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Magma supply likely exerts primary control on seafloor morphology of oceanic crust, but most studies have related morphology to spreading rate. Here we examine global patterns of morphology on mid‐ocean ridge (MOR) flanks in relation to magma supply derived from residual mantle Bouguer gravity anomaly (proxy for relative crustal thickness) and spreading rate. We use multibeam bathymetry to characterize morphology using both qualitative (descriptive) and quantitative approaches, and we compare results to both magma supply and spreading rate. Morphology becomes more isotropic and abyssal hills are more irregular and discontinuous as magma supply decreases, while roughness, area of steeper slopes, and anomalous fabric orientation increase. We interpret these changes to reflect changing magma distribution along‐axis, from large‐volume and spatially extensive to progressively reduced, increasingly localized, and more irregularly emplaced. Observed relations between crustal thickness and morphology imply that average thickness of purely magmatic crust in the Atlantic and parts of the Indian ridge system is significantly less than average seismically determined crust. Thus seismically defined crustal thickness in those regions likely includes significant non‐magmatic components such as serpentinized mantle. Excepting regions of extensive mantle exposure, most morphologic parameters that we examined are sensitive to estimated magma supply but not necessarily to spreading rate alone. We summarize our results in schematic models that relate morphologic variations to changes in magma supply and mantle serpentinization throughout the global MOR system. Finally, we note that combined qualitative and quantitative results of our study may be useful for developing automated morphologic classification schemes. Plain Language Summary: Mid‐ocean ridges encircle the globe and spread apart along their axes to form ocean crust. Seafloor morphology of crust on the flanks of different ridges can be highly variable. The variations classically have been attributed to differences in spreading rate but there are notable exceptions to this correlation. Here we use changes in gravity over different mid‐ocean ridges (MORs) together with spreading rate to infer magma supply to the ridges, and we examine how morphology varies with changes in the magma supply. We find that features such as long, linear, and structurally continuous abyssal hills correlate well with high magma supply while progressively rougher, steeper, and more irregular morphology forms as magma supply is reduced; this is observed irrespective of spreading rate, indicating that magma supply better predicts morphologic style. Observed relations between crustal thickness and morphology imply that seismically determined crustal thickness in the Atlantic and parts of the Indian Ocean MOR system includes significant components of non‐magmatic crust (e.g., altered mantle). Our study characterizes crustal morphology both qualitatively (visually) and quantitatively; correlations between these characterizations may be useful for developing automated morphologic classification schemes. Key Points: Variable morphology of global mid‐ocean ridge flanks is examined qualitatively and quantitatively using multibeam bathymetric dataChange in magma supply as derived from gravity and spreading rate, plus mantle serpentinization, explains observed morphologic variationsMorphologic changes indicate thinner magmatic crust than seismically determined crust in the Atlantic and parts of the Indian Ocean [ABSTRACT FROM AUTHOR]

Multibeam sonar and high-resolution seismic mapping are marine geophysical techniques frequently employed to map the distribution and type of marine sediments. Both techniques involve the transmission and reception of acoustic pulses reflected by the seafloor and typically generate consistent and satisfactory results at a relatively low-cost relative to direct sampling. However, mainly due to their operational peculiarities (frequency range, beam width, etc.), each method generates some discrepancies regarding sedimentary distribution for the same area. Here, we compare three well-established marine geophysical techniques (Multibeam Echosounder (MBES) bathymetry and backscatter intensity, Sub-Bottom Profiler (SBP) echo-characterization, defined as the acoustic response of marine sediments as a function of its sedimentological properties, and seismic amplitude) applied to characterize seabed geology, analyzing comparing the results observed from each method. The study area is the glaciomarine environment of King George Bay, South Shetland Islands, Antarctica. We demonstrate that each method responds to specific characteristics of the seafloor, mainly because of divergent interactions between the acoustic signal and morphological features at different scales and sedimentological interfaces. Despite some consistencies, considerable mismatches in terms of classification approaches are apparent. Nevertheless, we show how these different classification approaches can be interpreted together to enable more precise geological understandings. [ABSTRACT FROM AUTHOR]

Cold seeps are widely developed on the seabed of continental margins and can form gas plumes due to the upward migration of methane-rich fluids. The detection and automatic segmentation of gas plumes are of great significance in locating and studying the cold seep system that is usually accompanied by hydrate layers in the subsurface. A multibeam echo-sounder system (MBES) can record the complete backscatter intensity of the water column, and it is one of the most effective means for detecting cold seeps. However, the gas plumes recorded in multibeam water column images (WCI) are usually blurred due to the interference of the complicated water environment and the sidelobes of the MBES, making it difficult to obtain the effective segmentation. Therefore, based on the existing UNet semantic segmentation network, this paper proposes an AP-UNet network combining the convolutional block attention module and the pyramid pooling module for the automatic segmentation and extraction of gas plumes. Comparative experiments are conducted among three traditional segmentation methods and two deep learning methods. The results show that the AP-UNet segmentation model can effectively suppress complicated water column noise interference. The segmentation precision, the Dice coefficient, and the recall rate of this model are 92.09%, 92.00%, and 92.49%, respectively, which are 1.17%, 2.10%, and 2.07% higher than the results of the UNet. [ABSTRACT FROM AUTHOR]

Given a growing global population and shift to embrace the blue economy, a need for marine spatial planning (MSP) has emerged in South Africa to sustainably resolve the rising conflicts over the use of marine and seabed resources and services. A well-developed marine spatial plan yields numerous ecological, social and economic benefits. These are achieved through mediating between spatially conflicting economic drivers' interests (e.g. commercial fishing, tourism, mining), preventing their activities from compromising thresholds of an environment's sustainability. Within the MSP framework, high-resolution geospatial datasets are required to document and describe the seabed in the highest possible detail. At any scale, integrated analysis of seabed geomorphology and habitats is anticipated to greatly improve the understanding of ecosystem functioning from a multidisciplinary perspective, whilst improving MSP procedures and management of marine space. South Africa is the first of few African countries to have an approved and implemented MSP framework, but is still somewhat behind globally in implementing large-scale regional hydroacoustic surveys to cover the country's vast offshore territory. The deficiency of hydroacoustic surveys is perhaps due to a relative lack of funds and poor communication about the value of multibeam echo-sounder (MBES) derived data, whilst marine geoscience remains a scarce skill in the country. This review paper presents a geological perspective of MSP and explores (1) the value that seabed mapping offers MSP specifically and (2) the need to increase seabed mapping with MBES, using a recently initiated project from the South African east coast as a case study. [ABSTRACT FROM AUTHOR]

Accurate bathymetric data in shallow water is of increasing importance for navigation safety, coastal management, and marine transportation. Satellite-derived bathymetry (SDB) is widely accepted as an effective alternative to conventional acoustic measurements in coastal areas, providing high spatial and temporal resolution combined with extensive repetitive coverage. Many previous empirical SDB approaches are unsuitable for precision bathymetry mapping in various scenarios, due to the assumption of homogeneous bottom over the whole region, as well as the neglect of various interfering factors (e.g., turbidity) causing radiation attenuation. Therefore, this study proposes a bottom-type adaption-based SDB approach (BA-SDB). Under the consideration of multiple factors including suspended particulates and phytoplankton, it uses a particle swarm optimization improved LightGBM algorithm (PSO-LightGBM) to derive depth of each pre-segmented bottom type. Based on multispectral images of high spatial resolution and in situ observations of airborne laser bathymetry and multi-beam echo sounder, the proposed approach is applied in shallow water around Yuanzhi Island, and achieves the highest accuracy with an RMSE value of 0.85 m compared to log-ratio, multi-band, and classical machine learning methods. The results of this study show that the introduction of water-environment parameters improves the performance of the machine learning model for bathymetric mapping. [ABSTRACT FROM AUTHOR]

The evolution of alluvial megafans has mainly been investigated in unconfined settings; however, at the boundary of these large depositional systems, the development of fluvial channels can be affected by structural constraints with regional extent. Here we present the study of the eastern sector of the megafan of Isonzo River, in the Gulf of Trieste, where this system fed through the southern Alps is constrained by the Karst and Istria cliffs. Although this area is now submerged under the northern Adriatic Sea, stratigraphy from seismo-acoustic profiles, drill cores and multi-beam bathymetry allows us to reconstruct the paleochannel system of the Isonzo River in detail, which was likely active within the period of 21–17.5 ka cal BP, at the end of LGM. This was reconstructed for over 50 km and currently represents the longest abandoned fluvial channel in the Mediterranean seabed. The occurrence of the mountain fringe and competition with nearby alluvial systems forced the paleochannel to follow the present coastline and conditioned the slope of its thalweg to decrease almost to null, resulting the transformation from the megafan to the undifferentiated alluvial plain. [ABSTRACT FROM AUTHOR]

The Newfoundland and Labrador Shelves Bioregion, located on the glaciated continental shelf and adjacent continental slope of eastern Canada, is classified into units that reflect its great physiographic diversity. There are ten shelf units: bedrock zone, fjord systems, major inlet, shelf-crossing troughs, four types of offshore banks, basin, and disturbed (glaciotectonic) terrain. There are three units on the continental slope: channelized areas, trough-mouth areas, and large sedimentary drifts. A series of vignettes illustrates both the distinguishing characteristics of the principal geomorphic units and the morphologic diversity within them. A sediment mobility analysis reveals that wave- and current-generated disturbances are dominant and largely depth-controlled within the shelf units, while the south-flowing Labrador Current impacts sediment transport and mobility along the continental slope. [ABSTRACT FROM AUTHOR]

Shallow bathymetry is important for ocean exploration, and the development of high-precision bathymetry inversion methods, especially for shallow waters with poor quality, is a major research aim. Synthetic aperture radar (SAR) image data benefit from a wide coverage, high measurement density, rapidity, and low consumption but are limited by low accuracy. Alternatively, multibeam data have low coverage and are difficult to obtain but have a high measurement accuracy. In this paper, taking advantage of the complementary properties, we use SAR image data as the content map and multibeam images as the migrated style map, applying the VGG19 neural network (optimizing the loss function formula) for bathymetric inversion. The model was universal and highly accurate for bathymetric inversion of shallow marine areas, such as turbid water in Taiwan. There was a strong correlation between bathymetric inversion data and measured data (R2 = 0.8822; RMSE = 1.86 m). The relative error was refined by 9.22% over those of previous studies. Values for different bathymetric regions were extremely correlated in the region of 20–40 m. The newly developed approach is highly accurate over 20 m in the open ocean, providing an efficient, precise shallow bathymetry inversion method for complex hydrographic conditions. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of back-siltation in the foundation trench for the immersed tunnel segments in the deep water area of the Shenzhen-Zhongshan Link after dredging in the foundation trench was completed, a multi-beam bathymetry system was used to observe the deep water foundation trench. The thickness and intensity of back-siltation in the foundation trench are calculated according to the observation results and the corresponding back -siltation difference data diagram was drawn with the Hypack software, so as to reflect the status of back -siltation of the tunnel segments in the deep water area in different time and space. The results of analysis show that, the spatial and temporal distribution of back-siltation in the foundation trench for the immersed tunnel segments in the deep water area is significantly different, which reflects the back-siltation characteristics after the deep water foundation trench is dredged and formed, and provides reasonable reference data for the subsequent dredging for Shenzhen-Zhongshan Link project and other related projects. [ABSTRACT FROM AUTHOR]

Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100–2600 m. Pockmarks are most concentrated at 400–850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes – (1) large (>0.5 km2 area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (∼100–200 m diameter; ∼0.008–0.03 km2 area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic. [ABSTRACT FROM AUTHOR]

We present a very high-resolution bathy-morphological map of the offshore sector around the Scoglio d’Affrica islet (northern Tyrrhenian Sea, Italy). The study area covers a sector of 45 km2, between 3 and 85 m depth. Its central part, i.e. the apex of the Ridge, is characterised by a flat or gently sloping seafloor, where three mud volcanoes, and 250 pockmarks are recognised. Differently, the western and eastern Ridge flanks are steeper and characterised by 60 quasi-rectilinear escarpments and small ridges, more than 20 morphological highs, and elongated channels occasionally floored by bedforms. The seafloor shallower than 40 m is covered by Posidonia oceanica, forming compact and continuous or fragmented meadows intermingled with sandy patches. The main map represents the bathy-morphological setting of the area, which is largely affected by fluid seepage, providing insights for habitat mapping and preliminary marine geohazard assessment due to the violent gas outburst from mud volcanoes. [ABSTRACT FROM AUTHOR]

We present the bathy-morphological map at a scale of 1: 50,000 of the area around the submerged Ferdinandea Island, the ‘Neverland’ of the Sicily Channel (central Mediterranean Sea). We investigate an area of 100 km², between 10 and 350 m, which is part of a triangular morphological high, 360 km² wide, representing the SE-wards prolongation of the Adventure Bank. The study is based on the morphometric analysis based on high resolution multibeam, and sub-bottom CHIRP profiles collected in 2015. The area around the remains of Ferdinandea Island is morphologically shaped by the interplay between volcanic, tectonic, fluid seepage, and oceanographic processes. Since the study area is considered a hot spot of biodiversity affected by maritime traffic (especially in Ferdinandea Channel) and hosting communication pipelines, this map provides insights both for habitat mapping purposes and preliminary marine geohazard assessment due to the occurrence of historically active submarine volcanoes, pockmarks, and mass transport deposits. [ABSTRACT FROM AUTHOR]

Analysis of high-resolution multibeam bathymetry, sub-bottom profiles, and multichannel seismic reflection data provides a novel understanding of a large-scale submarine landslide in the Cochin offshore region, southwestern continental margin of India. This massive submarine landslide is referred to name as the "Cochin slide". The Cochin slide exhibits a U-shaped slide scar with an average gradient of ~ 2°, which opens in the NNE-SSW trend in the lower slope and Laccadive Basin. The slide scar has a width of ~ 46 km and a total perimeter length of ~ 60 km, estimated with a volume of ~ 240 km3 excavated from this region. A non-sinuous channel with a length of ~ 36 km and having incisions varying from ~ 140 to 40 m from head to toe has developed within the slide scar. The submarine channel might have formed after the slide event facilitating channel incisions in the upper slope. The mass transport deposits associated with the slide have distributed over a wide area (~ 5700 sq. km.) in the lower slope and Laccadive Basin, with a maximum run-out length of ~ 138 km. The preconditioning factors or trigger mechanisms for the Cochin slide could not be precisely established yet. However, sedimentation during different geological times and the occurrence of weak layers might have contributed to the slope instability. The morphology of the Cochin slide, its correlation with the extensive faulting in the continental shelf-slope province, the presence of structural elements, and records of previous earthquakes suggest that the tectonic/geological processes strongly influence the triggering of the slide. [ABSTRACT FROM AUTHOR]

The ocean covers 71% of the Earth's surface. At present, only about 20% of the seafloor topography (ST) has been directly measured by ships, and most areas are predicted from satellite altimetry‐derived gravity products. In this study, an adaptive nonlinear iterative (ANI) method is proposed to address two major problems in gravity ST inversion: linear approximation and empirical seafloor density contrast (SDC). In ANI, the SDC is adaptively estimated as an output, while higher‐order Parker expansion and modified Bott's iteration are combined to recover nonlinear topography. We apply our new method using the DTU21GRA altimetric gravity model and single‐beam bathymetry to predict the ST in a part of the South China Sea. Results reveal that the average SDC in the study area is 1.24 g/cm3, which compares well to CRUST1.0. The root‐mean‐square (RMS) error between the nonlinear model and single‐beam checkpoints is 102.1 m, which is improved by 34.5%, 29.2%, and 18.3% compared with the non‐gravity model, topo_24.1, and linear model, respectively. The RMS error between the nonlinear model and multibeam bathymetry is 91.0 m, which is better than the linear model. Analysis of two‐dimensional profiles shows that the nonlinear model reveals more terrain details than the linear model. Plain Language Summary: Seafloor bathymetry has important significance for understanding ocean tectonic evolution and ocean circulation. Bathymetric mapping with shipborne sonar instruments is feasible but expensive and time‐consuming. After decades of efforts, only about 20% of the seafloor topography (ST) is directly mapped, and the remaining is predicted by satellite altimetry‐derived gravity products. This study uses the latest gravity model and proposes a new method to refine the ST in a part of the South China Sea. The new method has several advantages. First, it does not require preset an empirical density parameter. Second, it is based on a more rigorous mathematical relationship between seafloor bathymetry and gravity. Using this method, we find that the density contrast between seawater and topography is far less than the theoretical value; the ST estimated by the new method can reveal more detailed terrain and improve accuracy, especially in rugged areas. Key Points: Seafloor topography (ST) and density contrast are simultaneously predicted by using altimetry‐derived gravity data and ship soundingsHigher‐order Parker expansion and iteration are applied to model the nonlinearities between gravity and bathymetryA refined ST model of the South China Sea has been constructed to reveal more terrain details [ABSTRACT FROM AUTHOR]

A High-Definition (HD) map is an essential component not only for autonomous vehicles but also for surveyors in favor of city management. Moreover, the HD map must be up-to-date by reflecting environmental changes continuously. The development of LiDAR Simultaneous Localization And Mapping (SLAM) techniques has provided an effective way to collect precise point clouds for the construction of HD maps, while traditional methods are time-consuming and labor-intensive on account of the complex street scene. Furthermore, life-long 3D mapping is quite necessary and challenging nowadays. In this paper, we introduce a novel change-aware 3D online mapping framework CAOM, 1 1 Code at https://github.com/DCSI2022/CAOM. using point clouds collected by Multi-Beam LiDAR (MBL) and Push-Broom LiDAR (PBL) for rapid city map update and change detection. Concerning the prior map with higher precision, heterogenous fusion is performed to rectify the SLAM drift, based on the View-Traced Clouds (ViTC) derived according to their view in common. Meanwhile, corresponding virtual range images are integrated with distance images to detect the 3D changes between the current map and the historical reference map offline. The detection results are later fused in a probabilistic way along with the homogeneous fusion process where a resilient graph consisting of diverse factors is established to maintain the local and global consistency of the final point cloud map. Compared with 3D-CSTM, the real-world experiments have shown an average 0.5 m and max 1.5 m improvement in the ATE (Absolute Translation Error) of the trajectory generated by our system. Quantitative measurements on the individual point accuracy are also conducted to verify the performance of 3D mapping with up to 16% improvement in comparison with respect to the 3D-CSTM method. The effects of the disparity detection and probabilistic fusion can be revealed from the small objects distinguished in the point cloud map as well as > 95% overall accuracy. [ABSTRACT FROM AUTHOR]

Only approximately 20% of the global seafloor topography has been finely modeled. The rest either lacks data or its data are not accurate enough to meet practical requirements. On the one hand, the satellite altimeter has the advantages of large-scale and real-time observation. Therefore, it is widely used to measure bathymetry, the core of seafloor topography. However, there is often room to improve its precision. Multibeam sonar bathymetry is more precise but generally limited to a smaller coverage, so it is in a complementary relationship with the satellite-derived bathymetry. To combine the advantages of satellite altimetry-derived and multibeam sonar-derived bathymetry, we apply deep learning to perform multibeam sonar-based bathymetry correction for satellite altimetry bathymetry data. Specifically, we modify a pretrained VGGNet neural network model to train on three sets of bathymetry data from the West Pacific, Southern Ocean, and East Pacific. Experiments show that the correlation of bathymetry data before and after correction can reach a high level, with the performance of R2 being as high as 0.81, and the normalized root-mean-square deviation (NRMSE) improved by over 19% compared with previous research. We then explore the relationship between R2 and water depth and conclude that it varies at different depths. Thus, the terrain specificity is a factor that affects the precision of the correction. Finally, we apply the difference in water depth before and after the correction for evaluation and find that our method can improve by more than 17% compared with previous research. The results show that the VGGNet model can perform better correction to the bathymetry data. Hence, we provide a novel method for accurate modeling of the seafloor topography. [ABSTRACT FROM AUTHOR]

Based on the multi-beam bathymetry survey system of the Dalian Bay Subsea Tunnel immersed tube installation project, the bathymetry survey accuracy of the multi beam bathymetry survey system is analyzed in view of the source of measurement error, and the comparison plate is arranged and the comparison elevation is controlled by leveling. After the external conditions are consistent, two kinds of multi-beam bathymetry survey systems and single beam bathymetry survey system are used to measure the comparison plate elevation. Compared with the results of leveling survey, the difference of bathymetric survey accuracy of different systems is analyzed to verify the accuracy of the multi-beam bathymetric survey system used in the Dalian Bay Subsea Tunnel. The analysis method presented in this paper can be used as a guide for verifying the accuracy of other bathymetry systems. [ABSTRACT FROM AUTHOR]

In the engineering construction of immersed tube tunnel, the foundation bed bathymetry is an important part of the foundation construction, and high -precision foundation bed bathymetry is an important guarantee for the quality of the foundation engineering. Relying on the gravel leveling test project of the submarine tunnel foundation bed of Shenzhen Zhongshan Link project, the research and application of high-precision detection technology based on multi-beam bathymetry system was carried out. The underwater same position parameter conversion comparison method was used to realize the testing and verification of the accuracy of multi-beam bathymetry system by geodetic high precision instruments. The calibration and error mandatory correction of the data processing model of multi -beam system by setting the underwater elevation ratio measurement steel plate effectively improves the accuracy of foundation bed laying. By comparing the multi-beam sweep data with the results of penetration measurement, the results are basically consistent, which indicates that the multi -beam bathymetry system meets the project needs. The high-precision detection technology of multi-beam bathymetry system for immersed tunnel foundation construction can provide reliable reference data for underwater foundation construction. [ABSTRACT FROM AUTHOR]

The formation and geology of oceanic plateaus are incompletely understood, in part because geophysical data are sparse and of low density. This paper presents an improved high‐resolution bathymetry map for southern Shatsky Rise, by combining newly acquired multibeam bathymetry data from several cruises and by filling in gaps in multibeam coverage with the SRTM15+ global bathymetry model. This map provides important insights on the evolution of Shatsky Rise from plateau forming, to post‐plateau secondary volcanism, to sedimentation, erosion, and sedimentary mass wasting. Tamu Massif is segmented by several subdued bathymetric troughs that divide the massif flanks into smaller rises. The segmentation pattern suggests Tamu Massif was built by a series of eruptions along a jumping triple junction. The distribution of secondary volcanic cones is non‐uniform, with most occurring on the southern and eastern flanks. Most of these secondary cones occur as short chains that parallel nearby magnetic lineations, suggesting control by spreading ridge parallel faults. These results suggest the evolution of Shatsky Rise was largely controlled by spreading ridges during its active volcanic phase. Numerous escarpments were identified around the plateau, a majority of which parallel bathymetry contours, suggesting these features developed because of differential subsidence of the rise massifs. The map reveals widespread mass wasting and downslope sediment movement, shifting sediment distribution and changing the surface morphology. Improved topography improves our understanding of the evolution of Shatsky Rise and emphasizes the importance of bathymetry data in deciphering the geodynamic evolution of large igneous provinces. Plain Language Summary: Shatsky Rise is a large oceanic plateau located in northwest Pacific Ocean offshore Japan. It formed from hotspot volcanism that erupted along a moving triple junction, forming volcanic mountains along the way, of which Tamu Massif and Ori Massif are the largest. We present new high‐resolution bathymetry map of southern Shatsky Rise by merging newly available multibeam data with existing data and filling gaps in coverage with ba/thymetry estimated from satellite altimetry. Studies considered Tamu Massif as a large edifice formed from voluminous ridge‐centered eruptions. However, the map reveals Tamu Massif to be segmented by several shallow valleys that divide it into five smaller mountains, each forming at a jumping triple junction, suggesting that Tamu Massif was built by a series of ridge‐centered eruptions. The map also shows non‐uniform distribution of secondary volcanic cones over Tamu Massif, majority of them located over eastern and southeastern flanks due to preferential volcanism occurring near the Pacific‐Farallon ridge. When a volcano becomes dormant, it becomes covered with sediments, a process often thought to be simple accumulation. We discovered evidence of substantial sedimentary movement that has occurred and is likely still occurring, suggesting that volcano morphology can significantly vary long after it becomes volcanically inactive. Key Points: We present a high‐resolution bathymetry map of southern Shatsky Rise with greater multibeam coverage revealing small‐scale surface featuresTamu Massif is subtly segmented into 5 smaller rises consistent with formation by series of ridge eruptions along a jumping triple junctionSecondary volcanic cones are distributed mainly over the southern and eastern flanks, and many have trends implying spreading ridge control [ABSTRACT FROM AUTHOR]

SUMMARY: Makran subduction zone is very active with ∼38 mm yr−1 convergence rate and has experienced great earthquakes in the past. The latest great earthquake of 1945 M w 8.1 event also triggered a large tsunami and led to ∼4000 casualties. However, due to incomplete historical seismicity records and poor modern instrumentation, earthquake mechanism, co-seismic slip and tsunami characteristics in Makran remain unclear. On 2017 February 17, an M w 6.3 earthquake rattled offshore Pasni of Pakistan in the eastern Makran, marking the largest event after the 1945 M w 8.1 earthquake with good geodetic and geophysical data coverage. We use a combination of seismicity, multibeam bathymetry, seismic profile, InSAR measurements and tide-gauge observation to investigate the seismogenic structure, co-seismic deformation, tsunami characteristics of this event and its implication for future major earthquakes. Our results indicate that (1) the earthquake occurred on the shallow-dipping (3°–4°) megathrust; (2) the megathrust co-seismically slipped 15 cm and caused ∼2–4 cm ground subsidence and uplift at Pasni; (3) our tsunami modelling reproduces the observed 5-cm-high small tsunami waveforms. The Pasni earthquake rupture largely overlaps the 1945 slip patch and disturbs the west and east megathrust segments that have not ruptured yet at least since 1765. With such stress perturbation and possible stress evolution effect from the 1945 earthquake, the unruptured patches may fail in the future. This study calls for more preparedness in mitigating earthquake and associated hazards in the eastern Makran. [ABSTRACT FROM AUTHOR]

This study investigates the postglacial sea-level history of eastern Cumberland Peninsula, a region of Baffin Island, Nunavut, where submerged terraces were documented in the 1970s. The elevation gradient of emerged postglacial marine-limit deltas and fiord-head moraines led Arthur Dyke to propose a conceptual model for continuous postglacial submergence of the eastern peninsula. Multibeam mapping over the past decade has revealed eight unequivocal submerged deltas at 19–45 m below present sea level (b.s.l.) and other relict shore-zone landforms (boulder barricade, spits, and sill platform) at 16–51 m b.s.l. Over a distance of 115 km from Qikiqtarjuaq to Cape Dyer, the submerged coastal features increase in depth toward the east, with a slope (0.36 m/km) less than that of the marine-limit shoreline previously documented (0.58–0.62 m/km). The submerged ice-proximal deltas, deglacial ice limits, and radiocarbon ages constrain the postglacial lowstand between 9.9 and 1.4 ka cal BP. The glacial-isostatic model ICE-7G_NA (VM7) computes a lowstand relative sea level at 8.0 ka, the depth of which increases eastward at 0.28 m/km. The difference between observed and model-derived lowstand depths ranges from 1 m in the west to 10 m in the east and the predicted tilt is significantly less than observed (p = 0.0008). The model results, emerging data on Holocene glacial readvances on eastern Baffin Island, and evidence for proglacial delta formation point to a Cockburn (9.5–8.2 ka) age for the lowstand, most likely later in this range. This study confirms the 1970s conceptual model of postglacial submergence in outer Cumberland Peninsula and provides field evidence for further refinement of glacial-isostatic adjustment models. [ABSTRACT FROM AUTHOR]

Small‐scale convection beneath the oceanic plates has been invoked to explain off‐axis nonplume volcanism, departure from simple seafloor depth‐age relationships, and intraplate gravity lineations. We deployed 30 broadband ocean bottom seismometer stations on ∼40 Ma Pacific seafloor in a region notable for gravity anomalies, measured by satellite altimetry, elongated parallel to plate motion. P‐wave teleseismic tomography reveals alternating upper mantle velocity anomalies on the order of ±2%, aligned with the gravity lineations. These features, which correspond to ∼300°–500°K lateral temperature contrast, and possible hydrous or carbonatitic partial melt, are—surprisingly—strongest between 150 and 260 km depth, indicating rapid vertical motions through a low‐viscosity asthenospheric channel. Coherence and admittance analysis of gravity and topography using new multibeam bathymetry soundings substantiates the presence of mantle density variations, and forward modeling predicts gravity anomalies that qualitatively match observed lineations. This study provides observational support for small‐scale convective rolls beneath the oceanic plates. Plain Language Summary: Covered by kilometers of water and therefore hard to access, Earth's oceanic tectonic plates have several features we cannot explain. Among these are linear undulations ("rolls") in the strength of gravitational acceleration at the sea surface. Using data from a rare underwater seismic experiment, we have produced 3‐D maps of seismic properties of the Earth's sub‐surface in a location of clear gravity rolls. We find linear blobs of fast and slow material in the mantle beneath the oceanic plate, parallel to the gravity features. These represent cold sinking and warmer rising material, revealing a highly dynamic convective system underneath the plate, which has long been theorized but not previously directly observed at this scale. Key Points: We use ocean bottom seismometer data to image elongated upper mantle P‐wave velocity anomalies, of order ±2%, striking parallel to free air gravity lineationsThese features extend >200 km deep, requiring thermal anomalies and small‐fraction partial melts related to volatiles in the asthenosphereAnomalies are inferred to arise from small‐scale convective cells beneath the plate with a planform parallel to absolute plate motion [ABSTRACT FROM AUTHOR]

Tectonic and climate evolution could be well archived in deep-water stratigraphy. Based on newly acquired high-resolution two-dimensional (2-D) multichannel seismic profiles and multibeam bathymetry, together with Ocean Drilling Program/International Ocean Discovery Program (ODP/IODP) data, this study investigated the late Miocene-Quaternary deep-water seismic stratigraphy, sedimentary evolution, and responses to regional tectonic and climatic variations at the northeastern margin of the South China Sea. The late Miocene-Quaternary stratigraphy consists of three units (i.e., SU-1, SU-2, and SU-3 from bottom to top) that are dated to 10.5-6.5 Ma (stage 1), 6.5-0.9 Ma (stage 2), and 0.9 Ma-present (stage 3), respectively. SU-1 is dominated by sheeted drifts with slight thickness variation, but SU-2 and SU-3 mainly consist of mounded, lenticular contourite drifts and channel-like moats. This suggests that the bottom currents intensified from stage 1 to stage 2, which was probably caused by the sill uplifting at the Luzon Strait under the influence of tectonic collision between the Luzon arc and Eurasia since ca. 6.5 Ma. SU-2 and SU-3 are separated by a basinwide high-amplitude seismic reflection, across which the average sedimentation rate shows a dramatic increase from ~28 m/m.y. in SU-2 to ~144 m/m.y. in SU-3. The high sediment supply since 0.9 Ma could be linked to the mid-Pleistocene climate transition, which resulted in abundant rainfall that promoted the Taiwan orogen to contribute more sediments to the South China Sea. This study indicates that the deep-water stratigraphy recorded the tectonic collision around the sole deep-water gateway (i.e., Luzon Strait) and mid-Pleistocene climate transition event at the northeastern South China Sea margin, which has important implications for understanding the relationships among the tectonic, paleoclimatic, paleoceanographic, and deepwater sedimentary processes in the largest marginal basin of the western Pacific Ocean. [ABSTRACT FROM AUTHOR]

The article scrutinizes stratigraphy, morphology, and origin of the terraced underwater slope of the Sambia Peninsula next to the Taran Cape, the SE Baltic Sea, using a combination of multi-beam and single-beam bathymetry, side-scan sonar survey, CHIRP, single-channel seismoacoustic data, and sediment grain-size results. The underwater slope and its minor landforms were formed by changes of a relative sea-level during the Late Pleistocene and Holocene. Landforms, such as terraces and palaeo cliffs, sinks, remnants, stacks, karst sinkholes, ravines, cuestas, and drowned valleys, are associated with positions of older shorelines, sea-level changes and outcropped Pre-Quaternary formations. Six main stages of the underwater slope development have been recognized. The most important topographic feature is a high palaeo cliff (10 m high) with its toe at a water depth of 26–34 m. The cliff was cut in Cretaceous deposits and has different age and origin in different locations. Its northern sector with a toe at a depth of 34–35 m is polygenetic, formed by tectonic faulting and subsequent abrasion at the Baltic Ice Lake stage. The southern sector, with a toe at a depth of 26–27 m, was cut by wave erosion at the Ancylus Lake stage. Terraces on the underwater slope at depths of 29 m, 34 m, 40 m, 43 m, 48 m and 52 m b.s.l. were formed probably by the Baltic Ice Lake and Yoldia Sea transgressions and survived owing to relatively rapid and short changes of the sea-level. At a depth of 0–26 m, at a sea-level slowstand, selective erosion formed a transgressive wave ravinement surface with karst and cuesta-like landforms on monoclinal Paleogene beds. The depths and the locations of described terraces and palaeo cliffs in the SE Baltic Sea allow us to rectify the relative sea-level curve for the Late Pleistocene-Holocene. [ABSTRACT FROM AUTHOR]

At present, only approximately 10% of the global seafloor topography has been finely modeled, and the rest are either lacking in data or not accurate enough to meet practical requirements. On the one hand, satellite altimeter has the advantages of large-scale and real-time observation, thus is widely used in the measurement of bathymetry, the core of seafloor topography. However, there is often room for improvement in its precision. On the other hand, multibeam echosounder bathymetric data is highly precise but normally limited to a smaller coverage, which forms a complementary relationship with the bathymetry derived from satellite altimetry. To combine the advantages of satellite altimetry-derived and multibeam sonar-derived bathymetry, we apply deep learning, which is powerful in the field of digital image automation, to perform multibeam sonar-based bathymetry correction for satellite altimetry bathymetry data. Specifically, we modify and improve a pretrained VGGNet neural network model with a depth of 19 layers to train on three sets of bathymetry data from the West Pacific, Southern Ocean, and East Pacific, respectively. Experiments show that the correlation of bathymetry data before and after correction can reach a high level, with the performance of R² being as high as 0.81 and the RMSE improved over 19% compared with previous research. We then explore the relationship between R² and water depth and conclude that it varies at different depths and thus the terrain specificity was a factor that affects the precision of correction. Finally, we use the difference of water depth before and after the correction to evaluate the correction results, and find that our method can improve by more than 17% compared with previous research. The results show that using the deep learning VGGNet model can better perform the correction of the bathymetry derived from satellite altimetry, thus providing a method for accurate modeling of the seafloor topography. [ABSTRACT FROM AUTHOR]

Lipari is the largest and most populated island in the Aeolian Archipelago, a UNESCO site, and a highly frequented touristic destination. As in many other insular settings, the low-lying coastal stretches in the E and NE sectors of Lipari are locally exposed to coastal erosion and flooding, enhanced by subsidence effects leading to local sea level rise. Most of these coastal sectors appear critical, being narrow and increasingly threatened by the risk of permanent inundation and beach disappearance. In this study, this setting is placed in the wider context of the decadal evolution of the main beaches, analysed through a multidisciplinary approach, which includes remote sensing techniques (aero-photogrammetry, unmanned aerial vehicle survey, and satellite data), offshore geophysical surveys (high-resolution multibeam bathymetry), and field observations. The results show a variable interaction in space and time between natural and anthropogenic factors in the long- and mid-term evolution of the studied coastal areas. Considering that part of the local economy at Lipari depends on beach tourism, proper future management is required in the view of natural risk reduction and in the light of future climate changes and related impacts. [ABSTRACT FROM AUTHOR]

A detailed map of the seafloor relief of a unique area of the intraplate lithosphere deformation in the Central Basin of the Indian Ocean was constructed for the first time. The data were obtained by a bathymetric survey with the use of a multibeam echosounder during the 42nd cruise of R/V Akademik Boris Petrov and cruise SO258 of R/V Sonne in 2017. The chaotic distribution of deformed hilly rises of an isometric shape and the significant difference in the morphology of all these rises are clearly shown. The new map did not confirm the existing concepts about the corrugated structure of the deformation area as a series of extended E–W undulations (linear ridges and troughs), which were considered to be formed by warping of the lithosphere by the N–S compression of the Indian Plate. The revealed morphology of the seafloor relief testifies to the mosaic-block pattern of the deformation area. This structure is formed by isometric deformed tectonic blocks, the different structure of which is determined by inhomogeneities in the lithosphere of the plate that existed at the time of the deformation. [ABSTRACT FROM AUTHOR]

Two wide-angle seismic reflection/refraction profiles were acquired to determine the velocity characteristics of the Meguma terrane and adjacent Avalonia northeast of the Cobequid-Chedabucto Fault Zone (CCFZ) in eastern Canada. Line 99–1 is located along the Scotian margin whereas line 99–2 crosses the Scotian margin and onshore Nova Scotia and extends into the Gulf of St. Lawrence. Velocity models were derived by forward modelling of travel times. P-wave velocities of 5.5–6.0 km/s and 6.0–6.4 km/s are interpreted to be metasedimentary rocks of the Goldenville and Halifax groups and granitic rocks, respectively. This inference is based on comparison with laboratory velocities of a suite of rock samples, offshore sampling, links to onshore geology with multibeam bathymetry, and gravity modelling. On both lines a low velocity zone (LVZ) >350 km wide and up to 15 km thick is present at mid-crustal levels. The LVZ is not observed beneath onshore Nova Scotia or northeast of Orpheus Graben, the offshore extension of the CCFZ. The crustal thickness of the Meguma terrane varies between 31 and 38 km; in contrast, the Moho is at a depth of 41 km beneath Avalonia. The velocity of the lower crust on line 99–2 is 6.8–7.1 km/s beneath the LVZ and Avalonia, and 6.6 km/s beneath onshore Meguma terrane. Poisson's ratios calculated from P- and S-wave velocities are 0.19–0.23 in the Meguma terrane crust; in contrast, Poisson's ratios of 0.24–0.25 are indicated for Avalonian crust. • Seismic reflection/refraction, gravity, and rock density/velocity data were obtained. • Two velocity/depth models were generated onshore and offshore of Nova Scotia, Canada. • Both models show an extensive low-velocity zone in the offshore Meguma terrane. • Meguma terrane has crustal structure different from that of adjacent Avalonia. • Avalonia extends only 30 km under Meguma terrane in faulted contact. [ABSTRACT FROM AUTHOR]

The central West Philippine Basin (WPB) comprises three contrasting geomorphologic provinces, the mantle-plume type Benham Rise in west, the volcanic arc-type Kyushu-Palau Ridge (KPR) at the east limit, and the in-between central rift hosting the deepest (∼7874 m) rifted seafloor. However, their morphic transit and dynamic interactions remain elusive owing to the insufficiency of relevant data. By incorporating new and previous multibeam bathymetry data fully enveloping the central rift, we synthesized a 3-band, 3-segment seafloor fabric of the central WPB and deduced its formation mechanisms. The bathymetry documents prominent across- and along-axis variations and variable landform assemblages, including: 1) overall trends of abyssal hill lineation swing counter-clockwise from ∼N100/105°E at a distance of 100 km from the fossil rift valley to ∼N85/95°E at a distance of ∼30/50 km, then clockwise to ∼N100/140°E in the rift valley, which recognizes three irregularly bands (I, II, and III ripping into II) and a rotatory spreading fabric; 2) the rift valley narrows westward from ∼85 km wide near the KPR to ∼25 km at Centric Deep, and then fades out to further west, synchronously from magmatic to amagmatic then to failed, indicating a northwestward propagating stirred by the KPR volcanism. Moreover, it is found in the middle segment that three major transform faults bend southwesterly into Southern Band I with their concaves pointing to the Benham Rise. Behaving as pseudo-faults, they are likely triggered by the former magmatism of the Benham Rise. Lying just at the intersection of a relict nodal basin and the western tip of the later PR, the Centric Deep might have resulted from overprinting amagmatic extension on former pull-apart. Thus, the geomorphic fabric featuring high spreading instability reflects strong magma-tectonic intervention by excessive magmatism of mantle plume and subduction arc. • An uneven 3-band, 3-segment geomorphic fabric is recognized in the central WPB. • The inner band is magma-richer and wider near the volcanic KPR than else segments. • The outer band sees transform faults curving to the Benham Rise in the west. • The unstable fabric results from two generations of magma-stirred rift propagator. [ABSTRACT FROM AUTHOR]

Three-dimensional deep-sea structures enhance substrate complexity and can shape numerous ecological hotspots that play critical roles in the diversity and distribution of benthic faunal assemblages. The characteristics of these features are not fully understood due to the logistical challenges of exploring at great depths and remote locations. One such deep-sea feature, the Wallaby-Zenith Fracture Zone (WZFZ) located in the East Indian Ocean, was mapped using a full-ocean depth multibeam echosounder system. Additionally, twelve baited landers and five crewed submersible dives were conducted in water depths between 4709 and 6591 m. We use seafloor bathymetry, bathymetric derivatives and video footage from the submersible dives to characterise the benthic structures, substrate types, habitat diversity, and the distribution of associated functional groups of megafauna for the WZFZ. The Benthic Terrain Modeler toolbox was used as an initial semi-automated step to generate benthic structural classes, which were further characterized through the inclusion of bottom salinity and temperature data collected by the scientific landers and integrated with the observations of seafloor substrate from the submersible video footage. This resulted in identification of nine benthic habitat classes characterised by unique seafloor morphological structure and substrate texture. A polymetallic nodule field, a possible extension of the previously reported Cape Leeuwen nodule field, was also observed along submersible transects conducted on the slopes of the WZFZ. The distribution and diversity of the functional megafauna groups observed are influenced by the deep-sea benthic habitats, defined by seafloor structures and substrate heterogeneity, especially the presence of hard substrates such as outcropping bedrock and polymetallic nodules within the WZFZ. • High resolution multibeam bathymetry of the Wallaby-Zenith Fracture Zone was mapped. • Structural classes and substrate types of the fracture zone were analysed. • A large polymetallic nodule field, a possible extension of the Cape Leeuwin nodules was discovered. • Benthic habitats were associated with megafauna functional groups. • Diversity and abundance of the benthic megafauna were supported by environmental heterogeneity. [ABSTRACT FROM AUTHOR]

Over the course of 10 months, the global Five Deeps Expedition (2018–2019) mapped ~550,000 km2 of seafloor of which 61% comprised new coverage over areas never before surveyed and ~30% was acquired from some of the ocean's deepest trenches and fracture zones. The deepest points of each ocean were mapped using a latest‐generation, full‐ocean depth Kongsberg EM 124 multibeam echosounder. These extreme depths were corrected using Conductivity, Temperature and Depth (CTD) data from sea surface to full ocean depth. The deepest place in each ocean were identified as the Brownson Deep, Puerto Rico Trench in the Atlantic Ocean (8,378 ± 5 m), an unnamed deep within the South Sandwich Trench in the Southern Ocean (7,432 ± 13 m), an unnamed deep within the Java Trench in the Indian Ocean (7,187 ± 13 m), Challenger Deep within the Mariana Trench in the Pacific Ocean (10,924 ± 15 m), and the Molloy Hole in the Arctic Ocean (5,551 ± 14 m). As part of the overarching mission of the Five Deeps Expedition, and to clarify beyond doubt the deepest point in the Indian, Pacific and Southern oceans, other sites were visited that had been postulated as potential deepest locations. This study has confirmed that the Horizon Deep within the Tonga Trench is the second deepest point in the Pacific Ocean (10,816 ± 16 m), the Dordrecht Deep within the Diamantina Fracture Zone is not the deepest point in the Indian Ocean (7,019 ± 17 m) and that in accordance with the guidelines of the Antarctic Treaty and International Hydrographic Organisation, although the Meteor Deep is the deepest point in the South Sandwich Trench (8,265 ± 13 m) it is located within the waters of the Atlantic Ocean and not the Southern Ocean. [ABSTRACT FROM AUTHOR]

Rocky reefs provide complex structures in the otherwise largely sand-dominated coastal North Sea. Therefore, these reefs are highly important natural habitats for the functioning of coastal ecosystems, as they provide shelter, refuge and nursery grounds for various mobile and sessile species. In the North Sea, the spatial distribution of these habitats has been intensively investigated over recent years. However, these studies generally provide static accounts of the current state of these reef systems, but limited data exist on the temporal variations in sediment dynamics at and around natural rocky reefs. In this study, we provide observations from a multiannual time series of hydroacoustic seafloor surveys conducted at an isolated rocky reef in the North Sea. We use multibeam bathymetry and side-scan sonar backscatter data in combination with video observations, sediment sampling, and sub-bottom profiler data to assess the long-term variations of the rocky reef system. The reef is located in water depths between 11 and 17 m with an areal extent of ~0.5 km2 and is surrounded by mobile sands. The topography of the rocky reef appears to create a distinct hydrodynamic system that permits mobile sands to settle or move into bathymetrical deeper parts of the reef. Our results suggest a very dynamic system surrounding the reef with large scale scouring, sediment reworking and transport, while the shallower central part of the reef remains stable over time. We demonstrate the importance of hydrodynamics and current scouring around reefs for the local variability in seafloor properties over time. These small-scale dynamics are likewise reflected in the spatial distribution of sessile species, which are less abundant in proximity to mobile sands. The hydroacoustic mapping and monitoring of seafloor dynamics at higher spatial and temporal resolutions presents an important future direction in the study of valuable coastal habitats. [ABSTRACT FROM AUTHOR]

Over the past decade, Multibeam Echosounders (MBES) have become one of the most used techniques in sea exploration. Modern MBES are capable of acquiring both bathymetric information on the seafloor and the reflectivity of the seafloor and water column. Water column imaging MBES surveys acquire significant amounts of data with rates that can exceed several GB/h depending on the ping rate. These large file sizes obtained from recording the full water column backscatter make remote transmission difficult if not prohibitive with current technology and bandwidth limitations. In this paper, we propose an algorithm to decorrelate water column and bathymetry data, focusing on the KMALL format released by Kongsberg Maritime in 2019. The pre-processing stage is integrated into FAPEC, a data compressor originally designed for space missions. Here, we test the algorithm with three different datasets: two of them provided by Kongsberg Maritime and one dataset from the Gulf of Mexico provided by Fugro USA Marine. We show that FAPEC achieves good compression ratios at high speeds using the pre-processing stage proposed in this paper. We also show the advantages of FAPEC over other lossless compressors as well as the quality of the reconstructed water column image after lossy compression at different levels. Lastly, we test the performance of the pre-processing stage, without the constraint of an entropy encoder, by means of the histograms of the original samples and the prediction errors. [ABSTRACT FROM AUTHOR]

The buildup of a continental rise and its morphological patterns depend on sediment transport and deposition via downslope slumps, turbidity currents, along‐slope contourites and other deepwater currents. These delivery mechanisms are central to source‐to‐sink reconstructions, yet untangling their individual roles is not straightforward. The current study focuses on the sink section of the Nile system at the northern Levant continental rise (eastern Mediterranean). During the Pliocene, fluvial systems from northern Africa and the Levant margin supplied sediments to the study area. This supply decreased significantly during the Quaternary because of two processes: (a) The aridification of North Africa made the Nile River the predominant contributor to the basin; (b) the topographic rise of the Levant landmass severely limited fluvial supply. Meanwhile, on‐going counter‐clockwise marine currents became the prevalent supply system to the Levant margin, and downslope sediment‐transport became the only source to the northern Levant continental rise, which became a significant sink of the larger Nile system. These conditions provide an excellent natural laboratory for understanding the individual role of downslope sediment‐transport processes in building a continental rise. This research is based on single‐channel sparker seismic data, multibeam bathymetry and four 7–8 m long piston‐cores collected over the northern Levant continental rise at water depths of 1200–1800 m, together with available multibeam bathymetry and industrial multi‐channel seismic reflection data. The results show a major depositional changeover during the Pliocene‐Quaternary transition from concordant aggradation to repeated deposition of >12 sediment wave subunits, interpreted as upslope migrating cyclic steps. Quantitative analysis of the sediment wave morphology at the seafloor and subsurface, along with core data, indicates that the immediate sediment source was the nearby shelf. The supply was regulated by basinward‐landward shifts of the shore‐parallel marine currents during lowstand‐highstand conditions (respectively). Hence, this case study highlights the connection between sea‐level change and sedimentation patterns on a continental rise. [ABSTRACT FROM AUTHOR]

Objectives: To overcome the problem that the current bathymetric filtering methods require manual intervention and are difficult to implement technically, a bidirectional cloth simulation filtering (BCSF) algorithm is proposed and implemented in this paper. Methods: Firstly, the transfer iterative trend surface is established to eliminate the negative anomalies and guarantee the continuous expression of the seafloor topography. Then, the filtering surface is established to solve the over-filtering problem of convex and concave seafloor topographies based on the proposed BCSF correction model. Finally, to further improve the effectiveness of the filtering, adaptive distance threshold is optimized and estimated. To evaluate the performance of the proposed algorithm, the BCSF algorithm is applied to shallow water multibeam bathymetry data. Results: The experimental results show that the BCSF algorithm can avoid the over-filtering. The elimination rate of the proposed BCSF algorithm is better than that of the CSF ( cloth simulation filtering) algorithm, which decreases from 12.87% to 0.76% for the whole study area and from 15.29% to 1.09% for local study area, respectively. Conclusions: Compared with the CUBE ( combined uncertainty bathymetry estimation) algorithm, the BCSF algorithm is more easily to implement and can retain more terrain de tails. Consequently, the BCSF algorithm has strong robustness and application prospects for multibeam bathymetry data. [ABSTRACT FROM AUTHOR]

In recent years, sonar systems for surface and underwater vehicles have increased in resolution and become significantly less expensive. As such, these systems are viable at a wide range of price points and are appropriate for a broad set of applications on surface and underwater vehicles. However, to take full advantage of these high-resolution sensors for seafloor mapping tasks an adequate navigation solution is also required. In GPS-denied environments this usually necessitates a simultaneous localization and mapping (SLAM) technique to maintain good accuracy with minimal error accumulation. Acoustic positioning systems such as ultra short baseline (USBL) and long baseline (LBL) are sometimes deployed to provide additional bounds on the navigation solution, but the positional uncertainty of these systems is often much greater than the resolution of modern multibeam or interferometric side scan sonars. As such, subsurface vehicles often lack the means to adequately ground-truth navigation solutions and the resulting bathymetic maps. In this article, we present a dataset with four separate surveys designed to test bathymetric SLAM algorithms using two modern sonars, typical underwater vehicle navigation sensors, and high-precision (2 cm horizontal, 10 cm vertical) real-time kinematic (RTK) GPS ground truth. In addition, these data can be used to refine and improve other aspects of multibeam sonar mapping such as ray-tracing, gridding techniques, and time-varying attitude corrections. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mapped detailed seafloor morphology of the axial seamount chain in the Laxmi Basin. • Carried out geophysical characterization of the Raman-Panikkar-Wadia seamount chain. • Inferred multiphased volcanic origin for the Raman-Panikkar-Wadia seamount chain. The Laxmi Basin, which is a deep ocean basin situating adjoining to the northwestern continental margin of India, contains a linear seamount chain consisting of the Raman Seamount, Panikkar Seamount and the Wadia Guyot, located over the axial basement high in the Laxmi Basin representing the Panikkar Ridge. The geomorphology of this seamount chain was studied by earlier researchers; however, its characteristic geophysical signatures, possible genesis and age of formation remains to be clearly established. We attempted for a detailed understanding of the morphological characteristics and the geophysical signatures over the spatial extent of these seamounts using a fresh set of multibeam bathymetry data and sea-surface gravity and magnetic anomalies, complemented by the existing seismic reflection sections. Based on the seafloor and basement topography signatures observed together from the multibeam bathymetry data and the seismic reflection sections, we infer that all the three seamounts are associated with the presence of surface/subsurface secondary peaks on their central parts. The free-air gravity anomaly maps show that the seamounts are associated with a very short wavelength gravity high, superimposed on the short wavelength gravity low representing the Panikkar Ridge. The magnetic anomaly maps suggest that all these seamounts are associated with complex magnetic signatures. Based on the presence of morphological features that are generally associated with the volcanic activity and by considering the above complex geophysical signatures and the updated magnetic isochron map of the Laxmi Basin, we support multiphased volcanic origin for the Raman-Panikkar-Wadia seamount chain, emplaced at an age younger to 63.28 Ma. [ABSTRACT FROM AUTHOR]

Both submarine landslides and submarine canyons can transfer large amounts of terrigenous quantities from the continental shelf to the deep sea. In some cases, they can have a close relationship to their spatial distribution, formation and evolution. Submarine landslides on the shelf–slope can provide early depressions for submarine canyons, representing the early stage of submarine canyons. The continuous downcutting process during the evolution of submarine canyons can steepen the gradient of the canyon sidewalls, which can lead to the occurrence of submarine landslides. However, the role of submarine canyons in the initiation of slope failure has been overlooked. In this study, high-resolution multibeam bathymetry data, submarine image data and 2-D seismic data were used to investigate two adjacent submarine landslides developed on the northern slope of the Xisha Trough and the spatiotemporal relationship of these landslides to the Central Canyon. We identified a steep downslope between the submarine landslides and the Central Canyon. The Central Canyon formation age was much earlier than those of the submarine landslides. The Central Canyon is filled with modern submarine landslide deposits. The characteristics of the multiple failure scarps indicate retrogressive failure of the submarine landslides. We suggest that the submarine landslides developed on the northern slope of the Xisha Trough Basin have finally been captured by the Central Canyon. We determined that the emptying of sediments at the end of the northern slope of the Xisha Trough Basin caused by the development of the Central Canyon caused the end of the northern slope of the Xisha Trough Basin to lose support, which may have affected the slope stability and could have even played a role in the initiation of submarine landslides. Consequently, the slope area along the Central Canyon may be susceptible to slope instability and slope failure processes. • The submarine landslides in the study area have finally been captured by the Central Canyon. • The Central Canyon may have influence or even play a role in the submarine landslides initiation. • The Central Canyon may be a trigger for landslides in the northern slope of the South China Sea. [ABSTRACT FROM AUTHOR]

In high latitude continental margins, glacio-seismotectonics becomes particularly relevant during postglacial unloading periods and related isostatic rebound. Based on multibeam bathymetry and parametric profiles, an unexpected active 30 km long NNW-SSE fault is imaged for the first time in the inner Storfjorden glacial trough, at the passive continental margin of the Barents Sea. The 10 km southern tip of the fault was surveyed in detail and it is characterised by a total fault throw of 65 m. The fault forms an asymmetric valley with an upraised block to its east (top at 245 m water depth), a downthrown block to the west (at 310 m water depth), and a most recent fault scarp with 8 m relief at the seafloor valley axis. Recent fault activity is evidenced by its morphological expression on the seafloor, the faulting of the glacial, glaciomarine and marine sediments and streamlined landforms formed during the last glacial-interglacial period. Mass-flow deposits along the upraised block would also indicate recent fault activity. This fault may trigger earthquakes of up to M W 6.2, based on the magnitude/length ratio of the detailed surveyed segment, which is similar in magnitude to those that occurred in the nearby northeastern regions during 2008–2012. In any case, earthquakes may reach up to M W 6.8 if the entire fault length is activated. Rather than the expected normal fault on the passive margin, this fault seems to be reversed and dipping eastwards. The integration of the Storfjorden glacial trough reverse fault with regional structures suggests that the fault activated the southwestward front of a wide, continental crustal block. These results are in accordance with a change in the stresses in the passive continental margin since the rifting stage, from extension to post-rift compression, and suggest that postglacial unloading may have favoured the fault development. • Glacio-seismotectonic active faulting deforms the Storfjorden glacial trough. • Faulting may produce earthquakes up to magnitudes of Mw 6.2 to Mw 6.8. • The fault may be reverse suggesting compression within the former passive margin. [ABSTRACT FROM AUTHOR]

The renowned Phoenician city of Tyre was settled on a small coastal island from which it resisted invasions and sieges for centuries. In 332 BCE, the city was taken when Alexander-the-Great built a 750 m-long causeway to seize the island. The causeway interrupted longshore sediment transport, forcing sand to accumulate along the causeway, creating a isthmus that today still connects the island to the mainland. This isthmus is no less than 530 m wide and 13 m high. We studied the impact of isthmus growth on city development during Antiquity, by combining archeological data, core stratigraphy, and multibeam bathymetry to track the paleogeographic evolution of the land-facing coast of Tyre, from the Holocene marine transgression up to today. In Phoenician time (900-300 BCE), sea-level markers indicate that relative sea level lied more than 2.5 m below current sea level, defining a 1500 × 600 m rocky island, 450 m longer in the south than the modern rocky headland. Between the island and the mainland, diffracted/refracted waves built a submerged sand bank that rests on eroded transgressive lagoonal clays. Along the mainland-facing coast of Tyre Island, Phoenician walls were built on the emerged end of the sand bank. Middle infrared spectroscopy (MIRS) shows that the sand of the bank and its successor isthmus is made of carbonate clasts (90–100%). 36Sr/37Sr ratios further indicate that these are modern bioclastic sands. Coeval, heterogeneous clay-rich sediments were deposited between the rocky island, and the sand bank. We interpret these as harbor sediments, deposited behind buried and/or submerged Phoenician breakwaters. The sand bank inflated dramatically after the building of Alexander's causeway, rising 5 m during the Hellenistic and Roman periods. It rose another 4 m–8 m in successive stages during Byzantine and Medieval times, up to the 19th century. The rapid growth of the sandy isthmus after 332 BCE led to the demise and burial of the harbors that had been developed along the mainland-facing coast. The Phoenician southern harbor of Tyre appears to have been buried in Roman times during the repurposing of the SE corner of the island for monumental baths. We interpret this repurposing as a response to the growth of the sandy isthmus, and suggest that the northern Phoenician harbor was then relocated to its present position. Subsequent relative sea level rise led to the erosion of the landfill overlying the southern harbor, exposing the formerly buried port on the seafloor. [Display omitted] • Tyre is a new island, with no ancient interglacial isthmus attached to it. • The sand bank on which Alexander's Causeway was built fills a deep natural harbor. • The sand bank is made of modern bioclastic sands coming from the south. • The Southern, Egyptian harbor of Tyre is buried under the monumental Roman Baths. • Repurposing of the southern harbor results from to the rapid growth of the isthmus. [ABSTRACT FROM AUTHOR]

Antecedent conditions and geology influence bedform dynamics and other sea-bed bottom current interactions on the continental shelf. However, the nature of this influence has not been well constrained, particularly on current-swept shelves. A variety of bedforms (narrow and broad sediment ribbons, comet marks and subaqueous dunes) are revealed by high resolution multibeam bathymetry and side scan sonar surveys of the mid-to outer "Wild Coast" shelf along the east coast of South Africa. The bedforms demonstrate a relationship to the geological framework of the shelf. The various bedforms occur in conjunction with bedrock-incised valleys and topographic depressions filled with transgressive sediment and bounded laterally by prominent rocky outcrops. These sediment sources are siphoned and mobilised by the Agulhas Current to create the contemporary shelf bedforms. Mechanisms of bedform development are associated with the interplay between the loci of sediment supply and associated grain size on the one hand and the current velocity and pathway of the Agulhas Current on the other. Sediment ribbons form parallel to the flow path of the Agulhas Current in narrow or broad forms that can be differentiated primarily by sediment grain size. With increased sediment availability from nearby bedrock-bound depocenters these transition along shelf to 2D dunes. A cross-shelf transition to 3D dunes on the outer shelf is marked by increased current velocity, grain size and decreased sediment availability outside of rock-bound depocenters. Rock outcrops affect current velocity and flow paths sufficiently to favour localised deposition over sediment stripping from the shelf. Comet mark forms develop from interactions between availability of finer sediment and perturbations of current flow paths by rock outcrops. This creates conditions that favour localised sediment scouring over deposition. With variability in sediment size, grain size and current flow, dunes fluctuate between active (sharp crested), inert (round crested) and degraded (flat crested) states. A lack of available sediment to replenish outer shelf dunes sees prolonged stasis, eventual dune splitting and breakdown under progressive current influence. Mid-shelf dunes have a greater capacity to recover from periods of stasis and short-term degradation due to greater availability of sediment. Dune migration rates are slower than previous regional estimates. Reasons for this are inconclusive and may be multifaceted. Possible reasons include inertial constraints, prolonged downcurrent reformation periods and longer dune relaxation associated with coarser grain sizes and a paucity of sediment on the outer shelf coupled with the Agulhas Current core migrating further in and offshore. This may explain the stability of the large barchan dunes and reduced movement of other sharp crested dunes relative to the regional migration rates. • Document sediment dynamics on a geostrophic-current dominated shelf. • Reveal influence of geological control on dune development. • Core of Agulhas Current directed by changes in shelf physiology. [ABSTRACT FROM AUTHOR]

One of the main challenges of underwater archaeology is to develop non‐invasive research of heritage sites in order to enable their further protection for future societies. This study explores, identifies and classifies archaeological objects in a shallow lake using underwater acoustics. We solved the aforementioned challenges by developing an innovative, object‐based, fuzzy‐logic classification of nine archaeological object categories based on multibeam echosounder bathymetry, 13 secondary features of bathymetry and 106 underwater diving prospections. We achieved an 86% correlation with ground‐truth samples, and 49% overall accuracy. The unique and repeatable workflow developed in this study can be applied to other case studies of underwater archaeology around the world. [ABSTRACT FROM AUTHOR]

The article reports information on the organization, performance, and main results obtained on expeditionary cruise 85 of the R/V Akademik Mstislav Keldysh to the Kara Sea on August 27–September 30, 2021. The main objective was to study the state of underwater radioactive waste disposals and ecology in the bays of Novaya Zemlya and in the Novaya Zemlya Depression. Sonar and video survey equipment, as well as gamma-ray spectrometers and unmanned underwater vehicles, were used for the research. Benthic and bottom sediment samples were taken for subsequent laboratory analysis. The locations of a number of potentially hazardous objects have been confirmed for the first time. Detailed information about known objects was obtained by multibeam mapping technology. [ABSTRACT FROM AUTHOR]

The Clarion Clipperton Zone (CCZ) hosts a valuable deposit of polymetallic nodules. Understanding the geology of this deposit is key to its effective exploration and future mining. Interpretation of satellite derived bathymetry elucidates large scale geomorphological units and structural units that characterize the area. The Main Map is includes distinct plains, rises, and lows of abyssal hills, steps and a trough along parts of the bounding fracture zone, seamount chains, fault zones and rifts. [ABSTRACT FROM AUTHOR]

This work presents a new high-resolution multibeam bathymetric map of a segment of active deep sea-floor spreading in the Atlantic Ocean, the northern Mid-Atlantic Ridge (MAR) at 45-46° N. New high-resolution bathymetry data were acquired using an Atlas multibeam echosounder onboard the research vessel Sarmiento de Gamboa during the EXPLOSEA-2 survey in 2019. The final map of the MAR (50 m cell grid size) at the original scale of 1:200,000 shows a segment of 140 × 35 km of the MAR, at water depths from 715 to 3700 m. This new high-resolution bathymetric map allows to better defining the submarine morphology of the Moytirra hydrothermal active field, the only high-temperature field identified between the Azores Archipelago (Portugal) and Iceland. ROV submarine observations reaching the deepest part of the system for the first time show giant anhydrite-sulfide chimneys up to 20 m high, active strong black smokers and polymetallic massive sulfides. [ABSTRACT FROM AUTHOR]

The accurate location of gas upwelling flows is still an open problem for non-invasive imaging techniques in populated areas. Gas blowouts of deep origin may represent a serious threat to human health in urban areas and should be correctly imaged with high-resolution for assessing the related hazards. In this work, we propose an integration of active (electrical resistivity tomography and high-resolution sub-bottom profiling complemented with the multibeam bathymetry) and passive (self-potential and ambient noise recordings) geophysical methods to image gas upwelling flows in the coastal area of Fiumicino (Central Italy), where the gas presence is well-documented by previous works. We demonstrate that merging seismic sub-bottom profiling and electrical resistivity tomography has enormous diagnostic potential for gas detection, since they combine the high resolution needed to correctly image the subsurface and the interfaces between different media with the high diagnostic capability of electrical methods to detect anomalies associated with the gas emissions. Passive seismic methods complement the analysis enabling an estimation of the shear-wave velocity through array measurements. Finally, the reconstruction of the natural electrical sources, inferred from the inversion of self-potential data, confirms the location of the near-surface gas upwelling flows assessed through the resistivity model. This work demonstrates that the integration of high-resolution active and passive seismic and electrical methods can be an effective choice for the accurate location of risk-prone areas by imaging the near surface gas pathways where borehole drilling is strongly limited if not forbidden. • An integrated geophysical approach is proposed for detection of gas migration. • We apply active and passive electrical and seismic methods in a coastal area. • Electrical methods highlight gas upwelling flows in the shallow subsurface. • We reconstruct the subsurface layering through high-resolution seismic data. • The proposed method is effective for the characterization of risk-prone areas. [ABSTRACT FROM AUTHOR]

A chain of paired mound and depression structures are presented in the southwestern continental shelf of the Ulleung Basin, East Sea, Korea. We integrate multibeam bathymetry to identify topographic features, sub-bottom profile and multi-channel seismic reflection data to confirm geological features, and piston cores to understand the sediments of the mounds and depressions. Paired structures occur with a northwest–southeast orientation at water depths between 130 and 150 m and have similar scales of 10–20 m in height and depth. The mounds consist of cold-water corals and authigenic carbonate with shelly sand, whereas, the surficial lithology of depressions are only composed of siliciclastic deposits. The mounds appeared to have grown from the depression based on the observation for morphological features in the cross-section profiles of the paired mound and depression structures. Seismic profiles show acoustic blanking anomalies and seismic chimneys, indicating that the topographic relief formed under the influence of gas seepage. The petrological and geochemical signature of carbonate chunks also displayed gas leak effects different from CWC. This study suggests a developmental history model with paired mound and depression structures, in which gas/fluid escape causes depressions and the selective coral growth creates mounds growing on one side of these depressions. The mounds had sufficiently grown, depressions would have been further developed in interaction with the bottom current. • The seafloor mounds consist of authigenic carbonate and cold-water coral that is L. pertusa. • Cold-water coral may have settled on authigenic carbonates that act as a hard bottom. • Cold-water coral colonized the mounds at least during the late Holocene. • The depressions initially are formed by gas and developed by the bottom current. [ABSTRACT FROM AUTHOR]

This study examines the role of deep pockmarks in acting as natural sediment traps. Multibeam bathymetry, single-channel seismic and sediment samples data were used for describing the morphology of pockmarks as well as the nature of sediments inside and outside these depressed features, in an area of Santos Basin (SW Atlantic upper slope), dominated by the strong flow of Brazil Current. Results show that the grain size and chemical composition of sediments inside pockmarks are distinct from the outside. Also, radiocarbon dating shows that Holocene ages are found only in samples located inside the pockmarks. Combination of sedimentological, geochemical and geochronological data allowed to recognise that deep pockmarks might present distinct sediment deposition processes when compared with those of shallow pockmarks, in which turbulence impedes sediment deposition, as reported in the literature. [ABSTRACT FROM AUTHOR]

The geology of eastern Sulawesi is widely known for its complexity due to multiple deformation stages. The geology on land has been studied excessively, but little assessment has been made on the offshore geology, thus the geological evolution of the area remains a subject of controversy. A thorough observation of high multibeam bathymetry dataset offshore and SRTM dataset onshore provides an understanding on the geological features relating to the tectonic deformation. Exquisite morphological features include carbonate buildups and gravitational collapse dominating the shelf areas whereas distinct form of ridges and seamount exists in the offshore. Structural features in this area including the major Tolo Thrust and South Sula Fault varied structural lineations on land with several polygonal extensional faulting and accretionary wedge on the west of the North Banda Sea. The existence of these features may indicate that the area was majorly deformed during Neogene, specifically relating to the opening of the Banda Sea due to the subduction rollback of Banda. [ABSTRACT FROM AUTHOR]