-1)). For comparison with PCB 153, we also conducted simulations for PCB 52, 101, and 180. The seasonal variations are similar to that of PCB 153. The mass balance of PCB 52 that has short half-life time and less hydrophobic property shows the different results compared with PCB 101, 153, and 180. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.chemosphere.2012.05.049

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

The finite volume coastal ocean model downscaling ocean reanalysis and forecast data provided by the Japan Coastal Ocean Predictability Experiment (JCOPE2) are used to forecast sudden Kuroshio water intrusion events (kyucho) induced by frontal waves amplified south of the Bungo Channel in 2010. Two-month hindcast computations give initial conditions of the following 3-month forecasts computations which consist of ten ensemble members. The temperature time series computed by these ten members are averaged to compare with that actually observed in the Bungo Channel, where sudden temperature rises related to kyucho events are remarkable in February, August, and September. Overall, the intense kyucho events actually observed in these months are predicted successfully. However, intense kyucho events are forecasted frequently during the period of May through June even though intense kyucho events are absent during this period in the actual ocean. It is suggested that the present downscaling forecast model requires reliable lateral boundary conditions provided by JCOPE2 data to which numerous Argo data are assimilated to enhance the accuracy. In addition, it seems likely that the model accuracy is reduced by small eddies moving along the shelf break.

DOI： 10.1007/s10236-011-0519-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

We investigated the feasibility of the ensemble Kalman filter (EnKF) to reproduce oceanic conditions south of Japan. We have adopted the local ensemble transformation Kalman filter algorithm based on 20 members' ensemble simulations of the parallelized Princeton Ocean Model (the Stony Brook Parallel Ocean Model) with horizontal resolution of 1/36A degrees. By assimilating satellite sea surface height anomaly, satellite sea surface temperature, and in situ temperature and salinity profiles, we reproduced the Kuroshio variation south of Japan for the period from 8 to 28 February 2010. EnKF successfully reproduced the Kuroshio path positions and the water mass property of the Kuroshio waters as observed. It also detected the variation of the steep thermohaline front in the Kii Channel due to the intrusion of the Kuroshio water based on the observation, suggesting efficiency of EnKF for detection of open and coastal seas interactions with highly complicated spatiotemporal variability.

DOI： 10.1007/s10236-011-0516-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Using in situ data from 88 cruises from 1987 to 2009 in the East China Sea, downstream nutrient flux (the product of velocity and nutrient concentration) and nutrient transport (integration of flux over a section) by Kuroshio were examined. The presence of a maximum nutrient flux core in the middle layer was confirmed. Seasonal variation in the nutrient flux was not significant and was much smaller than interannual variations. The change in the Kuroshio speed and current structure were major causes for interannual variations in the nutrient flux. The downstream nitrate transport by the Kuroshio in the East China Sea had a mean value of 170.8 kmol s(-1) and a standard deviation of 41.6 kmol s(-1). The mean seasonal nitrate transport ranged between about 161 and 177 kmol s(-1) and the absolute interannual variation from about 100 to 280 kmol s(-1). The phosphate flux and phosphate transport can be approximately estimated by the ratio (13.64) of nitrate concentration to phosphate concentration. The nitrate concentration in the middle and bottom layers across the Kuroshio in the East China Sea was found to increase significantly over the 23 year period, and especially after 2004 but not at ratios with oxygen that suggest increased remineralization of organic matter. The nutrient transport, however, did not increase significantly because increases in the surface layer were offset by decreases in the middle and bottom layers caused by reduction in velocity in the density ranges of 26.0 to 27.2 sigma(theta) below the Kuroshio.

DOI： 10.1029/2011JC007292

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Language：English   Publishing type：Research paper (scientific journal)  

To quantitatively understand the transport timescales of dissolved material discharged from large rivers into a semienclosed sea, the age of Yellow River water in the Bohai Sea was calculated with the constituent-oriented age and residence time theory (CART) and particle-tracking method. Yellow River water has a mean age of 3.0 years for the entire Bohai Sea. The spatial variation of the water age is significant: 1.2 years near the Yellow River estuary but 3.9 years in the Liaodong Bay. However, the temporal variation in water age is insignificant. The water particles released at the river mouth need only several days to reach the estuary area. The great water age (1.2 years) near the Yellow River estuary is caused by the presence of old water particles that initially left this area but returned to this area again. Without the reentry of Yellow River water from the Yellow Sea to the Bohai Sea, the mean age of Yellow River water in the entire Bohai Sea decreases to 1.2 years. Calculations without tidal forcing give a reduction in water age by more than 50%, suggesting that tidal forcing plays the most dominant role in controlling the age of Yellow River water in the Bohai Sea. Calculations without winds give an increase in water age by 20-30%, suggesting that wind forcing is secondary factor to the age of Yellow River water. Changes in discharge of the Yellow River and in thermal stratification have limited influence on the age of Yellow River water. © 2012 American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JC008263

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Language：English   Publishing type：Research paper (scientific journal)  

The tidal current in the Kurushima Strait of the Seto Inland Sea, Japan was successfully measured during July-August 2009 (36 days) among the three acoustic stations (KR4, KR5 and KR6), located on both sides of the strait. The travel time differences for the two sound transmission lines KR4-KR5 and KR4-KR6 are converted into the range-averaged currents along the transmission lines. The hourly mean of the range-averaged currents varied in the range from -31:1 to 53.8 cm/s for the KR4-KR5 and in the range from -45:4 to 48.7 cm/s for the KR4-KR6 with the error bars of 5.0 cm/s and 6.6 cm/s, respectively. The hourly mean along-line currents are further transformed into the geophysical coordinates with the variation range from -99:1 to 91.6 cm/s and the mean current of -6:6 cm/s for the eastward component V E, and that of (-54:2-31.5) cm/s and the mean current of -7:6 cm/s for the northward component V N. The cross-line volume transport varied in the range of (-17:928 to +17.569) × 10 4 m 3/s, resulting in the mean westward transport of 0:727 × 10 4 m3/s. This mean transport reaches a significant level over the error bar of 0:474 × 10 4 m 3/s. © 2012 The Acoustical Society of Japan.

DOI： 10.1250/ast.33.45

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Using in situ data from 88 cruises from 1987 to 2009 in the East China Sea, downstream nutrient flux (the product of velocity and nutrient concentration) and nutrient transport (integration of flux over a section) by Kuroshio were examined. The presence of a maximum nutrient flux core in the middle layer was confirmed. Seasonal variation in the nutrient flux was not significant and was much smaller than interannual variations. The change in the Kuroshio speed and current structure were major causes for interannual variations in the nutrient flux. The downstream nitrate transport by the Kuroshio in the East China Sea had a mean value of 170.8 kmol s-1 and a standard deviation of 41.6 kmol s-1. The mean seasonal nitrate transport ranged between about 161 and 177 kmol s-1 and the absolute interannual variation from about 100 to 280 kmol s-1. The phosphate flux and phosphate transport can be approximately estimated by the ratio (13.64) of nitrate concentration to phosphate concentration. The nitrate concentration in the middle and bottom layers across the Kuroshio in the East China Sea was found to increase significantly over the 23 year period, and especially after 2004 but not at ratios with oxygen that suggest increased remineralization of organic matter. The nutrient transport, however, did not increase significantly because increases in the surface layer were offset by decreases in the middle and bottom layers caused by reduction in velocity in the density ranges of 26.0 to 27.2 below the Kuroshio. Copyright 2012 by the American Geophysical Union.

DOI： 10.1029/2011JC007292

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DOI： 10.1007/s10872-011-0078-4

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DOI： 10.1007/s10872-011-0063-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

To investigate how salinity changes with abrupt increases and decreases in river discharge, three surveys were conducted along six sections around the Yellow River mouth before, during and after a water regulation event during which the river discharge was increased from similar to 200 to &gt; 3000 m(3) s(-1) for the first 3 days, was maintained at &gt; 3000 m(3) s(-1) for the next 9 days and was decreased to &lt;1000 m(3) s(-1) for the final 4 days. The mean salinity in the Yellow River estuary area during the event varied similar to 1.21, which is much larger than its seasonal variation (similar to 0.50) and interannual variation (similar to 0.05). Before the event, a small plume was observed near the river mouth. During the event, the plume extended over 24 km offshore in the surface layer in the direction of river water outflow. After the event, the plume diminished in size but remained larger than before the event. The downstream propagation of the plume (as in a Kelvin wave sense) was apparent in the bottom layer during the second survey and in both the surface and bottom layers during the third survey. The plume sizes predicted by the formulas from theoretical studies are larger than those we observed, indicating that factors neglected by theoretical studies such as the temporal variation in river discharge and vertical mixing in the sea could be very important for plume evolution. In addition to the horizontal variation of the plume, we also observed the penetration of freshwater from the surface layer into the bottom layer. A comparison of two vertical processes, wind mixing and tidal mixing, suggests that the impact of wind mixing may be comparable with that of tidal mixing in the area close to the river mouth and may be dominant over offshore areas. The change in Kelvin number indicates an alteration of plume dynamics due to the abrupt change in river discharge during the water regulation event. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2011.01.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A 30 km-range reciprocal sound transmission experiment was carried out on the line connecting Honshu and Shikoku (the first and fourth biggest main Japanese islands, respectively) in the central part (Aki-nada) of the Seto Inland Sea, Japan, during March-May 2010 to measure the mean current and temperature variations over the sea. The range-averaged current along the sound transmission line was estimated to have a mean and standard deviation of (3.8-4.4) +/- A (1.7-1.8) cm/s after converting the travel time difference data into currents, including a fortnightly tidal variation in the range of +/- 30 cm/s. The positive mean current implies slow water movement from the west to east through Aki-nada. The range-averaged speed of sound was estimated by converting from the mean travel time or one-way travel time into the speed of sound, and further converted into temperature for fixed values of salinity and depth, according to the standard speed of sound formula. Besides the precise measurement (to an accuracy of 0.01A degrees C) of semidiurnal and diurnal tidal variations and seasonal warming, the temperature data showed periodic variations with periods of 7.0 and 21.1 days that had never been observed in Aki-nada before. This study suggests that reciprocal sound transmission is a powerful technique for the long-term accurate measurement of mean current and temperature variations in coastal and inland seas.

DOI： 10.1007/s10872-011-0016-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A regional numerical model of the atmosphere was applied to an inland sea, the Seto Inland Sea in Japan, to study the influence of sea-surface temperature (SST) variations, accompanied by a tidal front, on the coastal winds in summer when tidal fronts fully develop. After confirmation of the model performance, two sensitivity simulations, which used spatially uniform SST with the highest and lowest values over the study area, were performed. The control and sensitivity simulations show that the mean wind speeds were apparently reduced by the low SST and the SST gradient accompanying the tidal front. The comparison of the terms in the momentum equations in control and sensitivity simulations indicates that the change of the perturbation pressure gradient force with the SST gradient is the most important factor in the modification of near-surface winds with SST variations. When the air flows across a tidal front, the air cools over the low SST area and warms over the high SST area. Consequently, the surface perturbation pressure increases over the low SST area and decreases over the high SST area. This adjustment in surface perturbation pressure produces an additional pressure gradient force with direction from the low SST area to the high SST area that decelerates the surface wind in the area upwind of the tidal front and accelerates the surface wind downwind of the tidal front.

DOI： 10.1007/s10546-010-9555-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

A three dimensional coupled biophysical model was used to examine the supply of oceanic nutrients to the shelf of the East China Sea (ECS) and its role in primary production over the shelf. The model consisted of two parts: the hydrodynamic module was based on a nested model with a horizontal resolution of 1/18 degree, whereas the biological module was a lower trophic level ecosystem model including two types of phytoplankton, three elements of nutrients, and biogenic organic material. The model results suggested that seasonal variations occurred in the distribution of nutrients and chlorophyll a over the shelf of the ECS. After comparison with available observed nutrients and chlorophyll a data, the model results were used to calculate volume and nutrients fluxes across the shelf break. The annual mean total fluxes were 1.53 Sv for volume, 9.4 kmol s(-1) for DIN, 0.7 kmol s(-1) for DIP, and 18.2 kmol s(-1) for silicate. Two areas, northeast of Taiwan and southwest of Kyushu, were found to be major source regions of oceanic nutrients to the shelf. Although the onshore fluxes of nutrients and volume both had apparent seasonal variations, the seasonal variation of the onshore nutrient flux did not exactly follow that of the onshore volume flux. Additional calculations in which the concentration of nutrients in Kuroshio water was artificially increased suggested that the oceanic nutrients were distributed in the bottom layer from the shelf break to the region offshore of the Changjiang estuary from spring to summer and appeared in the surface layer from autumn to winter. The calculations also implied that the supply of oceanic nutrients to the shelf can change the consumption of pre-existing nutrients from rivers. The response of primary production over the shelf to the oceanic nutrients was confirmed not only in the surface layer (mainly at the outer shelf and shelf break in winter and in the region offshore of the Changjiang estuary in summer) but also in the subsurface layer over the shelf from spring to autumn.

DOI： 10.5194/os-7-27-2011

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DOI： 10.5194/OS-7-111-2011

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DOI： 10.5194/os-7-111-2011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

As the first attempt to estimate the nutrient transport across the winter thermohaline frontal zone on the northern shelf of the South China Sea, the nutrient dynamics around the front and the effects of cross-frontal water exchange on nutrient transport were investigated using wintertime field observations. Both water temperature and salinity increased from coastal to oceanic waters, showing the presence of a thermohaline front. The concentrations of dissolved inorganic nutrients decreased oceanward, especially across the thermohaline front, while those of dissolved organic nutrients (i.e., dissolved organic nitrogen (DON) and dissolved organic phosphorus) showed patchy distributions. Ammonium was the major constituent of dissolved inorganic nitrogen, and DON was the main component of total dissolved nitrogen. Molar ratios of PO(4)(3-)/total dissolved phosphorus decreased from coastal to oceanic waters, indicating that PO(4)(3-) was rapidly removed and/or consumed from the water column and that organic matter degradation increased offshore, replenishing PO(4)(3-). Molar ratios of NO(3)(-)/(NH(4)(+) + DON) were 0.01-0.6, indicating dominance of regenerated nitrogen. Surface water convergence and bottom water divergence were identified in the across-shore velocity field, and the calculated across-shore nutrient fluxes suggest that the presence of the winter thermohaline front promotes the offshore transport of nutrients from coastal waters. The transport path begins with convergence of surface coastal waters toward the front, followed by the sinking in the frontal region and the oceanward movement through the bottom layer of the front offshore side. With an assumption of 500 km as the length of thermohaline front on the northern shelf of the South China Sea, the calculated offshore fluxes of nutrients across the entire front are larger than those from the Zhujiang (Pearl River) and the Changjiang (Yangtze River).

DOI： 10.1029/2009JC005951

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In September 2007 and in April and July 2008, sediment samples were collected from the southern intertidal area of Yellow River Delta to study the distribution pattern of benthic chlorophyll-a (Chl-a) content and its relations to sediment grain size. In study area, the Chl-a content increased from the north to the south. In the spring, the Chl-a content ranged from 0. 623-8. 734 μg · -1 g with an average of 2. 542 μg · g -1 and increased from high tide zone to low tide zone; while in summer and autumn, the Chl-a content ranged from 0. 307-5. 195 μg · g -1 (averaging 1. 832.g · g -1 ) and 0. 426-4.749 μg · g -1 (averaging 1. 591 μg -1 · g -1 ), respectively, and decreased from high tide zone to low tide zone. The sediments were unanimously composed of silt, with the median size ranging from 0. 025-0. 081 mm (averaging 0. 045 mm) and increased from high tide zone to low tide zone. The distribution pattern of benthic Chl-a was primarily affected by the grain size of sediment, and had significant correlation with the content of fine particles. There was a negative relationship between benthic Chl-a content and elevation height, suggesting that soft, flat, and stable sediment could benefit the growth and reproduction of benthic micro-algae.

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Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCIENCE PRESS  

Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports (VTs) of the Ryukyu Current in the region east of the northern Ryukyu Islands. The inverse calculation results show that the Ryukyu Current is dominated by a subsurface velocity core with maximum velocities from 15.1 to 80.0 cm/s, whose positions vary between 110 and 600 dbar and 27.2A degrees-28.2A degrees N along the transect. The mean velocity exhibits a subsurface velocity core with a maximum value of 24.6 cm/s at 326 dbar depth, a VT of 14.0 Sv (1 Sv a parts per thousand 10(6) m(3)/s), a vertical dimension of 800 m, and a horizontal dimension of 60 km. The seasonal mean velocities show that the Ryukyu Current is stronger in autumn than in other seasons. It is suggested that this seasonal variation is coincident with the intensification of the anticyclonic eddy south of Shikoku, Japan.

DOI： 10.1007/s11430-010-0022-2

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Language：Japanese  

By applying the nesting method, which embeds a fine mesh model within a course mesh model, we constructed a Kuroshio model within a Pacific model, a tide model for the inner part of Seto Inland Sea within a Seto Inland Sea model, and a tide resolving Kuroshio model for the waters around southern Japan within a northwestern Pacific model. The use of fine mesh reduces bathymetry change due to smoothing and the model bathymetry more closely approaches realistic conditions. This effect is remarkable at shelf slopes or scour holes where water depth changes sharply. In addition to bathymetry, horizontal gradients of water temperature and salinity are also sensitive to the change in mesh size, which is remarkable at the area close to the Kuroshio main stream where a sharp gradient can only be reproduced by the fine mesh model. With increases in the horizontal density gradient, the vertical shear of the current becomes large and the Kuroshio becomes more baroclinic. As we introduced tides into the Kuroshio model, in addition to tidal mixing effects in several coastal areas, the occurrence of internal tides and corresponding changes in the density field are found at the Satsunan Islands and Ogasawara Islands areas, where the bathymetry varies significantly. Compared to the model without tides, the Kuroshio in the model with tides moves close to the coast at the Tokara Strait, far from the coast offshore the Bungo Channel and close to the coast at the offshore areas from Shikoku Island to the Ogasawara Islands. Such onshore and offshore shifts in the Kuroshio path result in apparent variations in the water temperature and current fields from the Kuroshio main stream to Japan south coasts.

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Prerequisite(s) for ocean circulation models capable of hindcasting &quot;kyucho&quot; occurrence (a sudden coastal temperature rise induced by Kuroshio frontal waves) in the Bungo Channel, Japan, is investigated using long-term observed temperature and sea level time series, archived hydrographic data, and reanalysis data provided by the Japanese Coastal Ocean Predictability Experiment (JCOPE) group. Anticyclonic mesoscale eddies impinging on the Kuroshio front south of the Bungo Channel enhance the frontal sharpness, frontal wave growth, and activity of kyucho phenomena. A kyucho hindcast is carried out to examine the reliability of a numerical model including realistic anticyclonic eddies propagating south of Japan. The Finite Volume Coastal Ocean Model (FVCOM) for which boundary conditions are given by daily JCOPE2 reanalysis data is adopted in the present study. This numerical model does a reasonable job of hindcasting kyucho occurrence in 2003. It is therefore considered that forecasts of kyucho occurrence up to 2 or 3 months ahead are possible by using the FVCOM in conjunction with JCOPE2 forecast data. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2009JC005818

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

As the first attempt to estimate the nutrient transport across the winter thermohaline frontal zone on the northern shelf of the South China Sea, the nutrient dynamics around the front and the effects of cross-frontal water exchange on nutrient transport were investigated using wintertime field observations. Both water temperature and salinity increased from coastal to oceanic waters, showing the presence of a thermohaline front. The concentrations of dissolved inorganic nutrients decreased oceanward, especially across the thermohaline front, while those of dissolved organic nutrients (i.e., dissolved organic nitrogen (DON) and dissolved organic phosphorus) showed patchy distributions. Ammonium was the major constituent of dissolved inorganic nitrogen, and DON was the main component of total dissolved nitrogen. Molar ratios of PO43-/total dissolved phosphorus decreased from coastal to oceanic waters, indicating that PO43- was rapidly removed and/or consumed from the water column and that organic matter degradation increased offshore, replenishing PO43-. Molar ratios of NO3-/(NH4+ + DON) were 0.01-0.6, indicating dominance of regenerated nitrogen. Surface water convergence and bottom water divergence were identified in the across-shore velocity field, and the calculated across-shore nutrient fluxes suggest that the presence of the winter thermohaline front promotes the offshore transport of nutrients from coastal waters. The transport path begins with convergence of surface coastal waters toward the front, followed by the sinking in the frontal region and the oceanward movement through the bottom layer of the front offshore side. With an assumption of 500 km as the length of thermohaline front on the northern shelf of the South China Sea, the calculated offshore fluxes of nutrients across the entire front are larger than those from the Zhujiang (Pearl River) and the Changjiang (Yangtze River). © 2010 by the American Geophysical Union.

DOI： 10.1029/2009JC005951

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Prerequisite(s) for ocean circulation models capable of hindcasting "kyucho" occurrence (a sudden coastal temperature rise induced by Kuroshio frontal waves) in the Bungo Channel, Japan, is investigated using long-term observed temperature and sea level time series, archived hydrographic data, and reanalysis data provided by the Japanese Coastal Ocean Predictability Experiment (JCOPE) group. Anticyclonic mesoscale eddies impinging on the Kuroshio front south of the Bungo Channel enhance the frontal sharpness, frontal wave growth, and activity of kyucho phenomena. A kyucho hindcast is carried out to examine the reliability of a numerical model including realistic anticyclonic eddies propagating south of Japan. The Finite Volume Coastal Ocean Model (FVCOM) for which boundary conditions are given by daily JCOPE2 reanalysis data is adopted in the present study. This numerical model does a reasonable job of hindcasting kyucho occurrence in 2003. It is therefore considered that forecasts of kyucho occurrence up to 2 or 3 months ahead are possible by using the FVCOM in conjunction with JCOPE2 forecast data. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2009JC005818

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

This paper describes a reanalysis of the variability of water mass properties and currents in the western North Pacific using an ocean forecast system, Japan Coastal Ocean Predictability Experiment 2 (JCOPE2), to provide the basic description and information about the quality for data users. We have created the reanalysis data with high horizontal resolution of 1/12 degrees to describe the oceanic variability associated with the Kuroshio-Kuroshio Extension, the Ovashio, and the mesoscale eddies from 1993 to 2007. The products made by an eddy-resolving ocean model combined with the three-dimensional variational data assimilation well reproduced the mean water mass property in the western North Pacific and the interannual variations of the Kuroshio-Kuroshio Extension and the Oyashio coastal branch. From the reanalysis data, we found that both the mean kinetic energy of the Kuroshio Extension axis at the first meandering crest and southward intrusion of the Ovashio coastal branch were closely related with the horizontal distribution of both the Oyashio Water and North Pacific Intermediate Water within the appropriate interannual time scale. The reanalysis data also indicated that the north-south migration of the Kuroshio Extension associated with its regime transitions affected the decadal modulation of the Subtropical Mode Water formation in the recirculation gyre of the Kuroshio Extension.

DOI： 10.1007/s10872-009-0063-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The seasonal variation of water circulation in the Seto Inland Sea is investigated using a high resolution, three-dimensional numerical ocean model. The model results are assessed by comparison with long-term mean surface current and hydrographic data. The simulated model results are consistent with observations, showing a distinct summer and winter circulation patterns. In summer the sea water is highly stratified in basin regions, while it is well mixed near the straits due to strong tidal mixing there. During this period, a cold dome is formed in several basins, setting up stable cyclonic eddies. The cyclonic circulation associated with the cold dome develops from May and disappears in autumn when the surface cooling starts. The experiment without freshwater input shows that a basin-scale estuarine circulation coexists with cyclonic eddy in summer. The former becomes dominant in autumn circulation after the cold dome disappears. In winter the water is vertically well mixed, and the winter winds play a significant role in the circulation. The northwesterly winds induce upwind (downwind) currents over the deep (shallow) water, forming a "double-gyre pattern" in the Suo-Nada, two cyclonic eddies in Hiuchi-Nada, and anticyclonic circulation in Harima-Nada in vertically averaged current fields.

DOI： 10.1007/s10872-009-0062-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SEARS FOUNDATION MARINE RESEARCH  

Underway profiles of current velocity were combined with stationary profiles of temperature and salinity around a vertically mixed scour pit of the Seto Inland Sea throughout a semidiurnal tidal cycle. This was clone with the purpose of determining (a) whether flood flow is asymmetric relative to ebb over a pit with weakly stratified conditions. and (b) whether there is a dynamic transition from frictionally dominated tidal flow to advectively dominated tidal flow over the pit. These questions arose from previous studies elsewhere under stratified water columns, in contrast to the unstratified conditions at the study site. Observations showed an acceleration of the flood tidal flow over the pit and a deceleration during ebb. The flow acceleration over the pit during flood and deceleration during ebb was attributed to asymmetric patterns of flow convergence/divergence. In turn, these divergence patterns were influenced by the direction and strength of the baroclinic pressure gradient force, which was 10 to 30% of the advective term, despite the relatively weak horizontal gradients of order 10(-5) kg/m(4). The non-negligible influence of the baroclinic pressure gradient was possible from the relatively large depths that exceeded 100 m at the deepest part of the pit, compared to the surrounding depths of 30 m. From depth-averaged dynamical terms derived for flood and ebb phases of the tidal cycle, it was found that the advective terms became more important than frictional terms over the deep parts of the pit. Advection became more prominent than friction where the bottom slope exceeded the value of the bottom drag coefficient (similar to 0.003). Otherwise, frictional effects dominated outside the pit.

DOI： 10.1357/002224009791218850

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An analysis of surface current data obtained from 2002 to 2005 using long-range high-frequency radar provides the first evidence for the presence of biweekly (11-14 day) periodic variations of the Kuroshio axis northeast of Taiwan. This analysis clarifies the spatio temporal characteristics of these variations and reveals that cyclonic/anticyclonic eddies propagating along the shelf slope from the vicinity of the deep channel east of Taiwan induce these variations northeast of Taiwan. The behavior of the cyclonic/anticyclonic eddies on the shelf slope is well explained by 2nd-mode interior shelf waves advected by the Kuroshio&apos;s mean flow. Remote effects from the vicinity of the deep channel east of Taiwan, or from outside the East China Sea, are believed to play an important role in the generation of these biweekly periodic variations of the Kuroshio axis northeast of Taiwan. Moreover, on the shelf slope, these variations cause an on shore current across the shelf slope, suggesting topographically controlled upwelling. Therefore, the biweekly periodic variations of the Kuroshio axis northeast of Taiwan might contribute not only to the on shore transport of Kuroshio surface water but also to transport nutrient-rich Kuroshio subsurface water on to the shelf in the East China Sea. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2009.07.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The planar photosynthetically available radiation (PAR), turbidity and concentration of chlorophyll a (chl a), were measured at 26 stations in the Huanghai (Yellow) Sea during a cruise of China SOLAS from 19 to 27 March 2005. Due to low chl a (&lt;0.35 mg.m(-3)) in upper layers (above 5 in), suspended particulate matter became the major factor that influenced the turbidity in early spring. The calculated vertical diffuse attenuation coefficient of PAR, K-PAR, varied with water depths with a maximum value in the upper 5 m layer. The mean K-PAR in survey area was 0.277 +/- 0.07 m(-1) that is considerably higher than most of the other case 2 waters. Within the survey area, K-PAR also showed distinct regional characteristics, corresponding to the distribution of turbidity. Based on measurements, the relationship between K-PAR and turbidity as well as chl a was established. It was suggested that suspended particulate matter plays an important role in light attenuation in the Huanghai (Yellow) Sea in spring.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

The recent formation of the Kuroshio large meander southeast of the Kii Peninsula during the period from May to July 2004 has been simulated successfully in an eddy-resolving ocean forecast system (Japanese Coastal Ocean Predictability Experiment). The formation process was examined from the viewpoint of eddy-Kuroshio interactions using sensitivity experiments that had various initial conditions for eddies in March and May 2004. We confirmed that the large meander does not occur when the trigger meander southeast of the Kyushu Island has small amplitude and that the cyclonic eddy on the offshore side of the Kuroshio contributes to the large meander formation. Our results show that the large amplitude of the trigger meander southeast of Kyushu Island in April 2004 was caused by downstream advection of anticyclonic eddies along the Kuroshio in the East China Sea from east of Taiwan. The results suggest that the successive westward propagation of strong anticyclonic eddies in the subtropical frontal region from 2003 to 2004 was the origin of the formation of the Kuroshio large meander south of Japan in summer 2004. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JC004226

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The recent formation of the Kuroshio large meander southeast of the Kii Peninsula during the period from May to July 2004 has been simulated successfully in an eddy-resolving ocean forecast system (Japanese Coastal Ocean Predictability Experiment). The formation process was examined from the viewpoint of eddy-Kuroshio interactions using sensitivity experiments that had various initial conditions for eddies in March and May 2004. We confirmed that the large meander does not occur when the trigger meander southeast of the Kyushu Island has small amplitude and that the cyclonic eddy on the offshore side of the Kuroshio contributes to the large meander formation. Our results show that the large amplitude of the trigger meander southeast of Kyushu Island in April 2004 was caused by downstream advection of anticyclonic eddies along the Kuroshio in the East China Sea from east of Taiwan. The results suggest that the successive westward propagation of strong anticyclonic eddies in the subtropical frontal region from 2003 to 2004 was the origin of the formation of the Kuroshio large meander south of Japan in summer 2004.

DOI： 10.1029/2007JC004226

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The response of the density-driven circulation in the Chesapeake Bay to wind forcing was studied with numerical experiments. A model of the bay with realistic bathymetry was first applied to produce the density-driven flow under average river discharge and tidal forcing. Subsequently, four spatially uniform wind fields (northeasterly, northwesterly, southwesterly, and southeasterly) were imposed to examine the resulting cross-estuary structure of salinity and flow fields. In general, northeasterly and northwesterly winds intensified the density-driven circulation in the upper and middle reaches of the bay, whereas southeasterly and southwesterly winds weakened it. The response was different in the lower bay, where downwind flow from the upper and middle reaches of the bay competed with onshore/offshore coastal flows. Wind remote effects were dominant, over local effects, on volume transports through the bay entrance. However, local effects were more influential in establishing the sea-level slopes that drove subtidal flows and salinity fields in most of the bay. The effect of vertical stratification on wind-induced flows was also investigated by switching it off. The absence of stratification allowed development of Ekman layers that reached depths of the same order as the water depth. Consequently, bathymetric effects became influential on the homogeneous flow structure causing the wind-induced flow inside the bay to show a marked transverse structure: downwind over the shallow areas and upwind in the channels. In the presence of stratification, Ekman layers became shallower and the wind-induced currents showed weaker transverse structure than those that developed in the absence of stratification. In essence, the wind-driven flows were horizontally sheared under weak stratification and vertically sheared under stratified conditions. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2008.06.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

We investigated the behavior of the Yellow River plume in the Bohai Sea through a year and its controlling mechanisms using a numerical model driven by monthly averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal behavior of the Yellow River plume. In summer, the Yellow River plume extends northeastward into the central Bohai Sea
in autumn, it turns southward and flows into Laizhou Bay along the coast
in winter, most of the diluted water is found around southeastern corner of Laizhou Bay
and in spring, a low-salinity area appears in southwest Laizhou Bay. With the same model, several well-designed numerical experiments were performed to investigate the effect on the behavior of the Yellow River plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal currents promote the offshore spread of diluted water, while the tide-induced residual currents prevent the plume from extending further downstream (in the direction of Kelvin wave propagation). Wind stresses lead to pronounced changes in the path and shape of the plume. In autumn and winter, northwesterly or northerly winds drive the buoyant water into Laizhou Bay along the coast. In summer, the combination of southeasterly winds and thermal stratification drives the plume extend northeastward into the central Bohai Sea. By changing only the magnitude of wind stress or river discharge in the experiments, we examined the sensitivity of summertime plume to the magnitude of wind stress and river discharge. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JC004555

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

[1] We investigated the behavior of the Yellow River plume in the Bohai Sea through a year and its controlling mechanisms using a numerical model driven by monthly averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal behavior of the Yellow River plume. In summer, the Yellow River plume extends northeastward into the central Bohai Sea; in autumn, it turns southward and flows into Laizhou Bay along the coast; in winter, most of the diluted water is found around southeastern corner of Laizhou Bay; and in spring, a low-salinity area appears in southwest Laizhou Bay. With the same model, several well-designed numerical experiments were performed to investigate the effect on the behavior of the Yellow River plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal currents promote the offshore spread of diluted water, while the tide-induced residual currents prevent the plume from extending further downstream (in the direction of Kelvin wave propagation). Wind stresses lead to pronounced changes in the path and shape of the plume. In autumn and winter, northwesterly or northerly winds drive the buoyant water into Laizhou Bay along the coast. In summer, the combination of southeasterly winds and thermal stratification drives the plume extend northeastward into the central Bohai Sea. By changing only the magnitude of wind stress or river discharge in the experiments, we examined the sensitivity of summertime plume to the magnitude of wind stress and river discharge.

DOI： 10.1029/2007JC004555

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

We have developed a forecast system for the Kuroshio large meander with a high horizontal resolution (approximately 10 km). Using the system, we succeeded in predicting the path transitions of the Kuroshio from the nearshore nonlarge meander path to the offshore nonlarge meander path in 2003, and from the nearshore nonlarge meander path to the typical large meander path in 2004 as well as the occurrence of its triggering small meander south of Kyushu Island. We have also been developing a higher resolution forecast model for coastal oceans and bays south of Japan, where physical and biological states of the ocean are much affected by the path variation of the Kuroshio. This model, although the development is still under way, represents tides and tidal currents in two bays south of Japan in a realistic way.

DOI： 10.1007/978-0-387-49791-4_13

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Language：Japanese  

Applying the Princeton Ocean Model to the bathymetry of Chesapeake Bay, we studied the relation between estuarine circulation and wind-driven current. First, the model reproduced the estuarine circulation with average river discharge and tide. Then, four wind fields with different directions but with the same amplitude were applied to the pre-established estuarine circulation. The wind-induced changes in the salinity field concentrate on the stratification inside the bay and the plume area outside the bay. Depending on the wind direction, the stratification inside the bay is destroyed or weakened while the plume area is moved onshore or offshore. The flow field also shows apparent responses to the wind. However, a linear superposition of wind-driven current on estuarine circulation cannot explain all the wind-induced variations in the flow field. Winds change the density field, which in turn also changes the flow field. Moreover, winds change the turbulent field, which changes the flow structures. A clear intensification of eddy viscosity coefficient by winds has been shown by this study.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The response of the Chesapeake Bay to river discharge under the influence and absence of tide is simulated with a numerical model. Four numerical experiments are examined: (1) response to river discharge only; (2) response to river discharge plus an ambient coastal current along the shelf outside the bay; (3) response to river discharge and tidal forcing; and (4) response to river discharge, tidal forcing, and ambient coastal current. The general salinity distribution in the four cases is similar to observations inside the bay. Observed features, such as low salinity in the western side of the bay, are consistent in model results. Also, a typical estuarine circulation with seaward current in the upper layer and landward current in the lower layer is obtained in the four cases. The two cases without tide produce stronger subtidal currents than the cases with tide owing to greater frictional effects in the cases with tide. Differences in salinity distributions among the four cases appear mostly outside the bay in terms of the outflow plume structure. The two cases without tide produce an upstream (as in a Kelvin wave sense) or northward branch of the outflow plume, while the cases with tide produce an expected downstream or southward plume. Increased friction in the cases with tide changes the vertical structure of outflow at the entrance to the bay and induces large horizontal variations in the exchange flow. Consequently, the outflow from the bay is more influenced by the bottom than in the cases without tide. Therefore, a tendency for a bottom-advected plume appears in the cases with tide, rather than a surface-advected plume, which develops in the cases without tide. Further analysis shows that the tidal current favors a salt balance between the horizontal and vertical advection of salinity around the plume and hinders the upstream expansion of the plume outside the bay. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.csr.2006.08.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

A 1/18 degrees nested ocean model is used to determine locations, volume transports, and temporal variations of Kuroshio onshore fluxes across the shelf break of the East China Sea (ECS). The Kuroshio onshore flux shows strong seasonality: maximum similar to 3 Sv; 1 Sv equivalent to 10(6) m(3) s(-1)) in autumn and minimum (&lt;0.5 Sv) in summer. Another short-term (similar to 17 days) variation due to Kuroshio meanders introduces large fluctuations in the onshore fluxes but its seasonal average almost vanishes. The Kuroshio onshore fluxes have two major sources, Kuroshio intrusion northeast of Taiwan and Kuroshio separation southwest of Kyushu; the former provides larger onshore flux than the latter. Therefore, in addition to the waters from the Taiwan Strait and the Kuroshio separation region southwest of Kyushu, the water due to the Kuroshio intrusion northeast of Taiwan is also a major source of the Tsushima Warm Current. A vorticity equation is used to separate the contribution of surface Ekman transport to the Kuroshio onshore fluxes in the ECS from that relating to density fields. For the total Kuroshio onshore flux across the entire shelf break, its seasonal variation is primarily controlled by the Ekman transport while the change in density field is secondary. For the Kuroshio onshore flux at a fixed location along the shelf break, its seasonal variation is primarily related to the change in density field and the Ekman transport is secondary. Furthermore, the role of the Taiwan Strait water and the Kuroshio water across the shelf break on material transport in the ECS is examined with passive tracer experiments. In summer, about half of the tracer in the Tsushima Strait originates in the Taiwan Strait, while the other half comes from the Kuroshio. From summer to winter, the ratio changes dramatically; the contribution from the Taiwan Strait decreases to 20% and that from the Kuroshio increases up to 80%. The tracer originating in the Kuroshio water dominates the bottom layer of the continental shelf in the ECS throughout the year.

DOI： 10.1175/JPO2976.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Focusing on predictability of the Kuroshio meandering, we have done an ensemble forecast experiment; the application of the method to the problem addressed seems to be the first comprehensive attempt in the community of physical oceanography. By assimilating sea surface height anomaly into an ocean general circulation model in the preceding 40-day period, the observed Kuroshio meandering manifested south of Japan in November 1999 was successfully predicted 2 months before the event. The experiment yields a forecasting skill of the Kuroshio meander position for 60 days in the sense that the RMS error does not exceed the magnitude of the model climatic variation and those obtained from the non-assimilated simulation and persistence. In addition to a single trajectory forecast experiment, ensemble forecasts were conducted using 10 perturbed initial states generated by the breeding method. The predicted states realized as the ensemble members of the 80-day forecast are classified into two categories: large and non-large meander. It is found that the intensity of an anticyclonic eddy in the initial state seems to play a key role in selecting one of the two states.

DOI： 10.1029/2004JC002426

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Publisher：日本海洋学会  

燧灘全域, 来島海峡および備讃瀬戸西部において, 2002年5月末から8月中旬まで4回にわたりCTD観測を実施した。観測データを2層1ボックスモデルで解析することにより, 燧灘成層域上下層の海水交換に対する移流と水平・鉛直混合の寄与を明らかにするとともに, 各層の熱収支を定量的に評価した。その結果, 海水交換に対しての寄与は上下層ともに鉛直混合よりも水平混合が数倍大きく, さらに, 下層では水平混合が移流よりも大きいことが判明した。また熱収支からは, 成層域下層の加熱に対する鉛直混合の寄与は23%〜41%に過ぎず, 59%〜77%を水平混合と移流による加熱が占めていることも明らかになった。この結果は, 熱バイパス(Takeoka, 2002)が燧灘成層域下層の加熱に重要な役割を果たしていることを実証するものである。

DOI： 10.5928/kaiyou.14.429

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Language：English   Publishing type：Research paper (scientific journal)  

On the basis of the Princeton Ocean Model, a robust diagnostic model is developed to calculate the residual currents in the Hiuchi-Nada, a semi-enclosed bay of the Seto Inland Sea. The input water temperature and salinity data are from six hydrographic surveys in 2002, and the model results in the summer show a clockwise eddy in the western part of the bay and an anticlockwise eddy in the eastern part. The magnitude of two eddies is ∼10 cm/s. The modeled flow pattern is consistent with early observations derived from moored arrays. The two eddies are persistent throughout the summer because winds are usually weak and cannot influence their existence. The tide-induced residual currents are appreciable only in the close vicinity of the Kurushima Strait and Bisan Strait, the two straits connecting the bay to the other bays, and have little affect on the two eddies that are inside the bay. Thus the two density-driven eddies in the Hiuchi-Nada are the basic pattern of circulation in the summer. Using the calculated residual currents, we examined the intrusion route of waters from the Kurushima Strait and Bisan Strait with passive tracer experiments. The results show that the water in the Kurushima Strait intrudes into the bay mainly through the middle and bottom layers while the water in the Bisan Strait intrudes mainly through the surface layer. Furthermore, the tracer cannot reach the center of the anticlockwise eddy in the eastern part of the bay. This indicates that the eddy prevents water exchange between its center and outer edges and provides favorable conditions for the formation of oxygen-deficient waters in the central part of the eddy. Copyright 2004 by the American Geophysical Union.

DOI： 10.1029/2003JC002203

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

A high-resolution ocean general circulation model is developed to simulate connections between the Kuroshio path variations and mesoscale eddy activities as realistically as possible. The climatological mean of the modeled Kuroshio takes a nearshore nonlarge meander path. It is found that the model is capable of simulating two types of nonlarge meander state and a possible version of the large meander state. The offshore nonlarge meander is generated through interaction between the Kuroshio and an anticyclonic eddy. The large meander occurs just after significant intensification of the anticyclonic Kuroshio recirculation; successive intrusion of anticyclonic eddies from the upstream region is responsible for this process. Those anticyclonic eddies are advected by the Kuroshio from the region northeast of Luzon Island and increase the upstream Kuroshio volume transport on an interannual time scale. The cyclonic eddies propagating from the Kuroshio Extension region, on the other hand, weaken the Kuroshio meander after the merger. The Kuroshio path variations south of Japan thus seem to be closely related to eddy activities in the subtropical gyre system.

DOI： 10.1175/1520-0485(2004)034<2203:ROMEIT>2.0.CO;2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Netherlands  

A two-way nested model has been constructed and applied to the idealized ocean where a uniform mean flow impinges on the isolated Gaussian-shaped seamount and produces two eddies (cold and warm) in the depths. The performance of the nested model has been evaluated subjectively and objectively. Both subjective and objective analyses confirm the traditional view that the nested model can well capture the performance of isolated eddies. Objective analysis, however, reveals some quantitatively important features of a two-way nested model. One is penetration of improved features into the coarse domain and another is the deterioration of mean flow field inside the nested area, neither of which is clear from subjective analysis. With successful application of two-way nested model to the seamount problem, we expect that such a nested model will also be applicable to other oceanic phenomena, particularly to some coastal problems whose time scale is short and where the topographic effects are dominant. Copyright © The Oceanographic Society of Japan.

DOI： 10.1007/s10872-005-5781-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

A triply nested ocean general circulation model was used to examine how the model horizontal resolution influences the Kuroshio in the East China Sea (ECS) and the sea level variability. As the model resolution increases from 1/2degrees to 1/18degrees the path, current intensity, and vertical structure of the model Kuroshio and the variability of sea level become closer to observations. In general, the higher-resolution model improves the baroclinic as well as barotropic component of the Kuroshio and thus reproduces more realistic density and current fields. This improvement, in addition to better representation of topography, results in better reproduction of the interaction between baroclinicity and bottom topography, that is, JEBAR (joint effect of baroclinicity and bottom relief) in a high-resolution model. Modeling the Kuroshio in the ECS provides an ideal example of such improvement. In particular, the Kuroshio veering phenomenon at (30degreesN, 129degreesE) southwest of Kyushu is discussed, together with the seasonal meridional migration of the path. It is shown that JEBAR and advection of the geostrophic potential vorticity are two major contributions to the vorticity balance in this area. The summer intensification of JEBAR resulting from the intensified stratification yields a strong offshore volume transport across the shelf break, thereby leading to the southward shift of the veering latitude. In winter, the weakened JEBAR, combined with the increased wind stress curl, decreases the offshore volume transport in a considerable amount, explaining the northward shift of the veering latitude. The present reproduction of seasonal migration of the Kuroshio axis at 129degreesE is in good agreement with observation.

DOI： 10.1175/1520-0485(2003)033<0146:ATNOMF>2.0.CO;2

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Language：Japanese   Publisher：The Oceanographic Society of Japan  

The "Furiwakeshio" ("Kinan Bifurcation Current"), which is caused by the Kuroshio hitting the southwestern coast of the Kii Peninsula, is studied using a high-resolution OGCM. A hindcast experiment using the OGCM is analyzed and compared with the observed data in this area. The results are summarized as follows. The mean sea level around the Kii Peninsula is characterized by a cyclonic depression in the coastal zone and the bifurcation of contours between the Kuroshio and the "Furiwakeshio" offshore of the southwestern Ku Peninsula. The OGCM with 1/18-degree horizontal resolution cannot reproduce this climatology, but can reproduce the sea' level pattern quite similar to the observed bifurcation only in a snapshot sense. The model and observations are also compared for the sea level difference between Kushimoto and Uragami, a famous index of the Kuroshio large meander. Because of the insufficiency of resolution to reproduce the tiny cape called Shiono-misaki, the model fails in reproducing observed values over 25 cm and only results in values less than 25 cm. The bifurcation patterns of current vectors and temperature contours as observed in this area in 1997 by the synoptic hydrographic surveys were not reproduced by the model in the sense of a successful hindcast. The frequency of bifurcation events through 1997 was estimated by calculating the model's westward transport along the western coast of the Kii Peninsula. The frequency of the Furiwakeshio is under-estimated by the model by about 10% when compared with the observed frequency of about 78%. Nevertheless, the lifetime and spatial structure of the Furiwakeshio once it appeared in the model are quite similar to those of the actual phenomenon. The model result shows a series of events in which the anticyclonic and cyclonic disturbances propagating on the Kuroshio 's offshore side generate a torque that changes the direction angle of the Kuroshio path between Muroto-misaki and Shiono-misaki. This is thought to be the main mechanism which causes the Furiwakeshio and is a notable feature found by the present model study.

DOI： 10.5928/kaiyou.11.513

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Current measurements and conductivity-temperature-depth surveys of the lagoon and ocean at Majuro Atoll, the Republic of the Marshall Islands, were made from January 10 to 24, 1997. A vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements py Fourier transform. A three-dimensional, robust diagnostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles. We used the diagnostic model to examine the effects of wind stress, radiation stress, density gradients, and tidal stress on the exchange of water between the lagoon and the ocean. Wind effectively mixes the lagoon water in approximately 2 weeks. Tidal flushing appears to be restricted to a small area near the main channels connecting the lagoon to the ocean. Cross-reef-flat currents induced by radiation stress and flowing to the deep channels in the center of the northern boundary form the dominant mechanism for exchange between the lagoon and the open ocean, causing water to exchange completely with the ocean in about 15 days. Computer-generated particles tracked through the lagoon showed that radiation stress is also the main forcing mechanism for particle export from the lagoon. However, the coupling of tidal exchange through the Calalin Channel and wind-stress-induced mixing in the lagoon could also provide a significant export mechanism, particularly for particles originating uniformly inside the lagoon.

DOI： 10.1029/1999JC900065

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Observed zooplankton data show that the number of outer bay species of zooplankton appearing in the central part of Tokyo Bay have increased in recent years. Because these zooplankton cannot reproduce in the inner bay, they must be brought into the bay by the advective transport of the sea water from the adjacent open ocean (Nomura,1993 P. D. Thesis, Tokyo university of Fisheries). The increase of fresh water discharge is proposed as a mechanism for changing the residual current that is thought to bring the outer bay species of zooplankton into Tokyo Bay (Nomura,1996, Bulletinon Coastal Oceanography 34, 25-35). To clarify the variation of the residual current due to the increase of fresh water discharge quantitatively, a three-dimensional prognostic numerical model is developed.
To verify of the prognostic numerical model, the observed temperature, salinity and residual current during the summer of 1979 are reproduced firstly. The calculated result confirms the existence of two eddies that have been reproduced by a diagnostic numerical model (Guo and Yanagi, 1996, Journal of Oceanography 52, 597-616). The first one is the anticlockwise circulation in the head region of the bay and the second one the clockwise circulation in the central part of the bay. Apart from these two eddies, the strong gravitational circulation at the mouth of the bay, which flows out of the bay in the upper layer and into the bay in the lower layer, is also reproduced. Next, the river discharge is increased to the level of the summer of 1989 and the calculation is carried out again. The difference between these two calculated results is considered as the variation induced by the increase of fresh water discharge.
The calculated result shows that the increase of river water influences the residual current in the head region of the bay greatly. At the mouth of the bay, the gravitational circulation is strengthened by up to 0.5 cm/s. This variation of residual current is expected to bring more outer bay species of zooplankton into the inner bay from the adjacent open ocean. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0278-4343(98)80017-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Terra Scientific Publishing Company  

A three-dimensional tidal current model is developed and applied to the East China Sea (ECS), the Yellow Sea and the Bohai Sea. The model well reproduces the major four tides, namely M2, S2, K1 and O1 tides, and their currents. The horizontal distributions of the major four tidal currents are the same as those calculated by the horizontal two-dimensional models. With its high resolutions in the horizontal (12.5 km) and the vertical (20 layers), the model is used to investigate the vertical distributions of tidal current. Four vertical eddy viscosity models are used in the numerical experiments. As the tidal current becomes strong, its vertical shear becomes large and its vertical profile becomes sensitive to the vertical eddy viscosity. As a conclusion, the HU (a) model (Davies et al., 1997), which relates the vertical eddy viscosity to the water depth and depth mean velocity, gives the closest results to the observed data. The reproduction of the amphidromic point of M2 tide in Liaodong Bay is discussed and it is concluded that it depends on the bottom friction stress. The model reproduces a unique vertical profile of tidal current in the Yellow Sea, which is also found in the observed data. The reason for the reproduction of such a unique profile in the model is investigated.

DOI： 10.1007/BF02823285

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The detailed structure of the thermohaline front at the mouth of Ise Bay during winter has been investigated by intensive field observation. The transport of suspended matter from Ise Bay to the Pacific Ocean through the thermohaline front has also been investigated using the data from a time-series sediment trap, a current meter and a nephelometer moored at the bay mouth station. The mixed coastal and offshore water at the surface of the thermohaline front sinks to a depth of about 200 m in the offshore area.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Terra Scientific Publishing Company  

The residual currents in Tokyo Bay during four seasons are calculated diagnostically from the observed water temperature, salinity and wind data collected by Unoki et al. (1980). The calculated residual currents, verified by the observed ones, show an obvious seasonal variable character. During spring, a clear anticlockwise circulation develops in the head region of the bay and a strong southwestward current flows in the upper layer along the eastern coast from the central part to the mouth of the bay. During summer, the anticlockwise circulation in the head region is maintained but the southwestward current along the eastern coast becomes weak. During autumn, the preceding anticlockwise circulation disappears but a clockwise circulation develops in the central part of the bay. During winter, the calculated residual current is similar to that during autumn. As a conclusion, the seasonal variation of residual current in Tokyo Bay can be attributed to the variation of the strength of two eddies. The first one is the anticlockwise circulation in the head region of the bay, which develops in spring and summer and disappears in autumn and winter. The second one is the clockwise circulation in the central part of the bay, which develops in autumn and winter, decreases in spring and nearly disappears in summer.

DOI： 10.1007/BF02238323

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Authorship：Lead author   Publishing type：Internal/External technical report, pre-print, etc.  

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Language：Japanese   Publisher：日本気象学会  

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Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

DOI： 10.1007/s10872-020-00578-y

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Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

DOI： 10.1007/s10872-021-00619-0

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Language：Japanese   Publisher：海洋出版  

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Language：Japanese   Publisher：水産海洋学会  

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Language：Japanese   Publisher：日本気象学会  

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Language：Japanese   Publisher：瀬戸内海環境保全協会  

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Language：English   Publisher：Research Institute for Applied Mechanics, Kyushu University  

DOI： 10.15017/14172

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Other Link： http://hdl.handle.net/2324/14172

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Language：Japanese   Publisher：海洋出版  

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Language：Japanese   Publisher：海洋出版  

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