Sub-bottom Profiler Research Articles

Islands of the Tectonic Origin in the Shatt Al-Arab River, Southern Iraq

Several factors control the formation of river islands, such as tectonic factors, sedimentation, erosion, and human activities. This research is concerned with islands in the Shatt Al-Arab channel, which are likely to be traced back to tectonic factors in their formation. The islands of the Shatt Al-Arab River are distributed along its axis starting from the islands of Sindbad and Muhammadiyah, 15 km to the north of the city center of Basra, to the islands of Shatit, Al-Dawasir and Minauhi, 70 km south of the city center of Basrah. This study area is part of the Mesopotamia Plain, southern Iraq. The fieldwork period extended from the beginning of September 2012 to June 2013, which included making subsurface sections (longitudinal and transverse) of the bottom of the Shatt Al-Arab channel using the Sub-bottom profile Strata box device, imaging the topography of the river bottom in a side scan sonar, collecting the bottom sediments by a grab sampler. The volumetric analysis method uses the Master Sizer device based on the Folk classification to calculate the volumetric gradient of sediments. The study showed that the tectonic factor has a prominent role in the growth island Maino and as a result of the presence of sub-surface structures for the structure of the Siba, which appeared to affect the subsurface layers of the river bed near the island as it appeared in the survey sections of the Strata box device. There are some islands that more than one factor emerged as a reason for their formation and development, as in the islands of Muhammadiyah and Umm al-Rasas, where tectonic and sedimentary factors interfered in their formation and development due to the influence of sub-surface structures as well as the influence of nearby rivers such as the Karma and Karun Rivers.

Hydrographic surveys as an art of delineating the impact of climate change on the coastal environment

Marine acoustic techniques are quite efficient in remote seabed classifications and hydrographic investigations by providing highly detailed information about broad areas of the seafloor and the subsurface layers in a short period of time. Climatic change is considered as the forcing factor for the eustatic sea-level-rise along the Mediterranean coast, leading to the large coastal inundation and the subsidence of the ancient maritime installations, these ancient sites can be used as indicators for the relative changes in sea-level through later times. Marine surveys were carried out to delineate the coastal geomorphological changes associated with sea level rises and natural hazards along some areas on the coast of Alexandria during the last two millennia. Hydrographic and seismic surveys were implemented in the study area by using a multi-beam echo-sounder, side scan sonar, and sub-bottom profiler, then the acoustic data were calibrated with dated core samples and ROV camera images. Multi-beam is considered the most commonly used tool in harbor surveys utilizing the returned acoustic signals to measure the depth of the seafloor, while the side scan sonar instrument provides high-resolution images for the elevated structures from the seafloor depending on the backscatter strength of the signal, and the sub-bottom profiler uses chirp waves that deliver high resolution vertical images for the subsurface sediment situation. Results of sonar imaging and bathymetric mapping outlined submerged margins of archaeological remains related to ancient Ptolemaic and Greek ports. Seismic interpretations revealed significant changes in the coastal geomorphology, where the massive burial of the port structure indicated the occurrence of sudden natural hazards originated from seismic waves; therefore, a destructive tsunami wave accompanied by sediment slumping that followed by eustatic sea-level-rise seems to be the dominant factors for this dramatic burial. The research results showed the potentiality of hydrographic surveys in detecting climate change indicators.

Geophysical evidence for submarine methane seepage on the Western slope of Okinawa Trough

Identifying seafloor methane seepage efficiently has important implications for assessing environmental impact, reducing the uncertainty of top seal integrity, understanding the petroleum system, and mitigating the drilling hazards due to shallow gas influx. Pore water geochemistry analyses suggest that the study area has an extremely high methane seepage flux and active methane anaerobic oxidation processes. However, geochemical data cannot provide details about the internal seepages. The geophysical dataset from the Western slope of Okinawa Trough, including 2D high-resolution seismic, sub-bottom profiles, and bathymetry, gives us a good opportunity to understand the detailed characteristics of methane seepages in this study. Geophysical data have revealed numerous methane seepage-related features such as seismic chimneys, pockmarks, submarine domes, and amplitude anomalies, including bright spots and enhanced reflections. Pockmarks and domes are often associated with seismic chimneys, indicating that fluid migration is important in their formation. The various geophysical expressions may represent different stages of methane seepage. Fluid quickly drains, causing severe sediment deformation and forming pockmarks, whereas domes may indicate the early stages of fluid discharge. Chimneys that do not extend to the seafloor may indicate that the venting is gradual and focused. Flares linked to domes or pockmarks may indicate that the fluid migration is active. Several factors triggered the existence of methane seepages on the Western slope of the Okinawa Trough, including tectonic setting, overpressure and rapid sedimentation.

Insight into contrasting patterns of sedimentation from shelf edge to base-of-slope on the Mozambique-Zambezi margin (17°30′S-20°S) during the last 40 ka

The pattern of sediment dispersal and the location of sediment depocentres on continental margins can be very complex in both space and time. We aim at investigating how significantly external and internal factors, such as river runoff, bottom current and sliding can deviate the sediment dispersal from a simplistic fully sea-level controlled spreading. In this study we examined the sedimentation at two transects across the Mozambique-Zambezi slope between 17°20S-20°S, where multibeam bathymetry, sub-bottom profiler data and sediment cores were acquired. The period investigated spans the last 40 cal ka BP with a focus on the contrast between the last glacial (lowstand) and the Holocene (highstand) periods. Results show contrasting patterns of sediment dispersal, deposition and preservation. Sea level fluctuation remains the main forcing and most of the sediment from the Zambezi River settled on the inner shelf since the last sea level rise. However, we found that two major depocentres have developed on the upper slope during the Holocene consequent to the interaction of bottom currents with seabed morphologies at the shelf edge and at the upper slope. Early Holocene sliding in the north-east and in the south-west upper slope is a secondary but yet major factor of sediment transfer to the deep domain. Identified preconditioning factors for sliding on the slope are related to lowstand sediment loading and fluid circulation on the upper slope, and erosion at the base of slope of a plastered drift. Triggering must be related to margin wide mechanisms such as changes in hydrostatic pressure and reorganisation of sediment dispersal, subsequent to the post-glacial sea level rise, or maybe a period of regional seismicity. Climatic conditions in the Zambezi River watershed during the Bolling-Allerod and Younger Dryas periods are recorded and imprinted on the upper slope in the form of a detrital rich layer and a prominent slope-wide high-amplitude reflector. All over the continental slope, plastering of sediment deposits by bottom currents is pervasive and shows a morphological continuum from erosional scours at the base of slope to sediment waves on the upper slope and a possible interaction between along and across slope transport processes. We conclude that, in addition to sea level, the interplay of external and internal factors such as oceanic circulation and sliding, together with margin morphology, lead to the development of unexpected depocentres on the continental slopes. Thus, the study of modern marine analogues is crucial to avoid misleading interpretation of fossil deposits in terms of paleo sea level and more generally of paleo-environmental conditions.

Endospores associated with deep seabed geofluid features in the eastern Gulf of Mexico.

Recent studies have reported up to 1.9× 1029 bacterial endospores in the upper kilometre of deep subseafloor marine sediments, however, little is understood about their origin and dispersal. In cold ocean environments, the presence of thermospores (endospores produced by thermophilic bacteria) suggests that distribution is governed by passive migration from warm anoxic sources possibly facilitated by geofluid flow, such as advective hydrocarbon seepage sourced from petroleum deposits deeper in the subsurface. This study assesses this hypothesis by measuring endospore abundance and distribution across 60 sites in Eastern Gulf of Mexico (EGM) sediments using a combination of the endospore biomarker 2,6-pyridine dicarboxylic acid or 'dipicolinic acid' (DPA), sequencing 16S rRNA genes of thermospores germinated in 50°C sediment incubations, petroleum geochemistry in the sediments and acoustic seabed data from sub-bottom profiling. High endospore abundance is associated with geologically active conduit features (mud volcanoes, pockmarks, escarpments and fault systems), consistent with subsurface fluid flow dispersing endospores from deep warm sources up into the cold ocean. Thermospores identified at conduit sites were most closely related to bacteria associated with the deep biosphere habitats including hydrocarbon systems. The high endospore abundance at geological seep features demonstrated here suggests that recalcitrant endospores and their chemical components (such as DPA) can be used in concert with geochemical and geophysical analyses to locate discharging seafloor features. This multiproxy approach can be used to better understand patterns of advective fluid flow in regions with complex geology like the EGM basin.

Visualization of shallow subseafloor fluid migration in a shallow gas hydrate field using high-resolution acoustic mapping and ground-truthing and their implications on the formation process: a case study of the Sakata Knoll on the eastern margin of the Sea of Japan

Acoustic mapping enables an understanding of the surface distribution of shallow gas hydrate (GH) and related products. Acoustically characteristic materials such as fluid-seepage-related methane-derived authigenic carbonate and/or shallow GHs, may be widely distributed beneath the shallow seafloor of the Sakata Knoll. High-amplitude reflectors over the knoll are the top of gas-bearing permeable layers and connect to the reverse fault at the foot of the knoll. Shallow GH and bacterial mats were observed at the high-amplitude layer cut by depression and/or the locally disturbed seafloor. Acoustic blanking zones observed on the sub-bottom profiler sections are current gas migration routes from the depth to the seafloor. Optical observations indicate that fluid seepage is not active in the current seafloor, and it is not necessarily observed above the acoustic blanking zones or shallow faults reaching the seafloor. In the Sakata Knoll, the tectonically formed reverse fault and gas-bearing permeable layers play more important roles in fluid migration from depth to the summit area of the knoll compared to acoustic blanking and shallow faults. The depression at the summit area of the Sakata Knoll was formed by the dissociation of a shallow GH at around the last glacial maximum. Limited fluid seepage is currently witnessed within and around the depression and it is less extensive than that in the past. Such knolls, with tectonically formed large faults and an anticline are abundant in the area and they can be good reservoirs for shallow GH along the eastern margin of the Sea of Japan.

Post-500 ka and Holocene activity on distributed faults of the North Anatolian Fault system along the southern shelf of Marmara Sea, Turkey

Geodetic monitoring and patterns of seismicity indicate that the Northern Branch of the North Anatolian Fault (NAF) absorbs the majority of the relative motion between the Eurasia and Anatolia plates along the northern Marmara Sea. Nonetheless, historical seismicity documents that the Central Branch of NAF is also hazardous, with earthquakes diffusely occurring in the southern Marmara Sea. In order to better assess the seismic hazards facing large cities along the southern coast, we recently collected geophysical data across the adjacent shelf. These data include closely spaced high-resolution multichannel seismic profiles, sparker seismic profiles, CHIRP sub-bottom profiles, and multibeam bathymetric data. The stratigraphic and structural analyses of this new dataset and prior datasets highlight the geometry of three long faults and many shorter, discontinuous faults. The three longer faults are interpreted as primarily strike-slip fault zones. All the mapped faults are Late Quaternary active and, in fact, many fault segments are Holocene active. Smaller discontinuous faults are present in Gemlik and Erdek bays, some of them clearly active during Holocene time. This pattern of Late Quaternary active faults can account for the well-documented dispersed seismicity on the southern shelf. Based on the lengths of the various fault segments, we estimate that earthquakes with moment magnitude as high as 7.4 may occur along the southern shelf of the Marmara Sea. Therefore, the system of distributed faults that constitutes the Central Branch of the NAF in that area represents a significant seismic hazard for the southern coastal cities.

Acoustic backscattering properties of manganese nodules: Numerical and laboratory experiments based on Sub-bottom acoustic profile surveys

An underwater acoustic sensing system can be used to investigate the characteristics of manganese nodule deposits, such as the nodule size distribution and concentration. We numerically analyzed the relationship between the backscattering intensity obtained using a sub-bottom profiler (SBP) and the manganese nodule distribution by considering higher-order scattering terms among the nodules, in addition to the interaction between wave propagation and the combined effect of the manganese nodules and seafloor. Numerical experiments revealed that complex acoustic reflective waveforms and corresponding spectra increase in complexity with an increase in the sphere size. We categorized this scattering phenomenon with respect to several scattering regimes. As observed, the total reflection response can be attributed to the interference between the scattered waveforms from the nodules and the reflected waveforms from the seabed surface. The laboratory experiments were conducted using actual manganese nodules, and demonstrated a macroscopic decrease in reflectivity with an increase in the area ratio for different nodule sizes. It is, therefore, necessary to eliminate the wave interaction between manganese nodules and the seafloor to quantitatively estimate the density of the nodule distribution.

Glacimarine sediments from outer Drygalski Trough, sub-Antarctic South Georgia – evidence for extensive glaciation during the Last Glacial Maximum

South Georgia, one of the largest sub-Antarctic islands, is located within the Southern Ocean and is influenced by the moisture-supplying Southern Westerlies and the Antarctic Circumpolar Current, which are highly susceptible to Southern Hemisphere climate variability. Its unique location causes South Georgia's remaining ice masses to react sensitively to climate change, resulting in highly dynamic ice cap waxing and waning, as well as in geomorphological and sedimentological changes on the island and its continental shelf. Sediments around the island have been archiving this ice cap behaviour since at least the Last Glacial Maximum (LGM) and are therefore an important target to investigate past ice cap evolution and climate. Despite several interdisciplinary studies on land and in coastal areas, much of the glacial history is still poorly constrained due to a lack of offshore data. This study presents the, thus far, most distal marine sediment succession from outer Drygalski Trough on the mid-continental shelf of South Georgia. Composite multi-proxy-analyses, together with radiocarbon dating, sub-bottom profiler and high-resolution bathymetric data provide first insights into the evolution of a large glacial trough south of South Georgia since the LGM. Several moraines close to the shelf edge indicate shelf-wide glaciation during the local LGM, which, based on extrapolation of the oldest reliable radiocarbon date, occurred before 30 ka BP at the earliest. Basal stratified diamicton at the core site was interpreted as waterlain till deposited in a subglacial cavity with restricted seawater access and suggests grounding zone-proximal sedimentation in the early phases of deglaciation. The ice margin remained stable until ∼17.5 cal ka BP, when ice quickly retreated from the mid-continental shelf and sedimentation at the core site was dominated by hemipelagic suspension settling with some iceberg melting. Further retreat was interrupted by a local ice readvance and associated increased hinterland erosion during the Antarctic Cold Reversal (14.5–12.8 ka), as indicated by peak sedimentation rates (>190 cm ka−1) between 13.4 and 12.4 cal ka BP. In contrast, the continuous deposition of ice-distal to open-marine mud at rates of only ∼30 cm ka−1 throughout the Holocene indicate that any other LGM-subsequent glacier readvances reached significantly lesser extents and were probably confined to the fjord. Our data provide new evidence in support of a shelf-wide glaciation during the LGM and suggest rapid, but stepwise ice retreat during deglaciation.

Coexistence of Adjacent Siliciclastic, Carbonate, and Mixed Sedimentary Systems: An Example From Seafloor Morphology in the Northern Lesser Antilles Forearc

Three main types of factors commonly control the nature of the clasts, the arrangement of the distinctive lithologies, and the general architecture of turbidite systems: sedimentation rate and carbonate production; climates and glacio-eustatism; and morphology and tectonics. The coexistence of adjacent systems of distinctive nature is, however, scarcely documented, and the relative influence of each factor needs better constrain. In the Northern Lesser Antilles Segment (NLAS), carbonate and siliciclastic sediment sources coexist within a 150 km lateral distance, with carbonate platforms lying onto a volcanic substratum, and by a succession of spurs and triangular valleys that are bounded by active normal faulting. To better understand the factors controlling sedimentary processes from the carbonate platform sources to the deep-sea sinks, we used backscatter, bathymetry, multichannel seismic, and sub-bottom profiles. Sedimentary systems are dominated by siliciclastic input (by retrogressive erosion of confined canyons affecting the volcanic slope), carbonate input (by carbonate sediment transported by oceanic- and wind-driven submarine currents beyond the leeward edges of carbonates platforms), or both. In the mixed systems, the retrogressive erosion of the canyon head determines the nature of the source (volcanic on the slope, carbonate when the canyons reach the shelf edge). Glacio-eustatism has a key role in carbonate availability on the platform, as attested by the presence of drowned platforms. The main contribution of this study is the identification of the major role that tectonic activity plays in the short-distance coexistence of the distinctive sedimentary systems since fault-bounded V-shaped valleys in map view offer alternating leeward and windward edges favoring carbonate or mixed systems. Additionally, the steep slope gradient induced by normal faults and regional subsidence seems to be the main factor controlling sediment dispersal. It causes multiple line sources and the dispersion of gravity-driven currents under the effect of hydraulic jumps, thus preventing the formation of a channelized system. Our study provides a modern analog of adjacent systems dominated by distinctive lithologies in a tectonically active area. The results appear particularly appropriate to decipher the nature of ancient source-to-sink systems dominated by complex tectonics, paleo-bathymetry, and sediment routings.

Late Quaternary Evolution of a Submerged Karst Basin Influenced by Active Tectonics (Koločep Bay, Croatia)

Koločep bay is a 30 km elongated karst basin located between the Elafiti Islands and the mainland with a NW–SE general direction. The bay lies within the seismically active southern Dalmatia zone. Irregular grid sub-bottom profiles and two legacy reflection seismic profiles have been used to determine the overall morphology of the bay and to establish the seismic stratigraphy of its sedimentary infill. Three major seismic–stratigraphic units have been identified in the upper ~50 m of the ~120-meter-thick sedimentary sequence that lies above the karstified limestone bedrock. The karst polje basin was flooded due to sea-level rise before 12.1 kyr BP. The morphology of the bay implies complex influences of Late Glacial meltwater discharges, aeolian sand deposition, the existence of paleo–ponor/karst spring zones and buried Pleistocene river channels. The Pleistocene seismotectonic units are deformed in the NW and SE parts of the basin. The central part of the basin has no signatures of intensive tectonic activity during the Holocene. A major erosion event was identified that led to the formation of a basin within the older sedimentary infill. In the southern part of the basin, we have evidence of Holocene tectonic activity with the formation of erosional scarps on the seafloor of the bay.

Calibration and application of high-frequency submersible sub-bottom profiler for deep-sea surficial sediment measurement

We developed a high-frequency submersible sub-bottom profiler (HF-SSBP) instrument for taking deep-sea sediment measurement. In order to evaluate the reliability of profile data, a laboratory calibration method (LCM) was developed using illuminated acrylic standard boards in anechoic tank to form multi-layer reflections and evaluate the errors of the HF-SSBP. Two layer reflections induced by single boards in different thicknesses and ranges were performed and recorded, after which four layer reflections induced by two boards with an adjusted water crack were set and logged. The results showed that the HF-SSBP resolution was 44.9 mm in acrylic and its equivalent in the sediment was 28.5 mm. The absolute measure error was 7 mm with an acrylic board thickness of 100 mm, and the maximum measure error was 3.5 mm in different water thicknesses. As a test and application, deep-sea sediment measurement of the HF-SSBP was launched and compared with in situ sampling cores in the same site. The measurement thickness for sections A and B are 39.4 cm and 23.2 cm, respectively, corresponding to the sampling core of 39.8 cm and 23.7 cm. The two results are close as we expected. This work demonstrates the reliability and accuracy of the HF-SSBP measurement, thus providing a good choice for deep-sea submergence vehicles to carry this sonar instrument to obtain high-resolution stratum in deep-sea surficial sediments.

Contourite systems around the northern exit from the Vema Channel

Several drifts of different types and sizes are identified near the northern exit of the Vema Channel, within the projects Neogene-Quaternary contourites of the Central and South Atlantic and Lateral sedimentation in the deep ocean (on the examples from the Central and South-Western Atlantic). Herein, we discuss new results of a multidisciplinary study of sixteen sediment cores and high-resolution sub-bottom (seismoacoustic) profiles, to address the impact of Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) passing through the Vema gateway on contourite accumulation and erosion. To the west of the northern exit from the Vema Channel, an anticyclonic gyre of LCDW is instrumental in the development of contourite drifts and sediment waves. The contourite origin of generally silty terrigenous sediments in the Santa Catarina Plateau – São Paulo Plateau area is ascertained by both morpho-seismic and sedimentary characteristics. Sedimentary features include: a lack of primary sedimentary structures and pervasive bioturbation; sharp erosional contacts, local hiatuses and stiff mud horizons; some sandy/silty layers and indistinct bedding; mostly fine grain-size, very poor sorting and distinctive bi-gradational sequences; a high degree of correlation between the content of sortable silt (SS) in the total < 63 μm size fraction and SS mean sizes in all eight cores studied. Biostratigraphy, oxygen isotope records and ten new accelerator mass-spectrometry (AMS) 14C dates reveal the mid to late Quaternary age of this mainly terrigenous contourite depositional system (CDS).By contrast, the dominantly calcareous Ioffe Drift, overlying the Florianopolis Fracture Zone (FFZ) ridge to the northeast of the Vema Channel, is far from any source of terrigenous material, and accumulated in an area of low biological productivity. The overall asymmetric geometry, mainly lenticular, upward-convex seismic units separated by erosional unconformities, reflection truncation, small-scale moats dissecting the drift surface collectively indicate its contourite origin. The interpretation of the drift as the CDS is supported by sediment characteristics including common hiatuses corresponding in some cases to erosional contacts, pervasive bioturbation, generally poor sediment sorting, and more or less well-developed bi-gradational sequences. The erosion and deposition in the drift area are mostly controlled by the main LCDW branch following northeastward along the FFZ. Extensive erosion by bottom currents has created numerous hiatuses and markedly reduced the thickness of drift's sediments. The stratigraphic record from the Ioffe Drift sediment cores reveals an Upper Pliocene – Quaternary succession. The results of detailed analyses of six cores from the Ioffe Drift area, compared with two cores and the upper part of DSDP Site 516 from the Rio Grande Rise, notably the use of a SS analogue, provide new information on calcareous biogenic contourites deposited in the pelagic realm of the South Atlantic.

Sequential bedform development in mixed turbidite–contourite systems: An example from the Cosmonaut Sea, East Antarctica

Mixed turbidite–contourite depositional systems are commonly found on continental margins, but their bedforms and associated sedimentary processes have not been studied in depth. In this work, we used multibeam echo-sounder, sub-bottom profiling, and multichannel seismic data from the continental rise of the Cosmonaut Sea, East Antarctica, to (1) identify primary bedforms in a combined-current (i.e., turbidity current + contour current) channel–levee system and (2) infer bedform-associated sedimentary processes. Within turbidite channels and on adjacent levees and distal overbank deposits, scours, furrows, and sediment waves of varying dimensions and trends were identified. These bedforms are interpreted to have formed in two steps, which have been likely repeated over and over again through time. First, scours and sediment waves within the channels were formed by turbidity currents, while sediment waves on adjacent levees were likely formed by synchronous interactions between overspilled unconfined turbidity currents and the westward Antarctic Bottom Water (AABW) contour current. Second, after waning of the episodic turbidity currents, AABW flow created a field of erosional furrows on a distal overbank, with these furrows truncating the large field of sediment waves earlier generated by the combined flow of interacting currents. Bedform locations, orientations, and truncating relationships are key for identifying the likely origins of mixed-system bedforms.

Multiannual Seafloor Dynamics around a Subtidal Rocky Reef Habitat in the North Sea

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

Investigating the correspondence of acoustic amplitudes with penetrometer profiles in bottom sediments of a shallow coastal lake: Louisiana

This study correlates side-scan sonar and CHIRP subbottom acoustic amplitudes with cone penetrometer data to expand the limited understanding of the geotechnical properties of sediments in coastal Louisiana's bays. Using cone penetrometer profiles is a methodology for characterizing the sediment properties of the water bottoms and shallow subsurface sediments of coastal water bodies. This study is the first in Louisiana to investigate the potential value of applying this methodology combined with both side-scan sonar images and CHIRP subbottom amplitude analysis to the sediment characteristics of coastal bay bottoms. Penetrometer results demonstrate the sediment-related variability in the shallow subsurface of Sister Lake, in south-central Louisiana, with the majority of tip resistance values under 98.0 kPa (1.0 kg/cm2), with peaks to approximately 686.5 kPa (7.0 kg/cm2). An amplitude analysis technique identified different reflectance regions within Sister Lake from the CHIRP subbottom profile data. Acoustic reflectance is related to sediment “hardness” or resistance. The side-scan sonar and CHIRP amplitude reflectivity results are compared to penetrometer data that quantifies geotechnical properties of surface and near-surface sediments. Insight into the relative hardness of the coastal lake bottom and shallow subsurface deposits is gained through this technique, useful for: (a) identifying areas of erosion (previously buried and consolidated sediments) versus recent deposition; (b) delineating hard bottom areas suitable for cultch plants for state oyster seed grounds; and (c) informing the parameterization, calibration, and validation of numerical models used for predicting the response of coastal systems to future environmental conditions and restoration efforts. Results indicate three distinct penetrometer, side-scan and CHIRP signatures that identify different water bottom and substrate areas within Sister Lake including: 1) clay to organic clay; 2) silt to sand; and 3) oyster cultch and scattered shell. Although amplitude levels of high-resolution acoustic data do not directly quantify the geotechnical properties of bottom sediments, results indicate a close relationship. The analysis procedures developed in this study can be applied in other dynamic aquatic coastal environments by “calibrating” the use of synoptic acoustic methods for large spatial-scale water bottom characterization.

Detection of subsurface layers by Sub Bottom Profiling (SBP) of cross section of Shatt Al-Arab River at Al-Rebat branch, Basrah, southern Iraq

Two types of the subsurface layers were investigated by two Boreholes on the two banks of the Shatt Al Arab River near the old Al-Rebat port at Basrah city. Sub Bottom Profiling along the River section has also been investigated. The boring was carried out in two sides of Shatt Al-Arab at Al-Ashar and Al-Tanuma sides at Al-Rebat square. Marine geophysical investigations were made including Sub Bottom profile technique (SBP) using the Strata Box instrument. Besides, Acoustic Doppler Current Profiler (ADCP) technique was used along a 400 m section for determining the cross section of the River. the Boring Log Data of two Boreholes have been represented depending on SPT Values as the bearing Strength of subsoil layers profiles, which is matching with the sedimentary layers resulting from the seismic profiles for obtaining the geotechnical model of subsurface layers along cross section of the River. High bearing capacity layer is very dense sandy layer which appears at -22m of the elevation on sea level and extends to -29 m in left bank of the River. This layer is old deposits belonging to Dibdiba deposits (upper Miocene-Pleistocene).&#x0D; &#x0D;

Characteristics of sub-bottom profile acquired in Shatt Al-Arab River, Basrah-Iraq

A single sub bottom profile, nearly 1.0 km long, was acquired in Shatt Al-Arab River, at the river’s portion next to the downtown of Basrah city, 2010. The profile characterized by predominant ripple-marked features. Beneath the bottom, signal penetration was relatively low attributed to the existence of thick layer identified in the sub-bottom and interpreted as the main load bearing layer in the area. Riverbed multiple showed a strong presence and occupied the profile’s bottom. Interpretation beyond the riverbed multiple was not possible. Water bottom was flat, except for a buried object of undetermined type lying within the sediments of the bottom.&#x0D; &#x0D;

Sub-Bottom Profiler and Side Scan Sonar investigations, with the assistance of hydrochemical and isotopic analysis of Sawa Lake, Al-Muthana Governorate, Southern Iraq

A marine geophysical survey are including Sub Bottom Profilers and Side Scan Sonar integrating with under-water imagery, as well as hydrochemical and isotopic investigations have been carried out for Sawa Lake, one of the unique, shallow and closed water body in Iraq. The results showed that the depth of the Lake is shallow, ranged between 1 m in areas near the edges of the Lake and 2 m in the Lake center. The Recharge site has been detected exactly (this is a first recording (Nov. 2012)), as a hole. It has a longitudinal an axis of 50 m with NW-SE tren, which resembles the trending of the longitudinal axis of the Lake and Abu-Jir fault trending. The maximum width of this hole ranging from 23.0-29.5 m. The hole depth about 20 m, but may be greater then, because the emergence of a high proportion of noise in the geophysical sections. The Lake bottom is homogeneity and does not has any diacritical features. Also, the results showed discontinuous layers on either side of the hole due to the existance a number of caves under the bottom of the Lake extends into several meters with different dimensions and forms. Hydrochemical analysis of the water samples collected from different depths inside the hole by scientific diving with specefic equibments and the result showed that the water is NaCl type, with domination of Mg and Cl over Ca and SO4. The Stiff diagram, detected that very high TDS arising mainly from sodium and chloride, it is mostly typical marine water. Values of δ18O and δ2H in water samples of Sawa Lake, when plotted along the global meteoric water line shows that the three collected water samples from the lake, which have a similar isotopic composition, indicating that all of them are receiving water from the same flow zones, with diffuse recharge type. Also, the isotopic parameter showed that the Sawa lake water suffering from strong evaporation.

Structural Imaging of Acoustic Survey Using a Deep-Towed Sub-Bottom Profiler and Hydrophone Cable

High-resolution images are required for the exploration of mineral resources on and beneath the deep seafloor. Under the Strategic Innovation Promotion Program launched by the Council for Science, Technology, and Innovation in Japan, we developed a survey system using a deep-towed acoustic source and receivers that produces very high-resolution subseafloor images. Our system uses a subbottom profiler as the acoustic source and a hydrophone cable as receivers. These instruments are towed near the seafloor by a remotely operated vehicle (ROV). The subbottom profiler generates chirp signals in the frequency band of 700–2250 Hz, and 32 hydrophones with a receiver interval of 1 m record the reflected waves. The system also includes two recorder units that record the acoustic wavefield with a sampling interval of 0.1 ms. We carried out field surveys at two locations in Japan: one site is in the Sea of Japan where gas hydrates were discovered and the other site is near Okinawa Island where a plume from a hydrothermal smoker was recorded by an ROV camera. Pre-stack depth migration was applied to the processed data using velocity models with a constant velocity gradient below the seafloor. The vertical resolution was 0.5–1 m depending on the depth, and the horizontal resolution was about ten times larger than the vertical resolution. The resulting images show that detailed subseafloor structures can be clearly imaged by the deep-towed system, even at sea depths greater than 1000 m.