Seafloor Composition Research Articles

Sediment Characteristics Study at Sharm Obhur, the Red Sea using Multibeam Backscatter

Sharm Obhur, situated approximately 35 km north of Jeddah City along the Red Sea coast, is a prominent recreational area with diverse benthic habitats. Accurate mapping of seabed sediments is critical for characterizing marine ecosystems and elucidating benthic habitat distribution in this region. This study underscores the importance of assessing sediment distribution patterns in Sharm Obhur, particularly due to the prevalence of recreational activities and navigational traffic. This research investigates sediment dynamics in Sharm Obhur, a coastal creek near Jeddah, utilizing Multibeam Echo Sounder (MBES) backscatter data and grab sample analyses. The study focuses on understanding sediment distribution patterns and their implications for coastal management. MBES technology provides high-resolution data on seafloor composition and roughness, essential for assessing sediment types and bedforms. Through spatial alignment of MBES data with ground truth sediment samples, we analyze sediment characteristics and validate findings. Results indicate predominant sand presence with detectable mud in deeper channels and northern anthropogenically impacted areas. Gravel deposits correlate with coral formations near the creek edges. Tidal influence is evident, with increased sand presence at the creek entrance. The study demonstrates MBES backscatter's efficacy in mapping sediment distributions and seabed characteristics, benefiting marine science and coastal management. This research enhances knowledge of sediment transport processes, facilitating informed decision-making for sustainable coastal development and conservation efforts.

What could form a 35-km lineament of carbonate mounds on the ocean floor?

A multibeam survey carried out in November 2019 reveals a lineament of seafloor protrusions on the Santos Basin (SW Atlantic) continental slope. Shallow seismic data and seafloor composition suggest the lineament comprises a 35 km long arrangement of Cold-Water Coral (CWC) carbonate mounds, here named the Tupana Carbonate Ridge (TCR), defined in this contribution for the first time. Insights into genetic controlling factors of the TCR led to the analysis of single-channel seismic profiles that cross the lineament. Interpretation of deep seismic reflection data suggests a stratigraphic control provided by the lateral arrangement of coastal deposits formed during the protracted progradation that characterized a significant portion of Santos Basin's depositional history. Coastal sandstones encased in low-angle shelf-margin progradational wedges constitute a potential hydrocarbon reservoir supplied by the flow of fluids toward the surface through vertical structures. The ultimate source of fluids seems to be provided by halokinetic movements on a region depleted of salts known as the Albian Gap domain. This work questions the role of seafloor hydrodynamics in shaping the TCR morphology by eroding the carbonate mounds and forming elongated contourite systems.

Acoustic Seafloor Classification Using the Weyl Transform of Multibeam Echosounder Backscatter Mosaic

The use of multibeam echosounder systems (MBES) for detailed seafloor mapping is increasing at a fast pace. Due to their design, enabling continuous high-density measurements and the coregistration of seafloor’s depth and reflectivity, MBES has become a fundamental instrument in the advancing field of acoustic seafloor classification (ASC). With these data becoming available, recent seafloor mapping research focuses on the interpretation of the hydroacoustic data and automated predictive modeling of seafloor composition. While a methodological consensus on which seafloor sediment classification algorithm and routine does not exist in the scientific community, it is expected that progress will occur through the refinement of each stage of the ASC pipeline: ranging from the data acquisition to the modeling phase. This research focuses on the stage of the feature extraction; the stage wherein the spatial variables used for the classification are, in this case, derived from the MBES backscatter data. This contribution explored the sediment classification potential of a textural feature based on the recently introduced Weyl transform of 300 kHz MBES backscatter imagery acquired over a nearshore study site in Belgian Waters. The goodness of the Weyl transform textural feature for seafloor sediment classification was assessed in terms of cluster separation of Folk’s sedimentological categories (4-class scheme). Class separation potential was quantified at multiple spatial scales by cluster silhouette coefficients. Weyl features derived from MBES backscatter data were found to exhibit superior thematic class separation compared to other well-established textural features, namely: (1) First-order Statistics, (2) Gray Level Co-occurrence Matrices (GLCM), (3) Wavelet Transform and (4) Local Binary Pattern (LBP). Finally, by employing a Random Forest (RF) categorical classifier, the value of the proposed textural feature for seafloor sediment mapping was confirmed in terms of global and by-class classification accuracies, highest for models based on the backscatter Weyl features. Further tests on different backscatter datasets and sediment classification schemes are required to further elucidate the use of the Weyl transform of MBES backscatter imagery in the context of seafloor mapping.

Sedimentological Characterisation Of Sea Bottom Samples Collected Offshore Muara And Tutong, Brunei Darussalam

The study aims to get some additional knowledge on the modern seafloor composition offshore Brunei Darussalam by looking at the recent stratigraphic succession of the deposited sediments and their distribution patterns. For this reason, 10 shallow cores (22 to 46 cm thick) have been collected by scuba diving along two depth transects spanning from water depth of 20 to 60 m. One of the transects has been sampled north-northwest of the Muara village, just in front of the Brunei Bay and the other one off the coast near Tutong town, away from major sedimentary inputs. The results obtained portray two different sea bottom compositions and two different depth-related sediment distributions. The Muara transect is highly rich in mud and yielded abundant biogenic component at all investigated depths. The Tutong transect has a higher sand content but display constant changes along with depth. The sediment is mostly composed by biogenic grains such as rests of sponges, foraminifera, molluscs and echinoderms; the not biogenic grains are for the vast majority made of quartz. The sandy fractions of both transects have been tested for cyclicity and all cores can be described by functions with comparable periods, thus indicating that an oscillatory environmental event such as the alternation of the monsoon seasons, has similar influence on the seafloor of both transects.

Variations in felsic- versus mafic-sources in the Western Nordic Seas during MIS 1 to MIS 4

The goal of this paper is to employ quantitative methods to: first, describe the spatial variations in the quantitative non-clay and clay mineral composition of seafloor (surface) sediments; secondly, use those data to describe the temporal variations in mineral compositions of nine cores that extend (variously) between the present-day and ~85 ka BP; and thirdly, describe regional variations in the transport of felsic- versus mafic-rich glacial marine sediments at four sites close to Denmark Strait. K-mean clusters of recent seafloor samples (n = 156) distinguished four mineral facies, which characterize a range of mafic to felsic compositions. These samples serve as a training set to identify the down-core mineral facies in eight cores (n = 1053); the degree of provenance mixing is measured by fuzzy clustering on an unsupervised cluster analysis. Classification Decision Trees validate the mineral facies (only 6% misclassified) and indicate that variations in the weight % of pyroxene are of primary importance in defining cluster membership. Mineral compositions identify two end member core sites JM07-174GC (Greenland Sea) and LO9-18 (Reykjanes Ridge), while the cores north and south of the Greenland-Faroes Ridge (cores PS2644, MD99-2274, -2280, and -2323) are a mixture of mafic-rich and felsic-rich mineral facies. Variations in magnetic susceptibility and quartz wt% exhibit coherent runs of values above or below their medians in three of the cores occurred, indicating that these cannot be ascribed to random variations (p < .0001); they indicate the intermittent deposition of felsic-rich sediments to sites which today have ≤5 wt% quartz in surface sediments. Quartz-rich and low magnetic susceptibility intervals document increased glacially derived sediment transport most probably from NE Greenland and transported in the East Greenland Current. Comparison with the NGRIP isotope record indicates that the regional marine mineral sediment deposition is temporally variable.

Underwater Hyperspectral Imaging Using a Stationary Platform in the Trans-Atlantic Geotraverse Hydrothermal Field

Underwater hyperspectral imaging is a relatively new method for characterizing seafloor composition. To date, it has been deployed from moving underwater vehicles, such as remotely operated vehicles and autonomous underwater vehicles. While moving vehicles allow relatively rapid surveying of several 10–1000 m2, they are subjected to short-term variations in vehicle attitude that often compromise image acquisition and quality. In this study, we tested a stationary platform that was landed on the seabed and used an underwater hyperspectral imager (UHI) on a vertical swinging bracket. The imaged seafloor areas have dimensions of 2.3 m $\times $ 1 m and are characterized by very stable UHI data of high spatial resolution. The study area was the Trans-Atlantic Geotraverse hydrothermal field at the Mid-Atlantic Ridge (26° N) in water depths of 3530–3660 m. UHI data were acquired a 12 stations on an active and an inactive hydrothermal sulfide mound. Based on supervised classification, 24 spectrally different seafloor materials were detected, including hydrothermal and non-hydrothermal materials, and benthic fauna. The results show that the UHI data are able to spectrally distinguish different types of surface materials and benthic fauna in hydrothermal areas, and may therefore represent a promising tool for high-resolution seafloor exploration in potential future deep-sea mining areas.

Sensitivity of Texture Parameters to Acoustic Incidence Angle in Multibeam Backscatter

Texture analysis is one of the principal methods by which acoustic backscatter information is analyzed and classified. Recently, its application to the identification of subtle changes in acoustic images, such as the identification of marine life, has begun to increase. To utilize texture analysis for these purposes, the effect of survey geometry on texture parameters must be understood. A dense net of multibeam echo sounder data was recorded with a sixfold overlap to study the impact of the acoustic incidence angle on selected texture parameters derived from a Haralick gray-level co-occurrence matrix. The results show that a correlation of up to 0.29 exists between the beam angle and texture values in sedimentary facies. This correlation depends on the seafloor composition. The correlation is masked when seafloors of different compositions are considered, and it is reduced with decreasing image resolution. The observed effects are relevant when subtle seafloor changes are considered, and they may also be responsible for the comparably poor performance of texture analysis in several habitat mapping studies.

Megabenthic assemblages at the Hudson Canyon head (NW Atlantic margin): Habitat-faunal relationships

The distribution of megabenthic communities at the head of Hudson Canyon and adjacent continental shelf was studied by means of underwater video transects and still photo imagery collected using a towed camera system. The goal was to explore the relationships between faunal distribution and physical seafloor conditions and to test the hypothesis that increased seafloor heterogeneity in the Hudson Canyon supports a larger diversity of benthic communities, compared with the adjacent continental shelf. Hierarchical cluster analysis was performed to identify benthic assemblages as defined in imagery. The BIO-ENV procedure and the Canonical Correspondence Analysis were carried out to elucidate species groupings in relation to terrain variables extracted from bathymetric data. Species accumulation curves were generated to evaluate species turn over in and out of Hudson Canyon. The results indicate that seafloor morphology is the main physical factor related to benthic community composition and distribution. Assemblages dominated by sponges, zoanthids and cup corals colonized the canyon margins and flanks, and were associated with coarse-grained sediments, while sea pen assemblages were observed along muddy seafloor within the thalweg. An assemblage dominated by sea stars occurred on the shelf, associated with a sandy seafloor. Some assemblages were exclusively observed in the canyon area, suggesting that the increased variability of seafloor composition, together with the oceanographic processes specific to the canyon area, enhance beta diversity. The colonization by benthic suspension feeders within the canyon, in contrast to shelf assemblages, mainly composed of carnivores and detritus feeders could be favored the intense hydrodynamics at the canyon head that increase the availability of suspended organic matter.From the perspective of management and conservation of marine resources, the results obtained support the relevance of Hudson Canyon asa biodiversity hotspot. Such results are of particular significance in light of the recent action promoted by the Mid-Atlantic Fisheries Management Council, that restricts bottom trawling in most of the submarine canyons of the US Atlantic margin, including the Hudson Canyon, to protect cold-water corals from damage by fishing gear.

A snapshot of the Late Jurassic Western Tethys seafloor composition and morphology provided by the geochemistry of pelitic sediments (Corsica, Central Alps and Northern Apennines)

The chemical composition of fine-grained siliciclastic sediments is a powerful tool in provenance studies, either as a complement to other whole rock/single grain methods, or as a stand-alone method when other techniques are not applicable, and particularly in those cases where the coarser sediment fractions are not available or the regional-scale geologic framework is lost due major successive tectonic events. A comprehensive geochemical investigation of pelites from the post-rift deposits of the Ligurian-Piedmont ocean (sampled in tectonic units of the Alpine-Apennine orogen: Balagne Nappe, Corsica; Tuscan Nappe and Internal Ligurian units, Northern Apennines; Err-Platta units, Central Alps) has identified for the first time a major mafic-ultramafic input immediately following rifting. Key trace element ratios (e.g. LaN/YbN < 10; avg. Eu/Eu* = 0.73
0.06, 1SD; Th/ (Cr Ni V) < 0.03) show that the pelitic siliciclastic layers intercalated in the Radiolarite Formation (the first post-rift deposits) are systematically enriched in a mafic-ultramafic source component compared with the younger post rift sediments (Calpionella Limestone and Palombini Shale). Such a peculiar chemical fingerprint is interpreted as the result of erosion and distribution across the whole basin (even to continental domains) of intraoceanic ophiolitic debris by turbidity and bottom currents sweeping the sea floor at the time of deposition of the Radiolarite Formation. Exhumed mantle and gabbroic-basaltic rocks exposed at the morphologically articulated seafloor of the slowspreading Ligurian-Piedmont ocean were available to erosion during the whole time-span of the deposition of the Radiolarite Formation, whilst they became progressivey subordinate as a source as the basin floor was progressively covered by the siliciclastic input from the developing passive continental margins.

Nearshore substrate and marine habitat mapping to inform marine policy and coastal management

Colenutt, A., Mason, T., Cocuccio, A., Kinnear, R. and Parker, D., 2013. Nearshore high resolution substrate and marine habitat mapping to inform marine policy and coastal management.The Defra-funded National Network of Regional Coastal Monitoring Programmes of England, through collaboration with the Maritime and Coastguard Agency's Civil Hydrography Programme, are increasingly utilising cost-effective technology to achieve 100% seafloor coverage to International Hydrographic Organization (IHO) Order 1a standard, of the nearshore zone from about Mean Low Water Springs to approximately 1km offshore. Detailed specifications have been developed to ensure efficient acquisition of swath bathymetric data that are accurate, repeatable, maximise interoperability and are made freely available. Analysis of seabed substrate and habitat maps, which identify zones of exposed bedrock and surficial deposits of coarse, fine and mixed sediments, provide spatial detail of seabed features, such as sand waves, rock outcrops, pinnacles and scour and provide baseline conditions for monitoring of marine ecosystems. Interpretation and production of marine geology maps may also provide important information about seafloor composition and structure, physical properties and sedimentological and geological processes such as natural hazards. The methodology developed for data processing and interpretation combined with examples from a suite of detailed indicative substrate and marine habitat maps is presented. Interpretation of the full coverage swath bathymetry and acoustic backscatter information and ground-truthing data enables high resolution marine-related spatial and temporal substrate whilst habitat maps provide a sound multi-disciplinary scientific evidence base to inform development of European and UK marine environmental policy and planning, and are valuable tools for managing the sustainable use and conservation of coastal and marine resources, thus aiding the integration of terrestrial and marine planning regimes.

Historic (1900) seafloor composition in the Belgian–Dutch part of the North Sea: A reconstruction based on calibrated visual sediment descriptions

Concerns about human-induced degradation of marine ecosystems are presently being translated into European Directives aimed at a restoration of healthier seas. However, anthropogenic alterations are ancient and data on the pristine ecosystem are lacking, making the evaluation of their cumulative effects in the long run challenging. In the Belgian and Dutch parts of the North Sea, a historic data-set (the Gilson’s archive) exists to describe various compartments of the marine ecosystem in the first decade of the 20th century (1899–1914). The bulk of samples were acquired in the nearshore (up to 10 nautical miles off the coast) and further offshore in the Hinder banks area. In this contribution, we focus on the sediment information, which consists of 2200 visual descriptions of geo-referenced seafloor samples and 690 archived sub-samples, to reconstruct the seafloor composition 100 years ago. Estimates of mud levels, sand grain size, shell debris levels as well as occurrence of gravel, pebbles and cobbles were derived from the descriptions and standardized. Mud levels and sand grain-size categories were calibrated by means of grain-size analysis of archived samples ( n=383 analyses). Large patches of very high mud levels (50–100%) used to occur close to the shore, along the central and eastern coast. The visual sand grain-size categories display a significant trend in their median grain-size, enabling us to identify distinct patches of fine (<250 μm) and medium (250< X<500 μm) sands. High levels of shell debris were found in the offshore; in coastal waters, they fringed the high turbidity zone typical of this area. Gravel grounds were identified in gullies bordering offshore sand banks and were colonized with an abundant bushy epifauna. Long-term changes were briefly considered. The nearshore mud levels are reduced in the present-day due to specific human impacts. Thick layers of poorly consolidated mud now occur mostly in the artificially dug navigation channels, at disposal sites and around port areas. Offshore, richly colonized biogenic reefs of native flat oyster ( Ostrea edulis) were destroyed by targeted oyster fishery as early as in the 1860s. Since the 1920s, seabed disturbance caused by trawling activities steadily increased. We thereby demonstrate a degradation path from richly colonized biogenic reefs toward continuously disturbed sandy gravel grounds in the present day. Our conclusion is likely valid for many such grounds in the English Channel and southern North Sea. Major long-term changes observed thus far are clearly related to specific human activities. This reconstruction work will enable to better define the amplitude of human-induced changes in this portion of the North Sea, a necessary pre-requisite to the definition of meaningful environmental health targets.

Biological characterization of a whale-fall near Vancouver Island, British Columbia, Canada

Video analysis of a whale-fall discovered in the northeast Pacific Ocean, off Vancouver Island at a depth of 1288 m during ROV diving operations has identified 26 taxa of deep-sea benthic organisms inhabiting the seafloor immediately surrounding remnants of the whale skeleton. A photo-mosaic derived from high-definition video provides a quantitative visual record of the present condition of the site, the species richness, and substrate preference. Only the skull and caudal vertebrae remains of this large whale skeleton are estimated to have been approximately 16.5 m in length. Most organisms identified near the whale-fall are common benthic deep-sea fauna, typical of this water depth and seafloor composition. Much of this species richness comes from sessile suspension feeding cnidarians attached to the numerous glacial dropstones found throughout the area rather than the presence of the whale skeleton. Seep and bone specialists are rare (4 taxa) and may be, in part, a remnant population from a sulphophilic stage of whale-fall decomposition. Evidence of past colonization by Osedax sp. is visible on the remaining bones and we conclude that rapid degradation of the missing bones has occurred at this site as has been observed at whale-falls off central California in Monterey Canyon.

A Bayesian approach to seafloor classification using multi-beam echo-sounder backscatter data

Seafloor classification using acoustic remote sensing techniques is an attractive approach due to its high-coverage capabilities and limited costs. The multi-beam echo-sounder (MBES) system provides high-resolution bathymetry and backscatter information with 100% coverage. In this paper, we present a seafloor classification method that employs the MBES backscatter data. The method uses the averaged backscatter data per beam. It, therefore, is independent on the quality of the MBES calibration. Also, its performance is insensitive to seafloor type variation along the MBES swathe and corrections for the angular dependence of the backscatter are not needed. The method accounts for the ping-to-ping variability of the backscatter intensity. It estimates both the number of seafloor types present in the survey area and the probability density function for the backscatter strength at a certain angle for each of the seafloor types. Application of the method to MBES backscatter data acquired in a well-known test area in the North Sea shows very good agreement with available ground truth. The method’s discriminatory performance for this area is demonstrated to be comparable to that of taking samples of the sediment. All seafloor types known to be present in the area are resolved for. Application of the method to the Stanton bank data set shows clearly separable areas that differ in seafloor composition.

Holocene to modern fine-grained sedimentation on a macrotidal shoreface-to-inner-shelf setting (eastern Bay of the Seine, France)

This paper presents the results of an investigation on different timescales of the main mechanisms governing fine-grained sedimentation on a macrotidal sandy shoreface-to-inner-shelf setting with a supply of terrigenous sediment: the subtidal area of the southeastern Bay of the Seine (Calvados coast, France). Interpretation and calibration of side-scan sonar imagery clearly shows that compact clays crop out in water depths of 3–6 m. Radiocarbon dating and palynological studies of the material sampled using long cores from this subtidal area show that these relict sediments constitute the infilling of lateral valleys of the palaeo-Seine during the last 10 000 years. The lower parts of these deposits consist of compact clays that accumulated in a floodplain setting, later a salt marsh environment, and are succeeded by sediment with sand/mud couplets which formed in a tidal/estuarine system. The top of this sequence has been truncated by a wave erosion surface formed during the Holocene transgression. Today, the sediment accumulating is composed of fine sand, mixed with fine-grained sediment and sometimes temporarily covered by fresh mud. The more recent sedimentological data, compared with surveys in the 1960s–1970s, demonstrate both an increase in the erosion of the submerged earlier Holocene clays and an increase in the mud (silt+clay) content of the superficial sediments. On a seasonal timescale, the seafloor is affected by high-frequency variations in the nature of the contemporary sedimentary cover. Spatial and temporal observations of the seafloor composition have been undertaken during different seasons for four years (1998–2001) to study these sedimentation events. The sedimentation on the inner-shelf is at its maximum when veneers of fresh mud occur after some particular hydrological periods, i.e. sustained high-river outputs following several dry years (i.e. prolonged weak river flows), when significant volumes of mud have been stored within the Seine estuary. Such mud veneers result from: (1) the direct supply of river-born material, (2) the seaward shifting of the turbidity maximum, and (3) the resuspension of mud from the lower estuary (i.e. fluid mud and intertidal flats) under wind-waves, and have been termed ‘estuarine flood deposits’. On a longer timescale of at least the last decades, the southeastern Bay of the Seine is an area of erosion, but it is subjected to ephemeral fine-grained sedimentation on a seasonal timescale.

Experimental measurements of three-dimensional underwater sound propagation over a variable bathymetry laboratory scale model

Experimental measurements have been conducted giving a complete survey of the acoustic field from a point source in a three-dimensional shallow-water environment. The measurements have been conducted over a 1/10 000th scale model of the Santa Lucia Escarpment off the coast of California. The results of the experiment show three-dimensional propagation effects and areas of modal cutoff in the shallow-water regions. In addition, a discontinuity in the acoustic field was observed for propagation over a joint in the model. This observation has implications for localizing changes in seafloor composition from propagation measurements. Numerical predictions of the acoustic field for selected tracks in the survey show good agreement with the experimental results. [Work supported by the Office of Naval Research, Ocean Acoustics Program.]

Environmental Constraints on Drill Rig Configurations

Factors in determining an exploratory drilling vessel's efficient potential work capability for operations in the Eastern Seaboard coastal region are engineering oriented, predicated upon oceanographic and meteorological weather forecasting, seafloor composition, and order-of-magnitude vessel response amplitudes to sea conditions. Determined from vessel response information is the percentage of time exceedence for each motion when related to the drillfloor operational constraints of drilling, tripping, running casing, etc. The drillfloor activities are described as percentages of the total operation from which a cost-effective utilization factor is obtained or basically predicted vessel downtime. From an assigned utilization factor, the vessel's potential work capability is determined as a function of initial probable differences in capital costs and the comparative operational capabilities or limitations inherent in each vessel concept. The geometry of vessels reviewed covers a wide spectrum of twin-hull semisubmersibles, drillships, and bottom-supported multilegged self-elevating platforms.

A Sonic Device for Underwater Sediment Surveys

ABSTRACT A sonic device for roughly determining sea floor composition is described. It consists of a hydrophone encased in a watertight metal container designed to be dragged along the ocean bottom, and a suitable audio amplifier monitoring equipment located aboard a towing vessel. The frictional noises produced when the metal case is scraped along the bottom are picked up by the hydrophone and fed through cable to the amplifier. Since the noises caused by mud, sand, stony, and rock bottoms differ in character, it is possible to identify the bottom type by listening to the amplifier output. The device is especially useful for making a very detailed survey of a small area in shoal water for the purpose of constructing a sediment distribution chart.