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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 seawater-seabed interface affects the dynamic response of the seabed, but a detailed study on this topic has not been performed. In this paper, a general fluid/porous medium interface is introduced into the seawater-seabed model to control the permeability of the seawater-seabed interface. Analytical solutions for the seismic response of a nearly saturated seabed under oblique incidence P and SV waves are derived. The study revealed that the impacts of the interface conditions on saturated soil and nearly saturated soil are significantly different. For a saturated seabed, when the seabed permeability coefficient is k f ≤ 10 − 1 m / s , the effect of the interface conditions on the dynamic response of the seabed can be ignored. However, for a nearly saturated seabed, when the permeability coefficient is k f ≥ 10 − 4 m / s , the interface conditions have a significant impact on the dynamic response of the seabed. The interface conditions not only have a significant impact on the dynamic behavior of the soil near the interface but also have an impact on the displacement, pore water pressure, and effective stress of the soil in the whole sediment layer. Therefore, when the seabed is gravel, coarse sand, or fine sand, it is necessary to consider the impact of fluid/porous medium interface conditions on the dynamic response of the nearly saturated seabed. • Solutions for seismic response of different seawater-seabed interfaces are given. • Effect of interface on saturated and nearly saturated soil are totally different. • Gravel, coarse and fine sand should consider the impact of interface conditions. [ABSTRACT FROM AUTHOR]

The suction bucket jacket foundation has become a widely choice for supporting offshore wind turbines. Assessing the installation of the suction bucket foundation (SBF) is important as it significantly affects the stability of the offshore wind system and the overall project cost. Currently, experience with suction bucket jacket foundation installations primarily revolves around stiff clay and dense sand, drawing insights from North Sea projects (e.g. the design method reported by DNV-RP-C212). However, there is a shortage of publicly available knowledge concerning SBF installations in the South China Sea, characterised by deep-covered mud (i.e. very soft clay) and extensive layered soils. Existing design parameters may not adequately address these challenges, highlighting the need for a site-specific installation design method. This study introduces a tailored approach for evaluating design parameters of the SBF installation in the seabed conditions of the South China Sea. Utilising field data from 19 suction bucket jacket installations across the region, the proposed method undergoes rigorous validation and testing. The findings of this study aim to contribute to the advancement of offshore SBF installations in the intricate geological setting of the South China Sea. By presenting the SBF installation design method, the research offers practical guidance for both the evaluation of suction bucket jacket foundation installations and the optimisation of turbine locations in the region. • Unique field installation data and Methodology: Study on SBF installations in South China Sea introduces new evaluation method, adapted to the unique seabed conditions of the region, validated with 19 regional installations. • Two-Phase Installation Process and Challenges: The paper outlines SBF installation phases: self-weight, suction penetration. Emphasizes accurate suction pressure assessment for proper installation, avoiding issues. • Proposed New Evaluation Method: A novel CPT-based approach classifies design parameters using normalised velocity and drainage conditions, enhancing accuracy for South China Sea seabed. [ABSTRACT FROM AUTHOR]

The "septarian barite concretions" have garnered significant interest worldwide. This study presents the first detailed investigation of these sedimentary structures in Algeria, with a primary focus on elucidating their genesis through petrography, SEM-EDS, major and trace elements (including REEs), and sulfur isotope analysis. The sampled concretions occur in Upper Cretaceous-Paleocene marl layers from the Biban area, primarily in two main sectors (Koudiat Djebassa and Sidi Ziane), situated within the Southern Tellian Atlas in Northern Algeria (Maghrebides). While these barite concretions exhibit diverse morphologies, our analysis focuses specifically on oblate ellipsoidal concretions. The flattened shape of these concretions may stem from compressed echinoid tests or small, oblate septarian cracked concretions representing the flattened cores. Notably, these concretions feature an outer cortex of radial fibrous barite crystals, measuring centimeters in thickness. Petrographic examination coupled with SEM-EDS analysis suggests that concretion growth occurred from porewaters in unconsolidated, soft sediments at shallow burial depths beneath the sediment-water interface, manifesting in three growth episodes: (i) an initial stage characterized by primarily thin lamellar barite crystals intertwining to form rosette-like structures in concretion cores, (ii) a later stage marked by radial-fibrous barite crystal growth in concretion margins, and (iii) the filling of septarian cracks by barite. The presence of terrigenous sediment, particularly abundant in rosette-like barite crystals, indicates growth within highly porous sediment. Conversely, the radial fibrous outer cortex is related to an effective displacive growth mode. The δ34S values of the barite concretions (ranging from 16 ‰ to 24.4 ‰), consistent with seawater values, which document that seawater was the primary sulfur source. Furthermore, REE geochemistry further supports the seawater origin of diagenetic fluids rather than a hydrothermal one. Concretions are suggested to have formed in organic-rich, fine-grained sediments at shallow depth below the sea floor, in sedimentation halts, and as a result of microbial degradation of organic matter. Barium was supplied to porewaters within the methanogenic zone, precipitating as barite when, migrating upwards, reached the boundary with the overlying sulfidic zone. • We provide petrographical, SEM-EDS, major/trace elements, and sulfur isotope data on "septarian barite concretions" from Biban, north Algeria. • The results show that concretions formed at shallow depth below the sea floor during halts in sedimentation. • The oblate ellipsoidal shape of the barite concretions is due to the shape of the cores around which they grew. • REE geochemistry patterns reveal that concretionary growth is a result of diagenesis. [ABSTRACT FROM AUTHOR]

The prediction of object embedment into the seabed is important for the deployment and efficacy of submerged sensors and sensor networks, as well as for other applications such as unexploded ordnance risk assessment, subaquatic search and rescue efforts, or anchors and moorings. The embedment of objects into the seabed during placement depends on the strength parameters of the seabed sediment. However, a detailed characterization of seabed strength can be complex and costly since quality seabed samples and/or in situ testing are required. This study evaluates the importance of a detailed geotechnical seabed sediment characterization over seabed classification from geoacoustic surveying or accepting unknown seabed conditions for the prediction of seabed embedment of cylindrical objects. Monte Carlo simulation was applied to model the uncertainty of sediment strength parameters. The results suggest that prior knowledge of the general sediment type (e.g., fine-grained versus coarse-grained as determined from side scan sonar imaging) significantly improves the precision of the embedment predictions over unknown conditions, reducing the coefficient of variation (CV) in prediction of percent embedment (PE) by about 50 % to 65 %. Performing a detailed geotechnical testing of sediment strength represented a further improvement by 15 % to 35 % over the knowledge of sediment type. Both the mean and standard deviation of PE in fine-grained sediments are at least about 3 times the values for coarse-grained sediments indicating a wider distribution of PE with deeper embedment for cohesive fine-grained soils. The embedment behavior is a function of the method of deployment (free fall with a certain speed versus placement with no speed) in stiff cohesive sediments but is less relevant in soft sediments since PE values are always greater than 100 % (i.e., full embedment). Similarly, in cohesionless sediments, PE is always less than 50 %. [ABSTRACT FROM AUTHOR]

Organic carbon (OC) burial in river-dominated ocean margins plays a pivotal role in the global carbon cycle, impacting atmospheric CO 2 levels over the long term. Despite its significance, uncertainties persist regarding the influence of external environmental factors and intrinsic properties on sedimentary OC. In this study, we conducted a comprehensive analysis of surface sediments from the East China Sea, examining geochemical properties (including total OC content [TOC], Δ14C, δ13C, and C/N ratio), terrestrial biomarkers (n -alkanes), and mineral properties (such as specific surface area, Al/Si ratio, and mineral composition). Our aim was to shed light on the fate of sedimentary OC. The surface sediment's Δ14C values displayed significant spatial heterogeneity, delineating four distinct sub-regions. Strong positive correlations (all p < 0.01) were found between the ∆14C values and fine-grained sediments, specific surface area, and clay minerals, suggesting the potentially pivotal role of mineral protection in shaping the fate of sedimentary OC. The proportion of terrestrial OC gradually decreased towards the south, while marine OC proportion increased, corresponding to the enrichment of Δ14C. The co-variation of Δ14C values, mineral properties, and OC source proportions suggests that terrestrial OC may undergo progressive replacement by marine OC during southward transport. Temporal variations in ∆14C values indicated that seabed erosion led to a significant increase in ∆14C values (p < 0.01) in the coastal mud belt, a phenomenon likely common in river-dominated ocean margins globally due to the new sediment cycle during the Anthropocene. • The aging of sedimentary organic carbon is influenced by hydrodynamics and mineral protection. • River damming is likely responsible for the younger of sedimentary organic carbon in the coastal mud belt. • The loss and replacement of terrestrial organic carbon with marine organic carbon may determine the Δ14C values. [ABSTRACT FROM AUTHOR]

Our primary objective is to demonstrate a method that uses marine processes, principally seafloor scour, to broadly expose prehistoric landforms and associated localities. Too often, the loss of prehistoric strata to scour processes such as ravinement during broad-scale, continental shelf transgressions, are decried without the recognition of the potential for erosion at the local scale can expose those same strata for systematic study. The analysis of sea floor erosional features formed around artificial reefs by turbulent flows in the Georgia Bight have used interferometric side-scan sonar (SSS), Remotely Operated Vehicles (ROVs), ultra-high-definition videography (UHD), and sedimentological, palynological, paleontological, archaeological analytical techniques. These techniques were integrated within a geoarchaeological methodology focused on exploring the Continental Shelf for preserved evidence of prehistoric landforms, flora and fauna once thereon. A stepwise protocol was developed to first gather interferometric side-scan sonar data to be then processed by commercial software packages such as HYPACK Hydrographic and HYSWEEP together with HYSCAN and SONAR Wiz software. The sonar mosaics were imported to ArcGIS/QGIS software to characterize scour features/targets around artificial reefs that had exposed paleo-land surfaces previously obscured by the modern palimpsest sand sheet. Analysis of scours and depressions - "moats and comets" - adjacent to reef structures were evaluated using the profile tool within the HYPACK-HYSWEEP editor package. Symbology for the bathymetric raster layers was edited to provide a clear contrast and measurement at scour features. Measured GIS images were then classified as to scour extent and depth with respect to prevailing current directions responsible for producing turbulence. A ranking of the artificial reefs by factors such as scour depth and extent was used to guide subsequent investigation by ROVs. Sediment cores and grab samples were collected, and those samples underwent particle size analysis (PSA), macro-and micro-botanical analyses. All data – geophysical, GIS, video and geological – were collated and synthesized to produce an assessment of the potential of sea floor scour features to expose previously buried geomorphological/geological, paleontological and/or archaeological features of interest. • Introduces scour nuclei as locations for increased exposure of Quaternary land surfaces. • Introduces hybrid robotic and diver investigatory methodology. • Focuses on spatial and stratigraphic investigation of previously buried Quaternary land surfaces. • Cost-effective use of small-boat research platforms. • Demonstrated integration of geophysical data acquisition and GIS analysis and modelling of large datasets. [ABSTRACT FROM AUTHOR]

Based on a substantial number of seabed sediment samples and corresponding acoustic characteristic and physical property test data collected in the continental shelf area of the northwestern South China Sea, this study employed a sound speed ratio correction model to analyze the correlation between the sound speed ratio of seabed sediments and parameters such as porosity, density, mean grain size, and water content. This study resulted in the development of both single-parameter and double-parameter empirical formulas for the sound speed ratio of seabed sediments in this marine region. The determination coefficients (r2) for the single-parameter empirical formulas based on physical properties, excluding the mean grain size (r2 ≤ 0.75), were all above 0.78, indicating a strong correlation. Additionally, the fitting curve at 100 kHz was slightly greater than that at 50 kHz, consistent with the acoustic dispersion characteristics of sediments. To assess the applicability of the empirical formulas to different maritime areas, the formulas derived from the South Yellow Sea, East China Sea, and South China Sea were compared with those of the study area. The results indicated that the empirical formulas for the sound speed ratio established in this study have general applicability, especially for sediments with low porosity, high density, and low mean grain size. In addition, the determination coefficient of the dual-parameter empirical formula for the sound speed ratio–porosity–mean grain size is superior to that of the single-parameter empirical formula for the sound speed ratio–mean grain size. Through comparative studies with other marine areas, it was found that there are certain differences in the relationships between porosity and mean grain size established in different marine areas. Therefore, based on the rough sphere model, this study transforms the GS model into a single-parameter model built on either porosity or mean grain size. The error analysis results indicate that the single-parameter GS model has a smaller error than the measured data. However, the GS model controlled by a single parameter performs poorly compared to the predicted curves of the sound speed ratio–porosity and the sound speed ratio–mean grain size fitted in this study. This discrepancy may be attributed to the fact that the input parameters of the GS model are reference values, emphasizing the need for further research to determine suitable input parameters for the GS model in this marine area. • The empirical equations for the sound speed ratio were developed in this study in different marine regions. • The established empirical equations for the study area were compared with those for the South Yellow Sea, East China Sea, and other marine regions. • This study compared the empirical equations with the grain shearing (GS) theoretical model. [ABSTRACT FROM AUTHOR]

[Display omitted] Marine particles are key to the cycling of major elements on Earth and play an important role in the balance of nutrients in the ocean. Three main categories of marine particles link the different parts of the open ocean by shaping carbon distribution: (i) sinking; (ii) suspended, and (iii) ascending. Atmospheric carbon captured by phytoplankton in the surface water, is partly sequestered by sinking particles to the bottom of the ocean and plays an important role in controlling global climate. Suspended particles represent a significant source of organic carbon for heterotrophic microorganisms and are more likely to undergo remineralization compared to sinking particles. Ascending particles, depending on their composition, point of origin, and ascending velocity, may lead to carbon remineralization in the upper layers of the ocean in closer proximity to the atmosphere. Marine particles are hotspots of microbial activity and thus heavily colonized by microorganisms whose dynamics play an important role in organic matter degradation, aggregation and sinking, thus directly influencing the biological carbon pump efficiency. Microbiomes of marine particles differ depending on particle size, source, and age. Nevertheless, these factors are generally overlooked, and particles are mostly studied as "bulk" without considering the high heterogeneity between individual particles. This hinders our understanding of the carbon budget in the ocean and thus future predictions of climate change. In this review we examine known particle-types and associated sampling methods and identify knowledge gaps and emphasize the need for a better understanding of the single-particle ecosystem to enhance global upscaling rates. Furthermore, we introduce a novel concept: the 'lipid carbon shunt'. [ABSTRACT FROM AUTHOR]

A partitioned formulation of acoustic fluid–solid-saturated porous medium interaction problems is presented based on a generalized saturated porous medium (GSPM) model and a new localized Lagrange multiplier (LLM) method. In this formula, all various media are modeled as the GSPM and a novel, powerful continuous condition is proposed for the interaction interfaces. This condition applies not only to interfaces of two partitions but also to intersections of simultaneous interactions of any number of media with different porosities. A (u, p) frame is introduced between partitions and the LLM fields are used to connect partitions with the frame. Furthermore, finite element spatial discretization and time integration strategies are provided for both matching meshes and nonmatching meshes. This partitioned formulation is validated numerically by computing the dynamic response of a horizontally layered seawater-seabed-bedrock model subjected to plane waves. The application scenarios for this method include, but are not limited to, the dynamic coupling analysis of marine engineering structures and hydraulic engineering structures. Future work will present and discuss a set of benchmarks and applications that involve the responses of existing dams to seismic excitation. [ABSTRACT FROM AUTHOR]

The hadal Mariana Trench remains poorly understood. In December 2016, an array of high-resolution temperature loggers, attached to the ocean bottom seismometers (OBSs), was deployed from 1665 to 7520 m for two weeks across the Challenger Deep of the Southern Mariana Trench. The temperature variance spectrum reveals that the bottom water is mildly turbulent and it is mainly modulated by the semidiurnal internal tides. At the second deepest observation station (depth of 7015 m), the viscous subrange is resolved in the high-frequency spectrum. Applying the proposed method with Taylor's frozen field hypothesis and Kraichnan theoretical spectrum analysis, it is revealed that turbulent dissipation rate ɛ is 7. 8 × 1 0 − 10 m 2 / s 3 and flow speed U is 8.9 mm/s. Dissipation rates ɛ of all stations vary between 5. 9 × 1 0 − 11 and 1. 4 × 1 0 − 9 m 2 / s 3 , with the northern region of Challenger Deep experiencing stronger energy dissipation than the southern one. The vertical distribution of dissipation rate ɛ shows that it decreases with increasing depth from 1000 to 6000 m, but then increases to around 8000 m, which is consistent with previous observations and numerical simulations. The available turbulent mixing data indicates that the energy dissipation is vertically distributed in a distinct multilayer structure in the deep ocean of Challenger Deep, which is proposed to link to the intrusion of water mass in the deep Mariana trench. • The precise bottom temperature variance across the Challenger Deep was measured. • The bottom water is mildly turbulent with the theoretical spectra analysis. • The deep mixing is behaved in a multilayer structure, likely driven by intrusion. [ABSTRACT FROM AUTHOR]

• Instantaneous liquefaction within a non-cohesive seabed under progressive waves is analytically investigated. • Explicit solutions for the liquefied soil depth are derived to reflect the phase-lag effect. • Due to the phase-lag effect, the maximum liquefied soil depth would no longer appear exactly under the wave trough. • Instantaneous liquefaction potential is predominantly related to a combined parameter for waves and soils. Instantaneous liquefaction can be induced by the upward seepage force while waves propagating over a porous seabed. In this study, the instantaneous liquefaction within a non-cohesive seabed under progressive waves is analytically investigated and verified with the existing offshore observations. To characterize the instantaneous liquefaction potential, the vertical gradient of excess pore-pressure is employed, and the explicit solutions for the liquefied soil depth are then derived to reflect the phase-lag effect. Wave scale effect is further examined by comparative analysis of the liquefaction potential between laboratory and field conditions. It is indicated that, due to the phase-lag effect, the maximum liquefaction potential and the maximum liquefied soil depth no longer appear exactly under the wave trough; nevertheless, such phase difference relative to the wave trough wouldn't exceed π /4. Neglecting the phase-lag effects would considerably underestimate the liquefaction potential as well as the liquefaction depth. Moreover, both the liquefaction potential and the corresponding liquefied soil depth are predominantly related to the non-dimensional parameter I c for characterizing the combined influence of wave and seabed properties. [ABSTRACT FROM AUTHOR]

In the past, a large part of the seabed of the southern North Sea was covered by hard substrates, including oyster beds, coarse peat banks, and glacial erratics. Human activities, particularly bottom trawl fisheries, led to the disappearance of most of these hard substrates, resulting in the loss of its associated diverse benthic life as well. However, the introduction of human-made structures such as offshore wind farms in the North Sea, offers a chance to provide habitat of similar functionality as the former hard substrates. The offshore wind farm infrastructure generally contains layers of rock material deployed at the base of the wind turbine foundations and cable crossings, so-called scour protection, aiming to prevent seabed erosion. The scour protection offers a unique habitat for rock-dwelling benthic organisms in an otherwise mostly soft-bottom environment. By designing the scour protection to be more nature-inclusive, the biodiversity of benthic life can be increased. In this study we examined the effect of substrate material and grading of the scour protection on the epibenthic biodiversity in situ. This was done by deploying research cages containing crates (n = 15) with different types of substrates (concrete, granite, and marble) on the scour protection within an offshore wind farm in the Dutch North Sea. The study revealed a significant (p < 0.05) positive relation between available substrate surface (pebble size) and taxonomic richness. Furthermore, a biological trait assessment of living habits (Tube dwelling, Burrowing, Free living, Crevice dwelling, Epi /endobiotic, and Attached) revealed variations in habit modes across substrate types, with marble and concrete samples showing greatest divergence. Marble samples contained a higher prevalence of tube dwelling organisms, whereas concrete samples contained a relatively higher prevalence of free living, epi /endobiotic and crevice dwelling organisms. The findings support the value of nature-inclusive scour protection designs, emphasizing that both taxonomic and functional diversity can be enhanced by increasing the available surface area of the scour protection and incorporating a variety of substrate types. By adopting these nature-inclusive design components, the coexistence of renewable energy production and a diverse marine benthic community can be further optimized. • In situ research is needed to explore benefits of a nature inclusive scour protection. • Increasing the surface area of scour protection supports taxonomic richness. • Variation in substrate type in scour protection promotes faunal functional diversity. • Nature inclusive design of scour protection can enhance benthic biodiversity. [ABSTRACT FROM AUTHOR]

The vertical structure of internal tidal currents in the Jailolo Strait of the Indonesian seas is studied using the year-long mooring observations with two Acoustic Doppler Current Profiler instruments looking upward and downward, respectively, coving the full depth of the strait. The barotropic tides are extracted from the full-depth current profile measurements, showing the dominant M 2 , K 1 , and O 1 tidal currents with amplitudes of 13.5 cm s−1, 11.0 cm s−1 and 7.6 cm s−1, in nearly reciprocating movement in the direction of 34.5°, 63.1°, and 75.2° clockwise from due north. The internal tidal currents in the Jailolo Strait contributing to about 50% of the total kinetic energy are found to be dominated by the low baroclinic modes, with M 2 tide as the most dominant tidal constituent. High-frequency internal tides of D 3 and D 4 are observed, with baroclinic structure similar to that of M 2 tides, and are suggested to be stimulated by nonlinear processes. The complicated vertical structure of tidal currents in the Jailolo Strait is disclosed for the first time in history. Its potential impact on vertical turbulent mixing suggests its importance in global ocean circulation and climate. • The complicated vertical tidal current structure in the Jailolo Strait is disclosed for the first time in history. • Internal tides are generated in the ocean floor and nonlinear internal tides induced by the topography are observed. • The internal tidal currents in the Jailolo Strait are dominated by the low baroclinic modes. • The internal tidal currents in the Jailolo Strait contribute to about 50% of the total kinetic energy. [ABSTRACT FROM AUTHOR]

Paleocene deposits of the Subbetic Zone (southern Spain) provide outstanding evidence of the influence of sea mountains on deep marine currents. This part of the Betic Cordillera External Zones corresponds to the distal and deepest area of the original basin, where hemipelagic sedimentation prevailed during most of the Turonian-early Lutetian interval. This sedimentation is recorded by the so-called Capas Rojas and Quipar-Jorquera formations, units up to 250 m and 425 m thick, respectively, predominantly consisting of marls and marl/limestone alternations. These units draped and smoothed an irregular submarine topography of fault-bounded Mesozoic carbonate blocks. Some of these blocks became uplifted and subaerially exposed after a mid-Danian tectonic episode, transforming the Subbetic Zone in an archipelago during the late Danian-early Selandian interval. The emerged blocks were colonized by Microcodium -producing terrestrial plants, Microcodium consisting of aggregates of submilimetric monocrystalline calcite grains. Massive resedimentation of these grains into depressed zones of the archipelago resulted in discrete accumulations up to 100 m thick but of comparatively modest extent (≤150 km2) of calcarenites rich in Microcodium remains. The study of one of these calcarenite units, the Olivares Formation, demonstrates that most of its constituent Microcodium remains were brought to the deep sea by turbidity currents, but were subsequently reworked by oscillatory and unidirectional bottom-currents. The analysis of the Capas Rojas Formation in its type section and surrounding areas, where Microcodium -rich calcarenites are absent, demonstrates that the Danian-Selandian succession is riddled with hiatuses, which resulted in a drastic thickness reduction of the interval. Clearly, the rugged sea floor topography resulting from the mid-Danian tectonic event enhanced the sedimentary transport capacity of bottom-currents that, in addition to piling-up Microcodium -rich calcarenites in restricted zones, disturbed the hemipelagic sedimentation elsewhere in the Subbetic Zone. From late Thanetian times onwards the background hemipelagic sedimentation typical of the Capas Rojas progressively resumed throughout the Subbetic Zone, recording the gradual abatement of the sea floor relief by protracted erosion and/or subsidence. • Change of the bathyal Subbetic to an archipelago recorded by redeposited Microcodium • Pre- and post-archipelago weak deep-sea currents favored hemipelagic deposition. • The archipelago rugged sea-floor topography boosted the strength of deep-sea currents. • Deep-sea currents reworked calciturbidites and created hiatuses in hemipelagites. [ABSTRACT FROM AUTHOR]

Liquefaction poses a potential threat to the safety of subsea tunnel during the earthquake. In the ocean environment, wave pressure is considered as a normal loading applied at the seabed surface. This study proposed a fully coupled dynamic effective stress finite element model for subsea tunnel in liquefiable layered seabed under combined earthquake and wave action. Biot u-p formulation integrated with a modified generalized plasticity model was adopted for liquefaction analyses of the seabed. The proposed model was validated through a wave flume model test in terms of excess pore water pressure (EPWP). The results showed that the tunnel – soil dynamic interaction significantly increased EPWP near the tunnel. Increasing the wave height significantly increased the liquefaction depth of the seabed; however, the wave loading can either suppress the displacement of the tunnel during the earthquake or increase the uplift of the tunnel during the subsequent wave loading. When investigating seismic response of subsea tunnels in liquefiable soils under combined earthquake and wave action, the ground motion was suggested to be input simultaneously with the wave pressure. This study also highlights the effect of the thickness of liquefiable layer and frequency content of earthquakes on dynamic responses of subsea tunnels. • A fully coupled dynamic model was developed for subsea tunnel in liquefiable layered seabed under combined earthquake and wave action. • Wave pressure can either suppress the displacement of tunnels during the earthquake or increase the uplift of tunnels during the subsequent wave loading. • The ground motion was suggested to be input simultaneously with the wave for seismic analyses of subsea tunnels in the liquefiable soils. • The effect of the thickness of liquefiable layer and the frequency content of earthquakes on the dynamic response of subsea tunnels was investigated. [ABSTRACT FROM AUTHOR]

Monopiles are important structures in offshore wind engineering, primarily serving as foundations for wind turbines. When installed on a sandy seabed, local scour around monopiles can reduce their capacity, and is a significant hazard to be addressed in the design process. This paper provides a review of research related to local scour around monopiles, focusing on the following aspects: (1) identifying flow structures related to local scour, (2) synthesizing existing data on equilibrium scour depth and scour time-scale, (3) summarizing technology for observing local scour through laboratory experiments, numerical simulations and field observations, and (4) outlining the existing challenges and research opportunities. • This work reviews local scour around monopiles, covering flow processes, engineering assessment and scour observations. • The equilibrium scour depth and time scale around monopiles under various flow conditions has been summarized. • A discussion about filed observation of monopile scour is presented. • Knowledge gaps and research opportunities have been identified and listed in this paper. [ABSTRACT FROM AUTHOR]

High-resolution seabed sediment information is critical for a range of marine spatial planning applications in multi-use shelf environments. To establish this information for the Bay of Fundy, Canada, legacy seabed sediment measurements were obtained from regional data compilations, and eight parameters describing the grain size were modelled across the extent of the bay using high resolution acoustic seafloor mapping and oceanographic datasets. This was achieved using a purpose-made convolutional neural network configured for geospatial modelling of multivariate grain size parameters. Shared information between the response parameters enabled model training with partially complete observations from the varied legacy data sources, and an explicit multiscale model architecture ensured that environmental predictors were implemented at appropriate scales for modelling each parameter. This avoids typical exhaustive exploration and selection of scale-specific predictor sets that often precede model building. Compositional grain size parameters were additionally accommodated using appropriate output activation functions, providing an efficient alternative to compositional data transformation and imputation. Results agreed well with our current understanding of the surficial geology of the bay, and cross-validation was used to quantitatively evaluate map predictions. Of the eight predicted parameters, the mean grain size and mud (clay and silt) fractions were predicted with high accuracy (> 50% variance explained); the accuracy of grain size skewness was comparatively low (24% variance explained). Exploration of variable importance suggested that compiled acoustic backscatter was the most important environmental variable for predicting the grain size, but that geographic information describing the latitude and longitude within the bay was also highly useful. We hypothesize an interaction between these variables that enables location-specific prediction. Data layers of predicted grain size parameter values are made available for further sedimentological and ecological exploration, and for marine spatial planning activities within the bay. • Seabed sediment dataset compiled from legacy sources in the Bay of Fundy. • Remote sensing data describe morphology and oceanography of the bay. • Grain size parameters modelled spatially using remote sensing data. • Multivariate convolutional neural networks enable efficient geospatial modelling. • Model architecture accommodates compositional data and missing observations. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to investigate steady current scour around rectangular and square subsea caissons. The caissons, which are representative of subsea structures, have a submerged height ranging from 0.5 to several times their longest base dimension. The flow model used is based on the Reynolds Averaged Navier-Stokes equations, and the scour model simulates bed load and suspended load transport to predict the evolution of the seabed profile. The aim of this study is to investigate the mechanisms of local scour, specifically the contribution of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour. The model is validated through comparisons with experimental measurements, indicating reasonable agreement. Based on the numerical model results, the mechanisms of local scour around square and rectangular caissons are found to be qualitatively similar. If the flow is directed perpendicular to one of the caisson faces, both the horseshoe vortex and the local streamline contraction contribute to scour. The maximum scour depth is located at the two upstream corners of the caisson due to the combined effects of the horseshoe vortex and streamline contraction. When the flow approaches the caisson with a diagonal attack angle of 45°, the two upstream faces act like a streamlined wedge that splits the incoming flow. The study found that the horseshoe vortex almost disappears and the scour is primarily caused by the local velocity amplification at the two side corners. If the flow attack angle is 45°, the scour does not initiate near the upstream corner without the contribution from the horseshoe vortex. These findings are expected to serve as a valuable theoretical foundation for the design of scour protection. • Scour around subsea caissons is studied by fully three-dimensional simulations. • The contributions of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour are identified. [ABSTRACT FROM AUTHOR]

Distributed Acoustic Sensing (DAS) is a new method for recording oceanographic processes using seafloor fiber-optic cables, such as telecommunication cables. DAS returns spatially distributed measurements of cable strain, which can be related to hydrodynamic pressure, turning a submarine cable into a dense sampling array. A reinforced fiber-optic cable was installed in the cross-shore from the dune toe to ∼15-m-water depth at the USACE Field Research Facility in Duck, NC to quantitatively compare DAS strain to co-located pressure sensors. We develop a methodology for transferring DAS strain to dynamic pressure and evaluate the performance of DAS to measure shallow- and intermediate-water waves in the incident band (0.04–0.4 Hz). A frequency-dependent empirical transfer function from DAS strain to dynamic pressure at the seabed is derived from the ratio of strain and pressure power spectra. DAS-derived significant wave heights and peak periods were consistent with pressure sensors (typical rmse = 0.2 m and 1 s) over a wide range of dynamic conditions (0.24–4 m wave heights and 3–18 s periods). DAS data were input into the cBathy algorithm to calculate cross-shore bathymetric profiles and were used to calculate cross-shore wave reflection. Preliminary applications of DAS to record wave splitting and shoreline position were explored. With this field data, we demonstrate new applications of DAS for measuring nearshore processes and encourage further exploration. The promising potential of DAS lies in the near-bed data volume provided, real-time capability, and ability to sample in any weather or light. • Distributed Acoustic Sensing can measure nearshore ocean waves. • An empirical transfer function is proposed to convert cable strain to pressure. • DAS-derived pressure provides a wide resolution for ocean analyses. • DAS is promising for nearshore monitoring on existing or custom fiber-optic cables. [ABSTRACT FROM AUTHOR]

Geological understanding of the NE Atlantic and Arctic regions has increased greatly over the last two decades, revealing remarkable similarities. Continental extension in both regions onset during pausing or cessation of adjacent orogenies – the Verkhoyansk-Chukotka and Alpine orogenies – which relaxed compressional stresses and permitted extension. Severe extension accompanied by high-volume magmatism did not onset abruptly but was the culmination of long-term, regional tectonic and magmatic unrest. It was complex and piecemeal, with extension and volcanism occurring along multiple axes simultaneously, a process still ongoing in Iceland today. Large Igneous Province emplacement did not drive breakup but occurred as a consequence of continental extension. The High Arctic Large Igneous Province did not progress to breakup. As a result, much of the Arctic Ocean is floored by hyper-extended continental crust overlain by seaward-dipping reflectors. This crust resembles the passive margins of the NE Atlantic. The Alpha-Mendeleev Rise in the Arctic Ocean is a double-sided passive margin underlain by hyper-extended continental crust draped with seaward-dipping reflectors. A similar structure has been proposed for the Greenland-Iceland-Faroe Ridge. If correct, present-day volcanism in Iceland is building SDRs today. Up to ∼50% of the NE Atlantic Ocean oceanward of the continental shelves is likely underlain by at least some continental crust. For the Arctic Ocean this figure is ∼80%. Similar structures are found elsewhere, including the Madagascar Channel, the NW Indian Ocean, and the South Atlantic. These new ideas suggest promising directions of future study including assessing the true extent of continental crust in the oceans globally. • Orogenic stress relaxation allowed the NE Atlantic and Arctic Oceans to open. • LIP magmatism did not drive breakup but was a consequence of extension. • ∼80% the Arctic Ocean and ∼ 50% of the NE Atlantic Ocean contains hybrid crust. • The Arctic Alpha-Mendeleev Rise is a continental, double-sided passive margin. • The Greenland-Iceland-Faroe Ridge is underlain by hybrid crust. [ABSTRACT FROM AUTHOR]

An innovative trawling strategy for transitioning from conventional bottom trawling to semi-pelagic trawling (elevating the otter board but allowing the trawl net to contact the seabed) was developed to mitigate the effects of seabed impact, and its dynamic performance was evaluated. Experiments were carried out using a 1/18 scale physical model of the otter trawl at a speed of 0.6 m/s, and the warp length was tuned in the range of 4–8 m under constant-speed control of the trawl winch for validating the numerical simulations. Numerical simulations were then conducted to investigate the effects of towing speed and winch speed on the dynamic loads of the otter trawl system and movement of the otter board, eventually develop a fuzzy or proportion-integration-differentiation (PID) controller for the trawl system. Numerical results showed the sharp increase of the warp tension and the overshoot of the otter board at the constant-speed control occurred, and the magnitudes of both raised as the towing speed and winch speed increased. The otter board spread was significantly reduced during the transition to semi-pelagic trawling at a low towing speed. The use of fuzzy and PID control successfully eliminated the overshoot and diminished the high warp tension. • Effects of towing and winch speeds on the dynamic performances of otter trawl were investigated as the trawl tows semi-pelagically. • Trawl winch reeling in warp faster, both the maximum warp tension and the otter board overshoot larger. • A reduction of otter-board spread from the bottom towards semi-pelagic trawl occurs when the towing speed is low. • Automated trawl winch could eliminate the otter board overshoot and diminish the high warp tension for the semi-pelagic trawl. [ABSTRACT FROM AUTHOR]

Sloping seabeds often exist in offshore areas with complex structures. It is difficult to accurately analyze the seismic response characteristics of sloping seabeds based on the assumptions used for horizontal seabeds. The degree of saturation in nearly saturated soil notably affects the seismic response of seabeds. Therefore, we developed an analytical solution for the seismic response of a sloping, nearly saturated multilayer seabed. Using this solution, we analyzed the effects of the slope angle and soil saturation degree on the seismic response of the seabed. The results show that the seafloor inclination may has a minor impact on the seismic motion at a specific point, but it has a very significant effect on the overall site. A weak interlayer refers to a layer of material that has lower strength and/or permeability compared to the surrounding soil or rock. This layer can reduce the natural frequency of the seabed and increase the amplitude of long-period seismic components. In addition, the presence of a weak interlayer can lead to increased pore water pressure, decreased effective stress, and increased susceptibility to shear failure. These factors combine to reduce the stability of submarine slopes, highlighting the importance of understanding and managing the effects of weak interlayers in geotechnical engineering and coastal defense projects. • First-ever analytical solution for nearly saturated sloping seabed provided. • Seabed inclination influences seafloor seismic response, even in small sites. • Analysis of wake interlayer's impact on seismic response of sloping seabed. [ABSTRACT FROM AUTHOR]

Understanding the seismic characteristics of submarine sites and conducting seismic response analysis for such locations are crucial for the safety of marine engineering. However, due to a shortage of strong motion records, the ground motion of offshore earthquakes has not yet been fully characterized. The actual seabed conditions are highly intricate, necessitating consideration of factors such as the dynamic coupling effect between seawater and seabed, the strong nonlinearity of seafloor soft sediments, and the diverse nature of natural submarine terrain. In this study, the modified Davidenkov dynamic constitutive model is used to simulate the nonlinear behavior of the soil. The Coupled Acoustic-Structure method is utilized to simulate the interaction between seawater and seabed. Three typical and simplified terrains, namely flat terrain, valley terrain, and hilly terrain, are individually modeled. The measured seafloor ground motions with different frequency components are used as bidirectional seismic excitations input from the bedrock. The amplification factor in terms of CAV is introduced to evaluate the amplification of seismic ground motion characteristics at seabed surface with respect to those at the bedrock surface. The acceleration response spectra in both horizontal and vertical directions, as well as the corresponding vertical-to-horizontal response spectral ratios, at the representative points are obtained, respectively. Several key findings are consistent with the features of the observed offshore and onshore earthquake ground motions. Numerical examples are presented to illustrate the different influence rules of terrain condition, overlying water depth, and seismic intensity on the nonlinear seismic response characteristics. • Both the nonlinearity of soil and the seawater-seabed dynamic interaction are considered. • Three typical terrains, namely flat, valley, and hilly terrains, are individually modeled. • Bidirectional seismic input from the bedrock with different frequency components are adopted. • Amplification factors in terms of CAV in horizontal and vertical directions are adopted. • The acceleration response spectra as well as the vertical-to-horizontal response spectral ratios are respectively obtained. [ABSTRACT FROM AUTHOR]

Gassy clay deposits are widely distributed in marine sediments. Clarifying the influence patterns of the trapped gas phase on the mechanical properties of gassy clay is of significant importance. Establishing an in-situ strength parameter and consolidation coefficient inversion method based on CPTu is crucial for gassy clay characterization. In this study, gassy clay was prepared using the zeolite method. The variations of strength and consolidation parameters of gassy clay concerning gas content were obtained based on laboratory triaxial and one-dimensional tests. It was observed that the trapped gas phase enhances the undrained shear strength and hinders drainage. Specifically, gassy clay with a gas content of 3.5 % exhibited an 18 % increase in undrained shear strength compared to saturated clay and a 50 % reduction in consolidation coefficient. In addition, laboratory calibration chamber tests were conducted to investigate the cone penetration test (CPTu) in gassy clay with varying gas contents and penetration rates. The drainage effect during the CPTu penetration process in gassy clay was discussed. The reasons behind the variations in static cone penetration parameters under undrained conditions for normally consolidated gassy clay were analyzed by combining the results of triaxial tests and one-dimensional consolidation experiments. A proposed formula for the cone factor N kt was also provided under undrained penetration conditions. The accuracy of conventional methods for estimating the consolidation coefficient of gassy clay was verified, the basic properties of the gassy clay used in the indoor experiment are similar to those of the seabed gassy silt at the project site, and the environmental conditions are similar to those at locations with low initial pore pressure, such as mudflat or shallow sea bed, thereby offering a reference for in-situ testing of strength parameters and consolidation coefficients in gassy clay seabed. [ABSTRACT FROM AUTHOR]

• Experimental measurements in the wind tunnel on the drag and lift force of special unexploded ordnance (UXO). • Numerical simulations CFD of the drag and lift force of special UXO's. • Numerical simulations BEM of the added mass of special UXO's. • Polynomials for the drag, lift and added mass coefficients as a function of the Reynolds number and the burial depth. Unexploded ordnance (UXO) and Discarded Military Munitions (DMMs) are found in many coastal regions. These objects are constantly exposed to environmental influences such as saltwater, which causes corrosion, and waves and currents as well as mobile seabed sediments. The basic assumption to decide if an object is mobilised by waves and currents or not is to compute the critical loads that are needed to move it from its stable position on the sediment bed. The loads on the object are induced by hydrodynamic and hydrostatic forces as well as by friction, gravitation, and inertia. In this study, the hydrodynamic forces were calculated by analytical approaches and numerical simulations (CFD). These forces have been validated for the current-induced mobilisation by wind tunnel experiments. Finally, the dependency of the dimensionless coefficients for lift, drag and added mass of the Reynolds number and the burial depth is transferred into a resulting equation. [ABSTRACT FROM AUTHOR]

Magmatism and crustal structural characteristics are well-known phenomena that support understanding the marginal sea's tectonic evolution. The South China Sea (SCS) has become a natural laboratory for researchers to investigate the evolution of the marginal sea because of its complex tectonic background and multiple phases of magmatic activities. However, due to limitations in resolution and depth of observations, the evolutionary process of the SCS is still controversial. We use the latest processed multi-channel seismic reflection profile Line AB to evaluate the sedimentary sequences, crustal tectonics, and the Cenozoic magmatism in the southern SCS. The gravity modeling results indicate a reduction in crustal thickness from 18 km in the proximal domain to 7 km in the Continent-Ocean Transition (COT). The COT is roughly 35 km wide, representing a rapid break up process of the SCS. A high-velocity layer (HVL) of about 3 km thickness was formed in the continental slope crust, interpreted as post-spreading magmatic underplating. In addition, four sedimentary sequences, post-spreading magmatic intrusion, and the possible magma conduits were identified in the profile. Combining with previous ocean bottom seismometer (OBS) data, multi-channel seismic data, fault system data, and petrologic observations, we indicate the deep mantle magmatic material upwelled to the crust and further intruded into sediments along the hyper-extended crust or detachment faults during the post-spreading stage. We contend that cooling and heat shrinking within the SCS oceanic lithosphere have the potential to initiate decompression melt deformation in the continental slope. In summary, we construct a model of the origin and migration mechanism of extensive post-spreading magmatism in the SCS. Our research reveals the Cenozoic evolution and the HVL of the southern SCS, and provides a possible genesis for the anomalously young magmatism observed at the continental margin. • A high-velocity layer in lower crust is observed in southern South China Sea. • A narrow COT (∼35 km) was found in the southern continental margin. • The post-spreading magmatic underplating formed the HVL. • The extensional crust and detachment faults promote the post-spreading magmatism. • The cooling and heat shrinking of oceanic lithosphere reactivated the faults. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage (CCUS) is believed to be the most promising technology to mitigate climate change and global temperature rise. As an effective method for reducing carbon emissions, carbon dioxide (CO 2) storage on the seabed can be achieved by injecting captured CO 2 from offshore platforms into subsea storage sites, such as the sediment layers, depleted oil and gas reservoirs and deep saline aquifers, thereby permanently removing it from the atmosphere. Additionally, hundreds to thousands of meters of seawater above seabed storage layers provide naturally high seawater pressure and abundant barrier settings that can reduce leakage risk. Consequently, this has become an ideal storage location for long-term CO 2 storage. In order to thoroughly investigate the mechanism and potential of marine CO 2 storage and promote further development of CCUS, this paper provides a comprehensive description of theoretical research of marine CO 2 geological storage, including storage mechanisms, storage capacity, wellbore flow, CO 2 migration, cap rocks integrity and CO 2 leakage monitoring. The implementation status of global engineering projects is summarized. Currently, there are relatively few successful marine storage projects globally, with the majority of others still in the research and testing stages. Finally, the challenges and prospects of marine CO 2 storage are also discussed. This review demonstrates the enormous potential and promising future of marine CO 2 storage, but there are also leakage risks. It can be avoided through in-depth theoretical research to clarify the entire process of storage mechanisms and take corresponding technological measures. Ultimately, a new technology for large-scale efficient injection and enhanced storage of marine CO 2 storage will be formed. • Marine CO 2 storage has enormous potential and promising prospects. • The flow of CO 2 in the storage reservoir will cause phase change, heat transfer, storage leakage, etc. • Remote monitoring technology can prevent CO 2 leakage. • Storage projects require adequate funding and policy support. [ABSTRACT FROM AUTHOR]

This paper presents a novel 3D path planning method for the underwater glider (UG) that incorporates adaptive segment strategy, motion parameters optimization, and an improved JADE algorithm. The method aims to generate an energy-efficient path by adapting to ocean currents and seabed topography and selecting favorable motion parameters. We establish an energy consumption model for a blended-wing-body UG, examining the influence of motion parameters and ocean currents on its performance. The proposed method encodes an energy-optimal gliding path through multiple path segments, each defined by a set of path points, pitch angles, and diving depths. The fitness function, based on energy consumption, guides the optimization process. To enhance the optimization, we present an improved JADE algorithm with multi-mutation strategies, which adaptively updates the mutation operation and mean crossover probability. Our method was assessed and compared with a classical UG path planning method on 6 test scenarios. Simulation results confirm that adaptive segments and motion parameter optimization contribute to better adaptation to ocean environments and reduced energy consumption. • A 3D path planning method for underwater gliders with adaptive segments and optimal motion parameters was proposed. • An energy consumption model for a blended wing body underwater glider was established. • An improved JADE algorithm with multi-mutation strategies was presented as an optimizer for UGAPP. • Significant improvements have been achieved in terms of energy savings for the underwater glider compared to a classical method. [ABSTRACT FROM AUTHOR]

The deep-sea mining vehicle is one of the key equipment for deep-sea mining system, which needs to complete tasks such as traveling on the seabed, ore crushing, ore collection, and ore transportation. During the operation of deep-sea mining vehicles, real-time mapping of the surrounding terrain environment is a necessary guarantee for safety. Forward-looking sonars can perform real-time imaging of underwater environments without being affected by water turbidity, which has been gradually used in underwater environment exploration. In this study, a novel seabed terrain mapping algorithm based on occupancy-elevation grid map for deep-sea mining vehicles, which uses a wide aperture forward-looking imaging sonar is proposed. This paper proposes an inverse sensor model for forward-looking sonar, which can map pixels in the image to the occupied probability and elevation information corresponding to the real space, and use it to generate the occupancy-elevation grid map. Then, a local occupancy-elevation grid map can be constructed as a submap with the inverse sensor model and position information from sonar odometer or other sensors. And the poses of different local submaps are optimized based on factor graph to generate the global occupancy-elevation grid map. The proposed mapping algorithm is validated by both simulation experiments and real data from forward-looking sonar during sea trials. • Proposing an inverse sensor model of the forward-looking sonar to estimate the occupied probability and elevation. • Using 2-D probabilistic space carving to reduce the redundant impact of uncertainty on obstacle areas in sonar images. • Both the simulation and the dataset from sea trials proved that the proposed method can generate a reliable occupancy-elevation grid map successfully. [ABSTRACT FROM AUTHOR]

Bacteriohopanepolyols (BHPs) are widespread in bacteria and are used as lipid biomarkers for specific bacterial activities and environmental changes. However, deposition and degradation dynamics of BHPs are still poorly constrained in marine settings, thereby affecting their reliability as biomarkers. Here, we investigated BHPs in the water columns and sediments near the Changjiang Estuary to evaluate their origins, preservation and responses to seawater hypoxia and bacterial activities. Results indicated that bacteriohopanetetrol stereoisomer (BHT-isomer) in this area was predominantly BHT- x produced by Ca. Scalindua, present in hypoxic bottom seawater. 2-Methyl BHT and nitrogen-fixing cyanobacteria showed similar vertical distribution in the water column, as did amnio-BHPs (aminotetrol and aminopentol) and the aerobic methane oxidation (AMO) gene pmoA. 2-Methyl BHT, aminotetrol and aminopentol were thought to primarily derive from cyanobacteria and aerobic methanotrophs in seawater, respectively, despite other potential sources. Depth profiles suggest that in-situ production in sediments is not a major contribution to sedimentary BHPs, compared to the export and deposition from the water column. The abundances of unsaturated BHT and amino-BHPs in surface sediments were decreased compared with those in the water column, indicating that unsaturated BHT and amino-BHPs appear to undergo a certain degree of early diagenetic degradation. BHT-isomer and 2-Methyl BHT preserved preferentially over amino-BHPs. Additionally, BHT-isomer significantly correlated with anammox functional gene amx -16S rRNA, and 2-Methyl BHT significantly correlated with nitrogen-fixing functional gene nifH. This indicated that BHT-isomer and 2-Methyl BHT are suitable as biomarkers for anammox and cyanobacterial nitrogen fixation. The BHT-isomer ratio accurately reflects the situation in the water column and appears to be a very appropriate proxy for hypoxia. Conversely, sedimentary aminotetrol and aminopentol underestimate the importance of aerobic methane oxidation in seawater, as these are more rapidly degraded upon deposition to the sea floor. [Display omitted] • The origin, deposition and preservation of BHPs in coastal seawaters were studied. • BHT-isomer was mainly from Ca. Scalindua in hypoxic bottom seawaters. • Deposited BHT-isomer and 2-methyl BHT were preserved preferentially in sediments. • BHT-isomer and 2-Methyl BHT showed correlations with amx and nifH gene copies. • BHT-isomer ratio appears to be an appropriate proxy for seawater hypoxia. [ABSTRACT FROM AUTHOR]

Coastal engineers are deeply concerned about wave-induced seabed instability around monopile foundations. Most prior studies have primarily focused on the seabed response around monopiles on flat seabeds, often neglecting the presence of scour holes commonly found in engineering practice. This study thoroughly investigates seabed response and liquefaction around monopiles of scour holes. The examination involves analyzing 3D flow velocities, dynamic wave loads, pore pressures, soil effective stresses, and wave forces around a monopile with a scoured profile. The analysis uses a model that integrates the interactions between waves, seabed, and structures, and it is implemented within the OpenFOAM framework. The study meticulously assesses the impact of scour holes on seabed responses and liquefaction zones around monopile foundations. Numerical results reveal that: (1) The magnitude of the pore pressure within the scoured seabed is reduced relative to a flat seabed; (2) Considering the scour hole effect leads to a more uniform distribution of liquefaction depth around the monopile; (3) This effect intensifies with a higher saturation degree, while it exhibits a pattern of increase, followed by a decrease with an increase in permeability. • An integrated model for wave–monopile–scour seabed is developed on OpenFOAM. • Results of wave forces, pile responses, pore pressure, and liquefaction are analyzed. • The effects of the scour hole on the soil response and liquefaction are investigated. [ABSTRACT FROM AUTHOR]

The Deepwater Artificial Seabed (DAS) production system is proposed to provide a cost-effective solution for offshore field development in deep and ultra-deep waters. This paper conducts theoretical and experimental investigations on the nonlinear dynamic responses of the floating submerged Artificial Seabed-Mooring (ASM) coupling system in ISWs, thereby elucidating the acting mechanisms of ISWs from the perspectives of the time and frequency domains. A nonlinear coupled dynamic analysis method is developed by integrating the ISW theory application conditions, the dynamic ISW load model, and the iterative solution scheme. The laboratory experiments on the dynamic responses of the ASM system in ISWs are conducted in a large-scale density-stratified fluid flume. The temporal and spatial features of the dynamic behaviors of the ASM coupling system in ISWs are revealed through a comparative analysis between the experimental and theoretical results. The frequency-domain characteristics of the dynamic responses are clarified via the wavelet transform method in combination with the fast Fourier transform algorithm. Considering the inherent coupling effects, the effects of various influence factors on the nonlinear dynamic response amplitudes are systematically explored. The results indicate that the ASM system in ISWs exhibits a large-amplitude surge motion, a highly coupled synchronous heave motion with the surge response, and significant variations in mooring tensions. The frequency-domain components accounting for over 90% of the ISW waveform, surge motion, and heave motion are concentrated in the low-frequency regions below 0.103, 0.146, and 0.170 Hz, respectively. • A nonlinear coupled dynamic analysis method is developed and validated by the response experiments. • Laboratory experiments on the nonlinear dynamic responses induced by internal solitary waves are conducted. • Acting mechanisms of internal solitary waves are revealed through time- and frequency-domain perspectives. • Effects of various influence factors are explored considering the inherent coupling effects. [ABSTRACT FROM AUTHOR]

• Summarized natural and man-made stresses on the Changjiang River estuarine-coastal ocean continuum; • River damming, coastal reclamation, and pollutant discharge are destroying continuum's ecosystem; • Ocean warming also exacerbate threats to continuum's ecosystem; • The ecological processes of continuum might be divided into three stages since 1950 s; • Regime shift of continuum's ecosystem has been occurred after early 2000 s. The Changjiang River estuarine-coastal ocean continuum is a well-studied system that is undergoing significant changes due to human activities and climate change. While research has improved our understanding of its ecological importance, the changing external forces present challenges that require integrated knowledge. Here, we provide a comprehensive summary of the natural and man-made stresses on the continuum and identify knowledge gaps for future study. The construction of dams has led to a decrease of approximately 70 % in sediment loads from the Changjiang River, resulting in seabed erosion and a reduction in organic carbon and pollutant reservoirs in the continuum. In contrast, nutrient fluxes from the Changjiang River have shown increasing trends since the 1960 s, leading to changes in nutrient conditions and ecological processes in the continuum. These changes have altered the biomass and community structure of phytoplankton, leading to frequent harmful algal blooms and shifts in dominant species from diatoms to dinoflagellates. We also outline the impacts of coastal engineering and wetland reclamation, which have altered coastal geography, destroyed wildlife habitats, and weakened the filtering effect on pollutants. Additionally, ocean warming has increased threats to the ecosystem, exacerbating harmful algal blooms and facilitating the release of semi-volatile pollutants. In our review of the ecological processes in the continuum, we categorize the changes into three stages: the 1950 s to mid-1980 s (initial state), mid-1980 s to early 2000 s (ecosystem destruction begins), and early 2000 s to the present (critical transition in the continuum). Future research should focus on understanding the ecological responses to these changing processes in the estuarine-coastal ocean continuum. As other continuum ecosystems worldwide may be at different stages, studying the response of the Changjiang River estuarine-coastal ocean continuum will provide a comprehensive case study. [ABSTRACT FROM AUTHOR]

The characteristics between offshore and onshore ground motions are different based on the complex geological structure of the seabed. But the influence of seabed topography on the characteristics of offshore ground motions is less studied. Therefore, in order to analyze the influence of site conditions, local site topography and other factors on the characteristics of offshore ground motion, a numerical simulation method for the propagation process of offshore ground motion is proposed by combining the self-designed wave analysis program and the finite element dynamic analysis software. Firstly, different numerical models including canyon, ridge and slope are constructed to analyze the effect of different topography on the characteristics of the offshore ground motion. Besides, the influence of the seawater layer, the incidence angle of ground motion and the soft soil layer is also analyzed. Finally, a complex seabed site model is established to study the effects of different topographic coupling on the offshore ground motion. The seismic response of offshore slope, ridge and canyon site will be significantly amplified by P wave, and it is found that the seismic response is particularly enhanced at the inflection point of all kinds of topography. However, the effect of different topography on SV wave seismic response is limited. In addition, the water depth and the slit soft soil layer also affect the seismic response of the seabed site. • A numerical simulation method for the propagation process of offshore ground motion is proposed. • Different numerical models including canyon, ridge and slope are constructed to analyze the effect of different topography. • A complex seabed site model is established to study the effects of different topographic coupling on the offshore ground motion. [ABSTRACT FROM AUTHOR]

• Iceberg draft was modeled by the generalized structure of the group method of data handling. • Iceberg width ratio and the iceberg shape factor were the most influencing inputs. • The magnitude of iceberg drafts grew by increasing the value of the iceberg width. • A GS-GMDH-based equation was presented to estimate the iceberg drafts. The iceberg draft prediction is vital to mitigate the collision risk of deep keel icebergs with the seafloor-founded infrastructures, including the subsea pipelines, wellheads, hydrocarbon loading equipment, and communication cables crossing the Arctic and subarctic areas since the drifting icebergs may gouge the ocean floor and the physical and operational integrity of the submarine structures would be threatened. In this study, the iceberg drafts were simulated using the generalized structure of the group method of data handling (GS-GMDH) algorithm for the first time. The parameters affecting the iceberg drafts were determined, and five GS-GMDH models comprising GS-GMDH 1 to GS-GMDH 5 were developed utilizing those parameters governing. A dataset comprising 161 distinct case studies measured in the most significant field investigations of iceberg characteristics was generated, and the GS-GMDH models were trained through 60 % of the data, the rest of the data (i.e., 40 %) were considered for the GS-GMDH models' validation. By defining different scenarios, the most accurate GS-GMDH model and the most important input parameters were identified. The sensitivity analysis demonstrated that the iceberg width ratio (W / H) and the iceberg shape factor (S f) were identified as the most influencing input parameters. The comparison between the performance of the premium GS-GMDH model and the group method of data handling (GMDH), artificial neural network (ANN) algorithms, and the empirical models proved that the GS-GMDH model simulated the iceberg drafts with the highest level of precision and correlation along with the lowest degree of complexity. Based on the partial derivative sensitivity analysis (PDSA), the magnitude of iceberg drafts grew by increasing the value of the iceberg width and iceberg length. Ultimately, a GS-GMDH-based equation was presented to estimate the iceberg drafts for practical applications, particularly in the early stages of iceberg management projects and engineering designs. [Display omitted] [ABSTRACT FROM AUTHOR]

Consideration of tidal stream turbine (TST) interactions with the surrounding environment and the resultant local scour is vital for safe operation and maintenance. A numerical model with coupling actuator line method (ALM) and immersed boundary method (IBM) is developed for simulating hydrodynamics synchronously with the local scour process around the TST. The ALM is applied to treat the rotating turbine rotor while the sediment dynamics is integrated into the IBM to simulate the scouring morphology. The simulating performance of the proposed ALM-IBM coupling model is validated and demonstrated by modeling the mono-pile supported horizontal-axis TST upon scouring seabed under steady currents. The impact of the horizontal-axis rotating turbine rotor on the scour around the supporting mono-pile under steady currents is then investigated. The results show that the rotating rotor can accelerate near-seabed flow resulting in the enhanced equilibrium scour scale around the mono-pile. The contribution of the mono-pile on the equilibrium maximum scour depth is stronger than that of the rotating rotor under the clear-water condition. The existence of the mono-pile can enhance the local mass and momentum exchanges between the wake- and surrounding-flow fields, leading to the asymmetrical scoured seabed morphology. [Display omitted] • A numerical model is developed with coupling ALM-IBM. • Sediment dynamics and morphodynamics are integrated into ALM-IBM model. • Hydrodynamics upon scouring morphology around TST is accurately simulated. • Impact of rotating rotor on sediment scour around mono-pile is investigated. • Respective contributions of rotating rotor and mono-pile on scour are clarified. [ABSTRACT FROM AUTHOR]

The exponential increase in plastic production coupled with variable global waste management system efficiencies has resulted in large amounts of plastic waste entering the ocean every year. Although we know millions of tonnes of plastic have entered the oceans, we do not yet understand the patterns of its accumulation across space nor the drivers of these patterns. The deep ocean is expected to be a resting place, or reservoir, for most plastic pollution. Here, we conducted a rigorous, systematic review of previously published datasets to synthesize our understanding of macroplastic pollution (>5 mm) on the ocean floor. Using extracted data, we built predictive additive models to estimate the amount and distribution of plastic on the ocean floor. We built two models: one using data from remote operated vehicles (ROVs) and another using data from bottom trawls. Using the model built with ROV data, which was better-constrained, we estimate that 3 to 11 million metric tonnes (MMT) of plastic pollution resides on the ocean floor as of 2020. This is of similar magnitude to annual inputs from land and one to two orders of magnitude greater than what is predicted to be floating on the ocean surface. To improve future estimates and our understanding of global patterns, we provide recommendations for ocean floor monitoring of plastic pollution. [Display omitted] • Deep sea plastic sampling efforts to date concentrated in coastal marine environments. • The ocean floor reservoir contains 3–11 million metric tonnes of plastic pollution. • Macroplastic clusters around continents, close to human populations. • We highlight where gaps in sampling effort can be filled to improve future models. [ABSTRACT FROM AUTHOR]

Avoiding in-situ skidding of tracked deep-sea mining vehicles on soft sediment and reducing disturbance to soft sediments are the basic requirements for ensuring the regular operation of seabed mining. The in-situ skidding problem of the tracked deep-sea mining vehicle can be explained by the block shear failure phenomenon of deep-sea soft sediment. We analyzed the force state and elastic-plastic state of soft sediment disrupted by a crawling grouser and established the block failure model. The elastic-plastic failure range calculations obtained in the model is used to select the spacing between adjacent grousers to maximize the thrust provided by the grouser. Due to the irreversibility of plastic failure, the range of plastic zone failure is used to measure the extent of the sediment disturbance by the grouser. By analyzing the influence of multiple parameters on the failure range of the plastic zone, we provide direction for finding ways to reduce sediment disturbance. It is found that among these parameters, the grouser's width and height, which represent the shape parameters of the grouser, have the most critical effect on the plastic failure range of the sediment. But when the width exceeds 0.3 m, and the height exceeds 0.2 m, the benefit of reducing the failure range by increasing the grouser's width and height will be minimal. [ABSTRACT FROM AUTHOR]

María Magdalena Island is part of the Islas Marías Archipelago, located at the mouth of the Gulf of California. The island is composed of a gabbroic and basaltic sill complex that intrudes a sedimentary sequence. Its geology is drastically different to the rest of the archipelago that reflects a protracted geological history with continental affinity. It constitutes a rare example of an exposed ocean floor sequence. Neighboring María Madre, María Cleofas, and San Juanito islands contain silicic volcanic and granitoid rocks of mostly upper Cretaceous age. In contrast, 40Ar/39Ar ages of the gabbroic and basaltic sills from María Magdalena Island show younger magmatic pulses of late Miocene age (~ 8.7 and 6.9 Ma). María Magdalena samples are isotopically more evolved (87Sr/86Sr ~ 0.7027–0.7049, 143Nd/144Nd ~ 0.51305–0.51310) in comparison to the MORB-type Rivera plate basalts (87Sr/86Sr ~ 0.7024–0.7025, 143Nd/144Nd ~ 0.51323–0.51325). The presence of detrital zircons in the hosting sedimentary rocks and their siliciclastic nature suggest that María Magdalena Island was formed and uplifted in situ to its present position in the archipelago. Our data suggest that María Magdalena Island was formed in an evolved oceanic magmatic environment within a thinned continental crust setting since ~8.7 Ma, possibly related to the extensional tectonic regime associated to the separation of Baja California Peninsula from mainland Mexico. María Magdalena Island may be an extinct spreading center oriented in a ~ N-S direction that emplaced the Magdalena sills in an ~ E -W direction. Magmatism ceased as extension progressed. • Gulf of California ocean layer with sheeted gabbroic dikes in sedimentary sequences. • Thinned continental crust setting, related to the separation of Baja California. • 40Ar/39Ar dating reveals two magmatic pulses: ~ 6.9 Ma and ~ 8.7 Ma. • Isotopically more evolved than Rivera Plate MORBs, but geochemically more primitive. • Uplift of the island could have occurred due to obduction by pull-apart basins. [ABSTRACT FROM AUTHOR]

In order to examine the effects of crack properties on electrical resistivity and seismic velocity, we conducted simultaneous measurements of electrical resistivity, seismic velocity and porosity at brine-saturated hydrostatic pressures using mafic crustal rocks from the Oman ophiolite. The resistivity and velocity of the samples increase systematically with increasing confining pressure owing to the closure of cracks, as monitored by changes in porosity. Apparent formation factors of each sample are related to the porosity, but nonlinear relationships on logarithmic plots indicate that Archie's law cannot explain these experimental data. We evaluated the effect of crack porosity and aspect ratio for the measured velocity based on the effective medium theory, and the electrical resistivity was inferred from the crack porosity and connectivity according to the percolation model. The experimental velocity and resistivity results are consistent with the model calculations in terms of crack density, aspect ratio and connectivity. We applied a combined velocity-resistivity model to the geophysical logging and borehole data for the oceanic crust in Hole 504B. Our inversion results indicate that the seismic layer 2/3 transition is primarily caused by an alteration front controlled by interconnected cracks and fluid flow in the oceanic crust. • Electrical resistivity and seismic velocity of the Oman crustal sample were measured. • Joint model for electrical resistivity and seismic velocity was proposed. • Seismic layer 2/3 transition reflects a combination of crack and alterations. [ABSTRACT FROM AUTHOR]

Understanding and optimizing the extraction of offshore monopiles from the seabed in decommissioning operations give both environmental benefits and cost reduction. The literature highlights the significance of utilizing a vibratory hammer for the complete removal of monopiles in granular or non-cohesive seabed, e.g., sandy soil, offering a cost-effective alternative to the conventional cutting method. However, the available knowledge for applying this method to cohesive soil is limited. The present study examines vibratory pile extraction from cohesive soil, for both soft and stiff clays, with the aim of assessing the resulting extraction force required for pile removal. Coupled Eulerian-Lagrangian (CEL) analyses with two domains of pile and soil are performed using the finite element package ABAQUS. A modified Mohr-Coulomb (MCC) soil model is coded into a VUSDFLD subroutine to properly simulate the soil softening and shear strain rate dependency of seabed soil in an Eulerian domain. The importance of shear strain and softening effects is underscored for soft clay by demonstrating an approximately 20% reduction in the force needed to initiate cyclic extraction of the monopile compared to scenarios where these effects are not included. However, incorporating these effects does not affect the behavior of stiff clay. The present numerical findings show that adopting vibratory extraction method leads to more soil resistance in cohesive soils at the beginning of the extraction. Considering the added weight og the vibratory hammer which should be clamped to the monopile top head leads to exceedance of the required force than the one required for removal of the monopile without vibration (i.e., the pulling-out method). This demonstrates that the vibratory extraction method is not an efficient method for monopile extraction from clayey seabed despite its beneficial effects reported in the literature for sandy soil. • A Coupled Eulerian-Lagrangian (CEL) approach is used to study numerically vibratory pile extraction from soft clay. • In cohesive soil, vibratory monopile extraction demands more initial force than pulling out method. • Even by considering strain rate and strain softening, soil resistance in vibratory extraction exceeds pulling out method. • Soil degradation happens faster in softer clays after exposing to cyclic loading. • Applying higher frequencies of vibration results in more soil degradation and consequently lower soil resistance. [ABSTRACT FROM AUTHOR]

Deep-sea mining involves the extraction of valuable minerals from the ocean floor. The transportation of deep-sea mineral deposits from the seafloor to the surface is crucial for the success of deep-sea mining operations. The slurry pumping system is responsible for conveying a mixture of minerals, sediments, and water over significant distances. Designing a robust and efficient slurry pump necessitates meticulous consideration of various factors, including particle size, slurry concentration, system reliability, and more. This article presents a comprehensive, state-of-the-art review of airlift pumping, with a particular focus on three-phase flow systems. The manuscript is divided into two primary sections: an analytical approach and an experimental approach to the airlift system. The empirical methodologies discussed herein provide correlations for evaluating pump performance in both two-phase (air-water) and three-phase flow systems. Furthermore, the experimental findings shed light on how operational parameters impact system performance dynamics and flow regime transitions. Additionally, the paper discusses the utilization and advancement of airlift pumping systems in deep-sea mining operations. The technological advancements and challenges addressed within this paper offer valuable insights for improving the implementation methodologies for designing slurry pumping systems in the context of deep-sea mining operations. • Conducted a comprehensive review and presentation of airlift pumping systems, aiming to provide a thorough understanding of their mechanisms, advantages, and limitations for the vertical solid particle transport. • The empirical correlations for both two-phase and three-phase flow air-lift pumping systems are comprehensively presented, and their reliability is assessed through a comparative analysis with experimental results. • The experimental analyses presented by various authors have been thoroughly examined and organized in a table, including their variable geometrical and operational parameters, as well as significant findings. • The promising potential of air-lift pump systems in the emerging field of deep-sea mining is discussed in details. These discussions help us to understand the effective transport of solid particles from the ocean floor to the surface. [ABSTRACT FROM AUTHOR]

A serious threat affecting the Mediterranean Sea is the migration of Indo-Pacific marine species through the Suez Canal following its opening in 1869. This phenomenon gives extreme causes for concern as many non-indigenous species are highly invasive and seriously threaten native biodiversity. Particularly insidious are small-size taxa such as benthic foraminifera, which are able to invade wide areas un-noticed. The objective of this study is to evaluate the stage of invasion of non-indigenous foraminifer Amphistegina lobifera and the re-colonization of Amphistegina lessonii in two islands of the Pelagian Archipelago (Central Mediterranean) where both species were first recorded in 2005. Absolute abundances quantified in seabed and algal samples collected in 2014 were compared with those detected in 2005 and 2009. Results show that, in the innermost part of the neritic environment, amphisteginids were so abundant and widespread as to have replaced native benthic foraminifera just a few years after earlier reports. On Lampedusa Island, Amphisteginids seem to compete mainly with other symbiont-bearing foraminifera, such as the milioliid Peneroplis pertusus and Peneroplis planatus ; we hypothesize that the different algal symbionts housed by the invasive species could play an important role in the invasion success in the Mediterranean Sea. In the most severe case of amphisteginid invasion, as seen around the volcanic island of Linosa, the accumulation of their carbonatic remains is causing a sedimentation switch: increasing the content of white carbonatic sands and replacing the black volcanic substrates, as already observed in Indian Ocean atolls. • The Mediterranean Sea is undergoing the massive colonization by Lessepsian migrants of Indo-Pacific origin. • The proliferation of the invasive benthic foraminifera A. lobifera is drastically increasing. • Amphistegina lobifera is contributing to the increase of carbonate sediment in the coasts around Pelagian Islands [ABSTRACT FROM AUTHOR]

Scientific management of coral reefs is a global research topic due to their latent economic value and ecological significance. This research benefits from optical and acoustic remote sensing technology with high spatial resolution, sufficient coverage, and stable repeatability. However, each sensor with its own set of limitations, such as insufficient penetration ability, limited sensor resolution and range, which often hinder their applications in the precise classification of coral reef habitats. To address these issues, a novel scheme integrating airborne laser bathymetry (ALB), multibeam echo sounder (MBES) and the multispectral image is designed to serve large-scale and high-precision coral reef habitat sediments research. This scheme focuses on valuable attribute mining, inconsistent coverage, feature default, and redundancy according to multi-source data used in engineering demands. After per-system pretreating, numerous properties, including band, waveform, intensity, terrain, and derivative characteristics, are extracted and quantitatively analyzed to be responsible for habitat description. Subsequently, a complete seabed terrain is generated using the LightGBM regression model to establish the conversion relationship between satellite images and depth. Eventually, a new benthic habitat sediments classification method called RF-SAPSO-LightGBM is introduced with a powerful generalization ability. The unique functions of automatic default feature completion and optimal parameter search improve the discrimination ability of complex sediments. The results indicate that the new method outperforms five other approaches in sediment classification accuracy, and the combination of multi-source data provides more extensive coverage and higher accuracy with an overall of 87. 9%. In comparison, the accuracy values for multispectral image and terrain data alone are 74.5% and 54.7% respectively. • Optical-acoustic sensors were more effective when used together rather than separately for mapping coral reef habitat. • The SAPSO algorithm for LightGBM parameter optimization improved the sediment classification accuracy by 7.4%. • Feature completion effectively improved the accuracy of coral reef habitat mapping. • The RMSE of the derived depth by the LightGMB regression model reached 0.89 m. [ABSTRACT FROM AUTHOR]

Ocean surface waves and currents can interact to produce strong seabed shear stress and sediments mobilization affecting infrastructure safety, benthic habitat distribution and decision for sustainable development of the oceans. Modelled waves, tidal current and circulation current data for a 3-year period were used in a combined-flow sediment transport model to simulate the seabed shear stresses and the mobilization of observed sediments on the Canadian Atlantic Shelf. The modelling results are presented and analyzed to update the framework of seabed disturbance and sediment mobility on the Atlantic Shelf. The Atlantic Shelf is affected by strong waves and tidal currents. Maximum mean significant wave height over the modelled period can reach 3.5 m and mean tidal currents reach up to 1.2 m s−1. Our modeling results indicate that the mean wave and tidal current shear velocities both reach the maximum values of ∼4 cm s−1. Observed sediments on the Atlantic Shelf can be mobilized by tidal currents at least once during the modelled 3-year period over 30 % of the shelf area while storms can mobilize sediments over 35 % of the shelf area suggesting a slightly stronger sediment mobilization by storms. Furthermore, waves and currents interact to cause enhanced combined wave-current shear velocities >5 cm s−1 that is capable of mobilizing sediments over 63 % of the shelf area, double that due to tides or waves alone. The spatial variation of the relative importance of waves, tidal current and circulation current in mobilizing sediments was used to classify the Atlantic Shelf into six disturbance types. Wave-dominant and tide-dominant disturbance types are equally important and both occupy ∼25 % of the shelf area. Mixed disturbance is insignificant and accounts for only 3 % of the shelf area. Universal Seabed Disturbance Index (SDI) and Sediment Mobility Index (SMI) were applied to better quantify the exposure of the seabed to oceanographic processes and sediment mobilization, incorporating both the magnitude and frequency of these processes. The values of SDI and SMI on the Canadian Atlantic Shelf are found to be comparable to those on the Australian shelves and the Irish Sea shelf. These indices, together with the seabed disturbance type classification scheme, potentially can be used as standard parameters to quantify seabed disturbance and sediment mobility on other shelves of the world. • Wave, current and combined-flow sediment transport models applied on Canadian Atlantic Shelf. • Characterized magnitude and frequency of shear stresses and sediment mobilization due to various processes. • Mean combined wave-current shear velocity reaches >5 cm·s−1 and mobilizes sediments over 63 % of the shelf area. • Six disturbance types were classified and their spatial distribution mapped. • Shear stress and sediment mobility maps can be used in siting offshore infrastructure and informing marine spatial planning. [ABSTRACT FROM AUTHOR]

Bottom friction dissipation is a key factor for wave attenuation in nearshore environments presenting complex geomorphological structures, such as rocky or coral shores. The present paper reports on a series of laboratory experiments performed in a wave flume with controlled wave conditions and seabed structures. Using the frequency-integrated short-wave analysis and classical models for bottom friction and breaking dissipation, the wave friction factor and the hydraulic roughness parameter were estimated from the experimental data. The former varies from 0.17 to 98 while the latter varies from 0 to 0.291 m. The observations reveal the combined influence of several topographical metrics, including the standard deviation, the skewness, the directionality and the effective slope of the seabed elevation. A metric-based multi-varied model for the hydraulic roughness parameter is proposed and confronted with other field data recovered on coral and rocky shores. • A novel laboratory database for wave frictional dissipation over rough bottom. • Classical bottom friction models globally remain robust even for very large roughness. • Hydraulic roughness parameter is not solely controlled by standard deviation. • Metric-based hydraulic roughness model improves bottom friction modelling. [ABSTRACT FROM AUTHOR]

Existing force models for a vertical surface-piercing cylinder require water depth integration from the seabed to the free surface to determine the total inline force. However, acquiring the full wave kinematics profiles beneath the water surface presents a significant computational task. We revisit the finite water depth version of the well-known FNV theory (Kristiansen and Faltinsen, 2017) and propose a transformed version that expresses the total force solely in terms of the fully nonlinear wave properties at the free surface. This novel Transformed-FNV (T-FNV) formulation treats the Morison inertia term exactly and approximates the remaining two convective-derivative type terms with an assumption of slowly varying kinetic energy type terms. We evaluate the accuracy of this transformation against the original formulation, using wave kinematics obtained from fully nonlinear numerical simulations. Two T-FNV formulations are proposed with different input properties required. The first formulation uses the fully nonlinear wave kinematic properties at the free surface, whereas a fully approximated T-FNV formulation requires only the nonlinear free-surface elevation time history measured or calculated at the position of the column but in its absence. Both T-FNV formulations demonstrate good accuracy for wave forces for both deep and shallow-water cases against the original FNV model. The new T-FNV formulations also show the increased role of higher harmonics in the predicted force time histories when compared to those in the free-surface displacement, and the importance of using accurate higher order harmonic wave profiles in nonlinear force calculations. • We propose a transformation of the FNV theory to calculate wave loads on a cylinder. • This T-FNV expresses force with only nonlinear wave kinematics at the free surface. • We further propose an approximated T-FNV that uses only nonlinear surface elevation. • T-FNV shows an increased role of higher harmonics in force than surface elevation. [ABSTRACT FROM AUTHOR]

Naturally occurring microbially induced smectite-to-illite (Sm-I) reaction is of great interest to understand the control for the conventional Sm-I transformation, the source of bioavailable iron (Fe) in sediments, and the evolution of the microbial community in the deep biosphere. Direct comparisons of physico-chemical properties of illite-like phases including collapsed high-charge smectite and transient phase, and mature illite were performed for the organic matter (OM)-rich claystone in contrast with those of coeval OM-poor claystone (2163 m–2217 m below sea floor) buried at Nankai Trough (Integrated Ocean Discovery Program Site C0002). These clay layers are interbedded with 70°–90° dipping angle, such that they have nearly identical burial conditions of temperature, time, and fluid geochemistry except for OM content, one of the significant controls that can fuel heterotrophic microbial Fe (III) reduction. Unlike the abiotic Sm-I reaction, the local variations in the crystal structure, elemental composition, and oxidation states of Fe for the illite and illite-like phases in the OM-rich claystone suggest that illitization is promoted through the reduction of structural Fe (III) in smectite by microbial activity, however the effects of OM cannot be ruled out. • Illitization rate varies in OM-rich contrast with the coeval OM-poor claystone. • Illite-like phases showed various physico-chemical properties in OM-rich claystone. • Microbial Fe-reduction promotes the illitization in OM-rich claystone. [ABSTRACT FROM AUTHOR]