We develop a physics-informed neural network (PINN) to significantly augment state-of-the-art experimental data of stratified flows. A fully connected deep neural network is trained using experimental data in a salt-stratified inclined duct (SID) experiment. SID sustains a buoyancy-driven exchange flow for long time periods, much like an infinite gravity current. The data consist of time-resolved, three-component velocity fields and density fields measured simultaneously in three dimensions at Reynolds number= O(10^3) and at Prandtl or Schmidt number = 700 [1]. The PINN enforces incompressibility, the governing equations for momentum and buoyancy, and the boundary conditions at the duct walls. These physics-constrained, augmented data are output at an increased spatio-temporal resolution and demonstrate five key results: (i) the elimination of measurement noise; (ii) the correction of distortion caused by the scanning measurement technique; (iii) the identification of weak but dynamically important three-dimensional vortices of Holmboe waves; (iv) the revision of turbulent energy budgets and mixing efficiency; and (v) the prediction of the latent pressure field and its role in the observed asymmetric Holmboe wave dynamics. These results mark a significant step forward in furthering the reach of fluid mechanics experiments, especially in the context of stratified turbulence, where accurately computing three-dimensional gradients and resolving small scales remain enduring challenges.
References
[1] L. Zhu, X. Jiang, A. Lefauve, R. R. Kerswell, and P. F. Linden. New insights into experimental
stratified flows obtained through physics-informed neural networks. J. Fluid Mech., 981:R1, 2024.
How to cite: Lefauve, A., Zhu, L., Jiang, X., Kerswell, R., and Linden, P.: New insights into experimental stratified flows obtained through a physics-informed neural network, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18513, https://doi.org/10.5194/egusphere-egu25-18513, 2025.
In this contribution, we present 3D two-phase flow simulations of lock-release turbidity currents using sedFOAM. The Large Eddy Simulation is used for the turbulence modeling while the granular stresses are modeled using a frictional-collisional kinetic theory including interparticle friction (Chassagne et al., 2023). Simulations are performed for different bed slopes, initial volume fractions and particle diameter and density. The numerical results are compared with experiments in terms of front propagation and current shape (Gadal et al., 2023). The simulation results are further used to infer the mechanisms controlling the current attenuation, i.e. the current propagation speed reduction with time. We further use the model to analyse the influence of the flume geometry, free surface versus rigid roof.
How to cite: chauchat, J., sharma, M., Rastello, M., Bonamy, C., Gadal, C., Dossmann, Y., Mercier, M., and Lacaze, L.: 3D two-phase flow simulations of lock-release turbidity currents, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20195, https://doi.org/10.5194/egusphere-egu25-20195, 2025.
Buoyancy-driven flows play a fundamental role in shaping the dynamics of cryospheric aquatic systems, including ice-covered and proglacial lakes. These flows, driven by density contrasts resulting from variations in temperature, salinity, or meltwater input, regulate critical processes such as heat transport, nutrient distribution, and ice-ocean interactions. This study investigates the mechanisms underlying buoyancy-driven flows, their variability across diverse cryospheric settings, and their implications for heat and mass redistribution in aquatic systems. By integrating field observations, laboratory experiments, and numerical modeling, we explore the patterns of buoyancy-driven flows and their sensitivity to changing environmental conditions. Our findings emphasize the importance of convective dynamics and the nonlinear equation of state of water in governing heat exchange at solid-liquid interfaces, water column stratification, and localized mixing layers. This research enhances our understanding of fragile aquatic systems and provides new insights into the physics of the cryosphere.
How to cite: Ulloa, H. N., Estay, G., Wang, Z., and Noto, D.: Buoyancy-driven Flows in Cryospheric Aquatic Systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20409, https://doi.org/10.5194/egusphere-egu25-20409, 2025.
Temperature-induced density variations within fluids drive gravity-driven flows. Such flows occur for example in geophysical processes such as differential cooling or stratification dynamics in lakes. Heat transfer through the boundaries, whether in a lake or in a laboratory flume, can impact flows. The objective of this study is to evaluate numerically and experimentally the effect of these boundary conditions on thermal convective mixing in two different configurations. The first configuration is the thermal convective mixing in a box of water with cooled boundaries. The second configuration is a lock exchange gravity flow.
Numerical simulations were performed using OpenFOAM with a Large Eddy Simulation solver and the Boussinesq approximation for density effects. The sensitivity of the solution to different boundary conditions for heat transfer were analyzed. Experiments rely on an innovative phosphor thermometry technique able to measure spatial patterns of fluid temperature instead of common pointwise measurements. Notably, we introduce a novel approach that combines the use of a laser sheet and high-resolution CMOS sensors operated in a multi gate accumulation mode to extract the temperature pattern.
The choice of appropriate parameters in the boundary condition enabled the accurate representation of the temperature evolution and convective flow patterns observed in the experiments.
How to cite: Pons, M., Rousseau, G., Adelerhof, H., Carde, B., Giesbergen, M., Fond, B., Borisov, S., and Blanckaert, K.: A numerical and experimental investigation of the influence of heat transfer boundary conditions on convective mixing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4429, https://doi.org/10.5194/egusphere-egu25-4429, 2025.
The flow of a hyperpycnal river plume into a lake with an inclined bed and without any lateral confinement is a common occurrence in nature. A characteristic example of such geophysical fluid flow system is the one of sediment-laden dense river inflows in freshwater lakes (e.g. river Rhone - lake Geneva). In this case, the plunging process close to the river mouth, as well as its dependence on the properties of the inflow, affect critically the subsequent hydrodynamics in the lake. A better understanding of these flow processes is therefore significant for the effective management of the lake water quality and overall ecology. In this talk, we focus on the complex near-field plume dynamics and establish novel criteria for plunging, based on Large Eddy Simulations (LES) of an unconfined hyperpycnal saline plume over an idealized bed. More specifically, we focus on the effect of the variation of the inflow densimetric Froude number, Frd, which is the non-dimensional parameter describing the ratio between inertial and buoyancy forces acting on the plume. In particular, three simulations were performed at different values of Frd, within the range of values encountered in the plunging of river Rhone in lake Geneva. It is found that the near-field dynamics of the hyperpycnal plume is different in the unconfined plunging scenario compared to the case where the flow is confined by lateral walls and that it critically depends on Frd. Indeed, it is a well-established result that in the confined case the plunging of the hyperpycnal plume occurs at the location downstream where a balance between dynamic pressure forces (inertia) and the resisting hydrostatic pressure forces (gravity) is obtained. However, in absence of any lateral confinement the plunging begins immediately upon the entrance of the dense river water in the lake, due to lateral slumping. The slumping takes place at both lateral sides of the plume in the form of a collapse of the dense water column followed by a spread across the lake bottom that is very similar to a lock-release flow configuration. This results in an earlier departure of the plume from the lake surface in the unconfined case compared to the confined case under similar inflow conditions. We are able to determine the effect of Frd on the plunge curve, as well as the extend of the plunging zone on the lake bed, before the plume turns into a gravity current and continues its propagation down the slope. In addition, an explanation is provided for the field observations of surface leakage, where sediment-rich water is detected at the lake surface even downstream of the plunge curve. This explanation focuses on the effect of Frd on the dynamics of the turbulent mixing layers that develop at the interface between the incoming river water and the surrounding lake water. These mixing layers facilitate a substantial transfer of mass and momentum from the inflowing river water to the ambient lake water.
How to cite: Giamagas, G., Bonamy, C., Blanckaert, K., and Chauchat, J.: Near-field plunging dynamics of laterally unconfined hyperpycnal plumes over inclined beds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17770, https://doi.org/10.5194/egusphere-egu25-17770, 2025.
Hyperpycnal (denser) river inflows into lakes bring sediments, nutrients, oxygen and contaminants, which are crucial for the water quality. Due to the higher densities of hyperpycnal inflows, they abruptly descend toward the lake bottom upon entering the lake, a process called plunging, and subsequently continue flowing along the lake bottom as a gravity-driven underflow. This plunging is accompanied by mixing and entrainment of ambient lake waters, which causes dilution of the initial density excess of the river inflow. The mixing is parameterized by the plunging mixing coefficient Ep and is of critical importance as it conditions the fate and final destination of the contaminants carried by the river inflows. A recently proposed conceptual model (Thorez et al. 2024) for the plunging into an unconfined lake configuration highlights the importance of the lateral slumping motion of the river plume and secondary flow cells on each side of the plume with respect to the plunging mixing.
This study builds on previous research that suggests that Ep is affected by the geometry of the river mouth. We investigate with Particle Image Velocimetry (PIV) in laboratory experiments how the width-to-depth ratio at the river mouth (W0H−1) influences the plume hydrodynamics and Ep. Four different ratios, W0H−1 = 5.4, 9, 13.5 and 27, were investigated in a configuration that mimics the Rhône inflow into Lake Geneva. The laboratory experiments were performed in the Coriolis platform at LEGI (Laboratoire des Ecoulements Géophysiques et Industriels) at a scale of 1:60 that allows minimal scaling effect.
The distance of the plunge location from the river mouth, xp, and the corresponding depth, hp, were found to decrease with the aspect ratio. In addition, the size of the secondary flow cells on each side of the slumping river plume decreased with aspect ratio which tentatively explains the observed variations in Ep.
How to cite: Eze, K. O., Ammendola, A., Giamagas, G., Thorez, S., Negretti, E., Chauchat, J., and Blanckaert, K.: Effect of inflow channel aspect ratio on the plunging dynamics of an unconfined hyperpycnal plume over a sloping bed, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9640, https://doi.org/10.5194/egusphere-egu25-9640, 2025.
The dispersal of meltwater discharged from the St. Lawrence Valley is investigated from numerical experiments with a regional configuration of the MIT general circulation model representing the western North Atlantic during the last ice age. These experiments assume a horizontal resolution of 1/20o and a vertical grid with 21 levels in the upper 100 m, so that both the mesoscale eddy field and the vertical structure of the meltwater plume could be simulated in detail. Our goals are to identify possible mechanisms responsible for the offshore spreading of meltwater in the ocean during the deglaciation and to help the interpretation of paleoceanographic observations from the seafloor and sediment cores.
We find that meltwater discharged from the St. Lawrence Valley forms a buoyant plume which turns to the southwest along the continental slope under the action of the Coriolis force. Part of the meltwater is entrained away from the slope by meander crests and warm-core rings of the Gulf Stream (GS) between the St. Lawrence Valley and Cape Hatteras. The other part is diverted offshore by the opposing GS near Cape Hatteras, where the GS leaves the continental margin. In one experiment, meltwater is incorporated into a meander trough that pinches off and produces a cold-core ring, leading to meltwater transport into the subtropical gyre, or it flows southward along the slope inshore of the GS to the South Atlantic Bight. Sensitivity tests show that the buoyant plume spreads at a consistent rate of O(105 m2 s-1). A reduced-gravity two-layer model suggests that the spreading of the plume is governed by (i) the net ageostrophic motion produced by the total acceleration and the upwelling-favorable winds along the front of the plume and (ii) the advection of the front of the plume by the ambient geostrophic flow. In our experiments, meltwater in turn alters the upper part of the GS through meltwater-induced changes in cross-stream density gradients. Our results put constraints on the interpretation of ice-rafted debris found in (de)glacial sediments from the Sargasso Sea and of iceberg scours observed on the slope south of Cape Hatteras.
How to cite: Marchal, O. and Condron, A.: On the Spreading of Meltwater Plumes in the Ocean during the Last Deglaciation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2573, https://doi.org/10.5194/egusphere-egu25-2573, 2025.
The Mediterranean outflow from the Bosphorus advances through channels and delta features, reaching the shelf edge, spreading across the mid-shelf slope, and cascading down the steep continental slope. During the July 2024 cruise, intensive sampling along transects using CTD and Scanfish provided high-resolution data to better understand the pathways of the Mediterranean plume along the continental slope. This study explores the steering of Mediterranean streams through a complex channel network on the shelf, the evolution of distinct water properties—including dissolved oxygen content—and the eventual transition of the Mediterranean flow into neutrally buoyant layers.
To complement the observational data, the dynamics of the gravity current along the shelf-slope region of the Black Sea, characterized by anomalous temperature and oxygen levels were modeled. Model parameters were optimized and validated against the collected cruise data. These new hydrographic observations and modeling efforts shed light on the Mediterranean gradient flow's penetration into the Black Sea interior, advancing our understanding of its pathways and influence on regional water properties.
How to cite: Cokacar, T., Altıok, H., Yücel, M., and Örek, H.: Tracking the Mediterranean Outflow from the Bosphorus to the Continental Shelf Edge, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19603, https://doi.org/10.5194/egusphere-egu25-19603, 2025.
The Strait of Gibraltar is the site of a rich and complex physics where flows of different densities interact with a strongly rugged topography. These interactions produce many small-scale processes such as the development of hydraulic jumps, shear instabilities, internal solitary waves, which induce strong mixing and impact the Mediterranean outflow water masses. The dynamics of this gravity current emerging from the Strait and flowing along the canyons of the Gulf of Cadiz is conditioned by its prior evolution inside the Strait. In turn, this dense gravity current plays a crucial role on the large-scale oceanic circulation as it mixes with overlying North Atlantic waters thus modifying the properties of the deep-water masses and therefore, likely the regional and basin-scale circulations. Better understanding and describing these small-scale processes is essential to improve operational oceanic models and climate models since they occur below the grid scale of these models and therefore require parameterizations. Recently, the LEGI team has implemented a realistic setup of the Strait of Gibraltar with the adjacent Gulf of Cadiz and Alboran Sea on the Coriolis Platform at Grenoble, including the barotropic forcing (tide), the baroclinic one (lock-exchange), the Earth’s rotation and a realistic topography. The aim is to bring a better understanding of the small-scale physics which take place in this area. In addition to this experimental approach, centimetric resolution of hydrostatic and non-hydrostatic numerical simulations at the laboratory scale were carried out using the numerical code CROCO (Coastal and Regional Ocean COmmunity model – https://www.croco-ocean.org). A specificity of this code is to be able to efficiently resolve sub-mesoscale processes and to relax both the hydrostaticity and Boussinesq assumptions using a non-hydrostatic and compressible Navier-Stokes solver. The purpose of this numerical approach is manifold: explore ranges of parameters that could not be studied experimentally, develop diagnostic tools, investigate the impact of non-hydrostatic effects, evaluate numerical schemes and parameterizations, investigate more specifically each physical process. However, setting up such a realistic numerical configuration is challenging. For example, if we are interested in the purely barotropic forcing, it is essential to represent the tidal forcing identically as in the experiment. Likewise, when we focus on the purely baroclinic forcing, the inherent steep slopes related to the experimental setup put strong constraints on the numerical code. From these numerical simulations, non-hydrostatic effects on the gravity current dynamics are estimated and analyzed at the laboratory scale. They significantly modify hydraulic jumps formation, overflow transport and deep waters circulation in the Gulf of Cadiz. Boundary conditions, vertical resolution, explicit and implicit vertical mixing or viscous effects are all numerical factors that influence gravity current dynamics. All these features must be carefully studied since they impact both the fate of the Mediterranean waters when they flow into the Atlantic Ocean and the fate of the Atlantic waters flowing into de Mediterranean basin. The aim of this presentation is to present the work carried out up to date in the development of these numerical configurations and to present the associated preliminary results.
How to cite: Gouhier, B., Bordois, L., Auclair, F., Nguyen, C., Tassigny, A., Bardoel, S., Gostiaux, L., and Negretti, M. E.: Towards a numerical configuration of the Strait of Gibraltar at the laboratory scale: The HERCULES project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18582, https://doi.org/10.5194/egusphere-egu25-18582, 2025.
Understanding small-scale turbulent mixing in the ocean is fundamental for accurately modeling oceanic processes, predicting currents, and managing marine ecosystems. Global and regional ocean models rely on parameterizing turbulent mixing, yet this remains a significant source of uncertainty due to technical constraints and model-specific empirical assumptions. Furthermore, when coupled with biogeochemical models, a uniform mixing parameterization is typically applied to all tracers, overlooking the distinct properties of each. This study investigates the influence of turbulent mixing on macroscopic scales and examines the role of molecular diffusion coefficients, which are intrinsically the only irreversible processes affecting passive tracers. Using the CROCO model in a non-hydrostatic, compressible configuration, we conduct direct 3D numerical simulations of turbulence and mixing driven by Kelvin-Helmholtz instabilities. The analysis is based on tracking the properties of fluid particles in a tracer-density space and calculating an effective diffusion coefficient to quantify how fine-scale mixing impacts larger scales redistribution of tracer. The macroscopic scale is associated with the adiabatic rearrangement of the 3D density field into a stable 1D profile, following Lorenz rearrangement. The evolution of these 1D profiles, which only occurs during irreversible mixing, forms the basis for calculating the effective diffusion coefficient. Both theoretical considerations and numerical results in simplified configurations demonstrate that when the molecular diffusion coefficients for tracers and density are equal, the macroscopic effective diffusivity deduced from the density field can be applied to the passive tracer. To evaluate this principle of equality of macroscopic diffusivity, we conduct an experimental study of a gravity current in a large tank (3x0.15x0.2 meters) using a dual light attenuation technique to simultaneously observe the density and passive tracer fields. The same domain is simulated in the numerical model, enabling direct comparisons of mixing dynamics between experimental and numerical gravity currents. Results highlight the critical role of transverse instabilities in driving irreversible mixing. The latter locally modify mixing at macroscopic scale and possibly alter the equality principle.
How to cite: Andrieux, M., Morel, Y., Auclair, F., Dossmann, Y., Penney, J., and Haynes, P.: Mixing of tracers in stratified sheared flows , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17431, https://doi.org/10.5194/egusphere-egu25-17431, 2025.
This study analyzes turbidity currents across multiple systems using high-resolution oceanographic datasets and laboratory experiments. By comparing velocity trends throughout the turbidity currents, we identify two end-member types: short surge flows where peak velocity is followed by rapid decay in velocity and sustained flows where peak velocity is followed by a prolonged near constant velocity. Variability is explored across key parameters, including trigger, system type, slope, grain size, and distance offshore. The findings demonstrate that no single parameter explains all observed variations, with only grain size and distance offshore showing some degree of correlation with the type. Improved data quality, particularly on grain size variability within systems and individual flows, will be essential to understand the different types of flows and their relative process.
How to cite: Vendettuoli, D., Cartigny, M. J. B., Clare, M. A., Sumner, E. J., Talling, P. J., Blanckaert, K., Azpiroz–Zabala, M., Paull, C. K., Gwiazda, R., Xu, J. P., Stacey, C., Lintern, G. D., Simmons, S., Pope, E. L., Bailey, L. P., and Wood, J.: What controls the structure of turbidity currents?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4294, https://doi.org/10.5194/egusphere-egu25-4294, 2025.
How to cite: Rousseau, G., Pons, M., Adelerhof, H., Giesbergen, M., Carde, B., Fond, B., Borisov, S., and Blanckaert, K.: Temperature imaging of buoyancy-driven flows using lifetime-based laser-induced phosphorescence of particles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21856, https://doi.org/10.5194/egusphere-egu25-21856, 2025.
Hyperpycnal (negatively buoyant) river inflows into lakes or reservoirs plunge upon entry, generating gravity-driven underflows near the bed. When the density excess of these underflows is primarily due to high sediment concentrations, they are referred to as turbidity currents. If these underflows encounter a layer of equal density, they will detach from the bed and intrude into the water column, forming an interflow. In turbidity currents, such underflow-interflow transitions often happen through a process called ‘lofting’, whereby a flow that is initially negatively buoyant undergoes a buoyancy reversal due to sedimentation of particles. Direct observations of lofting are sparse, particularly in the field. As turbidity currents transport various constituents – not only sediment, but also contaminants, nutrients, and oxygen – originating from the river or eroded from the bed, their trajectory and final destination significantly influence the water quality of lakes and reservoirs. The latter highlights the importance of studying flow transitions such as lofting.
Field measurements of the turbidity current fed by the plunging Rhône River in Lake Geneva were conducted using a boat-towed ADCP along a grid of transects. The ADCP backscatter signal was used to achieve a first order estimate for the sediment concentration.
The measured velocity field reveals that in the longitudinal direction the Rhône River turbidity current initially breaks through the Lake Geneva pycnocline, detaches from the bed, rises vertically and intrudes into the pycnocline. Additionally, in the transverse direction the outermost parts of the current peel off and similarly rise and intrude into the pycnocline. This infers the presence of lofting in both longitudinal and transverse direction. In man-made dammed-river reservoirs, river valley walls provide a high degree of transverse confinement for turbidity currents, which might suppress the development of flow processes in transverse direction, such as transverse lofting. In most natural lakes, such confinement is not present. This infers a potentially significantly different underflow-interflow transition mechanism and resulting morphological impact between reservoir and lake settings.
The estimated sediment concentrations uncover a capacity of the lofting current to transport sediment-rich water away from the turbidity current centerline in transverse direction. This might influence the local bathymetry and support levee-building.
How to cite: Thorez, S., Lemmin, U., Barry, D. A., and Blanckaert, K.: Hydro-sedimentary processes of a lofting turbidity current revealed by gridded ADCP measurements in the field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8865, https://doi.org/10.5194/egusphere-egu25-8865, 2025.
This study explores the transformation processes and energy dissipation of internal solitary waves (ISWs) in the Arctic Ocean under varying ice keel geometries. Using a nonhydrostatic numerical model based on Reynolds-averaged Navier–Stokes equations under the Boussinesq approximation, we simulate the interaction of ISWs with groups of ice keels characterized by different configurations. The computational domain represents a simplified 2D stratified fluid with an idealized vertical density profile mimicking summer conditions on the Yermak Plateau. The ice keel geometries were parameterized using the Versoria function. The experiments involved ISWs with an amplitude of 20 m interacting with groups of ice keels characterized by varying numbers and lengths.The shapes of the ice keels were designed with common envelopes of differing heights and lengths, incorporating configurations with varying numbers of keels (1, 7, and 13).This approach allows for systematic and consistent comparisons of their effects on wave dynamics, energy dissipation, and the resulting mixing processes within the ocean's stratified layers. These shapes closely approximate the geometry of ice keels studied in the MOSAiC project, which provided valuable observational data and insights into the physical processes governing wave-ice interactions in the polar environment [1].
Key findings indicate significant energy dissipation for ISWs propagating through ice keel fields, with greater losses observed for larger numbers of keels. The highest energy dissipation occurred in cases with 13 keels due to increased reflections and turbulent mixing. Additionally, the interaction of ISWs with multiple keels enhances mixing in the stratified ocean layer beneath the ice. Variations in keel geometry and number intensify turbulence, contributing to a more complex wave field. Furthermore, these interactions generate second-mode internal waves that interact with first-mode waves and other second-mode waves, further intensifying energy dissipation and wave transformation. This mode-mode interaction creates a dynamic wave environment, emphasizing the role of keel morphology in polar ocean mixing.
These findings highlight the importance of ice keel geometry in modulating ISW dynamics and their contribution to upper ocean mixing processes. The study offers valuable insights into wave-ice interactions and their implications for Polar Ocean dynamics, with broader applications for understanding polar mixing processes and their influence on global ocean circulation.
[1] Nicolaus, Marcel & Perovich, Donald & Spreen, Gunnar & Granskog, Mats & von Albedyll, Luisa & Angelopoulos, Michael & Anhaus, Philipp & Arndt, Stefanie & Bünger, H. Jakob & Bessonov, Vladimir & Birnbaum, Gerit & Brauchle, Joerg & Calmer, Radiance & Cardellach, Estel & Cheng, Bin & Clemens-Sewall, David & Dadic, R. & Damm, Ellen & Boer, Gijs & Wendisch, Manfred. (2022). Overview of the MOSAiC expedition: Snow and sea ice. Elem Sci Anth. 10. 10.1525/elementa.2021.000046.
How to cite: Terletska, K., Maderіch, V., and Urbancic, G.: Impact of Ice Keel Geometry on Internal Solitary Wave Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3131, https://doi.org/10.5194/egusphere-egu25-3131, 2025.
Gravity currents, driven by density variations caused by gradients in temperature, salinity, or sediment concentration, arise due to hydrostatic imbalances between adjacent fluids. These flows play a pivotal role in a wide range of geophysical and engineering applications, shaping atmospheric, terrestrial, and subaqueous environments. In natural settings, the propagation of gravity currents often encounters uneven topographies, where the dynamics of the dense flow are significantly influenced by topographic features. Recent research has increasingly focused on understanding gravity currents moving through channels obstructed by finite-size patches of obstacles, which adds complexity to their behavior and mixing processes. This experimental study investigates the interaction mechanisms between gravity currents and such obstructions, providing insights into their dynamics and mixing implications through a non-intrusive image analysis technique based on light reflection to evaluate instantaneous density fields.
Laboratory experiments were conducted in a Perspex tank with dimensions of 3 m in length, 0.3 m in height, and 0.2 m in width. An array of rigid plastic cylinders, each with a diameter of 2.5 cm, was placed at a predetermined location spanning the entire width of the channel. The gravity current was reproduced using the lock-release technique with a density difference ∆ρ=6 kg/m³. A total of 12 full-depth lock-exchange experiments were performed to analyze the submergence ratio, i.e. the ratio between the initial current depth and the obstacle height, and the gap-spacing ratio, i.e. the ratio between the spacing of the bottom obstacles and the obstacle height.
The analysis of instantaneous density fields provides valuable insights into the complex dynamics of gravity currents. During the initial slumping phase, the front of the dense current advances at a constant velocity. However, upon reaching the obstacles, the gravity current slows down, leading to the emergence of distinct flow regimes. The evaluation of the density fields enabled a more detailed description of the flow evolution. It was observed that the front of the dense current detaches from the upstream face of each obstacle. In particular, the temporal and spatial evolution of the dimensionless depth-averaged density obtained by integrating the instantaneous density fields below a threshold of 2% excess density revealed significant phenomena near the current front. This region exhibited increased mixing and dilution as the ratio between the initial current depth and the obstacle height increased. Conversely, the influence of the spacing between the bottom obstacles appeared to be less significant.
How to cite: Adduce, C., Maggi, M. R., and Di Lollo, G.: Gravity currents interacting with bottom large-scale roughness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4480, https://doi.org/10.5194/egusphere-egu25-4480, 2025.
Turbidity currents represent a distinctive type of subaqueous density currents, characterized by a density excess that is due to the sediment load. Turbidity currents are important in lakes, reservoirs and oceans and have implications on hazard management, reservoir sedimentation and water quality. The existence of turbidity currents has been inferred in the 19th century from the existence of canyons on lake bottoms and in the 20th century from successive cable breaks of telecommunication cables on the ocean floor. From the 1990s on, Acoustic Doppler Current Profiler’s (ADCP) have allowed measuring vertical profiles of the velocity in turbidity currents. Most measurements were made in oceanic environments, however, and detailed measurements in lakes remain very scarce.
This study reports field measurements of turbidity currents in Lake Geneva, Switzerland, performed in 2016, 2017, 2018 and 2022. The measurements cover a broad range of control parameters and include an entire hydrological year. Additional data were obtained from simultaneous measurements with high-resolution thermistors in vertical profiles or along the lake bottom.
A total of twenty one turbidity current events were identified over the measurement period. For each event, characteristics such as the average and maximum flow velocity, the height, the duration and the dispatched volume of water were extracted from the ADCP velocity record. In addition, the suspended sediment concentration was estimated from the ADCP backscatter record and yielded estimations of the dispatched sediment volume.
The twenty one turbidity currents can essentially be separated in three classes: strong short-term events with velocities above 1 m s-1 that last up to approximately 24 hours, weak long-term events with velocities below 0.3 m s-1 that last several days, and weak short-term events with velocities below 1 m s-1 that last less than 12 hours.
How to cite: Zhang, X., Thorez, S., Barry, D. A., Lemmin, U., and Blanckaert, K.: Characteristics of turbidity current events in Lake Geneva, Switzerland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9181, https://doi.org/10.5194/egusphere-egu25-9181, 2025.
Diamantina Fracture Zone in the SE Indian Ocean is one of the less unexplored hadal zones (>6000 m) of our planet without human visits until recently. This study incorporates shallow sediments, submarine videos, and multibeam bathymetry data at a wide range of water depth and geomorphology to fully assess the sediment dynamics of the Diamantina Fracture Zone and their major causative factors. Grain size and organic geochemical analyses confirmed a primary marine source. Australian terrigenous input was indicated by an increasing silty contribution to the eastern hadal section of the fracture zone. Importantly, in the western to middle section, angular volcanic-rich sediments with a peak at 200-300 μm covered the underlying fine pelagic sediments and calcareous oozes, which were likely initiated during the Last Glacial Maximum. Susceptibility to slope failure was high due to localized topographical constraints, rather than earthquakes. The occurrence of sediment ripples at the west and densely-covered manganese nodules at the east implied the ocean bottom circulation with increasing current intensity, which also enhanced the possibility of the gravity-driven slope deposition. This research provides the first knowledge of the highly spatial heterogeneity of sediment dynamics in the remote deep Indian Ocean where continuous but fluctuating downslope and alongslope processes were developed.
How to cite: Yang, X., Huang, X., Zhang, H., and Peng, X.: Seafloor dynamics: sediment-ocean interactions in the Diamantina Fracture Zone (SE Indian Ocean), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9685, https://doi.org/10.5194/egusphere-egu25-9685, 2025.
The South China Sea (SCS) is one of the largest marginal seas on Earth, located at the convergence of the Eurasian, Pacific, and Indo-Australian plates. The basin formed through seafloor spreading during the Oligocene to Middle Miocene and has since been undergoing eastward subduction beneath the Philippine Sea Plate. This process has led to the gradual enclosure of the SCS since the Late Miocene. The region's dynamic tectonic setting, coupled with a tropical typhoon-prone climate, has contributed to the formation of numerous supercritical turbidity current (TC) bedforms within the SCS.
Supercritical bedforms have been documented at more than 20 sites in the SCS, including bedform trains found along canyon/channel thalwegs, as well as bedform fields in unconfined environments like levees, overbank or interfluvial areas, and fans at canyon mouths. The bedform trains along thalwegs typically consist of 5-19 bedforms and vary in length from a few kilometers to ~100 km. The unconfined bedform fields may contain several to over 30 rows of bedforms, covering areas ranging from 176 to 20,000 km². Both the confined and unconfined bedforms are considered supercritical based on their diagnostic morpho-depositional characteristics, including upslope migration, and backset dominant bedding, and erosional truncations on the lee side. The turbidite-dominated sediment components, crest orientation parallel to local isobaths, and their occurrence in canyons/channels and related environments, all suggest formation by TC rather than contour or other bottom currents.
Individual supercritical bedforms in the SCS can be identified as one of the two end members: cyclic steps and antidunes. Cyclic steps show upslope or downslope asymmetry, step-like morphology, and typical downstream-thinning backsets. Antidunes have symmetrical cross-sections, convex-upward structures, downstream-thickening backsets, and, when occurring with cyclic steps, smaller dimensions and aspect ratios. Occasionally, antidunes are superimposed on the stoss side of cyclic steps, identified as chutes-and-pools, representing a transitional type between antidunes and cyclic steps. Both confined and unconfined bedforms exhibit a wide range of wavelengths and wave heights, varying from smaller bedforms with wavelengths of 200-300 m and wave heights of several meters, to larger bedforms with wavelengths typically in the range of kilometers and wave heights reaching tens of meters or more. Confined bedforms are dominated by erosional to partially depositional cyclic steps, or by partially depositional antidunes. Unconfined bedforms are predominantly composed of fully to partially depositional cyclic steps and antidunes, with erosional cyclic steps and chutes-and-pools forming locally. In both cases, depositional bedforms are the most prevalent, likely due to high sedimentation rates resulting from the combined effects of rapid post-rift subsidence and ample sediment supply in the SCS. The widespread presence of supercritical bedforms highlights the important role that supercritical TCs play in SCS’s deep-water sedimentation.
This work was supported by the National Key Research and Development Program of China (2022YFF0800503) and the National Natural Science Foundation of China (91028003, 41676029, and 41876049).
How to cite: Zhong, G.: Supercritical turbidity-current bedforms in the South China Sea: An overview, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10010, https://doi.org/10.5194/egusphere-egu25-10010, 2025.
