This study evaluates seawater intrusion (SWI) in the sandy unconfined coastal aquifer of Pehuen Có (Buenos Aires Province, Argentina) through the integration of hydrodynamic analysis and vertical electrical soundings (VES). The objective was to characterize the geometry of the freshwater–saltwater interface and identify mechanisms controlling salinization in a low-exploitation coastal system. Hydraulic gradients indicate active groundwater discharge toward the sea under present conditions. The Ghyben–Herzberg relation predicts interface depths of about − 80 m at the beach front relative to mean sea level. However, geoelectrical data suggest that the main saline wedge is located between − 90 and − 140 m and is preferentially hosted in lower-permeability units underlying the sandy aquifer, highlighting the influence of stratigraphic heterogeneity on intrusion geometry. Additionally, a shallow salinization process (0–11 m depth) was identified in the beach sector. The observed resistivity patterns are consistent with a tide-influenced salinization process linked to the flooding of semipermeable Holocene marine deposits exposed in the intertidal zone, which may temporarily retain saline water and promote localized vertical mixing. Similar processes have been described in the literature under different conceptual frameworks, and are here inferred for the first time in the study area. Under sea-level rise scenarios, increased tidal inundation may intensify shallow salinization and modify vertical salinity distribution. The proposed conceptual model provides a useful framework for supporting groundwater management and coastal conservation strategies in similar sandy coastal environments, while acknowledging the limitations associated with the absence of independent validation of salinity distribution.
Coastal seas are critical interfaces where sediment transport, hydrodynamic processes, and biological productivity interact. Understanding the spatially heterogeneous drivers of phytoplankton dynamics in such systems is essential for deciphering coastal environmental evolution and mitigating ecological disasters. Using satellite-derived sea surface Chlorophyll-a (Chl-a) concentration data and multi-source environmental data from January 2003 to December 2022, we employed an integrated machine learning approach to investigate the spatiotemporal patterns and environmental controls of sea surface Chl-a concentrations in the waters off the Shandong Peninsula, China. By combining Empirical Orthogonal Function (EOF) analysis, K-means clustering, Random Forest (RF) modeling, and Shapley Additive Explanations (SHAP), we objectively delineated five subregions with distinct seasonal Chl-a patterns. These subregions exhibited contrasting phenology: summer high values occurred in the nearshore bays and the adjacent Bohai Sea (Subregion 1, 4, and 5), whereas autumn-winter and winter-spring high values characterized the eastern coastal current zone (Subregion 2) and the offshore Yellow Sea (Subregion 3), respectively. SHAP analysis revealed that the influence of sea surface temperature (SST), suspended sediment concentration (SSC, a proxy for sediment resuspension and light availability), and mixed layer depth (MLD) varied substantially across subregions—in both magnitude and direction. Furthermore, subregion-specific nonlinear thresholds were identified for these drivers, indicating shifts in dominant limiting factors (e.g., from nutrient to light limitation with increasing SSC). These findings provide quantitative insights into the linkages between sediment dynamics and coastal biogeochemical responses, with implications for understanding eutrophication events, harmful algal blooms, and sedimentary environmental evolution under changing hydroclimatic conditions.
High-resolution proxy records are essential for understanding climate variability on interannual to decadal timescales. In this study, fossil Porites corals from Tanmen, Hainan Island in the northwestern South China Sea, were used to reconstruct mid-Holocene sea surface temperature (SST) variability. Monthly-resolution SST was reconstructed from coral Sr/Ca ratios, yielding a 67-year record centered around 5200 year BP. In addition, coral growth rates were used to generate an annual-mean SST record spanning 180 years ( 5257–5076 year BP). Spectral analysis of the SST records reveals significant periodicities within the 2–7-year band, consistent with ENSO variability, and an additional periodicity around 20 years, which may be associated with Pacific Decadal Oscillation (PDO)–like variability. Comparison of SST parameters indicates that winter SST dominates SST seasonality and exhibits the strongest relationship with PDO signals. Phase analysis suggests that El Niño events occurred more frequently during positive PDO-like phases, whereas La Niña events were more common during negative PDO-like phases. These results indicate that ENSO and PDO influences, as well as their interaction, were likely already active in the northern South China Sea during the mid-Holocene.
Understanding coastal responses to climate and sea-level changes requires integrated proxy records. This study presents multiproxy evidence from the Baeksu tidal-flat core, providing a reconstruction of Late Quaternary environmental dynamics on the southwestern Korean Peninsula. Pollen, dinoflagellate cyst, and palynofacies analyses document recurring marine influence from MIS 5e to MIS 1. MIS 5e reflects warm and humid interglacial forests, whereas stadial phases such as MIS 5b are characterized by abundant Artemisia and Amaranthaceae, suggesting cooler and drier conditions. MIS 3 is distinguished by the coexistence of subtropical evergreen and cool-temperate taxa, implying a complex climatic regime distinct from that recorded in northern East Asian records. Recurrent Amaranthaceae peaks during MIS 5b, MIS 5a, and MIS 3 suggest episodes of salt-marsh expansion; however, variations in the Artemisia/Amaranthaceae ratio and palynofacies types imply different controlling factors, namely climatic aridity during MIS 5b versus sea-level rise during MIS 5a and MIS 3. The persistent dominance of Spiniferites spp. supports the interpretation of long-term marine influence, while shifts in palynofacies suggest changes in depositional processes associated with varying degrees of marine influence. Together, these integrated proxies highlight the value of coastal archives for resolving climatic and sea-level controls on Late Quaternary environmental change.
Along the macrotidal southwestern coast of Korea, roughly a thousand rocky islands are scattered across the nearshore. Diverse tidal flats have developed along the margins of this rocky archipelago. Because these bedrock islands are non-migrating, the associated tidal flats differ greatly from classical tidal flats in their sedimentation patterns and long-term evolution. In this study, we characterize the island-type tidal flat and document distinct sedimentation pattern and stratigraphic evolution during the late Quaternary. For this purpose, we collected about 40 m long borehole core from the mud flat of Imja Island. Sedimentary facies and grain-size analyses have been conducted. Diatom assemblages have been additionally obtained. For the chronostratigraphy of the archipelago tidal flat, 14C-AMS and OSL age dating methods were applied. Imja Island tidal flat deposits are divided into four unconformity-bounded units, the units directly overlying volcanic basement. The lowermost unit A, a sandy-silty fluvial package dated to 97 ± 8 ka (Unit A) is overlain by lacustrine floodplain mud (Unit B1) and peat-rich swamp deposits (Unit B2) that accumulated at 55–52 ka during the lowstand of sea level. Early-Holocene transgression produced a 7.9 m-thick, finely laminated salt-marsh sequence (Unit C) between 10 and 8.5 ka. The uppermost unit D comprises about 17 m-thick of heterolithic sand–mud couplets and bioturbated mud, showing nine stacked channel fills emplaced since 2.3 ka. Age–depth modelling indicates rapid accumulation during the early Holocene, a reduced rate through much of the middle to late Holocene, and renewed acceleration during the late Holocene. The late increase in sediment accumulation, despite relatively limited regional sea-level rise, suggests that autogenic tidal-channel migration and vertical stacking played an important role in controlling sedimentation within the bedrock-confined archipelago setting.
Tidal shear fronts, as dynamic phenomena influenced by local topography, commonly develop in tidal channels. The complex bathymetry of the tidal channels off the Jiangsu coast provides favorable conditions for tidal shear front formation; however, reports of such features in this region remain limited. In this study, two tripod observation systems were deployed during the spring of 2019—one on a shallow shoal adjacent to an oyster reef and the other within a deep tidal channel—to conduct continuous measurements over two tidal cycles. Both homogeneous and reversed shear fronts were identified and found to be closely associated with tidal phases. Within a tidal cycle, no shear fronts were observed during the early ebb tide. Homogeneous shear fronts appeared around the peak ebb phase, characterized by faster ebb flow in the channel and slower ebb flow over the shoal. In the late ebb phase, reversed shear fronts developed, featuring ebb-dominant flow in the channel and flood-dominant flow over the shoal. Shear fronts were absent throughout the flood tide. Bathymetric differences between the shallow shoal and deep channel primarily control shear front formation. Reversed shear fronts enhance sediment convergence between the shoal and deep channel, intensifying dredging demands. Flood-ebb asymmetry in shear-front development drives net sediment transport from the oyster reef, shoal, and deep channel toward the northeast sand ridge, potentially mitigating sedimentation impacts on oyster reef growth. Our findings underscore the role of tidal shear fronts in navigation channel maintenance and oyster reef conservation.
Off Northeast Greenland, the Wandel Sea extends between Morris Jesup Rise and Gakkel Ridge as an area where rapid environmental changes are driven by complex interactions between the ice sheet, ocean, and sea ice. However, geological data that can illuminate long-term trends are virtually missing. We hereby present novel sub-bottom and swath bathymetry data acquired on the Arctic margin of Northeast Greenland in 2024. They allow characterization of the regional sedimentary features, which provide unique insights into the recent cryospheric and oceanographic history of Northeast Greenland. Mega-scale glacial lineations and iceberg plough marks point to extensive glacial activity on the continental shelf, where potentially two northeastward flowing ice streams reached the shelf edge during recent glacial periods. Extensive mass transport deposits in the area are interpreted as glaciogenic debris flows, thus, further supporting recent cross-shelf glaciations. Finally, the described asymmetric channel-levee systems and sediment waves suggest a southward-flowing oceanic bottom current as the Arctic Throughflow. The results of this study provide context for further research concerning sedimentary control factors along the Northeast Greenland margin.
The Sahara Slide Complex is a giant submarine landslide affecting 50,000 km2 of the northwestern African continental margin with low slopes of 2°. Although multiple slides have been identified, the factors pre-conditioning slope failures remain poorly understood. Here, we analyze high-resolution seismo-acoustic data that reveal six individual glide planes trending parallel to the seismic stratigraphy. These glide planes can be traced from the headwall area into the surrounding sections with intact sediments on the seismic data, suggesting that they are connected to laterally continuous weak layers in the sedimentary succession. Based on regional studies, the genesis of such weak layers might be attributed to the deposition of diatom-rich ooze during glacial intervals and relative increase in hemipelagic clay deposition during interglacial periods. Density and permeability difference between upper hemipelagic clay and lower diatom oozes can easily generate overpressure and initiate slope failures. Other possible preconditioning factors are high sedimentation rates during interglacials and recurrent volcanic ash layers. However, based on the cyclic character of glide planes, we suggest that the deposition of weak layers with regional significance is controlled by glacial-interglacial variations. We conclude that these climatically controlled weak layers therefore represent an important pre-conditioning factor that determines the geomorphology of large submarine landslides offshore the northwestern Africa.
Sand nourishments are a common nature-based coastal protection measure at the German Baltic Sea coast to prevent dune breaches. These nourishments cover parts of the dune, the beach and extend into the shallow water. During a two-year campaign, changes in sediment properties before and after a sand nourishment at Ahrenshoop, located at the microtidal Baltic Sea, were followed by taking sediment samples in the nourished ecosystems. The nourishment led to a temporary increase in water content and a reduction in organic and carbonate content. After two years, the water content returned to pre-nourishment conditions, but the organic and carbonate content were still lower than before the nourishment. Although the nourished sediment was selected to have a similar mean grain size to the existing beach and dune, there were changes in the degree of sorting. During the two-year campaign, the sorting degree returned to conditions prior to the nourishment. Therefore, the changes in sediment conditions caused by the sand nourishments are only short-term and similar to changes appearing after nourishments at the coasts of tidal oceans. However, nourishments could have long-term consequences for coastal ecosystems due to the repetition of the nourishment every few years.
Heat flow is a critical parameter to characterize the Earth’s inner thermal state, providing essential constraints on understanding planetary energy budgets, deep processes, and thermal evolution. Despite the accumulation of over 90,000 heat flow measurements worldwide, challenges such as uneven data coverage, inconsistent measurement methods, and ambiguous data quality still restrict accurate assessment of regional thermal state. Machine learning methods are now being extensively introduced to predict heat flow, owing to their strong capacity in data mining. Here, we employ the XGBoost algorithm to predict the heat flow distribution across the China Seas, constrained by regional geological and geophysical observations. Our results indicate that present-day heat flow for the China Seas ranges from 38 to 153 mW/m² and displays remarkably lateral variations between and within each sea area. Specifically, the Bohai Sea (60–71 mW/m²) shows a pattern featured by high in southwest and low in northeast, potentially linked to differential lithospheric thinning. The Yellow Sea (58–83 mW/m²) also exhibits higher values in southeast and lower values in northeast. The heat flow for the East China Sea (50–153 mW/m²) increases from northwest to southeast, reflecting the subduction retreat of the Pacific Plate. The South China Sea (38–111 mW/m²) displays distinct variations across different sub-tectonic units. Overall, high heat flow anomalies coincide with the tectonically active areas of mid-ocean ridges, volcanic belts and rift zones, whereas low values are associated with trenches and continental shelf areas. This work demonstrates the applicability of the XGBoost model in heat flow prediction for tectonically complex marginal seas and provides new insights into regional thermo-tectonic evolution and geothermal resource assessment in China Seas.
Based on sedimentological and organic carbon and nitrogen geochemical analyses of four sediment cores from the Paleo-Yangtze Grand Delta, this study reconstructs sedimentary environmental evolution and organic matter (OM) significance since Marine Isotope Stage 6 (MIS 6). During glacial periods, MIS 6 was characterized by fluvial facies deposition, with organic carbon preservation primarily controlled by sediment grain size. The consistently positive δ13Corg values observed in MIS 2 sediments are attributed to an increased contribution from C4 plants. During interglacials, grain size remained key, although its influence was modulated by other factors. Despite the most extensive transgression in MIS 5, strong terrestrial input partially masked the marine signal. During MIS 3, a shelf–delta front–tidal flat sedimentary system developed, with sedimentary facies differentiation and grain size characteristics jointly regulating the organic carbon preservation pattern. By MIS 1, rising sea level further enhanced marine influence, leading to the formation of a shelf–tidal sand ridge–tidal flat depositional system. This study demonstrates that integrating organic carbon–nitrogen geochemistry with sedimentary facies analysis effectively traces OM sources and elucidates the glacial–interglacial environmental evolution. The findings advance our understanding of OM burial mechanisms under varying climate and sea-level conditions and provide insights into sedimentary and carbon–cycle responses of marginal seas to global change.
Accurate knowledge of the seafloor is fundamental for understanding marine geomorphology, ecosystem distribution, and sustainable use of ocean resources, yet knowledge distribution remains uneven across ocean basins. This study presents the first spatially explicit bibliometric analysis of seafloor-mapping research (i.e., bathymetric studies) in the Mediterranean Sea, synthesizing georeferenced studies from nearly 700 peer-reviewed publications (1966–2020). Using GIS-based mapping and a novel classification matrix combining research density and impact metrics, the study quantifies geographic disparities in data coverage and research contribution. Results highlight strong geographic imbalances in research effort, with high-output “Consolidated High-Impact Hubs” concentrated in limited regions, while extensive “Underrepresented Areas” persist elsewhere. Importantly, research impact does not consistently align with studies density: some low-output zones host high-impact research, whereas certain high-density areas show weaker alignment between volume and influence of research effort. These findings highlight both structural and methodological imbalances in seafloor mapping research and underscore the need for more geographically balanced and integrated bathymetric research efforts. The framework developed here provides a transferable approach to other regional seas for evaluating the spatial distribution and impact of seabed-mapping research in marine geosciences. It provides a quantitative baseline for directing future mapping initiatives, optimizing collaborative surveys, and improving the representativeness of seabed data across the Mediterranean Sea and its regional basins.
Estuarine ecosystems are highly dynamic environments that provide critical ecological functions but remain vulnerable to anthropogenic pressures. In this study, we investigated long-term sedimentary processes and their geomorphological consequences on habitat dynamics of the sedge Bolboschoenus planiculmis (Scirpus planiculmis) in the Nakdong River estuary, South Korea. By integrating high-resolution habitat distribution mapping, surface sediment analyses, and lithostratigraphic reconstructions from two estuarine sediment cores, we reconstructed environmental changes in the estuary during recent decades. The results showed that major anthropogenic interventions, including the construction of estuary dams and the Four Major Rivers Project, significantly altered river discharge regimes, accelerated sedimentation rates, and triggered changes in sediment texture. These processes caused elevation increase in the intertidal zone and a gradual shift toward supratidal conditions, thereby reducing the extent of sedge habitat. Moreover, core-based stratigraphy revealed event-scale sedimentary pulses and hydroclimatic signals coinciding with periods of reduced discharge and increased marine influence. These findings indicate that human-induced geomorphological transformations, interacting with changing hydrodynamic regimes, reshaped this coastal wetland habitat. The sedimentological imprint of these changes underscores the value of geological archives for assessing ecological vulnerability and provides a basis for habitat restoration and estuarine management under future anthropogenic and climatic stressors.
High-resolution paleoenvironmental reconstruction is crucial for understanding past climate dynamics and predicting future climate changes. Holocene oyster reefs (Crassostrea gigas) on the coastal plain of the western Bohai sea serve as valuable archives for deciphering the paleoclimate fluctuations. Micro-scale sclerochronology study of individual oyster shells and macro-scale analysis on reef development can track the different time-resolution paleoenvironmental changes. This study investigated buried Holocene oyster reefs from three sites on the western coast of Bohai Bay: Dawuzhuang (DW), Lingtou (LT), and Huanggang (HG). Multi-proxy approaches, including radiocarbon dating, stable and radiogenic isotopes (C, O, Sr) and morphological analysis, were applied to the oyster shells. In addition, argillaceous sediments in the oyster reefs were analyzed for organic carbon, total nitrogen, total sulfur and their isotopes. Results indicated that the DW reef, characterized by relatively lower δ13C, δ18O, and δ13Corg values, was situated in a proximal estuarine setting with significant freshwater influence. In contrast, the HG reef exhibited higher isotopic values, suggesting minimal freshwater input and higher salinity. The LT reef showed the highest TOC/TN ratio, indicating substantial contributions from freshwater aquatic plants. The DW reef oysters, benefited from high plankton productivity due to terrestrial input, developed broader, thicker, and larger shells. Oysters at the HG reef, lied in a shallow marine area away from the estuary with the high salinity and hydrodynamics, displayed the largest shell height and growth rate but the shortest lifespan. At the LT reef, the low-energy habitat of a lagoon or semi-enclosed bay, fine sediment and reduced sediment stress supported the longest oyster lifespans and slowest shell height and weight growth rate. This integrated analysis of shell and sediment proxies successfully reconstructs distinct paleoenvironmental conditions and ecological adaptations across the Bohai Bay oyster reefs since middle Holocene.
Having been discovered in both the atmosphere-ocean and ocean-seabed boundary for decades, drag reduction in the bottom boundary layer (BBL) has aroused widely attention in both academic and engineering area and plays an essential role in the physical processes such as turbulent mixing and transport of mass, momentum and heat. Yet, no consistence has been reached regarding to its mechanism owing to the complexities and difficulties involved to test the proposed theoretical hypothesis practically. An explicit relationship has been put forward in this study that the bottom drag coefficient Cd increases with current velocity in the BBL until a tipping point, over which Cd decreases inversely with the increasing velocity and the associated incrementing suspended sediment concentration (SSC). The in situ observations over an intertidal flat approved such a relationship, particularly indicating that drag reduction occurred with turbulent diffusivity tending towards a constant as the current velocity reached 0.4–0.5 m s− 1 with a high SSC of 600–800 mg L− 1 under normal weather conditions with mild winds. This suggested that turbulence was damped as a result of the high SSC in the BBL, which serves as an isolated layer to damp/block the drag/turbulence. In contrast, the turbulence or mixing being induced by tough waves under windy conditions turned out to be so intense as to penetrate the whole water column to reach the seabed. More supports of the formation of the high-SSC-resultant drag-reduction layer came from the observations that drag reductions occurred commonly in a series of environments with various sediment dynamic conditions at varied critical current velocities, though. The causal linkage of “high velocity – high SSC – weakened turbulence on the bottom – drag reduction” provides a promising and tangible start point, from which the mechanism of drag reduction and thus turbulence weakening might be revealed hopefully.
Spartina has rapidly expanded across East Asian tidal flats, profoundly modifying sedimentary environments and benthic communities. Analysis of invaded and non-invaded sites in the Dongmak tidal flat, Ganghwa Island, Korea, assessed ecological responses to physical eradication conducted between 2020 and 2024. Invaded sites contained finer sediments and exhibited higher sedimentation rates than non-invaded areas, reflecting the ability of Spartina stands to reduce current velocity and promote fine-particle deposition. After eradication, sediments progressively coarsened, organic matter and nutrient contents declined, and grain-size distributions converged toward those of non-invaded flats within four years. Macrobenthic assemblages displayed comparable mean richness and density across invaded sites, yet invaded sites supported simplified communities dominated by a few tolerant taxa. Following eradication, species richness and diversity increased while dominance declined, signaling recovery of community complexity. Formerly dominant taxa such as Perinereis linea and Glauconome chinensis decreased in abundance, whereas a broader suite of species, including the protected crab Helice tridens, became more prominent. Taken together, the results indicate that Spartina invasion drives persistent alterations in tidal flat ecosystems, whereas physical eradication can initiate recovery when supported by sustained monitoring. Ecological convergence with non-invaded flats requires a minimum of four years, underscoring both the urgency of early intervention and the necessity of adaptive, long-term strategies for coastal restoration.
The Tu Chinh – Vung May (TC-VM) basin is one of the Cenozoic rift basins along the continental margin of Vietnam, formed during the tectonic evolution associated with the opening of the East Vietnam Sea (EVS). This paper addresses the scarcity of geophysical studies in the basin by using gravity anomalies to investigate its structural and tectonic characterization. Several edge enhancement techniques are estimated on a synthetic model before applying them to the Bouguer field of the basin. Bouguer data maps upward continued to different heights, and the corresponding results are also analyzed. Finally, the gravity inversion is used to map the Moho structure of the basin. The outcomes show that the enhanced horizontal gradient (EHG) filter yields sharper signals over the boundaries, and avoids bringing false edges; therefore, its outputs are used to establish a new subsurface structural map where many NNE-SSW, NE-SW, and N-S trending structures are recognized in the basin. The identified structural trends show a close correspondence with the orientations of the two major seafloor spreading stages of the EVS and may therefore reflect the influence of the regional tectonic regime associated with these spreading events. The inversion result shows that the Moho depth of the basin is approximately 9.7–22.4 km with a mean depth of 17 km, which is in agreement with the depth from seismic data. The findings demonstrate that the tectonic evolution of the TC-VM basin is closely tied to the broader geodynamic processes of the EVS, influenced by its sea-floor spreading and opening.
To elucidate the spatial migration characteristics and driving mechanisms of the mud depocenter along the Zhejiang-Fujian coast during the middle to late Holocene, this study integrates high-resolution shallow seismic profiles ( 10,000 km acquired during 2012–2016) from the Zhejiang coastal area with high-precision AMS ¹⁴C chronostratigraphic data from multiple cores (D02, D03, D05), supplemented by comparative analysis of existing borehole data (e.g., ECS-1302, D12). Results reveal four reflective interfaces (T0, T1, T2, T3) within the Holocene strata, corresponding to the seabed surface, an internal unconformity formed at 2 ka, the Holocene maximum flooding surface at 7.7 ka, and the Holocene basal boundary, respectively. These interfaces delineate three seismic units: SU3 (early Holocene), SU2 (7.7-2 ka), and SU1 (post-2 ka). Comparative analysis of SU2 and SU1 isopach maps demonstrates that the mud depocenter migrated northward from the offshore area of the Oujiang River estuary mostly between 27° and 28° N to the coastal region near 29.5° N in Zhejiang around 2 ka. During the periods of 7–2 ka and 2–0 ka, variations in the intensity of Zhe-Min Coastal Current and the upwelling induced by the Kuroshio nearshore branch, along with shifts in the frontal position resulting from their interaction, led to the migration of the depositional center. Concurrently, Yangtze River Delta evolution and anthropogenic activities may have contributed to increased sedimentation rates. This study provides insights into the response of East Asian marginal sea depositional systems to late Holocene environmental perturbations, and offers a historical case for evaluating the Anthropocene synergy between human activities and natural processes.
Beaches worldwide play an essential role in shore protection under storm conditions. How to identify the threshold beach width for effective shore protection remains largely unresolved due to a scarcity of measured beach profiles with sufficient temporal and spatial resolutions. In this study, weekly to monthly surveys spaced 100 m along the shoreline have been conducted at Ortley Beach, New Jersey since Fall 2023. The survey covered beach changes induced by Hurricane Lee and Tropical Storm Ophelia in Fall 2023. About half of the lost beach volume recovered within 1–2 weeks after the passage of these storms. With the onset of winter, cold fronts caused significant longshore variations in beach/dune erosion. At the erosional hotspots, severe dune line retreat occurred where the dry beach was narrower. Results indicate a critical threshold of dry beach width of about 35 m, below which dune-line retreat becomes more likely, increasing risks to landward infrastructure. As the weather shifted to summer of 2024, the beach gradually recovered, but net shoreline erosion and beach volume loss persisted, which created a more vulnerable condition for the following winter until the renourishment in Spring 2025. A simple empirical equation for threshold beach width was developed by integrating grain size and offshore wave height, supplemented by long-term beach-profile measurements from North Sand Key along the west-central Florida coast. Accurate estimation of this threshold provides a useful indicator for emergency beach management during storm conditions.
A remotely operated vehicle (ROV) expedition coupled with a sub-bottom profiler survey was conducted at a recently reported submarine landslide site located in shallow waters of the Krishna-Godavari basin, Bay of Bengal. Multiple seepage locations were identified, characterised by active gas bubbling, white microbial mats, and black sulfidic sediments. Chemical analysis of dissolved gases at the bubbling site revealed the presence of methane, with significantly enhanced concentrations ( 172 nmol/L) close to the seabed when compared to that of seawaters. The generation of microbial mats is possibly driven by sustained methane seepage at the site. However, there are no signs of the presence of any cold seep ecosystem. The recently activated landslides possibly induced methane seepages due to a drop in lithostatic load at the study site. This study signified the role of submarine landslides in the generation of methane seepages from the seabed. The seep site appears to be in an early, evolving stage of cold seep development, characterized by localized microbial mat formation but lacking a fully developed chemosynthetic ecosystem. This offers an unique opportunity to investigate the biogeochemical dynamics and microbial community structure of a nascent cold seep environments. Discovery of methane seepage associated with landslides and bacterial mats Elevated dissolved methane concentrations in the water column. Potential site to explore the evolution of chemosynthetic ecosystems
