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Magma Paths of the Karthala and La Grille Volcanoes (Grande Comore) Revisited: New Evidence From Geomorphology and Geochemistry
No full textInternational audienceGrande Comore, the westernmost island within the Madagascar Comoros Volcanic (MCV) chain, hosts two juxtaposed basaltic volcanoes, Karthala and La Grille, with contrasting lava geochemical signatures and eruption frequencies. Their formation and dynamics have been explained either by a mantle plume or, more recently, as part of a transtensional volcano-tectonic system. Understanding their individual development is key to resolving persistent geodynamic contradictions within the Comoros and improving volcanic hazard assessment. We integrate the morphology and spatial distribution of scoria cones with a new database of lava, and, for the first time, tephra compositions to constrain magma pathways. We classify cone-dense regions into four main clusters (SGC, KAR, CGC, and LAG) and four sub-clusters (KARa, KARb, KARc, and LAGa). Within Karthala, cone size weakly correlates with primitive mafic magma compositions, whereas no such relationship occurs at La Grille clusters. This indicates a developed, shallow plumbing system beneath Karthala and its absence beneath La Grille. Cone base orientation reveals that Karthala and La Grille volcanism is influenced by regional rifting, but only Karthala is influenced by edifice loading. Edifice-induced compositional filtering promotes lateral migration of primitive magmas and vertical ascent of evolved magmas, while regionally controlled rift zones channel evolved magmas to the center of the island. Recent eruption convergence/resurgence cycles suggest that future eruptions at Karthala will likely be constrained to the edifice of Karthala while La Grille's rare eruptions have only tectonic triggers. Active areas on Grande Comore are thus well constrained and more widespread than previously thought.Plain Language Summary Grande Comore, a volcanic island in the Mozambique Channel, consists of two volcanoes: Karthala, which erupts frequently, and La Grille, which erupts infrequently. These volcanoes are additionally contrasted in compositional-and morphometric characteristics. Previous investigations have debated whether these contrasts are caused by the upwelling of a deep mantle plume or the product of regional tectonic forces. To better understand how the regional geology influences Grande Comore, we investigate the morphology, distribution, and composition of the smaller volcanic cones associated with Karthala and La Grille. The cones are grouped into different clusters based on the density of their distribution and are subsequently compared with each other. Our study found that Karthala's cone sizes are connected, and influenced by a shallow plumbing system, whereas La Grille's cones lack any evidence of a developed plumbing system. Rift orientations (expressed by cone basal orientations) confirm that magma propagation on Karthala is a product of stress induced from its edifice in addition to regional stresses. La Grille rifts only coincide with regional stresses, lacking any evidence of shallow magma storage. Understanding these differences helps improve predictions of future volcanic activity and related hazards on Grande Comore.</p
Consommation d’énergies renouvelables et attractivité des destinations touristiques en Afrique subsaharienne
No full textInternational audienceThe aim of this article is to assess the effect of the interaction between renewable energy consumption, GDP per capita, and CO2 emissions on the attractiveness of tourist destinations in sub-Saharan Africa over the period 1995-2019. A panel data model covering 29 countries shows that an increase in renewable energy consumption is positively associated with an increase in tourist attractions. They also reveal that the interaction between renewable energy consumption, GDP per capita, and CO2 emissions has positive and significant effects on the attractiveness of tourist destinations. We propose inclusive development policies aligned with climate goals (SDG 13), while calling on SSA countries to strengthen regional coordination around a shared vision of sustainable development, particularly through green tourism initiatives based on renewable energy (SDG 7).L'objectif de cet article est d'évaluer l'effet de l'interaction entre la consommation d'énergies renouvelables, le PIB par habitant et les émissions de CO2 sur l'attractivité des destinations touristiques en Afrique subsaharienne sur la période 1995-2019. Les données montrent qu'une augmentation de la consommation d'énergies renouvelables est positivement associée à une augmentation des attractions touristiques. Elles révèlent également que l'interaction entre la consommation d'énergies renouvelables, le PIB par habitant et les émissions de CO2 a des effets positifs et significatifs sur l'attractivité des destinations. Nous proposons des politiques de développement inclusives alignées sur les objectifs climatiques, tout en appelant les pays à renforcer la coordination régionale autour d'une vision commune du développement durable, notamment à travers des initiatives de tourisme vert basées sur les énergies renouvelables
When coral dies but fish remain: limits of local restoration under climate pressure (Bora Bora, French Polynesia)
No full textInternational audienceWhile global change presents significant threats to all environments, local scale conservation efforts such as coral restoration may help mitigate reef degradation. Our study investigates the combined effects of local coral restoration versus a coral bleaching event on coral health and fish assemblages. Between January and April 2024, approximately 60-70 marine heatwave days occurred across the Bora Bora region (French Polynesia). Two experiments were conducted on the fringing reef of Bora Bora: the first surveyed coral and reef fish communities in two biotopes (shallow fringing reefs and a deeper "reef drop") before and after the 2024 bleaching event; the second assessed fish communities at restoration sites managed by high school children (citizen science) at three time points: (i) before restoration, (ii) after restoration, and (iii) after bleaching. Our results show a significant decline in live coral on the shallow fringing reef (with or without reef restoration) after the 2024 bleaching event, whereas the deeper reef drop exhibited minimal change, highlighting a depth-related difference in reef vulnerability to thermal stress. Despite these changes in coral cover, fish abundance and richness remained relatively stable across time (before and after the bleaching event). Overall, our findings highlight the lack of resilience of coral reefs under heatwaves and provide useful insights into the limitations of small-scale restoration when faced with large-scale thermal stress. This underscores the urgent need to design local-scale restoration strategies that are better aligned with addressing global change, particularly in regions where healthy reefs are vital for the survival of local human communities
Metabolomics, Molecular Networking and Phytochemical Investigation of Psiadia dentata (Cass.) DC., Endemic to Reunion Island: Discovery of Novel Bioactive Molecules
No full textInternational audienceThe genus Psiadia (Asteraceae), widely distributed in Madagascar and the Mascarene Islands (Mauritius, La Réunion, Rodrigues), is traditionally used to treat bronchitis, asthma, colds, abdominal pain, and other inflammatory disorders. However, few studies have scientifically validated these traditional medicinal uses. To assess P. dentata as a valuable source of bioactive natural products, a combined 1H NMR-based metabolomic, molecular networking, and phytochemical study was conducted. Multivariate analysis (PLS-DA) of crude extracts from Psiadia species collected on Reunion Island enabled rapid discrimination of active extracts from P. dentata and revealed two methoxylated flavonoids and one coumarin as metabolites correlated with its antiplasmodial and anti-inflammatory activities. Additionally, UHPLC-DAD-ESI-QTOF-MS/MS molecular networking approach enabled detailed chemical profiling of this species, allowing the annotation of 25 compounds (1–25) in this species. Subsequent phytochemical investigation of P. dentata leaves led to the isolation and identification of 25 metabolites, including nine new diterpenes (26–34), one new coumarin (35), and 15 known compounds (1–8, 11, 18, 19 and 36–39) from the diterpenoid, flavonoid, and coumarin families. The structures of the new compounds were elucidated using spectroscopic methods, including extensive 1D and 2D NMR and HRESIMS analyses. Biological evaluation of the isolated compounds showed that compounds 1, 7, 26 and 27 showed antiplasmodial activity against Plasmodium falciparum (3D7 strain, IC50 = 7.25–13.46 μM). Compounds 7, 26, 27, 31 and 32 inhibited nitric oxide production (IC50 = 0.87–27.71 μM), indicating potential anti-inflammatory effects. Only compound 1 displayed moderate cytotoxicity against HepG2 and HT29 cancer cell lines (IC50 = 25.67 and 18.35 μM, respectively)
Salt-regulated triacylglycerol accumulation and biodiesel quality of Scenedesmus sp. BHU1 under two-stage cultivation
No full textInternational audienceMicroalgae efficiently sequester carbon and accumulate neutral lipids; however, challenges persist in achieving high triacylglycerol (TAG) and biofuel yields. This study presents a novel two-stage salt stress strategy that enhances neutral lipid accumulation, jet fuel production, and biodiesel quality in Scenedesmus sp. To address this, Scenedesmus sp. was cultivated under varying NaCl concentrations (0-0.4 M) and time intervals (0-12 days) using a two-stage process. In stage I, control cells (0 M NaCl) showed a higher CO₂ fixation rate (122.06 mg L⁻¹ d⁻¹), while 0.4 M NaCl-treated cells recorded the highest neutral lipid content (77.01 %). In stage II under 0.4 M NaCl at 8 days, 1.48 kg biomass yielded 1 kg microalgal oil, and 2.59 kg biomass produced 1 kg jet fuel. Further, second derivative spectra from FTIR spectroscopy revealed shifts in functional groups favoring neutral lipid synthesis (peaks at 2923 cm⁻¹ and 1746 cm⁻¹), while thermogravimetric analysis (TGA) showed decomposition of lipids and carbohydrates during pyrolysis. Additionally, CHNS analysis revealed maximum higher heating value (25.64 MJ/kg), and lower heating values (24.71 MJ/kg) in 8 th -day biomass. GC-MS analysis revealed a predominance of saturated fatty acids (SFAs; 66.67 %), particularly C16-C18, over monounsaturated fatty acids (MUFAs; 18 %) and polyunsaturated fatty acids (PUFAs; 16 %). Notably, biodiesel produced from 8 th day biomass met both the EN 14214 and ASTM D6751 standards, demonstrating the potential of Scenedesmus sp. for biodiesel feedstock. Importantly, biodiesel produced from the 8 th -day biomass met both the EN 14214 and ASTM D6751 standards. Thus, current study highlights the potential of salt supplementation in Scenedesmus sp. BHU1 to enhance triacylglycerol, supporting its use as a biodiesel feedstock
Alkali recondensation into chondrules
No full textInternational audienceWhile sub-mm melt droplets should rapidly lose alkali elements in a vacuum at liquidus temperatures, chondrules are only modestly depleted in them (by less than one order of magnitude). The detection of sodium in olivine cores has previously suggested very high saturating partial pressures of gaseous sodium, but we show that alkalis were lost during heating and recondensed at lower temperatures, essentially in the present-day chondrule mesostases. This recondensation was accompanied by mass-dependent enrichment in light isotopes (for multi-isotope alkalis such as K and Rb), but its limited extent indicates a cooling acceleration (or ''quenching''). The isotopic fractionation also constrains the ratio of the chondrule density and the cooling rate prior to the quench around 10 -6 kg.m -3 .K -1 .h suggesting densities above ∼ 10 -6 kg/m 3 . In a nebular context, this is achievable by radial and vertical concentrations near pressure bumps
Modeling the variability and sensitivity of OH emissions and validation through Krassovsky ratio ground-based observations
No full textInternational audienceOH airglow observation is a key component of understanding the dynamics of the Mesosphere -Lower Thermosphere, as its maximum altitude of roughly 87 km and the relatively good transmittance of the atmosphere make it an interesting tracer of middle atmosphere dynamics. Our study focuses on groundbased OH observation using both SWIR and visible cameras, with an instrumental setup capable of retrieving gravity-wave parameters and temperature in the OH layer, thus enabling measurements of the Krassovsky ratio (ranging from 1 to 10). These measurements provide us a good point of comparison with a model of OH perturbation by gravity waves, DOWRI, which we will present and describe in this article, introducing a new polarization relation on airglow intensity, supplemented by observational validation and SABER comparisons
Le prompt comme opérateur d'action : fabrique sémiotique hybride et interaction minimale avec les grands modèles de langage
No full textCette communication présente une mise à l'épreuve de la fabrique sémiotique hybride dans un cadre d'interaction minimale. La plateforme Hermes-HSF étudie les conditions où un modèle de langage produit une action dans un dispositif de médiations contrôlées. Nous comparons des politiques à prompt constant puis l'effet d'un enrichissement du prompt. Les résultats montrent que le comportement relève de l'agencement des médiations plutôt que du seul modèle, du seul prompt ou du seul environnement. Ils révèlent un couplage entre architecture du modèle et dispositif
Monitoring of slopes, rock faces and masonry walls in a 19th century public park: the example of the Buttes Chaumont Park (Paris, France)
No full textInternational audienceDeveloped on former gypsum quarries, the Buttes Chaumont Park is a 25-hectare geotechnical complex that is unique in the world. After three years of heavy work to create, in particular, an artificial cave, a lake and an island, the park opened in 1867 and has suffered gravitational hazards ever since (landslides, rockfalls and sinkholes). The BRGM has worked with the Paris City Council since 2021 to characterize the geological and geotechnical context, identify major gravitational hazards, and monitor the evolution of instabilities in slopes and rock/masonry walls. In this context, the BRGM has proposed, defined and followed a geotechnical supervision scheme including four levels of monitoring: detailed quarterly site visits since March 2023, bimonthly tacheometric surveys (operating since December 2022), monthly manual gauges measurements (since January 2024), and automatic extensometers and temperatures measurements (since March 2024). The interpretation of the data allows to confirm and/or complement the gravitational hazard mapping that had been carried out in 2022. By analyzing the correlation between displacement measurements and meteorological conditions, we could also differentiate between seasonal/daily trends mainly associated with temperature variations, and displacements associated with gravitational processes. These results help mitigate risks in the Buttes Chaumont Park in its current state, and adapt works planned in the coming years to restore and secure the park
Recent advances in lipid oxidation of bulk oils: Current insights and unresolved challenges
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616992/)International audienceLipid oxidation remains a major challenge in the food industry due to its detrimental effects on nutritional value, shelf life, and safety of edible oils. While the radical-based chemical mechanisms of lipid oxidation have been extensively studied, recent research highlights the importance of physical and supramolecular factors in bulk oils. This review provides an updated synthesis of current knowledge on lipid oxidation pathways, antioxidant mechanisms, and insights into the role of association colloids, particularly reverse micelles in bulk oils. Evidence indicates that association colloids act as reaction centers by concentrating water, hydroperoxides, and pro-oxidant metals at the oil–water interface, thereby accelerating radical initiation and propagation. Conversely, these interfacial structures may also enhance oxidative stability by promoting the targeted localization and synergistic action of antioxidants at critical reaction sites. The review discusses how intrinsic factors such as oil composition, amphiphilic constituents, water content, and oxygen solubility, together with extrinsic conditions, shape colloidal organization and oxidation kinetics. Special attention is given to the molecular structure of antioxidants, including polarity, spatial orientation of functional groups, and their impact on antioxidant efficiency, induction period extension, cutoff effects, and synergism. Recent advances in monitoring oxidation, including approaches targeting antioxidant depletion, are also addressed. Finally, key knowledge gaps and future research directions are identified, emphasizing the need for advanced structural characterization techniques and kinetic modeling to elucidate colloidal dynamics during oxidation. A deeper understanding of these interfacial and supramolecular phenomena is essential for developing more effective and sustainable strategies to control oxidation in bulk oils