Sub-bottom Sediment Research Articles

Effects of seabed corrugation and stratification on 3D acoustic propagation along the New England Shelf Break

Acoustic signals transmitted and recorded during the New England Shelf Break Acoustics Experiment in 2021 (NESBA) display evidence of complex scattering effects which were not captured in in situ modeling efforts. In particular, although the acoustic parabolic equation models used can predict later arrivals of a single transmission, initial arrivals show mismatch between model predictions and observation. In this presentation, estimates of sub-bottom sediment structure are supplemented by a high-resolution model of the bathymetry to simulate 3D sound propagation across a realistic seabed. The influence of the seabed corrugation and stratification on acoustic arrival times is examined in the context of the NESBA environment. [This research is supported by the Office of Naval Research].

Automatic Marine Sub-Bottom Sediment Classification Using Feature Clustering and Quality Factor

It has been proven that the quality factor (Q) is important for marine sediment attenuation attribute representation and is helpful for sediment classification. However, the traditional spectral-ratio (SR) method is affected by the interference effect caused by thin interbeds, which seriously degrade the performance of the SR method. Aimed at this problem, a novel method based on variational mode decomposition (VMD) correlation analysis is presented in this paper, which realizes the separation between interference reflections and effective signals. After obtaining the effective signals, a frequency band selection method is employed to weaken the influence of background noise. To better apply the proposed method to large-area sediment classification, a sediment clustering method based on texture features is introduced. Experiments on real data validate the effectiveness of the proposed method. The accuracy of the correlation analysis method using the modified parameters is 94 percent. The stability improvement in the standard deviation of the Q calculation can reach more than 90 percent. Moreover, the interpretation of sediment categories using the mean value of Q fits the drilling data well. It is believed that the proposed method has huge potential for the engineering applications in sub-bottom sediment classification.

Influence of stratified sub-bottom sediment layers on acoustic simulations in the New England shelf break environment

During the 2021 New England Shelf Break Acoustics (NESBA) Experiment, a large number of acoustic signal transmissions along and across the continental shelf were compared with combined physical oceanographic (PO) and ocean acoustic (OA) models. This experiment aimed to examine the influence of environmental changes in the water column on acoustic propagation in the shelf break environment. Sub-bottom surveys carried out by a combination of autonomous underwater vehicles (AUVs) and ship-board instruments revealed distinctly stratified sediment layers. Accounting for the properties of sub-bottom sediment layers is an integral component of diagnosing mismatch between experimental acoustic data and simulations, as these properties can influence the attenuation and scattering of received signals. A comparison of homogeneous half-space bottom models calculated at sea in May of 2021 and improved models which incorporate the results of sub-bottom surveys is presented, and the importance of this modeling consideration is examined for the purposes of data and model comparisons. [This work was supported by the Office of Naval Research.]

Prediction of Overpressure Zones in Marine Sediments Using Rock-Physics and Other Approaches

The paper discusses the problem of localizing zones of high pore pressure in sub-bottom sediments (first tens of meters under the seafloor). Prediction of the overpressure zones in the near-surface is required for the mitigation of risks at the early stages of the offshore hydrocarbon field exploration and development. The results of seismic data interpretation generally serve as the main source of information for this kind of problems, yet there are other methods to predict overpressure zones in the subsurface. The paper presents the results of the overpressure zone prediction using a set of methods including empirical ones, and the approach based on rock-physics modeling that features the soft-sand model of unconsolidated media effective properties. While the rock-physics modeling grants the most reliable result, it is also the most demanding method to the input data. Hence, it can be used to verify other methods of the overpressure zone prediction. We present the results of the overpressure zone prediction at the research site on the Black Sea shelf. The mitigation of the drilling risks via changing the drilling conditions is discussed in detail. As the drilling through the overpressure zones is often a necessity, the engineering solutions proposed in the paper can be applied elsewhere when facing similar problems typical for offshore exploration.

Microbial diversity of sub-bottom sediment cores from a tropical reef system

Microbial diversity of sub-bottom sediment cores from a tropical reef system

Contemporary geophysical surveys for marine sub-bottom sediments -Marine geophysical surveys for cable routes planning-

通信および送電のための海底ケーブルを敷設する前には，最適ルートを探索するために机上調査および原位置調査が実施される。原位置調査では，設計ルート周辺の地形・地質・障害物分布などを詳細に把握し，即時にルートを最適化する。特に，陸揚げ地点から最大水深1,500 m程度までの沿岸海域では，漁業活動や投錨などによるケーブル損傷を防ぐために，海底下1.0～2.0 m程度の深さでケーブルを埋設できるかどうかを評価する。このような調査では，音響を使った物理探査手法が主に採られ，また，磁気探査や電気探査も部分的に用いられる。

High-accuracy acoustic sediment classification using sub-bottom profile data

Sub-bottom sediment classifications have been widely used in marine science and engineering to obtain high-resolution information on types of sediments; however, these are often plagued by inaccuracies. Classification difficulties arise from the inability to effectively filter multiple reflections, extract representative lithology characteristic parameters, identify sub-bottom layer interfaces, extract image samples, control sample quality, optimise characteristic parameters, etc. To generate a highly accurate sub-bottom profile sediment map, a five-step classification method that considers two key lithology characteristic parameters of sub-bottom profile acoustic data was proposed. First, multiple reflections were filtered from the sea surface and sub-bottom layer interfaces of the primary signal. Second, two key characteristic parameters (relative backscattering intensity difference and attenuation compensation residual) were calculated. These reflect the relative differences in backscattering intensity and the attenuation compensation between adjacent interfaces based on the sound intensity attenuation model of a sub-bottom profile. Third, a combined method based on the sediment quality factor and peak trough of the echo signal loss level curve was employed to identify the actual interfaces between layers. An additional technique was proposed to determine the image sample width and preferred characteristic parameters. The resulting high-quality image samples and preferred characteristic parameters not only resulted in a faster convergence rate and increased ability of self-aggregation and identification, but also ensured that the training results met the convergence accuracy requirement. Ultimately, the preferred image samples were trained to classify the overall sub-bottom map of a selected test area of approximately 36 km2 in Bahai Bay, China. Compared with traditional methods, a considerably higher sediment identification accuracy was obtained. The experimental results indicate that the contribution rate of the two key lithology characteristic parameters was 65.49% according to principal component analysis, and the internal and external compatibilities were 97.98% and 84.76% for the training image samples, respectively. The total identification accuracy for the sub-bottom profile map was 98.2%. The two key characteristic parameters accurately captured the acoustic characteristics of sub-bottom sediments, significantly improving sediment classification. These results show that this method could be used to help refine the distributional estimates of submarine mineral resources.

Seabed Sub-Bottom Sediment Classification Using Artificial Intelligence

Kim, H.D.; Aoki, S.; Oh, H.; Kim, K.H.; and Oh, J., 2021. Seabed sub-bottom sediment classification using artificial intelligence. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 305–309. Coconut Creek (Florida), ISSN 0749-0208. Understanding fluid mud density and depth can contribute directly to the development of strategies to reduce dredging costs and other problems in coastal waterways. Although echo sounders are most commonly employed to measure depth, each country has different ways to classify the sub-bottom echo character classification. This study aims to train and test the YOLOv3 artificial intelligence model to classify sub-bottom profiles along with the Darknet-53 framework. Two dataset packages with different amount of image data were used to compare the model performance. The mean average precision (mAP), loss, average intersection of union (IoU), and F1 scores were compared to interpret the results between dataset packages. Throughout the study, it was observed that when the number of images used in training was higher, the model training performances improved. The results of this study show that the YOLOv3 model was successfully trained and tested on the sub-bottom profile datasets, resulting in a high accuracy of classification detection.

An Integrated Horizon Picking Method for Obtaining the Main and Detailed Reflectors on Sub-Bottom Profiler Sonar Image

A sub-bottom profiler (SBP) can capture the sediment interfaces and properties of different types of sediment. Horizon picking from SBP images is one of the most crucial steps in marine sub-bottom sediment interpretation. However, traditional horizon picking methods are good at obtaining the main horizons representing the main reflectors while ignoring the detailed horizons. While detailed horizons are the prime objective, many tiny structures caused by interference echoes will also be picked. To overcome this limitation, an integrated horizon picking method for obtaining the main and detailed horizons simultaneously is proposed in this paper. A total of three main process steps: the diffusion filtering method, the enhancement filtering method as well as the local phase calculation method, are used to help obtain the main and detailed horizons. The diffusion filtering method smooths the SBP images and preserves reflectors. Enhancement filtering can eliminate outliers and enhance reflectors. The local phase can be used to highlight all of the reflections and help in the choosing of detailed horizons. A series of experiments were then performed to validate the effectiveness of the proposed method, and good performances were achieved.

GAS SIPS AND SHALLOW ACCUMULATIONS OF GAS ON THE SHELF OF TURKEY IN THE BLACK SEA

It has been suggested that shelf and slope sediments of high deposition rate are methane sources, whereas the deep basin is methane sink. The methane production and migration in sediments may cause massive slope failures so methane is geologically important. Methane production is also economically important as methane seeps may indicate the presence at depth of hydrocarbon reservoirs, and methane hydrate may be an important source of energy. Recent studies in marine geology indicate potential geo-resources in the Turkish coast of Black Sea. The Black Sea sediments are rich in calcite and organic carbon, the latter showing a high degree of preservation due to anoxia in the waters below 100-150 m. Different marine geophysical surveys at different times were carried out in order to understand the sedimentary features of gas-saturated sediments in the Black Sea. Multibeam, side scan sonar, sub-bottom profiler and multi-channel seismic data were collected to make both high-resolution bathymetric and reflectivity maps of the seafloor. In some cruises, deep-tow combined side scan sonar and subbottom profiler was used to obtain acoustic images of both the seafloor surface and subbottom sediments. Several different structures were observed in the Black Sea basin as slumps, pockmarks, faults, gas chimneys, shallow gas accumulations and dome-like structures. Structures, which contain gas hydrates, are present on the seismic sections as strong acoustic reflections.

Evidence of cultural eutrophication of the Gulf of Gdańsk based on diatom analysis

Abstract The objective of this study was to reconstruct the environmental changes in the Gulf of Gdańsk in the last 200 years. Four subbottom sediment cores were analyzed with respect to diatom flora and anthropogenic effects. The so-called “anthropogenic assemblage” – a result of cultural eutrophication – was observed in the surface sediments. Changes in the species composition may have been caused by the increased use of fertilizers, nitrogen loads and increasing organic matter concentration. Three phases (A, B and C) were distinguished based on the floristic spectrum, which clearly indicates trophic changes in the study area.

The Study of Sub-Bottom Sediments in Petrozavodsk Bay of Lake Onega Using Complex Geological-Geophysical Methods of Data Analysis

The results of geological interpretation of data of engineering seismic surveys obtained during the field works at Lake Onega are given. Seismic-stratigraphic units specified on processed seismograms are characterized. The survey enabled us to compile a seismic-stratigraphic column of the Quaternary sediments of Lake Onega, which may be used to analyze the structure of the open part of the lake.

Seismic response of soft water-bottom sediments

The Municipal Government of Istanbul plans to construct a second subsea tunnel across the Bosphorus Waterway between the European and Asian sectors of the city, and a submerged tube tunnel across the Golden Horn Waterway which connects to the Bosphorus Waterway. High-resolution 2-D sparker seismic surveys were conducted to delineate geometry of the sub-bottom sedimentary sequence and geometry of the sediment-bedrock interface, and to determine the locations and depths for geotechnical boreholes. In this paper, we discuss aspects of the seismic response of water-bottom sediments. Unlike the usual behavior of water-bottom multiples with alternating polarity observed in the Bosphorus case, we find that the polarity of the water-bottom primary and first-order water-bottom multiples are the same in the Golden Horn case. The polarity behavior of the water-bottom multiples in the Golden Horn is convincing evidence that the low-velocity sub-bottom sediments can be described as a gas-charged suspension — a composition that consists of particles suspended in water with only slight grain-to-grain contact and biogenic gas. The results of the velocity analysis of the Golden Horn seismic data confirm the presence of low-velocity (550–650 m/s) soft water-bottom sediments with an average thickness of 18 m above the bedrock. This makes it imperative to design the foundation pillars for the planned submerged tube-tunnel with sufficient penetration deep into the bedrock.

Waterborne Electrical Resistivity of the Hypersaline Mono Lake

A short, waterborne streamer resistivity survey was conducted on Mono Lake in California. The lake, located on the eastern side of the Sierra Nevada Mountains, contains a significant amount of dissolved solids due to being a terminal lake with no outlet. The survey was conducted to determine if the method could be used to define subbottom sediments and other geological features to answer questions related to recent-past volcanic and tectonic events. The survey used a 15-meter dipole-dipole array towed at approximately 2 mph behind a small flat bottomed boat. The survey was limited in scope to collecting approximately 6,000 m of data within the western cove, where substantial core sampling has taken place. Comparison of the methods indicates the towed array can obtain good quality data despite the lake's conductivity being in excess of 84,000 uS/cm. The resistivity models reconstructed geological material upwards of 400 ohm-m to depths of 35 m, which likely represent hard rock below the lake. We conclude that the method could be used to map most of the shallow areas of the lake, where the water column is less than 20 m. The deepest areas of the lake, south of Paoha Island, would require streamer resistivity cables with an electrode spacing of at least 60 m.

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Paola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO2-rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted 13C isotopic composition and slightly positive δ18O values. By contrast, siderite concretions, generally found within the first 6 m of sediments on the alleged mud volcanoes, yielded positive δ13C and δ18O values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the 13C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13C-rich dissolved inorganic carbon (DIC) and 18O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO2.

A preliminary numerical model of three-dimensional underwater sound propagation in the Block Island Wind Farm area

The Block Island Wind Farm, consisting of five 6-MW turbines, is the first U.S. commercial offshore wind farm harvesting wind energy to generate electricity, located 3.8 miles southeast of Block Island, Rhode Island. In-situ underwater and airborne noise measurements were made during the construction and the first two months of the operational period for the purpose of environmental impact assessment. To better interpret the noise measurements and extend the noise propagation prediction beyond the coverage of listening stations, a three-dimensional underwater sound propagation model is created with a high resolution bathymetric map and a data-assimilated ocean dynamic model. The bathymetric map is made using the 3 arc-second U.S. Coastal Relief Model (CRM) with a 100-m horizontal resolution provided by the National Centers for Environmental Information (NCEI). The ocean model is extracted from the Regional Ocean Modeling System (ROMS) ESPreSSO (Experimental System for Predicting Shelf and Slope Optics) model covering the Mid-Atlantic Bight with a 5 km horizontal resolution and 36 terrain-following vertical levels. Temporal and spatial variability of noise propagation conditions is identified in the integrated acoustic and oceanographic model. Future model development incorporating surface wind waves and sub-bottom sediment layer structure will be discussed. [Work supported by BOEM.]The Block Island Wind Farm, consisting of five 6-MW turbines, is the first U.S. commercial offshore wind farm harvesting wind energy to generate electricity, located 3.8 miles southeast of Block Island, Rhode Island. In-situ underwater and airborne noise measurements were made during the construction and the first two months of the operational period for the purpose of environmental impact assessment. To better interpret the noise measurements and extend the noise propagation prediction beyond the coverage of listening stations, a three-dimensional underwater sound propagation model is created with a high resolution bathymetric map and a data-assimilated ocean dynamic model. The bathymetric map is made using the 3 arc-second U.S. Coastal Relief Model (CRM) with a 100-m horizontal resolution provided by the National Centers for Environmental Information (NCEI). The ocean model is extracted from the Regional Ocean Modeling System (ROMS) ESPreSSO (Experimental System for Predicting Shelf and Slope Optics) mo...

Vertical migration of fine-grained sediments from interior to surface of seabed driven by seepage flows–‘sub-bottom sediment pump action’

A scientific hypothesis is proposed and preliminarily verified in this paper: under the driving of seepage flows, there might be a vertical migration of fine-grained soil particles from interior to surface of seabed, which is defined as ‘sub-bottom sediment pump action’ in this paper. Field experiments were performed twice on the intertidal flat of the Yellow River delta to study this process via both trapping the pumped materials and recording the pore pressures in the substrate. Experimental results are quite interesting as we did observe yellow slurry which is mainly composed of fine-grained soil particles appearing on the seabed surface; seepage gradients were also detected in the intertidal flat, under the action of tides and small wind waves. Preliminary conclusions are that ‘sediment pump’ occurs when seepage force exceeds a certain threshold: firstly, it is big enough to disconnect the soil particles from the soil skeleton; secondly, the degree of seabed fluidization or bioturbation is big enough to provide preferred paths for the detached materials to migrate upwards. Then they would be firstly pumped from interior to the surface of seabed and then easily re-suspended into overlying water column. Influential factors of ‘sediment pump’ are determined as hydrodynamics (wave energy), degree of consolidation, index of bioturbation (permeability) and content of fine-grained materials (sedimentary age). This new perspective of ‘sediment pump’ may provide some implications for the mechanism interpretation of several unclear geological phenomena in the Yellow River delta area.

Soft sediment deformation in the shallow submarine slope off Nice (France) as a result of a variably charged Pliocene aquifer and mass wasting processes

Along the Ligurian slope near Nice, southeastern France, a combination of natural and man-made factors govern slope stability, and contributed to a devastating tsunamigenic landslide near Nice airport in 1979. Based on a total of 72 gravity and Kullenberg cores we characterise the architecture and facies of the subbottom sediment. A total of six sedimentary facies types were observed, three of which represent the Pliocene–Holocene background sediment in the wider Nice area while another three are associated with the 1979 landslide and tsunami. The three primary facies types are soft silty clay/clayey silt, somewhat indurated silt/sand interbeds, and Pliocene conglomerates underlying the former. The three other facies are poorly sorted mass wasting deposits up to pebble size, silt representing the finer fraction of the mobilised mass, and a tsunami-related bed into which plant debris and artefacts got amalgamated.Accompanying geotechnical results attest that significant strength variations exist when comparing measurements from the narrow shelf, shelf break and shallow slope as well as the 1979 slide scar. Factors such as groundwater charging in the more permeable horizons further lower the effective stress and, in places, approach lithostatic. Above such permeable silt/sand beds, deformation of soft clay is observed, suggesting that leaching of ions from the clay mineral surfaces and frayed edges also facilitates weakening and creep, micro-slumping and folding. Elevated water supply as well as hydraulic fracturing of the clayey sediment is further attested by pipes of cm-diameter and several decimeters length, which entrained very soupy mud. In the shallowmost deposits in and landward of the slide scar, we also observe remnants from the catastrophic deposition associated with the 2–3m high tsunami wave triggered in 1979, as attested by amalgamated sea grass and artefacts. Based on our observations and measurements on core-scale and earlier models based on in situ CPTu, we suggest that a significant part of the Quaternary delta and slope apron deposits are prone to being mobilised without a large external trigger, so that all in all a high risk for a landslide event of considerable size off Nice international airport is identified.

Sedimentation dynamics and metal loading in Lake Pyhäjärvi, Finland

Post-isolation (9,600 year BP) sedimentology in Lake Pyhajarvi, Finland, was studied using sub-bottom echo-sounding and sediment coring. The sediment sequence appeared in the echo-sounding profiles as two sections: (1) a lower section of homogenous, light grey gyttja clays, and (2) an upper section with dark layers of mainly clay gyttjas and gyttjas, here referred to as C_gyttja. We investigated the thickness and volume of sediments as well as their morphology and areas of accumulation. Approximately 77 % of the lake represents areas of accumulation, containing 34 and 1.3 million tons of dry matter and carbon, respectively. Spatial variability in sedimentological properties indicates that accumulation in the Kirkkoselka sub-basin was focused into the deepest areas since lake isolation. In the Isoselka sub-basin, however, accumulation was focused partially onto the flanks of the depression, whereas the deepest parts (23–27 m) of the sub-basin represent erosional areas. There appears to have also been sediment re-suspension and re-deposition, as indicated by erosion surfaces. This, combined with dune-like bottom morphology in the accumulation areas, provides evidence for the role of wind-driven bottom currents on sedimentation dynamics in the Isoselka sub-basin. Increases in Cu and Zn concentrations, driven by Pyhasalmi mining activities, were used as a geochemical marker for recent sedimentation (RS) between 1966 and 2008. As a consequence of wind-driven bottom currents, 60 % of the metals accumulated in the Kirkkoselka sub-basin and 40 % accumulated in the Isoselka sub-basin. There is a spatial correlation between amounts of C_gyttja and RS. In the middle of dune-like C_gyttja formations in the Isoselka sub-basin, the RS grain size is smaller than in other areas. Variations in RS are greatest along the borders of the accumulation area, likely a consequence of bottom currents in those areas.

Grounding‐line dynamics during the last deglaciation of Kveithola, W Barents Sea, as revealed by seabed geomorphology and shallow seismic stratigraphy

A marine geophysical study reveals a complex deglaciation pattern in the Kveithola trough, W Barents Sea. The data set includes multibeam swath bathymetry and sub‐bottom sediment profiler (chirp) data acquired for the whole extent of a palaeo, marine‐terminating ice stream, along with high‐resolution single‐channel seismic data from chosen profiles. The multibeam data show a geomorphic landform assemblage characteristic of ice streams. The results of a combination of seismic and chirp unit stratigraphy reveal that the seabed geomorphology is governed by a deeper‐lying reflector. The reflector dominates surface expressions of several subglacial and ice‐marginal units, each connected to a separate episode of ice‐margin stillstand/advance. Analysis of the combined data set has resulted in a conceptual model of the ice‐stream retreat. The model depicts complex deglaciation of a small, confined ice‐stream system through episodic retreat. It describes the formation of several generations of grounding‐zone systems, characterized by high meltwater discharges and the deposition of fine‐grained grounding‐line fans. The inferred style of grounding‐zone deposition in Kveithola deviates from that of other accounts, and is suggested to be intermediate in the previously described continuum between morainal banks and grounding‐line wedges. The results of this paper have implications for grounding‐zone theory and should be of interest to modellers of grounding‐line dynamics and ice‐stream retreat.