Several of Earth's intraplate volcanic provinces are hard to reconcile with the mantle plume hypothesis. Instead, they exhibit characteristics that are more compatible with shallower processes that ...involve the interplay between uppermost mantle flow and the base of Earth's heterogeneous lithosphere. The mechanisms most commonly invoked are edge‐driven convection (EDC) and shear‐driven upwelling (SDU), both of which act to focus upwelling flow and the associated decompression melting adjacent to steps in lithospheric thickness. In this study, we undertake a systematic numerical investigation, in both 2‐D and 3‐D, to quantify the sensitivity of EDC, SDU, and the associated melting to key controlling parameters. Our simulations demonstrate that the spatio‐temporal characteristics of EDC are sensitive to the geometry and material properties of the lithospheric step, in addition to the magnitude and depth‐dependence of upper‐mantle viscosity. These simulations also indicate that asthenospheric shear can either enhance or reduce upwelling velocities and the associated melting, depending upon the magnitude and orientation of flow relative to the lithospheric step. When combined, such sensitivities explain why step changes in lithospheric thickness, which are common along cratonic edges and passive margins, only produce volcanism at isolated points in space and time. Our predicted trends of melt production suggest that, in the absence of potential interactions with mantle plumes, EDC and SDU are viable mechanisms only for Earth's shorter‐lived, lower‐volume intraplate volcanic provinces.
Plain Language Summary
Intraplate volcanoes, which occur away from plate boundaries, are common across Earth's surface (e.g., Hawaii, Reunion, Cameroon, Eastern Australia), but their origin remains debated. The classically invoked hypothesis for their genesis centers around mantle plumes, buoyant columns of hot rock that ascend through Earth's mantle. Upon reaching the base of tectonic plates, plumes generate extensive melting and remain comparatively fixed, providing a mechanism for generating linear volcanic tracks that grow older in the direction of plate motion. Several intraplate volcanic regions, however, exhibit characteristics that are inconsistent with the mantle plume hypothesis: their eruptions are usually short‐lived, non‐age‐progressive, and only generate minor volumes of lava. Therefore, they are more likely to be driven by shallower processes, such as small‐scale convective instabilities that develop adjacent to step‐changes in the thickness of Earth's lithosphere, its rigid outermost shell. In this study, we utilize both 2‐D and 3‐D computational models to simulate these shallow processes, and we analyze their sensitivity to a range of key controlling parameters. Our results help to solve the puzzle of why such processes only produce volcanism at isolated locations and, in the absence of interactions with mantle plumes, limit their applicability to Earth's shorter‐lived, lower‐volume volcanic provinces.
Key Points
Edge‐driven convection is sensitive to upper‐mantle viscosity and the geometry and material properties of lithospheric steps.
Asthenospheric flow magnitude and orientation dictate whether edge‐driven cells are enhanced through asthenospheric shear or suppressed.
Melting associated with edge‐related processes can account for Earth's shorter‐lived and lower‐volume intraplate volcanic provinces.
Evidence suggests a correlation between the gut microbiota composition and weight loss caused by caloric restriction. Laparoscopic sleeve gastrectomy (LSG), a surgical intervention for obesity, is ...classified as predominantly restrictive procedure. In this study we investigated functional weight loss mechanisms with regard to gut microbial changes and energy harvest induced by LSG and a very low calorie diet in ten obese subjects ( n = 5 per group) demonstrating identical weight loss during a follow-up period of six months. For gut microbiome analysis next generation sequencing was performed and faeces were analyzed for targeted metabolomics. The energy-reabsorbing potential of the gut microbiota decreased following LSG, indicated by the Bacteroidetes/Firmicutes ratio, but increased during diet. Changes in butyrate-producing bacterial species were responsible for the Firmicutes changes in both groups. No alteration of faecal butyrate was observed, but the microbial capacity for butyrate fermentation decreased following LSG and increased following dietetic intervention. LSG resulted in enhanced faecal excretion of nonesterified fatty acids and bile acids. LSG, but not dietetic restriction, improved the obesity-associated gut microbiota composition towards a lean microbiome phenotype. Moreover, LSG increased malabsorption due to loss in energy-rich faecal substrates and impairment of bile acid circulation. This trial is registered with ClinicalTrials.gov NCT01344525.
Hydrodynamic modelling is an important tool for the development of tidal stream energy projects. Many hydrodynamic models incorporate the effect of tidal turbines through an enhanced bottom drag. In ...this paper we show that although for coarse grid resolutions (kilometre scale) the resulting force exerted on the flow agrees well with the theoretical value, the force starts decreasing with decreasing grid sizes when these become smaller than the length scale of the wake recovery. This is because the assumption that the upstream velocity can be approximated by the local model velocity, is no longer valid. Using linear momentum actuator disc theory however, we derive a relationship between these two velocities and formulate a correction to the enhanced bottom drag formulation that consistently applies a force that remains close to the theoretical value, for all grid sizes down to the turbine scale. In addition, a better understanding of the relation between the model, upstream, and actual turbine velocity, as predicted by actuator disc theory, leads to an improved estimate of the usefully extractable energy. We show how the corrections can be applied (demonstrated here for the models MIKE 21 and Fluidity) by a simple modification of the drag coefficient.
•We study the standard enhanced bottom drag parameterisation of tidal turbines.•For grid sizes smaller than the near field, the applied force is shown to be incorrect.•A newly derived correction based on actuator disc theory significantly improves results.•Results are presented for the MIKE 21 and Fluidity models.•An improved estimation of usefully extractable energy is derived.
Several of Earth's intra‐plate volcanic provinces lie on or adjacent to continental lithosphere. Although many are believed to mark the surface expression of mantle plumes, our limited understanding ...of how buoyant plumes interact with heterogeneous continental lithosphere prevents further progress in identifying mechanisms at the root of continental volcanism. In this study, using a suite of 3‐D geodynamical models, we demonstrate that the magmatic expression of plumes in continental settings is complex and strongly sensitive to the location of plume impingement, differing substantially from that expected beneath more homogeneous oceanic lithosphere. Within Earth's continents, thick cratonic roots locally limit decompression melting. However, they deflect plume conduits during their ascent, with plume material channeled along gradients in lithospheric thickness, activating magmatism away from the plume conduit, sometimes simultaneously at locations more than a thousand kilometres apart. This magmatism regularly concentrates at lithospheric steps, where it may be difficult to distinguish from that arising through edge‐driven convection. At times, the flow field associated with the plume enhances melting at these steps long before plume material enters the melting zone, implying that differentiating geochemical signatures will be absent. Beneath regions of thinner lithosphere, plume‐related flow can force material downwards at lithospheric steps, shutting off pre‐existing edge‐related magmatism. Additionally, variations in lithospheric structure can induce internal destabilization of ponding plume material, driving intricate magmatic patterns at the surface. Our analysis highlights the challenges associated with linking continental magmatism to underlying mantle dynamics, motivating an inter‐disciplinary approach in future studies.
Plain Language Summary
As explained by the theory of plate tectonics, most of Earth's volcanism concentrates on the boundaries between lithospheric plates. However, a significant class of volcanism occurs within plate interiors. This volcanism is usually associated with the ascent of mantle plumes — buoyant upwellings of hot rock that rise through the mantle toward Earth's surface. Yet, the exact link between mantle plumes and surface volcanism is not fully understood, particularly in continental regions where Earth's outermost shell — the lithosphere — exhibits substantial variations in thickness and composition, owing to a complex and protracted evolutionary history. In the present study, we use multi‐resolution 3‐D computational models to simulate the interaction between mantle plumes and heterogeneous continental lithosphere to demonstrate how the structure and geometry of this overlying lithospheric “lid” shape the volcanic response at Earth's surface. Our results provide new pathways toward understanding the link between surface volcanism and underlying dynamical processes within Earth's interior.
Key Points
The interaction between mantle plumes and continental lithosphere produces complex spatial and temporal magmatic trends at the surface
Lithospheric thickness gradients channel plume material toward areas of thin lithosphere, facilitating melting far from the plume conduit
Magmatic contributions from edge‐driven convection and mantle plumes can be challenging to distinguish in continental settings
Seismic tomography of Earth's mantle images abundant slab remnants, often located in close proximity to active subduction systems. The impact of such remnants on the dynamics of subduction remains ...underexplored. Here, we use simulations of multi‐material free subduction in a 3‐D spherical shell geometry to examine the interaction between visco‐plastic slabs and remnants that are positioned above, within and below the mantle transition zone. Depending on their size, negatively buoyant remnants can set up mantle flow of similar strength and length scales as that due to active subduction. As such, we find that remnants located within a few hundred km from a slab tip can locally enhance sinking by up to a factor 2. Remnant location influences trench motion: the trench advances toward a remnant positioned in the mantle wedge region, whereas remnants in the sub‐slab region enhance trench retreat. These motions aid in rotating the subducting slab and remnant toward each other, reducing the distance between them, and further enhancing the positive interaction of their mantle flow fields. In this process, the trench develops along‐strike variations in shape that are dependent on the remnant's location. Slab‐remnant interactions may explain the poor correlation between subducting plate velocities and subducting plate age found in recent plate tectonic reconstructions. Our results imply that slab‐remnant interactions affect the evolution of subducting slabs and trench geometry. Remnant‐induced downwelling may also anchor and sustain subduction systems, facilitate subduction initiation, and contribute to plate reorganization events.
Plain Language Summary
Subduction, the process where cold oceanic lithosphere descends into the mantle, is a time‐dependent process: old subduction zones cease while new subduction zones initiate, in cycles of tectonic plate motions. The cessation of subduction is accompanied by break‐off of the subducting slab from the surface plate, forming a slab remnant. The remnant continues sinking into the mantle and, in doing so, generates a flow field that may influence adjacent subduction systems. In this study, we present numerical simulations of subduction in a 3‐D spherical shell domain, and examine how subduction systems interact with a range of slab remnants. Our models show that sinking remnants can significantly enhance the sinking velocity of slabs within a few 100–1,000 km of the remnants, and can influence the spatial and temporal evolution of trench shape. Our results suggest that the existence of slab remnants may help to anchor and sustain subduction systems, and lead to an environment more favorable for the initiation of new subduction zones. Since such events are closely linked to reorganizations in global plate motions, we suggest that the location of pre‐existing remnants influences tectonic plate movements and, potentially, super continent cycles.
Key Points
Subducted slab remnants can enhance the sinking velocities of actively subducting plates by up to a factor 2
Slab remnants strongly influence trench motions and the evolution of trench shape at subduction zones located within a few 100–1,000 s of km
The flow fields interact such that the slab tip and remnant approach, thus strengthening mantle flow that can anchor subduction location
Many of the factors expected to control the dynamics and evolution of Earth's subduction zones are under‐explored in an Earth‐like spherical geometry. Here, we simulate multi‐material free‐subduction ...of a complex rheology slab in a 3‐D spherical shell domain, to investigate the effect of plate age (simulated by covarying plate thickness and density) and width on the evolution of subduction systems. We find that the first‐order predictions of our spherical cases are generally consistent with existing Cartesian studies: (a) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; and (b) wider slabs can develop along‐strike variations in trench curvature due to toroidal flow at slab edges, trending toward a “W”‐shaped trench with increasing slab width. We find, however, that these along‐strike variations are restricted to older, stronger, retreating slabs: Younger slabs that drive minimal trench motion remain relatively straight along the length of the subduction zone. We summarize our results into a regime diagram, which highlights how slab age modulates the effect of slab width, and present examples of the evolutionary history of subduction zones that are consistent with our model predictions.
Plain Language Summary
Subduction zones are locations where Earth's tectonic plates collide, and the denser plate subsequently descends into the mantle. They exert important controls on surface plate motions, plate boundary deformation, mountain‐building, seismic hazard, volcanism, and help to organize underlying mantle flow, which is the engine driving our dynamic Earth. As a result, this important process has been extensively studied through both analog and computational models. Here, we model the dynamics and evolution of subduction systems on an Earth‐like sphere, and find that: (a) older plates, which have spent longer cooling at Earth's surface, sink into the underlying mantle faster, at a shallower angle; and (b) narrower plates tend to develop “C”‐shaped trenches, whereas wider plates tend to develop “W”‐shaped trenches. Importantly, the influence of subducting plate width is strongly dependent on its age. We show how these two factors combined can explain key aspects of the evolution of several major subduction zones on Earth.
Key Points
Spherical models are used to examine the joint effect of slab age and width on free‐subduction dynamics
Older slabs enhance trench retreat whilst wider slabs can drive along‐strike variations in shape
The effect of plate width is strongly modulated by plate age, given its control on trench retreat
The effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics. Most existing studies have been executed in a Cartesian ...domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. Here, we simulate free‐subduction of composite visco‐plastic plates in 3‐D Cartesian and spherical shell domains, to examine the role of sphericity in dictating the dynamics of subduction, and highlight the limitations of Cartesian models. We identify two irreconcilable differences between Cartesian and spherical models, which limit the suitability of Cartesian‐based studies: (a) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (b) the reduction of space with depth in spherical shells, alongside the radial gravity direction, which cannot be captured in Cartesian domains. Although Cartesian models generally predict comparable subduction regimes and slab morphologies to their spherical counterparts, there are significant quantitative discrepancies. We find that simulations in Cartesian domains that exceed Earth's dimensions overestimate trench retreat. Conversely, due to boundary effects, simulations in smaller Cartesian domains overestimate the variation of trench curvature driven by plate width. Importantly, spherical models consistently predict higher sinking velocities and a reduction in slab width with depth, particularly for wider subduction systems, enhancing along‐strike slab buckling and trench curvature. Results imply that sphericity must be considered for understanding the dynamics of Earth's wider subduction systems, and is already a significant factor for slabs of width 2,400 km.
Plain Language Summary
Subduction zones delineate tectonic plate boundaries where one plate descends beneath another into the underlying mantle. Subduction is responsible for many of Earth's most distinctive geological features, including mountain belts, volcanic island arcs, and deep sea trenches. It has long been recognized that the shape of subduction zones is influenced by Earth's sphericity, but sphericity's importance for other aspects of subduction dynamics remains unclear, as the majority of existing modeling studies have been carried out in (easier to simulate) rectangular computational domains. Here, using subduction models with viscosity laws appropriate to mimic plate‐like behavior, we compare predictions from rectangular and spherical models. We show that because rectangular models cannot capture the reduction in space with increasing depth, they consistently underestimate sinking velocities of the subducting plate, which determine how plate temperatures and strength evolve during sinking. Furthermore, the difference in flow patterns that develop in rectangular and spherical models changes how the subducting plates bend, buckle and migrate. Our models show that the discrepancy between Cartesian and spherical subduction models increases with plate width. Results imply a critical width of less than 2,400 km at which sphericity must be considered when simulating Earth's subduction systems.
Key Points
Cartesian models of free subduction are strongly affected by domain size and sidewall boundary conditions
The reduction in space with depth on a sphere induces buckling during slab descent, concentrating buoyancy and increasing sinking velocity
Spherical models are important for simulating Earth's subduction systems, particularly for wider slabs
Background
Laparoscopic sleeve gastrectomy (LSG) has been identified as an innovative surgical approach for the treatment of obesity and is increasingly applied worldwide. However, data on outcome of ...LSG regarding nutrient deficiencies, protein status, and body composition are scarce.
Methods
Obese subjects (54; f:m = 4:1) scheduled for LSG were included in this study. Micronutrient analysis, protein status assessment, and bioimpedance measures were performed before and 1, 3, 6, and 12 months after LSG.
Results
In 51% of the subjects, at least one micronutrient deficiency was found prior to surgery. Baseline concentrations were below normal for 25-OH vitamin D (27%), iron (29%), vitamin B6 (11%), vitamin B12 (9%), folate (6%), and potassium (7%). Frequencies of deficiencies for vitamin B12, folate, iron, and vitamin B6 tended to increase following LSG within the first year after intervention. Also, parameters of protein status (albumin, transferrin, cholinesterase, and total protein) decreased. After surgery, bioimpedance measures indicated a reduction of total body fat, but also of body cell mass.
Conclusions
Preoperative micronutrient deficiencies were common in morbid obese individuals scheduled for LSG. LSG had a modest effect on micronutrient status by further reducing iron, vitamin B12, vitamin B6, and folate within the first year after intervention. Our data suggest that especially obese patients with preoperative deficits require control and supplementation of micronutrients and protein in the postoperative period. ClinicalTrials.gov identifier: NCT01344525
A new two‐layer model for impulsive wave generation by deformable granular landslides is developed based upon a discontinuous Galerkin finite element discretization. Landslide motion is modeled using ...a depth‐averaged formulation for a shallow subaerial debris flow, which considers the bed curvature represented by the local slope angle variable and accounts for inter‐granular stresses using Coulomb friction. Wave generation and propagation are simulated with the three‐dimensional non‐hydrostatic coastal ocean model Thetis to accurately capture key features such as wave dispersion. Two different techniques are used in treating wetting and drying (WD) processes during the landslide displacement and wave generation, respectively. For the lower‐layer landslide motion across the dry bed a classical thin‐layer explicit WD method is implemented, while for the resulting free‐surface waves interacted with the moving landslide an implicit WD scheme is utilized to naturally circumvent the artificial pressure gradient problem which may appear in the dynamic interaction between the landslide and water if using the thin‐layer method. The two‐layer model is validated using a suite of test cases, with the resulting good agreement demonstrating its capability in describing both the complex behaviors of granular landslides from initiation to deposition, and the consequent wave generation and propagation.
Sketch of the two‐layer system with model parameters defined. The lower‐layer landslide motion is along the non‐erodible bottom b with the curvature represented by the local slope angle θ.
Abstract
Calibration of unknown model parameters is a common task in many ocean model applications. We present an adjoint‐based optimization of an unstructured mesh shallow water model for the Baltic ...Sea. Spatially varying bottom friction parameter is tuned to minimize the misfit with respect to tide gauge sea surface height (SSH) observations. A key benefit of adjoint‐based optimization is that computational cost does not depend on the number of unknown variables. Adjoint models are, however, typically very laborious to implement. In this work, we leverage a domain specific language framework in which the discrete adjoint model can be obtained automatically. The adjoint model is both exactly compatible with the discrete forward model and computationally efficient. A gradient‐based quasi‐Newton method is used to minimize the misfit. Optimizing spatially‐variable parameters is typically an under‐determined problem and can lead to over‐fitting. We employ Hessian‐based regularization to penalize the spatial curvature of the friction field to overcome this problem. The SSH dynamics in the Baltic Sea are simulated for a 3‐month period. Optimization of the bottom friction parameter results in significant improvement of the model performance. The results are especially encouraging in the complex Danish Straits region, highlighting the benefit of unstructured meshes. Domain specific language frameworks enable automated model analysis and provide easy access to adjoint modeling. Our application shows that this capability can be enabled with few efforts, and the optimization procedure is robust and computationally efficient.
Plain Language Summary
Ocean circulation models have several unknown parameters that must be tuned for each application in order to produce physically meaningful results. The tuning process can be a very laborious and time consuming task. In this paper, we investigate an automated way to tune the model's friction at the sea bed to minimize the model's error in predicted sea surface height (SSH). The method is based on a novel way of defining the model's equations which enables solving such optimization problems automatically. The methodology is tested in the Baltic Sea. The modeled SSH is compared against observations at several tide gauges. We show that by optimizing the bottom friction, the model's capability to predict SSH improves significantly. Moreover, we show that the optimization process is robust and computationally efficient.
Key Points
Adjoint‐based optimization is used to optimize bottom friction coefficient in 2D water elevation model for the Baltic Sea
The discrete adjoint model is automatically generated by leveraging a symbolic representation of the discrete forward model equations
The optimization method is robust and results in significant improvement in the sea surface height performance at tide gauge locations
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