Sediment Density Research Articles

Inferring benthic megafaunal sediment reworking activity in relation to bottom water oxygen in Barkley Canyon, NE Pacific from video and acoustic imaging analysis

Sediment reworking activity influences benthic functioning expressed as nutrient fluxes and carbon cycling. Multiple studies have addressed sediment reworking based on observations from individual instrument types (e.g., video camera, side-scan sonar, multibeam), but none have considered reworking based on two or more complementary instruments. We therefore analyzed deep-sea megafaunal and reworked sediment traces by combining and comparing observations from non-invasive instruments, an underwater video camera and a rotary sonar, as part of the node of Ocean Networks Canada's NEPTUNE cabled observatory, located at 396 m depth in Barkley Canyon Upper Slope, NE Pacific Ocean. Specifically, we examined sediment traces and benthic megafaunal communities during two different sampling periods (May and September 2013) and at two different spatial scales of analysis. The camera images (∼0.5 m2) documented significantly lower megafaunal density during the period of reduced oxygen concentrations (May). Although we did not observe significant differences in sediment trace diversity and density between the two study periods, we were interested in how the relief traces generated by unidentified gastropods (likely the family Solariellidae) influenced sediment mixing. Relief traces showed higher density in low oxygen (May, 1.87 count m−2) than in high oxygen (September, 1.17 count m−2) conditions. Sonar images (∼1268 m2), which lacked sufficient resolution to allow identification of benthic organisms, documented distributions of biological pits (regions of low backscatter), a significantly greater proportion of bioturbated seafloor area, and increased in pit size with increased oxygen levels. Pits dominated sonar images at this location and persisted through the two study periods. Most sonar field of view subsections showed a significant increase in circularity of pit shapes, likely explained by increased reworked sediment with increasing oxygen concentration. We conclude that, except for relief burrows, higher reworked sediment area coincided with the highest oxygen concentration, which aligns with previously established reduced metabolic activity by benthos adapted to oxygen minimum zones. Furthermore, we emphasize the complementarity of the two imaging techniques (video and sonar) in understanding deep-sea benthic ecosystem dynamics, as well as the importance of considering multiple spatial scales when investigating proxies of bioturbation activity.

Electrogenic sulfur oxidation by cable bacteria in two seasonally hypoxic coastal systems

Cable bacteria can reach high densities in coastal sediments, and as a result of their unusual electrogenic lifestyle and intense metabolic activity, exert a major and distinct impact on biogeochemical cycling, both locally in sediments and at the ecosystem level. This appears to be particularly true for seasonally hypoxic systems, but the driving force behind the proliferation of cable bacteria in these systems is not well understood. Moreover, the metabolism of cable bacteria induces strong acid production, which can be buffered through carbonate dissolution in sediments. A strong depletion of alkalinity in the pore water is therefore expected in carbonate-poor sediments. To evaluate the impact of cable bacteria metabolism on sediment geochemistry, we performed field sampling and laboratory sediment incubations in two seasonally hypoxic sites: one carbonate-poor site with low levels of free sulfide in pore water (Yarra Estuary, Australia) and one carbonate-rich site with high free sulfide (Lake Grevelingen, The Netherlands). Active cable bacteria populations were found in both field locations, with higher abundance and activity observed in spring compared to autumn. The sediment incubations tracked the metabolic activity of cable bacteria over time (maximum 84 days), and confirmed the fast development of an electric network (cell doubling time: ∼19 h). These results suggest that cable bacteria are widespread in seasonally hypoxic systems, supporting previous findings. Cable bacteria acidified the sediment by > 1.5 pH units in 6–13 days (differing per site) and their activity accounted for >70% of the oxygen uptake. A clear subsurface accumulation of Fe2+ was observed after 8 days of Yarra sediment incubations, indicative of increased FeS dissolution as e-SOx developed. The increased availability of sulfide from FeS dissolution promotes a positive-feedback loop that we infer allowed for a faster development of cable bacteria in the carbonate-poor sediments. A depletion of total alkalinity was observed in the deeper Yarra sediment, whereas, a higher alkalinity efflux was previously observed in the carbonate-rich sediments from Lake Grevelingen. These results suggest a differential pH and alkalinity dynamic due to the interaction between the local carbonate content of the sediment and cable bacteria activity.

Estimation of carbon stocks in mangrove sediments in Ruyung Village, Mesjid Raya District, Aceh Besar Regency

Exploration related to blue carbon has increased recently. As one of the blue carbon ecosystems, the mangrove ecosystem is one of the coastal ecosystems that can absorb and store carbon. This research aims to calculate mangrove density and estimate carbon stocks in sediments in the mangrove ecosystem in Ruyung Village, Mesjid Raya District, Aceh Besar Regency. Mangrove density was calculated at three stations within 10 x 10 m transects. Sediment samples were also taken compositely, and carbon analysis was carried out in the sediment using the LOI (loss on ignition) method. There were two species of mangroves found at the research location, namely Rhizophora apiculata and Avicennia officionalis. The research results show that the average mangrove density at the research location is 0.20 ind/m2. The average soil density and sediment carbon stock at all research stations is 1.24 g/cm3 and 271.66 MgC/ha respectively. The mangrove ecosystem, both biomass and surrounding sediment, can store carbon, which is one of the ways to mitigate global warming.

Effect of High Cell Density to Lipid Content Microalgae Chlorella vulgaris on Photoautotrophic Cultivation

Chlorella vulgaris is one of microalgae types that has essential ingredients beneficial tohumans, such as being a source of good lipid. Chlorella sp. have high lipid content, up to30%, under autotrophic conditions considered as a promising candidate for commercial lipidproduction due to its fast growth and easy cultivation. High cell density sedimentation can beinvestigated as a starving method in cultivation to make microalgae conditions less favorablein obtaining nutrient to lipid accumulation. Starving is one of the stress conditions carried outwith the aim of reducing nutrients in the microalgae cultivation process. The aim of this studywas to determine the effect of high cell density on increasing lipid content in Chlorellavulgaris. The results of this study showed that high cell density method affected theproductivity of Chlorella vulgaris biomass. The data obtained were analyzed using ANOVAα=0.05. The highest productivity and lipid content was obtained from the control sample witha biomass value of 0.36±0.03 g/l and a lipid content of 56.2±4.6% (P<0.05). The conclusionof this study is high cell density may not increase the production of lipid content fromChlorella vulgaris

New physical and biological evidence of lateral transport affecting dinoflagellate cyst distribution in the benthic nepheloid layer along a land-sea transect off Figueira da Foz (Atlantic Iberian margin)

IntroductionThe production of resting cysts is a key dispersal and survival strategy of many dinoflagellate species. However, little is known about the role of suspended cysts in the benthic nepheloid layer (BNL) in the initiation and decline of planktonic populations.MethodsIn September 2019, sampling of the dinoflagellate cyst community at different water depths in the water column and in the bottom sediments, and studies of spatio-temporal changes in physical properties (temperature, salinity, density and suspended sediment concentration), were carried out along a land-sea transect off Figueira da Foz (NW Portugal) to investigate the dinoflagellate cyst distribution and the factors (physical and biological) affecting it. A clustering analysis was used to compare the BNL and sediment cyst records with the cyst rain recorded by a sediment trap at a fixed station. Furthermore, Lagrangian particle experiments enabled simulating cyst trajectories in the BNL 5 and 10 days before sampling and assessing cross-shore, vertical and alongshore transport within the studied region.ResultsA well-developed BNL was present during the survey, which covered a change from active (14th of September) to relaxed (19th of September) upwelling conditions. Organic-walled dinoflagellate cysts were dominant in all samples, although calcareous dinoflagellate cysts consistently occurred (at low abundances). High proportions of full cysts were observed in the BNL, of which a significant portion was viable as shown by excystment experiments. Moreover, BNL cyst records collected on the 19th of September along the land-sea transect were similar to the sediment trap cyst record but greatly differed from sediment cyst records. The heterotrophic small spiny brown cysts (SBC) and cysts of the autotrophic yessotoxin-producer Protoceratium reticulatum notably increased during the survey, in the BNL and in the water column above.DiscussionThe comparison of the BNL, surface sediment and sediment trap cyst records supported that the main origin of cysts in the BNL was the recent production in the water column. The spatial coincidences in the distribution of cysts and vegetative cells of Protoceratium reticulatum also supported that full cysts in the water column were being produced in surface waters. New data evidenced the presence of a significant reservoir of viable cysts in the BNL that have the potential to seed new planktonic blooms. Furthermore, back-track particle modelling evidenced that alongshore advection was the main physical mechanism controlling cyst dynamics in the BNL during most part of the survey period, being particularly intense in coastal stations (<100 m depth). Consequently, the sediment cyst signal is a mixture of locally and regionally produced cysts. We provide multi-disciplinary data evidencing that cysts recently formed in the photic zone can be laterally advected within the studied region through the BNL, contributing to a better understanding of the role of the BNL in cyst dynamics and tracing the seed sources of the new blooms.

Siltation behavior characterization and evaluation of permeable asphalt mixture based on computed tomography method

The pavement surface sediments are continuously transported into the pore structure of permeable pavement under hydraulic power, resulting in the loss of permeability function. Obtaining the siltation behavior of the permeable asphalt mixture is the key and foundation to achieving siltation prevention and control technology for permeable asphalt pavement. In this paper, a self-developed laboratory accelerated siltation test was designed, and X-ray diffraction (XRD), computed tomography (CT) experiments, intrinsic frequency tests were employed to explore the siltation behavior of permeable asphalt mixture. The test results reveal that the density of pavement surface sediments is approximately 15.2 g/m2 per day, and pavement surface rainwater contains 27.6% clay minerals, which exhibits induration consolidation property with dry-wet cycles. The blockage behavior caused by sand particles is 7.5% higher than that caused by clay. For the siltation contribution of permeable asphalt mixture, sand particles account for 81%, clay particles represent 7%, and the induration consolidation contributes 12% of the siltation. CT test results indicate that the lower 1/3 of permeable asphalt mixture is silted up with continuous adhesive deposition of clay. The dry-wet cycle is one of the key factors of hardening blockage, the hardening blockage primarily experiences three stages: stagnation and hardening, erosion and collapse, and deposition blockage. Intrinsic frequency test explores that the intrinsic frequency of permeable asphalt pavement is between 14,000 Hz and 15,000 Hz, and the intrinsic frequency of pavement surface sediment is 3968.83 Hz. The intrinsic frequency of pavement increases continuously with the transportation of surface sediment, and there is a good correlation between the siltation degree and intrinsic frequency of permeable asphalt mixture.

Salinity, mineralogy, porosity, and hydrodynamics as drivers of carbon burial in urban mangroves from a megacity

Mangrove ecosystems are an important blue carbon store but exhibit considerable variation in soil carbon stocks globally. Unravelling the conditions controlling carbon stock is critical for assessing current and future carbon budgets. Mangrove soil biogeochemical cycles can strongly influence carbon storage capacities. We thus investigated carbon sequestration and the environmental parameters shaping variability in biogeochemical cycling and carbon storage in sediment samples from four mangrove sites along an estuarine-to-marine gradient in Hong Kong, a megacity. Our results showed that organic matter in Hong Kong mangroves is sourced principally from autochthonous mangrove plants. Total nitrogen was higher in the freshwater-influenced sites and supplied from different sources. Marine-influenced sites had larger sulfur fractionations, reflecting higher marine-sourced sulfate concentrations and indicating a relatively open sulfate system. We estimated an average organic carbon stock of 115 ± 8 Mg C ha−1 in the upper 100 cm soil layer placing Hong Kong mangroves at the lower end of the global spectrum of the soil carbon stock. Carbon accumulation was found to be driven by a combination of higher total organic matter inputs, soil fluxes, and porosity. Notably, despite having the highest mass-specific soil organic carbon contents, Mai Po had the lowest integrated soil organic carbon storage (77 ± 3 Mg C ha−1). This was primarily due to lower sediment density and higher tidal pumping leading to a decrease in carbon retention. Total organic matter input, sediment characteristics, and hydrodynamics were the main factors influencing soil organic carbon storage. Overall, our results suggest that (1) while multiple parameters can enhance soil organic carbon content and increase carbon storage capacities, (2) hydrodynamics and sediment characteristics can increase the potential for leakage of carbon, and (3) high carbon content does not always equal high carbon sequestration and stock.

Thermodynamic Constitutive Model of the Gas Hydrate-Bearing Sediments Considering Anisotropy

Gas hydrate-bearing sediments (GHBS) are considered a significant potential energy source. However, the decomposition of hydrates can lead to various geological hazards. Therefore, a comprehensive investigation into the mechanical properties of GHBS is essential to ensure the safe extraction of gas hydrate. This paper presents a constitutive model for GHBS that incorporates anisotropy, based on the theory of thermodynamics. To account for the effects of hydrate filling and cementing, two parameters are introduced into the dissipation function of the model. The filling effect is expressed through the densification mechanism, which increases the density of the host sediment. The cementing effect is represented by the enhanced expansion of the yield surface. The yield function incorporates the spacing ratio [Formula: see text] and the teardrop shape parameter [Formula: see text], which govern the shape of the yield surface, as well as the anisotropy angle [Formula: see text], which signifies the anisotropic evolution law. The physical significance of these parameters is also elucidated. The anisotropic evolution is described by an exponential function. The proposed model is compared to both the test results and the existing constitutive model, and it is found that it provides more accurate predictions of the mechanical properties of GHBS.

Sedimentation Behavior of Flocculant-Treated Dredged Slurry under Filtration of Woven Geotextiles

Geotextile tubes have offered a cost-effective and convenient solution for the treatment of dredged slurry in recent years. Despite their benefits, the dewatering process of this method remains cumbersome and time-consuming. The incorporation of flocculants into dredged slurries has been shown to mitigate the clogging of geotextile tubes, thereby enhancing the efficiency of the dewatering process. To quantify the impact of flocculant addition on the dewatering performance, a series of laboratory tests were conducted to investigate the sedimentation behavior of flocculant-treated river-dredged slurries under filtration of woven geotextiles. The impact of different flocculants is evaluated with the sedimentation rates of dredged slurries, specifically nonionic polyacrylamide (NPAM) and cationic polyacrylamide (CPAM). Results demonstrated that both NPAM and CPAM, at an optimal concentration of around 250 mg/L, could substantially increase the settling rates of slurries when filtered through geotextiles. At equivalent flocculant concentration, NPAM outperforms CPAM in accelerating sedimentation rates. It is also evidenced that adding flocculants can significantly augment the particle size and permeability of slurries. After adding flocculants, the water content and dry density of the final sediments exhibit a more uniform distribution in the vertical direction compared to the original slurry. Furthermore, scanning electron microscopy was employed to analyze the micromorphology of the final sediments treated with different NPAM concentrations. The results showed that the slurries exhibited significant void structure under treatment with the optimal concentration of NPAM, demonstrating the flocculants’ effectiveness in enhancing the dewatering process of river-dredged slurries when filtered with geotextiles.

Spatial distribution characteristics of denitrification functional genes and the environmental drivers in Liaohe estuary wetland.

Genes nirS, nirK, and nosZ are specific for the denitrification process, which is associated with greenhouse gas N2O emission. The abundances and diversities of community containing these three genes are usually used as a common index to reflect the denitrification process, and they would be affected by differences in environmental factors caused by changes from warm to cold conditions. The quantification of denitrification in natural wetlands is complex, and straightforward identification of spatial distribution and drivers affecting the process is still developing. In this study, the bacterial communities, gene diversities, and relative abundances involved in denitrification were investigated in Liaohe Estuary Wetland. We analyzed the relative abundances, diversities, and communities of bacteria containing the three genes at warm and cold conditions using Illumina MiSeq sequencing and detected the potential environmental factors influencing their distribution by using a random forest algorithm. There are great differences in the community composition of the bacteria containing genes nirS, nirK, and nosZ. All the abundant taxa of nirS and nirK communities belonged to phylum Proteobacteria. Compared with the community composition of bacteria containing nirS and nirK, the community of bacteria containing nosZ is more diverse, and the subdivision taxa of phylum Euryarchaeota was also abundant in the community containing nosZ. The distribution characteristics of the relative abundance of nirS and nirK showed obvious differences both at warm and cold climate conditions. The oxidation-reduction potential, nitrite nitrogen, and salinity were detected as potential variables that might explain the diversity of nirS. The total nitrogen and nitrite nitrogen were the important variables for predicting the relative abundance of nirS at warm climate condition, while oxidation-reduction potential and pH contributed to the diversity of nirS at cold condition. The bulk density of sediment was detected as a potential variable affecting the relative abundance of nirK at warm and cold conditions, and diversity of nirK at warm condition, while nitrite nitrogen was detected as an important environmental factor for predicting the diversity of nirK at cold condition. Overall, our results show that the key environmental factors, which affect the relative abundance, diversity, and community of bacteria containing the functional denitrification genes, are not exactly the same, and the diversities of nirS, nirK, and nosZ have a higher environmental sensitivity than their relative abundances.

Deep-sea macrofauna community recovery in Kaikōura canyon following an earthquake-triggered turbidity flow

Sediment density flows can transport massive amounts of sediment across large distances and can have dramatic, long-lasting impacts on deep-sea benthic communities. A canyon-flushing event in Kaikōura Canyon, New Zealand, triggered by the 2016 Mw 7.8 Kaikōura Earthquake, which included significant submarine mass wasting, debris and turbidity flows, provides an excellent opportunity to investigate the effects of this type of large-scale natural disturbance on benthic communities. The macrofauna community in the canyon was well characterised before the disturbance and the canyon described as a deep-sea benthic biomass hotspot. Macrofauna community structure before and after the event was analysed in a time series of sediment cores from 8 sites (∼400–1300 m water depth) collected 10 years and 6 years before, and 10 weeks, 10 months, and 4 years after the disturbance. The benthic community structure showed significant variability at all time points, but immediately after the 2016 disturbance abundances of all macrofauna dramatically decreased. Four years after the disturbance the benthic community was similar to, but not yet comparable to the pre-event community. The average abundances of most macrofauna increased over the 4 years post-earthquake, with polychaetes and bivalves being key taxa in the recovery process, especially 10 months and 4 years after the disturbance. Infauna abundances >5 cm below the seabed, remained low even 4 years after the event but the overall pattern of vertical faunal distribution was trending towards a pre-disturbance state. Community recovery was investigated in relation to changes in the physical characteristics of the habitat caused by the disturbance, using variables derived from sediment cores (e.g., sediment texture, organic matter, and pigment content). While the environmental variables explained relatively little of the overall variability in macrofauna community structure, key variables identified were related to particle size structure and food availability and quality. The minimum threshold time for the macrofauna community to fully recover, based on within-community similarity, was estimated to be between 5.6 and 6.7 years, although recovery was predicted to take up to 9 years if higher recovery thresholds were used. The management implications of this study are considered in comparison to the few studies of large-scale disturbances in the deep sea, in terms of their relevance to the efficacy of the marine reserve that encompasses Kaikōura Canyon, and potential implications for our understanding of the impacts of anthropogenic disturbances such as seabed mining.

Assessing the Erosional Properties of Muddy Sediments: Asan Bay Case Study

The study's outcomes reveal that both the critical shear stress needed to initiate erosion and the sediment erosion rate are influenced by various parameters, including the bulk density of sediment and bed shear stress. This comprehensive analysis underscores the vital role that these parameters play in determining sediment erosion characteristics. The presented research contributes to the understanding of erosional behaviors of muddy sediments and their implications. The findings emphasize the importance of comprehending such properties, especially in designing effective erosion control structures and managing water bodies prone to erosion.

Development of a high-energy centrifuge model impact hammer for pile-driving

The offshore wind energy industry continues to expand rapidly around the world in response to the demand for clean energy. Research to investigate monopile performance under cyclic lateral loading needs to replicate the installation process as well as the cyclic loading regimes. This has provided the impetus for the development of model pile driving hammers for use in geotechnical centrifuges. This paper presents a new model-scale centrifuge impact hammer that is capable of in-flight driving of large-diameter piles into dense sediments with the flexibility of varying the energy during a test for a more controlled installation. The new hammer is activated by a pair of rotating cams, improving on the pneumatically activated hammer developed in the 1980s, giving greater energy and much better reliability. This paper provides full details of the hammer, together with data obtained at 80g acceleration, driving prototype 4 m wide (50 mm in model scale) piles into dense, dry sand to depths of over 20 m (over 5D) in <1000 blows.

Learning a surrogate Pekeris waveguide model

Underwater sound propagation models predict transmission loss (TL) given environmental parameters, such as seafloor sediment parameters. Also of interest is the reverse: Can seafloor parameters, such as sediment density, sound speed, and attenuation, be inferred from ocean acoustic data? This inverse problem can be addressed using information geometry tools for parameter identifiability analysis and model reduction, where we identify parameters that can be removed from a model without sacrificing accuracy. Critical to these methods for model reduction is the ability to evaluate derivatives of the model’s TL predictions with respect to model parameters. Automatic differentiation (AD) allows for rapid evaluation of a model’s derivatives but may face some challenges for implementation with sound propagation models, including models being written in “legacy code” and having non-differentiable points in the function space. Our solution is to train a surrogate machine learning (ML) model which can circumvent these challenges, and which we can apply AD to. We demonstrate this method using the Pekeris waveguide model of the ocean. We compare the surrogate and original model outputs and demonstrate the process of model reduction using a ML surrogate model. [Work supported by Office of Naval Research.]

Numerical Study of the Transport Process of Shallow Heat Carried by Turbidity Currents in Deep‐Sea Environments

AbstractTurbidity currents often originate from relatively high‐temperature water bodies near the coast of the upper continental shelf. Turbidity currents are the main carriers that transport land sediments to the deep sea. Their impact on heat exchange and material transport in the deep‐sea ecosystem is receiving more attention. However, presently, there are few studies on heat transport by turbidity currents. This article presents a coupled model of multiphase flow and heat transfer through laboratory experiments and numerical simulations. The effects of sediment particle size, density, and Froude number on the characteristics of turbidity current heat transfer are analyzed, and the heat flux carried by turbidity currents transporting upper‐layer heat into the deep sea is reproduced. The results indicate that turbidity currents are carriers of shallow heat into the deep sea. The temperature structure within turbidity currents follows a Gaussian function and can effectively preserve heat. The efficiency of the long‐distance transport of heat carried by turbidity currents is negatively correlated with sediment particle size and the velocity of turbidity currents, and positively correlated with sediment concentration. Turbidity current heat shock events in the future may have significant and far‐reaching impacts on deep‐sea ecosystems.

Well‐log integration and seismic‐to‐well tie off George V Land (Antarctica)

AbstractCenozoic sediments from the continental rise off the George V Land consist of silty/clayey facies variably rich in diatom ooze; these sediments hold a record of the glacial history of the Wilkes Subglacial Basin and are important for estimating the contribution of the East Antarctic Ice Sheet to global sea level changes during past transition to warmer climates. This is fundamental to predict future scenarios related to the global warming. The petrophysical properties of Antarctic marine sediments are influenced by the ice sheet dynamics and may affect the amplitude of seismic reflections. Through a seismic‐to‐well tie procedure, we investigate the origin of high amplitude reflections from Miocene‐early Pliocene deposits identified in two seismic lines crossing at the Integrated Ocean Drilling Program Expedition 318 drill site U1359. Downhole and core log measurements are preconditioned and merged to obtain complete velocity and density records from the sea floor to the bottom of the deepest of the four wells drilled at this site. We generate a synthetic trace by convolving the reflectivity series with the seismic wavelet obtained from the sea‐floor reflection and match the synthetic trace to the seismic data with a time variant cross‐correlation procedure. This procedure established a robust time‐depth relationship, not achievable from the available small‐offset seismic data. To our knowledge, this is the first seismic‐to‐well tying in the George V Land area. Based on results from synthetic data, the anomalous high amplitude seismic package can be linked to changes in density of sediments. Such changes are interpreted as representative for the alternation of diatom‐rich (warm climate) and silty‐clay layers with ice‐rafted debris (cold climate) inside the deposits. We suggest that the analysis of the characteristics and the distribution of similar seismic anomaly around Antarctica can give insight into the modality of past Antarctic ice sheet dynamics.

Significant improvement of mechanical properties of cold-spray-additive manufactured FeCoNiCrMn high-entropy alloy via post-annealing

In this work, equimolar FeCoNiCrMn high-entropy alloy (HEA) was fabricated by solid-state cold spray additive manufacturing (CSAM) technique and post-annealed. The microstructure evolution and mechanical properties of the deposits before and after annealing were systematically evaluated. The tensile test results revealed that the deposit annealed at 1000 °C for 2 h exhibited an excellent combination of tensile strength and ductility, with a doubled ultimate tensile strength of 455 MPa compared with the as-sprayed and significantly improved elongation (28%). The improved strength can be attributed to the healing of micropores and interparticle interfaces in the deposit due to the interface diffusion induced by high temperature. The recovery of ductility is the result of a significantly decreased dislocation density and enhanced metallurgical bonding at interfacial regions. For the first time, the current work demonstrated that the combination of CSAM and post-annealing strategy could achieve the strength-ductility synergy of HEA deposits. The results of in-situ analysis show that the mechanism of tensile deformation process includes particle separation, and it can be inferred that the preparation of dense sediments combined with post-treatment is the direction of further optimization.

Effects of Patch Density and Incoming Sediment on Flow Characteristics and Bed Morphology

This study focuses on the effects of vegetation patch density, bed condition, and incoming sediment on flow structure and bed morphology within and around a patch. The variation in upstream adjustment velocity is not well defined for low-density vegetation patches but decreases with increasing patch density in high-density patches. The length of the upstream adjustment region is greater for high-density vegetation. Incoming sediment causes a reduction in both the steady wake velocity and the length of the steady wake at a low density. The length of the recovery region increases with density when vegetation is sparse, but remains constant in a dense patch. Additionally, the length of the recovery region decreases due to incoming sediment. Turbulent kinetic energy is not affected by the bedform and incoming sediment when reaching its first peak. However, the second maximum of the turbulent kinetic energy increases when the bed is movable. The evolution of bed morphology is closely related to the flow structure and the growth of the von Karman vortex street. Both the rising length and the adjusted length decrease with increasing patch density, while the incoming sediment causes an increase in the adjusted length. Behind the patch wake, the first minimum elevation, maximum elevation, and second minimum elevation decrease as the patch density increases. These values, in turn, increase with the sediment supply upstream of the flume.

The Variability of Sedimentary Carbon Stock in Seagrass Ecosystem in Central Tapanuli, Indonesia

Blue carbon is a term to underline coastal ecosystem such as mangrove, seagrass, and tidal marshes capability as carbon sequestration where the organic carbon that stored in coastal sediment is greater than the organic carbon in living biomass. This study analysed the variability of sediment carbon stock in seagrass ecosystem in Central Tapanuli, Indonesia. LOI method was used to determine the carbon stock. Regression analysis showed that depth, and dry bulk density strongly influence the sedimen carbon stock in seagrass ecosystem (R2 = 0.77 in Hajoran and R2 = 0.79 in Jago-jago) where the total organic carbon stock in upper layer and denser sediment was higher than the organic carbon stock in middle/bottom layer sediment. Moreover, sediment type also influenced the carbon stock where sediment with finer grain size (11.80 – 13.46 Mg C/ha) captured more organic carbon than sand (6.54 – 10.34 Mg C/ha). By knowing this capacity, monitoring and maintaining coastal sediment and vegetation should become priority to mitigate the climate change.

Tectonic controls on effective elastic thickness of lithospheres around the Southeast Asian subduction zones

Southeast Asia has the most complicated convergent system on the Earth. The effective elastic thickness (Te) can be a constraint on the long-term flexural strength and deformation mechanism of the lithosphere. In this paper, we estimate Te over the Southeast Asia via the free-air admittance function calculated by the continuous wavelet transform. Sedimentary correction is performed to avoid the biases induced by the low density of sediments. The spatial variations of Te coincide well with the tectonic settings. The Northeast Indian Seamount Province and young oceanic basins correspond to the lowest Te (≤10km). The Sunda Shelf displays relatively low Te (10–20 km), where Cenozoic rifting and extension weakened the lithosphere. The Molucca Sea and most continental regions show high Te (≥40 km). Overall, Te shows dependence on the oceanic crustal age in our study area, and is influenced by intensive tectonic activities. Low Te (≤10km) in northern Sumatra and central Java subduction zone is consistent with the presence of a slab tear/window and mantle upwelling. Moreover, Te in Southeast Asia is either non-correlated with surface heat flow, or weakly correlated to Curie-point depth and seismic velocities at the 100 km depth. In some regions, e.g., the South China Sea and Sumatra-Java Trench, Te shows poor correlation with all geothermal proxies we employed. We argue that the geothermal state of lithosphere exerts very limited effects on integrated lithospheric strength in the tectonically active Southeast Asia, and apart from the temperature and composition, tectonic factors dynamically control the rigidity of the lithosphere.