Seafloor Research Articles

Venturi nozzles for desalination brine discharges

Seawater desalination is a reliable way to confront the growing challenges of freshwater demands in the world. Brine is the primary by-product of this process and needs to be carefully managed and discharged back into the sea. In coastal desalination plants, the use of submerged outfall as a pipeline laying on the ocean floor is a popular strategy to minimize the environmental impacts of brine discharge. The Venturi nozzle has been proposed as a more efficient method for dispersing brine into the ocean. However, it requires a high exit velocity, which poses limitations for steep nozzle angles in shallow waters. This study aims to investigate the benefits of a lower range of exit velocities in the Venturi nozzles. The 60° inclined dense jet from a Venturi nozzle was explored, numerically and experimentally, and the results were compared to those of a simple dense jet. Comparisons showed that the Venturi nozzle decreases the flow path and diminishes flow dilution at the critical points. However, this reduction can be compensated by increasing the discharge Froude number to reach the same trajectory as a simple jet. It is important to note that this compensation is intricately linked to the discharge velocity, and it makes the use of Venturi nozzles for brine discharge a challenging proposition in both deep and shallow waters.

Collective synchrony of mating signals modulated by ecological cues and social signals in bioluminescent sea fireflies.

Individuals often employ simple rules that can emergently synchronize behaviour. Some collective behaviours are intuitively beneficial, but others like mate signalling in leks occur across taxa despite theoretical individual costs. Whether disparate instances of synchronous signalling are similarly organized is unknown, largely due to challenges observing many individuals simultaneously. Recording field collectives and ex situ playback experiments, we describe principles of synchronous bioluminescent signals produced by marine ostracods (Crustacea; Luxorina) that seem behaviorally convergent with terrestrial fireflies, and with whom they last shared a common ancestor over 500 Mya. Like synchronous fireflies, groups of signalling males use visual cues (intensity and duration of light) to decide when to signal. Individual ostracods also modulate their signal based on the distance to nearest neighbours. During peak darkness, luminescent 'waves' of synchronous displays emerge and ripple across the sea floor approximately every 60 s, but such periodicity decays within and between nights after the full moon. Our data reveal these bioluminescent aggregations are sensitive to both ecological and social light sources. Because the function of collective signals is difficult to dissect, evolutionary convergence, like in the synchronous visual displays of diverse arthropods, provides natural replicates to understand the generalities that produce emergent group behaviour.

Characteristics of iron-manganese nodules containing nickel and cobalt in chromite deposits in Co Dinh, Thanh Hoa province

Along with the chromite ore bodies, very early on, geologists recorded the presence of cobalt (Co) and nickel (Ni) metal. The resource of cobalt and nickel is forecasted with over 3 million tons of Ni and over 260 thousand tons of Co metals. Until now, however, knowledge about the existence form and distribution of Ni and Co in chromite ore bodies is very limited. Researching the sludge in the chromite mines and in comparison with manganese nodules found in the ocean floor helps to detect the presence of particles of iron and manganese (Fe-Mn nodules) in granular sewage sludges and in primary chromite ore bodies. Fe-Mn hydroxides, including todorokite mineral, are believed to be the adsorption medium and forming of Ni and Co in the Co Dinh placer chromite. Determining the existence form and distribution of Ni and Co in chromite placer deposits has scientific and practical significance in sampling orientation, sample processing, geological exploration, and reserve and resource estimations, sorting and recovering technology of Co and Ni metals.

The dynamic analysis of fixed deep-water platform

The industrial progress is closely related with active using of hydrocarbons more than half of reserves of which lie in rock formations beneath seabed or ocean floor. For oil production at the great depth of immersion oil production fixed platforms are used most often. But using of such technological structures is not limited only to interest of oil and natural gas industry whereas they are important for navigation and military purposes. Offshore fixed platforms are exposed to effects of a high seismicity, wind, waves, strong undercurrents and an impulse impact during the movement of ice fields especially when exploitation in northern seas. The impact of different factors on the value of the period of natural oscillations ofthe offshore fixed deep-water ice-resistant platform with the depth of immersion 120 m that rests on the pile foundation was researched. Two discrete idealized models of the platform were used for the analysis: the first model that was implemented without taking into account the flexibility of the foundation and the second model where the flexibility of the pile foundation and the action of ground foundation were taking into account by the addition of elastic links that simulate the elastic connection between joints. Also, impacts of the connected mass of water media that was modeled in the form of additional distributed joints mass and the impact of the ice field that was modeled by the addition of additional links were investigated. The analysis showsthat values of periods of natural oscillations form increase by 8-20% when the flexibility of the pile foundation was taken into account; increase by 9-100% when the impact of the connected mass of water media was taken into account; decrease by 9-100% when the impact of the ice field and water media were taken into accountthat is significant when analyzing of stress-strain state of members of the structure.

Where is the (ancient) ocean floor?


 
 
 Фокусуємося на:
 тому, щоб зрозуміти, що дно океану динамічне і змінюється з часом. Іноді воно далеко, а іноді набагато ближче, ніж ми думаємо. Але де знаходиться дно океану?
 Мета навчання:
 У цьому занятті учні зрозуміють, що ми можемо знайти дно стародавнього океану на суші завдяки тектонічній активності.NB: Це потребує попереднього планування та може бути неможливим, якщо ваша школа знаходиться надто далеко від таких тектонічних утворень.
 Ключові слова:
 Осадонакопичення, осадові породи, тектоніка, історія Землі
 
 

Exploring the ocean floor in northeast Zealandia: The 2015 VESPA voyage

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Structural frame analysis of an electrically powered robotic subsea dredging crawler under static loading conditions

Robotic subsea dredging crawlers are dynamically and remotely controlled vehicles that are used for deep sea mining and recovery operations. These exploration machines are released from a mother ship and move around on the ocean floor using tracks. Current ocean crawlers such as the MK3 ROST are hydraulically powered. In this paper we develop a scaled-down model for simulating and performing static loading analysis of an electrically powered robotic subsea dredging crawler (EPRSDC). The modeling, simulation, and analysis were carried out using modelling software from Solidworks. The structural frame was assembled using the Tetrix max robotics kit. The kit's structural components were produced from 1050 aircraft-grade aluminum. The results were used in optimizing and for considering other materials, and the to identify specific areas to be reinforced in future crawler designs.

Application of the K-Means Algorithm for Clustering Production of Capture Fisheries in Maluku Province

Maluku Province has large natural resources with various potentials, from the ocean floor to the mainland. Capture fishery products are one of the leading sectors that contribute greatly to the GRDP of Maluku Province. The K-Means clustering algorithm is a suitable algorithm for grouping data objects that have the same identity. The purpose of this study is to cluster districts/cities in Maluku Province based on capture fishery products. The type of data in this study is secondary data sourced from the Maluku Province Central Bureau of Statistics (BPS) Publication in 2022. The result is that there are 3 districts/cities clusters in Maluku Province based on capture fishery products. Cluster 1 with the category of sufficient capture fisheries products, namely the Districts of Tanimbar Islands, Buru, East Seram, West Seram, South Buru, Southwest Maluku, Ambon City and Tual City. Furthermore, Cluster 2 with the category of many capture fishery products, namely the Aru Islands Regency and Southeast Maluku Regency. Furthermore, for Cluster 3, the category of capture fishery products is very large, namely Central Maluku Regency.

There is No JOIDES in Mudville

After almost 4 decades of research, the JOIDES Resolution will retire in 2024, leaving the ocean floor in peace (for now).

Shallow subtidal marine benthic communities of Nachvak Fjord, Nunatsiavut, Labrador: A glimpse into species composition and drivers of their distribution.

Marine fjords along the northern Labrador coast of Arctic Canada are influenced by freshwater, nutrients, and sediment inputs from ice fields and rivers. These ecosystems, further shaped by both Atlantic and Arctic water masses, are important habitats for fishes, marine mammals, seabirds, and marine invertebrates and are vital to the Labrador Inuit who have long depended on these areas for sustenance. Despite their ecological and socio-cultural importance, these marine ecosystems remain largely understudied. Here we conducted the first quantitative underwater scuba surveys, down to 12 m, of the nearshore marine ecology of Nachvak Fjord, which is surrounded by Torngat Mountains National Park located in Nunatsiavut, the Indigenous lands claim region of northeastern Canada. Our goal was to provide the Nunatsiavut Government with a baseline of the composition and environmental influences on the subtidal community in this isolated region as they work towards the creation of an Indigenous-led National Marine Conservation Area that includes Nachvak Fjord. We identified four major benthic habitat types: (1) boulders (2) rocks with sediment, (3) sediment with rocks, and (4) unconsolidated sediments, including sand, gravel, and cobble. Biogenic cover (e.g., kelp, coralline algae, and sediment) explained much of the variability in megabenthic invertebrate community structure. The kelp species Alaria esculenta, Saccharina latissima, and Laminaria solidungula dominated the boulder habitat outside of the fjord covering 35%, 13%, and 11% of the sea floor, respectively. In contrast, the middle and inner portions of the fjord were devoid of kelp and dominated by encrusting coralline algae. More diverse megabenthic invertebrate assemblages were detected within the fjord compared to the periphery. Fish assemblages were depauperate overall with the shorthorn sculpin, Myoxocephalus scorpius, and the Greenland cod, Gadus ogac, dominating total fish biomass contributing 64% and 30%, respectively. Understanding the composition and environmental influences within this fjord ecosystem not only contributes towards the protection of this ecological and culturally important region but serves as a baseline in a rapidly changing climatic region.

Modeling Morphodynamic Impacts and Optimization of Marine Hydrokinetic Arrays in Shallow Offshore Environments

Marine hydrokinetic (MHK) devices hold the promise of expanding renewable energy production by tapping into the power of waves and currents for electricity generation. However, these devices remain in the developmental stage, necessitating research to understand their environmental impacts, lower operational costs, and prevent equipment failures. In this study, we investigate various MHK array configurations to gain insights into their effects on wave patterns, water flow, and sediment conditions, considering both short-term and long-term morphodynamic changes under average and extreme conditions in shallow offshore environments. Our objectives encompass understanding the influence of mean and extreme environmental conditions on MHK devices, evaluating their impact on the bathymetry of the ocean floor, and exploring the role of different array configurations in morphodynamic evolution. Our findings, based on modeling these devices as static lumps, reveal that sediment erosion downstream of MHKs increases by 50% after one year of average conditions. When accounting for the absorption of 30% of the energy by MHK devices, downstream sediment deposition surges by almost 125%. Moreover, alterations in MHK arrays, such as spacing, size, and number, result in noticeable changes in sedimentation magnitudes during storm conditions. While long-term mean wave conditions have minimal effects on sedimentation, extreme wave conditions, akin to large storm events, bring about significant alterations in ocean floor bathymetry, potentially leading to costly maintenance of the MHK arrays. Our research provides a valuable framework for site analysis, enabling the estimation of maintenance needs and the optimization of array configurations to minimize sedimentation-related issues.

Analysis of the Mechanical Characteristics of Tunnels Under the Coupling Effect of Submarine Active Faults and Ground Vibrations

With the rapid development of modern transportation construction, the construction of cross-harbor tunnels has solved the problem of traffic connection between cross-straits, bays and islands. The construction of sub-sea tunnels has technical difficulties such as high difficulty of marine geological survey, close hydraulic connection between strata and seawater, and more developed adverse geology. Based on this, this paper studies the mechanical characteristics of the submarine tunnel under seismic action at the active fault. Firstly, the mechanical model of the universal fault interface is established, and the calculation model of the fault interface is theoretically derived by the method of vibration mechanics, and the influence of the change of the strength of the contact surface and the stiffness of the surrounding rock on both sides of the fault on the transfer coefficient is obtained. Secondly, based on the ground motion input method of two-dimensional homogeneous half-space field, the relevant program of viscoelastic artificial boundary ground motion input is written by MATLAB program, which lays the foundation and premise of load input for mechanical response calculation. Finally, the outcomes of the tunnel parameters and the interplay between the tunnel and the surrounding rock on the cracking of the tunnel lining shape and the mechanical response of the cross-fault sub-sea tunnel underneath seismic motion are mentioned, and it is concluded that the increase in seismic intensity for different seismic intensities under the sea floor has an essentially constant proportion to the increase in acceleration of the seismic response; the seepage effect under the sea floor for the tunnel lining structure reduces the seismic response displacement, velocity and The seabed seepage for the tunnel lining structure reduces the peak seismic response displacement, velocity and acceleration by about 20–35%.

New wiggles from old cables: Data processing and imaging considerations

Distributed acoustic sensing (DAS) using fiber-optic cables as sensors has become a standard measurement technique in many industrialized settings. Geophysical applications have been mainly commercialized in the borehole environment. When deployed on the seabed (SB), horizontal analysis of DAS data poses new challenges due to the particularity of the receiver response and characteristics of DAS data. Recent acquisition of a 2D towed-streamer (TS) survey following the path of a communication cable (installed in 1998), which is interrogated continuously throughout the TS acquisition, enables us to jointly analyze SB-DAS and conventional TS data recorded using modern hydrophone streamer from acquisition, through different processing stages up to a migrated image. The SB-DAS recording from the old communication cable enables us to generate excellent P-wave and converted wave (PS) images of the subsurface. However, care is needed when recovering the high spatial frequencies damped by the nature of DAS measurements (which also may depend on the hardware used) and demonstrating the recovery of the signal within the data processing (DP) sequence. Our focus is on the challenges associated with the DP of entrenched marine cables. Given a simple TS processing sequence as a reference, we examine an equivalent recommended practice for signal analysis, DP, and imaging of SB-DAS data.

Tectonics of the Continental Barents Sea Shelf (Russia): Formation Stages of Basement and Sedimentary Cover

Based on the results of field complex geophysical studies in the northwestern part of the Russian sector of the Barents Sea shelf, as well as on the processing and comprehensive interpretation of new and retrospective geophysical materials in the volume of 25 500 linear kilometers and deep well drilling data in the section of the Barents Sea sedimentary cover identified regional tectonostratigraphic units: (i) Paleozoic complex (between reflecting horizons VI(PR? ) and I2(P‒T)); (ii) the Triassic complex (between reflecting horizons I2(P‒T) and B(T‒J)); (iii) the Jurassic complex (between reflecting horizons B(T‒J) and V′(J3‒K1)); (iv) the Cretaceous‒Cenozoic complex (between reflecting V′(J3‒K1) and the Barents sea floor). According to the structural analysis’ results, three structural floors are established: the lower structural floor, which includes Riphean terrigenous-affusive sediments and Lower Paleozoic‒Lower Permian terrigenous-carbonate sediments; the middle structural floor is formed mainly by carbonate sediments of Upper Devonian‒Lower Permian; the upper structural floor combines terrigenous sediments of Lower and Upper Permian, Mesozoic and Cenozoic sediments. The authors present a new tectonic model of the Barents Sea region, including elements of all structural floors with subfloors. In accordance with the tectonic zoning, paleostructural and paleotectonic analyses, the article outlines the main stages of the Barents Sea shelf development: stage of the Late Proterozoic compression and Early-Middle Paleozoic continental rifting (I), Late Paleozoic stabilization stage (II), Early Mesozoic tectogenesis stage (III), Middle Mesozoic thermal subsidence stage (IV), Late Jurassic stabilization stage (V), Cretaceous sagging stage (VI) and the final stage as a Cenozoic uplift over a large part of the Barents Sea shelf (VII). In the northwestern part of the Russian sector of the Barents Sea shelf, synchronous dipping of the sedimentary cover basement took place, associated with spreading and formation of the Arctic Ocean.

Depth-dependent Variations in Elemental and Mineral Distribution in the Deep Oceanic Floor Sediments (WP21GPC04) near the Mariana Trench in the Western Pacific Ocean

Depth-dependent Variations in Elemental and Mineral Distribution in the Deep Oceanic Floor Sediments (WP21GPC04) near the Mariana Trench in the Western Pacific Ocean

Reflections and transmissions from a porous layer sandwiched between seawater and solid substrate

Ocean sediments are composed of a porous layer sandwiched between seawater and a solid elastic base. The reflection and transmission of acoustic waves from ocean sediments are essential in ocean engineering, seafloor seismology, etc. The existing reflection and transmission (R/T) formulas are determined by complex matrix equations in the order of 9 × 9 or higher. To obtain more concise R/T coefficient formulas, we established the propagator matrix of the coupled water-porous-layer-solid elastic system, wherein the above-water is ideal and the middle porous marine sediment is defined by the Biot–Stoll model. Based on the propagator matrix, the displacement R/T coefficients were given by a 3 × 3 matrix equation for two P-wave incidence cases: the down-going case from the water, and the up-going case from the ocean floor. For zero-frequency or zero-thickness limitation, the proposed R/T coefficient formulas are the same as the displacement R/T coefficients at a single fluid–solid interface. The numerical results of the reflected or transmitted waves in the above-water show that the R/T coefficients exhibit regular variations at frequencies far lower than the characteristic frequency. The R/T coefficient amplitudes decreased with increasing frequency at a fixed incidence angle and ratio between the thickness and wavelength.

Long-term carbon sequestration in the Eocene of the Levant Basin through transport of organic carbon from nearshore to deep marine environments

This study addresses a specific component associated with mass transport complexes in marine systems: the role of hyperpycnal flows, dense shelf water cascading, submarine canyons, distributary channels, and other transport mechanisms in transferring organic matter from continental and shallow marine settings into deep-marine environments. We speculate that during the Eocene, allowing for only 0.1‰ of shelf carbon to be preserved through transport mechanisms would account for up to 13.7% of all organic carbon burial. As such, the potential to mobilize through this mechanism large quantities of organic carbon is significant.Our case study focuses on a 150 m Eocene sequence composed of organic-rich chalks interleaved with displaced neritic limestones. TOC values range between 1.5 and 14%, averaging 4.5%. Displaced limestones are composed of a variety of poorly cemented mud- and wackestones, with low-diversity assemblages of large benthic foraminifera associated with planktonic foraminifera, suggesting deposition under low-energy conditions within the oligophotic zone on the outer ramp. Transport overprints include soft-sediment deformation, partially lithified rip-ups, folds, small diapirs, bed-scale imbrication, brecciation and syn-sedimentary shear. These features indicate detachment, movement and emplacement following initial sedimentation, in some cases more than once. Emplacement occurs into a chalk facies that can vary in appearance from darker (higher TOC) and lighter (lower TOC) lithofacies.Combination between the sedimentological, petrophysical, and elemental analyses indicates shifts between autochthonous and allochthonous sedimentation, whereas the organic geochemical analysis reveals a correlation between modes of sedimentation and preservation/composition of organic matter. Organic richness seems to increase within intervals of allochthonous sedimentation, with lower TOC values within intervals of autochthonous sedimentation. Organic matter preservation is enhanced due to poor oxygenation of the sea floor, further depleted by rapid burial beneath mass-transport deposits, increasing sedimentation rates and thus organic matter preservation. Horizons rich in organic matter may be derived from three different sources: organic matter with a fingerprint of terrestrial sources (e.g., enhanced contribution of plant leaf waxes) transported from nearshore environments; an allochthonous marine fingerprint with sulfurized hopanoids, which seem to be reworked from pre-existing Cretaceous organic-rich carbonates entrained within fined-grained micro-turbidites in the para-autochthonous facies; and productivity-derived organic matter deposited on the seafloor of the deep marine environment.This study demonstrates how transport mechanisms allow for the long-term burial of organic carbon in marine systems. When taking into consideration similar processes reported to occur in the world oceans today, it is clear that sediment transport and long-term burial of organic carbon is a fundamental part of the global carbon cycle.

Superlensing enables radio communication and imaging underwater

Wireless radio communications provide a backbone to our technological civilization. However, radio communications are widely believed to be impossible in many situations where radios are surrounded by conductive media, such as underwater or underground, thus making ocean exploration difficult and creating well-known mine safety problems. In addition, since most imaging techniques rely on electromagnetic waves, the difficulty of electromagnetic wave propagation through biological tissues, which are mostly made of water, also severely limits bioimaging. Here we show that contrary to common beliefs, radio signals may be efficiently propagated through water over useful distances. Both radio communication and radio imaging through water may be enabled by superlensing of surface electromagnetic waves propagating along the water surface. We have demonstrated underwater radio communication over distances of several hundred skin depth in the MHz frequency range, which would require sensitivity below 10−100 W in a conventional radio communication channel. We also demonstrated subwavelength super-resolution radio imaging in the GHz range by using water surface as a superlens. Our results indicate new ways to perform bioimaging, as well as marine life safe techniques of wireless radio communication and imaging underwater, which are essential for ocean and seafloor exploration. We also anticipate that the developed techniques will provide invaluable means of studying the extraterrestrial water worlds, such as potentially inhabitable Jovian moons.

Offshore seismicity clusters in the West Iberian Margin illustrated by 2 decades of events

Abstract. An analysis of 2 decades (2003–2022) of seismicity recorded by the Spanish and Portuguese seismic networks along the West Iberian passive margin has resulted in a better understanding of the distribution of moderate seismic activity in this intraplate submarine area. The study provides a precise trend of specific alignments inferred from the density maps of seismicity, giving an accurate depiction of event distribution along two wide stripes that extend for 700 km through the ocean floor in the WNW–ESE direction. These bands are parallel to the Africa–Eurasia plate boundary but are distinctly separated from its related seismicity by approximately 300 and 700 km, respectively. This is a sufficient distance to be considered intraplate activity. When trying to relate this seismicity to structural and geophysical features, a conclusive picture does not emerge. The earthquakes occur indiscriminately across thinned continental, hyperextended, and exhumed mantle rift domains. They fade out in proximity to undisputed oceanic crust, but some events extend beyond. The hypocentral depths signal a considerable number of events nucleating in the upper mantle. The focal mechanisms, although scarce, are predominantly strike-slip. Considering these observations, hypotheses ranging from subduction initiation and development of strained corridors to local structures of the margin are discussed in order to explain this relatively anomalous seismicity. However, some of them lack convincing arguments, while others are too vague. None of them are flawless, suggesting that several factors may be at play. Despite being one of the most probed passive margins in the world, the present geodynamic status of the West Iberian Margin manifested in its modern seismicity remains unknown. Interpreting these data within a global tectonic plate framework, together with the potential addition of seafloor seismometers, may provide the key to understanding this activity along one of the most archetypical margins of the Atlantic Ocean.

Submarine basalt xenoliths confirm the occurrence of post-rift volcanism in the Southern Santos Basin, SW Atlantic

We report here the finding and analysis of xenoliths of altered basalt clasts dredged from the top of two exhumed diapirs in the southern Santos Basin (SW Atlantic). The diapirs crossed the stratigraphic column from the Aptian and outcropped on the seafloor. Complemented by seismic data, these findings provide the first direct evidence of an Early Campanian post-rift magmatic event in the southern Santos Basin (SW Atlantic). One 82 Ma Ar–Ar age of these xenoliths indicates that the volcanism developed coeval with the intrusion of the Serra do Mar Alkaline Province rocks on land. The tholeiitic composition of the xenoliths excludes a genetic correlation with the alkaline province. Seismic reflection data indicate the possible source of the xenoliths from a 40-km-wide cluster of volcanic centers and sills located above the Aptian salt deposits (∼115 Ma), between the top-Turonian (90 Ma) and top-Campanian (72 Ma) interval. We suggest that salt diapirism peented the overlaying volcanic units and carried fragments upwards through the entire stratigraphic column to the ocean floor. Our findings stress that salt diapirism is an important mechanism for conveying unreachable subsurface fragments to the surface, particularly the ocean floor. With the expanding knowledge of the seascape worldwide, enhanced exploration of salt diapirism and its xenolith products has the potential of opening new windows to unknown parts of geologic history.