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Heat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust. [ABSTRACT FROM AUTHOR]

To fulfill the operational demands of deep-sea tracked mining vehicles traversing soft seabed substrates, an evaluation of the characteristics of these substrates was conducted, drawing a comparison with the land swamp black soil found in the buffalo's habitat. Employing the principles of biomimicry, two distinct types of bionic grouser were devised, replicating the configuration of the buffalo's hooves in both the horizontal and vertical planes. Utilizing self-constructed testing platforms, exhaustive examinations of the reinforcement efficacy of these bionic track grousers were undertaken, spanning from single-grouser to multi-grouser configurations and encompassing the entire track assembly. The findings unequivocally demonstrate a pronounced and consistent enhancement in traction force for both types of bionic grousers. Notably, the W-shaped bionic grouser, mimicking the horizontal contour of the buffalo's hoof, exhibits the most substantial increase in traction force. The maximum enhancement in traction force for individual bionic grouser exceeds 30%, while the overall track achieves an increase of over 19%. This research provides a valuable reference and establishes a foundational framework for the design of equipment tailored for the locomotion of deep-sea tracked mining vehicles across soft substrates. [ABSTRACT FROM AUTHOR]

With the recent, constantly growing interest in the critical geography of the oceans and critical toponymy, there is still plenty of space for theoretical, methodological and practical interconnections between these emerging subfields. Despite some sporadic examples of critical analysis of the names of the islands and seas, the ocean floor and the open ocean remain unexplored spaces in critical toponymic investigations. This paper aims to fill this gap by introducing the concept of the toponymic frontier, focusing on the spatial‐political dimension of the names of the natural submarine features (bathyonyms). Drawing on critical toponymy and critical geography of the oceans' theoretical literature and using the empirical database of more than 5000 bathyonyms and the secondary resources represented by the international media, official reports and governmental websites, this paper develops a base for a conceptual framework for analysing the marine place names as (geo)politically and political‐economically motivated symbolic elements of the oceanic voluminous realm. Finally, the paper paves the way for future debates related to the politics of place naming in the contested spaces of the hydrosphere and the generation of reinvigorated productive insights in critical toponymic studies. [ABSTRACT FROM AUTHOR]

Continental shelves experience many human pressures with demersal fisheries central to disturbing the ocean floor. However, ecological processes such as predation rates of benthos and their relationship with bottom fishing are often unknown for large marine ecosystems. We examined the amount of benthos consumed by 14 benthivorous fishes, the overlap between benthos predation and bottom fishing (dredge and trawl gear), and temporal trends in benthivorous fish abundance and the number of fishing trips on the northeast US continental shelf. Mean annual predation (biomass of prey removed) and 95% confidence intervals ranged from .0002 (.0001–.0003) to 3967 (1761–7112) t per 10‐min area squared grid cell and prey taxa for these benthivorous fishes. Predation and bottom fishing had overlapping footprints of activity, which were slightly stronger for dredge gear. Trophic success (ratio of prey biomass eaten to the biomass of the benthivore community per grid cell) revealed more Bivalvia, Gammaridea, and Polychaeta eaten in areas targeted by trawling with more fish biomass. In contrast, dredging did not target fish biomass, but these areas had increased (Echinoidea, Gammaridea, and other benthos) or decreased (Ophiuroidea) trophic success relative to dredging footprint, suggesting habitat preferences for benthic prey and demersal fisheries have converged rather than diverged. Despite declines in bottom fishing, recent increases in benthivorous fish abundance and growing interest in ocean floor use suggest that fisheries managers should ensure benthivores have sufficient prey resources relative to their community size and human pressures to promote long‐term sustainability of demersal fisheries and healthy ecosystems. [ABSTRACT FROM AUTHOR]

The discrepancy in the observed global mean sea level budget increased significantly since 2016, but the budget discrepancy over basin‐scales is unclear. In this contribution, we investigate the sea level budget discrepancies in major basins with observations from satellite altimetry, satellite gravimetry, and Argo floats. During 2016–2020, we find substantial discrepancy of 5.72 ± 0.98 mm/yr over the North Atlantic Ocean, and the basin scale discrepancies are smaller elsewhere. Our analysis suggests that three factors, including the wet tropospheric correction (WTC) effect, deep ocean warming signal, and the contemporary ocean bottom deformation (OBD), together reduce the discrepancy by only 1 mm/yr for the North Atlantic Ocean. We decompose sea level observations into the spherical harmonic domain and observe increased discrepancy in low‐degree variations of C10 and C21 since 2016. These two coefficients result in a contrasting signal between the North and South Atlantic Ocean and contribute to the large discrepancy over the North Atlantic Ocean. We further demonstrate that the C10 and C21 discrepancies are independent of the three factors. However, we find regional salinity biases in the Argo data that reduce the discrepancy for the North Atlantic Ocean. Our findings add to the debate about recent sea level budget and imply that further analysis of the Argo North Atlantic data set may be useful. Plain Language Summary: Global mean sea level rise observed by satellite altimetry was well explained by measurements from satellite gravity and Argo floats for 2003–2015. However, since 2016, a substantial portion of sea level rise is not adequately explained. This unexplained portion is defined as the sea level discrepancy. To address the discrepancy for 2016–2020, we quantify the sea level discrepancy over each of the ocean basins. We find that sea level rise is well explained over the South Atlantic Ocean, South Pacific Ocean and Indian Ocean, but a 5.7 mm/yr trend is not explained over the North Atlantic Ocean during 2016–2020. Further analysis reveals two underlying systemic discrepancies in sea level observations that produce a contrasting pattern over the North and South Atlantic Ocean and contribute to the sea level discrepancy over the North Atlantic Ocean. Biases the wet tropospheric correction (WTC), deep ocean warming, and contemporary ocean bottom deformation (OBD) do not appear to be responsible for the north‐south asymmetry. Our analysis points to a potential regional salinity bias in the North Atlantic Argo data set. Key Points: Basin‐scale discrepancies in the sea level budget are investigated using sea level observationsSea level discrepancy is substantially larger over the North Atlantic Ocean since 2016We identify a large halosteric contraction in the Argo North Atlantic data since 2016 which may be responsible for the sea level discrepancy [ABSTRACT FROM AUTHOR]

Expendable Bathythermographs (XBTs) are oceanographic instruments that fall through the ocean's water column and measure ocean temperature with depth. In many instances, however, XBTs continue to record temperature after they impact the seabed. Here we show evidence that XBTs produce unique temperature responses when they impact the seabed that depend directly on seabed physical properties. Specifically, standard‐use XBTs (e.g., T‐4s and T‐5s), when deployed above a mud‐rich seabed, require significant time (tens of minutes) to equilibrate to steady‐state seafloor temperatures after seabed impact. In contrast, XBTs deployed above sand‐rich sediments equilibrate to seabed temperatures rapidly (<5 min) after seafloor impact. One explanation for this difference in temperature response is that XBTs deployed above mud‐rich sediment penetrate into low permeability marine muds that jacket the XBT, where diffusive heat flow dominates. Both observations and numerical modeling results support the hypothesis that XBTs impacting muddy seafloors exhibit slow, diffusion‐dominated heat flow, while XBTs impacting harder, sand‐rich seabed sites exhibit rapid seafloor temperature equilibration, consistent with advection‐driven heat flow and little if any XBT seabed penetration. Given that >644k XBT measurements exist publicly (via the National Oceanographic and Atmospheric Administration website), and >74,000 XBTs record temperatures post seabed impact, we suggest that XBT data represents a large, low‐cost, and currently untapped data set for characterizing seabed physical properties globally. Plain Language Summary: Expendable Bathythermographs (XBTs) are hand‐deployable torpedo‐shaped single‐use thermistors that measure ocean temperature with depth by being dropped from a ship and transmitting temperature values along a thin copper wire that unspools from the XBT as it falls. When the XBT impacts the seabed, it often continues recording temperature, however, researchers focused on ocean temperature‐depth measurements typically ignore these data. Here, we take a first‐look at XBT temperature response after seabed impact for two different seabed settings: (a) a soft muddy seabed where XBTs may penetrate the seafloor, and (b) a hard, sandy seabed where the XBT likely fails to penetrate. We find that XBTs that impact a soft, muddy seabed show significantly slower rates of change in temperature after impact compared to XBTs that impact hard sandy sediment, consistent with numerical modeling temperature predictions for XBTs impacting and penetrating mud but failing to penetrate sand. XBT temperature response after seabed impact may therefore provide a crude but efficient tool for rapidly assessing seabed physical properties (such as seabed hardness). With more than 74,000 publicly available XBT seabed temperature measurements available in every ocean, XBTs may provide a useful tool for roughly characterizing seabed properties globally. Key Points: XBT temperature response after seabed impact varies depending on seabed physical propertiesXBT rates of temperature change after seabed impact are nearly an order of magnitude lower in mud versus sand due to XBT burial in mudXBTs may provide a crude but useful, rapid tool for assessing seabed physical properties globally [ABSTRACT FROM AUTHOR]

Side-scan sonar is a principal technique for subsea target detection, where the quantity of sonar images of seabed targets significantly influences the accuracy of intelligent target recognition. To expand the number of representative side-scan sonar target image samples, a novel augmentation method employing self-training with a Disrupted Student model is designed (DS-SIAUG). The process begins by inputting a dataset of side-scan sonar target images, followed by augmenting the samples through an adversarial network consisting of the DDPM (Denoising Diffusion Probabilistic Model) and the YOLO (You Only Look Once) detection model. Subsequently, the Disrupted Student model is used to filter out representative target images. These selected images are then reused as a new dataset to repeat the adversarial filtering process. Experimental results indicate that using the Disrupted Student model for selection achieves a target recognition accuracy comparable to manual selection, improving the accuracy of intelligent target recognition by approximately 5% over direct adversarial network augmentation. [ABSTRACT FROM AUTHOR]

Linear surface gravity wave scattering by a partial porous breakwater is studied in a two-layer ocean having an interface with bottom undulations. The partial breakwaters, namely surface-piercing breakwater (SPB) and bottom-standing breakwater (BSB), are considered. The continuity of fluid pressure and mass flux is applied at interface boundaries, while mass conserving conditions are employed to account for slope discontinuity in seabed geometry. Porous breakwaters' reflective and dissipative characteristics are studied under wave-wave interaction. The study reveals that when a mound bottom is present, more incident waves in interface mode are transmitted through BSB, while more waves in surface mode are dissipated. More incident waves in surface mode are transmitted through SPB, while more waves in interface mode are dissipated. In contrast, more transmission occurs in surface mode through both BSB and SPB for a slope-shelf bottom. However, the breakwater dissipates a substantial amount of incident-wave energy in interface mode. Further, a considerable reduction in wave transmission occurs due to higher reflection by the interface-piercing porous breakwaters, and the breakwaters experience high wave loads. Relatively, porous breakwater dissipates less wave energy in shallow depth. The study reveals that the dead water effect is weakened by the porous breakwater. [ABSTRACT FROM AUTHOR]

The present study outlines the hydrodynamic performance of stratified pile-rock breakwaters (SPRBs) in series using the analytical calculation under the framework of linearized potential flow theory. The rubble mounds are separated into two porous layers (surface and bottom layers) and tightly packed within the space available between the seaside and leeside vertical piles. The SPRB is installed on the elevated bed, and it is considered as a bottom rigid layer. The newly proposed breakwater is titled as stratified pile-rock breakwater and vertical piles are suggested to minimize the unwanted displacements of rubble mounds from frequent failures due to the incident wave stroke. The analytical model is developed based on the method of matched eigenfunction expansions (MMEEs) along with suitable boundary conditions to assess the hydrodynamic performance of the SPRB. The study results are compared with the literature based on experimental and analytical methods for specific conditions. The wave reflection, transmission, and energy damping by a series of SPRBs are reported for changes in incident wave properties and breakwater physical properties. The effect of layer porosity, angle of contact, free spacing, and number of breakwaters on the hydrodynamic coefficients is reported. The study suggested that a pair of SPRBs having 80% and 40% porosities for surface and bottom layers, with clear spacing, varied within 1 ≤ w/h1 ≤ 2, and the angle of contact varied within 30 deg ≤ θ ≤ 45 deg to achieve a 90% wave-damping when the relative wavenumber is k10h1 = 1. [ABSTRACT FROM AUTHOR]

Reconstructing the spatial patterns in thermocline depth is critical for understanding ocean‐atmosphere interactions. Previous foraminiferal proxies of thermocline depth focus on gradients between planktonic foraminifera living in the surface and subsurface ocean. However, both thermocline depth changes and stratification changes will impact this measure. In this study, we outline a method for reconstructing the tropical upper ocean vertical water column profile, enabling the separate assessment of thermocline depth and stratification changes. This method uses oxygen isotope data from surface and sub‐surface calcifying planktonic foraminifera (Globigerinoides ruber albus, Globorotalia tumida, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata) as well as data from benthic foraminifera from a core site below the thermocline. Using newly generated and compiled oxygen isotope data from Holocene‐aged marine sediments, we construct vertical profiles at 20 core sites in the Tropical Pacific Ocean. Quantitative estimates of thermocline depth along with error ranges from Monte Carlo simulations are extracted from the reconstructed profiles. There is a strong correlation between reconstructed Holocene and climatological thermocline depth, but the East‐West contrast in the depth of the thermocline is underestimated by 30%. Incorporating benthic information in thermocline estimates results in a dramatic improvement in the reconstruction of spatial gradients in thermocline depth compared to a simpler proxy, the difference in oxygen isotope ratio between a deeper calcifying planktonic species and the surface species, G. ruber. Plain Language Summary: The thermocline is a layer of the ocean where temperature changes rapidly, and the depth of this layer is related to many climatic phenomena. Understanding where and when this layer was deeper and shallower in the past is important to our overall understanding of the climate system. We outline a novel method to reconstruct the thermocline with microscopic shells collected from the sea floor. Our method can reconstruct the changes we see across the Pacific today and also recreate the changes found between the last ice age and today. Key Points: We show a novel method for reconstructing the upper water column using oxygen isotope measurements on multiple species of foraminiferaThis method can be used to quantitatively reconstruct spatial and temporal changes in thermocline depthIf a simple differencing method is preferred, thermocline depth can be most accurately reconstructed using subsurface species only [ABSTRACT FROM AUTHOR]

AbstractTo ensure the safety of subsea tunnel construction, it is crucial to prevent extreme deformation of the surrounding rock. An assessment and prediction study on the surrounding rock deformation induced by the excavation of the subsea tunnel using the three-bench method was conducted, based on Haicang Subsea Tunnel in Xiamen, China. A series of numerical simulations and on-site monitoring were conducted to reveal the evolution of the displacement field of the surrounding rock. The influences of various factors on the settlement trough of the surrounding rock above the subsea tunnel were also investigated, including seawater, bench length, and bench spacing. The rapid ring closure of the primary support by adopting short benches is imperative to control the arch settlement and settlement trough width. The settlement resulting from the excavation of the upper and middle benches contributed to 90% of the total deformation, as revealed by both numerical simulation and in-situ monitoring. Subsequently, an empirical formula was proposed to predict the settlement trough curves of surrounding rock at different depths above the seabed tunnel. [ABSTRACT FROM AUTHOR]

Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we show that Holocene fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the contourite drifts are due to high rates of sedimentation. Over the past 50 million years, sedimentation rates at the studied contourite drift sites have overall increased, coincident with decreasing atmospheric CO2 and a cooling global climate. Our work suggests that a ramp‐up of the bottom‐current carbon pump has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the overall global cooling after the Eocene Thermal Maximum. Plain Language Summary: Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we examine data from modern contourite drifts (large‐scale, alongslope‐trending bottom‐current deposits) across the globe and show modern fluxes of organic carbon into the drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1 to 2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the drifts are due to high rates of sedimentation in these deepwater environments, which are driven primarily by vigorous bottom currents—in other words, by a bottom‐current pump that is highly efficient at burying organic carbon. Our work suggests that a ramp‐up of the bottom‐current carbon pump, attributable to progressive intensification of global ocean circulation over the past 50 million years, has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the global cooling after the Eocene Thermal Maximum. Sedimentary records of past organic carbon fluxes in contourite drifts over geologic time could well prove useful in informing predictions of future climate. Key Points: Modern fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1The fluxes into the drifts are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zonesOver the past 50 million years, the bottom‐current pump has accelerated removal of carbon from the oceanic water [ABSTRACT FROM AUTHOR]

ABSTRACT Underwater archaeology relies on expensive and time‐consuming invasive methods for identifying and excavating objects buried in the seabed or identifying layers in shallow and intertidal environments. Especially shallow and intertidal environments are challenging due to locally high levels of sedimentation that offer good conditions for preserving organic material, that is, archaeological objects, in stabile and low‐oxygen environments. We present a system capable of dense (25 cm × 25 cm) survey coverage that enables nondestructive decimetre‐scale visualization of buried objects and sedimentary layers lying in the subsurface. The system comprises an autonomous surface vehicle (ASV) equipped with a single‐channel 2D Chirp sonar. A description of the vehicle design is presented, and results from five field tests demonstrate the ability of the system to collect high‐resolution acoustic data in a variety of shallow water environments. The system shows an example of the linearized zero offset reflectivity inversion dataset, visualizing a known buried shipwreck from the medieval period in Avaldsnes, Norway. The ASV system holds global implications as it can serve as a noninvasive first‐stage survey in sensitive heritage or archaeological areas. Areas where traditional methods are challenging, or invasive methods are dissuaded. [ABSTRACT FROM AUTHOR]

The article discusses the development and deployment of an indigenously designed low-cost underwater camera system for seabed videography in deep-sea environments, particularly focusing on cold seep ecosystems. It highlights the camera's technical specifications, cost-effectiveness, and its role in documenting marine biodiversity and ecological processes at significant depths.

Sea‐air methane flux was measured directly by the eddy‐covariance method across approximately 60,000 km of Arctic and Antarctic cruises during a number of summers. The Arctic Ocean (north of 60°N, between 20°W and 50°E) and Southern Ocean (south of 50°S, between 70°W and 30°E) are found to be on‐shelf sources of atmospheric methane with mean sea‐air fluxes of 9.17 ± 2.91 (SEM (standard error of the mean)) μmol m−2 d−1 and 8.98 ± 0.91 μmol m−2 d−1, respectively. Off‐shelf, this region of the Arctic Ocean is found to be a source of methane (mean flux of 2.39 ± 0.68 μmol m−2 d−1), while this region of the Southern Ocean is found to be a methane sink (mean flux of −0.77 ± 0.37 μmol m−2 d−1). The highest fluxes observed are found around west Svalbard, South Georgia, and South Shetland Islands and Bransfield Strait; areas with evidence of the presence of methane flares emanating from the seabed. Hence, this study may provide evidence of direct emission of seabed methane to the atmosphere in both the Arctic and Antarctic. Comparing with previous studies, the results of this study may indicate an increase in sea‐air flux of methane in areas with seafloor seepage over timescales of several decades. As climate change exacerbates rising water temperatures, continued monitoring of methane release from polar oceans into the future is crucial. Plain Language Summary: The amount of methane released from oceans into the atmosphere is uncertain. Most oceanic methane is stored in the seabed and can escape into the water at seafloor seeps, but the extent to which it escapes into the atmosphere remains unclear. This study uses a relatively new method, eddy‐covariance, to measure sea‐air methane fluxes during Arctic and Antarctic cruises. This is the first time this technique has been applied to sea‐air methane fluxes in both polar oceans. Our findings show that on‐shelf regions of the Arctic and Southern Oceans release methane into the atmosphere, with average fluxes of 9.17 ± 2.91 μmol m−2 d−1 and 8.98 ± 0.91 μmol m−2 d−1, respectively. We also identified areas with significant methane release in regions where methane has been found seeping into the water from the seabed. This study provides potential evidence that methane from seabed seeps may be directly emitted into the atmosphere in both the Arctic and Antarctic. Comparing with earlier studies, there is indication that the amount of methane released has increased over the last decades. As climate change drives increasing water temperatures, there is a potential for increased methane release from the seabed into the atmosphere, therefore on‐going observations of methane release from polar oceans are necessary. Key Points: Coastal regions of the Arctic Ocean and Southern Ocean are found to be sources of atmospheric methaneThe ocean releases elevated quantities of methane where seabed methane seeps have been observed in both the Arctic and Southern OceansThis study suggests a possible rise in methane release from oceanic areas with seabed seeps over last decades compared with a prior study [ABSTRACT FROM AUTHOR]

ABSTRACT Thick‐bedded halite sequences in the geological record are characterized by lateral variations, reflecting spatiotemporal variations in environmental forcing. Although temporal variations have been examined over seasonal scales or longer durations, there is a paucity of information regarding the dynamics of halite deposition at shorter durations of days and hours. Additionally, the influence of water discharges and surface salinity gradients remains poorly understood. Here, for the first time, in situ, hourly to weekly halite accumulation rates were measured on the Dead Sea floor (ca 20 m water depth), the only modern deep and hypersaline water body. Novel underwater photography methods were developed to directly observe halite precipitation at the lake floor, coeval with monitoring of the environmental drives, i.e. evaporation, meteorological and limnological conditions. Two fundamental environments were explored: a diluted plume environment arising from spring discharge; and a mixed hypersaline environment. The focus was on deposition during winter when the halite accumulation rate is highest, and the relationship between evaporation and halite accumulation is most straightforward since the water column is vertically uniform. Significant spatial variations in halite accumulation were found between the two environments, along with hourly variations in each environment. In the mixed hypersaline environment, over intra‐diurnal timescales, evaporation plays a more significant role in halite precipitation, whereas temperature has a greater impact on seasonal changes. In the diluted plume environment, the stability of the buoyant plume controls the rate of halite deposition; during windstorms, the plume is stirred, with higher surface water salinity and higher rate of halite accumulation. However, under calm winds, the plume is stable, with diluted surface water, and the rate of halite accumulation is a few times lower. Following these new findings, the implications for the interpretation of halite deposits are discussed. [ABSTRACT FROM AUTHOR]

Introduction: Autonomous Underwater Vehicles (AUVs) are capable of independently performing underwater navigation tasks, with side-scan sonar being a primary tool for underwater detection. The integration of these two technologies enables autonomous monitoring of the marine environment. Methods: To address the limitations of existing seabed detection methods, such as insufficient robustness and high complexity, this study proposes a comprehensive seabed detection method based on a sliding window technique. Additionally, this study introduces a sonar image stitching method that accounts for variations in image intensity and addresses challenges arising from multi-frame overlaps and gaps. Furthermore, an autonomous target perception framework based on shadow region segmentation is proposed, which not only identifies targets in side-scan sonar images but also provides target height measurements. Results: Comprehensive seabed detection method improves accuracy by 31.2% compared to the peak detection method. In experiments, the height measurement error for this method was found to be 9%. Discussion: To validate the effectiveness of the proposed seabed detection method, sonar image stitching method, and target perception framework, comprehensive experiments were conducted in the Qingjiang area of Hubei Province. The results obtained from the lake environment demonstrated the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Underwater terrain-aided navigation (TAN) can obtain high-precision positioning independently and autonomously under the conditions of a communication rejection space, which is an important breakthrough for the autonomous and refined operation of deep-sea autonomous underwater vehicles near the seabed. Although TAN originated in the aviation field, the particularity of the underwater physical environment has led to the formation of a different theoretical and technical system. In this article, the application background, operating principles, and most important technical aspects of underwater TAN are introduced. Then, the relevant algorithms involved in the two main modules (the terrain-aided positioning module and the iterative filtering estimation module) of the underwater TAN are reviewed. Finally, other cutting-edge issues in the field of underwater TAN are summarized. The purpose of this article is to provide researchers with a comprehensive understanding of the current research status and possible future developments in the TAN field. [ABSTRACT FROM AUTHOR]

This study reports a moored array dataset (MASCS 1.0) consisting of five buoys and four moorings in the northern South China Sea during 2014–2015. The dataset includes measurements of sea surface meteorological data using two sets of instruments: sea surface waves recorded using a wave recorder, temperature and salinity from the surface to a depth of 400 m, and at 10 m and 50 m above the ocean bottom using conductivity, temperature, and depth (CTD) recorders. It also includes currents from the surface to a depth of 850 m measured using acoustic Doppler current profilers (ADCPs) and at 10 m, 50 m, and 100 m above the surface measured using current meters. Additional measurements were taken for sea surface radiation, air visibility, chlorophyll, turbidity and chromophoric dissolved organic matter at Buoy 3, which was located at the center of the moored array. The dataset captures the effects of tropical cyclones Rammasun, Kalmaegi, Fung-wong, and Hagupit on the moored array, as well as the transition from summer to winter monsoon in the northern South China Sea. The data reveal oceanic processes in the upper and bottom ocean and are valuable for further studies on air-sea interactions and ocean dynamics. All the data described here are made publicly available from https://zenodo.org/records/12635331 (Zhang et al. 2024). [ABSTRACT FROM AUTHOR]

One of the most salient features of marine bryozoans is their well-calcified skeleton, and many species in this phylum are important reef-builders. To date, the molecular machinery responsible for skeletal formation in these key animals remains unknown. In this study we performed de novo transcriptome assembly from RNA from Cellaria immersa colonies collected in New Zealand, the first from the family Cellariidae. The assembly resulted in a set of 125,750 transcripts and was estimated to be 97.2% complete when compared to BUSCO core gene sets. A function was predicted for 61,442 (48.8%) of the translated proteins, using similarity searches against a range of databases using BLAST and InterProScan. Cellaria species form erect, heavily calcified arborescent colonies, which when abundant can create micro-forests or meadows on the ocean floor. RNA was extracted separately from younger distal and older proximal parts of the colonies, aiming to identify the key genes involved in biomineralization as the young zooids (at the distal growth margin) of the colony are more likely to be actively growing and calcifying compared to the old zooids of the proximal parts of the colony. Differential expression analysis was carried out to identify differential expression between the distal and proximal parts of the colonies. This showed that 506 (2.2%) of the transcripts were expressed more highly in the young zooids and 4,676 (20.4%) were expressed more highly in the old zooids. Over 50 protein families were identified as candidates involved in biomineralization in C. immersa based on the functional annotation, their expression pattern and literature. Transcripts encoding 24 such protein families were more highly expressed in the young zooids. This is the first such study on a heavily calcified species from the phylum Bryozoa, increasing the amount of 'omics' data available for C. immersa and the phylum. These data provide a resource for current and future studies of heavily calcified bryozoans, shedding a light on the biomineralization process in this phylum. [ABSTRACT FROM AUTHOR]

Finding prehistoric sites, on the sea floor off the United States, has proven to be a difficult task. Over four decades of innovative attempts have produced few discoveries. This discussion outlines the difficulties in finding submerged prehistory on the sea floor, examines current methodology(ies), and presents a new methodology that demonstrates promise based on research conducted over the past decade. The purpose of this discussion is to outline the problems facing archaeologists searching the sea floor for archaeological sites. It is less of a critique of past efforts and methodologies used in those attempts. Without those efforts, a reason for developing a different methodological approach would be unnecessary. Any "one size fits all" methodology is limiting, and the scant number of marine archaeological sites located off the shores of the United States can attest to the need for practitioners to continue refining their methods. This is especially the case on the continental shelf of the eastern United States, where sediment cover is often meters, or several meters, thick. This opportunistic methodology developed on the continental shelf of the Georgia Bight, western Atlantic Ocean, has located intact paleo-landforms with in situ, palaeoecological remains thereby offering promise for future archaeological discoveries. [ABSTRACT FROM AUTHOR]

We revisit the nature of the ocean bottom pressure (pb) seasonal cycle by leveraging the mounting GRACE‐based pb record and its assimilation in the ocean state estimates produced by the project for Estimating the Circulation and Climate of the Ocean (ECCO). We focus on the mean seasonal cycle from both data and ECCO estimates, examining their similarities and differences and exploring the underlying causes. Despite substantial year‐to‐year variability, the 21‐year period studied (2002–2022) provides a relatively robust estimate of the mean seasonal cycle. Results indicate that the pb annual harmonic tends to dominate but the semi‐annual harmonic can also be important (e.g., subpolar North Pacific, Bellingshausen Basin). Amplitudes and short‐scale phase variability are enhanced near coasts and continental shelves, emphasizing the importance of bottom topography in shaping the seasonal cycle in pb. Comparisons of GRACE and ECCO estimates indicate good qualitative agreement, but considerable quantitative differences remain in many areas. The GRACE amplitudes tend to be higher than those of ECCO typically by 10%–50%, and by more than 50% in extensive regions, particularly around continental boundaries. Phase differences of more than 1 (0.5) months for the annual (semiannual) harmonics are also apparent. Larger differences near coastal regions can be related to enhanced GRACE data uncertainties and also to the absence of gravitational attraction and loading effects in ECCO. Improvements in both data and model‐based estimates are still needed to narrow present uncertainties in pb estimates. Plain Language Summary: We revisit the nature of the ocean bottom pressure (pb) seasonal cycle by leveraging the mounting data from space gravity missions and their use in constraining model‐based estimates produced by the project for Estimating the Circulation and Climate of the Ocean (ECCO). We focus on the mean seasonal cycle from both data and ECCO estimates, examining their similarities and differences and exploring the underlying causes. Despite substantial year‐to‐year variability, the 21‐year period studied (2002–2022) provides a relatively robust estimate of the mean seasonal cycle. The pb annual cycle tends to dominate but the semi‐annual cycle can also be important in some regions. Amplitudes are enhanced near shallow coastal regions and can also vary more strongly across the coastal zone, pointing to the importance of changes in ocean bottom topography in shaping the seasonal cycle in pb. Comparisons of data and ECCO estimates indicate good qualitative agreement, but considerable quantitative differences in the magnitude and timing of maxima remain. Largest differences, which tend to occur near coastal regions, can be related to enhanced data uncertainties and also to the absence in ECCO of effects from gravitational attraction of land ice and water storage and related deformation of the ocean bottom. Key Points: Substantial differences remain in satellite and model‐based estimates of the mean seasonal cycle in ocean bottom pressure (pb)Differences between two satellite gravimetry products suggest largest uncertainties around many continental boundariesAbsence of gravitational attraction and loading effects and intrinsic ocean variability can lead to errors in model‐based pb estimates [ABSTRACT FROM AUTHOR]

Evidence of ancient Maya exploitation of salt, other marine resources, settlement, and sea trade is hidden in flooded mangrove landscapes on the cays, mainland, and in shallow offshore locations on the south coast of Belize. This article includes a discussion of the coastal economy from the Middle Preclassic through the Postclassic periods (600 B.C.–A.D. 1500). Data from sites discovered and excavated since 1982 in the coastal area of the Port Honduras and Paynes Creek National Park support a model of coastal reliance on marine resources and tree crops. The need for a regular supply of coastal salt to inland cities may have expanded the market for other marine resources. Obsidian imported from volcanic highlands documents long-distance trade throughout prehistory in the area. The island of Wild Cane Cay expanded its role in long-distance coastal trade after the abandonment of inland cities in southern Belize at the end of the Classic period. Inundation of the region documented from the depths of radiocarbon-dated archaeological deposits below the water table and from a sediment core indicates sea-level rise of at least 1 m that submerged the coastal sites. The waterlogged deposits provided an ideal matrix for preservation of vertebrate material at Wild Cane Cay. The red mangrove (Rhizophora mangle) peat below the sea floor in a shallow lagoon preserved wooden buildings. [ABSTRACT FROM AUTHOR]

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

Seabed topography is important for marine geophysics and geodesy. However, conventional seabed topography inversion methods based on gravity data are constrained to a linear fitting, neglecting the impact of nonlinear terms. In this paper, we propose an innovative method for seabed topography inversion by establishing fresh mathematical relationships through machine learning techniques based on the Smith and Sandwell (SAS) method. Utilizing global sea depth data from the National Geophysical Data Center (NGDC) and gravity anomaly data from satellite altimetry, our study employs the SAS method for seabed topography inversion. The improved SAS method, enhanced by the Genetic Algorithm-Backpropagation (GA-BP) algorithm, is specifically applied to invert the Huangyan Seamount Chain topography in the South China Sea. The accuracy is evaluated by seabed topography models, including EOTPO1, GEBCO-2023, and S & S V19.1. The results show the GA-BP method significantly reduces residuals and improves the accuracy estimated by the SAS inversion method. The Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) are decreased by 14.98% and 5.07%, respectively. The proposed method has valuable reference significance for future marine exploration endeavours around the world. [ABSTRACT FROM AUTHOR]

The seismic response of seabed is fundamental for researching the seismic response of marine structures. The one-dimensional transient response of an unsaturated seabed was studied in this paper. An analytical solution for a special case with infinite permeability coefficients and a semianalytical solution for a general case with arbitrary permeability coefficients were developed. The advantage of this semianalytical solution is that it can compute the behavior of unsaturated soils with very low permeability coefficients. During the derivation, the boundary conditions were transformed into homogeneous boundary conditions first, and then the eigenvalues and eigenfunctions were obtained. To obtain solutions in the time domain, the eigenfunction expansion method and the precise time-step integration method were employed. Through numerical examples, the reflection and transmission characteristics of three types of compression waves at the fluid–solid interface were elucidated. The impact of permeability coefficients and water saturation on the seismic response of the seabed was investigated through parametric analysis. When the soil is nearing saturation, even a slight change in saturation can lead to a drastic alteration in the seismic response of the nearly saturated seabed. [ABSTRACT FROM AUTHOR]

As a country with the fourth largest population in the world prone to tsunami disasters, Indonesia needs a reliable, timely early warning system to mitigate the impact of disasters. Indonesia cable-based tsunameter (INA-CBT) is an undersea tsunami detection system comprising undersea pressure sensors and a shore station connected by underwater fiber optics designed to provide early warning to the threatened area. Since this system performs a critical role in disaster mitigation, the system must be resilient to link failure and deliver timely warning information. This system is still in its early implementation and still on a small scale. Network-wise, it uses a proprietary Layer 2 (L2) communication protocol. Extending such a network to a larger scale and assessing the system’s performance may introduce challenges due to high costs and offer less flexibility. This paper aims to address those challenges and presents a scalable simulation framework of the INA-CBT system by using L2 open protocols such as spanning tree protocol (STP) and rapid spanning tree protocol (RSTP). The framework is conducted in OMNET++ simulator. The experiment shows that the downtime duration using STP and RSTP is still below the allowed value. RSTP shows a faster failover time than STP, but RSTP downtime duration fluctuates compared to a steady one of STP. The experiments also demonstrated that the variation of downtime is affected by two aspects: the number of ocean bottom units (OBUs) in the network and the position of their blocked port. [ABSTRACT FROM AUTHOR]

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Recently, integrated geophysical‐geological surveys in the Nankai subduction zone in Japan have revealed that slow earthquakes repeatedly occur beneath the outer wedge of the forearc. During December 2020 to February 2021, clustered slow earthquakes propagated around the frontal thrust of the accretionary wedge. The frontal thrust ramps up from the basal décollement and slips over trench‐filling sediment along the landward edge of the Nankai trough floor. Here, the Paleo‐Zenisu ridge has been subducted beneath the inner‐outer slope border. In addition, ocean floor topography and geologic structure revealed by seismic reflection surveys completed before 2022 document that the basement of the Philippine Sea Plate beneath the frontal thrust has a seamount and a horst‐like basement high. The northern edge of the basement high is located at the ramp‐up position of the frontal thrust. The 2020–2021 clustered slow earthquakes started at the Paleo‐Zenisu ridge and propagated to the topographic highs beneath the deformation front. Considering that the relative plate convergence between the upper Amurian Plate of the Nankai forearc and the subducting Philippine Sea Plate is ∼6.0 cm/year, the basement high at the deformation front has uplifted the frontal crest of the wedge at an average rate of 2.7–5.7 mm/year for several tens to hundred thousand years. These rates are among some of the highest rock uplift rates measured in the world. The slow earthquakes in the off‐Kumano Nankai Trough in 2020–2021 are a snapshot of a "living" Nankai frontal thrust during the megathrust interseismic period. Plain Language Summary: Slow earthquakes family: slow slips, very low frequency earthquakes, and tremors are significant events for understanding the interseismic dynamics between large earthquakes along the convergent plate boundary in the ocean. Slow earthquakes took place during December 2020 to February 2021 in the Nankai Trough in Japan and propagated along the frontal edge of the upper plate. Seismic reflection surveys revealed that seamount‐like and horst‐like basement highs exist beneath the front, collide with the upper plate, and uplift trench filling sediments by a ramp thrust. Even the incipient plate boundary of the décollement is initiated within the sediments beneath the Nankai Trough. Such a deformation feature around the front is a source candidate for the slow earthquakes. The uplift rate of the frontal crest of the upper plate presents the same order of a few to several mm/year as that of the foreland of the Himalayan Mountain belt. The slow earthquakes in the off‐Kumano Nankai Trough in 2020–2021 appear the first snapshot of a "living" Nankai frontal thrust during inter‐large seismic period. Key Points: Between 2020 and 2021, slow earthquakes propagated around the frontal thrust of the accretionary wedge in the Nankai Trough off KumanoSeamount and horst‐like basement highs beneath the frontal thrust cause uplift and are associated with the slow earthquake eventsThe average uplift rate of the frontal crest is 2.7–5.7 mm/year, approximately the same order as that of the Himalayan foreland [ABSTRACT FROM AUTHOR]

The structural design of offshore wind turbines is dominated by environmental conditions such as wind and waves, in addition to deadweight loads and loads from operation. Probabilistic combination approaches exist for the ultimate limit state (ULS) to estimate the simultaneous occurrence of extreme meteorological and oceanographic (metocean) environmental conditions at the site of an offshore wind turbine. The site-specific direction of action of the load parameters is mostly neglected in these approaches; the design of offshore wind turbines in the ULS is usually carried out for the most structurally unfavourable directional superposition of load parameters—which is not based on physical principles and wastes potential material savings. The reasons for different load parameters in different directions of action are the influences of nearby land masses and the topographic shape of the sea floor, atmospheric air circulation, and marine current systems. In this paper, wind and sea state data from the coastDat-2 WAM database are statistically analysed for two sites in the North Sea, common environmental contours are estimated using the example of significant wave height and wind speed, and the site-specific influence of the direction of the load parameters on the environmental contours are investigated. It is shown that, depending on the site under consideration, the direction of action can significantly influence the metocean environmental conditions and that direction-resolved probabilistic combination approaches can contribute to a safe and economic structural design of offshore wind turbines. [ABSTRACT FROM AUTHOR]

This study examines the current status and future potential of the offshore wind sector. Offshore wind is pivotal in transitioning to a low-carbon society and meeting rising energy demands, despite being capital-intensive. The industry aims to develop larger-scale wind farms in deeper ocean locations, with projections indicating significant cost reductions. To explore deeper ocean areas, specialized foundations like floating platforms moored to the seabed are required. This study proposes helical piles anchored in the seabed as a method to secure mooring lines. Using Plaxis 3D, a parametric examination was conducted on helical piles with two plates: one fixed at the pile's toe and the other varying in position between 0.5 and 13 m from the seabed surface. Load inclination angles (0, 20, 40, and 60 degrees) were used to simulate mooring line loads. Results indicate the optimal Zh/Z ratios for maintaining load-bearing capacity and stability: 0.12 (10 mm movements), 0.22 (25 mm), and 0.26 (50 mm) for small shaft diameters; and 0.34 (10 mm), 0.38 (25 mm), and 0.46 (50 mm) for large shaft diameters. These findings highlight the importance of specific load inclination angles based on shaft diameter and allowable movement for effective performance. [ABSTRACT FROM AUTHOR]

The Madagascar Basin is the primary pathway for Antarctic Bottom Water to ventilate the entire western Indian Ocean as part of the Global Overturning Circulation. The only way for this water mass to reach this basin is by crossing the Southwest Indian Ridge through its deep fracture zones. However, due to the scarcity of observations, the Antarctic Bottom Water presence has only been well‐established in the Atlantis II fracture zone. In May 2023, the Deep Madagascar Basin Experiment deployed three Deep SOLO Argo floats in the exit of the fracture zones that were more likely to transport Antarctic Bottom Water: Atlantis II, Novara, and Melville. These floats have been collecting temperature and salinity profiles every 3–5 days with high vertical resolution in the deep ocean. In the present paper, we use the first 7 months of float data to characterize the Antarctic Bottom Water in the deep fracture zone area, revisiting a half‐century puzzle about the Melville contribution. We also collected shipboard‐based profiles to calibrate float salinity and show it is within the Deep Argo program target accuracy. We find Antarctic Bottom Water in both Melville and Novara fracture zones, not only in Atlantis II. This is the first time the Novara contribution has been revealed. The floats also uncover their distinct properties, which may result from the different mixing histories. Plain Language Summary: The Antarctic Bottom Water is important to the climate of our planet. It brings oxygen and other elements to the bottom of the ocean when it sinks around the Antarctic (thus its name) and moves north. However, we haven't had many ways to measure it until recently. Here, we use a relatively new technology called Deep Argo floats, which are autonomous robots that measure temperature, salinity, and pressure from the surface all the way down to the bottom of the ocean and transmit the data via satellite to land every few days when they are on the sea surface. We put three of these robots near the deep fracture zones of the Southwest Indian Ridge. The ridge is like a big wall separating two rooms, with the fracture zones being corridors in the wall that allow water in the ocean bottom to move from one room to the other. We chose corridors we guessed could have Antarctic Bottom Water: Atlantis II, Novara, and Melville. The robots are helping to solve a big mystery that has been around for 50 years and, in just 7 months of their 4‐year missions, have already improved our understanding of the bottom of the ocean. Key Points: The floats collected the region's largest temperature‐salinity data set to date, with adjusted salinity meeting the Deep Argo target accuracyThe floats found a new abyssal ventilation source (Novara fracture zone) to the Madagascar Basin and solved the Melville inflow puzzleThe abyssal layer is fresher at the Melville fracture zone and saltier at Atlantis II, with Novara having intermediate water mass properties [ABSTRACT FROM AUTHOR]

Deep convection occurs periodically in the Gulf of Lion, in the northwestern Mediterranean Sea, driven by the seasonal atmospheric change and Mistral winds. To determine the variability and drivers of both forcings, multiple 1 year ocean simulations were run, spanning from 1993 to 2013. Two sets of simulations were performed: a control and seasonal set, the first forced by unfiltered atmospheric forcing and the other by filtered forcing. The filtered forcing was bandpass filtered, retaining the seasonal and intraday aspects but removing the high frequency phenomena. Comparing the two sets allows for distinguishing the effects of the high frequency component of the Mistral on the ocean response. During the preconditioning phase, the seasonal forcing was found to be the main destratifying process, removing on average 46% of the stratification needed for deep convection to occur, versus the 28% removed by the Mistral. Despite this, each forcing triggered deep convection in roughly half of the deep‐convection events. Sensible and latent heat fluxes were found to be the main drivers of the seasonal forcing during deep‐convection years, removing 0.17 and 0.43 m2s−2 of stratification, respectively. They were themselves driven by increased wind speeds, believed to be the low frequency signal of the Mistral, as more Mistral events occur during deep‐convection winters (34% vs. 29% of the preconditioning period days). An evolving seasonal forcing in a changing climate may have significant effects on the future deep convection cycle of the western Mediterranean Sea. Plain Language Summary: Deep convection occurs periodically in the Gulf of Lion (located in the northwestern Mediterranean Sea), when water at the surface of the ocean is cooled enough to mix freely with the deeper water below, sometimes reaching the sea floor. It's an important part of the overall circulation of the Mediterranean Sea that leads to an explosion in the phytoplankton population in the following spring. In the gulf, the surface cooling is caused by the atmospheric transition from summer to winter and the Mistral winds. The latter is a cool, dry northerly wind that flows through the Rhône Valley out over the gulf. In our study, we ran ocean simulations that included and excluded the non‐seasonal effects of the Mistral to determine the importance of the seasonal and Mistral forcing on deep convection. The seasonal forcing was found to have a larger role, and contained a low frequency part of the Mistral, elevating the average wind speeds during the winter. Changes in the seasonal forcing and ocean water composition will need to be studied to understand the evolution of deep convection in the Gulf of Lion and its consequences on the Mediterranean Sea dynamics and biology in a changing climate. Key Points: The seasonal atmospheric change is the main driver of destratificationWinters with deep convection have below average levels of stratification that the atmospheric forcing has to overcomeThe Mistral winds have a low frequency signature that elevates the seasonal wind speeds in the winter [ABSTRACT FROM AUTHOR]

Accurate prediction of the embedment depth of surface-laid pipelines is fundamental to determine in-service performance, which is closely related to the resistance the seabed provides during pipe-lay. The presence of a surficial crust overlying normally consolidated seabeds increases difficulties in accurately assessing the variation in penetration resistance with depth. In an attempt to address these difficulties, this paper presents results from a series of large-deformation finite-element analyses of a pipeline vertically penetrating crusty seabeds under undrained conditions. A detailed parametric study was carried out to examine the effects of crust strength geometry (strength ratio, crust thickness, and strength gradient) and softening properties (soil sensitivity and ductility) on the penetration response and the evolution of soil flow mechanisms. A surficial crust leads to higher penetration resistance relative to a normally consolidated seabed without a crust. The numerical analyses revealed the transition in failure mechanism as the pipe penetrates through the crust into the underlying clay. Separate mechanisms identified at various transition points allowed for a mechanism-based empirical approach that produces a depth profile of penetration resistance for crusts of varying strength characteristics and thicknesses. The accuracy of this simplified calculation method typically is within 10% of the numerical results, and is suitable for use in engineering practice providing an evidence-based approach for the calculation of pipeline penetration in seabeds with surficial crusts. [ABSTRACT FROM AUTHOR]

Offshore floating systems are held in position with chains that connect the floater to anchors embedded in the seabed. An essential component for calculating the overall mooring capacity is an accurate assessment of the holding resistance from the anchor chains. Existing studies generally simplify the (complex) chain geometry to that of a cylindrical bar, which does not account for the intricate geometry of the connected chain links. This paper reports on three-dimensional finite-element modeling that defined the capacity of a link of anchor chain in clay soil with consideration of the geometry of the chain links, including the influence from adjacent links. Both stud link and studless links were considered, along with the effect of embedment depth, link direction angle, and interface condition. The soil resistance acting on the chain links, represented by uniaxial bearing capacity factors Nn,max , Ns,max , and Nt,max along the normal, lateral, and axial directions of the chain link, respectively, were derived, and the soil failure mechanisms for these conditions are discussed. Equivalent bearing capacity factors Nq and Na were derived by converting the soil resistance to normal and tangential resistances (q and f) acting on an equivalent cylindrical bar. Ultimately, f/q was calculated to represent the friction coefficient, μ , which ranged from 0.2 to 0.4. [ABSTRACT FROM AUTHOR]

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

Using 9 years of full‐depth profiles from 55 Deep Argo floats in the Southwest Pacific Basin collected between 2014 and 2023, we find consistent warm anomalies compared to a long‐term climatology below 2,000 m ranging between 11 ± 2 to 34 ± 2 m°C, most pronounced between 3,500 and 5,000 m. Over this period, a cooling trend is found between 2,000 and 4,000 m and a significant warming trend below 4,000 m with a maximum rate of 4.1 ± 0.31 m°C yr−1 near 5,000 m, with a possible acceleration over the second half of the period. The integrated Steric Sea Level expansion below 2,000 m was 7.9 ± 1 mm compared to the climatology with a trend of 1.3 ± 1.6 mm dec−1 over the Deep Argo era, contributing significantly to the local sea level budget. We assess the ability to close a full Sea Level Budget, further demonstrating the value of a full‐depth Argo array. Plain Language Summary: Cold, dense waters formed near polar regions in both hemispheres, sink to great depths and fill‐up the majority of the world's deep ocean. Compilation of sparse observations of temperature from global ship‐based surveys at roughly 10‐year intervals worldwide have shown that sequestration of excess atmospheric heat into the deep ocean has caused these waters to warm steadily since the 1990's into the Present. Not only does this warming have implications for changes in large scale ocean circulation, but is also associated with warming‐induced sea level rise. Using a new data set collected between 2014 and 2023 from 55 freely drifting robotic floats (Deep Argo) which gather crucial bimonthly temperature and salinity data between the surface ocean and the ocean floor, we find the greatest warming trend at a depth of 5,000 m of 4 ± 0.3 m°C yr−1 and an associated sea level rise rate below 2,000 m of 1.3 ± 1.6 mm dec−1. Deep Argo data being collected in ocean basins worldwide are crucial in providing high resolution data of the warming deep ocean and its implications on global sea level, ocean mixing and large‐scale ocean circulation. Key Points: Nine years of Deep Argo data in the S.W. Pacific reveals continued warming in the abyss while the mid‐depths cooledWaters below 4,000 m show an accelerated warming trend with a maximum overall warming rate of 4.1 ± 0.31 m°C yr−1 at 5,000 mDeep ocean steric expansion contributed 1.3 ± 1.6 mm dec−1 to total the local sea level [ABSTRACT FROM AUTHOR]

Australia is yet to adequately grapple with the unique challenges that critical seabed infrastructure protection poses to its defence and national security. While the paramount importance of Australia's sea lines of communication are widely understood, Australia's seabed lines of communication are understudied and underappreciated. This article lays the foundation for an Australian strategy to protect critical seabed infrastructure that constitutes seabed lines of communications. The article first overviews critical seabed infrastructure in Australia's immediate region. Second, it examines various suspected cases of seabed warfare in Europe and the Indo-Pacific which targeted critical seabed infrastructure. Third, the article analyses Australia's response to date, before, fourth and finally, outlining how Australia, and in particular the Royal Australian Navy (RAN), ought to respond to the growing threat to seabed lines of communication. By systematically analysing seabed warfare trends since 2021 using reputable journalism, think tank reports and fresh regional responses, this article demonstrates Australia's seabed vulnerabilities, and novel resiliency strategies. [ABSTRACT FROM AUTHOR]

The passive estimation of harmonic sound source depth is of great significance for underwater target localization and identification. Passive source depth estimation using a single hydrophone with an unknown seabed geoacoustic property is a crucial challenge. To address this issue, a harmonic sound source depth estimation algorithm, seabed independent depth estimation (SIDE) algorithm, is proposed. This algorithm combines the estimated mode depth functions, modal amplitudes, and the sign of each modal to estimate the sound source depth. The performance of the SIDE algorithm is analyzed by simulations. Results show that the SIDE is insensitive to the initial range of the sound source, the source depth, the hydrophone depth, the source velocity, and the type of the seabed. Finally, the effectiveness of the SIDE algorithm is verified by the SWellEX-96 data. [ABSTRACT FROM AUTHOR]

A numerical model is presented for ship-induced sediment transport, focusing on the fundamental role of propeller jet flow. The new module has been implemented in the open-source numerical model FUNWAVE in order to reproduce the effect of the propeller on sediment transport. Numerical simulations have been performed for both stationary and moving vessel cases, as well as for different values of propeller revolution speed. Numerical results are presented for the propeller-induced velocity field and the resulting morphological evolution of the seabed. Qualitative similarities are observed between the numerical results and literature experimental findings, showing the ability of the model to mimic complex morphodynamic processes induced by ship propellers. Compared to stationary vessel cases, smaller scour depths are generated in moving vessel cases. It is concluded that the effect of the propeller provides a major contribution to the mobilization and suspension of seabed sediment, and it should not be neglected in numerical models for ship-induced sediment transport. [ABSTRACT FROM AUTHOR]

In the western South China Sea, the diversity and complex genesis of sand waves lead to difficulties in measuring the actual scour depth of offshore wind turbine foundations. The present study employs methods such as insitu multibeam echo sounding along with numerical simulation techniques, combined with regional hydrological and geological data, to reveal the scour depth of pile foundations under seabed sand wave migration conditions (SPFSWM). Unlike previous studies, this study examines pile foundation scour depth from both macroscopic and microscopic perspectives, and proposes a method for risk assessment and safety zoning during the service life of pile foundations (RASZ). Our findings demonstrate that the dominant flow directions in the modern hydrodynamic environment play a crucial role in shaping and migrating sand waves, providing guidance for macro-level offshore wind project siting. Moreover, the study quantifies the changes in pile foundation elevations during sand wave migration and assesses their impact on safety throughout the service life of various pile foundations. Additionally, by utilizing Flow3D's numerical model and combining it with sampling data, the maximum scour depth likely to be experienced by pile foundations was calculated, establishing a microperspective on the range of pile foundation scour and analytically examining the coupling mechanism between sand wave migration and pile foundation scour in stages. By considering SPF-SWM, we estimated the actual depth variations of pile foundations in the study area, enabling effective assessment of scour conditions during their service life. This also provides ideas for delineating safety and risk zones, thereby offering precise locational analysis for the construction planning of offshore wind farm pile foundations. [ABSTRACT FROM AUTHOR]

In January 2020, the footbridge connecting the seaward platform of the Pont del Petroli pier to Badalona beach collapsed due to the severe sea storm named Gloria. Approximately 15 m of the footbridge fell into the sea as a result of prolonged wave action and strong impacts. To understand the complex interaction between waves and structures that led to the pier's collapse during the storm, a composite modelling approach was developed. The loads on each pier element were initially evaluated using the meshless DualSPHysics code, which employs the Smoothed Particle Hydrodynamics (SPH) method. This evaluation was conducted under severe wave conditions analogous to those experienced during the storm. Numerical models informed the design of an experimental campaign carried out at the Maritime Engineering Laboratory of Universitat Politècnica de Catalunya -- BarcelonaTech, using the CIEM large-scale wave flume facility in Barcelona, Spain. Post-storm bathymetric surveys revealed significant alterations in the seabed profile near the affected infrastructure, including sediment deposition and a reduction in water depth from 10 m to 8 m. Consequently, it was anticipated that wave transformation and breaking in the vicinity of the structure would be substantially affected. To explore this phenomenon, various extreme wave impacts were experimentally simulated using focused wave groups. The physical model findings unveiled the forces that the pier endured during the storm Gloria. The results indicate that wave phases influence individual waves, with waves that are biased and asymmetric experiencing higher peaks than those focused on the crest. This insight helps to explain the structural failure of the footbridge during the storm and underscores the importance of considering wave phase impacts in the design and assessment of coastal infrastructure. The combined numerical and experimental approach provides a comprehensive understanding of the forces at play, contributing valuable knowledge to the field of coastal engineering and infrastructure resilience. [ABSTRACT FROM AUTHOR]