2,063 research outputs found
Submarine channel flow processes and deposits: a process-product perspective
No full textProcess-product studies have been central to the development of process sedimentology over the past few decades, with the ability to first measure flows, and then examine the resulting deposits, removing much of the ambiguity associated with previous interpretations. However, perhaps uniquely for large geomorphic systems on Earth, there are no field-scale process-product studies of submarine channels. In fact, there are remarkably few direct measurements even of the flow dynamics as a result of the difficulties of measuring these powerful, infrequent, and often inaccessible flows. Over the past decade, physical experimentation has provided the first process-product studies for model submarine channel systems, enabling us to link flow behaviour and sedimentation patterns. This has been supplemented by numerical simulations, particularly of submarine channel flow dynamics. Here for the first time, we synthesise these observations, in the context of our direct knowledge of submarine channels, to derive an overview of submarine channel flow dynamics, and process-orientated intra-channel architecture models for low and high latitude systems. In addition, we propose new models for the development and evolution of point bars and for inner bend sedimentary accumulations that can comprise point bars overlain by finer-grained oblique accretion deposits. The work reveals a rich range of flow behaviour and associated sedimentation patterns in submarine channels that are far more complex than in fluvial systems
Swept away by a turbidity current in Mendocino submarine canyon, California
No full textWe present unique observations and measurements of a dilute turbidity current made with a remotely operated vehicle in 400?m water depth near the head of Mendocino Canyon, California. The flow had a two-layer structure with a thin (0.5 to 30?m), relatively dense (<0.04?vol %) and fast (up to ~1.7?m/s) wedge-shaped lower layer overlain by a thicker (up to 89?m) more dilute and slower current. The fast moving lower layer lagged the slow moving, dilute flow front by 14?min, which we infer resulted from the interaction of two initial pulses. The two layers were strongly coupled, and the sharp interface between the layers was characterized by a wave-like instability. This is the first field-scale data from a turbidity current to show (i) the complex dynamics of the head of a turbidity current and (ii) the presence of multiple layers within the same event
The critical role of stratification in submarine channels: Implications for channelization and long runout of flows
No full textChannelized submarine gravity currents travel remarkable distances, transporting sediment to the distal reaches of submarine fans. However, the mechanisms by which flows can be sustained over these distances remain enigmatic. In this paper we consider two shallow water models the first assumes the flow is unstratified whilst the second uses empirical models to describe vertical stratification, which effects depth averaged mass and momentum transfer. The importance of stratification is elucidated through comparison of modeled flow dynamics. It is found that the vertically stratified model shows the best fit to field data from a channelized field-scale gravity current in the Black Sea. Moreover, the stratified flow is confined by the channel to a much greater degree than the flow in the unstratified model. However, both models fail to accurately represent flow dynamics in the distal end of the system, suggesting current empirical stratification models require improvement to accurately describe field-scale gravity currents. It also highlights the limitations of weakly stratified small-scale experiments in describing field-scale processes. The results suggest that in real-world systems stratification is likely to enable maintenance of velocity and discharge within the channel, thus facilitating sediment suspension over distances of hundreds of kilometers on low seafloor gradients. This explains how flows can travel remarkable distances and transport their sediment to the distal parts of submarine fans
Domestic support and the WTO negotiations
No full textIn their attempt to maximise trade benefits, agricultural trade negotiators must allocate scarce resources and consider trade‐offs across issues such as liberalising foreign border measures or reducing foreign domestic subsidies. Analysis and examples support the notion that more liberalisation will be achieved in the new WTO round by emphasis on lowering border barriers and export subsidies rather than attempting to discipline domestic farm subsidies directly. Analyses of EU grain policy, Korean rice policy and US sugar policy show how reduced export subsidy or more import access have substantial trade benefits, even if farmers are compensated with payments or price supports.International Relations/Trade,
The structure of the deposit produced by sedimentation of polydisperse suspensions
No full textTo interpret the deposits from particle-laden flows it is necessary to understand particle settling at their base. In this paper a quantitative model is developed that not only captures how particles settle out of suspension but also the composition of the final deposit in terms of its vertical distribution of grain sizes. The theoretical model is validated by comparison to published experimental data that has been used to interpret the field deposits of submarine sediment-laden flows (Amy et al., 2006). The model explains two intriguing features of the experimental deposits that are also observed in natural deposits. First, deposits commonly have an ungraded, or poorly normally graded, region overlain by a strongly normally graded region. Second, the normalized thickness of the ungraded region increases as the initial concentration of the suspension is increased. In the theoretical model, the poorly normally graded region results from a constant mass flux into the bed that persists until the largest grain size present within the flow has been completely deposited. The effect of increasing the concentration of the initial suspension is to increase the thickness of the poorly graded part of the deposit and to decrease its average grain size. This work suggests that deposits with relatively thick, poorly graded bases can form from relatively high-concentration polydisperse suspensions, when the initial volume fraction of sediment is greater than approximately 20% and indicates that it is important to include these hindered settling effects in models of depositing flows
Conceptual Design Automation: Abstraction complexity reduction by feasilisation and knowledge engineering
No full textIn order to keep innovating, engineers are working more and more with engineering software, providing them a way to cut away their routine and repetitive activities. Computer aided design and simulation software are for instance considered standard tools in most engineering companies. Today, to solve complex engineering design problems, multidisciplinary design optimisation (MDO) is increasingly used to automate the design process to support the engineer in finding a solution faster. To effectively use MDO, design frameworks such as the design and engineering engine (DEE) are required. More and more does engineering software provide a seamless integration of computer software and human knowledge, a focus point of the field of knowledge engineering (KE). This will free engineers from repetitive and routine tasks and allow them to use their full creative capacity and learn faster, increasing their productivity. This work contributes to the development of KE applications within the DEE to support the MDO process. The focus is on the conceptual design phase of complex systems engineering, responsible for providing an initial start vector for MDO. Aircraft design is taken as a guiding example as it is a typical case of a complex system.Design of Aircraft and RotorcraftAerospace Engineerin
Can turbidites be used to reconstruct a paleoearthquake record for the central Sumatran margin: Reply
No full textEfficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hage, S., Galy, V. V., Cartigny, M. J. B., Acikalin, S., Clare, M. A., Grocke, D. R., Hilton, R. G., Hunt, J. E., Lintern, D. G., McGhee, C. A., Parsons, D. R., Stacey, C. D., Sumner, E. J., & Talling, P. J. Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits. Geology, 48(9), (2020): 882-887, doi:10.1130/G47320.1.Burial of terrestrial biospheric particulate organic carbon in marine sediments removes CO2 from the atmosphere, regulating climate over geologic time scales. Rivers deliver terrestrial organic carbon to the sea, while turbidity currents transport river sediment further offshore. Previous studies have suggested that most organic carbon resides in muddy marine sediment. However, turbidity currents can carry a significant component of coarser sediment, which is commonly assumed to be organic carbon poor. Here, using data from a Canadian fjord, we show that young woody debris can be rapidly buried in sandy layers of turbidity current deposits (turbidites). These layers have organic carbon contents 10× higher than the overlying mud layer, and overall, woody debris makes up >70% of the organic carbon preserved in the deposits. Burial of woody debris in sands overlain by mud caps reduces their exposure to oxygen, increasing organic carbon burial efficiency. Sandy turbidity current channels are common in fjords and the deep sea; hence we suggest that previous global organic carbon burial budgets may have been underestimated.We thank C. Johnson, M. Lardie, A. Gagnon, A. McNichol, and the NOSAMS (National Ocean Sciences Accelerator Mass Spectrometry) team (Woods Hole Oceanographic Institution [WHOI], Massachusetts, USA) for their help with ramped oxidation system and isotopes. We thank the captain and crew of CCGS Vector. Support was provided by UK Natural Environment Research Council (NERC) grants NE/M007138/1 (to Cartigny) and NE/L013142/1 (to Talling), NE/P005780/1 and NE/P009190/1 (to Clare); a Royal Society Research Fellowship (to Cartigny); an International Association of Sedimentologists Postgraduate Grant and National Oceanography Centre Southampton–WHOI exchange program funds (to Hage); an independent study award from WHOI (to Galy); the Climate Linked Atlantic Sector Science (CLASS) program (NERC grant NE/R015953/1); and the European Research Council under the European Union’s Horizon 2020 research and innovation program (Grant 725955, to Parsons). We thank François Baudin, Xingqian Cui, editor James Schmitt, and three anonymous reviewers
On how thin submarine flows transported large volumes of sand for hundreds of kilometres across a flat basin plain without eroding the seafloor
No full textSubmarine gravity currents, especially long run-out flows that reach the deep ocean, are exceptionally difficult to monitor in action, hence there is a need to reconstruct how these flows behave from their deposits. This study mapped five individual flow deposits (beds) across the Agadir Basin, offshore north-west Africa. This is the only dataset where bed shape, internal distribution of lithofacies, changes in grain size and seafloor gradient, bed volumes, flow thickness and depth of erosion into underlying hemipelagic mud are known for individual beds. Some flows were 30 to 120 m thick. However, flows with the highest fraction of sand were less than 5 to 14 m thick. Sand was most likely to be carried in the lower 5 to 7 m of these flows. Despite being relatively thin, one flow was capable of transporting very large volumes of sediment (ca 200 km3) for large distances across very flat seafloor. These observations show that these relatively thin flows could travel quickly enough on very low gradients (0.02º to 0.05º) to suspend sand several metres to tens of metres above the sea floor, and maintain those speeds for up to 250 km across the basin. Near uniform hemipelagic mud interval thickness between beds, and coccolith assemblages in the mud caps of beds, suggest that the flows did not erode significantly into the underlying seafloor mud. Simple calculations imply that some flows, especially in the proximal part of the basin, were powerful enough to have eroded hemipelagic mud if it was exposed to the flow. This suggests that the flows were depositional from the moment they arrived at a basin plain location, and deposition shielded the underlying hemipelagic mud from erosion. Reproducing the field observations outlined in this exceptionally detailed field dataset is a challenge for future experimental and numerical models
The literary phenomenon of 'conflation’ in the reworking of Paul’s letter to the Colossians by the author of the letter to the Ephesians
No full textThis thesis is concerned with the nature of the relationship of the Letter to the Ephesians (Eph) to Paul's Letter to the Colossians (Col).The first three chapters seek to argue that this relationship should be designated as "literary dependent". In Chapter I the suggestion made by A.T. Lincoln (Dallas [Texas], 1990) that the contemporary redaction of the Letter of Aristeas by Josephus in his Jewish Antiquities, Book XII, §§ 11-118 is similar to the use the author of Eph made of Col, is exposed to critical review. Chapter II focuses on the phenomenon of repeated 'conflation' in Eph. This literary phenomenon entails that several 'Colossian' texts from different parts of Col are conflated by the author of Eph into one passage and is subjected to exhaustive analysis. It is argued that conflation is the main feature of the literary dependence of Eph on Col but does not occur in Josephus' reworking of the Letter of Aristeas. Chapter III continues the comparison between the method of reworking employed in the Jewish Antiquities and in Eph by pointing out that the fluctuation in verbatim agreement of one document with its source can be meaningful. Chapter IV provides the new synopsis of both letters on which the whole examination is based. This synoptic overview is a desideratum since the previous synoptic editions of the Greek text of both letters by E.J. Goodspeed (Chicago, 1933) and C.L. Mitton (Oxford, 1951) are not accurate enough and unsuitable for research that focuses on the conflations of 'Colossian' verses in Eph. The fifth and last chapter deals with the question why Eph is literary dependent on Col and shows that despite the literary dependence, the theology of Eph is distinctive in comparison with its source Col. The distinctiveness of Eph's theology consists in a critical modification of the stress which Col places on Christ's already accomplished victory over the cosmic powers (Co/ 2.15). In order to safeguard an authoritative reception of his modification of Col, the author of Eph presented his letter as the parallel letter of Col alluded to m Col 4.16. The literary dependence on Col is necessary both to modify its content and to present his own writing as its parallel letter
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