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• The analytical solution of multipoint ground motion in multilayer submarine field is derived for the first time. • The transfer function and coherence function of multipoint ground motion at this site are derived for the first time. • The influence of soil stiffness and sea water height on ground motion is analyzed. In ocean engineering anti-seismic filed, the marine environment is usually regarded as the coupling field of seawater-layered porous seabed-elastic bedrock. This paper presents a theoretical method to study the spatially variable seismic underground motions in stratified seabed system. Based on the potential flow theory, Biot's porous model and random vibration theory, the transfer function and coherence function model of the underground seismic motions in the marine coupling field are derived. On the basis of the above theoretical derivation, the program of the spatial variability seismic underground motions of the coupling field is simulated and developed, and its accuracy and effectiveness are verified. Moreover, the effects of soil stiffness and overlying seawater level on the seismic response are also analyzed. Numerical results show that spatially variable seismic underground motions are significantly different from those on the ocean bottom. The simulation of spatially variable seismic underground motions for layered seabed field is significant for both theoretical study and ocean engineering application. [ABSTRACT FROM AUTHOR]

This review paper delves into the geological history of Mallorca, focusing on the Middle to Late Pleistocene period and its impact on the landscape and climate of the island. The Quaternary, particularly, the Last Interglacial, represents a relatively short timeframe on the global chronological scale, yet it is notable for its climatic instability and complex alternation of glacial and interglacial phases, leading to fluctuations in sea levels. During the last interglacial, millennial-scale fluctuations, known as Dansgaard–Oeschger and Heinrich events, occurred. Aeolianites are thought to have formed during periods of sparse vegetation cover and abundant sediment availability from the sea bed or platform (Heinrich events), while colluvial deposits and paleosols are believed to represent periods of reduced sediment supply and enhanced pedogenesis (Dansgaard–Oeschger events). These different deposits reflect climatic shifts and sea-level changes, offering insights into the environmental history of the island. Fossil evidence, including Strombus bubonius (currently known as Thetystrombus lauts) or "Senegalese hosts," reveals past warm climatic fluctuations, particularly during the Last Interglacial. Myotragus balearicus exemplifies evolutionary adaptation and isolation on the island, offering a unique perspective on its paleontological legacy. The integration of stratigraphic characteristics and literature research on Optically Stimulated Luminescence (OSL) dating techniques provides a comprehensive temporal framework, spanning from Marine Isotope Stage 6 (MIS 6) to Marine Isotope Stage 2 (MIS 2), enabling the precise dating of geological events and a stratigraphic correlation. [ABSTRACT FROM AUTHOR]

By taking advantage of recent analytical advances, we herein develop the 226Ra/230Th isotope systematics as a novel tool for quantifying nitrate and dissolved silicate fluxes across the sediment–water interface of the deep-ocean floor. Sediment cores were retrieved from the seabed between 4927 m and 5951 m in the North Pacific Ocean. Downcore profiles of 230Th and both dissolved and total 226Ra were measured using a high-sensitivity inductively coupled plasma mass spectrometer. At all study sites, a marked deficit of total 226Ra with respect to 230Th was observed between 0 and 20 cm, indicating active migration of soluble 226Ra from the sediment into the overlying seawater. By constructing the mass balance of 226Ra in the sediment column, the flux of dissolved 226Ra across the sediment–water interface was estimated to range from 461 to 1320 dpm m−2 yr−1. When coupled to a diffusive transport model as developed by early investigators, these flux values of 226Ra enabled us to calculate the flux of any dissolved constituent of interest by measuring their bottom water concentrations and pore water "saturation" concentrations. Based on the 226Ra/230Th disequilibrium approach, the derived fluxes vary between 4.1 and 10.5 mmol m−2 yr−1 for nitrate and between 11 and 49 mmol m−2 yr−1 for dissolved silicate. A compilation of nitrate and silicate fluxes from the seabed in the deep Pacific Ocean shows that these values are consistent with historical flux measurements based on the conventional core incubation method in the same study region. In addition, both nitrate and silicate fluxes exhibit a clear depth-dependent trend. Overall, our results suggest that sedimentary diagenetic alterations at the North Pacific Ocean floor below ∼ 5000 m are efficient so that only < 2 % of the particulate organic carbon and < 12 % of the biogenic opal raining to the seafloor are ultimately preserved in the sediment. [ABSTRACT FROM AUTHOR]

Extreme environments are habitats for a diverse array of microorganisms, namely extremophiles, that have evolved unique biochemical adaptations to their geological setting. Some examples of extremophiles can be found in the subseafloor or near hydrothermal vents on the ocean floor. Cultivated strains of extremophiles have demonstrated the ability to tolerate temperatures (T) up to 122 °C and pressures (P) up to 125 MPa. Organisms depend on the stability of key metabolites, such as adenosine triphosphate (ATP), to survive and reproduce under these conditions. In order to maintain their intracellular ATP levels, living cells must compensate for the abiotic hydrolysis of ATP, which occurs at a particularly rapid rate at high temperatures. The role of high pressures and high temperatures in abiotic hydrolysis of ATP has been rarely investigated despite the potential for this phenomenon to contribute to limit the adaptation of microorganisms to simultaneous extreme temperatures and pressures. This study presents new data on the effect of pressure on the abiotic hydrolysis of ATP to adenosine diphosphate (ADP) at elevated temperatures. In situ Raman spectra were measured at high pressure and high temperature of the hydrolysis of aqueous disodium ATP solutions in two experimental systems: a hydrothermal diamond anvil cell (HDAC) and a gas-pressurized autoclave. These two systems permitted the determination of hydrolysis rate constants of ATP into ADP up to 1670 MPa at 80 °C, 100 °C, and 120 °C. The data exhibited Arrhenian behavior with a slight decrease in activation energy from 0.5 MPa to 140 MPa. The effect of pressure on ATP hydrolysis rate constants was found to be vanishingly low in the so far known vital range up to 125 MPa. Abiotic hydrolysis rates of ATP showed a pronounced increase at higher pressures. For example, at 100 °C, a rise in pressure from 365 MPa to approximately 1670 MPa results in a nearly tenfold increase in the ATP hydrolysis rate constant. When compared with the typical ATP turnover times reported in living cells, the abiotic ATP hydrolysis rates determined in this study provide insights into the pressure and temperature conditions that could be consistent with living microorganisms. [ABSTRACT FROM AUTHOR]

• Derived newly the 3D exact solutions for free-field soil-liquid responses for oblique incident P or SV waves. • Derived 2.5D equivalent seismic forces for seabed for 3D incident waves. • Used 2.5D finite/infinite element method for seabed seismic analysis for 3D incident waves. • Investigated the effect of liquid depth on the solid responses under both sub- and super-critical conditions. • Observed the suppressive frequencies are closely related to vertical incident angle and liquid depth. The seismic behavior of underwater half-space under arbitrary 3D incidence of P- or SV-waves is analyzed by the 2.5D finite/infinite element method. Firstly, the 3D responses of solid and liquid in free field are newly derived exactly, which cover both the sub- and super-critical conditions. Then, the equivalent seismic forces acting on the solid boundary of the 2.5D finite/infinite element method are merely computed from the free-field displacement for given earthquakes. Subsequently, the equation of motions for the underwater half-space under arbitrary 3D incident seismic waves are established in the 2.5D finite/infinite element system, with the key parameters specified. The proposed method was verified against the previous 2D solutions and inversely computed free-field solutions in frequency domain. Major conclusions drawn from the present analysis include: (1) The effects of liquid, concerning enlargement, reduction or disturbance, on the seabed responses become stronger for increasing liquid depth under sub-critical condition; (2) The seabed interior responses are less sensitive to the variation in liquid depth under super-critical condition; and (3) Under the super- and sub-critical conditions, respectively, more attention should be given to the interior response for P-waves and to the seabed surface response for SV-waves. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is the most abundant element in Earth's atmosphere, but is extremely depleted in the silicate Earth. However, it is not clear whether core sequestration or early atmospheric loss was responsible for this depletion. Here we study the effect of core formation on the inventory of nitrogen using laser-heated diamond anvil cells. We find that, due to the simultaneous dissolution of oxygen in the metal, N becomes much less siderophile (iron-loving) at pressures and temperatures up to 104 GPa and 5000 K, a thermodynamic condition relevant to the bottom of the magma ocean in the aftermath of the moon-forming giant impact. Using a core–mantle–atmosphere coevolution model, we show that the impact-induced processes (core formation and/or atmospheric loss) are unlikely to account for the observed N anomaly, which is instead best explained by the accretion of mainly N-poor impactors. The terrestrial volatile pattern requires severe N depletion on precursor bodies, prior to their accretion to the proto-Earth. [ABSTRACT FROM AUTHOR]

The quantification of anaerobic oxidation of organic matter in the global seabed is to a large extent based on transport-reaction modeling of pore water ions involved in the mineralization processes. As the predominant of these processes, sulfate reduction can be modeled from the depth distribution of sulfate and other relevant solutes. An active organoclastic sulfate reduction is typically characterized by sulfate profiles with a concave-down shape. We use here a comprehensive database to show that half of all competent sulfate profiles have an opposite, concave-up shape, which may appear inconsistent with this concept. We also show that there is a strong discrepancy between sulfate profiles obtained by gravity coring and by IODP coring, with generally much higher sulfate flux and shallower sulfate penetration depth in the gravity cores (the term IODP here covers the international ocean drilling programs, DSDP, ODP and IODP). The discrepancy is correlated with a selectivity for coring sites in the published studies, by which gravity coring is focused towards the ocean margins and continental shelf and towards high surface water productivity and high sedimentation rate. In contrast, IODP coring is more frequently done in low sedimentation regions and is largely absent from the continental shelf. As a result, estimates of sulfate reduction in the global seabed may be biased by a selection of only IODP core data for the modeling. Furthermore, the modeling of pore water profiles shows net rates of sulfate reduction, while 35S-radiotracer experiments show the higher gross rates of the process. Estimates from 35S-radiotracer measurements suggest that dissimilatory sulfate reduction oxidizes 77 Tmol yr−1 of organic carbon globally, which is 3- to 4-fold higher than recent data based on modeling of IODP data. The potential biases by global estimates of sulfate reduction in marine sediments are discussed. [ABSTRACT FROM AUTHOR]

The San Juan archipelago lies along the axis of tidal movement between Straits of Juan de Fuca and Strait of Georgia in the Salish Sea. The amplitude of the tidal exchange produces significant tidal currents between the islands, as well as in Rosario Strait to the east and Haro Strait to the west. These currents are of interest as a future source of electrical power generation, given the archipelago's dependence on electricity supply by a subsea cable from the United States mainland. Here, we evaluate the tidal current energy potential in this region through a re-analysis of measurements collected by the National Ocean Service (NOS) and a high-resolution numerical model. Given the considerable variations in water depth and vertical velocity profiles across candidate tidal energy sites, we consider the trade-offs between tidal turbines deployed from a floating platform and those anchored to the seabed. Measurement re-analysis indicates several locations that could support tidal current power generation by MW-scale turbines with an acceptable balance between turbine size, rated power, and capacity factor. Even for relatively large (30 m) turbine diameters, surface-deployed turbines would be expected to produce up to 30 % more electricity than the same turbine deployed near the seabed due to vertical shear, with this difference increasing for smaller diameter turbines. As anticipated for sparse measurements, the regional simulation identifies several locations with power generation potential more than twice as high as locations in the measurement re-analysis. These sites were either not surveyed or excluded due to data quality issues. A benchmark comparison at the measurement locations with the highest power generation potential shows relatively good model fidelity, though time-average power density disagreements of ± 50 % persist throughout the water column. In addition to the case study, we also treat three general considerations for measurement data: (1) the accuracy of energy generation estimates from hub height speed relative to rotor-averaged power density, (2) the feasibility of extrapolating profiles towards the surface and seabed, and (3) trends in energy generation with rotor size and position in the water column. Overall, these results demonstrate that models and measurements can be used in a complementary manner for tidal energy site assessment and that tidal currents could be an important source of electricity generation in the San Juan archipelago. • Locations in the San Juan archipelago could support tidal current power generation. • Turbines near the surface produce 30 % more power than those near the seabed. • Simulations indicate sites with more than 2x generation of those with measurements. • Hub-height speed is a good approximation for rotor-averaged kinetic power density. • Tangent or power law fits can be used to extrapolate measurements, when needed. [ABSTRACT FROM AUTHOR]

We searched late Miocene sedimentary rocks in an attempt to recover fossil micrometeorites derived from the Veritas asteroid family. This study was motivated by the previous identification of a pronounced 3He peak (4-5x above background) within marine sediments with ages between ∼8.5–6.9 Ma ago (Montanari et al., 2017. GSA Bulletin, 129:1357–1376). We processed 118.9 kg of sediment from the Monte dei Corvi beach section (Italy), the global type-section for the Tortonian epoch (11.6–7.2 Ma). Samples were collected both before and within the 3He peak. Although a small number of iron-rich (I-type) fossil micrometeorites were recovered from each horizon studied (N total = 20), there is no clear difference between the pre- and intra- 3He peak samples. All micrometeorites are compositionally similar, and three out of five horizons yielded similar abundances and particle sizes. Micrometeorites extracted from sediments at the base of the 3He peak were exclusively small (ø <75 µm), while micrometeorites extracted from sediments near the highest 3He values were relatively large (ø <270 µm). The recovered fossil micrometeorites are interpreted as samples of the background dust flux derived from metal-bearing chondritic asteroids. The presence of a 3He signature combined with the absence of fossil micrometeorites or extraterrestrial spinels (Boschi et al., 2019, Spec. Pap. Geol. Soc. Am. 542:383–391) unambiguously related to the Veritas event suggests that the Veritas family is composed of highly friable materials that rarely survive on the sea floor to become preserved in the geological record. Our data supports the existing hypothesis that the Veritas asteroid family is an aqueously altered carbonaceous chondrite parent body, one that contains minimal native metal grains or refractory Cr-spinels. The low yield of fossil micrometeorites at Monte dei Corvi is attributed to loss of particles by dissolution whilst they resided on the sea floor but also due to high sedimentation rates leading to dilution of the extraterrestrial dust flux at this site. As with other fossil micrometeorite collections (e.g. Cretaceous chalk [Suttle and Genge, EPSL, 476:132–142]) the I-type spherules have been altered since deposition. In most particles, both magnetite and wüstite remain intact but have been affected by solid state geochemical exchange, characterised by partial leaching of Ni, Co and Cr and implantation of Mn, Mg, Si and Al. In some particles Mn concentrations reach up to 16.6 wt%. Conversely, in some micrometeorites wüstite has been partially dissolved, or even replaced by calcite or ankerite. Finally, we observe evidence for wüstite recrystallisation, forming a second generation of magnetite. This process is suggested to occur by oxidation during residence on the seafloor and has implications for the use of fossil I-type micrometeorites as a potential proxy for probing Earth's upper atmospheric composition (oxidative capacity) in the geological past. However, solutions to the limitations of post-depositional recrystallisation are suggested. Fossil I-type spherules remain a potential tool for palaeo-climatic studies. [ABSTRACT FROM AUTHOR]

• A formula for characterizing the excitation condition of the nth-order Bragg resonance is derived. • The influence of various bed parameters on wave reflection, including Bragg resonant reflection, is investigated. • Zero reflections are closely related to the zero points of the Chebyshev polynomial of the second kind. • When there is no slope, there are N − 1 zero reflections between two Bragg peaks, otherwise all zero reflections disappear. • Higher-order Bragg resonance peaks beat faster, and the nth-order Bragg resonance peak has n local maxima. For water waves propagating over a finite periodic array of congruent trapezoidal bars on a sloping seabed or trenches dug on a sloping seabed, an analytical solution in terms of Taylor series to the modified mild-slope equation (MMSE) is constructed. Based on the analytical solution, influences of various topographic parameters (e.g., the slope of seabed, bar/trench number, bar height or trench depth, and bar/trench width) on the peak value, peak phase and zero reflection of Bragg resonances are investigated. Especially, starting from the original definition of Bragg resonances, a modified Bragg's law for characterizing the excitation condition of the n th order Bragg resonance is derived, which shows that the excitation of Bragg resonances depends entirely on the average phase velocity of the water wave within the bar/trench field. When the influence of the bar/trench field on the average phase velocity is quite small, the modified Bragg's law degenerates into the traditional Bragg's law borrowed from X-ray crystallography, which also reflects the essential difference between the water wave as a mechanical wave and the non-mechanical X-ray wave. In addition, for N bars/trenches on a flat seabed, there are at least N − 1 zero reflections between any two adjacent Bragg resonance peaks. When the bars are very low or the trenches are very shallow, the phase of the N − 1 zero reflections in those zero reflections is exactly the position of the N − 1 zero points of the Chebyshev polynomial of the second kind, U N − 1 (cos k 0 d) , where k 0 is the wavenumber on the flat seabed and d is the bar/trench spacing. However, once a sloping seabed is added, all these N − 1 zero reflections disappear possibly due to the destruction of the symmetry of the background bar/trench field. Finally, regardless of the number of bars/trenches, when the bar/trench width varies, the peak value of the n th order Bragg resonance oscillates periodically, leading to n local maxima. A comparative study shows that these characteristics are consistent with the band structure shown in the Bloch periodic gap map (PGM). [ABSTRACT FROM AUTHOR]

The time-domain motion of a finite depth ocean subject to an arbitrary (in both time and space) imposed displacement of the bottom is studied under the assumption of linear theory. This solution provides results for this limiting case which may be helpful for benchmarking. The focus is on the numerical simulation of the near-field waves with application to the simulation of tsunami waves. The fluid domain is assumed two-dimensional, and the effect of compressibility is included. The time-domain solution is built from the frequency domain solution taking a Fourier series expansion of the bottom motion. This expansion allows complex displacements to be simulated. The solution in the frequency domain is expressed as a sum over modes. The time-domain solution is calculated by numerical evaluation of the Fourier transform in time, allowing arbitrary time-dependent motion. This code is extremely efficient and highly accurate, and there is no time–stepping so that errors do not accumulate in time. The eigenfunction expansion method to obtain the velocity potential for a flat ocean bottom case is independently derived. A shallow water limit for all the above cases is provided, giving a method to check the correctness of the numerical solution. Separate treatment for all the situations under the compressible assumption is also performed. The horizontal and vertical particle velocities are graphically presented for the time-harmonic oscillation. Time-dependent surface wave propagation is computed to show the initiation of tsunami waves in the deep ocean and their subsequent propagation. The calculations presented here allow for the simulation of tsunami wave generation and to investigate various effects, including the role of acoustic gravity waves. It is shown that the compressibility is not always significant, but that when the water is either sufficiently deep or the rise sufficiently rapid, acoustic gravity waves are produced. It is shown that, in this case, the ocean surface undergoes a rapid oscillation and that this may be a method to detect tsunamis. [ABSTRACT FROM AUTHOR]

A Lagrangian flow model is used to investigate highly nonlinear, dispersive waves generated by moving seabed deformation (MSD) of an otherwise horizontal seabed. Applications include free surface wave responses to horizontal co-seismic displacements and to novel bed-driven wave making systems used in surfing competitions. This paper considers gravity waves in viscous liquid, without restrictions on wave steepness, dispersion coefficient, and flow regime. Numerical computations are carried out using a Moving Particle Explicit method, which provides a Lagrangian flow description with far fewer particles than existing meshless methods. We show that the MSD speed has different effects in shallow and intermediate water depths. In shallow water, raising the MSD speed to a transcritical value promotes generation of leading solitary waves as expected. In supercritical flow, the highly nonlinear dynamics promotes breaking of the precursor soliton. In intermediate depth, wave dynamics is dominated by nonlinearity and dispersion, which act concurrently to generate a large leading wave that travels faster than predicted by linear theory, followed by a train of dispersive, short, steep waves. These waves break, even at subcritical values of MSD speed. We show that strongly nonlinear viscous dynamics occurs in the presence of a steep seabed deformation. This triggers flow separation, linked to strong amplification of wave steepness. Finally, we show that an oscillating MSD is capable of generating higher harmonics by means of nonlinear wave–wave interactions. The model is validated and verified by comparison to previously published experimental data and approximate analytical solutions. [ABSTRACT FROM AUTHOR]

A model for tsunamis propagation is derived by coupling a weakly compressible liquid layer, standing for the ocean, to a viscoelastic solid layer of constant depth, representing the upper layer of the Earth. Below this layer, the Earth is assumed to be perfectly rigid. The resulting equations are averaged over the depth of the water layer for the liquid part and are integrated over the thickness of the solid layer for the solid part. The obtained system of equations is hyperbolic and admits an exact equation of energy conservation. The model is dispersive and includes an elastic branch, an acoustic branch and a gravity branch. The elasticity of the solid layer entails: (1) a reverse dispersion effect i.e. the phase velocity of the gravity branch decreases for small wave numbers if the wave number decreases; (2) an arrival time delay of the tsunami and (3) a leading negative phase i.e. a negative water elevation before the arrival of the main wave. All these effects are absent if the sea floor is assumed to be perfectly rigid. The arrival time delay due to elasticity comes in addition to the delay due to seawater compressibility. These effects are in agreement with previous works on tsunamis propagation. This preliminary model is a promising alternative approach for tsunamis propagation due to its ability to capture the main physical effects with a relatively simple mathematical structure of equations, which is easy to solve numerically. [ABSTRACT FROM AUTHOR]

In the past 10 years, the offshore wind energy harvest industry has developed rapidly worldwide. However, seismic waves would bring a great threat to the safety and stability of offshore wind turbines (OWTs). In this study, taking the marine geotechnics numerical software FssiCAS as the computational platform, adopting the generalized elastoplastic soil model Pastor-Zienkiewicz-Mark III (PZIII) to describe the complex mechanical behavior of seabed soil, the seismic dynamics, as well as the stability of a thin-walled monopile OWT with an equipped capacity of 1.5 MW and its seabed foundation are comprehensively investigated, by the way of finely modeling and meshing for the important components of the OWT, i.e., the blades, nacelle, and tower. The numerical results indicate that OWT and its seabed foundation strongly respond to the excitation of seismic waves, and there is intensive interaction between OWT and its seabed foundation. In the case of this study, the horizontal oscillation amplitude at the top of the turbine tower reaches 2m, the superficial seabed soil at the far field is liquefied with a depth of 3–4 m, and the liquefaction depth of the seabed soil surrounding the monopile reaches 5–6 m. Even so, the OWT involved in this study has no cumulative displacement, there is only vibration displacement. It is indicated that the OWT has good seismic stability. It is indicated by the comparative study that the complex mechanical behavior of seabed soil, the complex geometry and mass distribution of OWTs, and the consideration of the pore water in seabed foundations have a radical influence on the seismic dynamics of OWTs. The work presented could be a valuable reference for the evaluation of the seismic dynamics and stability of OWTs in the future. • Seismic dynamics of an OWT and its seabed foundation is explored. • A coupled numerical software FssiCAS is taken as the computational platform. • Complex dynamic behaviors of loose seabed foundation are described by PZIII model. • Complex geometry and mass distribution of blades and nacelle are modeled and meshed. • Soil liquefaction, intensive vibrating of OWT, seismic wave amplification are illustrated. [ABSTRACT FROM AUTHOR]

Subsea gas release incidents may result in catastrophic consequences, e.g., overturning of offshore floating structures, fire, and explosion. This paper developed a model to investigate the dispersion behavior of underwater gas released from the seafloor soil under combined action of current and wave. Eulerian-Eulerian model is used to track underwater gas dispersion trajectory. Porous model is utilized to describe the seafloor soil and simulate the penetration of gas released from seafloor soil. The numerical model is validated by comparing with small-scale experiments. The effect of release rate, current velocity and soil porosity is investigated. The parameters, e.g., rising time, horizontal dispersion distance and surfacing area are estimated. The uniqueness of this study is that underwater gas plumes are simulated considering the seafloor soil and the combined action of current and wave. The results indicate that the presence of seafloor soil has a significant effect on the migration shape and trajectory of underwater gas plume. The combined action of current and wave increases the dispersion distance of gas plume. This study can support risk assessment and emergency planning of subsea gas release accidents. [ABSTRACT FROM AUTHOR]

Seabed logging (SBL) is a direct and remote application of controlled source electromagnetic (CSEM) method to detect hydrocarbon resources beneath the seafloor in offshore conditions. In this method, electromagnetic waves are used to detect the resistivity contrast between various sediment layers. The current source of electromagnetic waves is a horizontal electric dipole (HED) antenna. The antenna design represents a challenge in shallow waters (less than500 m seawater depth) due to the presence of airwaves that lead to a low signal-to-noise ratio, hence hindering the detection of a hydrocarbon reservoir. A horizontal circular electric half-wave dipole will be used in this work as the source of electromagnetic waves. The numerical solution for the electric field response will be developed based on solving the Maxwell equations in two modes: the poloidal and toroidal modes. Simulation results have shown that the new antenna is able to detect the presence of deep hydrocarbon reservoirs (up to 5000 m) in shallow-water environment. Comparison of the average percentage difference in delineation between the circular and the HED was carried out. The new antenna results in 61 % delineation compared to 15 % for the HED at 5000 m hydrocarbon depth and 200 m seawater depth, indicating the ability of the antenna to disperse the airwaves. The results also show that the airwaves are significantly reduced from nearly 15000 m (for the HED) to 10000 m offset for the proposed antenna, hence increasing the signal-to-noise ratio. These results seem to indicate the potential for the new antenna to be used as an EM source for SBL in shallow-water environment. [ABSTRACT FROM AUTHOR]

Autonomous underwater vehicles (AUVs) are becoming increasingly popular for seabed coverage survey tasks but suffer from a serious problem of positioning error accumulation, which leads to low path tracking accuracy and a low coverage rate of the target area. A dual-stage AUV path planning (DSPP) approach was proposed within a simultaneous localization and mapping (SLAM) framework for coverage bathymetric surveys. In the first stage, a global coverage path is designed in a lawnmower style. Crossed paths are added to generate periodic loop closures in SLAM, which can improve the efficiency of online replanning. In the second stage, with a probabilistic neural network (PNN) used for feature-rich bathymetric sub-map identification, an entropy-based online path replanning approach was implemented using 20 templates to adjust the global path to produce accurate loop closures for positioning error correction. Two bathymetric datasets were used to test the proposed DSPP method using a self-developed experimental simulation system. Experiments verified that DSPP can significantly improve the positioning accuracy and coverage rate with acceptably longer paths. In a 6000 m × 5000 m area , the DSPP approach reduced the positioning error by 76% compared with the pure dead reckoning method, and the coverage ratio reached 98.15%. • Dual-stage coverage path planning for AUV bathymetric survey in SLAM framework. • Bathymetric sub-map classification using PNN for online path replanning of AUV. • Entropy-based path replanning algorithm for efficient position uncertainty reduction. [ABSTRACT FROM AUTHOR]

Floating offshore wind turbine (FOWT) is restrained by the mooring system, and the motion response of FOWT leads to complex interaction among the anchor, chain, and soil. The conventional aerodynamic-hydrodynamic-mooring model of FOWT typically assumes a fixed boundary constraint at the seabed for the mooring system, neglecting the interaction of anchor-chain-soil. The assumption affects the global responses of FWOT. This paper establishes a finite element model for the dynamic interaction of the anchor-chain-soil system based on the Coupled Eulerian-Lagrangian (CEL) method in Abaqus, introducing a method to approximate the interaction through equivalent stiffness and damping. Then, through joint simulation with OpenFast and Orcaflex, a fully coupled aerodynamic-hydrodynamic-mooring-anchor model of FOWT is developed to study the impact of the anchor foundation on the dynamic characteristic of FOWT. Compared with the new proposed aerodynamic-hydrodynamic-mooring-anchor model, it is found that the traditional model underestimates the maximum horizontal response of platform and overestimates the mooring line tension. • A method is proposed to simplify the anchor-chain-soil interaction as equivalent stiffness and damping. • A fully coupled aerodynamic-hydrodynamic-mooring-anchor of numerical model of FOWT is developed. • Compare the dynamic characteristics of the new model with those of the traditional model through numerical simulations. [ABSTRACT FROM AUTHOR]

A novel model is put forward to characterize the seismic response excited by vertical P-waves in a transversely isotropic and layered nonlocal poroelastic seabed. The proposed model integrates nonlocal parameter, anisotropy, and stratification to accurately examine wave propagation behavior. The fundamental equations for the underlying seabed are formulated using Biot's poroelastodynamic theory and Eringen's nonlocal theory. The wave equation for the overlying water is expressed in terms of the velocity potential. General solutions in both the poroelastic seabed and water layer are derived by solving the involved ordinary differential equations. Employing the newly devised and unconditionally stable propagator matrix scheme, semi-analytical solutions are derived for the time-harmonic response in a layered poroelastic seabed subjected to vertical P-wave excitation within the frequency domain. The validity of the proposed solutions is confirmed through rigorous comparison with the previously established analytical solutions. The influence of key material properties of seabed on the velocities of P-waves and free-field response in the poroelastic seabed is estimated in detail, along with the free-field response in a nonhomogeneous poroelastic seabed. • A semi-analytical dynamic seabed model by vertical P-waves is presented. • 1D rigorous nonlocal Biot theory is proposed. • Dual-variable and position (DVP) method is utilized for solving layered seabed. • Effect of nonlocal parameters and anisotropy on wave propagation is analyzed. • Free-field response in a nonhomogeneous poroelastic seabed is estimated. [ABSTRACT FROM AUTHOR]

In ice gouging analyses, the seabed is often simplified as a uniform material domain, over-looking the potential complexities inherent in layered seabed formations, which are wide-spread in numerous Arctic regions. This study investigates the pipeline response into the distinct seabed configurations, including layered soft over stiff clay, layered stiff over soft clay, and uniformly soft and uniformly stiff compositions, to ice gouging. This was achieved through comprehensive large deformation finite element (LDFE) analysis, employing a Coupled Eulerian Lagrangian (CEL) algorithm. Incorporation of the strain-rate dependency and strain-softening effects involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. The pipeline is explicitly incorporated into the model, allowing for a detailed investigation of its response to ice gouging phenomena within these layered seabed scenarios. This research demonstrates that simplifying a layered seabed into a uniform can be misleading. Such an approach can lead to significant errors, potentially overestimating or underestimating pipeline response to ice gouging. By incorporating these complexities, engineers can develop more optimized designs with enhanced safety margins in Arctic environments prone to ice gouging phenomena. • Arctic subsea pipelines are buried for physical protection against the ice scour. • Determining the minimum burial depth needs accurate modelling of the ice-seabed interaction. • Layered seabed strata are not covered in design codes and recommended practices. • The effects of layered seabed on buried pipeline Response to ice gouging was investigated. • Study reveals simplifying layered seabed to uniform domain yields inaccurate prediction of pipeline response to ice gouging. [ABSTRACT FROM AUTHOR]

Monopile foundations are commonly used to support offshore wind turbines (OWTs) in nearshore shallow waters, where the periodic ebb and flow of tides can cause severe seabed erosion around these foundations. Accurately predicting the progression of scour depth under these tidal conditions is crucial for the safety of OWTs. While a few empirical formulas for equilibrium scour depth in periodic tides have been proposed, they often overlook the backfilling effects during their derivation. Consequently, these methods fail to predict the progression of scour depth characterized by recurring scouring and backfilling processes. In this study, the scour progression under different tidal patterns, including square tides, symmetrical sinusoidal tides, and asymmetrical sinusoidal tides with various periods, is investigated using numerical methods. It is indicated by the results that deeper scour depths are produced by symmetrical tides compared to asymmetrical tides, while the highest scour depth is observed under square tides, potentially slightly exceeding that under unidirectional currents. Additionally, asymmetric scour depths at the front and back sides of the pile can result from the asymmetry of tides. Although scour progression is affected by tide periods, their impact on the equilibrium scour depth is limited. Furthermore, a new concept called normalized cumulative effective flow intensity is introduced, which plays a primary role in governing equilibrium scour depth. Based on this concept, prediction methods for both equilibrium scour depth and scour progression under sinusoidal tides, which closely resemble natural tidal patterns, are proposed. The accuracy of these methods is validated by experimental data from previous studies. These findings not only provide a method to optimize the design of monopile burial depth but also aid in the development of appropriate maintenance measures to prevent scour-induced damage to OWT foundations over their long lifespans. • Impact of tide period, pattern and asymmetry on the scour of monopiles is studied. • Symmetrical tides cause deeper scour depths than asymmetrical tides. • A new concept, normalized cumulative effective flow intensity, is introduced. • Prediction methods for scour depth and progression are proposed and validated. [ABSTRACT FROM AUTHOR]

A petrographic study of " Verde Prato " (trade name of an ophiolitic serpentinised peridotite quarried in Tuscany) revealed, next to a relict Cr-spinel, another opaque ore mineral apparently containing ca.17 wt% SiO 2. In order to unveil the origin of this anomalous composition, detailed SEM-EDS, μ-Raman spectroscopy and X-ray μ-diffraction investigations were undertaken, which provided useful but somehow contrasting indications. Therefore, in order to definitely unveil the nature of the unusual opaque mineral, a specific TEM study was undertaken. This showed the presence of submicroscopic euhedral Mn-Cr-Fe-spinels in a matrix of a 7 Å layer-silicate (Al-lizardite). Interesting, all the submicroscopic spinel grains were found to share the same crystallographic orientation, suggesting an origin from a single, larger, former crystal. This unusual type of alteration of the mantle spinel probably occurred on the ocean floor during the pervasive polyphase process of hydrothermal peridotite serpentinization. Overall, by mapping the different serpentinite microstructures and compositions, a polyphase serpentinization history consisting of at least eight different cycles has been suggested. Moreover, the spinel composition indicates that the alteration was accompanied by Mn-metasomatism, made possible by the close proximity of Mn-rich hydrothermal vents, such as "black smokers". [Display omitted] • Spinel alteration in " Verde Prato " lacks the common 14 Å-chlorite aureole. • Secondary spinel is a manganochromite, which entails Mn metasomatism. • Serpentinization was polyphasic and related to different tectonic activity stages. • Spinel altered into a nano-mosaic of spinel tesserae infiltrated by phyllosilicates. [ABSTRACT FROM AUTHOR]

Scour around monopile foundations is a major cause of offshore wind turbine failures, necessitating effective scour prevention measures to ensure the reliability of monopiles. This study investigates a new scour prevention strategy utilizing a vertical turbine rotor. This measure can not only effectively reduce scour around monopile foundations in complex flow field environments but also generate clean electricity, adding value. The effectiveness of the device in mitigating scour is evaluated through experiments. Subsequently, the impact of the flow field around the pile foundation and the seabed shear stress are examined using numerical simulations. The influence of the device's installation position on seabed shear stress is also discussed. The results indicate that the vertical rotating device significantly reduce scour around the pile foundation, thereby enhancing the reliability of monopile foundations. •New scour prevention measures using vertical rotation device is investigated. •Installation of a rotating device in front of the monopile can effectively prevent scouring. •The vertical rotation device reduces the intensity of eddy currents around the monopile. •A suitable mounting position optimizes the effectiveness of the rotating device in preventing scour. [ABSTRACT FROM AUTHOR]

The suction caisson foundation is a competitive alternative to the traditional solutions of driven piles or mudmat for platform jackets and subsea systems in deep-water engineering. A new model for predicting the bearing capacity of suction caisson in the clay-sand-clay seabed is proposed in this paper, based on the plastic limit analysis and silo analysis. Upon the assumption of the aspect ratio smaller than 1 and the heterogeneity factor larger than 1, the Hill-type failure mechanism of the overlying layer and the frustum failure mechanism of the interlayer are adopted to predict the bearing capacity. The effect of the interlayer thickness and the interval distance on the bearing capacity are discussed. Based on the analytical basis which takes into account the contribution of the interlayer to the bearing capacity, a comprehensive analysis of the performance of the new model in retrospectively predicting the bearing capacity of the suction caisson in the three-layer seabed is provided. Significant consistency at the small interval distance is shown. The new model has been suggested for application to the foundation design for the subsea production system, substituting for the inaccurate predictions of bearing capacity in the layered seabed by the traditional method. • We perform analyses to determine the vertical bearing capacity of suction caisson in the three-layer soil seabed. • The development of a conceptual model to predict the bearing capacity of suction caisson in were presented. • The thickness of the interlayer, the interval distance and the embed depth both have obvious impact on the bearing capacity. [ABSTRACT FROM AUTHOR]

• Early Carboniferous rodingites are reported in the Baixingtu area. • The Baixingtu rodingite was formed by seafloor metamorphism. • A broad ocean basin formed as the Hegenshan Ocean around 345 Ma. Rodingite, a metasomatic rock type related to the serpentinisation of ultramafic rocks, occurs as dykes or lenses in serpentinite of the ophiolitic mélange. The formation age, protolith and metamorphic context of the rodingites are crucial for evaluating the hydrothermal activity of the ancient ocean floor and the tectonic history of the ophiolite. This study presents particular research on metamorphic petrology, geochemistry and zircon U–Pb chronology of rodingites and their associated mafic–ultramafic rocks in the Baixingtu ophiolite, the middle segment of the Erenhot-Hegenshan ophiolite belt (EHOB), southeastern Central Asian Orogenic Belt. The mean metamorphic ages of rodingites are 345.8 ± 3.8 Ma, 339.9 ± 4.8 Ma, and 344.5 ± 9.2 Ma. According to the chlorite thermometer, the final mineral assemblages of rodingites formed at temperatures ranging from 114.99 °C to 351.10 °C. The high oxygen fugacity of nascent clinopyroxenes and the negative anomaly of Ce in adjacent serpentinites (δCe = 0.34–0.77) prove that rodingitisation occurs in shallow oceanic crust by the reaction of seawater with ultramafic rocks to produce Ca-rich fluids. Accordingly, the Baixingtu ophiolite was produced by an ocean floor metamorphism, whose rodingitisation occurred shortly after the formation of the oceanic crust. Combined with other ophiolite data from the EHOB, the Hegenshan Ocean was constantly generating new oceanic crust in the Early Carboniferous. [ABSTRACT FROM AUTHOR]

Indonesia is one of the sea cucumber-producing countries with small-scale fisheries activities in harvesting multi-species products. Few biological data are available for sea cucumber fished from the Indonesian sea floor. This study assessed species diversity and compiled a great amount of biometric data on commercial sea cucumber species observed from 23 locations representing east to west Indonesia, focusing on the intertidal habitats covering seagrass and coral reefs. A total of 4553 individuals of sea cucumbers belonging to 39 commercially valuable species were observed; size composition, length-weight relationships, and Fulton's condition factors were investigated. The assessment demonstrated that only several species were observed in large sizes. The current study added Holothuria flavomaculata and H. verrucosa to the list of exploited species nationally; therefore, 55 sea cucumber species have been confirmed under commercial harvest in Indonesia. Holothuria albiventer , H. excellens , H. flavomaculata , H. rigida , H. verrucosa , and Stichopus quadrifasciatus are discovered as newly reported species being fished for trade globally that have not yet been included in the FAO commercially important sea cucumber list. The body size frequency distributions show that most animals observed in the field during the study period were generally small; this may indicate that sea cucumber populations in Indonesia are under serious exploitation because exploited populations tend to have lower frequencies in larger classes. This is the first study to calculate the length-weight relationships of four species (Holothuria fuscocinerea , H. hilla , H. impatiens , and Stichopus vastus). Thus, the length-weight relationships of nine species in Indonesia have been investigated. Eight species analyzed in this study grow allometrically with a negative allometric. Fulton's coefficient condition factor displayed that almost all species in nearly all locations had high values, which indicates that local environmental conditions are favorable and support the physical health of the sea cucumbers. This current study provides novel data and will be beneficial in estimating weight in future fishery surveys to estimate stock biomass and catch volumes. It can also be used by the Indonesian scientific authority to recommend the wild catch size of the species involved in the trade to the management authority. • Two species are first reported as exploited species nationally. • A total of 55 sea cucumber species are confirmed under commercial harvest in Indonesia. • Five species are newly recorded as being fished for trade globally. • Most sea cucumbers observed were generally small, indicating that the populations are under serious exploitation. • Length-weight relationships and negative allometric growth of four species are first reported globally. [ABSTRACT FROM AUTHOR]

In this work, a novel guidance principle for underactuated autonomous underwater vehicles is introduced. This new method relies on the kinematic coupling between non-actuated and actuated degrees of freedom. It uses a newly introduced matrix called the Handy Matrix denoted H. The method allows reassigning unused degrees of freedom of the task to useful non-actuated DOF. The algorithm and design rules leading to the construction of H are also provided. Two different solutions based on matrix H are compared on a standard seabed scanning task. • Introduction of a new guidance principle based on kinematic couplings. • A new control method provides several trajectory tracking solutions for AUVs. • A new guidance principle allows robust and precise trajectory tracking for AUVs. • Simulation studies demonstrate several solutions provided by the new method. • A new matrix to enhance control of underactuated systems: the Handy matrix. [ABSTRACT FROM AUTHOR]

The design of a tracked mining vehicle (TMV) that can efficiently and safely travel on the deep seabed is the core technology in the deep-sea polymetallic nodule mining system, and one of the main aspects influencing the TMV's driving performance and efficiency is its travel speed. To overcome the current limitations of low mining vehicle efficiency and susceptibility to slipping and sinking, this study investigates the impact of travel speed on vehicle performance based on laboratory model experiments and numerical simulation methods. Initially, track driving model experiments were conducted, revealing that traction force increases with travel speed, analyzing the influence on the stage-wise variation of shear strength-displacement relationship between the track and sediment interface. An optimized traction force calculation model was proposed, and applied in multi-body dynamics software and validating its rationality. Multi-body dynamics simulation experiment results indicate a significant increase in the settlement amount of TMVs with increasing travel speed. However, the magnitude of the travel speed changes the variation pattern of settlement amount with travel displacement, and it was found that the slip rate during stable vehicle traveling is positively correlated with travel speed. The impact of travel speed on the performance of TMVs traveling on sediment eroded by jets in actual engineering was also analyzed. It is found that excessive or insufficient travel speed is detrimental to the performance of TMVs. In this study, when the travel speed is 0.7 m/s, the effect of weakening the mechanical strength of eroded sediment on TMV's driving performance is relatively small. This research provides a scientific theoretical basis for improving mining vehicle efficiency and enhancing mining capability. [ABSTRACT FROM AUTHOR]

This study comprehensively evaluates the thermal upheaval buckling of a functionally graded porous (FGP) pipeline laid on an arched concave seabed. The FGP pipeline is consolidated by graphene platelets (GPL). Symmetric schemes are used for both the pores and the GPL in the thickness direction of the pipeline. The energy method and thin-walled shell theory are adopted to develop analytical frameworks for the thermal instability of the FGP-GPL pipeline. Subsequently, the present results are contrasted with other closed-form solutions, which fully verify the feasibility of this study. Finally, a parametric analysis is conducted, emphasizing the critical temperature variations induced by diverse arch radius, porosity coefficients, graphene weight ratio, and geometric properties of the GPL. It has been found that the thermal stability of the FGP-GPL pipeline is improved by adding more anchors in a certain seabed and laying the pipeline in an arched concave seabed, respectively. The main novelties of the present work are summarized as: (1). develop analytical schemes to provide design guidance for practical applications as an FGP-GPL pipeline lays on an arched concave seabed; and (2). plot explicitly thermal equilibrium curves to illustrate the stability mechanism of an FGP-GPL pipeline laid on an arched concave seabed, respectively. • The FGP-GPLs pipeline deforms radially at a minimum temperature variation. • The critical temperature variation is predicted for the pipeline laid on the arched seabed. • Explicit equilibrium curves are illustrated for the pipeline laid on the arched seabed. • The arched seabed is helpful to resist the thermal buckling of the FGP-GPLs pipeline. [ABSTRACT FROM AUTHOR]

The International Seabed Authority (ISA), established under the United Nations Convention on the Law of the Sea, is responsible for the governance of deep-sea mining in areas of the ocean beyond national jurisdiction (DSM), including the adoption of rules, regulations and procedures (RRPs) relating to DSM. As a result of actions by the Republic of Nauru, the ISA had been under pressure for the last two years to adopt RRPs for exploitation by July 2023 or face the possibility of evaluating a DSM application in the absence of such RRPs. In July 2023, the ISA was not able to finalize the RRPs but signaled its intent to continue working on them, with a view to their adoption by 2025. Negotiations on the timeline for the adoption of the RRPs were contentious with some member States wanting a binding target date and others expressing concern of being bound to arbitrary deadlines. This paper identifies major issues that remain outstanding in the draft RRPs relating to exploitation and discusses the underlying drivers for their lack of agreement with the aim of providing an indication of the amount of work ahead for the ISA. We find that over 30 major regulatory issues remain outstanding because of not receiving sufficient time for discussion, divergent views amongst member States, and due to a lack of information and inputs to progress negotiations. These findings suggest that member States and prospective contractors should expect negotiations on the adoption of RRPs to continue long into the foreseeable future. • Adoption of regulations is one prerequisite to deep-sea mining in international waters. • We determine that more than 30 major issues in the regulations remain outstanding. • Issues remain outstanding due to divergent views and lack of information and time. • We conclude that the 2025 target date set for the adoption of regulations is unrealistic. [ABSTRACT FROM AUTHOR]

Inspired by the anisotropic shear behavior of the snakeskin, an innovative suction caisson with a bio-scale sidewall of the snakeskin is proposed, which is called the scale suction caisson (SSC). Compared with traditional suction caisson (TSC), the interface friction decreases when the SSC penetrates to the seabed, but increases as the SSC is pulled out. Therefore, the SSC has better installation and service performance than the TSC. The model tests are carried out to investigate the penetration behaviors of the SSC. The study shows the penetration resistance depends on the aspect ratio of the bio-scale surface, and the corresponding value increases with increasing the diameter of bio-snakeskin surface D 1 , but firstly decreases and then increases with increasing the height of bio-scale surface H 1. More sand bypasses the end of the sidewall into the SSC and the sand inside the SSC is loosened under the seepage, causing the soil plug inside the caisson. In the half-caisson model tests, the soil heave inside the caisson under the different penetration depths is captured with an HD camera, and the permeability coefficient k can be further calculated. Considering the variation of the permeability coefficient k , a method of calculating the critical suction is provided. • The suction, penetration resistance, and height of soil plug of the SSC are investigated. • Soil plug developing of the SSC is visualized and captured with an HD camera in the half-caisson model tests. • Considering the variation of the permeability coefficient, a method of calculating the critical suction is proposed. [ABSTRACT FROM AUTHOR]

Touchdown is a decisive step in the underwater deployment of the sea floor drill rig (SFDR), but the related research is still in its infancy. Therefore, a spatial seven degrees of freedom (DoF) dynamic model of the three-legged SFDR "Seabull Ⅱ" hard landing was established, and a simulation platform was built. In addition, the influence of landing conditions on the dynamic responses was understood through orthogonal simulations, which indicates that: (a) The maxima of outrigger axial-force-loads are mainly affected by the sediment elastic coefficient; the maximum of connecting strut lateral-force-load is mainly affected by the slope of the landing surface (SLS). (b) The acceleration-load is not a point that requires special attention for SFDR hard landing. (c) For control strategies, it is recommended to set the release height from seabed (RHFS) at 2–3 m, and to choose a smaller leg-opening-angle (LOA) based on the actual sea condition and seabed environment. (d) For the optimal design of the SFDR supporting system, it is advisable to increase the friction coefficient between the footpad and sediments by changing the structure and surface characteristics of the footpad, as well as to add a function of variable support area to the footpad. • A spatial 7-DoF dynamics model was established for a three-legged sea floor drill rig performing underwater hard-landing. • A simulation and analysis platform was built for hard landing of the sea floor drill rig with the help of MATLAB. • The effects of control and environmental parameters on the SFDR hard-landing are understood through orthogonal simulations. [ABSTRACT FROM AUTHOR]

In the marine environment, the seabed contains a certain amount of clay. Experimental studies show that the liquefaction susceptibility of the sandy seabed increases as clay content (CC) rises to a certain threshold, beyond which further increases in CC reduce liquefaction susceptibility. However, numerical models that describe the effect of CC on seabed liquefaction are very limited. This study proposed a dynamic poro-elasto-plastic finite element method model for analyzing liquefaction in the sandy seabed with CC below the threshold. Based on a series of undrained triaxial compression tests on sand-clay mixtures from existing literature, a unified constitutive framework was demonstrated to be effective for describing the liquefaction behavior of sand with low CC using one set of model parameters. Existing wave flume model tests validated the effectiveness of the proposed seabed model in describing the effect of low CC on excess pore water pressure (EPWP). Numerical results confirmed that adding a small amount of clay to the seabed increased the soil contraction and thus its liquefaction susceptibility. Wave-induced liquefaction was limited to a certain depth of the seabed, and the liquefaction depth was significantly affected by the CC. Adding a low content of clay the sandy seabed significantly increased both horizontal and vertical displacements under wave action, potentially leading to the instability of the seabed. This study provides a new method for accurately assessing the wave-induced stability of marine structures built on the sandy seabed containing certain amounts of clay. • Poro-elasto-plastic model evaluates effect of CC on wave-induced seabed liquefaction. • The methodology is validated at soil element and model test scales. • Liquefaction depth of seabed is greatly influenced by CC. • Higher CC increases horizontal and vertical displacements under wave action. [ABSTRACT FROM AUTHOR]

The Greenland Ice Sheet releases fresh water from ice melt, tundra snow melt, and solid ice at an increasing rate during recent decades resulting in an increasing amount of freshwater runoff into the ocean. As a result, freshwater runoff is changing the continental shelf circulation by increasing the amount of fresher water on the shelf that may then enter the deep ocean. Observational studies show that dense water does traverse the east Greenland shelf near the ocean bottom but it is unclear to what extent the transport of near surface fresh water, as a result of runoff, reaches deeper water and enters the Irminger Basin. Using 4 km resolution nested numerical model simulations with and without freshwater runoff, we show freshwater runoff increases salinity variability with increased baroclinicity. While higher salinity variability and baroclinicity suggest a greater potential for water mass exchange across the East Greenland Current, most freshwater runoff along east Greenland remains on the shelf. From freshwater runoff alone, salinity and salt mass decreases by 0.22% on the continental shelf compared to a 0.01% in the rest of the Nordic Seas. There is a 0.05% reduction in salt mass on the Greenland shelf region that makes up 8% of the simulation domain, suggesting little water exits the shelf along the east coast of Greenland. The largest reduction in salt mass occurs around Iceland, where substantial freshwater runoff exists. A calculation of baroclinic conversion rate suggests likely pathways for runoff to exit the continental shelf and enter deep water in the Denmark Strait and over the Greenland/Scottland ridge east of Iceland. Most of the fresh water, however, released along the east coast of Greenland continues towards Cape Farewell, outside our modeling domain, and into the Labrador Sea. • The fresh water runoff along the east coast of Greenland is investigated in a numerical ocean circulation model. • Most freshwater runoff along the east coast of Greenland is largely constrained to the continental shelf. • Freshwater runoff increases the baroclinicity and salinity variability along the east coast of Greenland. • The increased baroclinic conversion rate along the Greenland/Scottland ridge suggests a pathway for runoff to reach the deeper ocean. [ABSTRACT FROM AUTHOR]

The issue of seabed scour around offshore wind turbine foundations is a significant safety concern. In this study, local scour around a specific type of foundation, known as the large-diameter Mono-Column Composite Bucket Foundation (MCCBF) with six connectors, has been investigated through physical experiments. The study involved various flow conditions, including unidirectional flows, tidal flows, and combinations of regular waves and currents. It has been found that under similar flow intensity and orientation angles, unidirectional flow tends to cause deeper scour depths, but with a more limited extent compared to scour induced by tidal flows. The disparity in maximum scour depth between tidal and unidirectional flows decreases as flow velocity increases. Under regular wave-current interaction, both the scour depth and the scour extent are larger than those induced by unidirectional flow. The presence of lee-wake vortices and streamline contractions near the connectors results in larger scour depths on either side of the foundation, especially when the orientation angle is set to 0°. Different methods for predicting scour depth of the MCCBF were applied and discussed. • The local scour around a mono-column composite bucket foundation under various flow conditions has been investigated. • The scour depth under tidal currents is smaller than that under unidirectional flow. • The impact of six connectors on local scour would be considered. • Different scour depth prediction formulas have been compared and discussed. [ABSTRACT FROM AUTHOR]

• Detailed crustal structure of the Makran subduction zone revealed. • Subducting sediments consolidation observed below 4–5 km subseafloor. • Little Murray Ridge identified as a potential paleo-ocean boundary with low-density underplating. • Atypical upper crustal structure linked to magmatism and plate hydration. • Low-angle décollement and basement may facilitate large earthquake generation. The Makran subduction zone is atypical due to the thick sediment input and shallow subduction angles, and thus is highly susceptible to megathrust earthquakes. However, the thick sedimentary layers and their underlying crustal structure of the Makran slab are still poorly understood. Here we present a high-resolution crustal velocity model of the Makran subducting slab offshore Pakistan obtained from an active-source wide-angle ocean bottom seismic experiment, revealing fine structure in density and porosity. The results reveal that the incoming sedimentary layer is up to 8.5 km thick with an abrupt gradient change in porosity at 4–5 km depth, indicating a critical depth of compaction and consolidation. The igneous crust is 6–12 km thick with an average subduction dip angle of ∼2°. On either flank of the Little Murray Ridge, divergent crustal structures suggest the plausible existence of distinct tectonic provenances or divergent tectonic evolutionary trajectories for the oceanic crust on each side. The Little Murray Ridge may represent a remnant of the paleo-oceanic boundary, possibly associated with the phenomenon of low-density underplating. The subducting consolidated sediments and uppermost crust with high-water content could significantly influence earthquake rupture mechanisms at both the décollement and igneous basement interfaces. These findings suggest that the décollement and igneous basement interface both have the potential to trigger large earthquakes in the Makran subduction zone. [ABSTRACT FROM AUTHOR]

Marine structures are commonly situated near the mildly sloping sandy seabed characterized by the slope angles (α) not exceeding 10°. The seabed liquefaction can be triggered due to the generation of the excess pore water pressure (EPWP), posing a threat to the stability of marine structures. This study focuses on the analysis of wave-induced liquefaction in the mildly sloping (MS) sandy seabed. A dynamic poro-elasto-plastic seabed model is developed to simulate the behavior of the MS sandy seabed under wave loading. The results indicates that the loading cycle required to trigger the initial liquefaction decreased as the position moved from the toe towards the crest of the MS sandy seabed. The amplitude of shear stress increases with the loading cycle and tends to increase with growing α before liquefaction, resulting in a slower accumulation of EPWP with larger α. Both the horizontal and vertical displacements induced by wave action reach the maximum at the crest of the sloping seabed. Notably, the horizontal displacement is much greater than the vertical displacement in the seabed under wave action. The displacement of the MS sandy seabed depends on not only the shear stress amplitude developed in the soils but also the accumulation of EPWP required to trigger the liquefaction in the seabed. • A dynamic poro-elasto-plastic seabed model was proposed for analyses of wave-induced liquefaction in mildly sloping sandy seabed. • Wave-induced liquefaction characteristics of the mildly sloping sandy seabed were investigated. • Effect of D r and α on the EPWP and the associated displacement of the seabed under wave action was analyzed. [ABSTRACT FROM AUTHOR]

The Subcordilleran Plutonic Belt, formed in Early Jurassic times, is a short-lived batholith that developed during Gondwana dismembering. In our study, we analyzed both well-known and potential new localities of the belt of plutonic rocks, considering new whole-rock geochemical data as well as data from the literature. Additionally, new geochemical data from five samples and one U-Pb zircon date are presented from the diorites and granodiorites from the Cerro Catedral, at Bariloche (41°S). The obtained U-Pb age in zircon is Early Jurassic (192 ± 1.5 Ma). The granitoids of the Subcordilleran Plutonic Belt are calc-alkaline, of medium to high potassium. They exhibit similar alkali content than the granitoids of the Middle Jurassic-Cretaceous Patagonian Batholith, and lower alkalis than the volcanic and plutonic rocks of the Jurassic Chon Aike Silicic Large Igneous Province. These findings suggest that the Subcordilleran Plutonic Belt represents, in the region comprised within 39° and 45° S, an early stage of the Andean arc. Our observations indicate that while some granitoids in potential localities, such as Cerro Catedral, can now belong to the Subcordilleran Plutonic Belt, other sites, like Pilcaniyeu and Pilahue, may be associated with the plutonic facies of the Chon Aike Province. The Subcordilleran Plutonic Belt is an example of arc magmatism that developed during a period of major plate reorganization, along with the subduction of mature sea floor beneath the Gondwana margin, and the latter promoted slab roll-back processes and a subduction with extension tectonic regime. • The Cerro Catedral diorites have an U-Pb age in zircon of 192 ± 1.5 Ma. • The Cerro Catedral diorites are part of the Subcordilleran Plutonic Belt. • The granites of the Subcordilleran Plutonic Belt are calc-alkaline. • The granites of the Subcordilleran Plutonic Belt bear medium to high potassium. • The Subcordilleran Plutonic Belt developed during a major plate reorganization period. [ABSTRACT FROM AUTHOR]

Metarodingites are commonly garnet-bearing metasomatized mafic dykes within serpentinized mantle rocks. Garnet in metarodingites has the potential to preserve compositional and chronological information about the entire metamorphic-metasomatic evolution, from ocean floor formation to deep subduction. In this study, we investigate the chemical and chronological record of garnet, titanite, and zircon from metarodingites and garnet veins in chloritized blackwall, from the Zermatt-Saas zone in the Western European Alps. Garnet in the chlorite-rich metasomatic rind (blackwall) displays re-crystallization and new growth textures and therefore represents a second generation of garnet (Grt2), after the one in the metarodingite core (Grt1). Major and trace element mapping shows that Grt2 is richer in andradite and Ti-andradite components compared to the more grossular-rich Grt1 in the metarodingite. Moreover, we found that in both Grt1 and Grt2, Ti and U content are positively correlated, with U abundances up to 1.5 μg⋅g−1. Grt2 does not show rare earth element (REE) zonation, suggesting that REE transport was facilitaed by the presence of a fluid phase. We propose that the metasomatizing fluids from which Grt2 precipitated, were serpentinite-derived high-temperature brines capable of transporting Fe3+, Ti and REE. LA-ICPMS U–Pb dating of metarodingite garnet Grt1 samples yielded overlapping ages between 43.6 ± 0.9 and 44.1 ± 1.3 Ma, which are consistent with previous estimates of peak metamorphic conditions. Our data indicate that the metarodingite Grt1 grew within <2 Myr, suggesting a rapid burial rate of the unit or fast and pulsed garnet growth aided by the presence of fluids in the intergranular medium. Titanite from the blackwall sample yields an age of 45.0 ± 1.7 Ma and zircon rim an age of 48.0 ± 1.1 Ma, indicating that fluid release and chloritization occurred at peak conditions. U–Pb ages of garnet in the blackwall samples (Grt2) are significantly younger, yielding ages of 40.1 ± 0.9 Ma and 38.4 ± 0.8 Ma, respectively. The presence of multiple generations of metasomatic garnet in the blackwall suggests that periods of increased rock permeability occurred repeatedly, plausibily aided by deformation, as supported by the consistency of our multi-mineral geochronology. We show how garnet from metarodingites and blackwalls records the metamorphic-metasomatic history and can be used to obtain information on (de)hydration reactions and fluid flow during subduction. [Display omitted] • U–Pb dating of grossular-andradite garnet from eclogite facies rocks is a robust geochronometer. • During metamorphic hydration reaction and new garnet growth, REE distribution is transport limited. • High temperature brines transport Fe3+, Ti and REE. • Different ages of garnet veins indicate multiple events of fluid-rock interaction and pulsed fluid circulation. [ABSTRACT FROM AUTHOR]

The pile leg-mat foundation is a novel composite foundation designed for jack-up offshore platforms. The seismic response of such foundations in sandy seabeds is an issue that requires significant attention. In this study, shaking table tests were conducted under various input seismic waves to investigate the dynamic response of a seabed platform system subjected to seismic loads. The effects of the peak ground acceleration (PGA), seismic wave frequency, wave type, pile leg insertion depth, and pile length on the response of the seabed platform system were investigated. The results indicated that as the PGA increased, the acceleration response of the soil and platform model increased, increasing the accumulation of excess pore water pressure and the horizontal displacement of the platform model. The acceleration and horizontal displacement responses of the seismic wave with lower frequencies were higher than those with higher frequencies. The peak acceleration amplification factors under the measured and regular seismic waves showed significant differences, with the dynamic response of regular waves to the platform model being pronounced. Under seismic waves with low PGAs, the horizontal displacement of the platform model decreased with increasing pile leg insertion depth or pile length. • Shaking table tests for jack-up platform with pile leg-mat foundation on sandy seabed were conducted under various seismic wave conditions. • The seismic response such as acceleration, excess pore water pressure, and displacement of the seabed-platform system were revealed. • The effects of the seismic waves, pile leg insertion depth, and pile length on the seismic response of the seabed-platform system were investigated. [ABSTRACT FROM AUTHOR]

The paper introduces a novel method for simulating acoustic–shell interaction subject to seabed reflection. The vibration of thin-shell structure is analyzed using the finite element method (FEM) with Kirchhoff–Love shell elements. Exterior acoustic fields associated with seabed reflection is simulated by the boundary element method (BEM) with half-space fundamental solutions. Then the FEM and BEM are coupled to simulate interaction between acoustics wave and shell vibration in the context of isogeometric analysis. Finally, fast multipole method is formulated for the coupled system to accelerate computation and reduce memory storage. Numerical examples are provided to demonstrate the accuracy of the algorithm. • Analyzing acoustic–shell interaction by considering seabed reflection. • Coupling FEM and BEM based on half-space fundamental solutions. • Accelerating acoustic computation with fast multipole methods. [ABSTRACT FROM AUTHOR]

Large-diameter spudcan needs to be penetrated into seabed to provide bearing capacity for the jack-up rigs operating adjacent to existing jacket platforms. The platform piles are subjected to severe additional stresses induced by large volume of soil displaced during spudcan penetration, meanwhile the pile head is also subjected to horizontal loads transmitted from the platform. Therefore, it is necessary for the adjacent piles to evaluate the combined effect of spudcan penetration and pile head loads. The Coupled Eulerian-Lagrangian (CEL) method is adopted to investigate the effects of spudcan penetration on the soil reaction behavior of piles, and is firstly validated by available centrifuge model tests. Further, the p-y curves of the adjacent piles under three pile head loading conditions are analyzed, and the loading direction respect to spudcan penetration is observed to give different p-y responses. A modified soil reaction model is in turn proposed by modifying the API formula of ultimate lateral pressure to consider the effects of loading direction, as well as the overall softened soil reaction due to spudcan penetration. Finally, a pair of model tests are conducted to validate the proposed p-y curves of adjacent piles subjected to combined spudcan penetration and pile head loads. • The direction of pile head load was found to influence soil reaction curves originally proposed for active piles. • Variations of lateral soil pressures during spudcan penetration were investigated for different pile head loading directions. • A modified soil reaction model was proposed based on the API curves to consider the effects of spudcan penetration. • A pair of model tests with instrumented piles adjacent to spudcan penetration were conducted to validate the proposed model. [ABSTRACT FROM AUTHOR]

The northwestern shelf of the Black Sea has been affected by eutrophication and bottom hypoxia since the sixties. Consequently, the macrozoobenthos has suffered a well-established decline in biodiversity. However, the nature of the current benthic communities remains questionable. From 1995 to 2017, we compiled species and abiotic data for 138 sites over the shelf. Through an appropriate multivariate analytical approach, we identified benthic community changes solely due to organic pollution variations. Our results show signs of recovery with an increase in biodiversity and proportion of species vulnerable to organic enrichment. These changes were related to a decrease in riverine loads and subsequent eutrophication. However, some long-lived species typical of the area still did not exhibit noticeable recovery, which suggests that either the recovery process has not yet been achieved or some environmental conditions are still not met to warrant a sea floor ecosystem state substantially healthy. • Macrobenthos data are compiled at 138 sites from 1995 to 2017 on the northwestern shelf of the Black Sea. • A new replicable method is used to link changes in fauna composition to organic disturbances. • From the mid-nineties, better freshwater input quality had resulted in less organic pollution and hypoxia. • A decrease in organic pollution had led to higher biodiversity and proportion of more sensitive taxa. • The recovery process has not yet been achieved and do not exclude the concomitant effects of other anthropogenic pressures. [ABSTRACT FROM AUTHOR]

The Oceanic Anoxic Event 2 (OAE 2) is widely regarded as one of the most significant global-scale biological and environmental perturbations in the Mesozoic Era. However, the duration and driving mechanisms of this event at southern high latitudes remain largely unknown due to a lack of available geological records. Here, we present a cyclostratigraphic analysis of high-resolution records of lightness variability (L*) and gamma-ray attenuation (GRA) bulk density, which are associated with changes of marine primary productivity and continental weathering, respectively, from Site U1516 located in the Mentelle Basin, offshore southwest Australia. This analysis permits establishment of an astronomical time framework for a stratigraphic interval of 455.205–485.24 m rCCSF (revised Core Composite Depth below Sea Floor) by tuning the 100 kyr filter to short eccentricity. The studied section encompasses the entire OAE 2 interval at the depth of 460.13–473.94 m rCCSF. Based on the established high-resolution astronomical time scale using astronomical tuning of L* records to the short eccentricity cycles (100 kyr), the duration of OAE 2 is estimated to be ∼990 kyr at Site U1516. A relatively high amplitude of short eccentricity occurred at the build-up stage, accompanied by a gradual rise in obliquity amplitude during the recovery phase of the OAE 2. Combining previous proposals for enhanced oceanic water stratification and terrestrial weathering, we suggest that obliquity, coupled with short eccentricity, paced the evolution of this event at southern high latitudes by controlling insolation changes received by the Earth's surface. • The OAE 2 duration is ∼990 kyr at southern high latitudes. • Short orbital eccentricity amplified the large igneous province affection at the OAE 2 build-up stage. • The orbital obliquity paced the OAE 2 recovery stage at southern high latitudes. [ABSTRACT FROM AUTHOR]

• An underwater rotorcraft vehicle based on a U- joint was proposed. • ABSSMC can realize fixed-depth trajectory motion control in proximity to the seabed. • The proposed vehicle can reduce system energy consumption and enhance maneuverability. This paper proposes a novel underwater rotorcraft vehicle with a passively adjustable configuration based on a universal joint (URV-PAU), which addresses the issue of increased propeller load and control stability caused by the rigid structure of existing vehicles when tilted. Compared with designs that do not incorporate a U-joint structure, this vehicle can reduce energy consumption and enhance system manoeuvrability. First, a kinematic and dynamic model of the URV-PAU is established based on its configuration. Considering the nonlinearity of the system, the modelling errors of the dynamic model, and external disturbances, an adaptive backstepping sliding mode controller(ABSSMC) is designed to achieve motion control in proximity to the seabed. A prototype of the underwater rotorcraft vehicle was constructed according to the principles of modular design. Subsequently, underwater trajectory experiments were carried out within a water tank. The experiments demonstrated that the URV-PAU results in a reduction of approximately 10 % in system energy consumption and an improvement in system manoeuvrability compared with designs without a U-joint structure during motion at a constant depth. [ABSTRACT FROM AUTHOR]

Scour processes and corresponding scour protection measures have been extensively studied for vertical cylinders. Several formulations for estimating scour and determining the optimum size of rocks for scour protection are widely available in the literature. However, when studying other types of structures, the geometric variability of the structures, limits the application of available semiempirical formulations. Scour phenomena around complex structures have been investigated experimentally in reduced-scale wave-current basins. However, the number of tests focused on support typologies different from monopile structures is still limited, restricting the availability of semiempirical formulations focused on conceptual design of scour protection solutions or in the estimation of the free scour development. In this work, a better understanding of the scour processes around gravity-based foundations (GBFs) and the performance of different scour protection solutions is gained via experimental results obtained from a large-scale test programme (1:35 test scale), including combined wave and current tests. The experimental tests were divided into two main types: (1) free scour and (2) scour protection tests. The main conclusion was that the triggering of a horseshoe vortex is the main driver of scour processes together with the contraction of flow lines at the foundation contours. Since monopile semiempirical formulations are not suitable for scour prediction, a new semiempirical approach was obtained from the test results. Moreover, two distinct scour mitigation methods were analysed (rock protection and concrete mattresses). Based on the undisturbed mobility parameter, statistical and dynamic limits were defined considering the rock grading tested. Finally, for concrete mattresses, the design driver was identified, and the adaptability of these types of solutions to seabed changes was verified. • Hydrodynamics around Gravity Base Structures for offshore wind energy. • For the Gravity Base Structures assessed, identification of the scour process around large structures. • Evaluation of different scour mitigation strategies based on the installation of different protections around the foundation: - Rock pads (undisturbed mobility parameter limits were identified to pre-design scour protection (external stability) for quite similar structures). - Concrete mattresses (innovative solution): Assuming the stability of the concrete mattresses, the length of these elements was identified as the main design driver. [ABSTRACT FROM AUTHOR]

The dynamic responses of water-pile-soil system subjected to horizontal earthquakes considering seabed flexibility on hydrodynamic pressures is investigated in this paper. The hydrodynamic pressure on the pile is obtained by the inviscid compressible fluid theory and the absorption of pressure waves due to the seabed flexibility is modeled by using a reflection coefficient which is frequency independent. The horizontal resistance of the soil is obtained based on the viscoelastic dynamic continuum model. Based on the analytical solution for the seismic responses of the free-field soil, the numerical model for the seismic response of the pile is developed by using the finite element method. Parametric studies are further conducted to illustrate the influence of seabed flexibility on the seismic responses of the pile. • Numerical method to solve the horizontal seismic response of offshore piles considering water-pile-soil interaction. • Analysis of the influence of seabed flexibility on hydrodynamic forces of a rigid pile. • The influence of seabed flexibility on seismic response of offshore piles is quantitatively analyzed. • Emphasize the importance of seismic characteristics on structural seismic response. [ABSTRACT FROM AUTHOR]

Red Sea Deep Water is presently slow-moving, but was this true of the earlier Plio-Pleistocene (PP)? In seismic reflection records, the PP deposits are distorted by halokinetic deformation of their underlying Miocene evaporites. However, if reflections are flattened to a prominent reflector representing the top of the Miocene, they reveal mounded deposits within the earlier PP along both sides of the sea. Off Egypt, a plastered drift occurs along a salt wall. In the central Red Sea, they are mounded drifts. Seismic reflections from these deposits change shape gradually upwards to the modern seabed, which is commonly flatter, suggesting a gradual change in depositional conditions. To explain their origins, we appeal to other evidence. DSDP cores from the Late Pleistocene contain the rigid aragonite cements formed by restricted conditions, but not the lower and middle PP. Furthermore, mid-PP sedimentary δ18O values are similar to global ocean δ18O for that time, not enhanced as expected from excess evaporation. These data suggest that there was a greater exchange of Red Sea waters with the Indian Ocean during the mid-PP. That exchange may have allowed waters densified by evaporation in shallow regions of the northern Red Sea to flow south vigorously (the mounds would then be contourites). Alternatively, as the Pliocene seabed was shallower, wind-driven eddies may have affected more of the water column. Overall, the results indicate for the first time that deep circulation was stronger in the earlier PP compared with the present day. That circulation needs to be considered when evaluating organism dispersions across the Red Sea, regional climate, and influence of Red Sea Outflow Water on Indian Ocean Intermediate Water. During the Pliocene (about 3–5 million years ago), temperatures on Earth's surface were similar to those predicted in some models of Earth's future climate. This has led to researchers becoming interested in studying geological evidence of conditions during the Pliocene as a clue to Earth's future. In detail, however, the comparison may not be exact. In our article, we describe mounds of sediment that were originally formed on the bed of the Red Sea in the Pliocene. They appear similar to snow drifts, and like snow drifts, may have formed under steady currents. Sea water becomes dense with evaporation (making it more saline). At the present day, dense water created in the Gulf of Suez cascades down into the deep Red Sea as a slow current. Perhaps such movements were more vigorous in the Pliocene, helped by the water escaping through a deeper barrier in the south into the Indian Ocean? Alternatively, these mounds were formed by giant eddies, such as those on the surface of the modern Red Sea, which are moved by strong winds. In either case, the deep waters of the Pliocene Pliocene Red Sea were more vigorously moving compared to the quiescent deep waters of the modern-day. [Display omitted] • Seismic reflection images reveal mounded lower Plio-Pleistocene sediments. • Their geometries are similar to contourites, suggesting vigorous circulation. • Alternatively, these deposits may be results of wind-driven eddies. [ABSTRACT FROM AUTHOR]

From the Middle Jurassic to Early Cretaceous, the mudstone-dominated Agardhfjellet Formation was deposited during the prolonged shelf dysoxic-anoxic event (SDAE) recorded predominantly in the circum-arctic polar regions. Commonly, oceanic anoxic events (OAEs) throughout Earth's history are linked to the emplacement of large igneous provinces (LIPs). OAEs and LIPs, alone or jointly, are inferred to be triggers for severe biotic crises in Earth's history. However, the causes for SDAEs remain uncertain. To elucidate these causes, we document the geochemical features of the Agardhfjellet Formation using trace element concentrations and stable isotope ratios. The Agardhfjellet Formation, which consists of the Oppdalen, Lardyfjellet, Oppdalssåta, and Slottsmøya members in ascending order, formed during ∼13 Myr of prolonged dysoxic, anoxic, and euxinic conditions. The onset of shelf anoxia took place between deposition of the Oppdalen and Lardyfjellet Members. The extent of sea floor anoxia in the basin varied within the Lardyfjellet Member but likely persisted throughout most of the Slottsmøya Member. Mo/TOC and Mo EF /U EF ratios in the sedimentary rocks are consistent with the anoxic events. Enhanced continental runoff marked the Oppdalen, Oppdalssåta, and Slottsmøya members, contrasting with most of the Lardyfjellet Member, in which authigenic phases were widespread under anoxic conditions. Our results show that, compared to other OAEs, such as the Toarcian OAE (∼183 Ma) or the OAE2 (∼94 Ma), the Late Jurassic – Early Cretaceous SDAE recorded in the Agardhfjellet Formation is characterized by prolonged suboxic–anoxic condition, substantial water-mass stratification, and increased continental runoff. • The geochemical characteristics of the shelf dysoxic-anoxic event (SDAE) were studied. • The Kimmeridgian Lardyfjellet Member showed the strongest basin stratification. • Terrestrial input shift occurred between the Oppdalen and Larydjfellet members. • Basin stratification could be one of the major factors of the SDAE. [ABSTRACT FROM AUTHOR]