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Contrasting roles of ground, trees, ponds and grazing in carbon dioxide, methane and nitrous oxide fluxes of an African semi-arid savanna
No full textInternational audienceUnderstanding greenhouse gas fluxes in semi-arid ecosystems is critical for improving our understanding ofbiogeochemical cycles, particularly in underrepresented regions like the African Sahel. In these landscapes,greenhouse gas exchange arises from ground, trees, and water ponds, and is further shaped by environmentalconditions and grazing. The carbon dioxide, methane, and nitrous oxide fluxes were quantified from thesecomponents in a Sahelian savanna in Senegal, while also assessing grazing impacts and environmental drivers(soil water content, temperature, vapor pressure deficit, photosynthetically active radiation). The ground was anet carbon dioxide sink during the rainy season but shifted toward neutrality or weak emission in the dry season,consistently acted as a methane sink, and was a year-round nitrous oxide source. Seasonal ponds were strongmethane and nitrous oxide emission hotspots, with methane emissions being high enough to offset the sink of theoverall savanna landscape. Trees contributed to carbon dioxide and methane uptake via branches, whereas stemswere net methane and carbon dioxide emitters. Both stems and branches emitted nitrous oxide, and the presenceof trees enhanced carbon dioxide, methane and nitrous oxide fluxes from soils beneath their canopies. Grazingenhanced ground gross primary production, reduced methane uptake, while no effect was seen on nitrous oxidefluxes. Temporal variability of carbon dioxide and nitrous oxide fluxes was strongly linked to soil water contentand temperature, whereas methane fluxes showed no correlations with any of the measured drivers. These resultsdemonstrate that tree- and pond-mediated fluxes, together with grazing, substantially alter the greenhouse gasfluxes of savanna ecosystems and incorporating these effects is essential for accurately representing semi-aridsavannas in global greenhouse gas budgets
Reconstructing the freshwater paleoecosystems diversity of Toros-Menalla (Late Miocene, Chad) from an integrated faunal perspective
No full textAquatic environments are critical components of past ecosystems that shaped species distribution and survival. Yet in hominin-bearing fossil sites, they are often treated as uniform or poorly detailed elements of “mosaic” landscapes, failing to capture their ecological complexity. In the northern Chad Basin, the late Miocene Toros-Menalla area records vast perilacustrine systems where aquatic and terrestrial ecosystems were deeply interconnected. While terrestrial vertebrate assemblages have been well characterised as reflecting a heterogeneous landscape, the aquatic component remains poorly resolved. Variations in depositional settings, aquatic vertebrate diversity, stable isotope data, and field observations point to a more complex and dynamic network of freshwater habitats. An integrative study of aquatic and semi-aquatic vertebrate assemblages from five Toros-Menalla sites reveals distinct faunal structures reflecting different ecological preferences and depositional conditions, ranging from perilacustrine floodplains to swampy, vegetated, or marginal waters and large open waterbodies with current. These environments, distributed across several hundreds of meters up to 30 km, represent lateral habitat diversity rather than temporal succession, as most assemblages formed geologically instantaneously (except for TM266, where vertical mixing could be hypothesised). Comparison with the present-day Bol Archipelago on the northeastern shores of Lake Chad provides a suitable analogue for the Toros-Menalla paleoenvironment. There, interdunal water bodies of varying depth and connectivity create a dynamic network of aquatic habitats at a similar spatial scale. This study underscores the need for systematic, grid-based collection and sieving of fossils to capture representative aquatic biodiversity and structure, and to reconstruct freshwater paleoenvironments with greater ecological precision
A Comprehensive Database of Leaf Temperature, Water, and CO 2 Fluxes in Young Oil Palm Plants Across Diverse Climate Scenarios
No full textData and code availability: The raw data and scripts used to generate the final database are detailed and accessible on Zenodo (Vezy et al., 2025), the code is also accessible via a Github repository (https://github.com/PalmStudio/Biophysics_database_palm), and we also provide a companion website (https://palmstudio.github.io/Biophysics_database_palm) showing how computations were made and the main results. The code to trigger the FLIR camera and for logging the precision scale data is also available on dedicated Zenodo repositories (Vezy, 2025a, 2025b).Functional-structural plant models (FSPM) replicate plants' responses to their environment and are useful for predicting behavior in a changing climate. However, they rely on detailed measurements of traits, which are difficult to collect consistently across scales, often limiting model parameterization and thorough evaluation, and thereby reducing confidence in model predictions.Here, we provided a comprehensive dataset of structural and biophysical measurements from four oil palm plants (Elaeis guinnensis) grown under multiple controlled environmental scenarios, including varying CO2 concentrations, light, temperature and humidity conditions. The dataset included detailed reconstructions of the three-dimensional plant structures derived from terrestrial LiDAR point clouds, and enabled the parametrization of biophysical processes at the leaf scale such as photosynthesis and stomatal conductance, as well as the collection of plant-scale measurements (gas exchange measurements of CO2 and H20), which can be compared with FSPM simulations. The tree-dimensional reconstructions effectively represented the architecture of the plants and showed strong correlation with the measured total leaf area. Hence, future comparisons between simulated and observed physiological traits could be used to evaluate the quality of the physiological formalisms independently. By bridging the scales from individual leaves to the entire plant, this database allows modellers to both calibrate their biophysical models at a fine spatial resolution and evaluate their predictive accuracy at the plant scale. The provided data will facilitate benchmarking of biophysical models, help identify sources of model uncertainty, and ultimately enhance model predictions, which can be applied in various fields, from cognitive studies to decision support applications
Domoic acid production by a Pseudo-nitzschia australis strain under zinc and copper exposure
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Short note: on the determination of the relaxation time distributions using Bézier curves
No full textInternational audienceFor the interpretation of spectral induced polarization spectra, the determination of the relaxation time distributions (RTD) can be useful, for instance to extract the grain size distribution. However, this is an ill-posed problem, and retrieving the RTD often requires regularization during the inversion process. In this note, we use Bézier curves and simulated annealing to determine the RTD. The procedure that does not require any regularization nor smoothing, by reducing the number of parameters thanks to Bézier curves which are intrinsically continuous and infinitely derivable. We successfully applied our methodology to three examples (Cole–Cole model, Davidson–Cole model, and an experimental spectrum), demonstrating its interest and efficiency
Evaluating Quercus pollen as a valuable archive of past UV-B levels in the Central Mediterranean: Insights from comparative infrared spectroscopy analyses
No full textInternational audienceThe relative abundance of ultraviolet-absorbing compounds (UACs) in pollen and spore exine increases with prolonged and higher exposure to ultraviolet B (UV-B) radiation. This relationship has been extensively studied via transmission Fourier-transform infrared microspectroscopy (transmission micro-FTIR), primarily in Lycopodium spores and airborne Pinus pollen. However, traditional transmission micro-FTIR methods are prone to infrared light scattering and interference, resulting in spectral deformations and reduced reproducibility. Additionally, bisaccate pollen, like Pinus, can travel long distances and may not accurately reflect local UV-B levels. This study compares transmission and attenuated total reflection (ATR) micro-FTIR methods to assess their reproducibility and investigates Quercus pollen as a potential local UV-B proxy in the Central Mediterranean. Samples containing fresh (in situ), trapped (in mosses), and fossilized (from Holocene sediments) pollen grains were subjected to various chemical treatments, after which the macromolecular composition of single and clustered grains was characterized. Results show that ATR micro-FTIR yields significantly more reproducible data than transmission micro-FTIR, demonstrating the suitability of this method for systematic chemo-palynological studies. Quercus ilex pollen consistently display UAC-related absorption bands across modern and fossil samples, and treatment with hydrochloric acid, hydrofluoric acid, and sodium hydroxide does not significantly alter these signatures. A comparison with fresh and trapped Q. cerris and Q. pubescens pollen further supports these findings. These results suggest that relative UAC concentrations in modern and fossil Quercus exine likely reflect accumulated UV-B dosage, pinpointing Quercus pollen as a valuable local UV-B proxy for reconstructing past UV-B levels in the Central Mediterranea
Cocaine use in Europe: the need for cross-sectoral collaboration between security, justice, health, and social systems
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Comment on “Influence of layer thickness on time domain Brillouin scattering oscillation amplitude in multilayer films” [J. Appl. Phys. 136, 225302 (2024)]
No full textInternational audiencePicosecond acoustics allows for the probing of multilayered nanometric structures, with applications in various fields of fundamental research. In a recent study, Zhang et al.1 have reexamined the optical cavity effect that impacts time-domain Brillouin acoustic spectroscopy (TDBS) in such systems. This interference phenomenon arises from Fabry–Pérot cavities formed by the parallel interfaces within the stack. This has long been modeled either through a general solution based on Green’s functions or via analytical expressions derived from standard Fresnel formulas. In their study, Zhang et al. examined the Brillouin signal in a series of amorphous SiO2 layers grown on a Si wafer and capped with a metal Al transducer. This configuration had been thoroughly investigated as part of a larger effort to study high-frequency acoustic losses in silica glass by Ayrinhac et al. in Ref. 2. However, when attempting to reproduce these results, Zhang et al. failed to achieve quantitative agreement with the calculated expectations, due to poorly characterized samples and likely inadequate data processing. We show that simple optical reflectance measurements combined with appropriate data normalization can, in fact, fully account for such observations
Surface ice texture mapping of Planpincieux glacier reveals spatial mechanical heterogeneities
No full textInternational audienceCrystallographic textures or Crystal Preferred Orientations (CPO) of glacier ice significantly influence its mechanical behavior by transferring mechanical anisotropy from the single-crystal scale to the macroscopic scale. However, their spatial variability and impact on fluidity remain poorly constrained in temperate glaciers. This study presents a detailed mapping of surface crystallographic textures on the Planpincieux Glacier (Mont Blanc Massif, Italy), combining field measurements, surface velocity data, and numerical modeling to assess mechanical heterogeneities. Six sampling zones were analyzed using an Automatic Ice Texture Analyser (AITA), revealing distinct crystallographic texture patterns linked to local strain configurations and boundary conditions. Weak crystallographic textures in zones near the glacier margins and crevasse areas suggest limited viscous deformation, while stronger crystallographic textures indicate deformation under various shear boundary conditions with impact of dynamic recrystallization. The resulting textures are associated with a fluidity enhancement factor reaching up to 2.3 and a fluidity anisotropy up to 5.4. These findings underscore the importance of integrating texture impact into glacier flow models, particularly in temperate environments where recrystallization and complex stress regimes prevail
StripesCounter: A new image software for increment measurement in paleoclimate archives
No full textInternational audienceMost natural paleoclimate archives are accretionary material presenting periodic structures that bear environmental and/or chronological information. Here we present StripesCounter, an open access Python software designed for automated banding detection and measurement. As a study case, 16-year long profiles of daily growth increment measurements were conducted on a modern shell of the giant clam Tridacna gigas. High resolution images of shell thin sections were obtained using a confocal laser scanning microscopy and processed using StripesCounter. We demonstrate that StripesCounter provides highly reproducible and accurate results. The long time series of daily increments indicate that Tridacna gigas growth is strongly modulated by seasonal oceanographic variations, reflecting changes in sea surface temperature, precipitation, and salinity. Notably, growth profiles reveal semi-annual variations related to semi-annual variations in environmental factors, potentially linked to ENSO events. This automated growth increment analysis can be extended to other archives with cyclic structures, including tree rings, corals, and other biogenic or abiotic laminated materials. StripesCounter offers a powerful and accessible tool for generating long high-resolution, temporally explicit datasets, opening new perspectives for investigating rapid environmental changes across diverse ecosystems and geological timescales