Seafloor Research Articles

Hydrolysis rate constants of ATP up to 120 °C and 1.6 GPa: Implications for life at extreme conditions

Extreme environments are habitats for a diverse array of microorganisms, namely extremophiles, that have evolved unique biochemical adaptations to their geological setting. Some examples of extremophiles can be found in the subseafloor or near hydrothermal vents on the ocean floor. Cultivated strains of extremophiles have demonstrated the ability to tolerate temperatures (T) up to 122 °C and pressures (P) up to 125 MPa. Organisms depend on the stability of key metabolites, such as adenosine triphosphate (ATP), to survive and reproduce under these conditions. In order to maintain their intracellular ATP levels, living cells must compensate for the abiotic hydrolysis of ATP, which occurs at a particularly rapid rate at high temperatures. The role of high pressures and high temperatures in abiotic hydrolysis of ATP has been rarely investigated despite the potential for this phenomenon to contribute to limit the adaptation of microorganisms to simultaneous extreme temperatures and pressures. This study presents new data on the effect of pressure on the abiotic hydrolysis of ATP to adenosine diphosphate (ADP) at elevated temperatures. In situ Raman spectra were measured at high pressure and high temperature of the hydrolysis of aqueous disodium ATP solutions in two experimental systems: a hydrothermal diamond anvil cell (HDAC) and a gas-pressurized autoclave. These two systems permitted the determination of hydrolysis rate constants of ATP into ADP up to 1670 MPa at 80 °C, 100 °C, and 120 °C. The data exhibited Arrhenian behavior with a slight decrease in activation energy from 0.5 MPa to 140 MPa. The effect of pressure on ATP hydrolysis rate constants was found to be vanishingly low in the so far known vital range up to 125 MPa. Abiotic hydrolysis rates of ATP showed a pronounced increase at higher pressures. For example, at 100 °C, a rise in pressure from 365 MPa to approximately 1670 MPa results in a nearly tenfold increase in the ATP hydrolysis rate constant. When compared with the typical ATP turnover times reported in living cells, the abiotic ATP hydrolysis rates determined in this study provide insights into the pressure and temperature conditions that could be consistent with living microorganisms.

Evolution of a late Quaternary succession by interpretation of high‐resolution seismic and bathymetric data, Adriatic Sea

AbstractThis paper presents the results of the interpretation of a set of high‐resolution seismic lines integrated with multibeam echosounder data acquired in a coastal area in the Northern Adriatic Sea. The aim of the study was to reconstruct the stratigraphic evolution of a late Quaternary sedimentary succession offshore the town of Bibione, North‐Eastern Italy, by recognising the key unconformities, identifying the main depositional units, dating them and reconstructing the depositional environments in relation to relative sea‐level variations. Specifically, four sedimentary units, separated by erosional unconformities associated with the development of deep channels, were identified and dated based on literature information. By interpreting the seismic data, sedimentary dynamics were reconstructed and palaeoenvironments identified. The lower unit corresponds to a paludal environment, showing abundant gas seeps and accumulations (bright spots); the two intermediate units correspond to fluvial deposits, filling the deep incisions that characterise the bounding surfaces. Finally, the shallowest unit, bounded by a wave‐ravinement surface incised by tidal currents, corresponds to the Holocenic progradation of the coastal wedge. In addition, several vertical gas chimneys were identified, ranging in width from a few metres to 20–30 m. These were present in all units, often reaching the sea floor. Finally, elongated mounds, about 300 m wide, at the sea floor were recognised. The bathymetric and seismic characteristics of these elongated bodies and their relationship to adjacent sedimentary bodies suggest that they are probably methane‐derived carbonate formations known as ‘Trezze’ or ‘Tegnùe’. These names recall the fact that the trawls of the local fishermen were often hindered (‘tegnù’ in the Venetian language) or even cut off by these formations.

Tidal Seismicity in the Moon and Implications for the Rocky Interior of Europa

Seismology is a powerful tool for probing the deep interiors of planetary bodies. Just as deep moonquakes triggered by Earth’s tides occur on the Moon, as observed by the Apollo seismometers, icy moons of the giant planets may also have seismically active deep interiors, opening up future prospects for in situ seismic investigations at their surfaces. Of notable interest is Jupiter’s moon Europa, with its dynamic ice shell and potentially habitable subsurface ocean. In this work, we use different interior models of the Moon and model the tidal stress inside them to determine the most likely times and locations for the triggering of tidal moonquakes. Using the Mohr–Coulomb failure criterion, we derive cohesion and friction values for the lunar interior to match the observations of deep moonquakes by Apollo at a depth between 700 and 1200 km. By extending the same approach to different interior models of Europa, we show that Europa quakes triggered by the tides of Jupiter are 10 times more likely to occur than tidal moonquakes. The strength and depth of these tidal Europa quakes (euroquakes) strongly depend on the interior structure, with stronger events at the core–mantle boundary for liquid core models, while solid core models can be more prone to failure at the bottom of the ocean floor. Models without a metallic core favor failure in the upper third of the mantle with event strength similar to that in the solid core models.

Sediment dynamics and geomorphology in coastal areas affect long-term abundance of waders

Millions of migrating and wintering waders depend on coastal areas and estuaries for feeding and to replenish body reserves. These habitats are dynamic, with changing intertidal flats and sediments due to natural and climate-driven processes. The aims of this study were to examine whether physical conditions of intertidal flats such as geomorphology and sediment compositions could explain abundance of wader species, and furthermore whether changes in these conditions over time influenced changes in abundance of waders. In addition to physical structures such as datum (level), slope and sediment composition of intertidal flats, dynamic variables connected to tidal cycles such as distance of the waterline from the coast and duration of water cover were included. Penetration of the sea floor was measured as a proxy for sediment composition. The study was conducted in the Danish section of the Wadden Sea during 1981–1986 and 2008–2009 with additional data from 2020. The focus was on 12 widespread wader species. PCA analysis revealed that wader species were distributed in relation to tidal cycles such as duration of water cover and the position of waterline and to the physical structures, datum, slope and penetration, in decreasing order. With regard to the physical structures, pairwise comparisons of distribution of waders species showed that mean datum (level) was significantly different for 51 pairs of species out of 66 comparisons, mean penetration values differed for 34 pairs, and mean slope differed for 26 pairs of wader species. Long-term changes of physical structures of transects revealed that changes of densities of 10 wader species were significantly correlated with changes per year in one or more of the physical structures: seven wader species were significantly correlated with changes per year of mean datum (level) of transects (Lapwing was positively correlated while Avocet, Golden Plover, Grey Plover, Dunlin, Bar-tailed Godwit and Redshank were negatively correlated), five species with mean slope (Oystercatcher, Ringed Plover and Knut were positively correlated and Grey Plover and Redshank were negatively correlated), and three species with mean penetration values (sediment composition) of transects (Avocet and Bar-tailed Godwit were positively correlated and Lapwing was negatively correlated). The study shows that long-term changes of physical structures of intertidal flats affected abundance of wader species. The results are important for interpretation effects of erosion and accretion of coastal areas as consequences of natural and climate driven processes such as sea level rise and coastal squeeze.

Moats & comets - A methodology to explore for submerged prehistory at sea floor erosional features formed at artificial reefs, Atlantic continental shelf, GeorgiaUSA.

Our primary objective is to demonstrate a method that uses marine processes, principally seafloor scour, to broadly expose prehistoric landforms and associated localities. Too often, the loss of prehistoric strata to scour processes such as ravinement during broad-scale, continental shelf transgressions, are decried without the recognition of the potential for erosion at the local scale can expose those same strata for systematic study. The analysis of sea floor erosional features formed around artificial reefs by turbulent flows in the Georgia Bight have used interferometric side-scan sonar (SSS), Remotely Operated Vehicles (ROVs), ultra-high-definition videography (UHD), and sedimentological, palynological, paleontological, archaeological analytical techniques. These techniques were integrated within a geoarchaeological methodology focused on exploring the Continental Shelf for preserved evidence of prehistoric landforms, flora and fauna once thereon. A stepwise protocol was developed to first gather interferometric side-scan sonar data to be then processed by commercial software packages such as HYPACK Hydrographic and HYSWEEP together with HYSCAN and SONAR Wiz software. The sonar mosaics were imported to ArcGIS/QGIS software to characterize scour features/targets around artificial reefs that had exposed paleo-land surfaces previously obscured by the modern palimpsest sand sheet. Analysis of scours and depressions - “moats and comets” - adjacent to reef structures were evaluated using the profile tool within the HYPACK-HYSWEEP editor package. Symbology for the bathymetric raster layers was edited to provide a clear contrast and measurement at scour features. Measured GIS images were then classified as to scour extent and depth with respect to prevailing current directions responsible for producing turbulence. A ranking of the artificial reefs by factors such as scour depth and extent was used to guide subsequent investigation by ROVs. Sediment cores and grab samples were collected, and those samples underwent particle size analysis (PSA), macro-and micro-botanical analyses. All data – geophysical, GIS, video and geological – were collated and synthesized to produce an assessment of the potential of sea floor scour features to expose previously buried geomorphological/geological, paleontological and/or archaeological features of interest.

Origins and nature of large explosive eruptions in the lower East Rift Zone of Kīlauea volcano, Hawaii: Insights from ash characterization and geochemistry

Several powerful explosive eruptions have taken place in the populated lower East Rift Zone of Kīlauea within the past ∼750 years. These have created distinctive landforms, including a tephra rim enclosing Puʻulena Crater immediately south of the Puna Geothermal Venture power station, a tuff cone at Kapoho Crater near the eastern cape of the Island of Hawaiʻi, and a set of littoral cones, the Sand Hill in Nānāwale, where the 1840 lava flow poured into the ocean. Kapoho Crater tuff cone is the largest of these recent pyroclastic features. Mineral, glass, and melt inclusion analyses of tuff cone ash and later fissure-related scoriaceous materials also found within the crater indicate slightly evolved basaltic magmas (1120–1130 °C) that are compositionally similar to parts of the effusive lower East Rift Zone eruptions in 1955 and 2018. Tuff cone magmas were stored at depths of ∼2.5–3.5 km and had pre-eruptive volatile contents (0.5–0.8 wt% H2O, 280–340 ppm CO2, 1400–1800 ppm S) similar to other Kīlauea eruptions (e.g., 1959, 1960), suggesting that internal magma properties were unlikely to account for the unusual explosiveness of this eruption. Tephra componentry, grain-size analyses, and field observations confirm that the cone grew during a phreatomagmatic eruption mostly of vitric ash, probably where a fissure opened across the coastline or shallow ocean floor nearby. Supporting this hypothesis is the identification of at least two genera of marine diatoms within tuff cone strata. Sand Hill littoral cone ash is also vitric like that of Kapoho Crater, but distinctly coarser with abundant fluidal ejecta represented. In contrast, the Puʻulena Crater eruption deposited lithic ash and related blocks with minor juvenile magmatic contribution; a phreatomagmatic eruption that was dominantly phreatic. Differences in eruption styles are related to unique mechanics that tephra analyses help us interpret. While powerful explosive eruptions in the lower East Rift Zone are rare, they present a definite future hazard for inhabitants in this part of Hawaii.

Element mobility during basalt-water-CO2 interaction: observations in natural systems vs. laboratory experiments and implication for carbon storage

Today, carbon dioxide removal from the atmosphere is the most ambitious challenge to mitigate climate changes. Basalt rocks are abundant on the Earth’s surface (≈ 10%) and very abundant in the ocean floors and subaerial environments. Glassy matrix and minerals constituting these rocks contain metals (Ca2+, Mg2+, Fe2+) that can react with carbonic acid to form metal carbonates (CaCO3, MgO3 and FeCO3). Here, we present a data compilation of the chemical composition of waters circulating in basalt aquifers worldwide and the results of simple basalt-water-CO2 experiments. Induced or naturally occurring weathering of basalts rocks release elements in waters and elemental concentration is closely dependent on water CO2 concentration (and hence on water pH). We also performed two series of experiments where basaltic rock powder interacts with CO2-charged waters for one month at room temperature. Laboratory experiments evidenced that in the first stages of water-rock interaction, the high content of CO2 dissolved in water accelerates the basalt weathering process, releasing in the water not only elements that can form carbonate minerals but also other elements, which depending on their concentration can be essential or toxic for life. Relative mobility of elements such as Fe and Al, together with rare earth elements, increases at low pH conditions, while it decreases notably at neutral pH conditions. The comparison between experimental findings and natural evidence allowed to better understand the geochemical processes in basaltic aquifers hosted in active and inactive volcanic systems and to discuss these findings in light of the potential environmental impact of CO2 storage in mafic and ultramafic rocks.

FIRST REPORT ON THE UPPERMOST PERMIAN OSTRACODS FROM THE MASORE SECTION (EXTERNAL DINARIDES), SLOVENIA

The ostracod assemblages from the Upper Permian and Permian-Triassic transitional strata of the Masore section in the External Dinarides (Slovenia) were studied. Altogether 13 genera and 20 species of the orders Palaeocopida, Platycopida and Podocopida are identified and illustrated. All recovered ostracods belong to shallow marine taxa. The older fauna from the uppermost Permian and the younger fauna from the Permian-Triassic boundary strata are distinguished. The obtained fauna from the Permian Bellerophon Formation corresponds to the “benthonic ostracod Eifelian Mega-assemblage” occupying the shelf sea floors. This study presents the first report of ostracod faunas from the uppermost Permian and Permian-Triassic boundary interval of Slovenia. The recovered ostracod fauna display a distinct faunal change and yield important paleobiogeographic implications as it reveals similarity with stratigraphical equivalent faunas from some other neighboring localities in the western Paleotethys, such as Bulla in Italy, Komirić in Serbia, and the Bükk Mountains in Hungary.

The effects of bathymetry on the long-term carbon cycle and CCD

The shape of the ocean floor (bathymetry) and the overlaying sediments provide the largest carbon sink throughout Earth's history, supporting ~one to two orders of magnitude more carbon storage than the oceans and atmosphere combined. While accumulation and erosion of these sediments are bathymetry dependent (e.g., due to pressure, temperature, salinity, ion concentration, and available productivity), no systemic study has quantified how global and basin scale bathymetry, controlled by the evolution of tectonics and mantle convection, affects the long-term carbon cycle. We reconstruct bathymetry spanning the last 80 Myr to describe steady-state changes in ocean chemistry within the Earth system model LOSCAR. We find that both bathymetry reconstructions and representative synthetic tests show that ocean alkalinity, calcite saturation state, and the carbonate compensation depth (CCD) are strongly dependent on changes in shallow bathymetry (ocean floor ≤600 m) and on the distribution of the deep marine regions (>1,000 m). Limiting Cenozoic evolution to bathymetry alone leads to predicted CCD variations spanning 500 m, 33 to 50% of the total observed variations in the paleoproxy records. Our results suggest that neglecting bathymetric changes leads to significant misattribution to uncertain carbon cycle parameters (e.g., atmospheric CO2 and water column temperature) and processes (e.g., biological pump efficiency and silicate-carbonate riverine flux). To illustrate this point, we use our updated bathymetry for an Early Paleogene C cycle case study. We obtain carbonate riverine flux estimates that suggest a reversal of the weathering trend with respect to present-day, contrasting with previous studies, but consistent with proxy records and tectonic reconstructions.

Barite-bearing “septarian concretions” (upper Cretaceous – Paleocene) from the Biban area (north Algeria)

The "septarian barite concretions" have garnered significant interest worldwide. This study presents the first detailed investigation of these sedimentary structures in Algeria, with a primary focus on elucidating their genesis through petrography, SEM-EDS, major and trace elements (including REEs), and sulfur isotope analysis. The sampled concretions occur in Upper Cretaceous-Paleocene marl layers from the Biban area, primarily in two main sectors (Koudiat Djebassa and Sidi Ziane), situated within the Southern Tellian Atlas in Northern Algeria (Maghrebides). While these barite concretions exhibit diverse morphologies, our analysis focuses specifically on oblate ellipsoidal concretions. The flattened shape of these concretions may stem from compressed echinoid tests or small, oblate septarian cracked concretions representing the flattened cores. Notably, these concretions feature an outer cortex of radial fibrous barite crystals, measuring centimeters in thickness. Petrographic examination coupled with SEM-EDS analysis suggests that concretion growth occurred from porewaters in unconsolidated, soft sediments at shallow burial depths beneath the sediment-water interface, manifesting in three growth episodes: (i) an initial stage characterized by primarily thin lamellar barite crystals intertwining to form rosette-like structures in concretion cores, (ii) a later stage marked by radial-fibrous barite crystal growth in concretion margins, and (iii) the filling of septarian cracks by barite. The presence of terrigenous sediment, particularly abundant in rosette-like barite crystals, indicates growth within highly porous sediment. Conversely, the radial fibrous outer cortex is related to an effective displacive growth mode. The δ34S values of the barite concretions (ranging from 16 ‰ to 24.4 ‰), consistent with seawater values, which document that seawater was the primary sulfur source. Furthermore, REE geochemistry further supports the seawater origin of diagenetic fluids rather than a hydrothermal one. Concretions are suggested to have formed in organic-rich, fine-grained sediments at shallow depth below the sea floor, in sedimentation halts, and as a result of microbial degradation of organic matter. Barium was supplied to porewaters within the methanogenic zone, precipitating as barite when, migrating upwards, reached the boundary with the overlying sulfidic zone.

Experimental investigation of cohesive soil erosion and suspension caused by a Coandă-effect-based polymetallic-nodule collector

Coandă-effect-based collection stands out as the foremost technology in polymetallic-nodule mining due to the absence of direct contact between the collector and the ocean floor. Yet, this collection method disturbs the ocean floor, and minimizing such disturbance is crucial from an environmental viewpoint. To this end, a solid understanding of the interplay between the collector and the sediment bed is required. Therefore, we carried out a series of small-scale experiments, where a collector drives over a subaqueous clayey bed. These experiments provide the very first quantitative data on cohesive sediment erosion caused by a moving Coandă-effect-based collector, as well as on turbidity currents generated behind the collector head. This paper discusses the observations and findings derived from these experiments. Our findings reveal a logarithmic relationship between erosion depth and the flow impinging force applied on the clayey bed. An increased flow rate in the collection duct results in a slower turbidity current generated behind the collector head. This study enhances the ability to forecast sediment erosion caused by Coandă-effect-based collectors, offering the possibility to optimize the collector operational conditions and minimize the magnitude of the resulting sediment plumes.

Climate cyclicity-controlled recurrent bottom-water ventilation events in the aftermath of the Toarcian Oceanic Anoxic Event: the Jenkyns Event

AbstractEnvironmental perturbations of the Toarcian Anoxic Event and its associated carbon isotope excursion (CIE) occurred in a cyclic fashion indicating an orbital control mechanism. Sedimentary strata of the E. elegantulum ammonite subzone in the Lorraine Sub-basin, Luxembourg, exhibit eight sedimentary cycles, most of which postdate the CIE, implying that its termination did not coincide with a full recovery from environmental stress. Sea-level and temperature fluctuations of the Toarcian crisis were linked to a cryosphere demise in the Northern Hemisphere, which modulated stadial versus interstadial phases on the orbital 100 ka eccentricity frequency band. Upon stadial phases, enhanced wind strength in combination with lowered sea level disrupted stratified shelf waters and shifted the storm wave base close to the sea floor. Ventilation of bottom waters interrupted accumulation of laminated and organic-rich black shales, but formed organic-lean and non-laminated gray claystones enriched in terrigenous wax lipids and spores provided via aeolian transport from the hinterland due to the enhanced wind strength. Wind systems are assumed to have been driven by high pressure differences between the cryosphere in the North of the Tethyan shelf and the warmer costal lowland. This distinguishes the atmospheric turbulences after the CIE from the postulated intensification of the cyclones that accompanied the rapid warming at the beginning of the CIE. The deep-water ventilation event following the CIE in the Lorraine Sub-basin was accompanied by a parallel evolution in the SW German Basin, indicating a supraregional driving mechanism in paleobathymetric sub-basins susceptible to lowering of storm wave base. In sub-basins with greater water depth on the NW-Tethyan shelf, post-CIE orbitally driven atmospheric turbulences had a minor or no effect on water column stratification and deposition of organic-rich laminated black shales persisted. Graphical abstract

Sulfur cycling likely obscures dynamic biologically-driven iron redox cycling in contemporary methane seep environments.

Deep-sea methane seeps are amongst the most biologically productive environments on Earth and are often characterised by stable, low oxygen concentrations and microbial communities that couple the anaerobic oxidation of methane to sulfate reduction or iron reduction in the underlying sediment. At these sites, ferrous iron (Fe2+) can be produced by organoclastic iron reduction, methanotrophic-coupled iron reduction, or through the abiotic reduction by sulfide produced by the abundant sulfate-reducing bacteria at these sites. The prevalence of Fe2+in the anoxic sediments, as well as the availability of oxygen in the overlying water, suggests that seeps could also harbour communities of iron-oxidising microbes. However, it is unclear to what extent Fe2+ remains bioavailable and in solution given that the abiotic reaction between sulfide and ferrous iron is often assumed to scavenge all ferrous iron as insoluble iron sulfides and pyrite. Accordingly, we searched the sea floor at methane seeps along the Cascadia Margin for microaerobic, neutrophilic iron-oxidising bacteria, operating under the reasoning that if iron-oxidising bacteria could be isolated from these environments, it could indicate that porewater Fe2+ can persist is long enough for biology to outcompete pyritisation. We found that the presence of sulfate in our enrichment media muted any obvious microbially-driven iron oxidation with most iron being precipitated as iron sulfides. Transfer of enrichment cultures to sulfate-depleted media led to dynamic iron redox cycling relative to abiotic controls and sulfate-containing cultures, and demonstrated the capacity for biogenic iron (oxyhydr)oxides from a methane seep-derived community. 16S rRNA analyses revealed that removing sulfate drastically reduced the diversity of enrichment cultures and caused a general shift from a Gammaproteobacteria-domainated ecosystem to one dominated by Rhodobacteraceae (Alphaproteobacteria). Our data suggest that, in most cases, sulfur cycling may restrict the biological "ferrous wheel" in contemporary environments through a combination of the sulfur-adapted sediment-dwelling ecosystems and the abiotic reactions they influence.

Effect of static compression on near-field tsunami waves: Three-dimensional solution

An analytical solution of three-dimensional surface wave profiles due to arbitrary spatio-temporal disturbance of a circular ocean bottom in a compressible ocean is obtained by incorporating the influence of the static ocean background compression under the assumptions of linearized water wave theory. Time-domain simulations of the surface profile in three dimensions and the pressure distribution within the water column for a circular uniform rise and tilt are shown. The corresponding animation movies depict the temporal evolution of the surface profile and pressure field inside the water column eloquently, which was not shown in earlier literature. The impact of static compression is also discussed through the simulations. A novel analytical expression of the potential function for a generic tilted motion (rmcos(mθ),m∈Z) of the circular ocean floor is derived. An efficient numerical code is developed to find surface elevation and pressure distribution, implementing the inverse Fourier integral as matrix multiplication. Validation is performed for the specific case of a rising flat ocean floor, showing the oscillations due to acoustic-gravity modes. Initially, a simplified problem of a flat rising ocean bottom is solved using the eigenfunction matching method, which involves finding a particular solution for the nonhomogeneous ocean bottom condition and the solution for its homogeneous counterpart. Solutions are obtained using a newly developed inner product between the depth-dependent functions. Later, a Green function technique is used to incorporate the impact of the arbitrary spatio-temporal motion of the circular portion of the ocean bed. The solution obtained from the eigenfunction matching method is utilized to obtain the analytical form of Green’s function and, eventually, an expression of surface elevation and pressure distribution inside the ocean water column.

Flexural-gravity wave forces acting on a submerged spherical object over a flexible sea bed

ABSTRACT A study has been conducted to analyse the impact of an ice sheet on the flexural-gravity wave force acting on a neutrally buoyant, spherical object immersed in a sea in accordance with the linear wave hypothesis. The bottom of the sea is presumed to be protected by a surface composed of some sort of flexibility, and the top is enclosed by an ice sheet. The solution to a diffraction problem is established using the multipole method. The estimated vertical and horizontal flexural-gravity wave forces are visualized in relation to different immersion depths of the spherical body, depths of the fluid and various flexural rigidities of the ice plate and the flexible seabed. The approach adopted here is likely to be of immense significance in the construction of various spherical gadgets like a seabed pressure detector device for tsunami recognition or communication in crisis for a submarine in earthquake zones.

Correlation between acoustic velocity and physical parameters of sea floor sediments: a case study of the northern South China Sea

As the interface between seawater and the seabed, superficial sediments on the seabed are an important part of the marine acoustic field environment and are indispensable for marine resource investigations. Studying sediments several meters to hundreds of meters below the seafloor is highly valuable and important. This study processes and analyses the water depth, topography and bottom data and obtains the shallow bottom profile and topographic map of the northern continental slope of the South China Sea (SCS). The study analyzes the influence of physical parameter (including density, porosity, and grain size) on the acoustic velocity in sediments. Single-parameter and dual-parameter models are established to further examine this influence. The results show that porosity and density have greater influences on the acoustic velocity of sediments than does grain size. Finally, the acoustic properties of several typical stations with water depths are tested to analyze the variations in the acoustic properties of the shallow sediments in the northern SCS. The results show that the influence of each parameter on the prediction of the acoustic velocity of the sediment is in the following order: porosity>density>grain size. This study analyses and reveals the reason why the seafloor sediments in the local area cause the acoustic properties to change greatly. It may be caused by changes in the sediment type, lithology along with the depth. And the other reason is the development of interlayer in the land slope of the northern SCS.

Experimental Study Of Parsian Port Breakwater Toe Stability

The stability performance of toe layer in structures with single-layer concrete armoures such as accropods and Xblocks is more crucial regarding their fast instability propagation and failure mechanism. This paper presents the case study concerning toe stability of Pasrsian port breakwater by experimental tests on physical model in Tarbiat modares university wave flume. Parsian industrial port is located in the south of Iran at Persian Gulf coastline. Its nineteen berths in final phase will be protected by approximately 1500 meter breakwater which at the most critical section, W5, reaches the sea bed level of -25 m.C.D. Figure 1. In concrete armored breakwaters, heterogeneous packing could increase the porosity in top rows and eventually result in instability. Therefore the number of rows in which the concrete units can be placed would be limited. According to the SUGRA guidance for Accropode units, this the maximum number of rows shall be 20, which leads designers to consider toe berm for breakwaters in deep water. Hence, it was vital to conduct a comprehensive physical model study.

Two-stage exhumation of high-pressure rocks by corner flow and mud volcanism within an active subduction zone – A case study from serpentinite mud volcanoes along the Mariana convergent margin

During International Ocean Discovery Program (IODP) Expedition 366 cores were recovered from three serpentinite mud volcanoes containing clasts that originate from the subduction-channel along the Philippine Sea Plate – Pacific Plate boundary. The drilled and sampled mud volcanoes (Yinazao, Fantangisña, and Asùt Tesoru) are located at distances of 55 to 72 km from the Mariana Trench. Mafic rock clasts, embedded within a serpentinite mud matrix, from the flanks and summits of both Asùt Tesoru and Fantangisña Seamounts were analyzed for reconstruction of their metamorphic and deformational overprint in order to reveal the tectono-metamorphic conditions at the metamorphic peak within the subduction channel and the subsequent low-grade overprint during exhumation. Several seamounts comprise clasts of lower plate metabasites with different metamorphic overprint (from low-grade sub-greenschist facies to lower blueschist facies). The metabasites are also associated with clasts of fossiliferous carbonates and cherts with different degrees of metamorphic and deformational overprint, that also originated from the Pacific lower Plate. This implies that these rocks were exhumed from different depths within the subduction channel before being regurgitated within a serpentinite mud matrix. The blueschist facies metamorphic rocks, being affected by metamorphic pressures in the range of 11 to 13.8 kbar at minimum, were very likely exhumed from greater depth within the subduction channel before being captured by uprising, localized serpentinite mudflows, indicating evidence that corner flow is actually taking place along the Mariana convergent margin, and that the high-pressure rocks were exhumed by corner flow in an active subduction zone. Final exhumation, however, is related to the embedding of the rocks within a serpentinite mud matrix and the buoyant ascent of serpentinite mudflows along forearc fracture zones extending from the plate boundary to the upper plate sea floor.

Role of topographical disturbances on hydroelastic response of a floating membrane over a slippery bottom

Some disruptions occur at the bottom of the sea due to underwater explosions and natural disasters (e.g. tsunamis, submarine earthquakes, landslides, rock and asteroid falls, drastic changes in weather conditions, etc.). The current paper aims to study how a transitory ground disturbance affects the membrane deflection in a viscous fluid over a porous slippery bottom at a finite water depth in the presence of a floating elastic membrane. Three types of ground disturbance are considered such as H 0 ( x ) = δ ( x ) , H 0 ( x ) = e ( − x 2 / 2 ) and H 0 ( x ) = e − | x | Kundu et al. [Waves generated on running stream due to a disturbance on sea bed. Int J Appl Comput Math. 2020;6(2):1–17.] and Maiti and Mandal [Waves generated by bottom disturbance in an ice-covered ocean. Int J Appl Mech Eng. 2007;12(2):477–486.]. The Stokes stream function and wave potential boundary value problems are used to formulate this problem. The membrane deflection is obtained as infinite integrals using the Fourier, and Laplace transforms. These integrals are then evaluated using the steepest descent method. The effects of the bottom slip parameter, the fluid's viscosity, and the floating membrane's tension and mass on the membrane deflection are analyzed. The study reveals that the amplitude of the membrane deflection decreases, and the oscillatory pattern of the deflection curve is changed by reducing the value of viscosity. Furthermore, the membrane's deflection amplitude decreases with an increase in the values of mass and tension of the floating membrane. Moreover, the slippery bottom plays a vital role in reducing the amplitude of the membrane deflection.

Volumetric, embodied and geologic geopolitics of the seabed: offshore tin mining in Indonesia

ABSTRACT This paper introduces empirical research on tin divers’ bodily experience of seabed mining concerning offshore Bangka and Belitung Islands, Indonesia, critical seabed mining sites. To govern the seabed off these Islands, ‘classic’ geopolitical approaches such as marine spatial planning (MSP) and the Organisation for Economic Co-operation and Development (OECD) hierarchically construct the seabed through two-dimensional mapping and policy, occluding specific tin diving practices on the seabed. Moving from such flat geopolitical understandings of the ocean floor, this paper offers new engagements with feminist geopolitics, volumetric territory and social ocean studies to think about the seabed through its volume, the bodies that are immersed within and animate it, and its geologic materiality. It does so by examining intimate tin diving relations between human bodies, volumetric space and ore bodies in relation to the contemporary geopolitical making of the seabed territory. Whilst many scholars have engaged with this volumetric-embodied-geologic approach, this paper argues that the nexus of volumetric space, bodies (embodied experiences) and geologic materiality in tin diving are a crucial tactical point for diverse mining governance actors, sustaining dangerous labour, mining accidents and death in tin diving.