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Quantifying Tidal Dune Morphodynamics at the Laboratory Scale: A Combined Measuring and Modelling Approach
No full textInternational audienceUnderstanding the morphodynamics of tidal dunes is essential for improving predictions of sediment transport and seabed evolution in coastal and estuarine environments. This study advances our understanding through a combined experimental and numerical investigation into the short-term morphodynamic evolution of laboratory-scale tidal dunes under controlled conditions.Building on earlier flume experiments examining hydrodynamic interactions of reversing currents with fixed-bottom, sand-coated asymmetric compound dunes, we incorporated a cm-thick layer of unimodal sediment over the rigid dune models to simulate mobile-bed conditions. High-resolution Particle Image Velocimetry (PIV) was employed to capture detailed spatial and temporal dynamics of turbulent flows and the concurrent evolution of dune surfaces.Complementary numerical modelling utilised the oceanographic circulation model CROCO, incorporating its non-hydrostatic solver and the USGS sediment transport module. The lab-scale model application was calibrated and validated against the laboratory measurements, demonstrating exceptional agreement in the short-term evolution of dune morphology. Key findings include the accurate replication of observed boundary layer dynamics, sediment transport mechanisms, and morphodynamic changes under reversing tidal currents. These experiments establish a solid benchmark for validating non-hydrostatic models of tidal dune morphodynamics.This work underscores the transformative potential of integrating detailed physical experiments with advanced numerical models to refine our predictive capabilities for morphodynamic processes in tidal environments. The insights gained are particularly significant for coastal engineering and seabed mobility studies, with direct applications to the design and optimisation of offshore wind farm infrastructures
Modèles 3D multi-scalaires, lasergrammétriques et photogrammétriques, de sites ornés du massif de l’Erongo (Namibie, Afrique australe)
No full textInternational audienceLe nord du massif de l’Erongo (Namibie, Afrique australe) présente plusieurs sites ornés de premier ordre, dont l’étude nécessite une mise en contexte géomorphologique. Les granites et granodiorites du Crétacé affleurent sous forme de longues croupes et de chaos de blocs formant des abris dans lesquels se trouve l’art pariétal, ainsi que des séquences d’occupations humaines datant au moins de la fin du Pléistocène. Dans le cadre du projet ANR Cosmo-Art (ANR-21-CE27-0011 ; https://cosmo-art.org/), l’analyse des parois ornées et du contexte des chaos de blocs a motivé le déploiement d’une méthode de relevés 3D rapide et adaptée à ces environnements singuliers. A l’échelle du site (pluri-hectométrique), les relevés sont conduits par photogrammétrie avec un drone Mavic 2 pro. A l’échelle du chaos (pluri-décamétrique), les relevés sont réalisés avec un lidar terrestre Faro Focus 3D. Enfin, à l’échelle de la paroi (pluri-métrique), les relevés sont conduits par photogrammétrie avec un APN plein format. En combinant ces méthodes de numérisation, nous abordons les sites de façon multiscalaire tout en profitant de l’intérêt particulier que chacune apporte : couverture large et référencement simplifié avec le drone, justesse géométrique avec le lidar terrestre, haute résolution avec la photogrammétrie sur paroi. Avec cette approche, un site peut être relevé en une ou deux journées avec deux opérateurs. Plusieurs procédés et plusieurs logiciels d’assemblage et de consolidation sont ensuite testés (Register, Cyclone 3DR, Metashape, Cloud-Compare, Reality Capture…). Quatre sites ont déjà été traités, livrant une documentation homogène pour les analyses archéologiques et les études géomorphologiques : Ekuta, Leopard Cave, Fäckelträger et Seal Rock Shelter
Bats as bioindicators of environmental levels of heavy metals and legacy organic contaminants through non-invasive approaches
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Seamless nearshore topo-bathymetry reconstruction from lidar scanners: A Proof-of-Concept based on a dedicated field experiment at Duck, NC
No full textInternational audienceAccurate observations of the nearshore bathymetry, including within the breaking wave region, are critical for the prediction of coastal hazards, and improved understanding of sandy beach morphological response to storms. In this paper, we implement the recent Boussinesq theory-based depth inversion methodology of Martins et al. (Geophys. Res. Lett., 50 (2023), Article e2022GL100498) to single-and multibeam lidar datasets collected during a dedicated field experiment on a sandy Atlantic Ocean beach near Duck, North Carolina. Compared with common approaches based on passive remote sensing technology (e.g., optical imagery), lidar scanners present several key advantages, including the capacity to directly measure the beach topography, waveforms and the cross-shore variations in mean water levels due to wave action (e.g., the wave setup), leading to the seamless reconstruction of a vertically-referenced beach topo-bathymetry. Given the potentially gappy nature of lidar data, particular attention is paid to the robust computation of surface elevation spectral and bispectral quantities, which are at the base of the proposed non-linear depth inversion methodology. Promising results on the final topo/bathymetry are obtained under contrasting wave conditions in terms of non-linearity and peak period, with an overall root-mean square error below 0.3 m obtained along a cross-shore transect covering both shoaling and breaking wave conditions. The accuracy of the final bathymetry in the shoaling and outer surf regions is generally found to be excellent, with similar skills as previously obtained in laboratory settings (relative error < 10 -15%). Under the most energetic conditions, an underestimation of the wave phase velocity spectra is observed within the surf zone with all theoretical frameworks, potentially owing to surf zone vortical motions not yet accounted for in the present methodology. This underestimation of the wave phase velocities results in a relatively large overestimation of the mean water depth, between 30% to 100% depending on the theoretical framework. With the methodology described herein, lidars bring new perspectives for seamlessly mapping the nearshore topo/bathymetry, and its temporal evolution across a wide range of scales. Although currently limited to a single cross-shore transect, we believe that opportunities exist to integrate multiple remote sensors, which could address individual sensor limitations, such as coverage (lidar) or the incapacity to directly measure waveforms (optical imagery).</div
Experimental evidence that soil fauna drives plant root exudation patterns
No full textInternational audienceSoil fauna is an essential component of soil. However, its influences on root exudates are unknown. Through both direct and indirect interactions, soil fauna can affect the dynamics of interactions between plants, microbes, and soil environments. In this study, we used an original approach called EcoRoots, which features rhizoboxes with sorption traps and allows exudates on roots to be sampled with minimum soil and plant disturbance. We designed an experiment to determine the effect of springtails (Folsomia candida W.), earthworms (Lumbricus terrestris L.), or both on plant root metabolites of Poa annua L., a gramineous species. After nine weeks of experiments, soil fauna increased the nutrients in soil, but P. annua growth was reduced mainly in the presence of earthworms. With regard to P. annua exudation, we found specific assemblages depending on the fauna identity, with the interaction between springtails and earthworms bringing different exudates than the sum of the two single treatments. Plants in presence of soil faunal groups produced a higher richness of exudate metabolite than without soil fauna. We also found that earthworms had the greatest influence on metabolite patterns. The changes in root exudation were associated with differences in abiotic factors and microorganism communities, suggesting that both direct and indirect effects might explain these patterns. Nevertheless, distinguishing the mechanisms involved in the process remains complex. To conclude, we strongly recommend studying living soil or more real ecosystems to advance our understanding of root exudation and, more globally, soil interactions and ecology, whether in natural or agricultural ecosystems
A South American sebecid from the Miocene of Hispaniola documents the presence of apex predators in early West Indies ecosystems
No full textInternational audienceAbsence of terrestrial apex predators on oceanic islands lead to the evolution of endemic secondary apex predators like birds, snakes, and crocodiles and loss of defense mechanisms among species. These patterns are well documented in modern and Quaternary terrestrial communities of the West Indies, suggesting that biodiversity there assembled similarly throughoverwater dispersal. Here, we describe fossils of a terrestrial apex predator, a sebecid crocodyliform with South American origins from the late Neogene of Hispaniola that challenge this scenario. These fossils, along with other putative sebecid specimens from Cuba and Puerto Rico, show that deep-time Caribbean ecosystems more closely resembled coeval localities in SouthAmerican than those of today. We argue that Plio-Pleistocene extinction of apex predators in the West Indies resulted in mesopredator release and other evolutionary patterns traditionally observed on oceanic islands. Adaptations to a terrestrial lifestyle documented for sebecids and the chronology of West Indian fossils strongly suggest that they reached the islands in the Eocene-Oligocene through transient land connections with South America or island hopping. Furthermore, sebecids persisted in the West Indies for at least five million years after their extinction in South America, preserving the last populations of notosuchians yet recovered from the fossil record
Impact of leaf area index assimilation and gauge-corrected precipitation on land surface variables in LDAS-Monde: a case study over China
No full textInternational audienceA global land data assimilation system (LDAS-Monde) forced by the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis is used to simulate land surface variables (LSVs) over China from 1979 to 2019 at a spatial resolution of 0.25 degrees. LDAS-Monde is coupled with the CNRM version of the Total Runoff Integrating Pathways (CTRIP) to convert runoff into streamflow simulations. Four experiments are conducted, with and without assimilating satellite derived leaf area index (LAI) observations, with and without gauge-corrected ERA5 precipitation. Four independent reference datasets are used to assess the impact of different model setups over contrasting climate zones and land cover types. LAI assimilation tends to reduce simulated LAI, evapotranspiration (ET) and gross primary production (GPP), and increase soil moisture (SM) and streamflow. Over semi-arid areas, the corrected precipitation is generally larger than the original ERA5, leading to increased ET, SM and streamflow. Meanwhile, the overestimation of precipitation in relatively humid regions is significantly reduced, leading to a decrease in ET, SM and streamflow. Overall, LAI assimilation alone shows a general improvement for all LSVs, including GPP and ET fluxes, over regions with dense vegetation cover, but degrades streamflow. Precipitation correction shows a general improvement for all LSVs, especially for water-related LSVs (SM and river discharge), but shows little improvement for ET. The impact of LAI assimilation and precipitation correction is more pronounced over agricultural areas in southeastern China, where a wet bias of ERA5 is observed. Except for ET, the combination of LAI assimilation and precipitation correction performs best among all experiments
Reviews and syntheses: Best practices for the application of marine GDGTs as proxy for paleotemperatures: sampling, processing, analyses, interpretation, and archiving protocols
No full textMarine glycerol dialkyl glycerol tetraethers (GDGTs) are used in various proxies (such as TEX86) to reconstruct past ocean temperatures. Over 20 years of improvements in GDGT sample processing, analytical techniques, data interpretation and our understanding of proxy functioning have led to the collective development of a set of best practices in all these areas. Further, the importance of Open Science in research has increased the emphasis on the systematic documentation of data generation, reporting and archiving processes for optimal reusability of data. In this paper, we provide protocols and best practices for obtaining, interpreting and presenting GDGT data (with a focus on marine GDGTs), from sampling to data archiving. The purpose of this paper is to optimize inter-laboratory comparability of GDGT data, and to ensure published data follows modern open access principles
Idealized modeling of stratospheric aerosol injection deployment scenarios with two uncooperative actors
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Subduction‐Related Volcanic Activity as a Proxy for Global Subduction Flux Over the Past Billion Years, and Its Correlation With Geomagnetic Superchrons
No full textInternational audienceWe investigate the frequency of subduction‐related volcanic events over the past billion years. Our analysis reveals distinct peaks and troughs interpreted as significant fluctuations in global subduction flux. This approach has the advantage of being independent of paleogeographic reconstructions. However, it does not provide information on the spatial distribution of thermal heterogeneities at the core‐mantle boundary. This likely explains why the long‐term evolution of global subduction flux does not correlate in any simple way with the frequency of geomagnetic polarity reversals throughout the Phanerozoic. As an additional parameter, we suggest focusing on how variations in the Earth's inertia, due to changing subduction configurations over time, influence the thermal conditions at the core‐mantle boundary and, consequently, the magnetic reversal frequency