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Turbidity flows are known to be affected by the density difference between sediment plumes and the surrounding water. However, besides density, other factors could lead to changes in flow propagation. Such a factor is the presence of suspended organic matter. Recently, it was found that flocculation does occur within plumes upon release of a sediment/organic matter mixture in a lock exchange flume. In the present study, mineral sediment (illite clay) was released into the outflow compartment containing water and synthetic organic matter (polyacrylamide flocculant). Even though the density of water was barely affected by the presence of flocculant, flow head velocity was observed to be larger in the presence of flocculant than without. Samples taken at different positions in the flume indicated that flocs were created during the small current propagation time (about 30–60 s) and that their sizes were larger with higher flocculant dosage. The size of flocs depended on their positions in the flow: flocs sampled in the body part of the flow were larger than the ones sampled at the bottom. All these properties are discussed as a function of sediment–flocculant interactions. [ABSTRACT FROM AUTHOR]

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The controls on the development of submarine channel sinuosity are contested: slope gradient and Coriolis forcing have both been recognized as key governing factors: gradient via an inverse relationship (low sinuosity at high slope and vice versa), and Coriolis forcing through its effect on sedimentation patterns (reducing lateral bend migration, and hence sinuosity development, at high latitudes and/or in large channels). Using theoretical models to calculate the bulk properties of channelized turbidity currents, this study investigates the joint role of the Coriolis force and parameters including channel size, downchannel slope and turbidity current properties in the development of submarine channel sinuosity. Model validation is undertaken through the comparison of the calculated turbidity current tilting against the measured tilting of channel levees in the Northwest Atlantic Mid‐Ocean Channel; this approach is then used to evaluate the controls on channel sinuosity in nine other modern seafloor channels. The results indicate that the Coriolis force only becomes significant when the size of the channel, the slope gradient and flow conditions are within appropriate ranges instead of solely being dependent on latitude. Thus, thick and dense (≥1% bulk sediment concentration) flows traveling within steep‐gradient, small‐scale channels were shown to be relatively less susceptible to flow modification by Coriolis forcing even at high latitudes. On the other hand, thin and dilute (≪1% bulk sediment concentration) flows in shallow‐gradient, large‐scale channels showed susceptibility to Coriolis forcing at all latitudes. These results offer new insights into submarine channel evolution and intra‐channel sedimentation patterns. Plain Language Summary: Sediments are widely distributed in the oceans by underwater currents akin to powder snow avalanches. These "turbidity currents" may sculpt the sea floor to build submarine channels which, like rivers, may range in sinuosity from being virtually straight to highly sinuous. Several competing controls have been suggested to explain this variation. Some argue that slope is most important, with low sinuosity channels forming on high angle slopes and vice versa. Others claim that the Coriolis force, which affects flows moving across a rotating surface (such as the Earth), is the main control ‐ either via latitude alone (with high sinuosity channels restricted to lower latitudes) or only affecting channels that are large enough. To test these ideas we developed a new numerical modeling approach that looks at the combined effects of channel axis gradient, channel size and flow conditions. By modeling the tilt of turbidity currents flowing around bends we show that single factors cannot be used to explain channel sinuosity. The model is tested with real world data. Although sinuosity is generally greater at low latitudes there are exceptions; variations across a range of controlling factors can produce channels of any sinuosity at any latitude. Key Points: We present a novel methodology to assess the contested controlling factors on the development of sinuous channelsDeep and dense flows that pass through small channels in steep slopes, regardless of the latitude, promote sinuosityDilute and shallow flows that pass through large channels in low gradient systems hinder sinuosity development at any latitude [ABSTRACT FROM AUTHOR]

The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial organic carbon to the deep sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the submarine Congo Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ∼7 % of the dissolved and particulate organic carbon from the world's rivers. However, sediment and particulate organic carbon transport mechanisms that operate in the Congo Canyon and submarine canyons more globally are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps, and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the submarine Congo Canyon to the deep sea. We show that particulate organic carbon transport in the canyon axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 ms-1) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 ms-1) turbidity currents occur for 35 % of the time during monitoring periods and transport particulate organic carbon with mud and sand at an estimated transit flux that is more than 3 to 6 times the flux induced by tides. Organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo submarine fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally. [ABSTRACT FROM AUTHOR]

Submarine channels on the seafloor experience a range of turbidity current‐flood hydrographs. The characteristics of the flood hydrograph influence channel dimensions, the number of channel threads (i.e. braiding intensity) and the depositional properties of sandbars within the channels. However, the morphodynamic response of submarine braided channels to different hydrograph patterns is poorly understood. In this study, six geomorphic experiments are used to test how varied flood hydrographs affect the braiding intensity and sandbar geometry within submarine channels. Three experiments represent the control group with constant density‐current inflow, and three experiments use different time‐varying hydrograph patterns. The experiments show that, as the inflow‐to‐sediment discharge ratio increases, multiple small channels coalesce into a few main channels, causing a decrease in active braiding intensity defined by the channel threads with flow. When the flow returns to the initial low flow rate, active braiding intensity increases again. These observations show that the inflow‐to‐sediment discharge ratio determines the value of active braiding intensity. Additionally, active braiding intensity is directly proportional to dimensionless sediment‐stream power and dimensionless stream power, in agreement with previously established trends for both submarine and fluvial braided channels. In contrast to active braiding intensity changes, the measured sandbar aspect ratio and compactness ratio (i.e. ratio of planform area to perimeter) of submarine braided channels is insensitive to changes in the hydrograph. However, when inflows reach peak discharge, the higher transport capacity erodes pre‐existing deposits, forming noticeable erosional surfaces, and subsequently depositing thicker sandbars during that stage. These observations imply that sandbar planform morphology is largely insensitive to hydrograph, but hydrograph variability induces a greater variability in the resultant stratigraphic packages. The experimental results predict that field‐scale stratigraphy should be dominated by strata deposited during intervals of high flow, but that these strata will also exhibit reduced lateral continuity compared to formation scenarios with constant discharge. [ABSTRACT FROM AUTHOR]

Manned submersible dives in the northwest South China Sea encountered substantial amounts of plastic litter accumulated at the base of scours along the floor of a submarine canyon, which may associate with the depositional behaviors of turbidity currents. In this study, we conduct numerical simulations using field‐scale bathymetry to investigate the relationship between the canyon floor morphology, flow processes, and the locations and sizes of the plastic litter piles. The consistent deposition pattern caused by the numerical turbidity currents with different input parameters indicate that morphology of the canyon may exert a dominant influence on turbidite deposition. This is attributed to a significant reduction in shear velocity as simulated turbidity currents flowing through the scours on the canyon floor. Spatial correspondence between deposits of turbidity currents and plastic litter accumulation suggests that suspended sediments and plastic may undergo simultaneous dynamic processes during the transportation of turbidity currents. Plain Language Summary: The issue of marine plastic litter has attracted wide attention, particularly in terms of its transportation mechanisms and locations of accumulation on the ocean floor. Turbidity currents are subaqueous sediment‐gravity flows that can transport large amounts of sediment, nutrients and pollutants into the deep sea, yet there is sparse research on the dynamics of plastic litter transport under the control of turbidity currents, and its accumulation in the deep sea. Here, we present a series of numerical simulations of turbidity currents in a submarine canyon with various input parameters, when combined with observational data on topography and plastic litter distribution, confirm that turbidity currents constitute a plausible mechanism for the transport of plastic litter and for its accumulation in response to changes in flow associated with scours. In addition, we find that the concavity of the scours is also necessary for plastic litter accumulation, since it induces significant fluctuations in the shear velocity and the corresponding depositional process. Key Points: Numerical simulations were applied to investigate turbidity currents as a cause for plastic litter accumulations in a submarine canyonThe simulated turbidite deposits and observed plastic litter accumulations exhibit a strong spatial correspondenceThe morphology of the canyon floor may exert dominant influence on the plastic litter accumulations in submarine canyons [ABSTRACT FROM AUTHOR]

Numerical simulations have become an important tool for the estimation and mitigation of gravitational mass flows, such as avalanches, landslides, pyroclastic flows, and turbidity currents. Depth integration stands as a pivotal concept in rendering numerical models applicable to real-world scenarios, as it provides the required efficiency and a streamlined workflow for geographic information systems. In recent years, a large number of flow models were developed following the idea of depth integration, thereby enlarging the applicability and reliability of this family of process models substantially. It has been previously shown that the finite area method of OpenFOAM® can be utilized to express and solve the basic depth-integrated models representing incompressible dense flows. In this article, previous work is extended beyond the dense-flow regime to account for suspended particle flows, such as turbidity currents and powder snow avalanches. A novel coupling mechanism is introduced to enhance the simulation capabilities for mixed-snow avalanches. Further, we will give an updated description of the revised computational framework, its integration into OpenFOAM, and interfaces to geographic information systems. This work aims to provide practitioners and scientists with an open-source tool that facilitates transparency and reproducibility and that can be easily applied to real-world scenarios. The tool can be used as a baseline for further developments and in particular allows for modular integration of customized process models. [ABSTRACT FROM AUTHOR]

This is the second of a two-part New Zealand Journal of Geology and Geophysics Special Issue on understanding sedimentary systems in Aotearoa-New Zealand's Hikurangi Subduction Margin (HSM). This volume includes six research papers that explore sediment-tectonic interactions operating over a range of spatio-temporal scales. We take a distinctive perspective moving from the subduction deformation front in the Hikurangi Trough, upslope to the subduction wedge, and onshore to the Coastal Ranges. Temporally, papers span the onset of subduction in the Miocene, to disentangling provenance of turbidity currents triggered by the 2016 CE Kaikōura Earthquake. Collectively, the studies in the special issue reveal a complicated and continually evolving margin, where active tectonics and volcanism, coupled with vigorous climatic and oceanographic drivers, modulate erosion, transport, and depositional cycles of vast volumes of terrigenous sediment into ocean basins. Despite decades of significant research advances in our knowledge of the HSM, considerable scope remains for future work. A deeper understanding of fundamental tectonic-sediment interactions operating on active margins, along with the significant geohazards they pose remain outstanding research needs. Collectively, Volumes 1 and 2 highlight enduring interest in the HSM as a globally important natural laboratory for the study of subduction zone geoscience. [ABSTRACT FROM AUTHOR]

The 2016 Mw 7.8 Kaikōura Earthquake triggered simultaneous turbidity currents down ten submarine canyons along a 200 km stretch of the continental slope, east of New Zealand. Some discharged into the Hikurangi Channel which flows >1500 km northwards along the abyssal trench floor. To better understand provenance continuity in deep-sea sedimentary records, foraminiferal samples from the 2016 turbidites from 17 canyon and channel cores were used to investigate the source histories of these submarine gravity flows. Cluster analyses suggest the canyon provenances for most 2016 turbidite faunas should be determinable using a combination of the relative abundance of key benthic genera, planktic foraminiferal index (dissolution), absolute test abundance and planktic % of the foraminiferal faunas. Two ordinations (PCA, PCO) based on these parameters were used to infer provenance and flow history. One hundred kilometres down the Hikurangi Channel, faunas in the 2016 turbidite confirm a Kaikōura Canyon source. Further downstream, 200–500 km north of the confluence with Campbell, Cook and Opouawe canyons, faunas indicate that the 2016 turbidite in the northern Hikurangi Channel is a composite deposit, from an initial Opouawe-Cook canyon-sourced turbidity current over-ridden and partly mixed with, a Kaikōura Canyon-sourced flow that arrived sometime later. [ABSTRACT FROM AUTHOR]

Microplastics are widely distributed in deep oceans, with some of the highest concentrations reported in submarine canyons, which are thought to be closely related to turbidity currents. However, the turbidity current role in microplastic transport and deposition is poorly understood. Here, we present temporal variation in microplastic abundance and settling flux from sediment trap observations on the levee of Gaoping Canyon, offshore Taiwan, where turbidity currents occur frequently. The results showed that relatively high microplastic abundance and flux were consistent with the increases of near-bottom suspended sediment concentration caused by turbidity currents. The microplastics, dominated by polypropylene (59%) and polyethylene (21%), were probably derived from Taiwan coastal resuspension and river input and then transported into the submarine canyon by typhoon- or earthquake-triggered turbidity currents. During the turbidity currents, the average microplastic abundance and flux was 4137 particles per kilogram and 40.11 particles per square meter per day, respectively, showing an increase of 49% and 270%, respectively, compared to non–turbidity current periods. The total microplastic flux during the turbidity currents accounted for ∼76% of annual flux. Our study highlights turbidity currents to be the major hydrodynamic process in regulating microplastic transport and settling in a submarine canyon. [ABSTRACT FROM AUTHOR]

Submarine conduits are features responsible for transporting clastic debris from continents to the deep ocean. While the architecture of conduits has been extensively studied, the process of their inception remains unclear. This study highlights the possibility that some conduits are initiated by depositional processes involving turbidity currents. Here, we present the results of eight experiments where gravity currents were allowed to develop their own pathways. The simulation tank represented natural scales of continental shelves, slopes, and basins. The initial experiments involved sediment-laden flows with low density (1–10% in volume). In first experiment runs (Series I), sediment deposition occurred primarily on the shelf and slope, resulting in an asymmetric transverse profile. This asymmetry facilitated subsequent conservative currents (1034 to 1070 kg/m3 due to salt dissolution) flowing alongside during the second series, resulting in the formation of a constructive submarine conduit. This feature is analogous to gully formations observed in various locations. This study correlates these findings with gully-like features and proposes a model where non-confined density flows can evolve into confined flows through the construction of asymmetric topography. An evolutionary model is proposed to explain the mechanism, which potentially elucidates the formation of many submarine conduits. [ABSTRACT FROM AUTHOR]

Continental margins receive, process and sequester most of the terrestrial organic carbon (terrOC) released into the ocean. In the Arctic, increasing fluvial discharge and collapsing permafrost are expected to enhance terrOC release and degradation, leading to ocean acidification and translocated CO2 release to the atmosphere. However, the processes controlling terrOC transport beyond the continental shelf, and the amount of terrOC that reaches the slope and the rise are poorly described. Here we study terrOC transport to the Laptev Sea continental slope and rise by probing surface sediments with dual‐isotope (δ13C/Δ14C) source apportionment, degradation‐diagnostic terrestrial biomarkers (n‐alkanes, n‐alkanoic acids, lignin phenols) and 210Pbxs‐based mass accumulation rates (MAR). The MAR‐terrOC (g m−2 yr−1) decrease from 14.7 ± 12.2 on the shelf, to 7.0 ± 5.8 over the slope, to 2.3 ± 0.3 for the rise. Scaling this to the respective regimes yields that 80% of the terrOC accumulates on the shelf, while 11% and 9% of the accumulation occurs in slope and rise sediments, respectively. TerrOC remineralization is evidenced by biomarker degradation proxies (CPI of n‐alkanes and 3,5Bd/V) indicating 40% and 60% more terrOC degradation from slope to rise, consistent with a decline in terrOC concentrations by 57%. TerrOC degradation only partially explains this decline. An updated Laptev Sea terrOC budget suggests that sediment transport dynamics such as turbidity currents may drive terrOC shelf‐basin export, contributing to the observed accumulation pattern. This study quantitatively demonstrates that Arctic shelf seas are key receptor systems for remobilized terrOC, emphasizing their importance in the carbon cycle of the rapidly changing Arctic. Key Points: Terrestrial carbon export from the Laptev Sea shelf to the slope and rise is studied using δ13C/Δ14C, biomarkers and 210Pb mass accumulationThe accumulation of terrestrial carbon declines by 52% at the shelf edge and by 68% from slope to rise due to transport and degradation dynamicsA terrestrial carbon budget for the Laptev Sea suggests 80%–90% of the input is retained on the shelf via accumulation and re‐mineralization [ABSTRACT FROM AUTHOR]

Sediment gravity flows are ubiquitous agents of transport, erosion, and deposition across Earth's surface, including terrestrial debris flows, snow avalanches, and submarine turbidity currents. Sediment gravity flows typically erode material along their path (bulking), which can dramatically increase their size, speed, and run-out distance. Hence, flow bulking is a first-order control on flow evolution and underpins predictive modeling approaches and geohazard assessments. Quantifying bulking in submarine systems is problematic because of their large-scale and inaccessible nature, complex stratigraphy, and poorly understood source areas. Here, we map the deposits and erosive destruction of a giant submarine gravity flow from source to sink. The small initial failure (~1.5 cubic kilometers) entrained over 100 times its starting volume, catastrophically evolving into a giant flow with a total volume of ~162 cubic kilometers and a run-out distance of ~2000 kilometers. Entrainment of mud was the critical fuel, which promoted run-away flow growth and extreme levels of erosion. [ABSTRACT FROM AUTHOR]

ABSTRACT Turbidity current behaviour is affected by interactions with seafloor topography. Changes in flow dynamics will depend on the orientation and gradient of the topography, and the magnitude and rheology of the incoming flow. A better understanding of how unconfined turbidity currents interact with topography will improve interpretations of the stratigraphic record, and is addressed herein using three‐dimensional flume tank experiments with unconfined saline density currents that enter a horizontal basin before interacting with a ramp orientated perpendicular to flow direction. The incoming flow parameters remained constant, whilst the slope angle was independently varied. On a 20° slope, superelevation of the flow and flow stripping of the upper, dilute region of the flow occurred high on the slope surface. This resulted in a strongly divergent flow and the generation of complex multidirectional flows (i.e. combined flows). The superelevation and extent of flow stripping decreased as the slope angle increased. At 30° and 40°, flow reflection and deflection, respectively, are the dominant flow process at the base of slope, with the reflected or deflected flow interacting with the parental flow, and generating combined flows. Thus, complicated patterns of flow direction and behaviour are documented even on encountering simple, planar topographies orientated perpendicular to flow direction. Combined flows in deep‐water settings have been linked to the interaction of turbidity currents with topography and the formation of internal waves with a dominant oscillatory flow component. Here, combined flow occurs in the absence of an oscillatory component. A new process model for the formation and distribution of hummock‐like bedforms in deep‐marine systems is introduced. This bedform model is coupled to a new understanding of the mechanics of onlap styles (draping versus abrupt pinchout) to produce a spatial model of gravity‐current interaction, and deposition, on slopes to support palaeogeographical reconstructions. [ABSTRACT FROM AUTHOR]

Turbidity current deposition belongs to event deposition, which is of great significance to the study of neotectonic movement. However, turbidite deposits are rarely found in deep-sea basins. In this work, the particle size, mineralogy, and geochemistry of 14 deep-sea sediment cores from the Southwest Sub-basin (SWSB) of South China Sea (SCS) and its periphery are used to trace the sources of sediment and reveal the sedimentological and geochemical characteristics of deep-sea sediments. The results show that quartz and feldspar are the main minerals in the core sediments from the SWSB, and there are multiple layers of turbidites. Geochemical analysis reveals that the composition of the core sediments is close to that of the western margin of the SCS and is similar to that of the upper continental crust (UCC) and is inherited from terrigenous sediments. The Sr--Nd isotope results indicate that the sediment provenances of the SWSB are from the Mekong River, Sunda Shelf and Red River, showing the characteristics of multiple sources. Therefore, we propose that terrigenous materials from multiple sources can reach the deep-sea basin of the SWSB, and we also establish a transport model of deep-sea terrigenous sediment. Terrigenous materials were first carried by rivers and surface currents to the continental margins near the SWSB, and fine materials were subsequently transported by surface currents to the deep-sea basin, while coarse materials were subsequently transported by turbidity currents. Turbidity current deposits provide an approach for studying the transport of coarse materials in deep-sea basins of SWSB. [ABSTRACT FROM AUTHOR]

During the formation and evolution of the South China Sea, a series of multiscale submarine geomorphologies have been produced in the continental margin. The obvious submarine canyons and channels are widely distributed in the continental shelf and slope of the South China Sea. In the Taixinan Basin, several submarine canyons and channels termed as the Taixinan canyon‐channel system (TCCS) are distributed between the active and passive continental margins. Based on acquired ship‐borne multi‐beam bathymetry data in this study and the global GEBCO 2023 bathymetric dataset, we identify and define nine submarine canyons and seven submarine channels in the Taixinan Basin. The TCCS consists of the Dongsha, Taiwan, Jiulong, West Penghu, Penghu, Kaoping, Shoushan, Kaohsiung and the Fangliao canyons and submarine channels. The detailed geomorphological features of different submarine canyons and channels within the TCCS are analysed and summarized using multi‐beam bathymetry data and seismic reflection profiles across canyons. Based on the slope variations of the continental margin and the effects of turbidity currents and bottom currents on canyon, we propose a three‐stage evolutionary model of the TCCS. In the initial formation stage of canyon, the initial erosional grooves were created by tectonic activity on the continental slope and it represents the foundation of submarine canyons. During the growth and development stage, the submarine canyons are further evolved and the canyons began to deepen and widen from the continental slope to the deep‐water areas. It shows the weak erosion and sediment infilling within the canyons in this stage. On the northern continental slope of the South China Sea, continuous transportation and erosion of sediments led to the initial formation of grooves and it becomes the embryonic stage of submarine channels. The present stage of the TCCS was formed when the initial grooves on the continental slope have further developed and rebuilt under the erosion by the turbidity current and the scouring by the bottom current. In the last stage, the intense erosion by the turbidity current is supported by sediment waves around the submarine canyons and the migration of canyons is suggested by the cyclic steps formed within some canyons. [ABSTRACT FROM AUTHOR]

This study explores the hypothetical elimination of Japan's retirement earnings test (ET) for public pensions, focusing on its implications for older workers' labor supply and pension-claiming behaviors. The ET currently reduces public pension benefits for individuals aged 65 and older if their earnings exceed specified thresholds, potentially discouraging employment in this demographic. Notably, the Japanese ET influences both immediate and future pension benefits, thus diminishing current payouts for working pensioners and foregoing beneficial actuarial adjustments—adjustments based on actuarial calculations that would otherwise increase future benefits to account for delayed pension claims. This dual impact may discourage the labor supply and influence pension-claiming behavior among older workers. Through a survey-based experiment with male workers aged 40–59 years expected to face the ET upon retirement, we assess three reform scenarios as the first study in the literature: (1) eliminating future benefit reductions through actuarial adjustments, thereby enhancing the value of deferred pension claims; (2) removing immediate benefit suspensions to increase current pension payments directly; and (3) a comprehensive reform combining both approaches. Our findings reveal that eliminating reductions through actuarial adjustments increases the intensive margin (labor hours and income) and encourages delayed pension claims. Conversely, removing immediate benefit suspensions influences both the extensive margin (decision to work) and the intensive margin but leads to earlier pension claims. By highlighting the importance of differentiating between immediate and future benefit components in designing ET reforms, this study demonstrates their significant impact on labor supply and pension-claiming decisions. [ABSTRACT FROM AUTHOR]

Mixed turbidite–contourite depositional systems result from interactions between down‐slope turbidity currents and along‐slope bottom currents, comprising excellent records of past oceanographic currents. Modern and ancient systems have been widely documented along the continental margins of the Atlantic Ocean. Yet, few examples have so far been identified on the North‐west African continental margin, limiting understanding of the sedimentary and palaeoceanographic evolution in this area. This work uses two‐dimensional seismic reflection profiles to report, for the first time, the presence of three giant sediment mounds beneath the headwall region of the Sahara Slide Complex. The sediment mounds are elongated and separated by two broad canyons, showing a north‐west/south‐east orientation that is roughly perpendicular to the continental margin. These mounds are 24 to 37 km long and 12 to 17 km wide, reaching a maximum height of ca 1000 m. Numerous slide scarps are observed within and along the flanks of the mounds, hinting at the occurrence of submarine landslides during their development. Based on their geometries, external shapes, internal seismic architecture and stratigraphic stacking patterns, it is proposed that these sediment mounds comprise down‐slope elongated mounded drifts formed in a mixed turbidite–contourite system during four evolutionary stages: onset, growth, maintenance and burial. The significance of this work is that it demonstrates the gradual transition from a turbidite system to a full mixed turbidite–contourite system to be associated, in the study area, with the establishment of strong ocean currents along north‐west Africa. [ABSTRACT FROM AUTHOR]

The article focuses on the significant transport of terrestrial organic carbon by canyon-flushing turbidity currents in the Submarine Congo Canyon-Channel system, using detailed field data and geochemical analyses to quantify sediment and organic carbon movement. It describes the deployment of acoustic-Doppler current profilers (ADCPs) and Ocean-Bottom Seismographs (OBSs) to monitor turbidity currents and assess sediment erosion and deposition.

Dams are one of the most critical hydraulic structures worldwide. Sediment, entering the reservoirs of the dams with the water flow due to human interference in the dam catchment area, gradually destroys the functional storage through a deposition. Sedimentation threatens the sustainability of all reservoirs in the absence of adequate prevention and mitigation measures. Deposition of sediments in reservoirs can also affect the safe and proper operation of water intakes and bottom outlets belonging to the vital outlet structures. Turbidity currents are among the main impacts on dam reservoir sedimentation. One technique to decrease the impact of more sedimentation is to use bottom outlet gates that preserve the reservoir's useable volume. This procedure may affect the quality of water exiting the dam. The present study experimentally investigated the venting of turbidity current of lock exchange with varying concentrations on the rigid bed, while there were two outlet gates with various levels and diameters at the same time. According to the available information, in the case of , the average value of the concentrated input current was equal to the output concentration, which is the best level for the outlet gate installation based on the primary experimental conditios. The discharge efficiency is also higher when the inlet concentration is lower. [ABSTRACT FROM AUTHOR]

Bedforms associated with turbidite systems are commonly observed on seafloor. Previous studies have analysed bedform morphological and sedimentary features to determine their formation mechanisms and flow dynamics. However, the seafloor topography and ocean circulation have comprehensively influenced both down‐ and along‐slope turbidity flow processes, complicating the spatial distribution of the related bedforms. Three‐dimensional seismic data (3D) were used to depict the morphological and sedimentary features of the bedforms around the canyon mouth on the slope of the Rovuma Basin (offshore Mozambique), to reveal the spatial distribution and related flow processes of the bedforms. The results show that the spatial morphological and sedimentary features of the submarine bedforms at canyon mouths are controlled by the combined action of down‐ and along‐slope factors. The along‐slope bottom currents influence the deposition distribution of the turbidity current at the canyon mouth. However, slope breaks control bedform morphological and sedimentary features during downslope turbidity currents. Coarse‐grained material of turbidity current flows along the axial zone of the canyon mouth, forming a linear series of crescent‐shaped net‐erosional cyclic steps characterized by short steep stoss sides and long gentle lee sides. The fine‐grained material of the turbidity currents is deflected towards the northern flank of the axial zone by the bottom currents and deposited as undulating net‐depositional cyclic steps at upper reach of the northern flank, showing long gentle stoss sides and short steep sides. Slope breaks enhance the erosion on cyclic steps by altering the velocity of turbidity current, forming net‐erosional cyclic steps with the manifestation of both short and steep stoss and lee sides at lower reaches of northern flank. The turbidity current in the axial zone formed lateral flow diversions caused by the obstruction of the cyclic steps. The flow diversions converge with the downslope flowing unconfined turbidity current at the northern flank and constitute a confluence characterized by continuous variation of flow properties, forming the cyclic steps featuring irregular morphology. [ABSTRACT FROM AUTHOR]

Sand transport and its deposition in deep marine basins are controlled by diverse climatic, tectonic, physiographic and oceanographic processes. Disentangling the impact of each of these drivers on the sedimentary record is a fundamental challenge in the study of source to sink systems. In this study, we investigate seismic and borehole data by combining statistical and spectral analyses to identify the factors controlling sand deposition in the deep Levant Basin (Eastern Mediterranean) during the Pliocene–Quaternary (PQ). We interpret the sand content in boreholes from gamma ray (GR) logs and identify two major trends in sand/shale ratios. On a million‐year scale, we demonstrate that since the Early Pliocene (5.3 Ma), sand content gradually increased until it formed a ca. 100 m thick and widespread sheet of sand at the top of the section. On a shorter time scale, we identify oscillations in sand content depicting significant power of periodic components at the 350–450 ky, 90–150 ky and 10s ky bands. The long‐term increase in sand content reaching the deep Levant Basin is interpreted as a result of the Nile Delta propagation, which had continuously shortened the distance between the edge of the Nile delta that is the source of sand, and the deep Levant Basin. The superimposed short‐term oscillations are interpreted as Milanković cycles, reflecting hydroclimatic oscillations of water and sediment discharge into the Eastern Mediterranean Sea by the Nile River. This demonstrates the hydroclimatic control on sand deposition in the deep Levant Basin. Our observations are consistent with the development of a submarine channel system along with the accretion of the Nile delta, which may have served as a pathway for sand delivery via high‐energy turbidity currents that reached the Levant Basin. [ABSTRACT FROM AUTHOR]

The shelf‐slope margin is a geomorphic zone with a change in gradient between subaqueous shelves and slopes, which extends towards the submarine basin‐floor. It is important because it partitions distinct sedimentary and biogenic processes between the shallow and deep‐water realms. The initiation of a shelf‐slope profile from pre‐existing conditions, and the evolution of shelf margins in space and time has been the focus of numerous studies, particularly from seismic data sets on passive margins, although markedly less‐so from active tectonic settings. This study documents the initiation and evolution of a shelf‐slope margin in the well‐studied Eocene Aínsa Basin (Spanish Pyrenees) through the segmentation of a mixed carbonate‐siliciclastic ramp via contractional tectonics and differential subsidence. The basinward propagation of a series of thrusts through the ramp allowed the maintenance of shallow‐water, predominantly carbonate sedimentation on their uplifted hanging wall anticlines. Conversely, the deepened foot wall synclines became muddy slope environments, and their axes became the main loci of siliciclastic turbidity current bypass and deposition. The deflection of turbidity currents around uplifted areas towards the synclinal lows allowed for the continuation of carbonate production at the bathymetric highs, which kept pace with subsidence. The interface between shallow‐ and deep‐water sedimentation (i.e. the shelf‐slope margin) was an erosional and composite submarine scarp surface generated by several phases of large‐scale mass wasting of the aggrading shelf carbonates, and healing by onlap of slope turbidites against the scarp. Continued thrust propagation and basin deepening led to the progressive headward degradation of the surfaces, resulting in an apparent retrogradation of the shelf‐slope margin and onlapping slope deposits. This model for the tectonically controlled conversion of a submarine ramp into a shelf‐slope profile contrasts with conventional models that consider shelf‐slope margins to be inherently progradational after initiation. This study also challenges the notion that large‐scale degradational surfaces and thick successions of submarine landslides are inherently diagnostic of canyons and their fill. [ABSTRACT FROM AUTHOR]

A novel three-unit 8/4 wide-rotor bearingless switched reluctance motor has been designed to address the challenges of strong coupling and control difficulties between torque and suspension force in traditional bearingless switched reluctance motors. This motor features independent torque flux paths and suspension flux paths, allowing for separate control of torque and suspension force similar to traditional switched reluctance motors and active magnetic bearings. To tackle issues such as torque ripple, suspension force ripple, and reduced system robustness caused by external disturbances during operation, a torque sharing function and a suspension current PWM control strategy based on active disturbance rejection technology have been proposed. Firstly, mathematical models for the torque and suspension force of the three-unit 8/4 wide-rotor bearingless switched reluctance motor were established using Ansys simulation data and the Maxwell stress method. Subsequently, a torque sharing function and a suspension current PWM control system were developed based on these mathematical models. The endpoint of the commutation overlap zone was set at the maximum value of the phase inductance to eliminate the weak coupling effect of torque current on suspension force. Finally, active disturbance rejection control technology was introduced to compare its performance with that of traditional PID controllers in suppressing interference. Simulation results demonstrate that the proposed method ensures decoupling switching between each phase's motor torque and its associated suspension while enhancing anti-interference performance. [ABSTRACT FROM AUTHOR]

Submarine canyons and channels are globally important pathways for sediment, organic carbon, nutrients and pollutants to the deep sea, and they form the largest sediment accumulations on Earth. However, studying these remote submarine systems comprehensively remains a challenge. In this study, we used the only complete-coverage and repeated bathymetric surveys yet for a very large submarine system, which is the Congo Fan off West Africa. Our aim is to understand channel-modifying features such as subaqueous landslides, meander-bend evolution, knickpoints and avulsions by analyzing their morphometric characteristics. We used a new approach to identify these channel-modifying features via morphometric fingerprints, which allows a systematic and efficient search in low-resolution bathymetry data. These observations have led us to identify three morphodynamic reaches within the Congo Canyon-Channel. The upper reach of the system is characterized by landslides that can locally block the channel, storing material for extended periods and re-excavating material through a new incised channel. The middle reach of the system is dominated by the sweep and swing of meander bends, although their importance depends on the channel's age, and the time since the last up-channel avulsion. In the distal and youngest part of the system, an upstream migrating knickpoint is present, which causes multi-stage sediment transport and overspill through an underdeveloped channel with shallow depths. These findings complement previous less- detailed morphometric analyses of the Congo Canyon-Channel, offering a clearer understanding of how submarine canyon-channels can store sediment (due to channel-damming landslides, meander point bars, levee building due to overspill), re-excavate that sediment (via thalweg incision, meander propagation, knickpoint migration) and finally transport it to the deep sea. This improved understanding of the morphodynamics of the Congo Canyon- Channel may help to understand the evolution of other submarine canyon- channels, and assessment of hazards faced by seabed infrastructure such as telecommunication cables. [ABSTRACT FROM AUTHOR]

Fine‐grained authigenic magnetite has been recognized increasingly in iron‐rich marine environments affected by methane seepage and is a major sedimentary magnetization source. However, it is unknown whether this magnetite forms via microbial or abiotic processes. We report here abundant fine magnetite crystals, in close association with goethite, within coarse‐grained sediments from two adjacent methane seepage sites in the South China Sea. The magnetite‐ and goethite‐rich horizons have sharply increased Zr/Ti, Zr/Rb, Ti/Al, and Fe/Al ratios, probably reflecting deposition by turbidity currents. Deeper intervals have elevated pyrite content, positive δ34S excursions of chromium reducible sulfur, and low magnetic susceptibilities, which is consistent with past sulfate‐driven anaerobic oxidation of methane in environments with dynamically variable seepage intensity. In magnetically extracted aggregates (>63 μm), magnetite particles are mainly clustered euhedral crystals with 0.2–0.8 μm sizes, which will likely impact sedimentary magnetic signals. The fine, euhedral crystalline nature of the magnetite suggests formation in sulfide‐free, ferrous iron‐rich sedimentary environments. Based on 16S rRNA gene sequences, anaerobic methanotrophic archaea coincide with pyrite rich horizons. In contrast, two co‐occurring methanogenic archaea groups of the Methanomicrobia class (mainly Methanosarcina and Methanocella) are particularly abundant in turbidites but have low abundance in all other horizons. Increased Methanomicrobia abundances suggest that this class of archaea may be involved in microbial iron reduction in turbidites with abundant goethite as a reactive iron source, and that they apparently trigger magnetite formation. Our findings provide new clues to microbial magnetite formation in iron‐rich marine sediments. Plain Language Summary: Magnetite is a key source of sedimentary magnetic signals. Understanding the origin of magnetite in sediments is critical for proper interpretation of paleomagnetic records. Fine‐grained authigenic magnetite has been recognized increasingly in iron‐rich continental margin environments with high methane flux and represents a further important magnetization source in marine sediments. However, it is unknown whether this magnetite forms via microbial or abiotic processes. Here, we identify abundant fine magnetite crystals within iron‐rich subseafloor horizons from two adjacent methane seepage sites in the South China Sea. From magnetic, mineralogical, geochemical, and genomic analyses, we provide new constraints for understanding magnetite formation in iron‐rich sediments, where methanogenic archaea apparently perform microbial iron reduction and trigger magnetite formation. Key Points: We identify abundant fine magnetite crystals within subseafloor iron‐rich layers from methane seepage impacted sitesMethanogenic archaea coincide with magnetite‐rich horizons and are considered potential drivers of microbial iron reduction and magnetite formationOur findings have profound implications for the nature of paleomagnetic signals recorded in iron‐rich sediments, and for iron cycling in marine sediments [ABSTRACT FROM AUTHOR]

The evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides, can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub‐bottom profiles, high‐resolution sediment core analyses (X‐ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine‐grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro‐scale and micro‐scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross‐laminations and fining‐upward successions, which are attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross‐cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re‐establishment of benthos and associated biogenic structures, supporting the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record. [ABSTRACT FROM AUTHOR]

Volcanic flank collapses, especially those in island settings, have generated some of the most voluminous mass transport deposits on Earth and can trigger devastating tsunamis. Reliable tsunami hazard assessments for flank collapse‐driven tsunamis require an understanding of the complex emplacement processes involved. The seafloor sequence southeast of Montserrat (Lesser Antilles) is a key site for the study of volcanic flank collapse emplacement processes that span subaerial to submarine environments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from one of the most extensive mass transport deposits offshore Montserrat, which exemplifies multi‐phase landslide deposition from volcanic islands. The deposits reveal emplacement in multiple stages including two blocky volcanic debris avalanches, secondary seafloor failure and a late‐stage erosive density current that carved channel‐like incisions into the hummocky surface of the deposit about 15 km from the source region. The highly erosive density current potentially originated from downslope‐acceleration of fine‐grained material that was suspended in the water column earlier during the slide. Late‐stage erosive turbidity currents may be a more common process following volcanic sector collapse than has been previously recognized, exerting a potentially important control on the observed deposit morphology as well as on the runout and the overall shape of the deposit. Plain Language Summary: Disintegration of volcanic islands can cause very large landslides and destructive tsunamis. To assess the tsunami hazard of such events, it is crucial to understand the processes that are involved in their formation. We present new insights from seismic data and drill cores from a landslide deposit offshore Montserrat, a volcanic island in the Lesser Antilles Arc in the Caribbean. Our analysis reveals the emplacement of landslide material in several stages, including multiple volcanic flank collapses, incorporation of seafloor sediments and an erosive flow that carved channels into the top of the deposit right after its emplacement. We suggest that highly erosive flows are a common process during volcanic flank collapse deposition and that they play a significant role in the shaping of the deposit's appearance. Key Points: Landslide emplacement offshore Montserrat included volcanic flank collapses, sediment incorporation, and a late‐stage erosive flowHighly erosive flows are likely to be common processes during volcanic flank collapse depositionPre‐existing topography plays a major role in shaping flank collapse‐associated mass transport deposits [ABSTRACT FROM AUTHOR]

Regular release of sediment from reservoir has been increasingly adopted as a strategy for sustainable management. Here, we use a process‐based morphodynamic model to simulate the estuarine sediment dynamics impacted by turbidity current venting implemented by the Shihmen Reservoir during three typhoon events in 2008. Upon validation with the post‐event bathymetries, the model hindcasts reveal that mud releasing can be effective in mitigating reservoir siltation, yet may be a suboptimal strategy for alleviating coastal sediment deficit. A vast majority of the released muds were delivered through the estuary and exported to offshore by flood advection, wave dispersion, and tidal flushing. The flood‐driven sands, sourced mainly from downstream tributaries, were instead the major contributor to coastal sediment budget. However, mud mantling (covering and immobilizing sand deposits by the reservoir‐released muds) reduced sand availability and thus sand delivery to the coast. For the present case, 25% of the released muds were deposited along the way, presence of these mud covers reduced sand delivery by 15%, compared to a hypothetical scenario of clear‐water flood releases. The relative sand transport deficit is found to increase linearly with the degree of bed mud saturation, 1–D/R, with D/R the ratio of single‐event mud deposit to release. Given broad relevance to global reservoirs encountering the problems of siltation and coastal sediment deficit, our findings highlight that sustainable management needs to look beyond just a bulk amount of sediment, but it is critical to consider how different sediment fractions are interacting and impacted by human activities. Key Points: Increasingly adopted mud release strategy is effective to mitigate reservoir siltation yet suboptimal to alleviate coastal sediment deficitFlood‐driven tributary‐sourced sands dominate supply to coastal sediment budget yet sand delivery is reduced by mantling of released mudsSand delivery deficit (relative to sand delivery of clear‐water flood release scenario) increases linearly with degree of bed mud saturation [ABSTRACT FROM AUTHOR]

Taking the Midpoint Injection type Bearingless Permanent Magnet Synchronous Motor (MPI-BL-PMSM) as an object, to solve its problems of large torque pulsation and insufficient suspension force when adopting Midpoint Suspension Current Unilateral Injection (MPSC-UI), a Midpoint Suspension Current Bilateral Injection (MPSC-BI) solution is proposed. Based on the half-winding structure of MPI-BL-PMSM, and from the electromechanical energy conversion principle, the torque model for MPSC-BI solution is established. On this basis, the torque model for MPSC-UI method was derived. The correctness of the established torque mathematical models based on half-winding structure was verified through the finite element method (FEM), and the "dual-frequency" electromagnetic coupling characteristics of suspension current on electromagnetic torque were compared and analyzed from the perspectives of theoretical model and FEM simulation. The results indicate that the MPSC-BI method can effectively suppress or avoid the torque pulsation coupled by suspension current and can obtain about 1-time increase of controllable suspension force; the advantages of MPSC-BI solution in dynamic torque decoupling characteristics are demonstrated, while the only downside is that the coupling effect of torque current on radial suspension force is slightly greater than that of the MPSC-UI method. [ABSTRACT FROM AUTHOR]

Traditional mapping of bedforms in submarine canyons relied on vessel‐mounted and towed sensors, but their fine‐scale geomorphology and shallow structure requires higher resolution datasets. This study utilizes a high‐resolution dataset obtained from an autonomous underwater vehicle, combined with seismic reflection profiles and sediment cores, to analyse bedform sets within a 25.6 km long submarine canyon (canyon C14) in the northern South China Sea. A train of crescent‐shaped axial steps, indicative of cyclic steps formed by supercritical turbidity currents, is imaged along the canyon. Axial steps in the upper course show erosional truncations and sub‐horizontal reflectors on the lee and stoss sides, respectively, pointing to erosional–depositional cyclic steps formed by confined flows with high erosional capacity. This is facilitated by canyon narrowness and steeper axial gradient. After a transition segment, the lower course widens, with a gentler axial gradient, resulting in increased asymmetry and wavelength of axial steps. Backset bed deposits on the stoss sides of these steps indicate depositional cyclic steps with higher aggradation. Sediment filling, almost padding each cyclic step associated scour suggests the reworking of previously formed bedforms by gravity flows fed by destabilization processes on the canyon sidewalls and upstream lee faces and, possibly, by shelf‐edge and uppermost slope spillover into the canyon. At the lowermost course, cyclic steps transition to a furrow field, likely associated with flow velocity reduction facilitated by canyon floor widening and a further decrease in slope gradient. Flow braiding and re‐convergence, related to the erosion of fine‐grained deposits within the canyon floor, should have played a role to produce furrows under supercritical conditions. This work enhances our understanding of the detailed morphology and shallow relief configuration of bedforms in deep‐water submarine canyons, providing insights into their causative processes and evolution. [ABSTRACT FROM AUTHOR]

The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial carbon to the deep-sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the Congo Submarine Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ~7 % of the total organic carbon from the world's rivers. However, carbon and sediment transport mechanisms that operate in the Congo Canyon, and submarine canyons more globally, are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the Congo Submarine Canyon to the deep-sea. We show that particulate organic carbon transport in the canyon-axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 m/s) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 m/s) turbidity currents occur for 35 % of the time during monitoring periods and transport both muddy and sandy particulate organic carbon at an estimated transit flux that is more than ten times the flux induced by tides. Remarkably, organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River, and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents, together with background tidal currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo Submarine Fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally. [ABSTRACT FROM AUTHOR]

The pathway of dense river inflows into lakes, which affects the lake water quality, is not accurately predicted by existing models. The pathway of a dense riverine inflow in a lake with a submerged canyon is analyzed based on measurements during a 4‐month period of weakening lake stratification and weakening density excess between river and epilimnion. In line with models, the dense riverine inflow plunges upon entering the lake, continues as an underflow on the sloping lake bottom, and finally intrudes at its level of neutral buoyancy. Underflow and interflow velocities are O(0.1 m s−1). The river inflow is finally trapped in the pycnocline most of the time, even when the river's density excess and the lake's stratification are marginal. This trapping in the pycnocline is explained by the reduction of the inflow density excess due to the intense plunging mixing, which is an order of magnitude larger than that obtained in confined laboratory flumes. The pathway of the dense riverine inflow is affected by interactions of the underflow with the lake bottom and sedimentary processes. A canyon carved by the underflows confines and accelerates the underflow, which enhances its capacity to entrain and carry sediment. The entrainment of sediment that was previously deposited on the canyon bottom accelerates the underflow. Due to both effects, the underflow can temporarily break through the pycnocline and reach the hypolimnion. Existing models explain these observations qualitatively, but a quantitative prediction would require better parameterizations of the plunging mixing and the sedimentary processes. Plain Language Summary: The pathway of river inflows into lakes is not accurately predicted by existing models. We investigate the physical processes affecting the pathway of dense riverine inflow (i.e., inflow with a density higher than lake water) into a stratified lake. We investigate the conditions under which a dense riverine inflow get trapped in the pycnocline (the layer that separates warmer surface waters from cold deep waters) or break through it. Unprecedented long records of the temporal evolution of the pathway of the riverine flow into the lake during a period of weakening riverine density excess and lake stratification are conceptualized in a model, which extends existing concepts for dense riverine inflows. The entrainment of lake waters into the riverine inflow in the plunging region is larger than predicted by laboratory studies. This explains why the riverine inflow is trapped in the pycnocline most of the time. Flow confinement by a canyon carved by the riverine inflow into the lake bottom accelerates the riverine inflow and enhance sediment entrainment capacity causing short‐lived self‐accelerating turbidity currents along the lake bottom that break through the pycnocline and reach deep waters. Our results allow improved estimates of oxygen replenishment or sediment deposition from riverine water. Key Points: Plunging mixing into an unconfined ambient is an order of magnitude larger than in a confined ambientPronounced plunging mixing reduces the initial density excess explaining why the inflow is mostly trapped in the pycnoclineResuspension of lake bottom sediment can cause short‐lived self‐accelerating turbidity currents that break through the pycnocline [ABSTRACT FROM AUTHOR]

The evolution of turbidity currents covers multiple physical processes, such as fluid entrainment, self-acceleration, and sediment deposition, which are associated with sediment particle behaviors and yet not well understood. This study uses a fully coupled computational fluid dynamics and discrete element method model to investigate the particle-scale dynamics of turbidity currents and their responses to different bedforms. Results show that the turbidity currents controlled by viscous drag exhibit distinct flow features, including changes in morphology, velocity evolution, and other fluid/particle kinematic indicators, depending on their initial particle volume concentration. An increase in initial particle volume concentration enhances the fluid/particle motions accompanied by generating interfacial Kelvin–Helmholtz waves. The fluid/particle indicators, with the exception of the energy loss for particle–bed collisions, have strong relevance with particle concentrations, which can be described by linear or power-law functions. Furthermore, specific bedforms play unique roles in the propagation process and deposition pattern of turbidity currents. Slope beds enhance the motion, suspension, and collision of sediment particles, and cause wave-shaped sediment deposits along the slope particularly in the high-concentration case. By comparison, weakening of particle migration on obstructed and wavy beds is accentuated by blocking effects, mainly resulting from the convex bed morphology. However, the continuously convex and concave features diminish the blocking effect of wavy beds by intensifying particle motions along the lee sides of wave-shaped bumps. The particle-scale dynamics of turbidity currents is linked to the relative sizes of the underlying bedforms, which should be noted and further studied in our future work. [ABSTRACT FROM AUTHOR]

To reduce the coupling resulting from structural asymmetry and enhance the load-bearing capacity per unit area, a six-pole axial-radial active magnetic bearing (AR-AMB) has been suggested. To refine the precision of the mathematical model derived from the conventional equivalent magnetic circuit model, a modeling technique that employs flux density and magnetic field segmentation has been proposed. Firstly, the structure and operational principle of the six-pole AR-AMB are introduced. Subsequently, an improved model based on the flux density is established by considering the internal relationship between the iron core and air gap magnetic field in a magnetic bearing with pole shoes. The model addresses issues related to the accurate calculation of fringing magnetic flux and magnetic saturation of core materials while accounting for eddy current effects on suspension force. Finally, the accuracy of the theoretical analysis results has been validated through finite element simulation and experiment, and demonstrated that the rotor based on this model exhibits robust anti-interference capabilities. [ABSTRACT FROM AUTHOR]

Mass‐transport deposits are products of resedimentation phenomena involving a broad spectrum of gravity‐driven processes, and commonly have a high preservation potential in deep‐marine environments. This study documents various types of mass‐transport deposits that are interbedded with intensely bioturbated shallow‐marine calciclastic sediments deposited along a reflective coast during the middle and late Eocene. The sedimentary succession, located in the vicinity of Novigrad in northern Dalmatia, Croatia, comprises sediments deposited in a range of nearshore and carbonate ramp environments, and represents the infill of a thrust‐top (piggyback) basin of the North Dalmatian foreland basin. Five types of mass‐transport deposits, ranging in thickness from 13 cm to 6 m, have been identified: (i) calcilutite and calcarenite slumps; (ii) conglomeratic slump‐debrites with a 'dough‐like' appearance; (iii) blocky‐flow deposits bearing large blocks of beachface and/or shoreface deposits; (iv) rockfall deposits comprising scattered blocks of beachface conglomerates and shoreface calcarenites; and (v) 'classical' matrix‐supported debrites. Calciturbidites are rare and mainly comprise Ta and Tb divisions. Conglomeratic slump‐debrites are mostly found in association with offshore‐transition deposits, suggesting that mass flows were triggered above the storm‐wave base likely due to a combined effect of: (i) strong earthquakes related to the tectonic development of the basin; (ii) sediment destabilization due to pore‐water overpressure during forced regressions; and (iii) storm‐wave loading affecting the shallow seabed. Progressive deepening likely favoured mass‐flow transformations, although the overall paucity of turbidites suggests relatively short mass‐flow transport distance and turbidity current bypass to deeper realms. Multiple erosion phases and resedimentation processes from the Cretaceous to the late Eocene contributed to the diverse suite of extraformational clasts in the mass‐transport deposits studied. The mass‐transport deposits may be triggered and emplaced in shallow‐marine settings mainly during regressive stages of basin development, as the diverse gravel clast composition suggests significant tectonic influence. Although the mass‐transport deposits reported herein are relatively small, some of their peculiar sedimentary features and occurrence within shallow‐marine calciclastic deposits render them rather unique and suitable for a re‐assessment of the nature and evolutionary continuum of processes involved in subaqueous sediment mass transport, as well as the preservation potential of sedimentary features in high‐energy wave‐reworked environments. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines. [ABSTRACT FROM AUTHOR]

Across varied environments, meandering channels evolve through a common morphodynamic feedback: the sinuous channel shape causes spatial variations in boundary shear stress, which cause lateral migration rates to vary along a meander bend and change the shape of the channel. This feedback is embedded in all conceptual models of meandering channel migration, and in numerical models, it occurs over an explicit timescale (i.e., the model time step). However, the sensitivity of modeled channel trajectory to the time step is unknown. In numerical experiments using a curvature‐driven model of channel migration, we find that channel trajectories are consistent over time if the channel migrates ≤10% of the channel width over the feedback timescale. In contrast, channel trajectories diverge if the time step causes migration to exceed this threshold, due to the instability in the co‐evolution of channel curvature and migration rate. The divergence of channel trajectories accumulates with the total run time. Application to hindcasting of channel migration for 10 natural rivers from the continental US and the Amazon River basin shows that the sensitivity of modeled channel trajectories to the time step is greatest at low (near‐unity) channel sinuosity. A time step exceeding the criterion causes over‐prediction of the width of the channel belt developed over millennial timescales. These findings establish a geometric constraint for predicting channel migration in landscape evolution models for lowland alluvial rivers, upland channels coupled to hillslopes and submarine channels shaped by turbidity currents, over timescales from years to millennia. Plain Language Summary: The shapes of meandering rivers can cause patterns of flow and sediment movement that lead the channel banks to shift laterally, which in turn change the shape of the river. This feedback loop alters the landscape over time and creates erosion hazards to engineered structures and riverside habitats. In computer models that forecast this lateral migration process, time often advances in fixed, discrete steps, but the effect of this time step on the predicted channel migration is uncertain. We use a set of computer simulations with a common model of channel migration and find that the predicted channel trajectories are consistent if the channel migrates less than 10% of its width in one time step. The time step matters most for channels that are nearly straight. These findings establish a geometric restriction on the allowable time step for predicting channel migration in varied landscapes: for lowland rivers that migrate rapidly, the time step should be less than a few years; for mountain rivers that migrate slowly, the time step may be relaxed to thousands of years. These findings suggest an upper bound for the natural processes by which the mapview shape and lateral migration of the channel interact. Key Points: Meandering channels often show a planform‐migration feedback: planform geometry drives lateral migration, which alters planform geometryIn model runs with a fixed initial condition, channel trajectories diverge if the channel migrates >10% of its width in the feedback timescaleApplication to 10 natural rivers shows that predicted trajectories are most sensitive to the feedback timescale at channel sinuosity ≈1 [ABSTRACT FROM AUTHOR]

Turbidites and associated trace fossil assemblages have been extensively studied in modern and ancient sedimentary basins. However, benthic redox fluctuations induced by turbidity currents and relevant trace fossil suites (oxygen‐related ichnocoenoses) have rarely been demonstrated in geological records. Here, we present an example with a well‐preserved ichnocoenosis succession recording the detailed dynamic process of benthic marine oxygenation generated by turbidity currents in a Permian oxygen‐deficient basin. Millimetre‐ to centimetre‐scale sedimentological and ichnological analyses demonstrated that benthic‐marine oxygenation induced by distal turbidity currents recorded in fine‐grained calciturbidites from the anoxic basin began with a rapid, short‐lived oxygenation event marked by the Thalassinoides/?Scolicia ichnocoenosis, followed by a relative long‐term lower oxygen‐level stage indicated by the ichnocoenoses of Planolites‐Zoophycos and Zoophycos in turn, and ended with returning to the background anoxic benthic conditions represented by the laminated black shale. The sequential ichnocoenoses associated with turbidity current‐induced oxygenation events in the Permian oxygen‐deficient marine basin suggest that turbidity currents can prominently oxygenate anoxic/dysoxic bottom waters and have significant impacts on benthic communities in oxygen‐deficient basins. [ABSTRACT FROM AUTHOR]

Turbidity currents are important carriers for transporting terrestrial sediment into the deep sea, facilitating the transfer of matter and energy between land and the deep sea. Previous studies have suggested that turbidity currents can exhibit high velocities during their movement in submarine canyons. However, the maximum vertical descent velocity of high-concentration turbid water simulating turbidity currents does not exceed 1 m/s, which does not support the understanding that turbidity currents can reach speeds of over twenty meters per second in submarine canyons. During their movement, turbidity currents can compress and push the water ahead, generating propagating waves. These waves, known as excitation waves, exert a force on the seafloor, resuspending bottom sediments and potentially leading to the generation of secondary turbidity currents downstream. Therefore, the propagation distance of excitation waves is not the same as the initial journey of the turbidity currents, and the velocity of excitation waves within this journey has been mistakenly regarded as the velocity of the turbidity currents. Research on the propagation velocity of excitation waves is of great significance for understanding the sediment supply patterns of turbidity currents and the transport patterns of deep-sea sediments. In this study, numerical simulations were conducted to investigate the velocity of excitation waves induced by turbidity currents and to explore the factors that can affect their propagation velocity and amplitude. The relationship between the velocity and amplitude of excitation waves and different influencing factors was determined. The results indicate that the propagation velocity of excitation waves induced by turbidity currents is primarily determined by the water depth, and an expression (v2 = 0.63gh) for the propagation velocity of excitation waves is provided. [ABSTRACT FROM AUTHOR]

Submarine canyons enhance shelf–slope sediment exchange and influence hydrodynamic processes, with consequences for biogeochemical cycles. This work documents variations in the vertical export of biogenic matter on the northern shore of the lower St. Lawrence Estuary (LSLE, Quebec, eastern Canada), which is characterized by the presence of an active submarine canyon system. A total of three moorings were deployed from November 2020 to September 2021. One nearshore mooring (PDMc) was deployed in the main axis of the Pointe-des-Monts (PDM) canyon system and was equipped with an acoustic Doppler current profiler (ADCP), and two moorings equipped with sediment traps were deployed in the distal PDM canyon system (PDM-154, PDM-224) and offshore Baie-Comeau (BC-133). The ADCP data revealed the occurrence of a minor sediment remobilization event (December 2020) and a small turbidity current (February 2021) in the canyon. Concurrent elevated fluxes of total particulate matter, particulate organic carbon, particulate nitrogen, and chloropigments showed that these events left a signature in sediment traps PDM-154 and PDM-224 located > 2.6 km further offshore by enhancing lateral dispersion of resuspended sediments. The composition of diatom and dinoflagellate assemblages was similar in the canyon system and offshore BC, but the diatom bloom occurred 2 weeks earlier (in mid-April) at the PDM site. A bloom of the potentially toxic diatom Pseudo-nitzschia seriata was also observed during the second half of September 2021 at the BC site. Annual diatom and dinoflagellate fluxes were almost 2 times lower at the PDM site than at the BC site, possibly due to differences in riverine input and the structure of the water column, as well as increased sediment input and resuspension at the PDM site, leading to limited light availability. This study notably helps identify the relationship between near-bed canyon processes and biogenic matter export in the water column, thereby directly influencing the ecosystem offshore PDM. The study period further covered an anomalously nearly ice-free winter, and thus, in the context of climate change, it provides valuable insight into future trends of biogenic matter export in the LSLE. [ABSTRACT FROM AUTHOR]

Subaquatic channels, situated in lakes, fjords, submarine canyons and on deep-sea fan systems, exhibit diverse morphometric characteristics controlled by sediment transport processes, particularly turbidity currents. These processes play a significant role in transporting sediment, organic carbon, nutrients, and pollutants and pose hazards to critical infrastructure. This study examines a balanced set of subaquatic channels across various settings, sizes, and locations, employing novel data harmonization techniques to address biases toward larger channels. The analysis reveals consistent scaling relationships, particularly the dominant role of bankfull width, influencing bankfull depth, cross-sectional area, wavelength, and amplitude. The aspect ratio (width-to-depth) emerges as a significant parameter, reflecting a necessary channel compactness to maintain turbidity currents. Meandering development reveals relations between width, wavelength, and amplitude, with a preference for specific ratios. Meandering is most pronounced at channel beginnings, transitioning to straighter forms downstream, potentially influenced by flow dynamics and flow confinement. The study broadens the understanding of subaquatic channel evolution, emphasizing the importance of bankfull width and providing insights applicable across settings and scales. [ABSTRACT FROM AUTHOR]

The dam is one of the most prominent hydraulic constructions on the world. Sediment flows into dam reservoirs because of human involvement in the dam catchment region, eventually affecting its functional storage. Density currents are a key feature of sedimentation. The use of bottom outflow gates to preserve the reservoir's usable volume is one approach of mitigating the effects of sedimentation. This could have an effect on the quality of the water as it exits the dam. The purpose of this research was to see how well salt current from lock exchanges was vented at different levels and outlet gate sizes. Based on the latest study's experiments, this is the highest venting efficiency when the location of outlets is in the quarter of the bottom of the dam. The output concentration will be equal to the average concentration of the concentrated input current, which is the best height for installing the outlet gates, based on the maximum venting efficiency demonstrated in the recent study's experiments, which may be described as the best height for the turbidity current outlet gate. Discharge efficiency increases when the intake concentration is lower. [ABSTRACT FROM AUTHOR]

Southeastern Newfoundland, Canada, is home to the oldest Ediacaran fossils in the Avalonian Assemblage mostly being preserved beneath tuffites in association with microbial matgrounds. A unique fossiliferous surface at Upper Island Cove, known as the Allison Surface, exhibits three-dimensional preservation of Ediacaran fronds without an associated tuffite or microbial matground. Previous models have invoked entrainment of fronds within turbidity currents, or by their felling into erosive scours. Our work demonstrates that the fossils were preserved within beds before being partially exhumed and cast by a subsequent sandy turbidite. Many of the structures previously identified as rangeomorph stems are longitudinal erosional features within obstacle sours. Additional observations of stemmed/erect organisms coinciding with reclined taxa suggest cross-cutting/palimpsesting of frondose taxa with deeply emplaced holdfasts. Many of the fossil organisms are found within the top of a Td unit, with early pyritization probably aiding in their three-dimensional preservation. Most fronds are incomplete and oblique to the axis of the surrounding scours, indicating they were partly exhumed after burial. The scours likely formed in the lee of erect stemmed rangeomorph and arboreomorph taxa, which are commonly preserved as holdfasts on the surface, and occasionally crosscut buried fronds. The crosscutting of frondose taxa by holdfasts and the presence of pyritic tubes in the overlying sedimentary units suggests the preservation of three separate communities: 1) the initial Td entombed mainly reclined organisms; 2) a pre-turbidity current community of erect taxa with bulbous holdfasts that were the loci of obstacle scours; and 3) a later community of erect organisms preserved as holdfasts/stems. [ABSTRACT FROM AUTHOR]

Submarine levéed channels are often observed in submarine fans, although submarine fans without continuous levéed channels are also common depending on the composition of supplied sediments, particularly the proportion of muddy/sandy materials. However, parameters governing the inception of levéed channels have not yet been studied. Furthermore, depositional levéed channel topography has not been simulated in experimental flumes in any previous study conducted with dilute flows (flow concentration <10%). Herein, four experimental series were conducted (Series A, B, C and D) to simulate depositional submarine channels and to study their formative conditions. A mixture of sediment and saline water was used in the experiments, and both the width of an outlet diffuser and flow discharge rate were varied in the experimental series. A topography composed of a channel with two ridges resembling natural depositional submarine channels with levées was formed in all experiments. Comparisons between the experimental topographies and natural submarine fans revealed that two of the four experimental series produced channel levées with length to width ratios similar to those produced by natural systems. An experiment with half the outlet size produced a channel two times deeper (4.5 cm against 2.0 cm and 2.2 cm) as compared to other experiments. The flow discharge rate and outlet width were half of those observed in Series A and B. Furthermore, salt was removed from the initial mixture for one of the experiments, resulting in high natural levées with a short channel. This study demonstrated that dilute flows could form purely depositional channel levées without precursor or resultant erosive features. In addition, results revealed that the formation of submarine channels is related to two factors: channel width and muddy suspended sediment. [ABSTRACT FROM AUTHOR]

Flood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods. [ABSTRACT FROM AUTHOR]

Submarine channels parallel river channels in their ability to transport sediment. However, in contrast to rivers, sediment transport and bed-form development in submarine channels are less well understood. Many steep (>1°), sandy submarine channels are dominated by upstream-migrating bed forms. The flow conditions required to form these upstream-migrating bed forms remain debated because the interactions between turbidity currents and active bed forms are difficult to measure directly. Consequently, we used a depth-resolved numerical model to test the role of flow parameters that are hypothesized to control the formation of upstream-migrating bed forms in submarine channels. While our modeling results confirmed the importance of previously identified flow parameters (e.g., densiometric Froude number), we found that basal sediment concentration in turbidity currents is the strongest predictor of upstream-migrating bed-form formation. Our model shows how locally steep gradients enable high sediment concentrations (average >5 vol%) in the basal parts of flows, which allow the development of cyclic step instabilities and their associated bed forms. This new insight explains the previously puzzling observation that upstream-migrating bed forms are abundant in proximal, steep, sandy reaches of submarine channels, while their occurrence becomes more intermittent downslope. [ABSTRACT FROM AUTHOR]

The concentrations of 14 polycyclic aromatic hydrocarbons (PAHs) in the sediment of the Tatar Trough were studied. Despite the increase in PAH concentrations over recent decades, which is likely the result of the handling and transportation of fossil fuels, PAH levels and ecological risk were found to be low. The spatial pattern revealed that higher PAH concentrations were mainly in the deeper water sites, suggesting that trough slope failure transported the PAHs to the deeper part of the basin. There was no correlation between the PAHs and grain size or the PAHs and organic carbon that is related to the PAH input from a variety of sources and the heterogeneity of organic matter. The PAH composition, isomer ratio, and PCA identified two areas with different PAH sources. The most northern part of the Tatar Trough received petrogenic PAHs that are probably transported downslope from the northern Tatar Strait where fossil fuels are handled in some ports. Another trough part was polluted by the PAHs from the combustion of coal and biomass and the exhaust of marine vehicles. The minor presence of genes responsible for aerobic PAH destruction can be explained by the anaerobic degradation of PAHs or the spontaneous creation of favorable conditions that promote bacterial PAH oxidation. [ABSTRACT FROM AUTHOR]

Submarine canyons and channels are globally important pathways for sediment, organic carbon, nutrients and pollutants to the deep sea, and they form the largest sediment accumulations on Earth. However, studying these remote submarine systems comprehensively remains a challenge. In this study, we used the only complete-coverage and repeated bathymetric surveys yet for a very large submarine system, which is the Congo Fan off West Africa. Our aim is to understand channel-modifying features such as subaqueous landslides, meander-bend evolution, knickpoints and avulsions by analyzing their morphometric characteristics. We used a new approach to identify these channel-modifying features via morphometric fingerprints, which allows a systematic and efficient search in low-resolution bathymetry data. These observations have led us to identify three morphodynamic reaches within the Congo Canyon-Channel. The upper reach of the system is characterized by landslides that can locally block the channel, storing material for extended periods and re-excavating material through a new incised channel. The middle reach of the system is dominated by the sweep and swing of meander bends, although their importance depends on the channel’s age, and the time since the last up-channel avulsion. In the distal and youngest part of the system, an upstream migrating knickpoint is present, which causes multi-stage sediment transport and overspill through an underdeveloped channel with shallow depths. These findings complement previous less-detailed morphometric analyses of the Congo Canyon-Channel, offering a clearer understanding of how submarine canyon-channels can store sediment (due to channel-damming landslides, meander point bars, levee building due to overspill), re-excavate that sediment (via thalweg incision, meander propagation, knickpoint migration) and finally transport it to the deep sea. This improved understanding of the morphodynamics of the Congo Canyon-Channel may help to understand the evolution of other submarine canyon-channels, and assessment of hazards faced by seabed infrastructure such as telecommunication cables.

Turbidity currents have extensively been explored in quiescent environments. However, during several underwater activities (e.g., dredging and deep sea mining), generated turbidity currents could travel in opposite directions and interact with each other, which could largely influence their hydrodynamics and sediment transport capacity. Therefore, we carried out a set of dual-lock-exchange experiments to study the interaction of colliding turbidity currents. Our experimental results show that the interaction of identical currents results in the reflection of both currents with almost no mixing, forcing them to travel in the opposite direction of the pre-collision one. In contrast, when a turbidity current interacts with a lighter, less-energetic current, clear mixing is observed. Furthermore, it is revealed that the collision of turbidity currents reduces the suspended sediment transported by them, which is favorable from an environmental point of view, and slightly increases the vertical dispersion of particles. In the case of two identical counterflowing currents, a 35% reduction in mass flux, accompanied by a 6% increase in turbidity current thickness, was observed in our experiments.