Search Results (244)

Deoxygenation in marine ecosystems has received increasing attention. The variation of dissolved organic matter (DOM) during deoxygenation has been investigated in hypoxic and anoxic waters in coastal seas and open oceans. In the present study, the dynamics of DOM were investigated during summertime deoxygenation in the bottom water of the shallow coastal Bohai Sea, China. Dissolved organic carbon (DOC), chromophoric and humic-like fluorescent DOM (CDOM and FDOM) gradually increased in the bottom water during summer, which was mainly induced by biological activities in the water column and/or the surface sediment. The estimated net accumulation rates of DOC, CDOM and humic-like FDOM from June to early August in the bottom water were 0.11 ± 0.04 µmol L⁻¹ d⁻¹, 0.002 ± 0.0002 m⁻¹ d⁻¹ and 0.0004 ± 0.0001 R.U. d⁻¹, respectively. Moreover, the ratio of DOC to CO₂ accumulations was 0.08 in this duration in the bottom water. Compared with DOM in the bottom water prior to deoxygenation, the newly accumulated DOC contained more CDOM and humic-like FDOM that are considered to be microbially refractory. Full article

Introduction: The tub gurnard (Trigla lyra) is a demersal species of commercial interest whose long-term distributional dynamics remain poorly understood. Understanding spatial and temporal changes is essential for fisheries management and for assessing biogeographic shifts. Objective: To characterise the spatio-temporal distribution and persistence of T. lyra across Galician and Cantabrian Sea waters over a 33-year period (1993–2025) and to identify environmental and fishing drivers associated with observed changes. Methodology: We analysed data from the DEMERSALES bottom trawl survey series (1993–2025), for which the sampling design remained consistent throughout. Species distribution was modelled using a delta–GAM framework (presence–absence and positive values), complemented by a presence-only GAM fitted to Vessel Monitoring System (VMS) data; because these data were only available for 2009–2023, this model was restricted to that period for biological coherence. Environmental predictors included bathymetry, slope, sediment composition (organic matter, mud, fine and coarse sand), bottom temperature, and salinity. Spatial structure was assessed using aggregation curves, occupied area, centre of gravity, a Space Selectivity Index, and an Index of Persistence. Results: The occupied area increased from 45 to 963 km² (+2040%), accompanied by a sustained decline in the Space Selectivity Index and a westward shift of the distributional centroid (~20 km), indicating progressive range broadening. The frequency of occurrence rose from 4.5% in 1993 to 87.7% in 2025, reflecting a marked increase in spatial occupancy and encounter probability. Abundance increased sharply after 2015 (+47%), consistent with strong positive year effects in the GAM. Higher occurrence and densities were associated with muddy substrates, intermediate to high organic content, and depths of 100–300 m, matching the stable aggregation cores found along the shelf break. A reduction in trawling effort (−38% in mean intensity, −17% in swept area over 14 years) likely facilitated these trends. Conclusions: T. lyra expanded its distribution and shifted westward between 1993 and 2025, with persistent aggregation cores on the shelf break. No significant effect of temperature was found, suggesting that climate warming is not the primary driver; the expansion appears most plausibly to have been favoured by the decline in fishing pressure. Full article

Spatial and temporal variability of macrozoobenthic communities were investigated around three offshore gas structures with different architecture (a subsea well-site, a four-leg platform, and a one-leg platform) in the NW Adriatic Sea. Four post-installation surveys (two per year over two years) were conducted by sampling sediments at increasing distances from each structure (approximately 0, 30, 60, 120 and 1000 m from the structure edge). A total of 233, 271 and 260 taxa were recorded around Structures A, B and C, respectively, with polychaetes representing the dominant taxonomic group at all sites. Across all structures, community composition showed significant variability both among surveys and along the distance gradient. Near-structure stations (0–60 m) most frequently accounted for spatial dissimilarities, whereas communities at 120 and 1000 m were generally more similar. Early surveys around the well-site and the four-leg platform were characterised by low diversity and high dominance of the opportunistic polychaete Ditrupa arietina, suggesting a short-term disturbance related to installation. Post-installation trajectories differed among structures: community descriptors stabilized faster around the subsea well-site, while changes near the platforms extended for at least two years. At the one-leg and four-leg platforms, the progressive development of a bivalve mound (specimens of Mytilus galloprovincialis and/or Neopycnodonte cochlear fell from the submerged parts of the platforms) coincided with increased abundance, species richness and occurrence of hard-bottom associated taxa at 0 m stations. Overall, the results indicate that offshore gas structures can locally influence macrozoobenthic assemblages by modifying habitat heterogeneity and promoting site-specific community responses. Although based on post-installation observations only, this study provides site-specific evidence useful for future decommissioning planning in soft-bottom shelf areas. Full article

Deep-sea mining operations demand continuous, drift-free positioning over multi-day missions—a requirement that traditional acoustic dead-reckoning systems struggle to meet due to cumulative error accumulation and frequent DVL bottom-lock loss in sediment plume environments. Inspired by Google Cartographer’s 2D grid mapping paradigm, we present a prior map-based visual localization framework that decouples offline mapping from real-time localization, fundamentally eliminating drift through absolute image registration against pre-built seabed mosaics. By integrating adaptive keyframe selection, Multi-Scale Retinex (MSR) enhancement, and the AD-LG deep feature matching architecture, our system constructs globally consistent seabed maps for absolute positioning. The framework leverages deformable convolutions and LightGlue to effectively mitigate challenges such as low texture and non-rigid distortion. Quantitative validation on tank simulation datasets demonstrates significant superiority over IMU-only and standard fusion schemes; qualitative deployment on real Pacific CCZ imagery confirms near-real-time operational feasibility on an embedded Jetson Orin NX platform. This system establishes visual navigation as a viable backup to acoustic systems, addressing a critical gap in deep-sea mining vehicle autonomy. Full article

The Rio Grande Rise (RGR) is the largest oceanic plateau in the South Atlantic and represents a key natural laboratory for understanding oceanic plateau formation, deep-sea circulation, ecosystem functioning, and ferromanganese crust development. This study presents a critical synthesis of current scientific knowledge on the RGR, integrating geological, geophysical, oceanographic, biological, and geochemical evidence published over the last two decades. Geophysical data reveal a complex tectono-magmatic evolution involving Late Cretaceous plume-related volcanism, crustal thickening, rifting, and subsequent subsidence. The structural framework of the plateau is dominated by the Cruzeiro do Sul Rift, which plays a central role in controlling sedimentation, magmatism, and seawater circulation. Oceanographic studies demonstrate that the interaction between the southern branch of the South Equatorial Current and the complex topography of the RGR generates intense internal tides and bottom currents, strongly influencing sediment transport and benthic habitats. Biological investigations indicate that the RGR hosts diverse deep-sea communities, including sponge grounds, cold-water corals, and associated fauna, whose distribution is tightly linked to geomorphology and hydrodynamics. Ferromanganese crusts occurring on the plateau preserve valuable geochemical records of oceanographic and redox conditions, although their spatial distribution, thickness, and metal budgets remain incompletely constrained. Despite major advances, significant knowledge gaps persist regarding crustal structure, sedimentary evolution, ecosystem functioning, and mineral formation processes. This review highlights these uncertainties and outlines research priorities necessary to improve understanding of oceanic plateaus and deep-sea systems in the South Atlantic. Full article

Internal phosphorus loading is a key process sustaining eutrophication in stratified Baltic Sea coastal systems, yet its long-term dynamics in the Archipelago Sea remain poorly quantified due to limited deep-water monitoring and the absence of sediment time series. This study provides a multidecadal assessment of internal loading from the early 1980s to 2025 using two complementary indicators: (i) seasonal accumulation of total phosphorus in the surface layer (ΔTP) and (ii) the covariation between near-bottom oxygen depletion and dissolved inorganic phosphorus (DIP) release. Temporal associations with external phosphorus inputs from marine fish farming—highly variable during the study period—were analyzed to evaluate whether cumulative loading trajectories coincided with phases of intensified ΔTP. New measurements of drifting filamentous macroalgae from 2025 were additionally used to assess their seasonal contribution to the internal phosphorus pool and their relevance for mitigation. Results show a pronounced multidecadal strengthening of internal loading signals in the mid and inner Archipelago Sea. At the Seili station, ΔTP increased by approximately 6.8 µg L⁻¹ (≈3.4-fold) since the early 1980s. This trend coincided with long-term deterioration of near-bottom oxygen conditions and increasing DIP concentrations, consistent with enhanced sediment phosphorus release. Although cumulative aquaculture loading exhibited simple correlations with ΔTP, detrended analyses indicate that these relationships largely reflect shared long-term trends rather than direct causal linkages. Drifting filamentous macroalgae formed a substantial seasonal phosphorus reservoir (≈146 t P). Overall, internal phosphorus input to the Archipelago Sea has intensified markedly—by an estimated ~70% since the 1980s—highlighting the growing importance of sediment–water feedbacks and legacy phosphorus. Effective mitigation therefore requires strategies that address both internal recycling processes and external nutrient inputs. Targeted removal of drifting filamentous macroalgae may provide a complementary nutrient-export pathway in coastal management. 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

Investigations into the production of gas hydrates from marine sediments have demonstrated that commercial viability necessitates a daily gas production rate of 130,000 to 200,000 m³. However, the second-round trial production in the South China Sea yielded only 28,700 m³/day, falling short of the rule-of-thumb for economic feasibility. Given the coexistence of natural gas hydrates (NGHs) and shallow gas in the subsurface reservoirs of the South China Sea, a co-production strategy (simultaneously exploiting NGHs and shallow gas) was proposed to reduce costs and enhance production efficiency. In this study, a large-scale, three-dimensional, multi-phase, and multi-component model was established based on the NGHs–shallow gas symbiotic system in the Qiongdongnan Basin. A dual horizontal well configuration was designed to extract NGHs from the hydrate-bearing layer and natural gas from the underlying shallow gas layer. Co-production via dual horizontal wells expanded the hydrate dissociation zone from the near-wellbore region to deeper strata, particularly enhanced the dissociation of NGHs in the region between the two horizontal wells. By the 10th year of simulation, the peak and cumulative volume rate of CH₄ released from hydrate dissociation increased to 3.52 and 1.45 times under the co-production scenario, resulting in a 2.4-fold improvement in NGH recovery efficiency. Sensitivity analyses of bottom hole pressure and length of the horizontal intervals revealed that reducing bottom hole pressure significantly improved the daily and accumulative gas production from hydrate-bearing reservoirs. The length of horizontal intervals emerged as a critical factor influencing the dissociation of NGHs, whereas it had negligible impact on gas production from shallow gas reservoir with satisfied permeability. This study provides insights into optimizing the development of marine hydrate resources via integrated exploitation strategies. Full article

Sharm El-Luli, one of the most pristine embayments along Egypt’s Red Sea coast, is increasingly recognized as a sensitive sink for terrigenous inputs and emerging anthropogenic pressures. This study assesses the distribution, sources, and ecological and human health implications of heavy metals in bottom sediments collected throughout the lagoon. Concentrations of Fe, Mn, Zn, Cu, Pb, Ni, Cd, and Co were quantified and assessed using a suite of geochemical indicators and environmentally based indices. Sediment quality guidelines (SQGs; TEL–PEL and ERL–ERM) were applied to evaluate potential biological effects. Most metals exhibited background to minor enrichment, although localized elevations of Pb, Ni, and Zn suggest contributions from episodic wadi runoff and limited tourism-related inputs. I_geo and CF values generally indicated low to moderate contamination, while SQG comparisons showed that exceedances of TEL values occurred primarily for Ni and Pb, implying occasional risk for benthic organisms. Multivariate statistical analysis (PCA) separated metals into two principal components: a lithogenic component dominated by Fe, Mn, and Co, reflecting the influence of Precambrian source rocks; and an anthropogenic-mixed component (Pb, Zn, Cu, Ni) associated with terrigenous pulses and local human activity. Human health risk assessment (non-carcinogenic) showed hazard index (HI) values below unity for both adults and children, indicating negligible immediate health concerns, while potential carcinogenic risk raised in adults via ingestion for Cr followed by Cd and Ni than in children. The results highlight that while Sharm El-Luli remains relatively unimpacted, the lagoon’s geomorphology and low hydrodynamic energy promote metal retention, underscoring the need for continuous monitoring as coastal use intensifies. Full article

Evaluation of gas hydrate stability in marine sediments is commonly conducted assuming pure methane systems, although increasing drilling and logging evidence indicates that natural gas hydrates frequently contain minor amounts of heavier hydrocarbons. In the northern South China Sea, the presence of ethane has been widely reported, yet its influence on hydrate phase equilibrium and the distribution of the gas hydrate stability zone (GHSZ) remains insufficiently quantified. The results show that ethane is preferentially incorporated into large cages and promotes structure II hydrate stability, leading to lower dissociation pressures and higher stability temperatures compared with pure methane hydrates. Incorporation of as little as 1 mol% ethane systematically deepens the predicted base of the GHSZ and enlarges the hydrate-free gas coexistence interval beneath the bottom-simulating reflector (BSR). These effects indicate that conventional pure CH₄ models underestimate both the thickness of the hydrate stability zone and the potential extent of hydrate occurrence. At the regional scale, composition-dependent stability provides a coherent explanation for discrepancies between seismic BSR depths and hydrate predictions. This study establishes a composition-sensitive framework for regional GHSZ evaluation, demonstrating that even trace hydrocarbons must be considered to reliably assess hydrate occurrence, resource potential, and associated geohazards in continental margin settings. Full article

Global concerns regarding microplastics emerging in the environment have been raised recently. Using samples collected during the OceanXplorer mission in Aqaba, we explored the depth-based and regional variations of microplastics across pelagic and benthic zones. Microplastics (63.0–950.0 μm) from the surface seawater, middle seawater, bottom seawater, and deep-sea sediment were quantified and identified using a dissecting microscope and Fourier Transform Infrared microscope (μ-FTIR). The results revealed that the average abundance of microplastics was 6.7 ± 6.05 particles L⁻¹ in the pelagic zone and 2900 ± 1650 particles kg⁻¹ in the benthic zone. A size gradation of microplastics was observed across depths from 5 to 840 m, accompanied by a shift in particle types: fragments were the most common in the benthic zone, whereas fibers dominated the pelagic zone. μ-FTIR analysis identified the presence of the following polymers: polyethylene (PE), polyvinyl chloride (PVC), polyamide 6 (PA 6), and polypropylene (PP). These findings establish baseline data for future monitoring and management efforts addressing microplastic pollution in the Gulf of Aqaba. Full article

Along-slope bottom currents and down-slope (gravity-driven) turbidity currents coexist in the ocean and interact during their flow processes. The interaction between turbidity currents and bottom currents plays a crucial role in determining the lateral stacking of sediments and the direction of channel migration. Currently, there is ongoing debate regarding the migration direction, with two primary contrasting views: upstream migration versus downstream migration relative to the bottom current. However, due to the challenges in directly observing unidirectionally migrating channels in nature, the sedimentary hydrodynamics and underlying flow mechanisms remain poorly understood. In this study, we employ numerical simulations to systematically analyze the internal flow characteristics and depositional patterns within channels subjected to varying degrees of confinement. Our results demonstrate that variations in channel confinement influence the intensity of the interaction and the nature of the secondary flow, ultimately determining the spatial distribution of sediments. As confinement decreases, the migration pattern of a channel changes from negligible migration to migration in the downstream direction of the bottom current. Subsequently, it changes to migration in the upstream direction of the bottom current. This research provides a novel theoretical perspective for understanding the diametrically opposite migration directions of unidirectionally migrating channels and insights into the turbidity–bottom current interaction processes and the evolutionary mechanisms of deep-sea depositional geomorphology. Full article

Two Gram-negative aerobic halophilic bacteria, designated KMM 9989^T and KMM 9879, were isolated from a bottom sediment sample of the Okhotsk Sea, Russia. The novel strains grew in 0.5–4% NaCl, at 5–35 °C and pH 5.5–10.0. Phylogenetic analyses based on 16S rRNA gene and whole genome sequences placed strains KMM 9989^T and KMM 9879 within the family Roseobacteraceae, where they were clustered with their closest relative Marinovum algicola KCTC 22095^T. The average nucleotide identity (ANI) between strain KMM 9989^T and Marinovum algicola KCTC 22095^T was 81.4%. The level of digital DNA–DNA hybridization (dDDH) between the novel isolates KMM 9989^T and KMM 9879 was 97%, while between strain KMM 9989^T and Marinovum algicola KCTC 22095^T, it was 27%. Strains KMM 9989^T and KMM 9879 contained Q-10 as the predominant ubiquinone and C_18:1ω7c as the major fatty acid. The polar lipids were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, diphosphatidylglycerol, an unidentified aminolipid, two unidentified phospholipids, and three unidentified lipids. The genomic size of strains KMM 9989^T and KMM 9879 was determined to be 4,040,543 bp and 3,969,839 bp with a DNA GC content of 61.3 and 61.4 mol%, respectively. Both strains contained a common plasmid of 238,277 bp and a strain-specific plasmid (188,734 bp for KMM 9989^T and 118,029 bp for KMM 9879). It is suggested that the motility of KMM 9879 may be mediated by the presence of a complete fla2-type operon in the strain-specific chromid. Thus, based on the phylogenetic analyses and distinctive phenotypic characteristics, the novel marine strains KMM 9989^T and KMM 9879 are proposed to be classified as a novel species Marinovum sedimenti sp. nov. with the strain KMM 9989^T (=KCTC 8835^T) as the type strain of the species. Full article

The Northwestern Black Sea shelf, strongly influenced by Danube discharge and coastal activities, provides an effective setting for separating lithogenic controls from localized anthropogenic inputs. We applied a multi-proxy geochemical–radiometric approach to Romanian shelf waters and surface sediments. A CTD–Rosette was used to quantify nutrients, chlorophyll-a, TOC, and TN. Dissolved metals and PAHs were measured in seawater, while surface sediments were analyzed for CaCO₃, TOC, trace metals, and γ-emitting radionuclides. Multivariate statistics (PCA/FA) were used to resolve the dominant environmental controls. Summer stratification was characterized by the bottom-layer maxima of PO₄³⁻, SiO₄⁴⁻, and NH₄⁺ and a pronounced subsurface chlorophyll-a maximum at 12–16 m. Surface-water Σ16PAH ranged from 134 to 347 ng L⁻¹ and was dominated by low-molecular-weight compounds, with episodic nearshore enrichment in high-molecular-weight species. In sediments, CaCO₃ ranged from 7.6 to 29.9% and TOC from 0.11 to 0.96%. Trace metals were generally low. Pb and Hg peaked at nearshore station S23, whereas mean Ni (38.88 ppm) slightly exceeded the 35 ppm guideline, consistent with natural Fe/Mn-oxide association. PCA/FA identified a terrigenous axis (Fe-Al-Ti-V-Ni-Cr), a carbonate axis (CaCO₃; Sr where available), and an anthropogenic factor (Pb, Hg, HMW-PAHs). γ-spectrometry provided a compatible radiometric baseline that supports the multi-proxy interpretation. Full article

Sedimentary dynamics in the Palamós Canyon are influenced by river inputs and storm resuspension, as well as by bottom trawling on the canyon flanks. In this study, we estimate recent sediment deposition patterns along the canyon axis using the excess activity concentration of the short-lived radiotracer ²³⁴Th (half-life of 24.1 days). Sediment cores were obtained at various locations along the canyon axis from a depth of approximately 800 m to 2100 m in June 2023 and August 2024. Excess ²³⁴Th (²³⁴Th_xs) was detected in all sampled sites with variable penetration depths (0.5–3.5 cm). ²³⁴Th_xs-derived estimations of mixing rates decreased downcanyon from up to 15.6 cm² y⁻¹ at the canyon head (~800 m) to negligible mixing at the canyon mouth (~2100 m). ²³⁴Th_xs inventories, a proxy of recent sediment deposition, were high (1800–3490 Bq m⁻²) at the canyon head and at the upper canyon (~1400 m) close to fishing grounds and decreased downcanyon (82–694 Bq m⁻²) at the lower canyon (~1800 m) and canyon mouth. Inventories varied 2-fold across years presumably attributed to enhanced riverine and bottom trawling sediment fluxes. Similar ²³⁴Th-derived sediment deposition patterns can be found in submarine canyons worldwide, highlighting the value of this radiotracer for sedimentary dynamics studies in such complex environments. Full article