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A new, non‐dimensional ripple reset parameter and a stochastic point process model is used to estimate the likelihood of propagating ocean waves to form ripples on sandy seabeds. The ripple reset parameter is a function only of water depth, significant wave height, and mean grain size. Ripple formation is estimated by the magnitude of an intensity function based on a time series of the ripple reset parameter. The point process model is trained with a time series of observed waves and ripple change, and is then applied to predict the probability that a ripple field with a different geometry will form within a given time interval from another time series of wave data. The model is trained and tested with four field deployments at three field sites to determine its skill in predicting the ripple formation (a) at one field site over one time period after being trained with observations from the same site over a different time period, and (b) at one field site after being trained with observations from another field site. Results show that while the model is sufficient at predicting ripple formation in both scenarios, it is sensitive to the quality and quantity of the training data. Increasing the amount of training data greatly improves model performance. Employing a stochastic model based on a simple ripple reset parameter reduces tunable model parameters and provides a prediction of the probability for ripple formation given only a water depth, grain size, and time series of wave heights. Plain Language Summary: Ripples are small, hill‐like mounds of sand that are formed by water in the ocean moving back and forth by waves. Sand ripples can cause an increase of sand movement on the seafloor, can cause ocean instrumentation to respond unexpectedly, and can bury and expose objects. Understanding when they form is important for scientists to measure and predict ocean dynamics. If the average height of the waves, the water depth, and the sand grain diameter is known, we can predict whether or not the waves will form ripples with mathematical equations. Previously, the equations to predict ripple formation required a lot of difficult to obtain ocean information. We developed an equation and model to quickly and easily predict the likelihood of ripples forming by waves in a specific size sand and water depth. Key Points: A ripple reset parameter based on wave height, water depth, and grain size is presentedA stochastic model based on the ripple reset parameter can predict the probability of ripple formationThe model accurately predicted ripple resets at three different field sites without calibration [ABSTRACT FROM AUTHOR]

AbstractWith the development of offshore wind power projects worldwide, the stability of deep and shallow sea wind power sites has become a crucial concern. Internal solitary waves (ISWs) are nonlinear and large amplitude waves in the stratified ocean. Their strong vertical and horizontal motion and vorticity and turbulence caused by fragmentation have an important impact on the marine environment, seabed sediments, and marine engineering. This study focuses on the interaction between ISWs and the seabed of wind power sites in deep and shallow seas. Specifically, we investigate the interaction between ISWs and monopile foundations or floating fan plate anchor structures in the seabed. Through the simulation of CFD software and Comsol software, a law of seabed pore pressure variation during the effect of ISWs on the structure can be well demonstrated. Our results demonstrate that ISWs induce the accumulation of excess pore water pressure around the structures. The monopile foundation experiences negative excess pore water pressure at its bottom and the plate anchor at its top. The pore water pressure at the bottom of the monopile foundation initially decreases and then increases. In contrast, the pore water pressure at the right side of the monopile foundation increases, decreases, and then increases. This phenomenon promotes the settlement of the structure. At the bottom of the plate anchor, there is a sharp increase in positive excess pore water pressure by ISW. The pore water pressure above the plate anchor structure initially decreases and then increases, while below the plate anchor, it increases and then decreases. This phenomenon leads to the movement of the anchorage structure and instability of the surrounding soil. The influence of ISWs on the seabed bottom intensifies with the obstruction of the structure, resulting in significant positive pressure at the bottom. Between the two anchoring structures, there is increased seepage of pore water, making the seabed more prone to instability. Through the study of this article, we know that ISW has different effects on the force of monopile foundation and plate anchor structure, which provides a favorable basis for its design and maintenance. [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]

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]

The research was conducted to provide information about the physical characteristics of Erelu reservoir in Oyo West Local Government Area, Oyo, in Oyo State. Data acquisition featured sounding by means of an echo sounder and for depth and position determination by means of a GPS while the tidal data used were based on existing data. Initial processing performed on the observed bathymetric data included; sorting with PowerNav and HYPACK 2018. Further processing was carried out using ArcGIS 10.7 and SUFFER 2016 software. The modified normalized difference water index (MNDWI) was used to extract the shoreline of the study area, while the digital shoreline analysis system (DSAS) was used for shoreline analysis. The results of the analysis showed that the maximum and minimum depths observed were 6.03m and 0.56m respectively 2023 an indication that the water is shallow. The surface area and volume values obtained were 120.94ha and 2975635.28943.13m³. Based on a linear and areal analysis, the bathymetric survey revealed that the maximum length and area reached in 2022 were 7855.171m and 84.506ha respectively, while the minimum length and area in 2017 were 7460.733m and 78.303ha respectively. Based on the results from DSAS, it was deduced that the accretion rate was high, while the erosion rate was minimal. Finally, the processed depths were analysed and presented in the form of charts, which may be used in the near future for planning and decision-making for proper management of the reservoir. [ABSTRACT FROM AUTHOR]

There are many problems with the vertical installation of suction buckets due to the complex ocean wave current and seabed geological conditions. In this paper, a set of tests were developed to study the mechanism of incline rectification of the suction bucket foundation based on resistance-reduced vibration on local side walls (RRV-LSW). In this experiment, the dynamic evolution process of pore water pressure around the suction barrel foundation was monitored from three angles of vibration frequency, initial inclination angle and load, and the influence of local cyclic vibration parameters on the slope velocity of the suction barrel foundation was quantified. The results indicate that a tilted suction caisson foundation can be effectively corrected through lateral wall vibration, and the correction effect is closely related to the vibration frequency, initial tilt angle, and static pressure load. [ABSTRACT FROM AUTHOR]

The current scallop fishery sector allows many scallops to remain in specified fishing zones, and this process leads to heavy losses in the sector. Scallop fishermen aim to harvest the remaining scallops to reduce their losses. To achieve this, a fisherman must understand the scallop ecology on the seafloor. In our previous study, we proposed a method for measuring scallops using wheeled robots. However, a wheeled robot must be able to resist disturbance from the sea to achieve high measurement accuracy. Strong anchoring of wheels against the seafloor is necessary to resist disturbance. To better understand anchoring performance, we confirmed the wheel anchoring capacity in water-containing sand in an experiment. In this experiment, we towed fixed wheels on water-containing sand and measured the resistance force acting between the wheel and the sand. Afterward, we considered the resistance force as the wheel anchoring capacity on the water-containing sand. The experimental results capture the tendency for the anchoring capacity of sand with/without water to increase with sinkage. The results also demonstrate that the anchoring capacity of water-containing sand is lower than that of non-water-containing sand. However, the results indicate that when the wheels possess lugs, their presence tends to increase the wheels' anchoring capacity in water. [ABSTRACT FROM AUTHOR]

The current scallop fishery sector allows many scallops to remain in specified fishing zones, and this process leads to heavy losses in the sector. Scallop fishermen aim to harvest the remaining scallops to reduce their losses. To achieve this, a fisherman must understand the scallop ecology on the seafloor. In our previous study, we proposed a method for measuring scallops using wheeled robots. However, a wheeled robot must be able to resist disturbance from the sea to achieve high measurement accuracy. Strong anchoring of wheels against the seafloor is necessary to resist disturbance. To better understand anchoring performance, we confirmed the wheel anchoring capacity in water-containing sand in an experiment. In this experiment, we towed fixed wheels on water-containing sand and measured the resistance force acting between the wheel and the sand. Afterward, we considered the resistance force as the wheel anchoring capacity on the water-containing sand. The experimental results capture the tendency for the anchoring capacity of sand with/without water to increase with sinkage. The results also demonstrate that the anchoring capacity of water-containing sand is lower than that of non-water-containing sand. However, the results indicate that when the wheels possess lugs, their presence tends to increase the wheels’ anchoring capacity in water.

The accurate mapping of seafloor substrate types plays a major role in understanding the distribution of benthic marine communities and planning a sustainable exploitation of marine resources. Traditionally, this activity has relied on the efforts of marine geology experts, who accomplish it manually by examining information from acoustic data along with the available ground- truth samples. However, this approach is challenging and time-consuming. Hence, it is important to explore automatic methods to replace this manual process. In this study, we investigated the potential of deep learning (U-Net) for classifying the seabed as either "bedrock" or "non-bedrock" using bathymetry and/or backscatter data, acquired with multibeam echosounders (MBES). Slope and hillshade data, derived from the bathymetry, were also included in the experiment. Several U-Net models, taking as input either one of these datasets or a combination of them, were trained using an expert delineated map as reference. The analysis revealed that U-Net has the ability to map bedrock and non-bedrock areas reliably. On our test set, the models using either bathymetry or slope data showed the highest performance metrics and the best visual match with the reference map. We also observed that they often identified topographically rough features as bedrock, which were not interpreted as such by the human expert. While such discrepancy would typically be considered an error of the model, the scale of the expert annotations as well as the different methods used by the experts to manually generate maps must be considered when evaluating the predictions quality. While encouraging results were obtained here, further research is necessary to explore the potential of deep learning in mapping other seabed types and evaluating the models' generalization capabilities on similar datasets but different geographical locations. [ABSTRACT FROM AUTHOR]

Abstract 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 (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.

The sinking of outfall pipeline is the key link in the process of shipping and installing marine outfall pipelines. A steel pipeline with a length of 500 m and an inner diameter of 1 m is taken as the research object. The critical depth of pipe sinking is determined by numerical analysis and the equivalent stress of S-shaped pipe section is taken as the limiting condition. The buoyancy, number and spacing of the airbag are determined by the buoyancy aid safety factor and negative buoyancy of the pipe section. The sinking of the outfall pipeline is finally realized by means of multiple underwater sinking. The elevation error, axial error and flange joint gap in the engineering example all meet the acceptance requirements, which proves that the sinking technology is reliable and the application effect is good, and can provide reference for the construction of the same type of outfall pipelines. [ABSTRACT FROM AUTHOR]

The design of artificial reefs must be based on the criteria of both durability and serviceability. In this respect, the seabed subsidence rate related to the weight of the reefs and of their foundation system should be limited. The horizontal drift of the reefs during their life should be small too. In this study, pertaining to the behavior of artificial reefs made of microsilica concrete and realized with foundations in bamboo near the international airport of Hong Kong, 1-year monitoring data and calculations of reef foundation settlements are shown and discussed to assess the performance of the adopted mixed foundation and to deduce the nature of the long-term subsidence. The subsidence related to the settlements of the foundations was monitored using a Multibeam Echo Sounder System. It was found that the observed subsidence rate cannot be justified by the primary consolidation of the soils forming the seabed. Indeed, secondary consolidation seems to play an important role. Overall, after one year of service, the artificial reefs are considered to be effective in terms of limitation of both subsidence and drift. [ABSTRACT FROM AUTHOR]

Internal solitary waves (ISWs) occur in stratified seawater and are characterized by substantial amplitudes and short periods. ISWs engender significant interactions between seawater and seafloor topography. They resuspend seabed sediments in various ways, and the submarine canyon acts as a main channel for transporting the suspended sediments from the shallow sea to the deep sea. Among the seas worldwide where ISWs are prevalent, the South China Sea exhibits the largest amplitude of ISWs, and the ISWs directly interact with the seafloor topography near the Dongsha area in the northern South China Sea. Through the analysis of the water profile and high-resolution multi-beam detection data in the vicinity of the Dongsha area, it was found that the submarine canyon exerts a great impact on the sediment resuspension and the bottom nepheloid layer formation induced by ISWs. The observation results show that the concentration of suspended particulate matter within the submarine canyon is remarkably higher than that outside the canyon. The concentration at the bottom of the canyon can reach twice that of the outside regions, forming a vast bottom nepheloid layer. In addition, with the presence of the submarine canyon, the suspended matter carried by the ISWs accumulates in the water column above the canyon, leading to a higher concentration above the canyon. ISWs not only could influence the submarine canyons, but also interacted with it. This interaction enhanced the resuspension and transport of seafloor sediments along submarine canyons and trenches. This study deepens the understanding of the effect of ISWs on sediment resuspension in submarine canyons. [ABSTRACT FROM AUTHOR]

This document is a corrigendum for an article titled "Seabed classification of multibeam echosounder data into bedrock/non-bedrock using deep learning." The corrigendum addresses minor inaccuracies in the article, specifically regarding metrics values for multiple-input models and misclassification values in tables. The corrections have been made to the tables and corresponding confusion matrices. The authors apologize for the errors and state that they do not change the scientific conclusions of the article. [Extracted from the article]

The accurate mapping of seafloor substrate types plays a major role in understanding the distribution of benthic marine communities and planning a sustainable exploitation of marine resources. Traditionally, this activity has relied on the efforts of marine geology experts, who accomplish it manually by examining information from acoustic data along with the available ground-truth samples. However, this approach is challenging and time-consuming. Hence, it is important to explore automatic methods to replace this manual process. In this study, we investigated the potential of deep learning (U-Net) for classifying the seabed as either “bedrock” or “non-bedrock” using bathymetry and/or backscatter data, acquired with multibeam echosounders (MBES). Slope and hillshade data, derived from the bathymetry, were also included in the experiment. Several U-Net models, taking as input either one of these datasets or a combination of them, were trained using an expert delineated map as reference. The analysis revealed that U-Net has the ability to map bedrock and non-bedrock areas reliably. On our test set, the models using either bathymetry or slope data showed the highest performance metrics and the best visual match with the reference map. We also observed that they often identified topographically rough features as bedrock, which were not interpreted as such by the human expert. While such discrepancy would typically be considered an error of the model, the scale of the expert annotations as well as the different methods used by the experts to manually generate maps must be considered when evaluating the predictions quality. While encouraging results were obtained here, further research is necessary to explore the potential of deep learning in mapping other seabed types and evaluating the models’ generalization capabilities on similar datasets but different geographical locations.

This article aims to clarify the obligations of States under the law of the sea to put children's human rights at the heart of decision-making on the protection of the marine environment, particularly at the ocean-climate nexus. The relevance of the provisions of the United Nations Convention on the Rights of the Child and in particular, children's human right to be heard in the context of existing provisions on deep-sea mining activities under the International Seabed Authority and the Agreement on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction are discussed. Reflections on more ambitious approaches to integrating intergenerational dialogue within international ocean fora, as ways to implement intergenerational equity and protect humankind at the ocean-climate nexus, on the basis of good practices in the area of children's human rights are offered. [ABSTRACT FROM AUTHOR]

Studying the dynamic changes in the coastline of the northeastern Caspian Sea is significant since the level of the Caspian is unstable, and the coastline change can cause enormous damage to the ecology, economy, and population of the coastal part of Kazakhstan. In this work, we use remote sensing and Geographic Information System (GIS) technologies to study the changes in the coastline of the northeastern Caspian Sea and predict the extent of flooding with increasing water levels. The proposed methodology for creating dynamic maps can be used to monitor the coastline and forecast the extent of flooding in the area. As a result of this work, the main factors affecting changes in the coastline were identified. After analyzing the water level data from 1988 to 2019, it was revealed that the rise in water level was observed from 1980 to 1995. The maximum sea level rise was recorded at −26.04 m. After that, the sea level began to fall, and between 1996 and 2009, there were no significant changes; the water level fluctuated with an average of −27.18 m. Then, a map of the water level dynamics in the Caspian Sea from 1988 to 2019 was compiled. According to the dynamics map, water level rise and significant coastal retreat were revealed, especially in the northern part of the Caspian Sea and the northern and southern parts of Sora Kaydak. The method for predicting the estimated flooding area was described. As a result, based on a single map, the flooding area of the northeast coast was predicted. A comparative analysis of Landsat and SRTM data is presented.

The rapidly expanding built environment in the northern Gulf of Mexico includes thousands of human built structures (e.g. platforms, shipwrecks) on the seabed. Primary-colonizing microbial biofilms transform structures into artificial reefs capable of supporting biodiversity, yet little is known about formation and recruitment of biofilms. Short-term seafloor experiments containing steel surfaces were placed near six structures, including historic shipwrecks and modern decommissioned energy platforms. Biofilms were analyzed for changes in phylogenetic composition, richness, and diversity relative to proximity to the structures. The biofilm core microbiome was primarily composed of iron-oxidizing Mariprofundus, sulfur-oxidizing Sulfurimonas, and biofilm-forming Rhodobacteraceae. Alpha diversity and richness significantly declined as a function of distance from structures. This study explores how built structures influence marine biofilms and contributes knowledge on how anthropogenic activity impacts microbiomes on the seabed. [ABSTRACT FROM AUTHOR]

The observation and detection of the subsea environment urgently require large-scale and long-term observation platforms. The design and development of subsea AUVs involve three key points: the subsea-adapted main body structure, agile motion performance that adapts to complex underwater environments, and underwater acoustic communication and positioning technology. This paper discusses the development and evolution of subsea AUVs before proposing solutions to underwater acoustic communication and positioning navigation schemes. It also studies key technologies for the agile motion of subsea AUVs and finally gives an example of a solution for implementing underwater AUVs, i.e., the disk-shaped autonomous underwater helicopter (AUH). This paper will provide guidance for the design of subsea AUVs and the development of corresponding observation and detection technologies. [ABSTRACT FROM AUTHOR]

The conclusion of the Convention on the Legal Status of the Caspian Sea in 2018 was intended to put an end to a very long and difficult negotiation process to determine the legal regime for this closed water body, which has no natural connection with the World Ocean. The Convention was supposed to fill the gaps in the management of this water area that existed in the framework of the previous Soviet-Iranian agreements of 1921 and 1940, which were in force but not up to date, and to give all the Caspian states common and equal rights and powers to use and exploit the spaces and resources of this maritime region. However, up to 2022, the Convention has not entered into legal force, as one of the Caspian countries — the Islamic Republic of Iran — has not yet ratified this regional agreement, considering that it is the most disadvantaged party. Despite the resolution of the Caspian Sea seabed delimitation issues in its northern part in previous years, the problem of delimitation in its southern part may require both enormous efforts and time, further complicating the current situation. There is as yet no final understanding as to what delimitation models can be used here to satisfy the interests of all the states involved. Moreover, the implementation of the norms and provisions of the 2018 Convention requires the drafting and signing of new bilateral and multilateral documents that close a whole series of “gaps” in the proposed convention regime. In fact, the fate of the 2018 Convention depends on how these contradictions will be resolved. The analysis of these problems is the focus of this paper.

Under stormy weather conditions, offshore structures have been severely damaged by heavy sea wave loading. Many researchers have conducted investigations on damaged structures and revealed that the damage to the structures is emphasized by the disintegration of the seabed caused by sea wave loading on the seabed. The previous study by authors conducted model sea-wave loading tests on sand ground and revealed that the disintegration of the seabed and associated scouring were caused by the upward seepage flow as a response to sea-wave loading, which reduced the effective stress in the seabed. Breakwaters consisting of concrete blocks have been monitored for years, and it has been reported that they sink every year by a fraction of a meter in accordance with stormy wave conditions. This study conducted a series of model tests on a block equipped with a three-axial accelerometer to detect its attitude when rested on a seabed with generated upward seepage flow. The sinking behavior of the block in the seabed during the gradual increase in the hydraulic gradient of seepage flow was carefully observed to clarify the fundamental mechanism of the sinking of the block. Consequently, this study found the critical condition of the hydraulic gradient under which the sinking of the block is initiated is independent of the density of the seabed material. In the scheme of model tests, the applicability of the three-axis accelerometer for the detection of the block, even under the critical hydraulic gradient attained, was demonstrated. [ABSTRACT FROM AUTHOR]

Digital bottom models are commonly used in many fields of human activity, such as navigation, harbor and offshore technologies, or environmental studies. In many cases, they are the basis for further analysis. They are prepared based on bathymetric measurements, which in many cases have the form of large datasets. Therefore, various interpolation methods are used for calculating these models. In this paper, we present the analysis in which we compared selected methods for bottom surface modeling with a particular focus on geostatistical methods. The aim was to compare five variants of Kriging and three deterministic methods. The research was performed with real data acquired with the use of an autonomous surface vehicle. The collected bathymetric data were reduced (from about 5 million points to about 500 points) and analyzed. A ranking approach was proposed to perform a complex and comprehensive analysis integrating typically used error statistics—mean absolute error, standard deviation and root mean square error. This approach allowed the inclusion of various views on methods of assessment while integrating various metrics and factors. The results show that geostatistical methods perform very well. The best results were achieved with the modifications of classical Kriging methods, which are disjunctive Kriging and empirical Bayesian Kriging. For these two methods, good statistics were calculated compared to other methods (for example, the mean absolute error for disjunctive Kriging was 0.23 m, while for universal Kriging and simple Kriging, it was 0.26 m and 0.25 m, respectively). However, it is worth mentioning that interpolation based on radial basis function in some cases is comparable to Kriging in its performance. The proposed ranking approach was proven to be useful and can be utilized in the future for choosing and comparing DBMs, mostly in mapping and analyzing seabed changes, for example in dredging operations. The research will be used during the implementation of the new multidimensional and multitemporal coastal zone monitoring system using autonomous, unmanned floating platforms. The prototype of this system is at the design stage and is expected to be implemented. [ABSTRACT FROM AUTHOR]

Marine Geological Institute acquired high-resolution seismic and acoustic data during a survey in the Waipoga Trough-West Papua in 2018. The profiles show acoustically blanking, turbid, and cloudy occur along the trough floor over 3,000 km2. Many accoustic chimneys are breaking through the seabed of recent and subrecent sediment layers. It is suggested due to the local expulsion of methane gas. The pockmarks occur as transparent and turbid acoustic characteristics. They locally have relief down to 2-10 m below the seafloor with horizontal dimensions up to 25 -100 m in width. Methane formation due to the rapid deposition of organic-rich sediment down the uplifted area around the trough, associated with thrust fold tectonics is suggested as a triggering agent for the acoustic anomaly formation. [ABSTRACT FROM AUTHOR]

Leg placement and removal are the two most critical operational modes for dynamically positioned jack-ups when working close to an offshore asset. Any positional deviation may lead to collision and damage to the asset. The industry operates with a weak link between the dynamic positioning (DP) system and the jacking system. Current DP systems operate without any sensors identifying the hydrodynamic force variations on the legs and spudcans, which vary between different leg and spudcan designs. When the spudcan is near to the sea bottom, the hydrodynamic force must be reported to avoid large positional deviations driven by the DP system. This article promotes a mechanismtomeasure these forces using Computational Fluid Dynamics (CFD) analysis to analyze the jack-up behavior, when the spudcan assembly is operating close to the sea bottom. [ABSTRACT FROM AUTHOR]

The seabed landscape around the Summer Isles (NW Scotland) hosts classic examples of subaqueous moraines formed at a Late Pleistocene tidewater ice-sheet margin. This suite of moraines, now within the Wester Ross Marine Protected Area, records oscillatory retreat of the grounding line of (one or more) large outlet glaciers receding from the open waters of the Minch into the fjords of Loch Broom and Little Loch Broom at the end of the last (Weichselian / Devensian) glaciation. The moraines, probably the best-studied examples in UK waters, formed by a combination of pushing, dumping and/or squeezing of sediment at the grounded tidewater glacier front. Their absence in some basins suggests that the glacier front was un-grounded (partially floating) in areas of deeper water. Some of these seabed moraines can be connected to ice-sheet moraines onshore, assigned to the Wester Ross Readvance, and dated to ca. 15.5 ka BP. Geomorphological evidence strongly suggests that the whole sequence represents relatively slow and punctuated ice-front retreat over a period of decades to centuries. Continued protection of these rare and distinctive seabed moraines is important, both on geological and ecological grounds. The moraines represent the first underwater Scottish Landform Example in this long-running series. [ABSTRACT FROM AUTHOR]

We investigated the presence and diversity of cetaceans in the Mediterranean Sea, analysing the data collected by 32 different research units, over a period of 15 years (2004–2018), and shared on the common web-GIS platform named Intercet. We used the encounter rate, the species prevalence, and the Shannon diversity index as parameters for data analysis. The results show that cetacean diversity, in the context of the Mediterranean basin, is generally quite low when compared with the eastern Atlantic, as few species, namely the striped dolphin, the bottlenose dolphin, the fin whale, and the sperm whale, dominate over all the others. However, some areas, such as the Alboran Sea or the north-western Mediterranean Sea, which includes the Pelagos Sanctuary (the Specially Protected Area of Mediterranean Interest located in the northern portion of the western basin), show higher levels of diversity and should be considered hotspots to be preserved. Primary production and seabed profile seem to be the two main drivers influencing the presence and distribution of cetaceans, with the highest levels of diversity observed in areas characterized by high levels of primary production and high bathymetric variability and gradient. This collective work underlines the importance of data sharing to deepen our knowledge on marine fauna at the scale of the whole Mediterranean Sea and encourages greater efforts in the networking process, also to accomplish the requirements of the Marine Strategy Framework Directive, with particular reference to Descriptor 1: biological diversity is maintained. [ABSTRACT FROM AUTHOR]

India's role in maritime trade dates back to 1500s as it is bordered with Indian Ocean which is open sea. But it gradually declined when the state was invaded by colonial powers and made forced participation in the World Wars. During the wars Indian Ocean catered as major maritime trade route and hence a lot of warships sank, seized weapons were dumped in the ocean. The dumped weapons include nondeactivated biological and chemical weapons that pose perpetual threat to India and other coastal states. Since Cold War, there was a rise in militarization in the seabed which eventually led to arms race. With digitalization, the facility of remote access has further geared up the arms race in the seabed. There are bundle of laws in the global parlance to regulate the same but the increasing arms race in the seabed creates doubt with respect to the effectiveness. In this outset, it is important to analyse whether India being a coastal state be able to survive the consequences from such arms race and dumped weapons in the seabed with its existing legal framework. For this study, this research paper makes conceptual understanding along with historic analysis of dumping of weapons ad arms race in the seabed. Further the paper conducts thorough study on the existing international legal framework and the territorial laws of India in this regard. The paper also analyses the present trends in seabed arms race in the seabed and put forth suggestions for the state's better future and security of its people. [ABSTRACT FROM AUTHOR]

Seabed morphology maps and data are critical for knowledge-building and best practice management of marine environments. To facilitate objective and repeatable production of these maps, we have developed a number of semi-automated, rule-based GIS tools (Geoscience Australia’s Semi-automated Morphological Mapping Tools - GA-SaMMT) to operationalise the mapping of a common set of bathymetric high and bathymetric low seabed Morphological Features. The tools have a graphical user interface and were developed using Python scripts under the widely-adopted proprietary ArcGIS Pro platform. The utility of these tools was tested across nine case study areas that represent a diverse range of complex bathymetric and physiographic settings. Overall, the mapping results are found to be more consistent than manual mapping and allow for capture of greater detail across a range of spatial scales. The mapping results demonstrate a number of advantages of GA-SaMMT, including: 1) requirement of only a bathymetry grid as sole data input; 2) flexibility to apply domain knowledge to user-defined tool parameters, or to instead use the default parameter settings; 3) repeatability and consistency in the mapping outputs when using a consistent set of tool parameters (user defined or default); 4) high-degree of objectivity; and 5) efficiency in mapping a large number (thousands) of seabed morphology features in a single dataset. In addition, GA-SaMMT can comprehensively quantify the characteristics of individual seabed bathymetric high and low features, respectively generating 34 and 46 metrics for each type of feature. Our results indicate that attribute metrics are invaluable in the interpretation and modelling of mapped Morphology Features and provide insights into their formative processes and habitat potential for marine communities.

The design of artificial reefs must be based on the criteria of both durability and serviceability. In this respect, the seabed subsidence rate related to the weight of the reefs and of their foundation system should be limited. The horizontal drift of the reefs during their life should be small too. In this study, pertaining to the behavior of artificial reefs made of microsilica concrete and realized with foundations in bamboo near the international airport of Hong Kong, 1-year monitoring data and calculations of reef foundation settlements are shown and discussed to assess the performance of the adopted mixed foundation and to deduce the nature of the long-term subsidence. The subsidence related to the settlements of the foundations was monitored using a Multibeam Echo Sounder System. It was found that the observed subsidence rate cannot be justified by the primary consolidation of the soils forming the seabed. Indeed, secondary consolidation seems to play an important role. Overall, after one year of service, the artificial reefs are considered to be effective in terms of limitation of both subsidence and drift.

Internal solitary wave (ISW) is often accompanied by huge energy transport, which will change the pore water pressure in the seabed. Based on the two-dimensional Biot consolidation theory, the excess pore water pressure in seabed was simulated, and the spatiotemporal distribution characteristics of excess pore water pressure was studied. As the parameters of both ISW and seabed can affect the excess pore water pressure, the distribution of pore water pressure showed both dissipation and phase lag. And parametric studies were done on these two phenomena. Due to influenced by the phase lag of excess pore water pressure, the penetration depth under the site of northern South China Sea with total water depth 327 m, induced by typical internal solitary wave increased by 26.19%, 53.27% and 149.86% from T0 to T0.5 in sand silt, clayey silt and fine sand seabed, respectively. That means the effect of ISW on seabed will be underestimated if we only take into accout the penetration depth under ISW trough, especially for fine sand seabed. In addition, the concept of "amplitude-depth ratio" had been introduced to describe the influence of ISW on seabed dynamic response in the actual marine environment. In present study, it is negatively correlated with the excess pore water pressure, and an ISW with smaller amplitude-depth ratio can wide the range of lateral impacts. Our study results help understand the seabed damage induced by the interaction between ISW and seabed. [ABSTRACT FROM AUTHOR]

Wave-induced liquefaction of the seabed is a geohazard frequently encountered in shallow waters. Although widely discussed, most studies paid attention to the seabed response under a single sequence of wave loading. However, the seabed suffers from repeated 'wave loading-dissipation' phases in a real ocean environment. In this study, a homogeneous sandy seabed model is established to investigate the mechanism of wave-induced liquefaction by considering the existence of currents. Finite element analyses are conducted by incorporating a kinematic hardening elastoplastic model into the commercial package Abaqus. The constitutive model is validated against centrifugal wave tests. Parametric studies are conducted to demonstrate the effects of relative densities, current, and wave-loading history on the seabed response. The predicted excess pore pressure, effective stress paths, and associated variation of relative density are discussed in detail. The results show that the densification of soils significantly enhances the resistance against liquefaction, which provides new insight into the mechanism of residual liquefaction during wave sequences. [ABSTRACT FROM AUTHOR]

Context: Seamounts are abundant geomorphological features creating seabed spatial heterogeneity, a main driver of deep-sea biodiversity. Despite its ecological importance, substantial knowledge gaps exist on the character of seamount spatial heterogeneity. Objectives: This study aimed to map, quantify and compare seamount seascapes to test whether individual habitats and seamounts differ in geomorphological structuring, and to identify spatial pattern metrics useful to discriminate between habitats and seamounts. Methods: We mapped and classified geomorphological habitat using bathymetric data collected at five Southwest Indian Ridge seamounts. Spatial pattern metrics from landscape ecology are applied to quantify and compare seascape heterogeneity in composition and configuration represented in resulting habitat maps. Results: Whilst part of the same regional geological feature, seamounts differed in seascape composition and configuration. Five geomorphological habitat types occurred across sites, which within seamounts differed in patch area, shape and clustering, with ridge habitat most dissimilar. Across seamounts, the spatial distribution of patches differed in number, shape, habitat aggregation and intermixing, and outcomes were used to score seamounts on a gradient from low to high spatial heterogeneity. Conclusions: Although seamounts have been conceptualised as similar habitats, this study revealed quantitative differences in seascape spatial heterogeneity. As variations in relative proportion and spatial relationships of habitats within seamounts may influence ecological functioning, the proposed quantitative approach can generate insights into within-seamount characteristics and seamount types relevant for habitat mappers and marine managers focusing on representational ecosystem-based management of seamounts. Further research into associations of sessile and mobile seamount biodiversity with seascape composition and configuration at relevant spatial scales will help improve ecological interpretation of metrics, as will incorporating oceanographic parameters. [ABSTRACT FROM AUTHOR]

Complex bottom topography and the presence of floating ice significantly complicate the use of traditional sampling methods in Arctic coastal waters, forcing to look for alternative approaches. One such technique is underwater imagery, which has grown in popularity in recent decades based on its effectiveness in hard-to-reach places. We demonstrate that an underwater video mosaic can be a reliable method for comparative analysis of Arctic habitats under the glacier influence and glacier influence-free habitats. The filming was carried out in the upper sublittoral (2–65 m) of Hornsund and Isfjorden areas, representing two ice-free and two glaciated bays. Video footage was obtained using an ROV mounted and "drop-down" video cameras and transformed into 148 video mosaics. Based on the lowest possible taxonomic level, 31 biological features (morphospecies) were identified and ascribed to benthic functional groups based on their feeding and mobility type. The morphospecies and functional groups were used for the comparative analysis to reveal the ecologically meaningful differences in benthic community structure in different Arctic benthic habitats. We discovered greater abundances of motile scavengers in glacier-influenced bays whereas glacier influence-free bay had more sessile suspension filters and glacier influence-free riverine bay was dominated by discreetly motile and deposit feeders. Underwater imagery mosaics have proven to be a fairly reliable tool for fieldwork-efficient quantitative characterization of benthic communities in the hard-to-reach Arctic's upper sublittoral. [ABSTRACT FROM AUTHOR]

Contemporary cultural geographies have increasingly addressed subterranean and deep spaces through questions of access to earthly materials and the politics of resource extraction. This article engages with these themes through an investigation into the ‘doings’ or practices of seabed access. It does so by following the embodied and material experiences of two human geographers, an artist, a scientific coordinator and a microbiologist, who together undertook a day trip to learn shallow sediment coring in the Wadden Sea mudflats of Northern Germany. Stemming from a research project concerned with the accessibility of the seabed in international waters (how society can access its ‘common heritage’), we examine how taking samples from even the most accessible type of seabed – a shallow coastal mudflat within national waters that is not covered by seawater during low tide – presents a myriad of considerations, challenges and complications. We argue these are vital in examining the cultures of access – the embodied and material limits that define and shape participation in environments in which you and I have rights. These considerations, challenges and complications ranged from physical strength and balance requirements to an understanding of tidal movements, access to simple but specific equipment, appropriate clothing and private transport. We use ethnographic reflections and our photographic engagements to consider sedimentary relations: how we can and do relate to the seabed. [ABSTRACT FROM AUTHOR]

Mapping of coralligenous banks was carried out along the continental shelf of the northern and western margin of Sardinia Island (Italy, western Mediterranean Sea) in the context of the European Marine Strategy Framework Directive (MSFD, 2008/56/EC). Coralligenous banks are bioconstructions produced by calcareous coralline algae. Seafloor mapping was carried out through multibeam echosounder surveys and video transects, using a Remote Operating Vehicles (ROV), in areas not formerly explored. A high-resolution digital model of the seabed (DTM) was obtained from multibeam data. A total surface of 436 km2 of sparse patches of coralligenous banks was mapped in the depth range ~40-160 m. A final map of coralligenous habitat distributions along the western and northern continental shelf of Sardinia (scale 1:250,000) was produced. The base-map is formed by the shaded DTM of the seabed. Other mapped features include the edge of the continental shelf and the distribution of rocky seabed.

In spite of a proliferation of academic and policy-oriented interest in deep sea mining (DSM), this paper argues that two underlying questions remain underexplored. The first relates to what exactly the seabed is; the second to who the stakeholders are. It is argued that a greater interrogation of how the seabed is defined and understood, and a deeper consideration of how stakeholders are identified and the politics of their inclusion, is crucial to the enactment of policy and planning techniques. Through the analysis of current regulations to govern DSM in both national and international jurisdictions, this paper critically examines these seemingly banal but vital questions in different contexts. It is contended that most regulations are 'fuzzy' when it comes to addressing these questions, with the result that different understandings of the seabed and the implications of mining are ignored and that who stakeholders are and how they are defined causes many relevant voices to be unheard. It is argued, therefore, that it is imperative to address these often-overlooked questions directly in order to inform future seabed policy and governance. [ABSTRACT FROM AUTHOR]

This study aims to provide baseline data on microplastic (MP) concentrations in beach and seabed sediments of the SW Black Sea coast, and to identify possible sources of MP pollution in the area. MP concentrations in beach sediments in urbanised coastal areas, as well as in all seabed sediments, were on average higher than in other parts of the Black Sea and most other European seas. Urban coastal areas showed the highest average MP concentrations (mean ± SD): 464.44 ± 272.50 MP·kg -1 dry sediment in beach samples, 825.93 ± 396.30 MP·kg -1 dry sediment in seabed samples, while coastal sediments in an area with no local anthropogenic activities had significantly lower average MP concentrations: 84.44 ± 147.57 MP·kg -1 in beach samples, and 550.62 ± 245.71 MP·kg -1 in seabed samples. Possible identified sources of MPs include sewage water discharges, urban waste, coastal fisheries and aquaculture, as well as accumulation of marine litter on beaches and in adjacent offshore areas, serving as sources of secondary MP pollution., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Abstract Background and objectives The environmental effects of static gear fishing include habitat-level effects such as permanent changes to the physical environment and the structure of the benthic and epibenthic communities. Ecosystems subjected to prolonged exposure to pressure from static gear may undergo permanent changes and may never regain their prior ‘unfished’ state even if the fishing pressure is removed entirely. These long-term changes to physical structure of benthic habitats have implications for benthic biodiversity and ecosystem functioning. Despite this, the understanding of habitat and static fishing gear interactions is limited- with most studies focusing on the impact of mobile fishing gear. The rise of ecosystem-based fisheries management (EBFM), where managers and decision-makers manage target species within their environmental context while protecting essential ecosystem services and components, has led to an increased demand for ecosystem-level reference points. A systematic review could provide clarification on the short and long-term impacts of commercial static gear fishing on benthic community diversity. Methods This review will examine primary studies on the relationship between static fishing gear, intensity, and benthic biodiversity to answer the primary question ‘How do different types of static fishing gear affect benthic species richness and abundance?’. A structured search will be conducted in English. The search terms used to find relevant data to answer the research question were chosen specifically for this review and were generated using the R package litsearchr. Captured articles will be screened against pre-defined eligibility criteria. The internal and external validity of remaining studies will be classified using a pre-defined framework. Studies meeting validity will be used for data extraction. Data to be extracted includes data on study design, intervention, study results, habitat and geographical context. Outcome data (such as sample sizes, means and measures of variation such as confidence intervals, standard deviations, and standard errors) will also be extracted. Information on effect modifiers will also be collected where available as well as metadata on study methodologies and general article identifiers. Data will be used for both narrative and quantitative synthesis techniques.

Unmanned underwater vehicles (UUV) face maneuverability and rapidity challenges when they are applied for detecting and repairing submarine oil and gas pipelines, and fiber cables near the seabed. This research establishes numerical models of the bare UUV and self-propelled UUV near the seabed using the computational fluid dynamics (CFD) method. The effect of dimensionless distance Hd and R e L on the hydrodynamic performance of the vehicle and the interaction between the hull and the propeller is investigated. The range of Hd is 1.5D–10D, and the R e L is 9.97 × 105~7.98 × 106. Findings indicate that: (1) There is an obvious strong coupling between the hydrodynamic performance of the bare UUV and Hd. With the increase of Hd, the hydrodynamic performance such as C d , the absolute value of C l and m y decreases continuously and finally tends to be stable. The absolute values of C d and C l increase with the increase of R e L . The change trend of m y is opposite to that of C l . (2) The variation trend of hydrodynamic performance of the self-propelled UUV with Hd is consistent with those of the bare UUV. Additionally, it increases to some extent, respectively, compared with the bare UUV. (3) The self-propelled characteristics such as t , η H , w and η i are weakly related to Hd. The t and η i increase with the increasing of R e L , while η H and w decrease with the increasing of R e L . [ABSTRACT FROM AUTHOR]

Plastic pollution is an arising problem of our generation. Tons of plastics are globally produced affecting different coastal ecosystems. Plastics pile and end up in coastal areas, at the ocean surface, and in the coastal seabed. Almost 70% of plastics made are known to eventually sink in water, and it is suspected that ever-increasing amounts of plastics are accumulating in seabed sediments. However, there are limited studies on macroplastics in coastal seabeds in the different coastal ecosystems in the Philippines. This study aims to determine the prevalence, types, and density of macroplastic litters in the coastal seabed of Sultan Naga Dimaporo (SND), Lanao del Norte. A 100-m transect line with four quadrats measuring 5 m x 5 m, was delineated parallel to the seabed at the beaches of Barangay Pikalawag, Dabliston, Koreo and Sugod. Results revealed that all four sites were contaminated with plastic litter in which 55% were from Pikalawag, a residential area, 16% from Dabliston, a mangrove area, 15% from Sugod, a beach/tourism area, and 14% from Koreo, a non-residential area. The plastic density was 1.32 items/m for Pikalawag, and 0.32 to 0.37 items/m for the other areas. The waste collected was primarily food packaging (17%), plastic fragments (16%), and plastic bags (11%). The highest polymer type was LDPE (40%) followed by both multilayers (13%) and PET (13%). Based on the clean coast-index, Pikalawag can be categorized as extremely dirty while the other three sites were moderately clean. Overall, this study showed how the prevalence and composition of plastic litter vary in different coastal seabeds in SND, Lanao del Norte. [ABSTRACT FROM AUTHOR]

The article describes research on the use of local linear smoothing methods to remove artefacts resulting from the lossy compression of seabed's digital terrain model (DTM). In practice, when creating seabed models, DTM based on a regular grid is most often used. When recording larger surfaces, the amount of data collected in the structure can be very large (millions or even hundreds of millions of points) as discussed by Maleika et al. (2011). In such a case, it is possible to significantly reduce the amount of this data by using lossy compression methods. The vast majority of these methods divide the entire surface into small blocks and compress each of them independently. In the process of reconstruction (decompression), clearly visible distortions called artefacts form at the boundaries (edges) of these blocks. In the study, the author described the methods of linear data approximation, enabling the removal of distortions at the boundaries of blocks in the lossy compression/reconstruction process, while maintaining high model accuracy and International Hydrographic Organization (IHO) standards. During the research, methods based on polynomials (from the 1st to 9th degree) and linear approximation, cubic approximation and smoothing spline interpolation were tested. The developed smoothing method was then modified to work locally in places where compression artefacts occur. In the next stage, distortion-dependent smoothing was additionally developed so that the power of the smoothing method would be dependent on the amount of the distortion present. All tests were carried out with the use of three different test surfaces, assessing the obtained results both objectively (calculating the model error at the 95% confidence level) and subjectively (by visually assessing the distortions at the interface of the compression blocks). The results obtained were presented on many figures and tables and interpreted. Finally, the test plots after the developed distortion-dependent local smoothing method were shown in order to assess the obtained effects. The experiments presented in the paper and the results obtained show the true potential of linear smoothing methods in removing distortions resulting from the use of lossy compression methods of seabed's DTM. [ABSTRACT FROM AUTHOR]

It is estimated that within the UK exclusive economic zone (UK EEZ), 524 Mt of organic carbon (OC) is stored within seabed sediment. However, the stability and potential vulnerability of OC in these sediments under anthropogenic stressors, such as bottom trawling activity, remains poorly quantified. To improve our understanding of the areas where sedimentary OC is likely to be at greatest risk from trawling events, we have developed a carbon vulnerability ranking (CVR) to identify areas of the seabed where preventative protection may be most beneficial to help maintain current OC stocks while further research continues to shed light on the fate of OC after trawling (e.g., remineralization, transport, and consumption). Predictive maps of currently available fishing intensity, OC and sediment distribution, and sediment OC lability have been generated within ArcGIS using fuzzy set theory. Our results show that the west coast of Scotland represents one of the key areas where sedimentary OC is potentially at greatest risk from bottom trawling activity. This is due mainly to the high reactivity of these OC rich sediments combined with the pressures of repetitive trawling activity within inshore waters. Our research shows that these OC hotspots are potentially at risk of disturbance from bottom trawling activity and should be prioritized for the consideration of future safeguarding (management) measures to ensure emissions are minimized and to provide greater protection of this natural carbon capital resource.

In order to study the liquefaction of the seabed around the pipeline under wave loading, a two-dimensional numerical model was established based on Biot’s partly dynamic equation (u-p model). The dynamic response of the seabed around the pipeline under wave loading was investigated in detail, and the wave loading was applied on the seabed surface through pore pressure boundary. Based on the validation of the numerical model, the response and liquefaction of the seabed around the pipeline under wave loading were studied. The pore pressure, vertical effect stress, and liquefaction range of the seabed at different pipeline buried depths were investigated and the effects of wave height, soil permeability, and saturation were discussed. The results show that the pipeline buried depth has significant effects on the response and liquefaction of seabed under wave loading. The pipeline induces the vertical effective stress concentration of seabed around the pipeline. The effects of wave height, soil permeability, and saturation on the seabed response under wave loading are significant. The results provide a theoretical basis for the safety and stability of submarine pipeline in marine environment.

The observation and detection of the subsea environment urgently require large-scale and long-term observation platforms. The design and development of subsea AUVs involve three key points: the subsea-adapted main body structure, agile motion performance that adapts to complex underwater environments, and underwater acoustic communication and positioning technology. This paper discusses the development and evolution of subsea AUVs before proposing solutions to underwater acoustic communication and positioning navigation schemes. It also studies key technologies for the agile motion of subsea AUVs and finally gives an example of a solution for implementing underwater AUVs, i.e., the disk-shaped autonomous underwater helicopter (AUH). This paper will provide guidance for the design of subsea AUVs and the development of corresponding observation and detection technologies.