Search Results (373)

This study focuses on the Labrador Coastal Current (LCC), which is the coastal branch of the Labrador Current System (LCS). We characterize the LCS by combining existing Global Drifter Program (GDP) data with new surface drifters deployed by the Community-based Observations of Nunatsiavut Ocean Circulation (CONOC) project, specifically designed to fill the near-coast gap where the LCC lies. Autonomous ocean gliders are used to map hydrography and infer baroclinic and barotropic circulation components of the LCS. Tidal currents are generally weak across most of the shelf but are notably stronger in areas such as the Hudson Strait and the Strait of Belle Isle. The main Labrador Current (MLC), over the shelf break, exhibits strong currents (ca. 0.5 m/s) while the LCC, closer to the Labrador coast, shows moderate speeds of up to 0.25 m/s. Combining drifter- and glider-derived velocities, we find that the surface velocities in the LCC are predominantly barotropic (ca. 70%) while in the MLC they are predominantly baroclinic (ca. 70%). While volume transports in the MLC are several times larger than the LCC, their freshwater transports are comparable in magnitude. These observations provide crucial detail on the dynamics and watermass properties of the LCC. Full article

Global satellite missions with the capability to measure ocean surface currents are continually being proposed. This new observation type is expected to significantly improve ocean model analysis and forecast skill. The potential impact of assimilating sea surface currents from the proposed wide-swath Ocean Dynamics and Surface Exchange with the Atmosphere (ODYSEA) mission is investigated in this study. An Observing System Simulation Experiment (OSSE) is set up with a 1 km Navy Coastal Ocean Model (NCOM) analysis-forecasting system in the Gulf of America domain over a 4-month time period. When compared to an experiment with only the standard data streams of temperature, salinity, and sea surface height anomaly observations from in situ and satellite platforms assimilated, the inclusion of ODYSEA-like sea surface current observations leads to a 13% and 17% reduction in the domain and time averaged root mean squared error (RMSE) for surface u and v components, respectively, as well as an improvement in the current velocity throughout the upper water column. The assimilation of the sea surface current observations also leads to an improvement in the model sea surface height, although there is a negligible to slight degradation in the temperature and salinity at depth, which is likely due to the explicit geostrophic assumption made within the velocity assimilation methodology. Full article

Introduction: Elasmobranchs play a vital role in marine food webs through top-down control and the structuring of ecosystem stability, yet more than one-third of species face extinction. The Maldives, a recognised Indian Ocean hotspot for shark and batoid diversity, designated its EEZ as a shark sanctuary in 2010, but multispecies elasmobranch occurrence patterns and environmental drivers remain poorly characterised in Lhaviyani Atoll in the central Maldives, which hosts two Important Shark and Ray Areas (ISRAs). Recreational SCUBA networks can turn routine dive activity into long-term conservation evidence, already informing nearly 10% of the western Indian Ocean ISRAs. Objective: To characterise spatiotemporal patterns of elasmobranch assemblages in Lhaviyani Atoll (2017–2024), quantify how environmental and geomorphic drivers shape relative abundance, diversity, and hotspots, and provide evidence for targeted elasmobranch conservation. Methodology: A seven-year opportunistic dive-log dataset of 12,732 SCUBA surveys and 142,994 elasmobranch records across 94 dive sites was analysed. Effort-standardised relative abundance and community metrics (Shannon diversity, Pielou’s evenness) were modelled against sea surface temperature (SST), salinity, dissolved oxygen, chlorophyll-a, zonal current velocity, substrate type, and reef geomorphology using generalised additive models (GAMs). Spatial analyses identified persistent northern-rim aggregation areas aligned with ISRAs. Results: Twenty-eight species (14 sharks, 14 batoids) were recorded, including 23 threatened on the IUCN Red List (4 Critically Endangered, 12 Endangered, 7 Vulnerable). Relative abundance and diversity peaked during the late southwest monsoon (August–September) and declined during the northeast monsoon (December–March). After 2021, diversity and evenness increased while overall abundance declined. Relative abundance was primarily driven by SST, salinity, and current velocity; for sharks, dissolved oxygen and chlorophyll-a were additionally significant, whereas batoid abundance was driven mainly by temperature, oxygen, and current velocity. Four persistent hotspots along the northern atoll rim were identified, with sharks concentrated along exposed slopes and channels, and batoids distributed broadly within lagoonal habitats. Conclusions: Long-term citizen science dive-log monitoring is cost-effective for elasmobranch conservation in remote tropical seascapes. These results show how dive-industry partnerships can inform conservation governance over a decade after sanctuary designation, supporting targeted, habitat-focused management as shark and batoid conservation frameworks continue to evolve. Full article

Variable-amplitude vibrating screens are widely adopted for screening frozen sea buckthorn berry particles. Investigating their motion characteristics and particle behaviors on the screen surface is essential for optimizing the screening process and improving equipment performance and screening efficiency. In this work, a variable-amplitude vibrating screen is taken as the research subject. Its structural composition and working principle are elaborated, and kinematic simulations are conducted via RecurDyn. The results reveal that the vertical amplitude and velocity of the screen surface increase gradually from the feed end to the discharge end, which facilitates rapid particle penetration. Meanwhile, the horizontal velocity remains stable across all sections of the screen. Specifically, crank length governs the screen amplitude, while crank rotational speed determines the vibration frequency. A dynamic model of particles and the screen surface is established by combining EDEM 2024 and RecurDyn V9R4, and two-way coupling of the discrete element model is realized. Coupled simulation results indicate that the dynamic screening efficiency rises with increasing crank length and rotational speed, reaching the maximum at a crank length of 20 mm and a rotational speed of 208 r/min. Crank parameters exert remarkable effects on the thickness of the particle layer and the quantity of penetrated particles: a thicker particle layer leads to a longer residence time of materials on the screen. Field tests are carried out to verify the model accuracy. It turns out that the simulation results are basically consistent with experimental data. In conclusion, crank length and rotational speed are critical influencing factors for variable-amplitude vibrating screens. Research on the screen’s motion characteristics and particle behaviors can provide a theoretical reference for its efficient operation and optimal design. Full article

As critical air-dropped acoustic sensors for underwater target detection, sonobuoys are frequently compromised by severe hydrodynamic self-noise induced by sea-surface wave excitation, which masks target signals and degrades detection performance. While structural optimizations have traditionally been employed, effective signal-processing-based noise suppression remains challenging because the noise is non-stationary and physically coupled with buoy motion. To address the limited physical interpretability of conventional decomposition methods, this study proposes a physically guided self-noise suppression framework: VMD Constrained by DCCA Correlation (VMD-DCCA). The main contribution is the incorporation of the Detrended Cross-Correlation Analysis (DCCA) coefficient between the sonobuoy’s vertical velocity and the acoustic data as a correlation-dependent constraint within the Variational Mode Decomposition (VMD) optimization process. This motion prior allows more targeted isolation of motion-induced components than standard data-driven decomposition. Simulation and controlled water-tank results show that VMD-DCCA outperforms EEMD and standard VMD, achieving an SNR improvement of approximately 15 dB at an input SNR of −9 dB. The reconstructed signal also preserves visible narrowband spectral lines in the time-frequency representation. These results demonstrate the potential of the proposed method for controlled or post-processing sonobuoy self-noise reduction, while validation under irregular open-ocean conditions remains necessary. Full article

The Arabian Sea is a key region for global marine biogeochemical research, yet the distribution characteristics and influencing factors of dissolved oxygen and chlorophyll a concentration in its central oxygen minimum zone still require further in-depth investigation. Based on survey data and reanalysis data from 2024, this paper analyzes the distribution characteristics and underlying causes of chlorophyll a concentration and dissolved oxygen using empirical orthogonal function (EOF) decomposition of chlorophyll a concentration and dissolved oxygen saturation along the depth direction, combined with the distribution of the barrier layer, Ekman pumping induced by wind fields, and the diagnostic vertical velocity distribution calculated from ADCP-observed flow velocities. Taking approximately 10° N as the boundary, the chlorophyll a concentration in the layer shallower than 35 m exhibits a distribution pattern of high in the northwest and low in the southeast, while the water layer between 45 m and 95 m shows a pattern of low in the northwest and high in the southeast. A thick barrier layer exists in the southeastern region, whereas the barrier layer in the northwestern region is thinner or absent, resulting in lower surface chlorophyll a concentration in the southeast. ADCP observations indicate that horizontal flow velocities are higher in the south, bringing oxygen-rich water from the south, which leads to higher dissolved oxygen saturation in the southern region compared to the northern region in water shallower than 45 m. At the 65 m water layer, the higher chlorophyll a concentration in the south may result in relatively low dissolved oxygen. The hypoxic zone (dissolved oxygen saturation less than 30%) begins to appear at depths below 105 m, with its southern boundary located between 9° N and 11° N, and this boundary gradually shifts northward as depth increases. The diagnostic vertical velocity between 9° N and 11° N is higher than that in other regions, which may hinder the northward movement of oxygen-rich water from the south. In the southern region, influenced by wind stress, the vertical water movement induced by Ekman pumping is relatively significant, which may lead to a slight increase in dissolved oxygen saturation in water layers with a depth below 125 m. Full article

Arctic shipping lanes are gradually opening, creating an urgent demand for unmanned surface vehicles (USVs) capable of safe and efficient navigation in drifting-ice environments. However, dense, highly dynamic sea ice poses significant challenges for existing obstacle-avoidance approaches. This study proposes a dynamically weighted hybrid obstacle avoidance algorithm integrating an improved VO module and an enhanced APF module. The optimized VO method refines the velocity sampling strategy and incorporates DCPA/TCPA-based risk screening to eliminate high-risk candidate velocities. The improved APF method introduces adaptive parameter regulation, virtual-target-based local minimum escape, and historical-velocity-driven oscillation suppression. Furthermore, a real-time dynamic weighting mechanism is designed to balance the contributions of the VO and APF modules according to the instantaneous environmental risk level. Extensive simulation experiments demonstrate that the proposed algorithm achieves reliable collision avoidance performance, high navigation efficiency, and strong environmental adaptability for USVs operating in dynamic Arctic drifting-ice environments. Full article

In recent years, climate change has increasingly shaped the potential habitat distribution of marine fishes, rendering this topic a focal area in marine ecology and biogeographical research. Using the MaxEnt modeling approach, this study projects the current and future potential habitats of eggs and larvae of two ecologically and economically important coastal species, the Liza haematocheilus and the Harpadon nehereus, across the nearshore waters of Zhejiang Province. Distribution records of early life stages and key environmental variables were integrated to model suitability under present-day conditions and three Shared Socioeconomic Pathway–Representative Concentration Pathway climate scenarios: SSP2-4.5, SSP3-7.0, and SSP5-8.5. Results identify sea surface salinity, surface current velocity, and sea surface temperature as the primary drivers of habitat suitability for Liza haematocheilus early-life stages; in contrast, chlorophyll-a concentration emerges as an additional significant predictor for Harpadon nehereus, alongside the aforementioned three variables. Under contemporary climatic conditions, high-suitability habitats for Liza haematocheilus eggs and larvae are predominantly concentrated in estuarine and island-adjacent nearshore zones, constituting 40.76% of the total predicted suitable area. For Harpadon nehereus, high-suitability areas are broadly distributed across nearshore shelf waters, representing 65.57% of its total modeled suitable habitat. Projected under future scenarios, the largest absolute increase in high-suitability area for Liza haematocheilus occurs under SSP3-7.0 in the 2050s (+0.38 × 10⁴ km²), whereas Harpadon nehereus exhibits its greatest expansion under SSP5-8.5 in the 2090s (+0.45 × 10⁴ km²). Collectively, the total suitable habitat area for Liza haematocheilus is projected to expand across all three scenarios, while that of Harpadon nehereus remains relatively stable overall—yet its high-suitability fraction increases markedly under high-emission, high-warming conditions. These findings suggest that ongoing climate warming may facilitate range expansion and enhanced nursery habitat availability for both species in Zhejiang’s coastal zone, positioning them as potential ecological beneficiaries of regional climate change. Full article

A microscale vortex embedded in a cold front over the Pearl River Estuary was observed by weather radars in Hong Kong on the evening of 2 March 2026. This paper presents an observational and simulation study of this vortex. In addition to the reflectivity and Doppler velocity data, the three-dimensional wind field associated with this vortex was analyzed using two radar-based analysis methods. Updrafts were present within the vortex, and the formation of the vortex appears to be related to the horizontal wind shear within the frontal zone and vertical motion triggered by a mid-tropospheric wave. Three commercial aircraft flew across the vortex at low altitude southwest of Lantau Island. Flight data showed marked fluctuations in vertical velocity, including both upward and downward air motions, together with severe turbulence within the vortex. The vortex is therefore of both meteorological interest and operational significance for aviation safety. The event was also simulated using the Weather Research and Forecasting (WRF) model with 200 m resolution. The model reproduced the observed vertical motions and turbulence intensity reasonably well in comparison with aircraft observations. Sensitivity tests with varying sea surface temperature and local terrain over Hong Kong showed no significant impact on the formation of the vortex, confirming that the event was primarily driven by horizontal wind shear in the frontal zone and vertical motion triggered by mid-tropospheric waves. Full article

The tectonic setting of Taiwan and its surrounding regions is characterized by the complex interaction between the northwest-oriented Ryukyu subduction zone and the east-oriented Manila subduction zone. Within this subduction framework, the elastic thickness of the lithosphere (Te) serves as a critical parameter for elucidating the mechanical behavior of the area. In this study, we employed the admittance–correlation method to estimate Te values across Taiwan and adjacent territories. The findings indicate that sedimentary loading results in an overestimation of the maximum Te by approximately 50 km; after adjustment, the Te values range from 0 to 60 km throughout the study area. On Taiwan, Te values predominantly lie between 20 and 30 km, decreasing to 10–20 km near the margins adjacent to the Ryukyu and Manila subduction fronts. The Philippine Sea Plate exhibits comparatively higher Te values, ranging from 40 to 65 km. The spatial distribution of Te broadly corresponds with major tectonic subdivisions. Statistical analyses reveal a weak negative correlation between Te and surface heat flow (r = −0.44) and a weak positive correlation with shear-wave velocity anomalies at a depth of 100 km (r = 0.22), suggesting that the thermal structure exerts only a moderate influence on lithospheric strength in this region. Nonetheless, within oceanic crustal domains, the relationship between Te and oceanic crustal age largely adheres to models of crustal cooling and lithospheric thickening, consistent with isotherm depths of approximately 200–400 °C. Additionally, dynamic topography associated with slab subduction may locally diminish Te by up to 25 km. Cross-sectional profiles through northern Taiwan and the Philippine Sea block reveal pronounced coupling between subduction geometry and Te distribution. The observed spatial patterns of Te reflect the mechanical imprint of prolonged tectonic evolution, with the orientation of Te gradients generally aligned with the direction of maximum principal compressive stress. Collectively, these results suggest that subduction geometry and tectonic processes are important factors influencing the spatial variability and evolutionary trajectory of lithospheric strength in Taiwan and its environs. Full article

With the rapid depletion of terrestrial mineral resources, the global demand for deep-sea mineral resource exploitation has become increasingly urgent. The hydraulic lifting system centered on deep-sea mining pumps is internationally recognized as the most commercially viable deep-sea mining system. In this paper, a deep-sea mining pump is taken as the research object, and the flow and wear characteristics of solid–liquid multiphase transport within the pump are investigated. Results show that as particle concentration increases, the non-uniformity of pressure and velocity distributions in the impeller flow channel also increases, indicating that particle-induced disturbances significantly compromise flow field uniformity. As the particle diameter increases, the wear dead angle area continues to expand, and the wear patterns and extents on each surface of the impeller and guide vane differ significantly. The particle collision frequency, particle kinetic energy, flow field structure, and shielding effects collectively influence the variation in wear amount. Full article

The circulation of the North Atlantic Ocean plays a vital role in the Earth’s climate system. Numerous studies, primarily through computer simulations, have examined the stability of the Atlantic Meridional Overturning Circulation (AMOC) in a warming climate. Some of these studies predict a potential collapse of the AMOC in the foreseeable future, which would require a significant influx of freshwater into the subpolar North Atlantic (NA) and Nordic Seas. Paleoreconstructions of NA circulation indicate a major shift in the position of the subpolar cold front, which either precedes or coincides with substantial changes in AMOC dynamics. These changes in the front position imply a significant alteration in circulation patterns, beginning with the noticeable restructuring of the subtropical and subpolar gyres. This would lead to modifications in the Gulf Stream system and the North Atlantic Current (NAC), affecting the thermohaline fields and the position and strength of these two current systems. Although some models predict a significant slowdown or even collapse of the AMOC, recent observational studies have offered a more cautious perspective. For instance, the Gulf Stream system exhibits high resilience to perturbations caused by ongoing sea surface warming. In this study, we analyzed the decadal variability of temperature and salinity from in situ observations, along with upper-ocean currents in the subpolar NA (SPNA). We found that the thermohaline pattern of the upper ocean layers in the SPNA and Nordic Seas has remained resilient for over 70 years. The deceleration of the AMOC is evident but relatively modest, with average velocities in the upper layers decreasing by less than 10–15% over 30 years. This deceleration was also inconsistent throughout the NAC region. Furthermore, the subpolar front migration over 70 years, as manifested in isotherm spatial variability, reached a maximum of 3° of latitude, with spatial variability of the yearly 10 °C isotherms being lower. Overall, the conclusion regarding the resilience of the NAC aligns well with that of the Gulf Stream, with no substantial changes in the position or intensity of the subpolar gyre. We conclude that while the AMOC is susceptible to some deceleration due to ongoing surface warming and/or high-latitude freshening, it may also be sufficiently resilient to withstand these changes. Although it cannot be entirely ruled out that the AMOC may reach its tipping point within this century, an analysis of data on decadal variability in the upper arm of the AMOC suggests that such a collapse is unlikely to occur. Full article

To ensure the safe operation of floating LNG offloading hoses in bow-loading systems, this study investigates the key factors affecting the dynamic response of an LNG offloading hose string. A fully coupled dynamic model of the hose string, the LNG carrier (LNGC), and the FLNG is established based on the lumped-mass method. The sensitivities of hose loads and deformation indicators to the hose-string length, vessel stand-off distance, tanker-heading offset, internal flow velocity, ocean current speed, and wave height are quantified. Based on these results, a low-load operating configuration is identified and a preliminary operational envelope is proposed. The results show that, under the considered operational sea state, a hose-string length of 170.6 m and an FLNG–LNGC distance of 80 m yield the minimum effective tension. The recommended limiting environmental conditions for safe operations are a surface current speed of 1.1 m/s and a maximum wave height of 7.0 m. The present study provides a practical basis for preliminary configuration design, response assessment, and operational-limit determination of floating LNG export hoses in bow-loading applications. The main contributions of this study are threefold. First, a coupled time-domain framework combining AQWA-based vessel motions and OrcaFlex hose dynamics is established. Second, the effects of key configuration and environmental parameters are systematically quantified. Third, a preliminary operating envelope and a recommended configuration are proposed based on effective tension, bending moment, and curvature. These contributions distinguish the present study from previous work focusing mainly on local hose mechanics or qualitative system description. Full article

Ocean warming driven by climate change is altering regional circulation patterns and the balance of hydrodynamic forcings in semi-enclosed seas. Understanding how these changes affect ocean circulation and stratification is critical, as they directly influence marine productivity and ecosystem functioning in highly sensitive regions such as the Gulf of California. This study examines the hydrodynamic response of the Gulf of California under three climate change scenarios (SSP1–2.6, SSP2–4.5, SSP5–8.5) projected from 2015 to 2100 using the CNRM-CM6-1-HR global climate model. We evaluate changes in sea surface temperature, surface circulation, and the relative contributions of dominant dynamic forcing mechanisms at annual and interannual scales. Results reveal a basin-wide warming trend accompanied by an increased frequency of extreme heat events. Surface current velocities weaken throughout the Gulf, exhibiting a consistent negative trend, with the strongest decline occurring under SSP5–8.5 in the central basin ($-5.1\times {10}^{-4}$ m s⁻¹ year⁻¹). Wind speed also shows a general decreasing tendency, contributing to reduced circulation intensity and enhanced stratification. The analysis of dimensionless numbers indicates moderate but consistent changes in the relative balance among inertial, baroclinic, and wind-driven processes. Although their proportions vary slightly across scenarios, the dominant forcing hierarchy remains largely preserved, suggesting a gradual modulation in forcing intensity rather than a fundamental reorganization of the hydrodynamic regime. These findings highlight spatial contrasts in climate sensitivity within the Gulf of California and underscore the importance of regional-scale assessments for anticipating future changes in circulation dynamics and marine ecosystem responses. Full article

Suspended sediment concentration (SSC) strongly influences estuarine erosion–deposition processes, navigation safety, and coastal engineering stability. However, conventional remote sensing techniques are limited to surface SSC and cannot characterize vertical sediment structures. In this study, Landsat 8 OLI imagery was combined with in situ SSC profiles from six stations in the Guan River Estuary–Haizhou Bay system to retrieve full-depth sediment distributions. A band-combination inversion model using (B3 + B2)/B1 achieved the highest accuracy (R² = 0.679), and an improved vertical distribution model was developed by incorporating turbulent shear (G) into the Rouse framework. Results indicate that surface SSC ranged from 0.15 to 0.86 kg/m³, while middle- and bottom-layer SSC reached up to 1.20 kg/m³ and 1.77 kg/m³, respectively, exhibiting a consistent east–high and west–low spatial pattern. Settling velocity (SSV) varied from 3 × 10⁻⁶ to 1.49 × 10⁻² m/s and showed a positive correlation with SSC at low concentrations and a negative correlation at high concentrations due to flocculation effects. This integrated framework provides a rapid, low-cost method for full-water-column sediment assessment in estuaries and coastal zones, supporting engineering design, navigation maintenance, and sediment management. A better understanding of sediment transport processes in Haizhou Bay is important for maintaining shoreline stability and ecological balance in this semi-enclosed coastal system. The findings of this study provide a scientific basis for sediment management and environmental regulation, which can contribute to the long-term sustainable development of coastal environments in the Yellow Sea region. Full article