Shallow Water Depth Research Articles

Water depth estimation from Sentinel-2 imagery using advanced machine learning methods and explainable artificial intelligence

The estimation of water depth in coastal areas and shallow waters is crucial for marine management and monitoring. However, direct measurements using fieldwork methods can be costly and time-consuming. Therefore, remote sensing imagery is a promising source of geospatial information for coastal planning and development. To this end, this study investigates advanced machine learning (ML) methods and redesigned morphological profiles for water depth estimation using high-resolution Sentinel-2 satellite imagery. The proposed framework involves three main steps: (1) morphological feature generation, (2) model training using several ML methods (Decision Tree, Random Forest, eXtreme Gradient BOOSTing, Light Gradient Boosting Machine, Deep Neural Network, and CatBoost), and (3) model interpretation using eXplainable Artificial Intelligence (XAI). The performance of the proposed method was evaluated in two different coastal areas (port and jetty) with reference data from accurate hydrographic data (Echo-sounder and differential global positioning systems). The statistical analysis revealed that the proposed method had high efficiency for depth estimation of the coastal area, achieving a best R2 value of 0.96 and Root Mean Square Error (RMSE) of 0.27 m in water depth estimation in the shallow water of Chabahar Bay in the Oman Sea. Additionally, the higher impact and interaction of the morphological features were verified using XAI for water depth mapping.

Assessment of the Attractiveness and Passage Efficiency of Different Fish Passage Solutions at a Hydropower Plant by Combining Fine Scale 2D-Telemetry and Hydraulic Numerical Modelling

Mitigation measures for downstream-migrating Atlantic salmon smolts (Salmo salar L.) are commonly insufficiently attractive to enable safe entrance and passage with no delay. Combining 2D telemetry with hydrodynamic modelling has been shown to be a good tool to better understand the influence of hydrodynamic factors on the migration route choice of fishes. In this study, we investigated the smolt downstream migration at a hydropower plant in Belgium that offers five migration routes, including two Archimedes screws and one nature-like fishway. At the hydropower plant, the Archimedes screws were the most used migration routes, due to higher discharges and more important water depths at their entrance. The weir and the canal intake were less used by the smolts. The nature-like fishway turned out to be less used, with 23% of the smolts. Its associated crossing time was significantly longer, probably due to shallow water depths and high flow velocities. The nature-like fishway had the potential to become a good migration route for salmon smolts after improvements to increase attractiveness and passage efficiency. Moreover, the Archimedes screws were not detrimental to the smolts and did not cause any significant delays to the crossing time.

A global assessment of estuarine tidal response to sea level rise

Climate change induced sea level rise (SLR) is one of the greatest challenges threatening the sustainable management of estuaries worldwide. Current knowledge regarding SLR and estuarine hydrodynamics is primarily focused on individual case studies, which provides limited guidance on how different estuary typologies will respond to SLR. To expand the current knowledge, this research used an idealised hydrodynamic approach to analyse the tidal range dynamics of 25 real-world estuaries with diverse shapes and boundary conditions, providing insights into estuarine response to SLR-induced tidal variations. Under present-day conditions, short length estuaries with wide entrances, deep waters, strong convergence, macro-tidal conditions, low values of roughness, and low upland river inflows are likely to experience amplified tidal range patterns; whereas lengthy estuaries with narrow entrances, shallow water depths, micro/meso-tidal conditions, high values of roughness, and high upland river inflows often exhibit a mix of dampened-amplified or fully dampened tidal range patterns. Under the effects of SLR, estuarine tidal range dynamics change depending on their present-day tidal range patterns. Where the present-day tidal range pattern is either dampening, a mix of dampening/amplification, or amplification, SLR increases (up to 61 %), moderately increases (up to 26 %), and slightly decreases/increases (up to 5 %) the tidal range of estuaries, respectively. Considering the relationship between an estuary's present-day tidal range pattern and its response to SLR, the presented approach may be useful in providing an initial assessment of SLR effects in estuaries worldwide. This approach may also help to identify sites most impacted by future SLR, and to direct decision-making towards evidence-based management approaches.

Preliminary design and dynamic analysis of constant tension mooring system on a 15 MW semi-submersible wind turbine for extreme conditions in shallow water

Floating offshore wind in China faces the challenge of shallow water depths and frequent typhoons, which are very different from the environmental conditions in European waters. The performance of the mooring system directly affects the overall cost of the floating offshore wind turbine and its survivability in extreme conditions. Under extreme conditions in shallow water, line dragging or breaking can frequently occur when the floating platform restrained by a conventional chain catenary mooring system drifts with waves. A constant tension mooring system concept is proposed to solve the design challenges of shallow water mooring systems in harsh conditions for floating wind turbines. The newly proposed mooring system consists of clump weight and winch wires, which release kinetic energy by increasing the platform's moving distance and ensuring that the instantaneous maximum mooring force never exceeds the breaking strength of the chain. Based on the time-domain potential flow theory, the coupling dynamic response of the UMaine VolturnUS-S semi-submersible reference wind turbine moored by a constant tension mooring system is studied. The mooring line tension and the platform motion are analysed. By comparing with the traditional catenary mooring system, it is found that the constant tension mooring system can significantly reduce the length of the mooring line used and the maximum mooring line tension. It completely prevents the mooring chain from being tightened and the turbine from being damaged by excessive mooring loads, effectively improving the survivability of a floating offshore wind turbine in extreme conditions in shallow water areas.

Wave Generation by Fluidized Granular Flows: Experimental Insights Into the Maximum Near‐Field Wave Amplitude

AbstractTsunamis can be generated by an impulsive displacement of water resulting from the entrance of pyroclastic density currents (PDCs). The maximum wave amplitude is of primary interest regarding tsunami modeling and applications to hazard assessment. This study explores tsunami generation by fluidized granular flows and analyzes published relationships predicting maximum wave amplitudes from PDC characteristics. A fluidized column of glass beads is released from a reservoir, flows down an inclined plane and enters a water‐filled flume, generating waves. Fluidized flows of greater mass enter the flume with greater velocities; however, all the analyzed flows impact the water with a supercritical impact Froude number. Flows of greater mass generate a single, high‐amplitude wave, followed by a longer‐period trough. The solitary‐like leading wave propagates along the flume with a nearly constant amplitude. In contrast, the leading wave is followed by a low‐amplitude trough and a second low‐amplitude crest when generated by lower mass flows. Dispersive effects are stronger for waves produced by flows of lower masses, causing the decrease of the amplitudes with distance from the shore. Increased breaking and dissipation cause decreased amplitudes of the waves generated in shallow water depths. The predictive equations, determined based on the impact Froude number and the water depth in the constant‐depth section of the flume, provide relatively good predictions of the maximum wave amplitudes. A new approach is proposed, which calculates the impact Froude number considering the water depth value where the wave generation occurs, providing an improved understanding of the wave generation process.

Do highly anthropized hydrological conditions in marshes influence fish communities according to their life‐history strategies?

AbstractAlterations of natural hydrology in aquatic ecosystems are known to strongly impact the community composition of different taxa. Surprisingly, literature on the potential influence of hydrology on fish community composition is still very scarce in agricultural marshes, where canals represent one of the few remaining aquatic habitats. This study is aimed to address this research gap by monitoring fish communities in independent hydrological units differing in hydrology management over a 6 years period. We predicted variable fish responses to the hydrological context according to different life‐history strategies (opportunistic, equilibrium, or periodic species). Periodic and opportunistic species were the most frequently observed. Despite differences in hydrology between canals (but little variation over years), we found that hydrology explained only a very low proportion of variation in the composition of fish communities. In particular, the flooding duration of meadows in early spring did not influence the composition of fish communities, not even the abundance of periodic species expected to rely on such temporary habitats. Instead, fish communities were more influenced by local habitat variables (aquatic vegetation cover, turbidity, tree roots, and refuges under the canal banks). The hydrological management of most hydrological units for agricultural purposes (i.e., severe flood abatement in spring and shallow water depth in canals in summer) was found to be incompatible with conservation goals to promote more diverse fish communities between hydrological units. Therefore, we call for further investigations in similar habitats covering a larger range of hydrological conditions.

Estimating stocking weights for Atlantic salmon to grow to market size at novel aquaculture sites with extreme temperatures

Land-based hatcheries are now capable of growing large Atlantic salmon (Salmo salar) post-smolts (approximately 150 – 1000 g), which means that marine net-pens can be stocked with substantially larger fish compared to traditional stocking sizes (< 150 g). This stocking strategy typically aims to reduce the time required for fish to grow to market size in the marine environment and limit risks (e.g., exposure to pathogens and diseases, opportunities for escapes). This study investigates another potential application of this strategy: the use of novel sites in areas previously considered unsuitable for aquaculture due to seasonally cold temperatures. The thermal-unit growth coefficient (TGC) model was applied to estimate the stocking weight needed to reach a harvest size of 5.5 kg, based on observed degree days for three sites. High resolution, depth-partitioned temperature time series from coastal locations in Atlantic Canada were used to represent a short, medium, and long growing season, as constrained by seasonal temperature extremes. Growing days for model inputs were defined as temperatures > 4 °C and trending up for stocking, < 18 °C to account for heat stress, and > -0.7 °C to avoid superchill conditions. Different TGC values were applied to simulate remedial, average, and elite growth performance. There was a range of model stocking weight estimates for each site (1.5 – 2.5 kg, 0.94 – 2.8 kg, and < 0.1 – 0.52 kg, for the short, medium, and long season sites, respectively). Results were sensitive to the number of degree days, heat stress threshold, and TGC value. At the two sites where season length was constrained by superchill, fish with a stocking weight of approximately 1.5 kg could grow to market size in shallow water depths (< 15 m), assuming elite growth performance. This investigation suggests that with appropriate growth performance assumptions and high-resolution temperature data, large post-smolt stocking strategies could enable the use of novel sites in coastal areas previously considered unsuitable for aquaculture.

Influence of ambient water coloration on habitat and conspecific choice in the female Lake Malawi cichlid, Metriaclima zebra.

Female cichlid fish living in African great lakes are known to have sensory systems that are adapted to ambient light environments. These sensory system adaptations are hypothesized to have influenced the evolution of the diverse male nuptial coloration. In rock-dwelling Lake Malawi mbuna cichlids, however, the extent to which ambient light environments influence female sensory systems and potentially associated male nuptial coloration remains unknown. Yet, the ubiquitous blue flank coloration and UV reflection of male mbuna cichlids suggest the potential impacts of the blue-shifted ambient light environment on these cichlid's visual perception and male nuptial coloration in the shallow water depth in Lake Malawi. In the present study, we explored whether and how the sensory bias of females influences intersexual communication in the mbuna cichlid, Metriaclima zebra. A series of choice experiments in various light environments showed that M. zebra females 1) have a preference for the blue-shifted light environment, 2) prefer to interact with males in blue-shifted light environments, 3) do not show a preference between dominant and subordinate males in full-spectrum, long-wavelength filtered, and short-wavelength filtered light environments, and 4) show a "reversed" preference for subordinate males in the UV-filtered light environment. These results suggest that the visual perception of M. zebra females may be biased to the ambient light spectra in their natural habitat by local adaptation and that this sensory bias may influence the evolution of blue and UV reflective patterns in male nuptial coloration.

Authigenic greigite in late MIS 3 sediments: Implications for the Yellow Sea Cold Water Mass and Yellow Sea Warm Current evolution

Yellow Sea current conditions during the late Marine Isotope Stage 3 (late MIS3, 40–30 ka B.P.) highstand remain unknown. Here, environmental magnetism, geochemistry, particle size, and scanning electron microscope methods are employed to analyze core YS01A with a basal age of 40 kyr from the South Yellow Sea mud deposits. Greigite formed in marine sedimentary layers with thickness >7 m during early diagenesis. Greigite formation is related to the redox state and total organic content (TOC) availability, which are controlled, respectively, by the Yellow Sea Cold Water Mass (YSCWM) and the Yellow Sea Warm Current (YSWC). In MIS1 (7–0 ka B.P.), a strong YSWC brought greater TOC, and a strong YSCWM (thickness of 48 m) resulted in a strongly reducing low-oxygen environment. This led to massive magnetite dissolution and pyrite preservation. In late MIS3 (37–31 ka B.P.), the weak Kuroshio Current and East Asian Winter Monsoon (EAWM) resulted in a low-intensity YSWC that provided less TOC. A weak YSCWM (thickness of 35 m), caused by shallow water depths and a weak EAWM, contributed to a less reducing sedimentary environment. Thus, pyritization was interrupted and greigite was preserved. Greigite content can, thus, be used to trace the development of Yellow Sea currents. During a period of slow sea level rise at 41–37 ka B.P., minor greigite formed with most magnetite being preserved, which indicates that the environment started to become reducing. This can be interpreted as due to initial formation of a thin and weak YSCWM. During the 37–31 ka B.P. highstand, the greigite content increased, which suggests more reducing conditions related to establishment of a thicker and intensified YSCWM. In addition, the greigite content decreased progressively, which may have resulted from YSWC weakening. Our results suggest that greigite can be used as a simple tool to reflect current evolution in the Yellow Sea, which can give a better understanding of continental shelf environment change.

Dynamic and loss analysis of flood inundation in the floodplain area of the lower Yellow River considering ecological impact

The floodplain area in the lower Yellow River plays the function of flood detention and undertakes the production and living functions of residents. Because the Yellow River basin is one of the most serious flooding areas in China, the Yellow River seriously threatens the safety of people’s lives and property and social stability and development in the floodplain area. It is significant to carry out flood inundation dynamic analysis and flood loss assessment in the lower Yellow River. Taking the zonal flood detention of the Jiahetan-Gaocun section as an example, a two-dimensional flow mathematical model is established by using MIKE 21. Through the numerical simulation of flood routing during the flood detention operation, the flood detention effect of the floodplain area is analysed, and the flood inundation dynamic analysis and flood inundation loss evaluation are carried out. The results show that the maximum absolute error of water level calculated by the model in the measuring station is only 0.77 m. So, it is reliable to use MIKE 21 to simulate the flood process and flood diversion in the lower Yellow River. The flood with a peak discharge of 4000 m3/s and 7000 m3/s basically reaches the maximum submerged area after 100 h, with the maximum submerged areas of 173.72 km2 and 323.47 km2, respectively. Autumn grain, as the main source of income for floodplain residents, is severely lost in shallow water depth, so they are severely lost in both floods. Therefore, when opening a floodplain as a flood storage and detention area, it is important to consider their loss. The flood simulation analysis results and flood inundation loss evaluation results can provide a scientific basis for the rational utilization of flood storage and detention areas in the lower Yellow River.

Six wave interaction equations in finite-depth gravity waves with surface tension

Three wave resonant triad interactions in two space and one time dimensions form a well-known system of first-order quadratically nonlinear evolution equations that arise in many areas of physics. In deep water waves, they were first derived by Simmons in 1969 and later shown to be exactly solvable by Ablowitz & Haberman in 1975. Specifically, integrability was established by introducing a system of six wave interactions whose symmetry reduction leads to the well-known three wave equations. Here, it is shown that the six wave interaction and classical three wave equations satisfying triad resonance conditions in finite-depth gravity waves can be derived from the non-local integro-differential formulation of the free surface gravity wave equation with surface tension. These quadratically nonlinear six wave interaction equations and their reductions to the classical and non-local complex as well as real reverse space–time three wave interaction equations are integrable. Limits to infinite and shallow water depth are also discussed.

Investigation of turbulent flows using spillway models aiming to aid downstream migration of fish

AbstractDams and other flow control structures constitute obstacles to upstream and downstream aquatic habitats, reducing life‐cycle success and even eliminating diadromous and potamodromous fish species from river basins. Providing effective passage past hydroelectric dams is critical for restoring habitat connectivity and sustaining populations of fish species. Surface water release over spillways is effective in diverting fish from turbines and establishing a safe bypass for downstream migrants. Developing an effective passage system over spillways requires both biological knowledge of fish behavior and abilities, as well as hydraulic knowledge of spillway flows to provide hydrodynamic conditions that fish may exploit. The present study experimentally investigates several depths, velocity, and turbulence fields intended to promote the downstream migration of fish over spillways. Instantaneous velocity fields were measured in an open recirculating rectangular water channel. A 90° standard spillway model, as well as a spillway model with a modified upstream face slope of 45°, were tested for two water depths. The results show the presence of a distinct recirculation bubble at the heel of the 90° standard spillway with the shallower water depth. It was concluded that the upstream recirculation bubble may be suppressed by either increasing the water depth or decreasing the upstream face slope. Decreasing the upstream face slope also resulted in a more uniform distribution of acceleration and lower turbulence along the upstream face of the spillway. The modified spillways provide more suitable hydrodynamic conditions for downstream migrants.

Assessment of nylon versus polyester ropes for mooring of floating wind turbines

With the development of floating wind turbines comes the need for mooring systems suitable for shallow water depths. Compliance becomes challenging for mooring systems composed of chain and wire rope. Polyester ropes can improve compliance, but the even lower stiffness of nylon may further reduce mooring line loads. However, fatigue lifetime of nylon ropes has been limiting. This paper presents results of stiffness and fatigue tests on long lay polyester and nylon ropes and evaluates the performance of two mooring systems for a floating wind turbine. The fibre ropes’ complex stiffness behaviour is modelled by the Syrope model, with mooring analyses based on fully coupled time-domain simulations. Nylon ropes reduce the dynamic loads in the mooring system, particularly wave frequency loads. This improves the fatigue lifetime of all components, allowing a reduction of the chain cross-section area by ∼40% compared to the polyester-based mooring system. The long lay nylon ropes show excellent fatigue properties. With the reduced loading, the lifetime is longer for the nylon ropes than the polyester ropes. Ultimate loads are also reduced when using nylon, allowing reduction of the breaking load by ∼30%. This gives a thinner and lighter rope than the equivalent polyester rope.

Non-Hydrostatic Numerical Model of Bragg Resonance on Periodically Submerged Breakwater

The Bragg resonance (BR) of a reflection coefficient resulting from the propagation of monochronic waves over periodically submerged breakwater was studied using the non-hydrostatic numerical model SWASH (Simulating WAves till SHore). Bragg resonance occurs when the incident wavelength is approximately twice the structural length of a periodic structural breakwater according to Bragg’s law and conditions. This study aimed to investigate the dynamics of Bragg resonance at water depths of 0.2, 0.3, and 0.4 m as the number of periodically submerged breakwater and their wavelengths changed. Specifically, this study focused on the Bragg resonance point of occurrence at a ratio of two structural wavelengths to the incoming wavelengths (2S/L). Regular waves were propagated over two periodically submerged breakwaters, with increasing structural wavelengths from 1 to 2 m at 0.2 m intervals. The results showed that Bragg resonances rapidly increase in value as the water depth decreases, but do not shift in their point of occurrence as the number of periodically submerged breakwaters increases. However, the Bragg resonance shifts leftward in 2S/L as the structural wavelength increases, with a slight increase in value at shallower water depths. More incident wave energy is reflected when the number of periodically submerged breakwater increases compared with when the structural wavelength of the periodically submerged breakwater increases. The differences in the Bragg resonance values are associated with the changes in the number of periodically submerged breakwater. Additionally, the shift in the point of occurrence was influenced by both water depth and structural length. This causes the Resulted Bragg resonance to deviate from the Expected Bragg resonance, which could be the reason why Bragg resonance does not mainly occur at 2S/L=1, as stated by Bragg’s law.

Critical assessment of U, Ba and Ni as redox and productivity proxies in organic-rich sediments underneath dynamic, highly productive waters

Sediments of the continental shelf anoxic zones of the Benguela upwelling system (BUS) and the Peruvian upwelling system are present-day hotspots of trace element accumulation. However, contribution of the lithogenic trace element fraction and early diagenetic transformation processes are poorly constrained. The identification of source and accumulation mechanisms is necessary for the validation of trace elements as proxies for productivity and redox cycling, notably in highly dynamic upwelling systems such as the BUS. Here, we analyzed redox- and biosensitive elements (U, Ba, Ni), lithogenic tracers (Al, Ti, Zr), total organic carbon (TOC) and P in eleven short sediment cores from the Namibian shelf (ca. 22–25°S) as well as grain size fractionated hinterland samples from the Tsauchab Valley at Sossusvlei (∼25°S). These samples help to constrain the lithogenic trace element contributions, a prerequisite for a realistic interpretation of marine authigenic trace element data. Our findings corroborate previous findings that Zr is a sensitive tracer of the coarse fraction in marine sediment for dust input and/or sediment reworking. Hence, the combined analysis of the coarse fraction (Zr), organic matter, and P enrichments (TOC/P) differentiates between a calm, organic matter-rich central shelf environment and a more energetic phosphorite-rich southern shelf environment. A significant correlation of U with P in cores from the southern shelf corroborates previous findings of U incorporation into apatite, the initial formation of which requires oscillating oxic to sulfidic redox conditions. Non-apatite associated U dominates in the cores from the central shelf, where it is only enriched in the buried, anoxic parts of the sediment. This also supports oscillating oxic to sulfidic redox conditions in surface sediment, where U may be recycled. Hence, U accumulates either (i) in apatite under oscillating oxic to sulfidic conditions or (ii) in buried anoxic sediment sections. This strongly questions the use of U as indicator of suboxic conditions but rather anoxic conditions. While lithogenic fractions of U were negligible, the lithogenic fractions of Ba and Ni were found to be elevated. The calculation of authigenic Ba when accounting for lithogenic Ba from the Sossusvlei fine fractions gives more realistic authigenic Ba values. The high Ba enrichment in the BUS is interpreted as uptake of Ba by diatoms and/or nucleation of barite in P-rich diatom remains, as suggested previously. Given the shallow water depth of the cores, barite formation must already take place in subsurface waters (<50 m water depth) as opposed to previous suggesting greater water depths. The lithogenic background of Ni strongly varies from 23°S to 25°S based on Sossusvlei data and the literature. When authigenic Ni contents are calculated accordingly and plotted versus TOC, more systematic trends are seen (compared to total Ni versus TOC). Essentially all cores show an increase in the authigenic Ni/TOC ratio with sediment depth suggesting better preservation and retention of Ni as compared to TOC consistent with previous observations in sediments from the Peruvian upwelling system. This trend corroborates the use of Ni as a productivity indicator for upwelling sediments.

Fish Boat Building as a Supporting Facility for Lobster Cultivation in Banyuwangi

The economic condition of the coastal communities of East Java, especially in Banyuwangi, is strongly influenced by the tourism and fishing sectors. This condition needs to be developed with supporting facilities such as the procurement of fishing vessels. Procurement of fishing vessels must be designed with a feasibility study on vessel operations. In general, coastal conditions have shallow water depths and are often used by coastal communities for lobster cultivation. The supporting fishing vessels must be able to maneuver properly and not damage the ecosystem so that the existence of coral reefs is maintained. The fishing boats that support lobster aquaculture are designed with good maneuverability by taking into account the speed, the result of the waves formed and the capacity of the ship. The results of the design of fishing boats supporting lobster cultivation obtained that the main size of the ship is 13.00 meters long, 3.00 meters wide and 0.8 meters draft with a speed of 12 knots, reaching a designed mileage of 30 km in shallow water operational conditions

Using UAVs and Photogrammetry in Bathymetric Surveys in Shallow Waters

The use of UAV (unmanned aerial vehicle) platforms and photogrammetry in bathymetric surveys has been established as a technological advancement that allows these activities to be conducted safely, more affordably, and at higher accuracy levels. This study evaluates the error levels obtained in photogrammetric UAV flights, with measurements obtained in surveys carried out in a controlled water body (pool) at different depths. We assessed the relationship between turbidity and luminosity factors and how this might affect the calculation of bathymetric survey errors using photogrammetry at different shallow-water depths. The results revealed that the highest luminosity generated the lowest error up to a depth of 0.97 m. Furthermore, after assessing the variations in turbidity, the following two situations were observed: (1) at shallower depths (not exceeding 0.49 m), increased turbidity levels positively contributed error reduction; and (2) at greater depths (exceeding 0.49 m), increased turbidity resulted in increased errors. In conclusion, UAV-based photogrammetry can be applied, within a known margin of error, in bathymetric surveys on underwater surfaces in shallow waters not exceeding a depth of 1 m.

Bivalves from the Changhsingian (upper Permian) Bellerophon Formation of the Dolomites (Italy): ancestors of Lower Triassic post‐extinction benthic communities

AbstractDiverse shallow marine fossil assemblages from the Changhsingian Bellerophon Formation (Dolomites) record late Palaeozoic marine life immediately before the end‐Permian mass extinction. We classified c. 6500 bivalves from western Dolomites localities, identifying 26 species including one new family (Ladinomyidae), three new genera (Ladinomya, Lovaralucina, Gardenapecten) and 10 new species: Acharax frenademezi, Bakevellia (Bakevellia) preromangica, Edmondia hautmanni, Etheripecten stuflesseri, Ladinomya fosteri, Lovaralucina covidi, Palaeolima badiotica, Promytilus merlai, Tambanella? stetteneckensis and Volsellina carinata. The occurrence of three Eumorphotis species with different stratigraphic distributions, leads us to propose an upper Permian ‘Lower Eumorphotis Zone’, divided into E. praecurrens, E. striatocostata and E. lorigae subzones, and distinct from the existing Lower Triassic Eumorphotis Zone (here renamed ‘Upper Eumorphotis Zone’). Palaeoecological analysis produced six biofacies and four ecofacies, based on richness, dominance and ecological lifestyle. The bivalves inhabited lagoonal to nearshore environments affected by stressed conditions: high temperatures, high salinity, shallow water depths, low oxygen and high terrigenous input. The upper Bellerophon Fm is characterized by increasingly fully marine conditions, although eurytopic taxa still suggest stressed conditions. Bivalve richness of the upper Permian Bellerophon and Lower Triassic Werfen formations was compared to estimate the genus‐level extinction rate. The disappearance of almost half (47%) of Bellerophon Fm genera is remarkably low compared with other, coeval bivalve faunas. Pre‐extinction bivalve faunas were dominated by stress‐adapted taxa (Unionites, Eumorphotis, Bakevellia, Towapteria) able to thrive in extreme environmental conditions, survive the end‐Permian mass extinction, and become the dominant biotic component of Lower Triassic benthic communities globally.

Optical Satellite-Derived Bathymetry: An Overview and WoS and Scopus Bibliometric Analysis

A technical and scientific overview regarding satellite-derived bathymetry (SDB)—one of the most promising and relatively cheap methods of shallow water depth determination—is presented. The main goal of the article is to present information about the possibilities of the SDB method to meet the demanding standard of bathymetric measurements in coastal mapping areas up to 20 m deep, i.e., up to depth areas where the largest number of ports and access waterways are located, as obtained using the bibliometric analysis. The Web of Science (WoS) and Scopus scientific databases, as well as R studio applications Bibliometrix and Biblioshiny, were used for scientific analysis. The bibliometric analysis presents the quantitative aspects of producing and disseminating scientific and professional articles with SDB as their topic. Therefore, the purpose of this study was to give the academic community an insight into the current knowledge about the SDB method, its achievements and shortcomings. The results of the bibliometric analysis of articles dealing with SDB show that most authors use empirical statistical methods. However, in recent years, articles using automated artificial intelligence methods have prevailed, especially the machine learning method. It is concluded that SDB data can become a very important low-cost source of bathymetric data in shallow coastal areas. Satellite methods have been proven to be very effective in very shallow coastal areas (up to a depth of about 20 m), and their biggest advantage is that the depth data obtained in this way are relatively low cost, while major limitations are associated with the parameters that determine the properties of the atmosphere and water column (clear atmosphere and water column) and bottom material. Procedures for different bathymetric applications are being developed. Regardless of the significant progress of the SDB method, which was manifested in the development of sensors and processing methods, its results still do not meet the International Hydrographic Organization (IHO) Standards for Hydrographic Surveys S-44.

Controls on shallow gas distribution, migration, and associated geohazards in the Yangtze subaqueous delta and the Hangzhou Bay

Shallow gas is generally extensively distributed in the Holocene muddy sediments and gas seepage has been increasingly reported to induce geohazards in coastal seas, but controls on gas distribution and migration remain elusive. This study explores gas distribution and migration in the Yangtze subaqueous delta and the Hangzhou Bay using high-resolution acoustic profiles and core data. Shallow gas is widely detected by the common presence of acoustic anomalous reflections including enhanced reflection, gas chimney, bright spot, acoustic blanking, and acoustic turbidity. The gas front depth is generally less than 17.5 m, and is meanly shallower in the Hangzhou Bay than in the Yangtze subaqueous delta because of relatively shallower water depth and coarser Holocene sediments in the Hangzhou Bay. Shallow gas is inferred to be a biogenic product, and its distribution is highly contingent on the Holocene stratal thickness and water depth. Active gas migration and seepages are evident, and recently increasing occurrences of gas seepage can be ascribed to global warming and seabed erosion due to sediment deficit. The findings warn us to pay more attention to the positive feedback loops of gas seepages with global warming and seabed erosion for the associated geohazard prediction and reduction, typically in the highly developed coastal regions.