The Jiangsu coast is rich in tidal flat resources, but its coastline has changed significantly since the 1980s due to natural and human factors. We used remote sensing and numerical modelling to compare the M₂ tidal current under five coastline configurations, while keeping the bathymetry and tidal forcing unchanged. The results show: (1) the mean seaward-advance distances across the four intervals summed to 2.66 km, and the cumulative calculated seaward-advance area was equivalent to 35.4% of the combined nearshore and offshore tidal-flat area surveyed in 2008. (2) The overall tidal current pattern differed little among the five coastline cases, and the regular and irregular semi-diurnal boundary moved landward by only 32% of the sum of the four interval-mean coastline advances. (3) The differences in M₂ amplitude and phase among the five coastline cases were concentrated in nearshore areas shallower than 10 m, whereas the differences over most of the model domain were small. (4) The largest M2 amplitude reduction occurred in Xiaomiaohong in the 2023 case relative to 1981, at about −41.4%, followed by Lanshayang at about −8.1%, while Xiyang saw little change. (5) M₂ tidal energy is delivered from the East China Sea to the convergence point of the Radial Sand Ridges via three pathways. Among the five coastline cases, the energy flux per unit width increases by less than 6.0 kW/m along the northern coast of Jianggang and in the southeastern offshore area, while decreasing by up to −8.0 kW/m in the eastern offshore region and tidal channels. (6) Three M₂ tidal current amphidromic points were identified east of Lianyungang, and their positions differed only slightly among the five coastline cases. The strongest responses to coastline configuration occur in nearshore channels, while the regional tidal-current pattern differs little among cases.
Seabed sediment mobility in the Persian Gulf reflects episodic near-bottom forcing, heterogeneous sediment properties, seasonal hydrography, and basin morphology. We present Ocean View v2.0, integrating ocean reanalysis, a static-predictor Random Forest (RF) estimate of median grain size (D50), Shields-based mobility diagnostics, and PRE–EVENT–POST composites for January 1996–December 2025.A 95th-percentile threshold of domain-maximum bottom-current speed (0.3106 m s−1) identified 18 extreme months among 359 valid monthly fields. Event composites show concentrated forcing and conditional mobility, with prominent values toward the eastern Persian Gulf and Strait of Hormuz and additional axial concentrations. Around Ras-e-Motaf, relatively fine estimated grain sizes coexist with elevated forcing. Higher-density winter and spring EVENT patterns in the western and northwestern Gulf are regionally distinct from the most prominent sediment-normalized forcing toward Hormuz. EVENT–POST contrasts show strong relaxation near Hormuz alongside local enhancement elsewhere; they describe differences between phase means rather than continuous persistence.The RF reduced pooled spatially held-out error relative to constant-grain baselines, although external transferability remained limited. Its spatially varying D50 field allows local grain-size estimates to modify entrainment thresholds and calculated mobility. Across tested event-threshold and drag-coefficient scenarios, the area with composite relative mobility M > 1 spans 2.23–4.93% of the common finite domain. These estimates use a non-cohesive entrainment relation and do not establish observed erosion or sediment transport. Ocean View v2.0 thus provides a basin-scale framework for comparing hydrographic and sediment-normalized responses and prioritizing targeted observations and process-based modelling.
The study revealed the sediment dynamics of Galveston Bay (GB), Texas, by coupling Neural-Network based End-Member Modeling Analysis (NNEMMA) and Grain Size Trend Analysis (GSTA). About 189 grab sediment samples collected from Upper Galveston Bay (UGB) and Trinity Bay (TB) revealed that GB is a silt-dominated estuary (regional mean ≈53%), followed by sand (≈35%) and clay (≈12%). Silt is concentrated in TB, central UGB, and the San Jacinto Estuary regions, whereas sand fringes along the bay margins and shoals, particularly in eastern TB and near Eagle Point along the southwestern margin. NNEMMA identified five dynamic grain size populations (EM1 - EM5) in GB, with EM3 (medium silt) dominating (bay mean ≈37%). EM3 hotspots are observed across TB, tapering southwestward into UGB, indicating the Trinity River as the primary source of fine sediment in GB. EM2 (fine silt ≈20%) is prominent in southern TB. EM5 (fine sand ≈15%) and EM4 (very fine sand ≈14.5%) are concentrated along the bay margins, particularly along the eastern margin. EM1 (clay ≈13.5%) highlights a random distribution, indicating event driven (e.g., cold fronts) sediment distribution. Suspension transport is the dominant mechanism governing sediment transport and deposition in GB. GSTA reveals a dominant northwesterly net sediment transport toward the Bayport area from TB and the inner bay, as well as minor flows from the Seabrook area, which implies shoaling along the northwestern margin. The study aims to guide GB management decisions regarding maintenance, dredging, and erosion control and to inform the potential fate and transport of particle-bound contaminants, such as mercury.
Marcasite–pyrite samples from the Semenov-1 seafloor massive sulfide (SMS) deposit (13°30.87' N, Mid-Atlantic Ridge) were re-investigated to explain their significant Au (0.51–4.76 ppm) and Ag (9.7–70.8 ppm) enrichment, which is found to be related to the presence of accessory low-fineness Au–Ag alloys, lenaite, a Ag sulfide and a Ag–Sb–Cu sulfosalt. The Ag content of most Au–Ag alloy grains is 20.1–49.0 wt%, with one grain containing 7.22 wt% Ag. Their median Ag content (37.9 wt%) exceeds more than four times that of native gold from other SMS deposits (8.2 wt%). A low temperature (83–224 °C) of low-saline (0.6–3.2 wt% NaCl-equiv.) phase separated fluid was most likely the primary controlling factor leading to the precipitation of this peculiar mineral assemblage. According to physicochemical modeling (no boiling considered), the Ag species mainly transported as AgCl2– were quantitatively predominant over the Au species in the hydrothermal fluid; the dominant Au(HS)0 complex was replaced by Au(OH)0 after the deposition of Au–Ag alloys under relatively low S activity. These formation conditions and the composition of Au–Ag alloys are similar to those of low-sulfidation epithermal deposits. The presence of one high-fineness native gold grain could possibly be explained by its entrapment and transportation by the hydrothermal fluid from the subseafloor. New data on Au–Ag minerals show a precious metal potential of base metal-poor SMS deposits.
