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

The value of artificial intelligence and machine learning applications for use in heritage research is increasingly appreciated. In specific areas, notably remote sensing, datasets have increased in extent and resolution to the point that manual interpretation is problematic and the availability of skilled interpreters to undertake such work is limited. Interpretation of the geophysical datasets associated with prehistoric submerged landscapes is particularly challenging. Following the Last Glacial Maximum, sea levels rose by 120 m globally, and vast, habitable landscapes were lost to the sea. These landscapes were inaccessible until extensive remote sensing datasets were provided by the offshore energy sector. In this paper, we provide the results of a research programme centred on AI applications using data from the southern North Sea. Here, an area of c. 188,000 km2 of habitable terrestrial land was inundated between c. 20,000 BP and 7000 BP, along with the cultural heritage it contained. As part of this project, machine learning tools were applied to detect and interpret features with potential archaeological significance from shallow seismic data. The output provides a proof-of-concept model demonstrating verifiable results and the potential for a further, more complex, leveraging of AI interpretation for the study of submarine palaeolandscapes. [ABSTRACT FROM AUTHOR]

This article explores the advancements and challenges in seabed prospecting technology, emphasizing the importance of seabed geophysical data in understanding the planet and driving marine energy resource exploration and deep earth science research. It calls for further technical refinement in ocean bottom geophysical prospecting techniques and the integration of seabed exploration technology with big data and artificial intelligence. The article also introduces a special issue on seabed prospecting technology, which includes research papers covering a range of prospecting methods and geophysical applications. The document provides summaries of various research studies related to seismic data analysis and exploration, offering key findings and methodologies used in each study. [Extracted from the article]

ABSTRACT The present geophysical research aims to evaluate the applicability of multichannel analysis of surface waves (MASW) on mapping ultrashallow underwater ancient masonry remnants. The work presents the analysis from a single seismic line using MASW and seismic refraction tomography (SRT) methods and its corresponding electrical resistivity tomography (ERT) section surveyed at the submerged prehistoric site of Agioi Theodoroi area located 10 km eastern of Heraklion, Crete, Greece. The 2D MASW velocity model exhibits significant correspondence with the resistivity structure extracted from the ERT data, showing lateral S‐wave velocity (Vs) variations at the positions where the high resistivity anomalies exist. The analysis of synthetic seismic data calculated from a respective model reproduced a comparable S‐wave velocity pseudo‐section with the real data. However, the investigated targets (submerged buried masonry) appear shallower and wider in MASW sections than in the real world and the corresponding synthetic models, due to insufficient vertical and horizontal resolution of this method. Surface waves travelling through the seafloor sediments (Scholte‐waves) demonstrate very low velocity values. This makes them suitable for the detection of shallow and relatively large (> 0.5 m) underwater manmade structures, providing the enhancement of MASW method resolution, by utilizing a high frequency (> 100 Hz) seismic source, recording short Scholte wavelengths (≤ 1 m) and using shorter (≤ 0.5 m) receiver spacing and array length. Consequently, the results of this work demonstrate the potential in employing conventional seismic techniques in the delineation of underwater antiquities and the revealing of the cultural dynamics in very shallow off‐shore archaeological sites. [ABSTRACT FROM AUTHOR]

The Baltic Sea basins, some of which only submerged in the mid-Holocene, preserve Stone Age structures that did not survive on land. Yet, the discovery of these features is challenging and requires cross-disciplinary approaches between archeology and marine geosciences. Here, we combine shipborne and autonomousunderwater vehicle hydroacoustic data with up to a centimeter range resolution, sedimentological samples, and optical images to explore a Stone Age megastructure located in 21 m water depth in the Bay of Mecklenburg, Germany. The structure is made of 1,673 individual stones which are usually less than 1 m in height, placed side by side over a distance of 971 m in a way that argues against a natural origin by glacial transport or ice push ridges. Running adjacent to the sunken shoreline of a paleolake (or bog), whose youngest phase was dated to 9,143 ±36 ka B.P., the stonewall was likely used for hunting the Eurasian reindeer (Rangifer tarandus) during the Younger Dryas or early Pre-Boreal. It was built by hunter-gatherer groups that roamed the region after the retreat of the Weichselian Ice Sheet. Comparable Stone Age megastructures have become known worldwide in recent times but are almost unknown in Europe. The site represents one of the oldest documented man-made hunting structures on Earth, and ranges among the largest known Stone Age structure in Europe. It will become important for understanding subsistence strategies, mobility patterns, and inspire discussions concerning the territorial development in the Western Baltic Sea region. [ABSTRACT FROM AUTHOR]

The East China Sea, situated at the intersection of the Eurasian, Philippine Sea, and Pacific plates, is characterized by complex geology influenced by tectonic phenomena such as plate movements, volcanism, faults, and uplifts. Crustal density structure inversion provides a thorough understanding of the region's geological history as well as Earth's dynamical evolution, providing critical insights into seismic disaster mitigation, resource exploration, marine environmental protection, and maritime safety. The inversion process, on the other hand, presents challenges in data quality, quantity, model complexity, uncertainty, and computational resources. With the advancement of next-generation satellite gravity measurements and developing inversion techniques, the inversion of marine crustal density structures promises to be more precise and comprehensive. We explored the density distribution in the East China Sea and surrounding areas using an innovative wavenumber domain three-dimensional density imaging method along with high-precision global satellite gravity data. By overcoming data quality and computing resource constraints, wavenumber domain three-dimensional density imaging has transformed the discipline of marine geophysics, successfully delivering accurate density distributions in the study area. We were able to get a more precise and comprehensive characterization of the crustal density structure by combining high-precision satellite gravity data and cutting-edge imaging methods. Our investigation has unveiled previously unknown details about density distribution in the East China Sea and its environs. The East China Sea shelf displays smooth low-density perturbations at 18 km depth, whereas the trench–arc–basin region exhibits increasing density perturbations. Notably, the Okinawa Trough, which is surrounded by the Tokara Volcanic Ridge and the Ryukyu Trench, displays strong positive anomalies with a north–northeastern to northeastern orientation. In contrast, the Ryukyu Ridge and the Philippine Sea Basin exhibit smaller negative values and substantial northwestward positive density trends, respectively. These findings indicate diverse material distribution, which provides important insights into the area's geological evolution and tectonic processes. This study adds new insights into density distribution in the East China Sea and adjacent regions, offering information on the geological complexity of the region. The research lays the groundwork for future research on crustal dynamics and enhances the field of marine geophysics and related disciplines. [ABSTRACT FROM AUTHOR]

The African–Antarctic sector of the Southern Ocean is the least studied part of the World Ocean; its structure and evolution of the tectonosphere remains debatable. The complex development history of the region under study, accompanied by manifestations of intense magmatic and tectonic activity, has contributed to the formation of a number of large underwater ridges and rises. Identifying the features of the deep structure of the tectonosphere on the basis of the analysis of geophysical information and understanding the geodynamic nature of the morphostructures of the region under study is an urgent problem of marine geophysics and geodynamics. The structural analysis of the anomalous gravity and magnetic fields of the studied region was carried out. Zoning scheme by the anomalous fields as well as a generalized scheme have been constructed. The results of these studies made it possible to identify heterogeneous blocks of the lithosphere, which were formed on different spreading ridges and are separated by submarine rises. [ABSTRACT FROM AUTHOR]

An algorithm for optimizing the trajectories and movement sequence of a fleet of marine seismic survey vessels in solving the problem of marine seismic surveys using bottom stations is presented. The algorithm is based on solving the traveling salesman problem with mixed deliveries and collections of goods (TSPDC). A description of the algorithm extension to a problem that takes into account static closed zones that simulate ice and meteorological conditions unsuitable for the ship movement is given. The Dubins path algorithm provides a path close to the minimum and takes into account real characteristics of the ship movement and its speed when performing various types of work (installing bottom stations, collecting stations, maneuvering, etc.). The scientific novelty of the study lies in applying the solution of the TSPDC to problems of marine geophysics with the condition of presence of closed zones and developing an algorithm for optimizing the work of seismic vessels with the use of bottom stations, which is relevant in the conditions of the Arctic shelf during the period of limited navigation. The algorithm described in the article makes it possible to take into account the return of the vessel for collecting the equipment when working with bottom stations in the transition zone. The developed algorithm for planning marine seismic surveys formed the basis of the application software. The formalization of the problem, the results of the algorithm operation, and examples of planning on test data are presented. The possible limitations for the proposed algorithm are raised. The obtained results are applicable for further use in the implementation of tasks on optimizing the work plan for marine seismic surveys with several vessels, both when planning seismic surveys and when adjusting plans directly on the ship. The use is also justified if it is necessary to reenter the profile (for example, when reworking out a defective work area). [ABSTRACT FROM AUTHOR]

Marine multichannel and wide‐angle seismic data constrain the distribution of seamounts, sediment cover sequence and crustal structure along a 460 km margin‐parallel transect of the Hikurangi Plateau. Seismic reflection data reveals five seamount up‐to 4.5 km high and 35–75 km wide, with heterogeneous internal velocity structure. Sediment cover decreases south‐to‐north from ∼4.5 km to ∼1–2 km. The Hikurangi Plateau crust (VP 5.5–7.5 km/s) is 11 ± 1 km thick in the south, but thins by 3–4 km further north (∼7–8 km). Gravity models constructed along two seismic lines show the reduction in crustal thickness persists further east, coinciding with a bathymetric scarp. Gravity data suggest the transition in crustal thickness may reflect spatial variability in deformation and lithospheric extension associated with plateau breakup. Variability in the thickness of subducting crust may contribute to differences in megathrust geometry, upper‐plate stress state and high‐rates of contraction and uplift along the southern Hikurangi margin. Plain Language Summary: The thickness of crust arriving at subduction zones exerts a major influence on the configuration, structure, and distribution of stresses at plate boundaries. A region of thickened oceanic crust, the Hikurangi Plateau, is subducting beneath the North Island of New Zealand. To understand the structure of this Plateau, we analyze seismic data along a 460 km long transect, which reveals five large seamounts, and a 3–4 km reduction crustal thickness between the southern and northern areas of the Plateau. Gravity data show this difference is persistent across the plateau and reveal structures suggesting the crust may have thinned when the Hikurangi plateau separated from a second plateau (Manihiki), which is thought to have formed at the same time. We propose that the subduction of thicker crustal along the southern Hikurangi margin may contribute to the shallow angle of the subducting plate, and high rates of uplift and deformation in the overthrusting plate. Key Points: Crustal thickness of the Hikurangi Plateau reduces by ∼30% between the southern (10–11 km) and northern (7–8 km) PlateauCoincident contrasts in plateau fabric may attribute the thickness contrast to rifting from the Manihiki PlateauThickness contrasts may impact the geometry of the subducting plate and rates of upper‐plate compression and uplift along the Hikurangi margin [ABSTRACT FROM AUTHOR]

The boundary between the overriding and subducting plates is locked along some portions of the Cascadia subduction zone. The extent and location of locking affects the potential size and frequency of great earthquakes in the region. Because much of the boundary is offshore, measurements on land are incapable of completely defining a locked zone in the up‐dip region. Deformation models indicate that a record of seafloor height changes on the accretionary prism can reveal the extent of locking. To detect such changes, we have initiated a series of calibrated pressure measurements using an absolute self‐calibrating pressure recorder. A piston‐gauge calibrator under careful metrological considerations produces an absolutely known reference pressure to correct seafloor pressure observations to an absolute value. We report an accuracy of about 25 ppm of the water depth, or 0.02 kPa (0.2 cm equivalent) at 100 m to 0.8 kPa (8 cm equivalent) at 3,000 m. These campaign survey‐style absolute pressure measurements on seven offshore benchmarks in a line extending 100 km westward from Newport, Oregon from 2014 to 2017 establish a long‐term, sensor‐independent time series that can, over decades, reveal the extent of vertical deformation and thus the extent of plate locking and place initial limits on rates of subsidence or uplift. Continued surveys spanning years could serve as calibration values for co‐located or nearby continuous pressure records and provide useful information on possible crustal deformation rates, while epoch measurements spanning decades would provide further limits and additional insights on deformation. Plain Language Summary: The Cascadia subduction zone has produced large earthquakes and tsunamis whose potential size and interval is affected by the amount and distribution of locking between the tectonic plates. A large portion of the subduction zone is offshore, where typical land‐ and satellite‐based methods are ineffective at measuring crustal changes. Seafloor water pressure observations can be used to measure height changes, but pressure gauges inherently drift at rates typically greater than the expected vertical seafloor deformation rates. The absolute self‐calibrating pressure recorder (ASCPR) measures the true, absolute, sensor‐independent seafloor pressure by addressing and correcting sources of error caused by the internal piston gauge calibrator and recording pressure gauges. The accuracy of our measurements is about 25 ppm of the water depth, or about 2.5 cm of height per 1,000 m of water. Campaign survey‐style measurements using the ASCPR at seven benchmarks off the coast of Newport, Oregon from 2014 to 2017 establish a long‐term record of absolute measurements that can be referenced by studies decades or more in the future or can estimate and correct drift of nearby continuous pressure gauges. Continued measurements can provide insights on seafloor deformation and thus locking in Cascadia. Key Points: Campaign‐style surveys of absolute calibrated seafloor pressure measurements were made in the Cascadia subduction zone from 2014 to 2017These sensor‐independent measurements act as long‐term, absolute reference values that can be used for future vertical deformation studiesWe document and quantify the sources of error in the technique with a total uncertainty of ∼25 ppm, or ∼0.25 kPa per 1,000 m water depth [ABSTRACT FROM AUTHOR]

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use. [ABSTRACT FROM AUTHOR]

The main sources of the ambient seismic wavefield in the microseismic frequency band (peaking in the ∼0.04–0.5 Hz range) are earth's oceans, namely the wind‐driven surface gravity waves (SGW) that couple oscillations into the seafloor and the upper crust underneath. Cyclones (e.g., hurricanes, typhoons) and other atmospheric storms are efficient generators of high ocean waves that in turn generate distinct microseismic signatures. In this study, we perform a polarization (i.e., three‐component) beamforming analysis of microseismic (0.05–0.16 Hz) retrograde Rayleigh and Love waves during major Atlantic hurricanes using a virtual array of seismometers in Eastern Canada. Oceanic hindcasts and meteorological data are used for comparison. No continuous generation of microseism along the hurricane track is observed but rather an intermittent signal generation. Both seismic surface wave types show clear cyclone‐related microseismic signatures that are consistent with a colocated generation at near‐coastal or shallow regions, however the Love wavefield is comparatively less coherent. We identify two different kinds of intermittent signals: (a) azimuthally progressive signals that originate with a nearly constant spatial lag pointing toward the trail of the hurricanes and (b) azimuthally steady signals remaining nearly constant in direction of arrival even days after the hurricane significantly changed its azimuth. This high complexity highlights the need for further studies to unravel the interplay between site‐dependent geophysical parameters, SGW forcing at depth and microseismic wavefield radiation and propagation, as well as the potential use of cyclone microseisms as passive natural sources. Plain Language Summary: Ocean waves are responsible for the generation of microseisms, faint ground vibrations with complex characteristics and which comprise a major portion of the background seismic noise of the earth. In this study, we implement an onshore seismic detection method to study microseisms generated by cyclones in the North Atlantic ocean (hurricanes), as these are known to be major generators of large ocean waves. We observed that cyclones only seem to generate detectable microseisms as they move over certain regions in the ocean, namely near coastal or shallow water regions. The direction of arrival of these microseisms is sometimes constant, at other times it shifts azimuth along with the hurricanes. Understanding the relationship between ocean waves and cyclone‐related microseisms is an important step for the potential use of these vibrations to study the earth, ocean and atmosphere. Key Points: Primary and secondary microseismic Love and Rayleigh waves excited by Atlantic cyclones were detected via onshore polarization beamformingWe observed microseisms related to cyclones as they pass over the northwestern Atlantic margin off NewfoundlandSome microseisms have constant direction of arrival, others are azimuthally progressive and reflect the advance of the cyclone [ABSTRACT FROM AUTHOR]

The presence of Risso's dolphins (Grampus griseus) in Southern Calabrian waters of the Ionian Sea is poorly known. During dedicated cetacean research started in the summer of 2019 in the stretch of Calabrian waters between Brancaleone and Botricello, a pod of Risso's dolphins was recorded for the first time. This observation occurred of Siderno and Locri at about 8.3 km from the shore where the sea depth is 720 m, a bathymetric feature that is in line with the known deeper water habitat preference of the species. This Risso's dolphin pod was composed of at least 14 individuals. The latter were photo-identified. One individual showed signs of a serious injury due to a probable vessel accident that severed partly into its back behind its dorsal fin. Most of the individuals observed were mature to old with their frontal area already light grey to white. This scientific report contributes new knowledge on the distribution of the species in the Central Mediterranean Sea which may better address effective conservation management efforts for the species. Further monitoring and management are needed for this endangered species, especially in a geographic area that was previously unstudied for an extended period, despite past stranding events and citizen sightings of cetaceans being recorded occasionally. [ABSTRACT FROM AUTHOR]

Important evidence related to sea-level fluctuation, human evolution and dispersal that took place onshore during the Late Pleistocene and Holocene eras, are currently found underwater due to the sea-level rise. In this study, we present submarine relative paleo sea-level indicators found offshore the Lebanese coastline, at large from the prominent ancient city of Byblos. Two different submarine erosional terrace sequences were identified at depths ranging from −40 to −25m ("distant" sequence) and −11 to 0m ("nearshore" sequence) below present sea level, by using a combination of high-resolution geophysical means and terrain data analysis techniques. In the absence of datings, a model that uses relative sea-level curves for different uplift rates and examines the terraces' formation for various cliff retreat rates (derived from literature and on-field GPS measurements) was built. This model indicates the most possible time frames of the submarine terraces' (STs) formation. The "nearshore" terrace sequence is suggested to have originally been formed during Marine Isotope Stage 5a (MIS5a) sea-level highstand, while it was possibly re-flattened during the first MIS1 sea-level slowdown (8–6 ka BP). The "distant" sequence formation is placed between the MIS4 to MIS3 transition (∼62–50 ka BP), and during MIS3 sea-level highstands within 45–35 ka BP. It was also found that a long-term uplift rate of 0.28–0.37 mm/a and cliff retreat rate of 0.03–0.09 m/a best fit our data and existing onshore relative sea-level indicators. The formation of the STs at this time was further supported by chronologically intercurrent uplifting events that facilitated their formation and preservation. Finally, our model supports recent ice-sheet reconstructions related to higher MIS3 values since sea-level curves that were tested for this scenario (eustatically reaching up to −37/−38m depth), proved more successful in the formation of the "distant" sequence. [Display omitted] [ABSTRACT FROM AUTHOR]

Using the first high-resolution geophysical data set collected from the uThukela Banks Marine Protected Area (MPA), we reveal a plethora of hitherto unknown or poorly resolved seabed features. In tandem with several remotely operated vehicle dives, we improve on the previous National Biodiversity Assessment map for the area and reveal a more complex picture of the seabed geology and geomorphology on which the MPA is predicated. The upper slope (-120 m and deeper) is dominated by small canyons, gullies and rills that occasionally extend to the shelf edge and form a series of slumps. Suspected cold-water corals were imaged on the interfluves of the Thukela Canyon. The mid to outer shelf (-60 to -100 m) is mostly rocky, and is composed of Pliocene-age siltstones for the most part. Aeolianite shorelines are found at depths of 60 m and 100 m, in which palaeo-lagoons and parabolic aeolian dune systems are also preserved. These features provide habitat for mesophotic corals and demersal fishes. Overlying and abutting hard rock substrates are unconsolidated sandy sediments that are mobilised by the inshore movement of the Agulhas Current. An inshore mud belt characterised by pockmarks associated with free gas expulsion is mapped for the first time. A well-developed palaeo-drainage pattern is also revealed, posing exciting new opportunities for the study of benthic communities associated with palaeo-estuaries and lagoons now exposed at the seabed. Several new habitats, both inside and out of the MPA boundaries, should form the basis for future research within the MPA, in addition to informing expansions of the MPA. Significance: • Using a newly collected geophysical data set, we provide an unprecedented glimpse into the newly proclaimed uThukela Banks Marine Protected Area. • We reveal a complexity of marine habitats hitherto unknown from previous biodiversity surveys. These habitats include areas of possible expansion given the recognition of keystone species that occur just outside the MPA limits. [ABSTRACT FROM AUTHOR]

Newly acquired high-resolution geophysical data from four glacial cross-shelf troughs of the Labrador Shelf, namely the Okak, Hopedale, Makkovik and Cartwright troughs, are presented in this study. These cross-shelf troughs were repeatedly excavated by the former Laurentide Ice Sheet (LIS) during past glaciations. We map and describe three previously unknown grounding-zone wedges (GZWs) from an area where only sparse information about the retreat of the LIS is available. Based on our geomorphological analysis, we derive the dynamics and the direction of the ice retreat. For the Okak, Makkovik, and Cartwright troughs, the newly identified GZWs indicate fast-flowing ice streams with a high sediment load. We propose that a stable ice grounding-zone paralleled the present-day coastline in the Okak and Makkovik troughs, while in the Cartwright Trough, an ice-margin retreat towards the outlet of Lake Melville is more likely. We date available sediment samples of the deposits that onlap one of the GZWs to 14.5 ka cal BP and can show that the discovered GZWs must be older. This new information updates our understanding of the dynamics of the LIS, particularly at its eastern boundary, the Labrador Shelf and Sea, which is important to better reconstruct the effects of the LIS dynamics on global ocean currents and climate. • Discovery of three grounding-zone wedges on the Labrador Shelf. • Indications for fast-flowing ice streams with high sediment load during deglaciation. • Update of the ice-margin chronology based on the glacial retreat processes. [ABSTRACT FROM AUTHOR]

At the northern tip of the Betic realm (SE Iberian Peninsula), some troughs (synclines) and elevations (anticlines) alternate, marking the present-day coastal lobed morphology of cape-bounded bays, where subsidence and uplift conditions prevailed, respectively. In this study, we were able to establish a clear coastal evolution. To this end, we considered the sedimentological and palaeoenvironmental conditions, the palaeogeographical reconstruction, and recent tectonics until Middle Pleistocene times (MIS 5) through the interpretation of onshore cores, raised marine deposits and geophysical profiles. In this regard, as reflected by both onshore and offshore information, there seems to be a stratigraphical gap from the end of the Pliocene to MIS 15 (Middle Pleistocene). In areas under uplift conditions, linked to tardive Alpine tectonics, the deposits of ancient shorelines and raised beaches were located at different post-depositional elevations, which were dated from odd MIS 15 to MIS 5 using amino acid racemization. Only deposits aged MIS 7 and MIS 5 are roughly at the present-day sea level or some meters above. In the troughs, which remain mostly as lagoons and salt marshes, subsidence did not allow the sedimentary record to be discerned. However, many borehole cores were recovered, attesting lagoonal, marsh, sabkha, or alluvial environmental conditions, which were usually unconnected from the sea. Micropaleontological and amino acid racemization dating revealed these cores to be of MIS15 to MIS5 age. Offshore seismic research revealed five erosive-bounded deposits that are stacked accretionary prisms corresponding to highstands between odd MIS 15 and MIS 5. In contrast, even MISs can be correlated to the erosive horizons that separated the seismic units, reflecting lowstands. In this regard, some bars, at a range of distances from the present-day coastline, protected wetlands from marine influence, allowing the development of diverse sub-environments under changing paleogeographical and paleoclimatological conditions. • Deposits of ancient shorelines and raised beaches were AAR dated from odd MIS 15 to 5. • MIS 7 & MIS 5 deposits are roughly at the present-day sea level or some meters above. • Ancient bars protected wetlands from marine influence allowing some sub-environments. • Offshore erosive-bounded deposits (stacked accretionary prisms) ensued in highstands. • Subsidence and uplift prevailed during Quaternary in the Iberian Mediterranean realm. [ABSTRACT FROM AUTHOR]

Understanding the temperature-dependent sound scattering and acoustic radiation force of a spherical shell is crucial for a number of applications, including marine geophysics, underwater sonar systems, and underwater imaging. In the present study, a multiphysics vibroacoustic analytical framework is developed to investigate axially symmetric underwater temperature-dependent sound scattering and acoustic radiation force phenomena. The analysis focuses on a submerged structure consisting of a functionally graded (FG) sandwich spherical shell with piezoelectric layers subjected to a nonlinear thermal environment. The power-law distribution is assumed to describe how the FG core material's properties change as a function of thickness and temperature. The coupled vibroacoustic equations are obtained through the implementation of Hamilton's method, utilizing the principles of electromechanical coupling and the Kirchhoff-Love thin shell concept. After that, Fourier series expansions are used to solve the governing partial differential equations. The accuracy and adaptability of the method proposed in this work are shown by comparing the current results to those found in the literature and in COMSOL Multiphysics® finite element (FE) simulations. The far-field scattering form function and radiation force function versus frequency range are studied with a focus on the effects of electric voltage, temperature variations, and gradient index. • Increasing power-law index leads to lower backscattering and radiation force. • Decreasing shell temperature causes overall reduction in backscattering and radiation force. • Increasing the electrical voltage decreases the backscattering and radiation force. [ABSTRACT FROM AUTHOR]

Seismic waves from earthquakes recorded on the seafloor are composed of complex multiple arrivals. Here, distributed acoustic sensing (DAS) observations along a cable located offshore the Sanriku Coast, Japan, show that the local earthquake wavefield is particularly rich in Scholte waves. We introduce a processing pipeline to extract these surface waves from DAS records. We then invert hundreds of dispersion curves along a section of the cable to form a shallow high‐resolution shear‐wave velocity model. Moreover, we focus on the possible generation mechanisms of Scholte waves through a series of 2D and 3D full‐wavefield numerical simulations. We show that water phase reverberations greatly contribute to the generation of Scholte waves on the ocean floor. This study demonstrates the potential of DAS to observe and better understand a poorly known marine wave phenomenon and image the offshore shallow seismic structure with an unprecedented spatial resolution. Plain Language Summary: Distributed acoustic sensing (DAS) is a measurement technique that has recently demonstrated its utility for marine geophysics. DAS offers the possibility to observe the seismic wave at a scale and an extent previously unattainable with traditional passive seismic surveys. Here, we use a linear DAS array located offshore the Sanriku Coast, Japan. We propose a processing pipeline to extract surface waves from local earthquake DAS records and obtain hundreds of measurements along the cable. These measurements are used to infer a high‐resolution model of the near‐shore subsurface. Supported by a series of numerical simulations, we suggest that acoustic reverberations in the water column greatly contribute to the generation of surface waves on the ocean floor. This study further demonstrates that DAS can be used to understand marine wave phenomena better and image offshore seismic structures. Key Points: Passive high‐resolution Vs imaging of shallow sedimentary layers with ocean‐bottom distributed acoustic sensing and low‐magnitude earthquakesGridded slant‐stack method to extract Scholte waves from local earthquake wavefieldsFull‐wavefield simulations suggest that water phase reverberations generate Scholte waves at the ocean floor [ABSTRACT FROM AUTHOR]

Marine multichannel and wide‐angle seismic data constrain crustal structure along a 530 km margin‐parallel transect of the Hikurangi subduction zone. The subducting Hikurangi Plateau crust (VP 5.0–7.4 km/s) is ∼1 km thicker (11 ± 1 km) and mantle velocities are ∼0.2 km/s higher (VP 8.3–8.5 km/s) beneath south/central Hikurangi relative to north Hikurangi. In the overthrusting plate, an abrupt 0.5 km/s south‐to‐north reduction in forearc wavespeeds occurs in concert with a change in seismic reflection character. We analyze legacy seismic data to show that the forearc transition likely reflects lateral variability in the updip extent of the Torlesse Backstop. Furthermore, we map this unit along‐strike and note a broad correlation between the backstop and down‐dip extent of shallow slow‐slip. We propose that the geological architecture of the overthrusting plate contributes to spatial variability in the location of shallow frictional transitions along the Hikurangi margin, impacting both seismic and tsunami hazard. Plain Language Summary: Some subduction zones produce the largest earthquakes and tsunami on Earth, while others slip freely. To understand what factors impact subduction zone slip behavior, we analyze seismic data along a 530 km long transect spanning a transition from strong (south Hikurangi) to weak (central/north Hikurangi) interseismic locking. From south‐to‐north, we find that seismic wavespeeds in the overthrusting plate undergo an abrupt (∼10%) reduction, which coincides with a reduction in seismic reflectivity. We show that these changes likely reflect differences in the offshore (updip) extent of basement rocks within the forearc crust, which we map using seismic data. These maps also show that the offshore extent of basement rocks is broadly correlated with the maximum depth of shallow slow‐slip events. We propose that geological architecture of the overthrusting plate may contribute to spatial variability in megathrust slip‐behavior, impacting both seismic and tsunami hazard along the Hikurangi margin. Key Points: Coincident reductions in seismic wavespeeds and lower‐crustal reflectivity occur from south‐to‐north along the Hikurangi forearcLegacy seismic reflection data attribute the forearc transition to along‐strike differences in the updip extent of the Torlesse BackstopShallow slow‐slip is focused updip of the backstop, suggesting it may impact the location of shallow frictional transitions at Hikurangi [ABSTRACT FROM AUTHOR]

In this article, we present the algorithm, that allows to optimise the time and cost of marine seismic surveys. The application of a heuristic, algorithm is proposed for solving the traveling salesman problem on a series of graphs, to which the seismic observation system is reduced. The proposed algorithm assumes work with towed equipment and use of bottom stations. The algorithm provides a path close to the minimum, taking into account the real geometry of ships and their speed of passing various sections. The scientific novelty of the work lies in the application of the genetic algorithm for optimal planning, taking into account the closure of the work zones, to the problems of marine geophysics. The use of artificial intelligence methods allowed for the first time to develop a system that provides the ability to promptly adjust work plans depending on the changing meteorological and other conditions, including when working with several vessels using bottom stations. The paper describes the methodology, development of the algorithm and results in the form of applied software, and examples of planning on test data. [ABSTRACT FROM AUTHOR]

Sub-bottom profiling traditionally uses low-frequency signals (less than 20 kHz) to examine layered structures of the bottom sediment in large depth, but it has some limitations in deep-sea surveying. The surficial sediment within several meters under the water–sediment boundary in the deep sea cannot be distinguished clearly. In this study, a high-frequency sub-bottom profiler (HFSBP) was developed and applied to a manned deep-submergence vehicle (DSV), named Deep-Sea Warrior, to obtain a centimeter-level resolution stratum of several meters in the deep-sea surficial sediment. Twelve diving tests were carried out, the diversity of surficial benthic profiles on the northern slopes of the South China Sea was shown up for the first time and as many as four layers profiles were obtained in the low bending canyon region, rock surface profiles, discontinuous stratum structures and thick surficial sediment in the deeper region. Continuous and clear stratum structures within a range of about 2 m on the seabed surface sediment were obtained in 11 of the 12 dives. As the dive sites took a certain dispersive distribution, it reflected that the stratum structure of surficial sediment was prevalent in the northern slopes area of the South China Sea for the most part. To verify the effectiveness of HFSBP, a laboratory test in an anechoic tank was performed, and the experiment results verified the layered ability and the thickness measurement stability of it. The comparison was performed with shipboard data of deep-sea sub-bottom profiler (SBP) Bathy-2010, and the HFSBP results were obviously better than those of Bathy-2010 measurement. The clear and continuous fine layered data obtained by HFSBP may help scientists in new area research in marine geophysics. [ABSTRACT FROM AUTHOR]

Dynamic wedge failure produces short‐wavelength seafloor uplift efficiently with diminishing shallow slip on the plate interface, generating impulsive tsunami. For ria coasts with prevalent small‐wavelength bathymetric and geomorphologic features, such as the Sanriku coast of Japan, impulsive tsunami can be amplified to produce large runup. We model tsunami propagation and runup of the 1896 Sanriku tsunami by using the seafloor deformation from dynamic rupture models of Ma and Nie (2019) for a MW 8 earthquake with inelastic wedge deformation. The nonlinear Boussinesq equation is solved by a nested‐grid finite‐difference method with high‐resolution bathymetry data. We show that an inelastic deformation model with extensive wedge failure produces impulsive tsunami similar to those observed offshore the Sanriku coast in the 2011 Tohoku earthquake and generates large runup remarkably consistent with the 1896 Sanriku tsunami. As an alternative to previous models based solely on fault slip, we suggest that the impulsive tsunami and large runup along the Sanriku coast observed in the 2011 Tohoku earthquake can be explained by inelastic wedge deformation north of 38.5°N. Plain Language Summary: The Sanriku coast hosted several of the most devastating tsunami in recorded history of Japan, including the 1896 Sanriku tsunami and 2011 Tohoku tsunami. The runup on the Sanriku coast in both tsunamis were up to 40 m. It is unclear why such large runup can occur. Large near‐trench slip north of 38.5°N in the Japan Trench were inferred to generate the devastating 2011 tsunami on the Sanriku coast, which is, however, inconsistent with the bathymetry observations. Here we show that the inelastic failure of wedge sediments north of 38.5°N due to dynamic stress can generate efficient short‐wavelength seafloor uplift with diminishing slip at the trench, consistent with the bathymetry observations, which produces impulsive (short‐period) tsunami that can be amplified by the rugged Sanriku coast. An inelastic wedge deformation model of the 1896 Sanriku earthquake is shown to generate impulsive tsunami similar to what was observed offshore the Sanriku coast in the 2011 Tohoku tsunami and produce tsunami runup remarkably consistent with the observed runup of the 1896 Sanriku tsunami. Dynamic failure of thick wedge sediments north of 38.5°N in the Japan Trench likely plays an important role in the generation of the devastating 2011 Tohoku tsunami. Key Points: Inelastic wedge deformation produces impulsive tsunami due to short wavelength of seafloor upliftA simple inelastic wedge deformation model can explain the large runup of the 1896 Sanriku tsunamiThe impulsive tsunami and large runup along the Sanriku coast in 2011 can be due to inelastic deformation north of 38.5°N [ABSTRACT FROM AUTHOR]

During the past 20,000 years approximately one-quarter of the continental landmass of Australia was inundated by postglacial sea-level rise, submerging archaeological evidence for use of these landscapes. Underwater archaeological sites can offer substantial insights into past lifeways and adaptations to rapidly changing environments, however the vast scale of inundation presents a range of challenges in discovering such sites. Here we present a suite of methods as a model methodology for locating sites in submerged landscapes. Priority areas for survey were based on palaeoenvironmental contexts determined from the onshore archaeological record. Remote sensing was used to identify seabed composition and indicators of palaeolandscapes where high potential for human occupation and site preservation could be identified in Murujuga (or the Dampier Archipelago), northwestern Australia. Target locations were surveyed by scientific divers to test for the presence of archaeological material. Application of this methodology resulted in the discovery of the first two confirmed sub-tidal ancient Aboriginal archaeological sites on Australia's continental shelf. Survey methods are discussed for their combined value to identify different classes of landscapes and archaeological features to support future underwater site prospection. [ABSTRACT FROM AUTHOR]

Distributed acoustic sensing (DAS) is an emerging technology that repurposes a fiber-optic cable as a dense array of strain sensors. This technology repeatedly pings a fiber with laser pulses, measuring optical phase changes in Rayleigh backscattered light. DAS is beneficial for studies of fine-scale processes over multi-kilometer distances, long-term time-lapse monitoring, and deployment in logistically challenging areas (e.g., high temperatures, power limitations, land access barriers). These benefits have motivated a decade of applications in subsurface imaging and microseismicity monitoring for energy production and carbon sequestration. DAS arrays have recorded microearthquakes, regional earthquakes, teleseisms, and infrastructure signals. Analysis of these wavefields is enabling earthquake seismology where traditional sensors were sparse, as well as structural and near-surface seismology. These studies improved understanding of DAS instrument response through comparison with traditional seismometers. More recently, DAS has been used to study cryosphere systems, marine geophysics, geodesy, and volcanology. Further advancement of geoscience using DAS requires several community efforts related to instrument access, training, outreach, and cyberinfrastructure. DAS is a seismic acquisition technology repurposing fiber optics as arrays of dynamic strain sensors at 1- to 10-m spacing over kilometers. Easy DAS installations have availed time-lapse geophysical sensing in formerly inaccessible sites: urban, icy, and offshore areas. High-frequency wavefields recorded by DAS are analyzed with array-based methods to characterize seismic sources and image the subsurface. DAS has shown low-frequency sensitivity in the laboratory and field, for slow hydrodynamic and geodynamic processes. [ABSTRACT FROM AUTHOR]

On October 2016, during a geophysical survey in the Naples harbour aimed at evaluating its geo-archaeological potential, a wooden-hulled shipwreck was found along with a large amount of wreckage material. Cartographic evidence and preliminary underwater survey of the shipwreck have led its identification as the corvette Flora, which was deliberately burned 8 January 1799, along with five other ships and about 100 minor vessels of the Bourbon fleet before the French army arrived in Naples. This represents the first find and in situ underwater observation of an 18th-century sailing vessel in the bay of Naples. Our research contributes to knowledge of the events that led to the destruction of the fleet in 1799 and provides new, still preliminary, insights into the construction details of Bourbon vessels. [ABSTRACT FROM AUTHOR]

The Sanriku ocean‐bottom seismometer system uses an optical fiber cable to guarantee real‐time observations at the seafloor. A dark fiber connected to a Distributed Acoustic Sensing (DAS) interrogator converted the cable in an array of 19,000 seismic sensors. We use these measurements to constrain the velocity structure under a section of the cable. Our analysis relies on 24 hr of ambient seismic field recordings. We obtain a high‐resolution 2‐D shear‐wave velocity profile by inverting multimode dispersion curves extracted from frequency‐wave number analysis. We also produce a reflection image from autocorrelations of ambient seismic field, highlighting strong impedance contrasts at the interface between the sedimentary layers and the basement. In addition, earthquake wavefield analysis and modeling help to further constrain the sediment properties under the cable. Our results show for the first time that ocean‐bottom DAS can produce detailed images of the subsurface, opening new opportunities for cost‐effective ocean‐bottom imaging in the future. Plain Language Summary: Distributed Acoustic Sensing (DAS) is a relatively new measurement method that has the potential to convert existing fiber optic communication infrastructure into arrays of thousands of seismic sensors. In this research, we connected a DAS to a cable that was originally installed at the bottom of the ocean to sustain a seismic and tsunami observatory in the Sanriku Region. We show that this new type of measurement can provide reliable information to image and explore the shallow subsurface under this fiber cable. This is the first time such analysis is performed in an oceanic environment, and our methods could be readily exportable to other fiber‐optic cables that are the backbones of our modern telecommunication. Key Points: Ocean‐bottom Distributed Acoustic Sensing is used to image shallow VS structureRayleigh wave phase velocity dispersion curves are extracted from frequency‐wave number analysisReflection image is obtained from autocorrelations of ambient seismic field [ABSTRACT FROM AUTHOR]

• The acquisition of high-density bathymetric data up to the water line, resulted in the definition of a high-resolution baseline bathymetric surface of the Methoni bay and strait. • Ultra high-resolution bathymetric products allowed for detailed seafloor mapping of the nearshore zone of Methoni bay, investigation of wrecks or features of archaeological interest and for 3D visualisation of underwater antiquities. • Side-scan sonar mosaics show the spatial distribution of large manmade underwater features such as the submerged ancient breakwater or the submerged prehistoric settlement and the spatial distribution of large natural underwater features such as the underwater mount or the sand basin across the Methoni strait. • The dense grid of seismic profiles collected in the project area, documents the extension of the prehistoric settlement beyond the surficial ruins and support the 3D reconstruction of buried shipwrecks. • The fusion and spatiotemporal analysis of geoarchaeological data support the decision-making processes of stakeholders for maritime spatial planning, site preservation management, towards sustainable growth. The 'Evolved GE.N.ESIS Project' highlights the underwater cultural heritage resources off the coast of Methoni, Greece that could locally drive sustainable socioeconomic growth. An integrated marine geophysical survey, a hydrographic survey, and a GNSS survey were conducted off Methoni, recording six historic wreck sites, artefacts, the ruins of a submerged prehistoric settlement, and the town's ancient harbour/breakwater, as well as the geophysical properties of the underwater environment. The preliminary project results present bathymetric surfaces, backscatter intensity and magnetic maps, drawings, and seismic reflection profiles of the underwater antiquities and of the seabed, all fused in a 3D geographical platform. The results also shed light on the archaeological potential of the site, the nearshore physical processes, and their effect on the underwater archaeological resources. The project outcomes have shown that the establishment of an underwater archaeological park and diving sites at the cultural heritage sites will support cultural tourism development in the area and will have a positive impact on local socioeconomic development. The underwater archaeological park should comply with the basic principles of a site management plan – one that is established in the context of an integrated coastal management plan that identifies the maritime synergies or conflicts among human activities, archaeological resources, and the local environment, and utilises the 3D synthesis of marine knowledge from the project outcomes as a decision-making tool. [ABSTRACT FROM AUTHOR]

This paper presents the seafloor survey results obtained in 2016 and 2017 using four deep-towed vehicles, developed by the Institute of Undersea Technology at National Sun Yat-sen University, for investigating mineral resource potential offshore northeastern Taiwan. The deep-towed vehicles include the Abyss Twist-pair Imaging System (ATIS), the Video-guided Multi-corer (V-Corer), the TV-guided Grabber (TVG), and the Fiber-optical Instrumentation Towed System (FITS). The seafloor video surveys and sampling were conducted at five survey sites in the southern Okinawa Trough through five survey cruises. A total of 82.69 km of seafloor survey tracks were accomplished and plenty of seafloor characteristics and ecological phenomena were observed through the four deep-towed vehicles. The seafloor survey results, including the video data and the samples of animals, sediments, and mounds, have been provided to different scientific teams for conducting research on marine geophysics, marine geology, marine geochemistry, and marine ecology. The video data can be cross-checked and used as the supporting evidence for the analysis results from the scientific researchers. [ABSTRACT FROM AUTHOR]

The Norwegian government and also the universities were unprepared for an offshore oil province. Very little information about the offshore geology was then available due to the thick cover of Quaternary and Tertiary sediments in the North Sea basins. The potential for oil and gas in the North Sea could not have been predicted before the Norwegian Continental Shelf (NCS) was opened for petroleum exploration and drilling in 1965. Statements from the Geological Survey of Norway (NGU) in 1958 that there was no potential for oil offshore Norway referred specifically to the coastal areas, where no oil has been found. The midline principle was introduced in 1964, through an agreement with the UK. A continental shelf committee led by Jens Evensen from 1963 to1965 prepared the legal aspects and the regulations applicable for oil companies applying for licences to explore and produce oil and gas offshore Norway. A proposal for a Norwegian petroleum-related research project in 1964 was not funded and it took several years before petroleum-related teaching and research were established. After several dry wells the Ekofisk Field was discovered late 1969-early 1970, making it clear that Norway would become a significant oil-producing country. However, at that time nearly all the expertise was inside the major international oil companies and petroleum-related research at Norwegian universities and research institutes had a slow start. In 1972, Statoil and the Norwegian Petroleum Directorate (NPD) were established and also government funding for petroleumrelated teaching and research. This was met with considerable scepticism and resistance from some students and faculty and some claimed that a general education in geology would be sufficient. The University of Bergen developed a strong research group in marine geophysics and later one in petroleum geology. The need for petroleum-related teaching and research created a great challenge for the Norwegian universities. The standard was variable and the output of graduates with a professional qualification was generally too low. What we know about sedimentary basins and many fundamental geological processes is the result of petroleum prospecting and data from drilling and seismic data, contributing to Norwegian geology and general geological principles. [ABSTRACT FROM AUTHOR]

Rockfish, particularly yelloweye (Sebastes ruberrimus) and quillback (Sebastes maliger), are vulnerable to overfishing because they mature late and have affinity for shallow water (50–200 m) habitats. Because studies relating habitat characteristics with the distribution and presence of rockfishes at large scales (100s of kilometres) remain scarce, we sought to investigate the relationships between benthic characteristics with the presence–absence and abundance of rockfishes caught in longline surveys in nearshore waters of southern British Columbia. Habitat parameters were calculated from a 20 m resolution bathymetry layer. Yelloweye and quillback were examined separately and combined with 19 other rockfish species in a species aggregate (total rockfish); occurrence data were fitted with generalized linear mixed effects models, and abundance data were fitted with zero-inflated mixed effects models. The relationship between rockfish abundance with presence–absence and slope, distance to rocky habitat, and fine bathymetric position index suggests that these species prefer rocky, steep habitat. While underwater visual observation data offer measures of visual fish habitat and abundance, longline surveys may be a more cost-effective method for large-scale studies. [ABSTRACT FROM AUTHOR]

Highlights • Macrofauna was studied along bathymetric transects in three areas of the Mediterranean. • Canyons and open slopes were investigated in Catalan, Ligurian and South Adriatic margins. • Assemblages were significantly different among regions, as shown by high δ-diversity. • This was likely due to changes in food supply as a consequence of the longitudinal position. • Canyons and adjacent open slope showed a very high β-diversity. Abstract Macrofaunal assemblages were studied along bathymetric transects in six canyons and four adjacent open slopes of the Mediterranean Sea. The different areas investigated were located approximately along a longitudinal gradient at similar latitudes. Three regions were investigated: the Catalan (from 334 to 1887 m depth), the Ligurian (from 222 to 2005 m depth) and the South Adriatic margins (from 196 to 908 m depth). The analysis of the meso-scale distribution of assemblage structure and biomass showed significant differences among regions, which resulted in high values of δ-diversity. Clear differences in trophic composition were also observed, and a decreasing pattern in the individual body size of macrofaunal organisms moving Eastward. These patterns were apparently linked to changes in food supply, whereas macrofaunal abundance and number of taxa showed a decrease pattern with increasing water depth. When the assemblage structure was compared between canyons and adjacent open slope, a very high β-diversity was observed, indicating that the bottom topography exerted a strong effect on the assemblage characteristics. [ABSTRACT FROM AUTHOR]

Abstract Using a submerged pipeline section modeling the touchdown zone (TDZ) of a steel catenary riser (SCR), a sequence of contrast experiments were carried out to investigate the influences of seabed stiffness and water damping. Acceleration signals and bending strains at discrete positions along the TDZ pipe model were recorded during the testing, and by dealing with response-only data using the frequency domain decomposition method (FDDM) the results characterizing TDZ dynamic behaviors were acquired. These results indicate that under the excitation from the seabed model the complex modal responses appear with much higher frequencies than the end-loading one, similar to the dynamic response of a SCR TDZ, whose practical vibration frequencies are much higher than the heave motion of a hull. Identifications of complex modal parameters have proven to be effective using experimental response data, and this identification process can be applied in SCR TDZ monitoring to investigate seabed stiffness influences and water damping effects. Highlights • Scaled SCR TDZ monitoring simulation tests are carried out in a flume and bending strain data and acceleration signals are recorded. • Different seabed stiffnesses and water damping conditions are simulated to acquire comparable test results. • The feasibility of FDDM had been verified for TDZ modal identification from response-only data. • SCR TDZ vibration is a high-frequency complex modal response when the seabed stiffness has an important influence. [ABSTRACT FROM AUTHOR]

Abstract Fatigue response of steel catenary risers (SCR) in the touchdown zone (TDZ) is significantly affected by riser-seabed interaction. Non-linear hysteretic riser-seabed interaction models have been recently developed to simulate the SCR cyclic embedment into the seabed. Despite the advancements achieved in the prediction of non-linear hysteretic riser-seabed interaction, several inconsistencies have been recently identified in the nodal performance of some of the popular models. These limitations need to be resolved by proposing new models or improving the existing models. However, it is necessary to evaluate the influence of the identified shortcomings of the existing models on the global performance of the riser. In this paper, the influence of nodal inconsistencies observed in a popular riser-seabed interaction model on the global performance of the riser was comprehensively examined in the TDZ. The riser embedment profile, cyclic contact stress, contact stress envelop, mean shear force, cyclic bending moment, and consequently the cumulative fatigue damage was investigated. The study showed that the soil model overestimates the riser embedment and other global responses. Recommendations were made to overcome the identified shortcomings of the existing models in future developments. [ABSTRACT FROM AUTHOR]

Abstract Increased interest in paleoenvironmental studies is a result of climatic changes occurring at present and predicted for the future. Such studies could be done using the stable isotope compositions (δ 2H and δ 18O) of kaolins, which provide knowledge on the paleoenvironmental conditions prevailing during the time of kaolinisation. In this study, the stable isotopic compositions of clay-size fraction of kaolins occurring in Cretaceous and Tertiary Formations of the Douala Sub-Basin in Cameroon are presented, with the aim of reconstructing the paleoenvironmental conditions of the Sub-Basin. To achieve this, the clay-size fraction (< 2 μm fraction) of 8 kaolinite-rich samples were analysed for their δ 2H and δ 18O compositions, and results were reported as part per mil (‰) relative to the SMOW standard. The δ 18O values of kaolins found in the Cretaceous–Tertiary Formations of the Douala Sub-Basin varied between +18.2 and +21.0‰, whereas the δ 2H values varied between –69 and –53‰. Nine of the eleven samples plotted on the right of the supergene–hypogene line. Five of these nine samples plotted very close to the kaolinite line, which represents the composition of kaolinite in equilibrium with meteoric water at 20 °C; suggesting a supergene weathering origin of these kaolins. The determination of the temperature of kaolinisation yielded mean formation temperatures of 22 ± 2 °C and 27 ± 6 °C for Cretaceous and Tertiary kaolins, respectively. Excluding the two samples falling in the hypogene field, averages of kaolinisation temperatures were 20 and 25 °C during the Cretaceous and Tertiary periods, respectively. These temperatures are slightly below the present mean annual temperature in Douala (27 °C), thereby suggesting that the climate was becoming warmer from the Cretaceous to the Present. Therefore, Douala had a cooler and rainy climate during the Cretaceous, and the climate is gradually becoming hotter and more humid, favouring the refinement of existing kaolins and the kaolinisation of kaolin-forming minerals in the Sub-Basin. [ABSTRACT FROM AUTHOR]

Abstract Incorporating prior geological knowledge in geophysical process models often meets practical meshing challenges and raises the question of how much detail is to be included in the geometric model. We introduce a strategy to automatically repair and simplify geological maps, geological cross-sections and the associated meshes while preserving elementary consistency rules. To identify features breaking validity and/or the thin features potentially problematic when generating a mesh, we associate an exclusion zone with each model feature (horizon, fault). When these zones overlap, both the connectivity and the geometry of the geological layers are automatically modified. The output model enforces specific practical quality criteria on the model topology and geometry that facilitates the generation of a mesh with lower bounds on minimum angles and minimum local entity sizes. Our strategy is demonstrated on an invalid geological cross-section from a real-case study in the Lorraine coal basin. We further explore the impacts of the model modifications on wave propagation simulation. We show that the differences on the seismograms due to model simplifications are relatively small if the magnitude of simplifications is adapted to the physical problem parameters. [ABSTRACT FROM AUTHOR]

Abstract Marine magnetic data extracted from the geophysical database of the SHOM (the French Hydrographic and Oceanographic Service) offer a first overview of the magnetic offshore environment in the Gulf of Saint-Malo (Brittany, France). Their cross-interpretation with available geological and geophysical knowledge provides a new land and sea model of the western part of the Late Proterozoic North Armorican Cadomian belt. In particular, marine data exhibit relatively intense and heterogeneous magnetic signatures, mainly interpreted as the offshore prolongation of plutonic, volcanic, and metamorphic geologic formations recognized onshore. Imprints of major faults well known on land can be inferred at sea from discontinuities and shifting of magnetic anomalies or followed by high-resolution bathymetry. An impressive and dense dolerite dyke swarm propagated on more than 50 km from the coast seaward. Dykes are characterized by both 1-km-deep and less than 50-m-deep superficial magnetic responses, suggesting the existence of deeply rooted super dykes to which individual small-scale structures are connected. [ABSTRACT FROM AUTHOR]

Abstract As a sill constricting the exchange of deep water masses between the Nordic Seas and the North Atlantic, which forms an essential part of the Atlantic Meridional Overturning Circulation, the dynamic height of the Greenland Scotland Ridge and thus its overflow have an important influence on global climate. Several DSDP, ODP, and IODP sites have been drilled in the North Atlantic to shed light on the overflow and climate development. Reconstructions of bathymetry and sediment thickness have been put forward as well as calculations of the potential temperature of the conduit feeding the Iceland plume. The available studies have been screened to construct a conceptual model for the evolution of the palaeo-circulation in the North Atlantic and identify possible weaknesses in our knowledge. Details, e.g., timing and location, about the onset of the overflow are unknown, and especially the Paleogene development remains enigmatic. The database for this period is inadequate, and covers only small areas. The discussion centres on the earliest traces of the overflow leading to formation of sediment drifts in the eastern North Atlantic. More data provide a better base to reconstruct variations for the Neogene overflow, but also appears insufficient for in-depth analyses in time and space. Sediment drifts in the Iceland Basin indicate a first Iceland Faroe Ridge overflow for the early Miocene. Denmark Strait overflow appears to have started in mid-Miocene times, but evidence for this still is sparse. Grids of high-resolution seismic reflection data across all sediment drifts and all limbs of the Greenland Scotland Ridge combined with deeper drill sites targeting the complete sedimentary column down to basement are needed to fully understand the chronology of the Greenland Scotland Ridge overflow and its detailed impact on climate. Highlights • conceptual model for the GSR overflow chronology is constructed based on published hypotheses • late Oligocene/early Miocene deep water circulation appears to have been present only in the eastern North Atlantic • deepening and widening of the GSR allowed overflow of the IFR and later the DS since the early, resp. middle Miocene • large gaps in the distribution of the available datasets lead to conflicting suggestions for the timing of the overflow [ABSTRACT FROM AUTHOR]

Abstract 210Pb and 210Po are naturally occurring radionuclides that are commonly used as a proxy for particle and carbon export. In this study, the distribution of the 210Po/210Pb pair was investigated in the water column of the Barents, Kara and Laptev Seas and the Nansen, Amundsen and Makarov Basins in order to understand the particle dynamics in the Arctic Ocean during the 2007 sea-ice minimum (August–September). Minimum activities of total 210Pb and 210Po were found in the upper and lower haloclines (approx. 60–130 m), which are partly attributed to particle scavenging over the shelves, boundary current transport and subsequent advection of the water with low 210Pb and 210Po activities into the central Arctic. Widespread and substantial (> 50%) deficits of 210Po with respect to 210Pb were detected from surface waters to 200 m on the shelves, but also in the basins. This was particularly important in the Makarov Basin where, despite very low chlorophyll-a levels, estimates of annual new primary production were three times higher than in the Eurasian Basin. In the Nansen, Amundsen and Makarov Basins, estimates of annual new primary production correlated with the deficits of 210Po in the upper 200 m of the water column, suggesting that in situ production and subsequent export of biogenic material were the mechanisms that controlled the removal of 210Po in the central Arctic. Unlike 210Po, 234Th deficits measured during the same expedition were found to be very small and not significant below 25 m in the basins (Cai et al., 2010), which indicates, given the shorter half-life of 234Th, that particle export fluxes in the central Arctic would have been higher before July–August in 2007 than later in the season. Highlights • Largest dataset of 210Pb and 210Po in the Arctic Ocean to date. • Minimum 210Pb and 210Po activities in the halocline reflect scavenging on the shelf. • Potential use of the 210Po/210Pb proxy as an indicator of annual new primary production. • Substantial deficits of 210Po in surface and subsurface waters of the Makarov Basin. • Higher particle export in the central Arctic before July–August in 2007. [ABSTRACT FROM AUTHOR]

Abstract Remote mapping of bathymetry can play a key role in gaining spatial and temporal insight into fluvial processes, ranging from hydraulics and morphodynamics to habitat conditions. This research introduces Multiple Optimal Depth Predictors Analysis (MODPA), which combines previously developed depth predictors along with additional predictors derived from the intensity component of the HSI color space transformation. MODPA empirically selects a set of optimal predictors among all candidates utilizing partial least squares (PLS), stepwise, or principal component (PC) regression models. The primary focus of this study was on shallow (<1 m deep) and clearly flowing streams where substrate variability could have a pronounced effect on depth retrieval. Spectroscopic experiments were performed under controlled conditions in a hydraulic laboratory to examine the robustness of bathymetry models with respect to changes in bottom type. Further, simulations from radiative transfer modeling were used to extend the analysis by isolating the effect of inherent optical properties (IOPs) and by investigating the performance of bathymetry models in optically complex and deeper streams. The bathymetry of the Sarca River, a shallow river in the Italian Alps, was mapped using a WorldView-2 (WV-2) image, for which we evaluated the atmospheric compensation (AComp) product. Results indicated the greater robustness of multiple-predictor models particularly MODPA rather than single-predictor models, such as Optimal Band Ratio Analysis (OBRA), with respect to heterogeneity of bottom types, IOPs, and atmospheric effects. The HSI intensity component enhanced the accuracy of depth retrieval, particularly in optically-complex waters and also for low spectral resolution imagery (e.g., GeoEye). Further, the enhanced spectral resolution of WV-2 imagery improved bathymetry retrieval compared to 4-band GeoEye data. Highlights • A robust bathymetry method: Multiple Optimal Depth Predictors Analysis (MODPA) • Intensity components of HSI color space are incorporated in MODPA. • Intensity predictors enhanced the accuracy of depth retrievals. • Enhanced spectral resolution of WorldView-2 improved bathymetry retrievals. • Evaluation of atmospheric compensation (AComp) product of DigitalGlobe [ABSTRACT FROM AUTHOR]

Submarine channels share morphological similarities with rivers, but observations from modern and ancient systems indicate they are formed under processes and controls unique to submarine settings. Morphologic characteristics of channels--e.g., width, depth, slope, and the relationships among them--can constrain interpretations of channel-forming processes. This work uses morphometric scaling relationships extracted from high-resolution seafloor bathymetry to infer connections between morphology and process in submarine channels. Analysis of 36 modern channels in five geographic regions shows that channel widths vary regionally (from <100 m to >10 km wide) but occupy the same range of aspect ratios (~10:1-100:1). This suggests an autogenic control on aspect ratio, perhaps resulting from feedback processes in levee growth and/or bank erosion, and allogenic (e.g., sediment supply, grain size) controls on channel width. Submarine channel aspect ratios tend to decrease with increasing dimensions, while the opposite relationship has been observed for fluvial channels, likely due to opposing relationships between flow discharge and channel distance. Additionally, observation of an apparent lag between channel thalweg and levee responses to gradient changes suggests that thalweg and levee deposition and erosion may be partially decoupled due to the vertical structure of turbidity currents, with thalweg evolution driven by the basal, higher-shear-stress portion of the flow and levee evolution by the dilute upper portion. The data presented here provide a basis for predicting channel metrics in exploration scenarios, in which data coverage may be sparse. This documentation of a diverse suite of channels also captures the range of scales and variability exhibited globally by submarine channel systems, providing context for local studies. [ABSTRACT FROM AUTHOR]

A combination of the facies-geodynamic and radiolarian methods allowed us to determine the morphometric and temperature conditions for the initial accumulation of the Mesozoic siliceous-volcanic allochthonous complexes from the tectonic slabs of the Okhotsk-Koryak Orogenic Belt, which involves different marginal marine and ocean water areas and heterogenous marine rises. The radiolarian analysis made it possible to estimate approximately the paleolatitudinal position of these complexes and to reveal the pattern of the Mesozoic climate change in the Pacific and worldwide: from the warm Triassic through the Jurassic cooling to the Cretaceous optimum; the stages of warming demonstrate the dependence on global superplume episodes. [ABSTRACT FROM AUTHOR]

ABSTRACT Zuckerman, S. and Anderson, S., 2018. Bathymetry and water-level estimation using X-band radar at a tidal inlet. Knowledge of bathymetry in coastal areas is a key factor for maintaining shipping channels, identifying hazards to navigation, and measuring sediment transport processes. Remote-sensing techniques are crucial for this purpose, because in situ methods are often costly, time-consuming, and less frequent in occurrence. This paper presents a derived bathymetry and water-level retrieval algorithm that operates on time-series X-band marine radar data. The algorithm is designed to operate on a long-term continuous data stream, generating updated water-level measurements and bathymetry maps as new data are collected. In step 1, individual data sets are first processed to retrieve dominant wave numbers over a pyramid of overlapping tiles. In step 2, depths are estimated at each pixel location in the domain using the shallow-water wave dispersion relation. Last, results from step 2 are used to estimate the current water level. Updated water levels are used to tide correct a series of individual depth estimates, which are averaged together to produce an updated bathymetry map. In this way, no a priori or external data sources from the survey area are required. A 2-month-long experiment was conducted at Beaufort, North Carolina, to test the algorithm and quantify the frequency at which adequate signal levels were present for valid retrievals. Derived bathymetry and water-level results are presented and compared against ground truth. Derived measurements agree well with ground truth, although bathymetry accuracy degrades in areas of the domain with large bottom gradients or strong tidal currents. [ABSTRACT FROM AUTHOR]

In this article, we derive and prove the well-posedness of a deep water model that generalizes the Saut–Xu system for nonflat bottoms. Then, we present a new numerical method based on a splitting approach for studying this system. The advantage of this method is that it does not require any low-pass filter to avoid spurious oscillations. We prove a local error estimate and we show that our scheme represents a good approximation of order 1 in time. Then, we perform some numerical experiments that confirm our theoretical result, and we study three physical phenomena: the evolution of water waves over a rough bottom, the evolution of a KdV soliton when the shallowness parameter increases and the homogenization effect of rapidly varying topographies on water waves. [ABSTRACT FROM AUTHOR]