Search Results (59)

Temporal variations in diurnal internal tides (ITs) and near-inertial waves (NIWs) in the southern South China Sea (SCS) are characterized, based on two 13-month moored current observations. Diurnal ITs, dominated by O₁ and K₁, are found to exhibit spring–neap cycles of about 14 days and significant seasonal variations. The incoherent components explain 54% and 56% of the total energy in the diurnal band, which further complicates its temporal variabilities. As for NIWs, wind energy input serves as the primary energy source and three strong events are observed. Tropical cyclone RAI passed through two moorings during the event 1 period, and triggered a peak near-inertial kinetic energy of 19.55 J m⁻³ (18.82 J m⁻³) at two moorings. After generation, the NIWs propagated downward to around 300 m, becoming the most intense event observed at DA2. In contrast, the NIWs response to tropical cyclone NOCK’s passage during event 3 was relatively weaker. The near-inertial KE generated by NOCK was confined to depths shallower than 150 m, with the average near-inertial KE being only 85% (52%) of that during event 1 for two moorings, despite the near-inertial energy input from NOCK being nearly 400% that of RAI. The modulation of background vorticity is considered the primary factor resulting in the difference in intensity of two NIW events. The penetrating depth of NIWs under the modulation of anticyclonic eddies was more than twice that under the cyclonic eddies. Furthermore, the strongest NIWs during event 2 that were observed below 350 m at mooring 2 (183% stronger than average) were also related to a strong anticyclonic eddy. Full article

Coastal waters, particularly in micro-tidal estuaries, are highly vulnerable to water quality changes driven by salinity intrusion. Effective coastal water management requires a detailed understanding of the dynamic processes in estuaries to mitigate the effects of salinity intrusion. This study focuses on the Brisbane River estuary (BRE), Australia, to investigate salinity intrusion and flushing time under varying freshwater inflows. A coupled MIKE 21 FM hydrodynamic (HD) and transport (TR) model was used to assess salinity transport during a neap–spring tidal cycle. The 2D model was calibrated and validated for the 2008 and 2011 flow events using field data on water levels and salinity. Results show an increase in tidal amplitude landward under low river flow conditions, while tidal damping was observed under higher river discharge, reducing the BRE salinity during spring tides. This study found that salinity intrusion is highly sensitive to freshwater availability, with river discharges of 150 m³/s and 175 m³/s identified as critical thresholds to maintain salinity levels below 1 PSU at the estuary mouth during ebb and flood tides, respectively. Flushing time analysis indicates that the BRE takes approximately 302 h to completely displace saline water when the river discharge is optimized at 150 m³/s. Modifying the BRE estuary mouth—through channel widening or deepening—enhanced the flushing process, significantly reducing salinity levels. This study demonstrates that optimizing freshwater discharge and modifying the estuary mouth can provide effective solutions for managing salinity intrusion in micro-tidal estuaries. Full article

Coastal development such as sea reclamation, port terminals, and breakwater construction has significantly altered the southwestern coastline of Laizhou Bay, changing the regional hydrodynamic environment. To explore how tidal range and tidal prism respond to these 20-year coastline changes, this paper selected the southwestern coastline data of Laizhou Bay in 2000 and 2020, established a 2-D tidal model, and studied the impact of the 20-year coastline changes on tidal range and tidal prism in this sea area. The results show that during the 20 years from 2000 to 2020, most of the bay area’s coastline was in a growth trend of advancing toward the sea, 85.3% of the cross-sections were growth areas, 11.9% were dynamic stable areas, and there was almost no erosion area. Affected by reclamation activities, the area of the southwestern part of Laizhou Bay decreased by 11.66%, the coastline increased by 63.27%, and the center of mass moved 2.22 km to the northeast. The reclamation of tidal flats caused the potential energy of tidal waves in the bay to increase, the maximum possible tidal wave in the southwestern part of the bay showed an increasing trend, and the bay top between Weifang Port and Guangli Port increased particularly significantly, with a maximum increase of 22 cm. The spring tide period, neap tide period and average tidal prism in the southwestern bay decreased by 4.79%, 3.29%, and 4.24%, respectively. The reclamation of tidal flats is the main reason for the decrease in tidal prism in the southwestern part of the bay. Full article

Weird horizontal shapes of branches, in large branching estuaries, often cause significant flood risks and environment-related problems. People usually resort to engineering methods to improve the horizontal shape of the weird branches and solve related issues. The responses of the riverbed evolution of a branching estuary to anthropogenic activity are complicated because of complex estuarine hydrodynamics and sediment transports, especially when the project locates specially (e.g., at estuary outlets). The North Branch of the Yangtze Estuary has a narrow upper reach which is almost orthogonal to the South Branch and has a trumpet-shaped lower reach with a wide outlet. The weird horizontal shape of the North Branch brings significant flood risks to cities along this branch, the shrinkage of its entrance, and other problems. In this study, a regulation of the North Branch, which is launched at Guyuan Sand (GYS) just outside the exit of the North Branch, is taken as an example. The GYS regulation aims to improve the weird horizontal shape of the North Branch by building new layouts of outlets, by which people decrease the flood risk of the surrounding cities. The GYS regulation is studied using a 2D numerical model. The riverbed evolution of the Yangtze Estuary in a typical hydrological year is simulated, while the water/sediment fluxes at cross-sections of branches in the estuary during a spring/neap tide are quantitatively calculated. It is found that the regulation changes the rotational flows near the shore, and further reshapes the estuarine circulations of mass inside the outlets, especially exchanges of water/sediment between different branches. The regulation directly changes the riverbed evolution at the outlet of the North Branch, and meanwhile has significant indirect influences on the riverbed evolution of the entrance of the North Branch. The varying riverbed evolution at the entrance of the North Branch and the varying water/sediment fluxes, under different designs of regulations, are related and analyzed. An essential improvement for the weird horizontal shape of the North Branch by an engineering method is shown to be possible, while the regulation mechanism of the engineering method and the response of estuarine riverbed evolution to the regulation are clarified. This study provides a new insight for improving estuarine branches with weird horizontal shapes, by reshaping the tidal processes and the accompanying sediment transports in a branching estuary. Full article

This study modelled possible ways of reducing salinity in the Seomjin River estuary to improve habitats for corbicula, which are important components of the ecosystem (ecologically and commercially) in the Seomjin River. Additionally, we analyzed the salinity reduction effects of structural measures to sustain optimal salinity. To do this, salinity measurement facilities were installed at crucial habitat locations in the Seomjin River estuary. After ensuring the reliability of the model, numerical simulations were conducted. Salinity changes were analyzed for four major locations (Dugok, Shinbi, Mokdo, Hwamok) and simulated under various conditions, resulting in concentrations of 4.7 psu in Dugok, 16.0 psu in Shinbi, 19.2 psu in Mokdo, and 28.2 psu in Hwamok. Additionally, this study analyzed reduction effects by applying three reduction scenarios (riverbed restoration, submerged weir, and groyne) by simulating the numerical model. The reductions in salinity for the submerged weir (SWS-1 to 3) and groyne (GS-1 to 3) scenarios were minimal, below 1 psu, indicating a very limited reduction effect. In conclusion, the salinity concentration in the Seomjin River estuary is dominated by the neap tide, and the salinity intrusion distance is influenced more by the spring tide. The Songjeong discharge strongly impacts the spring tide, while the neap tide is less dominant due to salinity stratification. Among the salinity reduction scenarios, riverbed restoration has the most critical effect, but artificial reduction measures may pose challenges in terms of cost and practicality. Full article

The Jiangsu Coast (JC), China, is an area susceptible to the impact of tropical cyclones (TCs). However, due to the lack of available on-site observation data, nearshore sedimentary dynamic processes under the impact of TCs have not been fully explored. This study developed a 3D wave–current–sediment numerical model for the JC based on the Finite Volume Community Ocean Model (FVCOM) to investigate sediment dynamic responses to TCs under various scenarios, including different tracks, intensities of TCs and tidal conditions. The validation results demonstrated the model’s satisfactory performance. According to the simulation results, typhoons can significantly impact the hydrodynamics and sediment dynamics. During Typhoon Lekima in 2019, strong southeasterly winds substantially increased the current velocity, bottom stress, wave height, and suspended sediment concentration (SSC). Three typical landfall-type typhoons, with prevailing southeasterly winds, brought significant sediment flux from southeast to northwest along the coast, while the typhoon that moved northward in the Yellow Sea induced a relatively small sediment flux from north to south. Typhoons could also induce stripe-like erosion and deposition, which is closely related to seafloor topography, resulting in seabed thickness variations of up to ±0.3 m. Additionally, strengthening typhoon wind fields can lead to increased sediment flux and seabed morphological changes. Typhoon Winnie, particularly at spring tide, had a greater impact on sediment dynamics compared to other landfall typhoons. Numerical simulations showed that the typhoon-induced net sediment flux within the spring tidal cycle could increase by 80% to 100% compared to the neap tidal cycle, indicating the significant influence of tidal conditions on sediment transport during TC events. Full article

Carbon export from mangrove forests to the oceans partly acts as a sink for atmospheric CO₂, exceeding the rate of carbon burial in mangrove soils. Primary production in ecosystems adjacent to mangroves may prevent degassing and enhance further carbon export from mangroves to the oceans. In this study, we continuously monitored carbonate chemistry parameters (pCO₂, dissolved inorganic carbon (DIC), total alkalinity (TA)) and dissolved organic carbon (DOC) in a tidal flat adjacent to a fringe mangrove forest over a spring-neap tidal cycle. Mean pCO₂ during the entire period was 923 ± 318 μatm, and the export of TA, DIC, and DOC from the mangroves to the ocean was 36 ± 26 mmol m⁻² d⁻¹, 42 ± 39 mmol m⁻² d⁻¹, and 10 ± 9 mmol m⁻² d⁻¹, respectively. Semi-monthly pCO₂ variations in the mangrove front were controlled by the tidal level during spring tide and by photosynthesis and respiration on the tidal flat during neap tide. This means that during neap tide, photosynthesis on the tidal flat offset the increase in pCO₂ caused by the porewater export from the mangrove soil. The DIC/TA export ratio in this study was 1.17 ± 0.08, which was lower than the global average of 1.41 ± 1.39, indicating that the tidal flat adjacent to the mangrove forest may act as a buffer zone to mitigate the increase in pCO₂, resulting in much of the exported DIC being stored in the ocean. Full article

The primary afferent system in the rat’s spinal cord starts to develop in the third last week of gestation. First, the pseudounipolar DRG neurons extend their centripetal long primary axons, targeting rostral supra-segmental nuclei in the spinal cord. Meanwhile, the subsequent innervation of the juxta- and intra-segmental spinal levels enables the three subdivisions to commence integrating a complex network with the body periphery. This process may continue to refine and adapt the system life-long. The experimental data elucidated the steps involved in developing the cytoarchitecture by separating the axons of the long and intermediate subdivisions from the short subdivision. Here, we present a blueprint of the features of the long primary afferent axons developing in sequential waves. The pioneering long afferent axons targeted the dorsal gracile nuclei at spring tide and Clarke’s nuclei at neap tide in ventrally bent trajectories. The paradigm’s myelotomy blocked these pioneering fibers from stepping down the developmental cascade, rendering an unknown phenotype. This reflected a hypothetical transition hub stationed on the assembly line, delineating a critical period. The paradigm also affected the neuropil’s ripening independently from the long primary afferent system. The data disclosed that fetal hyposaturation yielded an in vivo genomic engineering capability. Fetal tissue was susceptible to hyposaturation, showing remarkable versatility early in fetal life. The translational impact may favor research into the elusive etiology of clinical syndromes concerning the afferent system relating to fetal hyposaturation. Full article

During the cofferdam construction of the toe reinforcement project at the Qiantang River Estuary, the scouring of the riverbed at the groin head often led to the collapse of geotube groins due to strong tidal currents. Based on field experience, employing a combination of clay and geotubes proved to be a more effective solution to this problem. This study adopted a flume model experiment to investigate the scouring and deposition around geotube groins and mixed clay–geotube groins. The results indicated that the influence of tidal surges on geomorphic changes surrounding the groins was more pronounced during spring tides than during neap tides. Under the same flow conditions, the scour depth at the head of the geotube groin was notably deeper than that of the mixed clay–geotube groin. Additionally, sediment silting behind the mixed clay–geotube groin was significantly greater than that behind the geotube groin. The clay component of the mixed clay–geotube groin served to mitigate the head scour, enhancing the overall structural stability to a certain extent. The geotube groin, with its surrounding scour pits expanding over time, experienced increasing tensile strain. This resulted in the rupture of the geotextile material, the loss of internal sand and, ultimately, groin collapse. It was found that mixed clay–geotube groins were better suited for cofferdam construction in strong tidal estuaries compared to geotube groin alternatives. Full article

Internal solitary waves (ISWs) with features such as large amplitude, short period, and fast speed have great influence on underwater thermohaline structure, nutrient transport, and acoustic signal propagation. The characteristics of ISWs in hotspot areas have been revealed by satellite images combined with mooring observation. However, the ISWs in the Timor Sea, which is located in the outflow of the ITF, have not been studied yet and the characteristics are unrevealed. In this study, by employing the Synthetic Aperture Radar (SAR) images taken by the Sentinel-1 satellite from 2017 to 2022, the temporal and spatial distribution characteristics of ISWs in the Timor Sea are analyzed. The results show that most of ISWs appear in Bonaparte basin and its vicinity. The average wavelength of the ISWs is 248 m, and most of the wave lengths are less than 400 m. The peak line of ISWs is longer in deeper water. The underwater structures of two typical ISWs are reconstructed based on the Korteweg–de Vries (KdV) equation combined with mooring observation. This shows that, compared with the two-layer model, the continuous layered model is more suitable for reconstructing the underwater structures of ISWs. Further analysis shows that both the rough topography and the spring-neap tides contribute to the generation of ISWs in the Timor Sea. This study fills a gap in knowledge of ISWs in regional seas, such as the Timor Sea. Full article

Recurrent green tide has been widely studied due to its severe damage to coastal ecosystem. Jinmeng Bay, a popular resort in northeastern China, has suffered from green tide events since 2015, after the constructions of artificial islands and submerged reefs. To investigate the potential impacts of artificial islands and reefs on the water quality in Jinmeng Bay, a MIKE 21 numerical model was established by coupling a hydrodynamic model with a transport model of Chemical Oxygen Demand (COD) and nitrate ion (NO₃⁻). The changes in the water quality in Jinmeng Bay by the initial, first-stage and current construction conditions of artificial islands and submerged reefs were simulated. The model results indicated that: (1) The artificial islands and reefs in Jinmeng Bay hinder the tidal currents and weaken the tidal actions. (2) The weakened tidal actions at the estuary lead to the accretion of COD and NO₃⁻. The neap tides generate a littoral zone with the high concentration of COD and NO₃⁻, and the spring tides maintain the zone at the estuary. (3) NO₃⁻ is more sensitive than COD to the variation of hydrodynamic conditions. The NO₃⁻ concentration in the north of Conch artificial island is altered significantly, where the construction of the artificial structures decrease the concentration by ~30%, while the demolition of the connection road increases the concentration beyond its initial values by 16~21%. (4) Under the current construction conditions, the rising concentrations of COD (up to 2%) and NO₃⁻ (up to 40%) increase the frequency and scale of green tides in Jinmeng Bay considerably. Therefore, continuous monitoring of water quality is required for this region. Full article

Many estuaries have been damaged by such material movements as marine debris, suspended sediment, and pollutants. Understanding the estuarine circulation system is necessary to solve such problems. Salt transport analysis provides an insight into hydrodynamic processes about material circulation in the estuary. In this study, to understand the mechanisms of salt transport, a three-dimensional hydrodynamic model was applied in the hypertidal estuary system—Yeomha Channel in Gyeonggi Bay. The simulation period of the model was a total of 245 days (20 January to 20 September 2020), including the dry and wet seasons. The model results for the temporal variation in tide, current velocity, and salinity were validated by comparing them with the observed in-situ data. The total salt transport (F_S) was calculated in three cross sections of the Yeomha Channel and was decomposed into three components (Q_fS₀: advective salt transport; F_E: steady shear dispersion; F_T: tidal oscillatory salt transport). During the dry season with strong tidal forces, the total salt transport patterns were mainly dominated by Q_fS₀. During the wet season with high river discharge, the total salt transport patterns were determined by the balance between Q_fS₀, F_E, and F_T. The long-term tidal constituents (MS_f and M_m) were the main mechanisms causing Q_fS₀ with the spring–neap variation during the dry season. The tidal trapping effect, caused by a phase difference of less than 90° between tidal current and salinity, generated landward F_T in the dry and wet seasons. In addition, the high river discharge during the wet season decreased the phase difference between tidal current and salinity to less than 70°, resulting in a much stronger landward F_T. This study suggests that the long-term tidal constituents and tidal trapping effect are unique characteristics that contribute to material circulation in the hypertidal estuary. Full article

Stratification and mixing of the water column is an important dynamic process in the estuary, which plays a significant role in the estuarine circulation, mass transport and energy exchange. Based on the multi-station synchronous observation data from 26 February to 6 March in 2011 during dry season in the North Channel of the Changjiang Estuary, the Richardson number, the Simpson number and the potential energy anomaly of water were calculated to analyze the tidal variation of the mixing and stratification processes. The roles of the depth-mean straining, longitudinal advection, non-mean straining and tidal stirring in the processes of mixing and stratification of the water column were analyzed by calculating the contribution terms of the time-derivative of potential energy anomaly. The results show that the mixing and stratification of the water column in the North Channel have significant spatiotemporal variation. Stability of the stratification gradually decreases from neap tide to spring tide. In the reaches of salt wedge migration, permanent stratification develops during neap and mean tide, with stability increasing on the flood and decreasing on the ebb, which is dominated by longitudinal advection. During spring tide, periodic stratification develops, with development of stratification on the flood and its breakdown on the ebb, which is dominated by longitudinal advection and tidal stirring. In the main reaches of saltwater intrusion, permanent stratification develops during neap tide, with stability increasing on the ebb and decreasing on the flood, which is dominated by depth-mean tidal straining. During mean and spring tide, periodic stratification occurs, with development of stratification on the ebb and its breakdown on the flood, which is controlled by depth-mean tidal straining and assisted by tidal stirring. In the North Channel, tidal advection is the main stratifying agent in the salt wedge migration reaches, and tidal straining is the main stratifying agent in the main reaches of saltwater intrusion. Full article

The runoff of the Jiulong River (JLR) is a key parameter that affects the estimation of pollutant flux into Xiamen Bay (XMB). The precise runoff estimation of the JLR can be used to determine the accuracy of the pollutant flux estimation flowing into XMB. In this study, to analyze the hydrological dynamic characteristics and identify the correlation between fixed-site real-time ocean current observations and cross-sectional navigation flow observations, we conducted six navigation observations on two cross-sections of the JLR estuary during the spring tide and neap tide in the normal season, wet season, and dry season in 2020. Simultaneously, we measured hydrological observation data by a fixed-site buoy located in the JLR estuary and collected runoff data that were measured upstream of the JLR. The results showed that the average correlation coefficient between the average velocity of the fixed-point buoy and average velocity of the section was more than 0.90, higher than expected, the minimum average deviation was 4%, and the minimum sample standard error was 5.7%, which was a good result. In this study, we constructed a model for estimating the runoff of the JLR into the sea. The findings demonstrated that Acoustic Doppler Current Profiler (ADCP) online monitoring data were useful to estimate runoff of the JLR with high accuracy, could promote the accuracy of estimated pollutant flux of the JLR’s discharge into XMB, and could provide more scientific and reliable basic data for future load flux estimation research. Full article

In an estuary, stratification processes play a major role in inhibiting estuarine circulation, sediment transport, and the estuarine ecosystem. A detailed examination of the salinity stratification through the gradient Richardson number and the potential energy anomaly equation has been undertaken along the West Channel of the Pearl River Estuary, China. The results show that the estuarine circulation within the West Channel is much weaker on a spring tide than that on a neap tide, exhibiting apparent spring–neap tidal variability. The calculated gradient Richardson number displays its intratidal and spring–neap tidal variability within the West Channel, indicating the existence of intratidal and spring–neap tidal variability of stratification. In addition, the tidally averaged change rate of total potential energy anomaly within the West Channel suggests more than a 4.53 × 10⁻³ W·m⁻³ increase from spring to neap tides, demonstrating strong stratification on a neap tide. The longitudinal advection and the longitudinal depth-mean straining are the leading physical mechanisms contributing to intratidal and spring–neap variability of salinity stratification within the West Channel. However, the effects of the lateral terms cannot be ignored especially on a neap tide. Full article