Search

Coastal oceans, traditionally seen as a conduit for transporting atmospheric carbon dioxide (CO2)-derived anthropogenic carbon (CANT) to open oceans, exhibit complex carbon exchanges at their interface. South China Sea (SCS) exemplifies this complexity, where interactions with the Pacific, particularly through Kuroshio intrusion, challenge the understanding of CANT source and variability in a coastal ocean. Contrary to prevailing paradigm expectations, our high-resolution, long-term data reveal that CANT in the SCS primarily originates from Pacific water injection across the Luzon Strait rather than atmospheric CO2 invasion. Over the past two decades, the SCS has experienced increasing CANT levels, with notable interannual fluctuations driven by El Niño and La Niña events influencing Kuroshio intrusion, generating anomalously high and low CANT inventories, respectively. This highlights an overlooked CANT transport pathway from open to coastal oceans, responsible for cumulative ocean acidification that has already affected coral reefs enriched in the SCS located west of the Coral Triangle. [ABSTRACT FROM AUTHOR]

Gut contents and nitrogen isotope ratio (δ15N) analyses were conducted on splendid alfonsino Beryx splendens collected in the vicinity of Kuroshio from May 2015 to November 2016 (n = 708) to identify their feeding habits in the Western North Pacific. Micronektonic fish, shrimp, and squid were the dominant prey species, with the Decapoda Acanthephyra quadrispinosa, Prehensilosergia prehensilis, Cephalopoda Enoploteuthis chunii, Chiroteuthis calyx, Teleostei Sigmops gracilis, and Gonostoma elongatum. These micronektons are common in the Kuroshio Current; thus, B. splendens is a possible opportunistic feeder. Gut content weight (GCW), occurrence (%O) of fish and squid, and δ15N were significantly increased with the fork length (FL) of B. splendens. Only the %O of shrimp does not show a significant relationship with the FL of B. splendens. These indicated the ontogenetic shift of dominant prey from shrimp to fish. Fattened specimens could also prey on a greater number of fish. The seasonality of GCW and %O values was high in spring and autumn and low in summer and winter. This seasonality indicated that the feeding habits of B. splendens are controlled by primary productivity in the surface layer and/or by maturity. When the Kuroshio flowed in the north of Hachijojima Island, the GCW was significantly increased, and some organisms, including C. calyx, G. elongatum, and S. gracilis, were preyed on more. While the offshore area of the Kuroshio has low productivity, B. splendens can actively prey in this area, indicating that it is an important feeding ground for this species. [ABSTRACT FROM AUTHOR]

Trace element analysis of otoliths from core to edge was used to reveal differences in habitats of larvae and early juveniles of Japanese jack mackerel (Trachurus japonicus) caught in the East China Sea (ECS), Pacific Ocean, and Sea of Japan. Multi‐element signatures (Sr:Ca, Mg:Ca, Na:Ca, K:Ca, and Ba:Ca) were analyzed with multivariate statistics to determine whether these element signatures provide insight into regional population structure. The median values of elements: Ca ratios in otolith core region differed significantly among areas, with most elements between the ECS and the Pacific Ocean or Sea of Japan showing significant differences. The Sr:Ca ratios exhibited a V‐shaped trend from the otolith core to the edge, which was likely related to the vertical habitat layer shift of larvae and early juveniles of T. japonicus. Canonical analysis of principal coordinates using the element: Ca ratios and the hatching day were re‐classified according to the sampling area with higher accuracy in the ECS (88–95%) and the Sea of Japan (76–83%) compared to the Pacific Ocean (69–72%). These results indicate that the proportion of eggs, larvae, and early juveniles transported by the Kuroshio Current from the southern ECS—the main spawning ground—to the Pacific Ocean or the Sea of Japan is low and that juveniles distributed in the coastal waters off southwestern Japan may have originated from local spawners. These results suggest that determining the elemental composition of larvae and juveniles of T. japonicus is effective in determining the habitat differences of this species in the three regions. These findings will help to understand population structure and recruitment process of this species around Japan. [ABSTRACT FROM AUTHOR]

Mesoscale eddies – ocean vortices with spatial scales of tens to hundreds of kilometers and time scales of months to years – are among the most energetic forms of flow in the ocean, and may act as significant transporters of floating microplastics. Yet, shipboard observation has thus far not clarified the abundance and transport of microplastics in mesoscale eddies. We conducted floating microplastic surveys in an intense cyclonic mesoscale eddy with a large sea surface height depression (approximately 0.8 m), a so-called cold-core ring, in the Kuroshio Extension recirculation gyre (KERG) southeast of Japan. The concentration of microplastics within the eddy (460 × 104 pieces/km2) was one or two orders of magnitude higher than in the adjacent oceanic waters, likely due to the acquisition of microplastics from the microplastic-rich Kuroshio Extension (KE) when detaching, as well as the horizontal entrainment of particles by the eddy. Our examination by using an assimilation product showed that most particles captured by the eddy remained within for several months while the eddy moved clockwise in the KERG. These results suggest that mesoscale eddies are of importance in the transportation and redistribution of microplastics on the ocean surface. [ABSTRACT FROM AUTHOR]

Winter precipitation over eastern China displays remarkable interannual variability, which has been suggested to be closely related to El Niño–Southern Oscillation (ENSO). This study finds that ENSO impacts on eastern China precipitation patterns exhibit obvious differences in early (November–December) and late (January–February) winter. In early winter, precipitation anomalies associated with ENSO are characterized by a monopole spatial distribution over eastern China. In contrast, the precipitation anomaly pattern in late winter remarkably changes, manifesting as a dipole spatial distribution. The noteworthy change in precipitation responses from early to late winter can be largely attributed to the seasonally varying Kuroshio anticyclonic anomalies. During the early winter of El Niño years, anticyclonic circulation anomalies appear both over the Philippine Sea and Kuroshio region, enhancing water vapor transport to the entirety of eastern China, thus contributing to more precipitation there. During the late winter of El Niño years, the anticyclone over the Philippine Sea is further strengthened, while the one over the Kuroshio dissipates, which could result in differing water vapor transport between northern and southern parts of eastern China and thus a dipole precipitation distribution. Roughly the opposite anomalies of circulation and precipitation are displayed during La Niña winters. Further analysis suggests that the seasonally-varying Kuroshio anticyclonic anomalies are possibly related to the enhancement of ENSO-related tropical central-eastern Pacific convection from early to late winter. These results have important implications for the seasonal-to-interannual predictability of winter precipitation over eastern China. [ABSTRACT FROM AUTHOR]

To test the potential of high‐resolution satellite image analysis for assessing and predicting the mesoscale (<10 km in this study) effects of climate and environmental change on temperature and primary productivity in fishing grounds, we conducted satellite image analysis around an island in a coastal strait west of Japan from 2018 to 2023. We observed a distinct north–south gradient in sea surface temperature (SST) and chlorophyll a concentration (CHL) over approximately 20 km of the transect, which was likely affected by the current system. The model configuration suggests that the frequency of southward currents during winter–spring can control the magnitude of spring phytoplankton blooms. In the study region, an increase in SST at a rate of 0.06–0.13°C y−1 occurred during the study period, accompanied by a decrease in CHL. The north–south gradient in the rate of change suggests that the variation in the temperature and flow rate of the Kuroshio Current into the study area was due to these abrupt changes. The relationship between the annual mean SST and CHL was also spatially heterogeneous, showing a higher sensitivity of CHL to SST in the southwest of the island than in the north. In addition to the intrusion of warm and oligotrophic Kuroshio waters, the spread of less saline and more eutrophic coastal waters likely influenced this spatial heterogeneity. The satellite image analysis in the present study successfully revealed mesoscale mosaics of environmental conditions in coastal fishery grounds. [ABSTRACT FROM AUTHOR]

Deep atmospheric convection is often observed over the Kuroshio in the East China Sea (ECSK). However, the mechanisms by which warm oceanic currents fuel transient deep convection are not fully understood. This study investigates an atmospheric cold front that brought heavy precipitation as it traversed the ECSK in April 2004. The southwesterlies ahead of the cold front advected moist and warm air, creating a zone with high convective available potential energy (CAPE) values. As the cold front approached the ECSK, the pre‐frontal high CAPE values coalesced with those over the warm current that substantially strengthened the deep convection, with precipitation rate increasing from 3 mm hr−1 to 10 mm hr−1. A numerical model well simulated the marked increase in precipitation over the ECSK, permitting the isolation of the ECSK's influence by contrasting the control (CTRL) run with an experiment with smoothed sea surface temperatures (SMTH run). Results show the ECSK contributed to 46% of the precipitation over the warm current. The ECSK was found to amplify ascending motion and elevate neutral buoyancy levels, extending its effect up to the tropopause. Furthermore, the strengthened deep convection significantly lowered the sea level pressure (SLP) over the ECSK and impressed upon the time‐mean SLP field. An additional experiment with lowered SST underscored the high SST's critical role in deep convection. This case study suggests a novel pathway by which the effects of warm oceanic currents influence the upper troposphere under extreme conditions with strong baroclinic instability. Plain Language Summary: Warm ocean currents like the Kuroshio in the East China Sea can shape the weather above, often causing towering clouds and heavy rainfalls. Understanding how this happens is key to better weather forecasts. Our research focused on an event in April 2004, when a cold front passing over the Kuroshio led to intense rain. We used satellite data and computer simulations to see how the warm current influenced the storm. We found that the Kuroshio, by warming and adding moisture to the surface air, strengthened the storm and increased its height, resulting in more rainfall. This effect also left a noticeable imprint on the sea‐level pressure field. These results are important because they help us understand and better predict the impact of warm ocean currents on severe weather events. Key Points: An atmospheric cold front swept over the East China Sea Kuroshio (ECSK) and produced heavy precipitation over the warm currentThe ECSK increased surface moist entropy, which intensified the precipitation from deep convectionThe cold‐frontal deep convection projected the ECSK's effect up to the tropopause [ABSTRACT FROM AUTHOR]

Background: There are still few studies which have addressed pain management in breast reconstruction in the acute phase. We conducted the current study in Japan to identify the effect of Pectoral Nerve Block Type II (PECS II) and Serratus Plane Block (SPB) for acute postoperative pain after tissue expander (TE) insertion. Methods: Patients who underwent TE reconstruction from January 2016 to April 2017 were divided into groups treated with (LB) and without (Control) nerve block using levobupivacaine. Participants responded a questionnaire about acute postoperative pain for 7 days after operation. Results: A total of 46 women participated in the study. On a visual scale analog (VAS) for pain at rest and during movement, pain intensity was significantly lower in the LB group than in the Control group on postoperative day (POD) 0 (p = 0.04, p < 0.001), POD 1 (both p < 0.001), and POD 2 (p = 0.008, p = 0.03). There was significantly less use of painkillers in the LB group on POD 0 (p = 0.04) and POD 1 (p = 0.02). Conclusions: Combined use of PECS II block and SPB would be effective for managing acute pain in the Japanese population after breast reconstruction using TE insertion. Level of evidence: Level IV, Therapeutic. [ABSTRACT FROM AUTHOR]

As cross‐shelf gradients of most properties are typically much steeper than those in the alongshore direction, transport across isobaths tends to be inhibited, particularly at oceanic fronts where cross‐shelf gradients are markedly pronounced. Consequently, variations in cross‐shelf gradients may exert a significant influence on offshore transport; however, this influence is not yet well understood. This study employs reconstructed daily suspended sediment concentration (SSC) data from the Yellow Sea's offshore region to investigate the dynamics of offshore transport. Our analysis on an interannual scale shows that offshore SSC correlates more with temperature gradients at the oceanic front than with winter storms, despite the latter's vital role in causing frontal instability. The observed increase in offshore transport over the past two decades is likely connected to Kuroshio Current warming, which has strengthened the horizontal density gradient at the oceanic front, driving the strengthened offshore transport of coastal sediments during instability episodes. [ABSTRACT FROM AUTHOR]

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

As one kind of submesoscale instabilities, symmetric instability (SI) with spatiotemporal scales of O (100) m–O (1) km and O (1) hour exerts significant effects on vertical material transports and forward energy cascade in the ocean. The potential vorticity (PV) is an important conservative parameter controlling quasi‐geostrophic flows, whose budget can be modulated by SI. However, due to the small spatial scale of SI which is hardly resolved by most current observations and regional models, how SI affects the PV budget and how big the effect is remain unclear. In this work, the effect of SI on the PV budget in the surface mixed layer (SML) of the Kuroshio Extension region is quantitatively analyzed based on high‐resolution simulations by applying an existing SI parameterization scheme. Compared with the case without SI effects, negative PV is found to be eliminated in the SML in the SI‐parameterized case. The negative‐PV likelihood in the SI‐parameterized case is decreased by up to 12% due to SI. Analysis of the PV budget indicates that SI contributes to the PV budget mainly by modulating the friction term. The friction term tends to generate negative PV but its magnitude is decreased by 35% due to SI. Apart from the frictional term, both advection and non‐adiabatic terms are also found to be modulated by SI. This work sheds light on the contribution of SI in the PV budget in the ocean mixed layer and suggests a significant role of SI in quasi‐geostrophic PV dynamics. Plain Language Summary: Potential vorticity (PV) is a conservative but dynamically active tracer and an important indicator to characterize instability in the ocean. Traditionally, PV is applied to quasi‐geophysical dynamics, such as large‐scale circulation (O (1,000) km) and mesoscale currents (O (100) km). As the link between meso‐ and micro‐scales, submesoscale symmetric instability with spatial scales of O (100) m–O (1) km contribute to the PV budget, potentially modulating the quasi‐geostrophic dynamics. This work quantitatively evaluates the effect of SI on the PV budget by applying a parameterization scheme. Key Points: The effect of symmetric instability (SI) on potential vorticity is evaluated by applying a parameterization schemeElimination of negative potential vorticities is mainly caused by the friction effect with magnitude decreased by 35%The advection and non‐adiabatic effect are also found to be modulated by SI [ABSTRACT FROM AUTHOR]

Long-term cross-correlational structures are examined for pairs of sea surface temperature anomalies (SSTAs) and advective forcing parameters and sea surface height anomalies (SSHAs) and current velocity anomalies (CVAs) in the East/Japan Sea (EJS); all these satellite datasets were collected between 1993 and 2023. By utilizing newly modified detrended cross-correlation analysis algorithms, incorporating local linear trend and local fluctuation level of an SSTA, the analyses were performed on timescales of 400–3000 days. Long-term cross-correlations between SSTAs and SSHAs are strongly persistent over nearly the entire EJS; the strength of persistence is stronger during rising trends and low fluctuations of SSTAs, while anti-persistent behavior appears during high fluctuations of SSTAs. SSTA-CVA pairs show high long-term persistence only along main current pathways: the zonal currents for the Subpolar Front and the meridional currents for the east coast of Korea. SSTA-CVA pairs also show negative long-term persistent behaviors in some spots located near the coasts of Korea and Japan: the zonal currents for the eastern coast of Korea and the meridional currents for the western coast of Japan; these behaviors seem to be related to the coastal upwelling phenomena. Further, these persistent characteristics are more conspicuous in the recent decades (2008~2023) rather than in the past (1993~2008). [ABSTRACT FROM AUTHOR]

The establishment of a global ocean assimilation system is of great significance for the utilization of observational data. In this study, a new global ocean assimilation system was established using the EAKF assimilation module and the MPI-OM global ocean circulation model with a grid refining the South China Sea (SCS) and part of Pacific region. Considering computational cost, static ensemble was utilized as the background ensemble. To assess the role of static ensembles, three different static ensembles were selected to compare assimilation experiments. The assimilation of sea surface temperature (SST) and sea surface salinity (SSS), as well as Argo profiling data, was conducted. Firstly, the model performance of the assimilation system on a global scale was evaluated using the profile data, which can reduce the temperature and salinity biases by approximately 50%, resulting in a decrease of the globally-averaged temperature and salinity biases to 0.4 ℃ and 0.1 PSU, respectively. Considering about the specific of the grid, we focus on the SCS and the equatorial region. Comparison of buoy data with the model results indicates that assimilation significantly improves the simulation of the tropical thermocline, with correlation coefficients suggesting that the assimilation with seasonal static ensemble yields the best results. Secondly, the impact of different ensembles on the SCS where significant monsoon influence exists was investigated, revealing distinct differences in current field among the three assimilation experiments. For the experiments with background ensembles include information on seasonal variations, the assimilation improves the model's ability in reproducing the intrusion of the Kuroshio Current into the SCS. [ABSTRACT FROM AUTHOR]

Mesoscale wind stress perturbations induced by sea surface temperature (SST) perturbations have a feedback effect on the ocean by influencing air–sea heat and momentum fluxes. Unlike the thermal feedback mechanism, which is well understood, the momentum feedback still needs to be studied, especially the respective roles of divergent and rotational wind components. In this study, momentum feedback was examined using an ocean model and an empirical equation, which solved wind stress field perturbations from their divergence and curl estimated from time‐evolving downwind and crosswind SST gradients. Through several numerical experiments, it was found that both the divergent and rotational wind can induce positive and negative temperature changes at varying regions and depths. This modulating effect is weak, with a maximum SST change of about 0.4°C on average, but it can reach the deep ocean beyond 1000 m. [ABSTRACT FROM AUTHOR]

To understand the larval distribution, size variation, and stable isotope ratios of Japanese eel leptocephali in relation to the salinity front and their feeding ecology, larvae from 7 research cruises (2002–2013) in the North Equatorial Current (NEC) spawning area were examined. The smallest early‐stage larvae were distributed south of or near the salinity front, confirming that the salinity front is an important oceanic feature to understand spawning locations of the Japanese eel. Larger size larvae tended to distribute into higher latitudes. Transport to northern latitudes with their growth would facilitate transport into the Kuroshio region, but retention in the Subtropical Countercurrent (STCC) might be detrimental. Preleptocephalus isotope ratios reflected maternal ratios, but feeding‐stage leptocephali (8–56 mm) tended to have higher ∂15N values at lower latitudes typically in areas south of a salinity front. Feeding larvae quickly assimilate isotope ratios from the NEC after spawning and early growth. Large differences of ∂13C values of larvae between the NEC and STCC might vary with spatial baselines in the two currents. However, diel vertical migrations should be considered, because the isotope ratios in particulate organic matter distinctly depend on the depth. Comparisons among Japanese eel larvae and other taxa of leptocephali in the NEC illustrate the need for further studies on the trophic ecology of leptocephali. [ABSTRACT FROM AUTHOR]

Water exchange in the Luzon Strait (LS) is critical for layered circulation in the South China Sea (SCS); however, observational evidence of sandwich‐like water exchange is scarce. This study presents a comprehensive analysis of the meridional and zonal spatial patterns of water exchange in the upper and middle LS, along with its seasonal variations in a sigma–pi diagram using Argo profiles. As observed viewed from the perspective of SCS, inflow and outflow occur in the upper and middle layers, respectively. Upper‐layer Kuroshio intrudes into the SCS primarily in the northern and central regions of the LS, extending along the continental shelf into the inner SCS. A significant middle‐layer eastward outflow is evident at 26.7–27.56 kg/m3 (500–1,500 m) in the northern part of the strait, extending to 123°E. The Kuroshio intrusion intensifies during the winter, whereas the middle‐layer outflow is most pronounced in the autumn. Plain Language Summary: Understanding the circulation in marginal and inland seas is closely tied to comprehending the exchange of water between straits connecting neighboring oceans. The Luzon Strait, as a semi‐enclosed marginal sea, holds a pivotal role in shaping the layered circulation in the South China Sea. This study utilizes an extensive data set of Argo profiles to provide observational evidence of a layered zonal water exchange in the upper and middle Luzon Strait, offering detailed insights into the meridional and zonal patterns of water exchange and how they vary with the seasons. It reveals that inflow and outflow processes occur in the upper and middle layers observed viewed from the perspective of South China Sea, respectively. The upper‐layer intrusion of the Kuroshio is more prominent during the winter, while the middle‐layer outflow is most noticeable in the autumn. This research enhances our understanding of water exchange in the Luzon Strait and contributes to our knowledge of processes like water renewal, heat and salt budgets, and biogeochemical cycles in the South China Sea. Key Points: A novel insight into water exchange in the upper and middle Luzon Strait is provided using the sigma–pi diagramMeridional distribution of inflow (outflow) zonal water exchange in the upper (middle) Luzon Strait are describedUpper‐layer inflow was enhanced in winter, whereas middle‐layer outflow was significant during the autumn [ABSTRACT FROM AUTHOR]

The layered structure and seasonal variation of the water exchanges in the Sulawesi Sea areas, as well as the corresponding dynamics, are investigated using HYCOM data. A net inward water mass transport is identified in the upper and intermediate layers in the Sulawesi Sea and it is compensated by the net outward transport in the deep layer. As an important source of this net inward transport, the southward flow through the Sibutu Passage (denoted hereafter as Sibutu Flow) reaches 5.06 Sv in winter, accounting for ∼43% of the net inflow. However, it decreases substantially to 1.79 Sv in summer, accounting for only 12% of the inflow. Further analysis reveals that this Sibutu Flow modulates the seasonal variation of the corresponding outward flow at the Makassar Strait, the major exit of the water mass in the Sulawesi Sea. In winter, the enhancement of the Sibutu Flow associated with the greater intrusion of Kuroshio water into the Luzon Strait produces a stronger eastward pressure gradient force, suppressing the surface intrusion of the Mindanao Current. Conversely, this pressure gradient force weakens and shifts westward in summer, permitting a larger water intrusion from the eastern section. Given that the outward Makassar Flow is the main passage of the Indonesian Throughflow (ITF), our study highlights the essential role of the Sibutu Flow in modulating seasonal variabilities of the ITF via the Makassar Strait and, thus, the transfer of water masses and heat content between the Pacific and Indian Oceans. Plain Language Summary: The inward flows respectively through the Mindanao‐Sulawesi section (denoted hereafter as Min‐Sul Flow) and the Sibutu Passage (denoted hereafter as Sibutu Flow) bring water into the Sulawesi Sea, whereas the outward flow through the Makassar Strait (denoted hereafter as Makassar Flow) takes water out of the Sulawesi Sea. This forms a pathway of Indonesian throughflow and transports water mass from the Pacific to the Indian Ocean in the upper and intermediate layers. Our analysis on the relations among the transports through the three main entrances/exits of the Sulawesi Sea indicates that the transport by the Makassar Flow is significantly negatively (positively) correlated with that by the Sibutu Flow (Min‐Sul Flow). In contrast, the transport by the Sibutu Flow is highly negatively correlated with that by the Min‐Sul Flow. Further analysis reveals that the Sibutu Flow, which is associated with monsoon and intrusion of Kuroshio water into the Luzon Strait, modulates the Makassar Flow by suppressing the surface intrusion of Mindanao Current through the eastward pressure gradient force. Moreover, we found that this inhibition effect manifests a seasonal variation, that is, it is enhanced (weakened) in winter (summer), leading to a corresponding stronger (weaker) Makassar Flow. Key Points: The Sibutu pathway plays an important role in modulating the seasonal variation of the southward flow along the Makassar StraitThe surface intrusion into the Makassar Strait is suppressed in winter due to the intensification and eastward‐shifted pressure gradient forceThe water exchange between the upper/intermediate and deep layers of the Sulawesi Sea is revealed from the water volume budget analysis [ABSTRACT FROM AUTHOR]

Periodic eddies are a type of eddy that occur almost annually in fixed timeframes with similar patterns and trajectories. Nearly every year from April to June, under the combined effect of the barotropic instability of the mean flow and wind work, a cyclonic eddy (the Taiwan Cyclonic Eddy, TCE) forms in the southwest of Taiwan, then propagates westward, and finally dissipates near the Dongsha Islands. TCE exerts a significant impact on the Kuroshio intrusion into the South China Sea (SCS) and water exchange. Based on multi‐year in situ and satellite observations, this study reveals the thermohaline structure and evolutionary process of the TCE. The evolutions of the three‐dimensional structures of temperature, salinity, and geostrophic velocity of the TCE are analyzed based on reconstructed data. The TCE shows important interannual variations associated with El Niño–Southern Oscillation (ENSO), and the relationship between ENSO and the TCE is modulated by the Pacific Decadal Oscillation (PDO). In the negative phase of the PDO, the intensity of the TCE is significantly correlated with the Niño‐3.4 index. In contrast, in the positive phase, the ENSO–TCE relationship becomes weak and non‐significant. Further investigations indicate that these differences are related to the establishment of the low‐latitude Pacific–East Asian Teleconnection, influencing local wind stress curl in the region. This offers a new perspective on understanding the interannual variation of periodic mesoscale eddies in the SCS. Plain Language Summary: The Taiwan Cyclonic Eddy (TCE) represents a significant periodic mesoscale eddy in the South China Sea (SCS), demonstrating annual occurrences and profound impacts on regional oceanography and climatological dynamics. This study expands on multi‐year in situ and satellite observations to elaborate the three‐dimensional thermohaline structure and dynamic behavior of the TCE, emphasizing its seasonal consistency and interannual variability influenced by major climatic oscillations such as El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). The TCE's formation is primarily driven by the instability of the background current and significant wind forcing. Its interannual variation shows a non‐stationary relationship with ENSO, which is significantly modulated by the PDO. The study enhances our understanding of the interannual dynamics of the TCE by highlighting how shifts in large‐scale climatic conditions can directly alter the local structural and dynamic characteristics of the eddy. Understanding the TCE's formation and variation is vital as it affects water exchange in the SCS, and thus influences local marine ecosystems in the region. By studying this phenomenon, scientists can better predict the impacts of such eddies on marine and climatic environments. Key Points: The Taiwan Cyclonic Eddy (TCE) forms annually from April to June southwest of Taiwan due to current instability and wind forcingMulti‐year observations show the TCE has significant vertical extensions and temperature/salinity anomalies, impacting local conditionsThe TCE's evolution is tied to El Niño–Southern Oscillation and influenced by Pacific Decadal Oscillation phases, being stronger in negative phases due to enhanced teleconnections and wind adjustments [ABSTRACT FROM AUTHOR]

The Kuroshio Loop Current (KLC) is an important form of Kuroshio intrusion into the northeastern South China Sea (NESCS), which has significant influences on dynamical and biogeochemical processes in the NESCS. Recent studies suggested that the KLC is a hot spot of submesoscale processes (submesoscales) with spatiotemporal scales of O(1–10) km and O(1–10) days, but submesoscales' roles in energy cascade and salt and heat transports remain obscure. Here, we investigate this issue through analyzing outputs from a 1/48° simulation. The kinetic energy exchange rate between submesoscale and larger‐scale processes (KER) is overall positive in the KLC region, which suggests the dominance of forward cascade. The magnitude of KER is comparable with the temporal change rate of larger‐scale kinetic energy in the upper 200 m. We also find that magnitude and direction of KER are closely associated with strain rate and horizontal divergence of background flows, respectively. In addition, the KLC region shows elevated submesoscale salinity and heat diffusivities with magnitudes reaching O(102) m2 s−1. During the KLC period, horizontal mixing by submesoscales can transport 0.90 × 1013 kg salt and 0.71 × 1020 J heat westward into the NESCS interior, which are an order of magnitude larger than those caused by the mesoscale eddy shedding from the KLC. These results suggest that submesoscales play important roles not only in energy cascade but also in salt and heat transports in the KLC region. Therefore, the roles of submesoscales should be taken into account when studying energy, salt, and heat budgets in the NESCS. Plain Language Summary: As the western boundary current of the North Pacific subtropical gyre, the Kuroshio can intrude into the northeastern South China Sea (NESCS) in the form of Kuroshio Loop Current (KLC), which modulate the tracer and energy budgets of NESCS through shedding eddies. Although previous studies have reported that the KLC region is abundant with submesoscale processes (submesoscales) with spatiotemporal scales of O(1–10) km and O(1–10) days, their roles in cross‐scale energy transfer and salt and heat transports are poorly known. Here, the above issues are examined through an analysis of outputs from a 1/48° ocean simulation. We find that larger‐scale processes generally feed submesoscales through a forward energy transfer in upper 200 m, whose rate is comparable in magnitude with the temporal change rate of larger‐scale kinetic energy. Furthermore, the horizontal mixing effect of submesoscales can transport a huge amount of heat and salt westward into the NESCS interior during the KLC period. The salt and heat transports are an order of magnitude larger than those caused by the mesoscale eddy shedding from the KLC. The above results suggest that submesoscales associated with the KLC play important roles in the energy, heat, and salt budgets in the NESCS. Key Points: Submesoscales in the Kuroshio Loop Current (KLC) are examined using high‐resolution simulation outputsEnergy exchange between submesoscales and KLC plays an important role in the local energy budgetHorizontal salt and heat transports by submesoscales are much larger than those by mesoscale eddy shedding from the KLC [ABSTRACT FROM AUTHOR]

The East China Sea (ECS) is one of the largest marginal seas in the world with high primary productivity and a large area of low dissolved oxygen. This study observed the low‐oxygen bottom water on the outer‐edge shelf of ECS in summer seasons of 2018–2020. The contributions of various water masses to low‐oxygen waters were quantified, and the interaction between low‐oxygen water and Kuroshio water was validated by a mixing model using heavy rare earth elements (HREEs) together with potential temperature, and salinity. For further reliability verification, tracers such as δ34S and 226Ra were additionally utilized to avoid the non‐conservative processes on the shelf area. The low‐oxygen water on the shelf was clarified to be linked to the inner/middle shelf water, and dominated by Kuroshio Subsurface Water (KSSW, 81% ± 3%) and influenced by a non‐negligible extent of pore water (3.0% ± 0.5%). Our findings revealed the transport of low‐oxygen water from the outer‐shelf edge to the Kuroshio area, whose dissolved inorganic nitrogen and dissolved inorganic phosphorus contributions to Kuroshio were 34%–82% and 35%–83%, respectively. The nutrients of low‐oxygen water were regulated primarily by the origins of water and secondarily by organic matter remineralization (DIN: ∼17% and DIP: ∼24%). As control factors, the tide, especially spring tide largely enhanced the water contribution of pore water to low‐oxygen water by 67%, and the El Niño‐Southern Oscillation potentially affected the contributions of KSSW and mid‐shelf water to low‐oxygen water. Plain Language Summary: The significant expansion of low‐oxygen area is a growing concern in the East China Sea (ECS). In the summer of 2018–2020, we identified and quantified the origins of low‐oxygen bottom water on the outer‐edge shelf of ECS. Using multi‐chemical tracer approaches, we found that Kuroshio Subsurface Water (KSSW) was the primary contributor, while mid‐shelf water, and pore water were found to have a non‐negligible contribution to low‐oxygen bottom water. Additionally, the transport of low‐oxygen water to the Kuroshio was confirmed. The contribution of pore water was revealed to increase significantly during spring tide, and the contributions of major water sources (KSSW and mid‐shelf water) had an enhanced variability under El Niño‐Southern Oscillation (ENSO) events. These results suggested that the effects from tide and ENSO events on low‐oxygen water should get more attention. Low‐oxygen phenomena are being intensified by global warming and strong stratification in other shelf seas/coastal seas. Our approaches and findings could provide additional and fresh ideas for future related studies in term of low‐oxygen water. Key Points: Low‐oxygen water on outer‐edge shelf of East China Sea was estimated using multiple chemical tracers with 9% ± 2% mid‐shelf water contributionPore water was first revealed to supply nutrients (∼10%) to low‐oxygen water, with an amplified water contribution (67%) under spring tideEl Niño‐Southern Oscillation possibly influenced the interannual variability in contributions of low‐oxygen water's main water masses (Kuroshio Subsurface Water and mid‐shelf water) [ABSTRACT FROM AUTHOR]

This study investigated the dynamic and thermal responses of cyclonic eddies (CEs) to Typhoon Surigae in the western North Pacific Ocean using satellite data and a coupled ocean–atmosphere model. Observations and simulations revealed that the typhoon enhanced the two preexisting CEs (C1 and C2). After the typhoon passed the two eddies, the sea surface height (SSH) lowered and the eddy velocity increased above 200 m. C1 was stretched with elliptical deformation accompanied by an SSH trough and jets on the sides of the typhoon track at the eddy edge. The comparative experiments indicated that the typhoon caused the SSH of C1 and C2 to lower by 53.52% and 25.14% compared to conditions without the typhoon, respectively, and the kinetic energy of C1 and C2 to increase by 12 times and 65.76%, respectively. The positive vorticity anomaly input from the typhoon to the CEs was the main mechanism for the enhancement of the CEs. The enhanced CEs modulated the typhoon-induced sea surface temperature (SST) cooling, causing the temperature within the eddies to decrease by upwelling and mixing, and the SST cooling became significant at the center of the CEs and propagated westward with the eddies. This study also revealed that typhoons can significantly perturb eddy dynamic structures by enhancing or generating cyclonic cold eddies and eradicating anticyclonic eddies, thereby weakening the Kuroshio Current transport via eddy–Kuroshio interactions. [ABSTRACT FROM AUTHOR]

The East China Sea Kuroshio (ECS‐Kuroshio) and the Ryukyu Current are the major poleward heat carriers in the North Pacific. Anomalous changes of ECS‐Kuroshio and Ryukyu Current could exert substantial influence on the climate in mid‐latitude regions. However, owing to limited observations and coarse resolution of climate models, how they might change under anthropogenic warming remains unknown. Here, we find an accelerating ECS‐Kuroshio (1.5 Sv) and a decelerating (−2.2 Sv) Ryukyu Current using in‐situ observation during 1958–2022, equivalent to 7% strengthening and 20% weakening in the 65 years. The trend is also simulated by four high‐resolution climate models, with multi‐model ensemble‐mean acceleration (deceleration) of the ECS‐Kuroshio (Ryukyu Current) of 1.2 ± 0.6 Sv (−6.2 ± 2.5 Sv) over 1950–2050. The weakening subtropical wind field reduces their summed transport o. Enhanced stratification, which induces uplift of current system and weaker topography‐flow interaction, leads to the intensifying ECS‐Kuroshio and disappearing Ryukyu Current. Plain Language Summary: The East China Sea Kuroshio (ECS‐Kuroshio) and the Ryukyu Current are the major components of western boundary current (WBC) system in the North Pacific. They transport large amount of heat poleward, maintaining the mid‐latitude region warm and habitable. In this study, we find that in both observation and high‐resolution numerical models, the ECS‐Kuroshio is intensifying and the Ryukyu Current is rapidly declining. Particularly, in climate models, the Ryukyu Current is predicted to experience a 45% weakening during 1950–2050. Weakening wind field in the North Pacific tends to reduce the total transport of WBC system. The rapid weakening of the Ryukyu Current is credit to the enhanced stratification under global warming, which induces uplift of the Kuroshio east of Taiwan. Hence, less water will be blocked by bottom topography (Ilan Ridge) and bifurcates into the Ryukyu Current. Our finding highlights the needs for comprehensive studies on the local and climate effects of the evolution of the WBC system in the North Pacific. Key Points: The East China Sea Kuroshio is intensifying while the Ryukyu Current is rapidly declining in a warming climateThe change is mainly caused by enhanced stratification which induces uplift of current system and weaker topography‐flow interaction [ABSTRACT FROM AUTHOR]

Evaporation duct anomalies are always present above various oceanic processes, and their response to ubiquitous mesoscale eddies in the Kuroshio Extension region is quantitatively analyzed for the first time in this study using a synthetic analysis method based on reanalysis data sets and eddy trajectory data sets. The results indicated that the spatial distribution of evaporation duct anomalies is characterized by a monopole pattern, mainly modulated by the amplitude of anticyclonic eddies (AEs) and by the radius of cyclonic eddies (CEs). For AEs, the coupling strength is 0.7 m (2.9 M) per meter increase in amplitude, while for CEs, the coupling strength is 0.2 m (0.6 M) per 100 km increase in radius for the average evaporation duct height anomalies (evaporation duct strength anomalies) within the radius range. The modulation of evaporation duct anomalies by eddies is further examined. Plain Language Summary: Mesoscale eddies typically carry water with different characteristics from the surrounding environment, allowing them to transport moisture and energy at the ocean–atmosphere interface, thereby influencing the characteristic properties of evaporation ducts over the sea. To date, researchers have focused on the effects of various oceanic and atmospheric processes on evaporation ducts. However, there has been a persistent lack of research on the properties of evaporation ducts under the impact of mesoscale eddies. In this study, the variability in the evaporation duct environment under the influence of eddies and the underlying mechanisms are statistically analyzed. The results showed that ubiquitous mesoscale eddies could moderately modulate evaporation duct properties, which in turn could influence the effectiveness of shipborne radar technology, such as electromagnetic propagation, communication, and target detection. Key Points: The response of evaporation ducts to different eddy parameters is quantitatively determinedAnticyclonic (cyclonic) eddies with larger amplitudes (radii) exhibit stronger evaporation ductsAnticyclonic (cyclonic) eddies explain 5% (10%) of the total variance in evaporation duct properties [ABSTRACT FROM AUTHOR]

This study conducted sensitive and precise analyses of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) concentrations and trace concentrations of nitrate and nitrite (N+N) and soluble reactive phosphorus (SRP) in seawater. The methods were applied to investigate the distributions and controls of N+N, SRP, DON, and DOP in the oligotrophic Kuroshio Current (KC) area off eastern Taiwan during warm seasons. The water in the studied area was classified into four major types: typical Kuroshio water (KW), KW influenced by the East China Sea water, KC influenced by the South China Sea (SCS) water, and KW influenced by the SCS water and river plumes, which is confined to the coastal zone. Nutrient distributions in KC revealed very low N+N (0.002-0.40 mM) and SRP (0.015-0.125 mM) concentrations but high DON (<8 mM) and DOP (<0.3 mM) concentrations above the nutricline depth, which accounted for >80% of TDN and TDP, respectively; theses concentrations can primarily be attributed to strong, permanent surface stratification. Among the water types, KW had the lowest N+N, SRP, DON, and DOP concentrations but greatest chlorophyll maximum depth and nutricline depth, except for in locations influenced by island-induced upwelling. The concentrations of all nutrients increased by various degrees in the other water types, which was attributed to the exchange and mixing of different water masses and coastal uplift of subsurface waters. KW was not only highly oligotrophic but also N+N-limited reflected from very low [N+N]/[SRP] ratio (0.02-0.15) in the mixed layer (ML). Overall, the N+N limitation and high nitrate anomaly value (N*: 2.47 ± 0.16 mM) above the nutricline depth strongly indicate prevailing N2 fixation at the surface of KW. Very high DON/DOP ratio in KW (16.9-69.1) probably resulted from the release of N-rich organic nutrients from phytoplankton including N2 fixers at the surface and faster recycling of DOP than DON in deep waters. Persistent coastal uplift of subsurface water occurs everywhere over the shore-side region of the KC, resulting in increasing surface concentrations of nutrients and chlorophyll a. Overall, the aforementioned physical and biogeochemical processes determined the upper-ocean distributions of nutrient species in warm seasons. [ABSTRACT FROM AUTHOR]

The Pollution Nagasaki (PN) section of the East China Sea (ECS) is a typical area for studying the complex hydrographic dynamics between Changjiang River discharge and Kuroshio, displaying intense variations of environmental gradients from nearshore to offshore. However, the temporal and spatial changes of microbial communities along the PN section have long been overlooked. In this study, we performed a comprehensive investigation into the abundance, diversity and ecology of free-living (FL) and particle-associated (PA) microbial communities in seawater samples along the PN section during both summer and winter. Distinct hydrological conditions and resulting environmental gradients were observed between summer and winter, with clear features of intrusive Kuroshio subsurface water in summer and strong vertical mixing of seawater in winter. Bacterial abundance along the PN section was higher in summer (1.11  ×  108 copies·L−1 – 7.37  ×  108 copies·L−1) than in winter (1.83  ×  106 copies·L−1 – 1.34  ×  108 copies·L−1). Microbial diversity, as indicated by α-diversity indices, remained at relatively stable levels in summer, while a clear decreasing trend was observed in winter along the PN section. Additionally, the winter communities exhibited a more evident spatial shift along the PN section compared to the summer communities. 16S rRNA gene amplicon sequencing showed that microbial community composition varied considerably between different seasons (summer and winter) and lifestyles (FL and PA), with a notable dominance of Ralstonia species. in winter. Regarding the assembly of microbial communities, the stochastic process represented by dispersal limitation was the dominant process in summer, while the deterministic homogeneous selection was the most important process in winter. Correspondingly, distinct topological properties of the microbial co-occurrence networks were shown between different seasons and along the PN section. These results enhance our understanding of how hydrological conditions influence dynamic changes of microbial communities along the PN section, providing new insights for the microbial community assembly and interactions in such a complex environment. [ABSTRACT FROM AUTHOR]

The anticyclonic eddies (ACEs) shed from the Kuroshio intrusion often interact with internal waves (IWs). Those interactions are complex but play an important role in the biogeochemical effects in the northern South China Sea (SCS). However, previous studies on these interactions have mainly focused on physical processes, while biological responses to their interactions have been unclear. In this study, results of two field cruises with focus on two sets of high-frequency time-series observations over the continental slope of the SCS during the summers of 2016 and 2017 revealed that phytoplankton in the euphotic zone were affected by both IWs and ACEs shed from the Kuroshio Current. Distinct surface distributions of phytoplankton were attributable to different sources of the water, Kuroshio intrusions and the plume from the Pearl River. However, similarities of phytoplankton biomass and community composition in the subsurface chlorophyll maximum layer in both years could be explained by the similar upward transport of nutrients induced by combinations of small-amplitude IWs and mature ACEs in 2016 and large-amplitude IWs in 2017. The distinct vertical distributions of the phytoplankton community in both years were attributable to the different responses of phytoplankton groups to the direct effects of isopycnal uplifting, bottom-up controls, and top-down controls. Our results showed that the ecological effects of the interactions between IWs and ACEs shed from the Kuroshio water were complex, and those complex effects further influenced the structure of this marginal sea ecosystem. [ABSTRACT FROM AUTHOR]

An adjoint-free four-dimensional variational (a4dVar) data assimilation (DA) is implemented in an operational ocean forecast system based on an eddy-resolving ocean general circulation model for the Northwestern Pacific. Validation of the system against independent observations demonstrates that fitting the model to time-dependent satellite altimetry during a 10-day DA window leads to substantial skill improvements in the succeeding 60-day hindcast. The a4dVar corrects representation of the Kuroshio path variation south of Japan by adjusting the dynamical balance between amplitude/wavelength of the meander and flow advection. A larger ensemble spread tends to reduce the skill in representing the observed sea surface height anomaly, suggesting that it is possible to use the ensemble information for quantifying the forecast error. The ensemble information is also utilized for modification of the background error covariance (BEC), which improves the accuracy of temperature and salinity distributions. The modified BEC yields the skill decline of the Kuroshio path variation during the 60-day hindcast period, and the ensemble sensitivity analysis shows that changes in the dynamical balance caused by the ensemble BEC result in such skill deterioration. [ABSTRACT FROM AUTHOR]

From 2001 to 2020, three typhoons with similar moving paths and intensities were found to trigger markedly different cooling off northeastern Taiwan. They were typhoons Utor (2001), Nuri (2008), and Hagupit (2008), which led to maximum sea surface temperature (SST) cooling temperatures of 8.8, 2.7, and 1.4 °C, respectively. The drastic cooling discrepancy implies that the existing understanding of the key mechanism leading to the cooling off northeastern Taiwan could be insufficient. For further exploring the key reason(s) contributing to the marked discrepancy, a regional oceanic modeling system (ROMS) was used to reconstruct the background oceanic environment corresponding to three typhoon passages. Results show that the wide radius of maximum winds of typhoon Utor contributes to the strongest SST cooling by enhancing the Kuroshio intrusion (KI) onto the shelf northeast of Taiwan. Heat budget diagnostics explain why including tidal forcing can substantially promote SST cooling. The process was associated mainly with a stronger vertical advection tied to the influence of de-stratification by tidal mixing. Finally, warmer Taiwan Strait currents, driven by wind forcing the typhoons to pass zonally through the north South China Sea, intruded clockwise into the Longdong coast and accelerated the recovery of sea surface cooling around Longdong. [ABSTRACT FROM AUTHOR]

The present study investigates characteristics and origins of the intraseasonal oscillation (ISO) contributing to the extreme rainfall in Henan Province, China in July 2021. Significant 10–30-day and 30–60-day ISOs feature the extreme rainfall in Henan and jointly account nearly 52% for the total rainfall from 17 to 22 July. The related intraseasonal low-level circulations exhibit a meridional dipole pattern with a cyclonic anomaly over the western North Pacific and an anticyclonic anomaly over the Northeast Asia, which originate from the tropical and mid-to-high latitude ISO forcings in the upper and lower level. While the northwestward/northward-propagating Boreal Summer ISO (BSISO) and the mid-to-high latitude wave train contribute to the southern and northern nodes of the dipole pattern, respectively, the preceding cold sea surface temperature (SST) anomaly over the Sea of Japan and Kuroshio Extension region further strengthens the northern node through stabilizing the atmosphere and suppressing the convective activity. It is noteworthy that the concurrence of the 30–60-day BSISO and the mid-latitude SST anomaly could facilitate the BSISO convection to propagate further north and intrude the mid-latitude region. This unique relationship is infrequent in the past forty years with an occurrence probability of only 7.8% and tends to occur under the warmer-than-normal SST mean state in the mid-latitude North Pacific. The present study highlights the influence of the mid-latitude SST anomaly involved in the intraseasonal air-sea interaction, which may also be a potential precursor for the subseasonal prediction of the extreme rainfall in Henan. [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs) are oceanic conditions characterized by extremely high sea surface temperature (SST) anomalies that last for several days to years. Because MHWs have devastating effects on marine ecosystems and significant impacts on fisheries, understanding future MHWs is important for adapting to upcoming climate changes. In this study, we examined future changes in MHWs in the northwestern Pacific Ocean (18–53ºN, 117ºE–170ºW) under two CO2 emission scenarios using a high-resolution ensemble (four members for each scenario) simulation product using a high-resolution ocean model that satisfactorily resolves the Kuroshio, Kuroshio Extension, and SST fronts. Following global warming, MHWs based on a threshold in the historical period (1981–2005) will increase and intensify (i.e., occur with higher SST anomalies than before). In the historical period, the annual MHW days ranged from 20 to 34 days. Annual MHW days increase to 63–313 days (188 days–all year round) depending on the region under the high CO2 mitigation (emission) scenario at the end of the twenty-first century of 2076–2100. Furthermore, we investigated the spatial details of future MHWs. Future MHWs reflect the magnitude of SST variability in addition to that of sea surface warming in the twenty-first century; future MHWs are less frequent and more intense in the subtropical–subarctic frontal zone with large SST variability than in other regions. [ABSTRACT FROM AUTHOR]

During August 2017, the Kuroshio began to follow its large meander (LM) path, and this was 12 years after the last LM event. Such LM events lead to the formation of an inshore cyclonic eddy (ICE) within the Kuroshio inshore region between the Kuroshio and the southern coast of Japan. We analyzed data from repeated seasonal surveys along a transect that followed 138°E, and from additional surveys, satellite observations, Argo floats, and a high-resolution reanalysis dataset to describe the temporal variation of the LM and ICE between 2017 and 2021. Cross sections from the repeated surveys highlighted the variations in the water mass structures. The time series of the indicators of the ICE intensity such as the Kuroshio volume transport and the planetary contribution of potential vorticity (Q) in the ICE revealed a maintenance trend in their intensity during the observation period. High-Q water was distributed in the ICE during the LM period compared to the non-LM period, and showed a clear seasonality within the shallower layers, suggesting the injection of Q via the advection from the upstream region in summer. Additional surveys captured an eddy that became detached from the ICE during summer 2020. This detached eddy had a Q value greater than the ICE and velocity similar to the Kuroshio, suggesting that the main stream had become temporarily separated. The structures and volume transport of warm water intrusions into the inshore region were also examined, and centrifugal instability was considered to be one of their generation mechanism. [ABSTRACT FROM AUTHOR]

Submesoscale processes significantly influence the air‐sea interaction, heat budget and the distribution of physical and biogeochemical tracers in the upper‐ocean. We study the spatiotemporal characteristics and generation mechanisms of submesoscale vertical heat transport (SVHT) at the Kuroshio Extension using a submesoscale‐permitting simulation. Compared with the commonly used Boxcar and Hanning filters, the clean‐cut feature of the Butterworth filter in the wavenumber domain makes it a proper filter to diagnose SVHT. SVHT is systematically upward, peaking in winter. Through causality analysis, we find that, among the basic factors (mixed layer depth, strain rate, surface wind stress, and horizontal buoyancy gradient) from the conventional submesoscale generation mechanism scalings, mixed layer depth plays the leading role in modulating the intraseasonal variation of SVHT. Using the budget of submesoscale temperature variance and causality analysis, we find that advection also plays an important role in regulating SVHT. This work suggests that the choice of appropriate spatial filter is important for SVHT diagnosis and including advection may help improve submesoscale parameterization schemes. Plain Language Summary: Ocean currents with horizontal spatial scales of O(0.1–10) km and temporal scales of hours‐days are defined as submesoscale processes. Submesoscale processes are characterized by large vertical velocity, driving significant vertical heat transport. In this study, we investigate the spatiotemporal features of submesoscale vertical heat transport (SVHT) and the corresponding mechanisms in the Kuroshio Extension region using a high‐resolution numerical simulation. We find that the diagnostics of SVHT is sensitive to the extraction method of submesoscale processes based on spatial scales. SVHT is systematically upward with pronounced seasonal variability, reaching its peak in winter. The intraseasonal variation of SVHT is controlled by multiple factors simultaneously, among which the mixed layer depth plays the most important role. Advection also has influence on SVHT variability. This study offers a better understanding of the dynamic mechanisms driving SVHT, while also highlights the importance of proper filter selection in SVHT diagnostics. Key Points: The estimation of submesoscale vertical heat transport is sensitive to the choice of spatial filterAmong the conventional factors, mixed layer depth is the top regulator of the submesoscale vertical heat transport intraseasonal variationThe advection process can also modulate the intraseasonal variability of submesoscale vertical heat transport [ABSTRACT FROM AUTHOR]

Off the east shore of China, thermal front plays a crucial role in modulating coastal biogeochemical environment. Based on multi‐source observational and reanalysis products, decadal variation and regulatory mechanism of Zhejiang‐Fujian coastal front (ZFCF) were investigated. The intensity of ZFCF showed a two‐stage inversed varying trend over past four decades: a downtrend from 1982 to 2002 followed by an uptrend from 2002 to 2022. During 1982–2002, sea surface temperature (SST) experienced more pronounced warming in inshore areas than offshore due to weakening of the southward coastal current, and this primarily led to the downtrend of ZFCF. Within 2002–2022, opposite SST trends were observed on two sides of ZFCF, that is, the ZFCF kept intensifying due to the cooperation of cooling inshore and warming offshore. The enhanced coastal current driven by stronger monsoon and increased Yangtze River discharge cooled the inshore area, then the cooling was further facilitated by intensified heat loss in the upper layer of the plume. Meanwhile, the onshore shift of Kuroshio led to strengthened intrusion of warm water into the East China Sea, heating the offshore side of ZFCF and thus intensifying the front. Plain Language Summary: Oceanic fronts delineate the boundaries of different water masses and, in coastal regions, front zones are closely associated with biological habitats and hydrodynamics. Located along the East China Sea (ECS), the Zhejiang‐Fujian coastal front (ZFCF) is a region of high biological production, and the famous Zhoushan fishing ground is in that front zone. In this study, we found the ZFCF showed significant decadal variations based on 40 years of satellite observations of sea surface temperature: the intensity of ZFCF exhibits a negative trend during 1982–2002 and a positive trend during 2002–2022. These processes were primarily driven by the combined effects of the terrigenous runoff, coastal current and the Kuroshio Current, with the latter two factors closely related to the variabilities of local winds. The current study provides critical insights into the long‐term change of the ZFCF and we aim to better understand the coastal environments in the ECS. Key Points: Zhejiang‐Fujian coastal thermal front kept weakening within 1982–2002 while intensifying during 2002–2022Weakened coastal current dominated the downtrend of front intensity in the context of global warmingEnhanced coastal current and increased runoff together with stronger westward intrusion of Kuroshio governed the uptrend of front intensity [ABSTRACT FROM AUTHOR]

Millennial‐scale nitrogen (N) cycling processes in marginal seas and their response to climate change have not been well understood. Here, we present high‐resolution (ca. 110 years) organic nitrogen isotope (δ15Norg) data since the last deglaciation (16.1 ka) derived from a highly resolved sediment core in the northern South China Sea, aiming to explore millennial‐scale N cycling processes in this area. Unlike most bulk nitrogen isotope (δ15Nbulk) records from the South China Sea, the δ15Norg records show a clear response to well‐defined climatic episodes during the last deglaciation and early Holocene (EH, ∼11.7 to 9 ka), but exhibit a gradually decreasing trend in mid‐to‐late Holocene (since ca. 9 ka). During the last deglaciation and EH, the upper water column N dynamics are controlled by the lateral transport of surface nitrate from eastern tropical Pacific (ETP) presumably via the North Pacific Intermediate Water (NPIW) and to some extent, influenced by the altered input of terrigenous matter driven by sea level change. The significant decrease in δ15Norg since the mid‐Holocene (at ca. 9 ka) can be best explained by the increase in local N2 fixation forced by enhanced El Niño. This mechanism is consistent with modern observations. Overall, our results may reflect the main controlling factors of surface ocean N dynamics have shifted from zonal transport of nitrate from the ETP to El Niño since the mid‐Holocene. Plain Language Summary: The South China Sea (SCS) is an ideal area in which to study past changes in the low‐latitude oceanic nitrogen (N) pool using sedimentary N records. However, reconstructions of past oceanic N cycling in the SCS based on different δ15N proxies reveal distinct characteristics through the last deglaciation. Based on sedimentary organic nitrogen isotopic values, our results show that there is a clear response to well‐defined climatic episodes over the last 16.1 ka. Global mean ocean nitrate δ15N change, mainly through the NPIW intrusion, is the primary control of upper water column N dynamics during climate episodes of the last deglaciation and EH, while the strengthened N2 fixation (via the Kuroshio Intrusion into the SCS) forced by the El Niño is proposed as the main cause for the significant decrease in δ15Norg since the mid‐Holocene. Key Points: Sedimentary δ15Norg records the millennial‐scale changes in the N dynamics of the northern South China Sea and shows clear response to typical climatic episodesN dynamics during the last deglaciation and early Holocene are forced by the transport of nitrate signal from eastern tropical Pacific via the intrusion of North Pacific Intermediate WaterA significant decrease in δ15Norg since the mid‐Holocene can be best explained by enhanced N2 fixation forced by El Niño [ABSTRACT FROM AUTHOR]

Dinoflagellate is one of the most diverse and pervasive protists and a fundamental player in the marine food web dynamics and biogeochemical cycles. While possessing different nutritional strategies from purely autotrophy or heterotrophy to mixotrophy, some of them are also known as toxic harmful algal bloom (HAB) formers over the world. Despite their ordinariness, their diversity and biogeography are understudied in the open ocean compared with coastal region. As the first metabarcoding survey covering the Kuroshio current region from the offshore of Okinawa to the south of Honshu, we investigated the distribution of free-living dinoflagellates using the hypervariable V4 and V9 regions on 18S rRNA and their relation to ambient environments influenced by this oligotrophic but highly productive current in the northwest Pacific Ocean. We observed community structures differentiated by depth and nutrient concentrations. Most species annotated are autotrophic or mixotrophic and had a distribution correlated to warmer surface water, whereas heterotrophic species correlated to high nutrient levels or deeper layer. Our results also confirmed the overall high genetic diversity of dinoflagellates that decreased with depth and onshore. Most species present at stations offshore, and the relative abundance of HAB assemblages was lower at nutrient-rich stations on the continental shelf than stations influenced by the Kuroshio current, exhibiting the role of the Kuroshio transporting dinoflagellates including HAB species. To fully understand the dynamics of dinoflagellate communities in marine ecosystems, further seasonal monitoring is foremost for correlating dinoflagellates and environmental factors while completing the reference genomic database. [ABSTRACT FROM AUTHOR]

We demonstrate the key role of off-equatorial subsurface temperature anomalies in driving the phase transition of Tropical Pacific Decadal Variability (TPDV) using observation and model experiments. During the positive phase of TPDV, anomalous atmospheric responses in the off-equatorial northwestern Pacific induce positive Ekman pumping. The resulting negative subsurface temperature anomaly generated then propagates along the North Equatorial Countercurrent pathway towards the central basin, causing a sign reversal of the equatorial sea-surface temperature anomalies around three years later. Moreover, the positive phase of TPDV possibly changes the state of the Kuroshio Extension through tropical-extratropical interaction, which subsequently projects onto the footprint of the Pacific Meridional Mode, thereby amplifying subsurface-produced disturbance 0–12 months before the cold peak phase. The cold phase is completely established after five years. Similarly, the same dynamic applies to the reversed phase, leading to a preferred decadal oscillation driven by off-equatorial subsurface temperature anomalies and extratropical-tropical ocean-atmosphere interaction. [ABSTRACT FROM AUTHOR]

Aim: Plants distributed between southern Taiwan and the north of the Philippines are spread among numerous small islands in an area crossed by the powerful Kuroshio current. Oceanic currents can be effective seed-dispersal agents for coastal plant species. Moreover, the Luzon Strait is an area prone to tropical cyclones. The aim of this study is to look at the dispersal capability of an endangered coastal plant species, the Mearns fig (Ficus pedunculosa var. mearnsii), using both experimental and population genetics methods. Location: Southern Taiwan, the Philippines, and the islands between Luzon and Taiwan Island. Methods: This study combined two types of analysis, i.e., buoyancy experiments on syconia and double digest restriction-associated DNA sequencing (ddRAD), to analyze the population genetics of the Mearns fig. Results: We first discovered that mature Mearns fig syconia could float in seawater. They have a mean float duration of 10 days to a maximum of 21 days. Germination rates varied significantly between Mearns fig seeds that had undergone different durations of flotation treatment. Population genetic analysis shows a high degree of inbreeding among various Mearns fig populations. Moreover, no isolation by distance was found between the populations and individuals. Main conclusions: From our analysis of the genetic structure of the Mearns fig populations, we can clearly highlight the effect of the Kuroshio oceanic current on the seed dispersal of this fig tree. Comprehensive analysis has shown that Mearns fig seeds are still viable before the mature syconium sinks into the seawater, and so they could use the Kuroshio Current to float to the current population locations in Taiwan. [ABSTRACT FROM AUTHOR]

Kuroshio intrusion (KI) is a key process that transports water from the western Pacific Ocean to the northern South China Sea (nSCS), where KI-induced surface water mixing often causes variations in microbial assemblages. Yet, how interannual KIs affect the biogeography of diazotrophs and associated environmental factors remains poorly characterized. Here, by quantifying the degree of KIs in 2 consecutive years, coupled with monitoring the diversity and distribution of nitrogenase-encoding nifH phylotypes with quantitative PCR and high-throughput sequencing, we show that changes in the diazotrophic community structure in the nSCS are highly correlated with KI-induced variations in a range of physicochemical parameters. Specifically, the filamentous cyanobacteria in the genus Trichodesmium were more abundant at stations strongly affected by KI and thereby with a deeper mixed layer and higher surface salinity and temperature; the unicellular N 2 -fixing cyanobacteria in group B (UCYN-B) were more abundant at stations least affected by KI and correlated with nutrient availability, whereas UCYN-C and the γ -proteobacteria were prevalent at stations moderately affected by KI. The neutral community model further demonstrated that dominant diazotrophic subcommunities were significantly affected by environmental factors in 2017 when KI was stronger compared to 2018 when KI retreated. Our analyses provide insightful evidence for the role of KI in shaping the diazotrophic community structure primarily as a stochastic process, implying a potential region-scale redistribution of diazotrophs and nitrogen budget, given that KIs are projected to intensify in a future warming ocean. [ABSTRACT FROM AUTHOR]

The Asian tiger mosquito, Aedes albopictus, is a significant public health concern owing to its expanding habitat and vector competence. Disease outbreaks attributed to this species have been reported in areas under its invasion, and its northward expansion in Japan has caused concern because of the potential for dengue virus infection in newly populated areas. Accurate prediction of Ae. albopictus distribution is crucial to prevent the spread of the disease. However, limited studies have focused on the prediction of Ae. albopictus distribution in Japan. Herein, we used the random forest model, a machine learning approach, to predict the current and potential future habitat ranges of Ae. albopictus in Japan. The model revealed that these mosquitoes prefer urban areas over forests in Japan on the current map. Under predictions for the future, the species will expand its range to the surrounding areas and eventually reach many areas of northeastern Kanto, Tohoku District, and Hokkaido, with a few variations in different scenarios. However, the affected human population is predicted to decrease owing to the declining birth rate. Anthropogenic and climatic factors contribute to range expansion, and urban size and population have profound impacts. This prediction map can guide responses to the introduction of this species in new areas, advance the spatial knowledge of diseases vectored by it, and mitigate the possible disease burden. To our knowledge, this is the first distribution-modelling prediction for Ae. albopictus with a focus on Japan. [ABSTRACT FROM AUTHOR]

Ocean currents play a role in both facilitating and impeding connectivity of marine organisms' populations, serving as key drivers and potential barriers. The emergence of Taiwan around five million years ago (Mya) impacted the Kuroshio Current which later shaped the distribution of marine organisms. In this study, we examined how the Kuroshio Current influenced the distribution and population divergence of the marine red alga Dichotomaria elegans (Galaxauraceae, Nemaliales). Through phylogenetic analysis, species delimitation, and morphological comparison of Taiwanese species, we determined its phylogenetic position relative to other species within the D. marginata complex of the genus Dichotomaria. We uncovered the hidden cryptic diversity within the D. marginata complex in Taiwan and proposed the new combinations D. elegans and D. latifolia based on Galaxaura elegans and G. latifolia. Genetic analysis based on three loci (mitochondrial cox2-3 and cox1, and plastid rbcL) from 32 locations across the Philippines, Taiwan, and Japan revealed three allopatric lineages within D. elegans. The first lineage is restricted to the northern Philippines and southern Taiwan, while the second has a broader latitudinal range along the Kuroshio Current. The third lineage is found in southeast Luzon, Philippines, close to the bifurcation of the North Equatorial Current, near the start of the Kuroshio Current. The divergence of the first two lineages during the mid-Pliocene (~3.7 Mya) coincided with the emergence of Taiwan, with the current dynamics accentuating their separation. The Kuroshio Current exhibited a dual impact on the biogeography of D. elegans: promoting the dispersal of the second lineage towards higher latitudes and preventing the first lineage from moving northward. Principal component analysis showed that habitat conditions and morphologies differed between the two D. elegans lineages. This study provides insights into the cryptic diversity of Dichotomaria in Taiwan, as well as the genetic divergence, biogeographical patterns, and ecological associations of D. elegans, highlighting the interplay of island formation and currents shaping the diversification of seaweeds in the Northwest Pacific Ocean. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System—Acoustic ranging combination technique (GNSS-A) is a seafloor geodetic observation technique that achieves an accuracy of centimetres by combining high-rate GNSS data with acoustic ranging. The technique determines the seafloor position by acoustic ranging between the sea surface and multiple seafloor stations, using GNSS data from the sea surface station. Here, the gradient state of the underwater sound speed structure (SSS) is a significant source of error. The open-source software GARPOS can reduce the effect from underwater gradient structures by retrieving the underwater disturbance as a parameter projected onto the sea surface and seafloor. To evaluate the effects of underwater disturbances, a quantitative comparison of the model parameters is necessary. In this study, we developed a representation method to evaluate features of the ocean field. Here, the expression method was described in the order of a formulation and an interpretation in the case of a 2-D cross-section and extension to the case of an actual 3-D field. This method makes it possible to evaluate SSS states in the GNSS-A observations. As an example, we showed the correlation between the anomaly of the expressed ocean state and the anomaly of the seafloor station position, showing that this expression method is an effective index for correcting bias errors. Additionally, we used the data from sites located in the Kuroshio area, a strong current near Japan, to show that the ocean state can be quantitatively interpreted using this expression method. [ABSTRACT FROM AUTHOR]

As the most significant interannual signal in the tropical Pacific, the influence of ENSO on the interannual variability in TC genesis location in the western North Pacific (WNP) has received much attention in previous studies. This paper mainly emphasizes the underlying SST factors independent of the ENSO signal and explores how they modulate interannual tropical cyclone genesis (TCG) latitude variability. Our study finds that the meridional sea temperature gradient (SSTG) between the Kuroshio Extension and the WNP still has a significant effect on the interannual variability in the TCG latitude after removing the effect of ENSO (r = 0.6). The interannual forecasts of the TCG latitude were effectively improved from 0.67 to 0.81 when the ENSO-independent SSTG and ENSO were regressed together in a multi-linear regression. We then propose an ENSO-independent physical mechanism affecting the TCG latitude. The equatorward (poleward) SSTG excited the positive (negative) Pacific–Japan telecorrelation pattern over the WNP, forming Rossby wave trains and propagating northward. A significant cyclonic vortex (anticyclonic vortex) with strong convective development (suppression) developed near 20° N, leading more TCs to the northern (southern) part of the WNP. These findings provide a new perspective for the prediction of the interannual variability in the TCG latitude. [ABSTRACT FROM AUTHOR]

The vertical buoyancy flux Bf under the turbulent thermal wind (TTW) balance B f TTW plays an important role in restratifying the surface mixed layer in winter. So far, most of the global ocean models are too coarse to resolve this process. In this paper, a scale-aware parameterization is proposed for B f TTW and implemented in a hierarchy of regional ocean simulations over the winter Kuroshio Extension with horizontal resolutions ranging from 27 to 1 km. The parameterization depends on the Coriolis parameter, model-simulated turbulent vertical viscosity, horizontal density gradient, and a scaling relationship to adjust for the effects of model horizontal resolution on the simulated horizontal density gradient. It shows good skills in reconciling the difference between B f TTW in the coarse-resolution simulations (27, 9, and 3 km) and in the 1-km simulation where B f TTW is well resolved. Furthermore, implementation of the parameterization improves the simulated stratification in the surface mixed layer in coarse-resolution simulations. [ABSTRACT FROM AUTHOR]

The Kuroshio occasionally carries warm and salty North Pacific Water into fresher waters of the South China Sea, forming a front with a complex temperature–salinity (T–S) structure to the west of the Luzon Strait. In this study, we examine the T–S interleavings formed by alternating layers of North Pacific Water with South China Sea Water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a free-floating wave-powered vertical profiling float to calculate the fine-scale parameters Turner angle, Tu, and Richardson number, Ri, we identified areas favorable to double-diffusion convection and shear instability observed in a T–S interleaving. We evaluated the contribution of double-diffusion convection and shear instabilities to the thermal variance diffusivity, χ, using microstructure data and compared it with previous parameterization schemes based on fine-scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu > 60; Ri < ¼). In particular, χ associated with salt finger processes was an order of magnitude higher (6.7 × 10−7 K2 s−1) than in regions where only velocity shear was likely to drive mixing (8.7 × 10−8 K2 s−1). [ABSTRACT FROM AUTHOR]

Marine particle dynamics and carbon export, involving extracellular polymeric substances (EPS) like transparent exopolymer particles (TEP) and Coomassie Brilliant Blue‐stained particles (CSP), are poorly understood. Although TEP adhesive properties may enhance carbon export by facilitating aggregate formation, their low density can also enhance particle suspension. Factors influencing TEP regulation of particle dynamics remain unclear. To investigate EPS contributions to particle dynamics, we investigated ratios of TEP to particulate organic carbon (POC) and of CSP to POC in suspended and sinking particles collected with marine snow catchers. Samples were collected in a subarctic region near Hokkaido during a spring phytoplankton bloom and in the oligotrophic, subtropical Kuroshio region. At Hokkaido, the mean TEP : POC ratio of sinking particles (0.075 μg Xeq. : μg C) was > 30× lower than in suspended particles (2.3), consistent with a model prediction of selective retention of buoyant TEP‐rich particles in the upper water column. In the Kuroshio region, sinking particles also contained fewer TEP than suspended particles; however, the TEP : POC ratio of sinking particles (1.0) was > 10× higher than at Hokkaido, suggesting that TEP constitute a significant carbon component of sinking particles. These findings indicate that TEP facilitate aggregation of high‐density particles and particle sinking in the Kuroshio region. Distributions of CSP : POC ratios between suspended and sinking particles resembled TEP : POC ratios in both regions, implying a significant contribution of CSP to particle dynamics. We propose that EPS have divergent effects on suspension and sinking of marine particles, which vary with particle composition and biogeochemical conditions. [ABSTRACT FROM AUTHOR]

The present-day climate (the recent 100–150 years) obviously constitutes the structure of a global intra-system rhythmic process with an individual rhythm of about 60 years. In turn, each of the rhythms is presented by the two climate phases of about 25–35 years characterized by qualitative differences: one phase is relatively continental, while the other is humid. Globality and quasi-synchronism of environmental changes are accompanied by planetary structures: the Global Atmospheric Oscillation (GAO) in the atmosphere and the Multidecadal Oscillation of the Heat content in the Ocean (MOHO) discovered relatively recently. Unexpected and rapid qualitative phase changes in the climate, which first focused attention in the mid-1970s of the last century, were titled "climate shifts". The revealed features of the present-day climate are of exceptional scientific and practical interest and deserve the development of methods for predicting the timing of the forthcoming climate shift. Arising unexpectedly and accompanied by rapid significant changes, these shifts identified the problem of understanding the nature and establishing the processes and mechanisms causing them. First of all, of interest are phase changes in the thermodynamic state of the climate system components: the ocean, atmosphere, and continents. As a result of the World Ocean (WO) thermohydrodynamics numerical modelling, it is shown that MOHO is localized in the layer of the main thermocline, where the most important elements of the WO circulation are located. The performed study based on observational data allows us to conclude that, during the phase of the WO thermal discharge (1975–1999), the two key systems of currents, the Kuroshio and the Gulf Stream, were under similar thermodynamic conditions. [ABSTRACT FROM AUTHOR]

Investigating latent heat flux (LHF) variations in the western boundary current region is crucial for understanding air–sea interactions. In this study, we examine the LHF trend in the East China Sea Kuroshio Region (ECSKR) from 1959 to 2021 using atmospheric and oceanic reanalysis datasets and find that the LHF has a significant strengthening trend. This strengthening can be attributed to sea surface warming resulting from the advection of sea surface temperatures. More importantly, the LHF trend has an apparent seasonal dependence: the most substantial increasing trend in LHF is observed in spring, while the trends are weak in other seasons. Further analysis illustrates that the anomaly of air–sea humidity difference plays a pivotal role in controlling the seasonal variations in LHF trends. Specifically, as a result of the different responses of the East Asian Trough to global warming across different seasons, during spring, the East Asian Trough significantly deepens, resulting in northerly winds that facilitate the intrusion of dry and cold air into the ECSKR region. This intensifies the humidity difference between the sea and air, promoting the release of oceanic latent heat. These findings can contribute to a better understanding of the surface heat budget balance within western boundary currents. [ABSTRACT FROM AUTHOR]

North Pacific subtropical mode water (NPSTMW) is formed as a low-stratification water mass in the wintertime mixed layer south of the Kuroshio Extension (KE). In a recent period of 2018–2021, the KE jet was in a persistent stable dynamic state. But based on analysis of Argo observation, the mean volume of NPSTMW in the ventilation region dropped anomalously by ∼ 21 % during 2018–2021 relative to 2012–2015, when the KE jet was likewise stable. Moreover, the NPSTMW volume in a denser density range (approximately σθ>25.2 kg m -3) has started to decrease since 2018. The decreases in the NPSTMW subduction and formation rate are associated with anomalously shallow wintertime mixed-layer depth (MLD) and weak heat loss in the NPSTMW formation region. The decrease in air–sea heat exchange acts to weaken the vertical mixing and decrease the MLD, resulting in the weakening of subduction. The interannual variations in the air–sea heat exchange and wintertime MLD reflect the variability in the overlying atmosphere, which is correlated with a Pacific Decadal Oscillation (PDO) shift in 2018–2021. When the PDO shifted from its positive phase to a negative phase in the analysis period, the effects of local wind stress anomalies seemed to play an evident role in driving the variability in NPSTMW on interannual timescales. The MLD and heat loss change during the cold season in 2018–2021 were strongly coupled with the poleward shift of the westerlies – which cause weaker wintertime wind and easterly wind anomalies over the NPSTMW formation region. The declines in heat loss and southward Ekman transport, owing to the wind stress anomalies, further prohibit upper-ocean convection and mixed-layer deepening and cooling. Additionally, the insufficient development of wintertime MLD in 2018–2021 may also be associated with the significantly intensified preconditioning of near-surface stratification (< 150 m depth) due to the persistent near-surface warming and the weak vertical entrainment process in winter. [ABSTRACT FROM AUTHOR]

This study examines the interannual and seasonal variations in the distribution of radioactive materials released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in the surface layer of the Kuroshio Extension (KE). Focusing on the contrasting flow conditions in 2015 (southward) and 2021 (northward) - significant oscillatory phases of the KE's mean flow axis - the research analyzes the impact of seasonal variations on particle transport pathways. The findings reveal distinct seasonal patterns: summer releases primarily follow the eastward KE movement, while winter releases exhibit a southward trajectory. The study further quantifies the transport timescales, demonstrating that particles can reach the Luzon Strait within 10 months, subsequently diverging northward along the Kuroshio and northwestward along the Kuroshio Branch Current, potentially entering the South China Sea within 13 months. This research contributes valuable insights into the seasonal dynamics governing the dispersion and transport of Fukushima-derived radioisotopes in the surface ocean, highlighting the crucial role of the KE in influencing their trajectories. [ABSTRACT FROM AUTHOR]

The Yangtze River estuary (YRE) are strongly influenced by the Kuroshio and terrigenous input from rivers, leading to the formation of distinct water masses, however, there remains a limited understanding of the full extent of this influence. Here the variation of water masses and bacterial communities of 58 seawater samples from the YRE and its adjacent waters were investigated. Our findings suggested that there were 5 water masses in the studied area: Black stream (BS), coastal water in the East China Sea (CW), nearshore mixed water (NM), mixed water in the middle and deep layers of the East China Sea (MM), and deep water blocks in the middle of the East China Sea (DM). The CW mass harbors the highest alpha diversity across all layers, whereas the NM mass exhibits higher diversity in the surface layer but lower in the middle layers. Proteobacteria was the most abundant taxa in all water masses, apart from that, in the surface layer masses, Cyanobacterium, Bacteroidota, and Actinobacteriota were the highest proportion in CW, while Bacteroidota and Actinobacteriota were the highest proportion in NM and BS; in the middle layer, Bacteroidota and Actinobacteriota were dominant phylum in CW and BS masses, but Cyanobacterium was main phylum in NM mass; in the bottom layer, Bacteroidota and Actinobacteriota were the dominant phylum in CW, while Marininimicrobia was the dominated phylum in DM and MM masses. Network analysis suggests water masses have obvious influence on community topological characteristics, moreover, community assembly across masses also differ greatly. Taken together, these results emphasized the significant impact of water masses on the bacterial composition, topological characteristics and assembly process, which may provide a theoretical foundation for predicting alterations in microbial communities within estuarine ecosystems under the influence of water masses. [ABSTRACT FROM AUTHOR]