Three-dimensional submerged wall jets and their transition to density flows: Morphodynamics and implications for the depositional record

Jets that expand from an orifice into an ambient water body represent a basic flow model for depositional environments related to expanding flows. Momentum-dominated jets evolve into gravity-dominated density flows. To understand this transition and its sedimentological relevance, three-dimensional tank experiments with submerged wall jets were conducted, systematically varying parameters such as the initial density difference, bed slope, grain size and sediment supply. Bedform successions could be subdivided into those related to the jet and those related to the density flow. Jet deposits included early-stage bedforms, scours and mouth bars. Early-stage bedforms are asymmetrical dunes that spread concentrically from the orifice. Sediment entrainment by eddies from the expanding jets led to the formation of scours and mouth bars. Flows with lesser initial density difference produced more elongate scours. Conversely, scours became deeper for denser incoming flows. Coarser-grained sediment caused the formation of higher and steeper mouth bars and vice versa. The transition from momentum-dominated jets to gravity-dominated density flows occurred approximately at the mouth-bar crest. Hydraulic jumps were absent in the expanding jet regions and at the transitions to density flows. Instead, complex flow patterns and circulations were inferred from the velocity measurements within the scour and at the mouth-bar crests. Bedform trains related to the density flow were controlled by the grain size and sediment supply. Coarse-grained sediment and high supply rates caused strong mouth-bar aggradation and flow splitting, leading to the formation of bedform trains laterally adjacent to the mouth bar. Fine-grained sediment and low supply rates caused the formation of bedform trains downflow of the mouth bar. The symmetrical bedforms deposited by the density flows always displayed an in-phase relationship with the flow, indicating that they were antidunes. The experimental jet deposits resemble successions known from subaqueous ice-contact fans and deep water channel-lobe transition zones

Sedimentation resulting from road development, Cape Tribulation Area

The aims of the study were: to quantify the amount of sediment being carried by the streams of the Cape Tribulation area under both natural conditions and in disturbed areas adjacent to the New Road; to quantity the amount of sediment in the water column adjacent to the reefs; and to put into context the amount of increased sedimentation directly due to road developmen

Direct Numerical Simulation of Transverse Ripples: 2. Self-Similarity, Bedform Coarsening, and Effect of Neighboring Structures

Coupled bed-flow direct numerical simulations investigating the early stages of pattern formation and bedform (ripple) interactions were examined in a previous paper (Part 1), making use of the resolved flow field. In this paper (Part 2), we compare our results to published experimental data and provide an extensive quantitative analysis of the bed using spectral analysis and two-point correlations. The effect of the mobile rippled bed on the flow structure and turbulence is investigated locally (at specific streamwise locations) and over the entire computational domain. We show that developing ripples attain a self-similar profile in both the shape and the corresponding bed shear stress. We demonstrate the importance of neighboring structures, especially upstream neighbors, on bedform dynamics in terms of the growth, decay, and speed of ripples. Finally, we examine the defect-free interactions in the later stages of bed evolution, which primarily lead to wave coarsening. Key Points Isolated ripples maintain a self-similar shape and bed shear stress profiles Bedform-bedform interactions can significantly modify bedform celerity Spectra of bed height variation suggest a Reynolds number dependenc

Direct Numerical Simulation of Transverse Ripples: 1. Pattern Initiation and Bedform Interactions

We present results of coupled direct numerical simulations between flow and a deformable bed in a horizontally periodic, turbulent open channel at a shear Reynolds number of Reτ = 180. The feedback between the temporally and spatially evolving bed and the flow is enforced via the immersed boundary method. Using the near-bed flow field, we provide evidence on the role of locally intense near-bed vortical structures during the early stages of bed formation, from the emergence of quasi-streamwise streaks to the formation of incipient bedform crestlines. Additionally, we take a new look at a number of defect-related bedform interactions, including lateral linking, defect and bedform repulsion, merging, and defect creation, and show that the underlying mechanisms, in these flow-aligned interactions, are very similar to each other. Consequently, the interactions are labeled differently depending on the geometry of interacting structures and the outcome of the interaction. In the companion paper, we compare our results to published experimental data and provide an extensive quantitative analysis of the bed, where we demonstrate the importance of neighboring structures, especially upstream neighbors, on bedform dynamics (growth/decay and speed) and wave coarsening. Video files of bed evolution are available in the supporting information. Key Points Mesoscale resolved simulations show the different mechanisms for bedform-bedform interactions to be very similar to each other Similar to laminar flows over dunes and ripples, a positive phase shift is observed between bed shear stress and topology even in mesoscale-resolved turbulent flow field Simulations match Coleman and Melville (1996) theory on bedform initiation from a flat be

On the definition, evolution, and properties of the outer edge of gravity currents: A direct-numerical and large-eddy simulation study

Gravity currents are flows driven by the action of gravity over fluids with different densities. Here, we focus on gravity currents where heavier fluid travels along the bottom of a sloping bed, underneath a large body of stagnant lighter ambient fluid. The thickness of the current increases due to entrainment of ambient fluid into the current. Direct numerical and large eddy simulations of gravity currents and a wall-jet transporting a passive scalar field are performed. We focus on the rate of penetration of mean momentum and mean concentration of the agent responsible for the density difference (temperature, salinity, or sediment volume fraction) into the ambient fluid. The rates of penetration of turbulence-related quantities (i.e., turbulent kinetic energy, Reynolds flux, and stress) into the ambient are analyzed. A robust methodology for defining the upper edge of these quantities and thereby defining the current thickness using these different mean and turbulent quantities is presented. A comparison between downstream evolution of the gravity current with the corresponding behaviors of canonical wall-bounded turbulent flows is presented. The present understanding of turbulent/non-turbulent interface (TNTI) is extended to include subcritical flows where, due to the strong effect of stratification, the TNTI is buried well within the upper edge of the current and confined right above the inner near-bed layer. The present work sheds light on the striking difference between the different definitions of thickness (momentum, concentration, turbulence, etc.) in subcritical gravity currents, where stratification suppresses turbulence in the upper region of the current.Fil: Salinas, Jorge S.. University of Florida; Estados UnidosFil: Balachandar, S.. University of Florida; Estados UnidosFil: Zúñiga, Santiago Luciano. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Shringarpure, M.. No especifíca;Fil: Fedele, J.. No especifíca;Fil: Hoyal, D.. No especifíca;Fil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Slope dependence of self-similar structure and entrainment in gravity currents

Results from seven direct and large-eddy simulations of gravity currents on slopes ranging from 0.14° to 2.86° that span from the subcritical to the supercritical regime are studied. By considering a long domain, attention is focused on the near-self-similar state approached by these currents far downstream. In the self-similar limit, the various shape factors, local Richardson number, entrainment coefficient, velocity scale and basal drag coefficient reach a constant value, while the current height, volume and momentum fluxes continue to increase linearly. Their dependence on slope is presented.Fil: Salinas, Jorge S.. University of Florida; Estados UnidosFil: Zúñiga, Santiago Luciano. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Shringarpure, M.. No especifíca;Fil: Fedele, J.. No especifíca;Fil: Hoyal, D.. No especifíca;Fil: Balachandar, S.. University of Florida; Estados Unido

Anatomy of subcritical submarine flows with a lutocline and an intermediate destruction layer

Turbidity currents are sediment-laden flows that travel over a sloping bed under a stagnant ambient fluid, driven by the density difference between the current and the ambient. Turbidity currents transport large amounts of carbon, nutrients and fresh water through oceans and play an important role in global geochemical cycling and seafloor ecosystems. Supercritical currents are observed in steeper slopes. Subcritical currents are observed in milder slopes, where the near-bed and interface layers are prevented from interacting across the velocity maximum. Past works show the existence of such a barrier to vertical momentum transfer is essential for the body of the subcritical current to extend over hundreds of kilometers in length without much increase in height. Here we observe the body of subcritical currents to have a three layer structure, where the turbulent near-bed layer and the non-turbulent interface layer are separated by an intermediate layer of negative turbulence production. We explain the mechanism by which this layer prevents the near-bed turbulent structures from penetrating into the interface layer by transferring energy back from turbulence to the mean flow.Fil: Salinas, Jorge Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Florida; Estados UnidosFil: Balachandar, S.. University of Florida; Estados UnidosFil: Shringarpure, M.. No especifíca;Fil: Fedele, J.. No especifíca;Fil: Hoyal, D.. No especifíca;Fil: Zúñiga, Santiago Luciano. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

Australian spiny mountain crayfish (Euastacus, Parastacidae) and their ecotosymbiotic temnocephalan flatworms (Temnocephalida, Platyhelminthes) may have co-occurred and interacted through deep time, during a period of major environmental change. Therefore, reconstructing the history of their association is of evolutionary, ecological, and conservation significance. Here, time-calibrated Bayesian phylogenies of Euastacus species and their temnocephalans (Temnohaswellia and Temnosewellia) indicate near-synchronous diversifications from the Cretaceous. Statistically significant cophylogeny correlations between associated clades suggest linked evolutionary histories. However, there is a stronger signal of codivergence and greater host specificity in Temnosewellia, which co-occurs with Euastacus across its range. Phylogeography and analyses of evolutionary distinctiveness (ED) suggest that regional differences in the impact of climate warming and drying had major effects both on crayfish and associated temnocephalans. In particular, Euastacus and Temnosewellia show strong latitudinal gradients in ED and, conversely, in geographical range size, with the most distinctive, northern lineages facing the greatest risk of extinction. Therefore, environmental change has, in some cases, strengthened ecological and evolutionary associations, leaving host-specific temnocephalans vulnerable to coextinction with endangered hosts. Consequently, the extinction of all Euastacus species currently endangered (75%) predicts coextinction of approximately 60% of the studied temnocephalans, with greatest loss of the most evolutionarily distinctive lineages

Phylogenetic Codivergence Supports Coevolution of Mimetic Heliconius Butterflies

The unpalatable and warning-patterned butterflies _Heliconius erato_ and _Heliconius melpomene_ provide the best studied example of mutualistic Müllerian mimicry, thought – but rarely demonstrated – to promote coevolution. Some of the strongest available evidence for coevolution comes from phylogenetic codivergence, the parallel divergence of ecologically associated lineages. Early evolutionary reconstructions suggested codivergence between mimetic populations of _H. erato_ and _H. melpomene_, and this was initially hailed as the most striking known case of coevolution. However, subsequent molecular phylogenetic analyses found discrepancies in phylogenetic branching patterns and timing (topological and temporal incongruence) that argued against codivergence. We present the first explicit cophylogenetic test of codivergence between mimetic populations of _H. erato_ and _H. melpomene_, and re-examine the timing of these radiations. We find statistically significant topological congruence between multilocus coalescent population phylogenies of _H. erato_ and _H. melpomene_, supporting repeated codivergence of mimetic populations. Divergence time estimates, based on a Bayesian coalescent model, suggest that the evolutionary radiations of _H. erato_ and _H. melpomene_ occurred over the same time period, and are compatible with a series of temporally congruent codivergence events. This evidence supports a history of reciprocal coevolution between Müllerian co-mimics characterised by phylogenetic codivergence and parallel phenotypic change

Fullerene‐like structures of Cretaceous crinoids reveal topologically limited skeletal possibilities

There are few cases where numbers or types of possible phenotypes are known, although vast state spaces have been postulated. Rarely applied in this context, graph theory and topology enable enumeration of possible phenotypes and evolutionary transitions. Here, we generate polyhedral calyx graphs for the Late Cretaceous, stemless crinoids Marsupites testudinarius and Uintacrinus socialis (Uintacrinoidea Zittel) revealing structural similarities to carbon fullerene and fulleroid molecules (respectively). The U. socialis calyx incorporates numerous plates (e.g. graph vertices |V| ≥ 197), which are small, light, low‐density and have four to eight sides. Therefore, the corresponding number of possible plate arrangements (number of polyhedral graphs) is large (≫1 × 1014). Graph vertices representing plates with sides >6 introduce negative Gaussian curvature (surface saddle points) and topological instability, increasing buckling risk. However, observed numbers of vertices for Uintacrinus do not allow more stable pentaradial configurations. In contrast, the Marsupites calyx dual graph has 17 faces that are pentagonal or hexagonal. Therefore, it is structurally identical to a carbon fullerene, specifically C30‐D5h. Corresponding graph restrictions result in constraint to only three structural options (fullerene structures C30‐C2v 1, C30‐C2v 2 and C30‐D5h). Further restriction to pentaradial symmetry allows only one possibility: the Marsupites phenotype. This robust, stable topology is consistent with adaptation to predation pressures of the Mesozoic marine revolution. Consequently, the most plausible evolutionary pathway between unitacrinoid phenotypes was a mixed heterochronic trade‐off to fewer, larger calyx plates. Therefore, topological limitations radically constrained uintacrinoid skeletal possibilities but thereby aided evolution of a novel adaptive phenotype