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Organic geochemical investigations of an MIS 5 fire in the Palaeolithic deposits of Ormesson (Seine-et-Marne, France): Anthropic or natural?
No full textInternational audienceDespite the central role of fire in Pleistocene and Palaeolithic lifeways, the relationship among hominins, fire, and their environment remains unclear. Ancient combustion residues hold a wealth of molecular data that may help to resolve some of these questions, yet standardised guidelines for reconstructing past fire traces are notably lacking. In this study, we examine extensive combustion residues overlying Middle Palaeolithic deposits from the open-air site of Ormesson (France). To determine whether the combustion residues are of natural or human origin, multiproxy approaches including anthracology, lipid biomarker, and benzene polycarboxylic acid (BPCA) analyses are applied. These techniques are used to characterise organic matter and pyrogenic carbon compositions in the deposits, providing insights into surrounding vegetation, palaeoenvironmental shifts, and the production parameters involved in the formation of the char assemblage. Lipid biomarker evidence suggests that the pre-fire local environment featured abundant coniferous vegetation (e.g., Pinaceae taxa), which is supported by anthracological evidence for a predominance of Pinus cf. sylvestris/nigra complemented by Betula sp. taxa. The post-fire environment saw a contraction of coniferous vegetation, concurrent with an expansion of deciduous taxa, grasses and herbaceous material. The combustion event, which resulted in 67 % of the charcoal assemblage exhibiting vitrification, produced PyC contents of up to 362 g/kg OC in soil samples and 443 g/kg OC in charcoal samples, with aromatic condensation values of up to 34 %. BPCA-derived predictions of heat treatment temperatures yielded values of approximately 300–400 °C for charcoal samples and 400–550 °C for soil samples in the burned layer, constituting the first instance in which quantitative temperature estimations are obtained from BPCA results. Based on the integrated evidence, we accept the null hypothesis that the studied combustion residues are natural in origin. However, the similarity of archaeometric and geochemical signatures from natural and human-controlled fires underscores the need for interdisciplinary, multiproxy efforts to improve the identification of past fire regimes
Uncertainty in projected changes of Indian Summer Monsoon Rainfall by CMIP6 models
No full textInternational audienceA robust and trustworthy rainfall projection over the Indian landmass is vital for devising climate adaptation strategies. However, past studies show large inter-model spread in Indian Summer monsoon (ISM) rainfall projections thus calling for more detailed investigations on the underlying process. In the present study, we investigate this aspect using Coupled Model Intercomparison Project Phase 6 (CMIP6) model projections (Shared Socioeconomic Pathways, SSP5–8.5) and historical simulations. The Multi-Model Ensemble mean (MME) results show intensification of ISM rainfall at the end of the 21st century with ISM rainfall increasing by 1.6 ± 0.8 mm/day under SSP5–8.5 scenario. A moisture budget analysis for the MME further infers that the thermodynamic effect (TH) due to global warming plays a dominant role in enhancing ISM rainfall in the projections, with its dynamic counterpart (DY) assuming an additional contribution. It is also revealed that both DY and TH terms contribute to the inter-model uncertainty in ISM rainfall, but with DY dominating over the other this time. The inter-model uncertainty in DY and ISM rainfall changes is linked to inter-model spread in interhemispheric thermal contrast which in-turn depends on the diversity in Equilibrium Climate Sensitivity (ECS) and Global Mean Temperature (GMT) among the models. Intriguingly, when we remove the inter-model diversity in ECS through a GMT scaling, an Atlantic meridional surface temperature gradient, involving both land and ocean, emerges as a crucial driver in controlling the uncertainty in both DY and ISM rainfall changes, and drives large-scale monsoon circulation changes over African and the Indian subcontinents
Sensitivity of thermal evapotranspiration models to surface and atmospheric drivers across ecosystems and aridity
No full textInternational audienceEvapotranspiration (ET) lies at the core of the energy-water-carbon coupling, particularly under changing climate conditions. Yet, the sensitivity of ET models to key environmental drivers remains insufficiently understood, especially in understanding how thermal-based ET models respond to distinct influences of soil and atmospheric water stress across ecosystems. In this study, we examine the sensitivity of ET to key environmental drivers, including land surface temperature (LST), air temperature (TA), vapor pressure deficit (VPD), downward solar radiation (DSR), and fractional vegetation cover (FVC), using three representative thermal remote sensing (RS) models (STIC, TSEB, and SPARSE) together with global eddy covariance measurements.At the global scale, variance-based sensitivity analysis (Sobol' method) reveals a transition in the dominant driver of ET sensitivity from water-limited to energy-limited regimes: soil dryness (indicated by LST − TA) dominates ET variability up to an aridity index (ratio of precipitation to reference ET) of 0.54 (± 0.06), beyond which DSR becomes the primary driver. Seasonal variability and ET partitioning emphasize the critical role of soil dryness in driving soil evaporation variability, particularly during growing seasons. Furthermore, a water stress test is conducted across four representative sites with varying vegetation cover types. Results show that ET sensitivity to soil dryness nearly doubles during the drought period compared to climatological norms at the grassland site. In contrast, transpiration in forests is more strongly influenced by VPD under moderate drought stress. Analysis indicates that soil dryness generally exerts stronger control on ET than VPD. However, when vegetation cover exceeds 0.49, the influence of VPD anomalies on ET becomes comparable to soil dryness stress.This research advances our understanding of ET dynamics under increasing drought frequency and intensity. It highlights the potential of forthcoming high-resolution thermal-based RS ET products for early drought hazard warnings, climate-resilient decision-making, and sustainable agricultural water management
Integrative assessment of biohydrogen and biomethane production from Brittany and Caribbean Sargassum (Ochrophyta, Fucales)
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Locating enzyme activities and nutrients in the rhizosphere: Combining zymography and DET methods
No full textInternational audienceOrganic fertilization is a recognized sustainable practice in agriculture and represents a major nutrient source for microbes and plants in these systems. Microbes produce hydrolytic enzymes to mineralize nutrients from organic forms into mineral forms to satisfy their own needs, and thus can compete with plants for these mineralized nutrients. Thus, interactions between plants and microbes in the rhizosphere determine nutrient availability and flows. We investigated these relations, using a spatial approach that combined zymography with the method of diffusive equilibrium in thin films (DET) to localize enzyme activity and N and P availabilities simultaneously. Basil (Ocimum basilicum L.) was grown in rhizoboxes filled with an organo-mineral crop soil (MS) or 100 % organic peat soil (OS) that was unfertilized or fertilized locally with horn meal for 20 days. In general, enzyme activities were higher in MS than in OS, but the stimulation of leucine aminopeptidase (LAP) activity and associated decrease in nutrient availability was 2 times as strong in OS as in MS. A rhizosphere effect, in which rhizodeposits stimulated enzyme activity, was clearly observed in OS. Fertilization increased LAP activity and nutrient availability near the location of fertilization, which increased basil growth in OS but not in MS. β-glucosidase, acid phosphatase and N-acetyl-glucosaminidase activities responded weakly to fertilization and the rhizosphere. By relating enzyme activities mapped by zymography to nutrient availability mapped by DET, we identified microbial hotspots in the rhizosphere where most nutrient mobilization processes and competition between plants and microbes occurred
Un œil numérique sur les cimes: Comment le non-invasif redéfinit la carte archéologique en montagne
No full textApport du Lidar HD de l'IGN et de la photogrammétrie par drone ✓ 23 années de prospection pédestres ✓ 882 structures inventoriées Apport du Lidar HD de l'IG
Amplified Arctic–boreal fire regimes from permafrost thaw feedbacks
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Verres aluminoborosilicatés dopés au bismuth synthétisés sous haute pression : rôle du bismuth sur la solubilité de l'iode
No full textInternational audienceBismuth-aluminoborosilicate glasses have gained interest as a possible matrix for nuclear waste immobilisation, as bismuth-based sorbents have enhanced affinity for volatile radioisotopes removal. Conjointly, it has been recently demonstrated that using high-pressure conditions is an interesting tool to improve volatile elements retention during glass synthesis. This study tries to combine these two fields showing significant improvement in 129-iodine incorporation into the structure of Bi-bearing glasses synthesised under high-pressure conditions (1 GPa and 1250°C) by comparison with Bi-free glasses or Bi-containing glasses obtained at ambient pressure. Two series of glasses have been investigated in the SiO2-Al2O3-B2O3-Na2O-CaO-Bi2O3 system, either with high (~13 mol.% Al2O3) or low (~5mol.% Al2O3) Al2O3 and Bi2O3 content ranging from 0.5 to 16 mol.%. We show that I incorporation increases with increasing Bi2O3 and can reach up to 2.8 mol.%, which is much higher than Bi-free comparable glasses synthesised under the same conditions. The 11 B NMR analysis demonstrated a drastic decrease in the proportion of tetrahedral BO4 with increasing Bi2O3 content regardless of the alumina content. 27 Al displayed a large majority of IV Al, with a steady increase of CN Al for the Al-rich series, and nearly constant CN Al for the Al-poor series as we increase Bi2O3 content. O 1s XPS spectra demonstrates a clear change towards a general depolymerisation of the glass structure with increasing Bi2O3 content. It confirms the network-modifier role of Bi 3+ in such a glass system and explains the increase in I content. This work paves the way for new glass composition to be synthesised using high-pressure to address the worldwide issue of the volatile nuclear wastes.Les verres à base aluminoborosilicatés dopés en bismuth ont suscité un intérêt croissant en tant que matrice potentielle pour l'immobilisation des déchets nucléaires, notamment car les sorbants à base de bismuth présentent une affinité accrue pour l'adsorption des radio-isotopes volatils. Parallèlement, il a récemment été démontré que l'utilisation de conditions de haute pression constituait un outil intéressant pour améliorer la rétention des éléments volatils lors de la synthèse du verre. Cette étude tente de combiner ces deux domaines en montrant une amélioration significative de l'incorporation de l'iode dans la structure des verres contenant du Bi; synthétisés dans des conditions de haute pression (1 GPa et 1250 °C) par rapport aux verres sans Bi ou aux verres contenant du Bi obtenus à pression ambiante. Deux séries de verres ont été étudiées dans un système a base silicaté, avec une teneur élevée (~13 mol.% Al2O3) ou faible (~5mol.% Al2O3) en Al2O3 et une teneur en Bi2O3 comprise entre 0,5 et 16 mol.%. Nous montrons que l'incorporation d'I augmente avec l'augmentation de Bi2O3 et peut atteindre jusqu'à 2,8 mol.%, ce qui est beaucoup plus élevé que les verres comparables sans Bi synthétisés dans les mêmes conditions. L'analyse RMN 11B a démontré une diminution drastique de la proportion de BO4 tétraédrique avec l'augmentation de la teneur en Bi2O3, quelle que soit la teneur en alumine. Le 27Al a montré une grande majorité d'Al IV, avec une augmentation régulière de CN Al pour la série riche en Al, et un CN Al presque constant pour la série pauvre en Al à mesure que nous augmentons la teneur en Bi2O3. Les spectres XPS O 1s montrent un changement clair vers une dépolymérisation générale de la structure du verre avec l'augmentation de la teneur en Bi2O3 . Cela confirme le rôle de modificateur de réseau du Bi 3+ dans un tel système de verre et explique l'augmentation de la teneur en I. Ces travaux ouvrent la voie à la synthèse d'une nouvelle composition de verre à haute pression pour répondre au problème mondial des déchets nucléaires volatils
The MeerKLASS On-the-Fly continuum survey: pipeline design and validation
No full textInternational audienceThe MeerKAT Large Area Synoptic Survey (MeerKLASS) is designed to map large areas of the Southern sky for cosmology using the single-dish HI intensity mapping (IM) technique, while simultaneously delivering a wide, high angular-resolution interferometric survey. We present the design and first results of the MeerKLASS On-the-Fly (OTF) continuum data, which exploits the visibilities recorded during fast, constant-elevation scans. This observing mode enables fast commensal imaging over several hundred of square degrees on a nightly basis. We describe the OTF survey strategy and pipeline, focusing on handling challenges introduced by the current MeerKAT fixed-delay correlation observing mode, which causes decorrelation (smearing). We implement a correction scheme based on time-dependent phase rotation, direction-dependent PSF modeling, and wide-band faceted deconvolution with \texttt{DDFacet}. Using UHF-band and pilot L-band data, we demonstrate the recovery of high-quality 2-second snapshot images and deep mosaics over hundreds of square degrees. After smearing correction we are able to achieve a resolution of arcsec and arcsec with an rms sensitivity of and in the UHF and L-band respectively. The full survey will cover at 544-1088 MHz, and after the delay tracking fix implemented we expect to reach at arcsec resolution. The continuum OTF data products will support diverse science goals, including galaxy and AGN evolution, diffuse cluster emission, large-scale structure and cosmology, rotation-measure synthesis, and transient searches. MeerKLASS-OTF thus establishes an efficient path to wide-area commensal surveys with MeerKAT and provides a key technical precursor for SKA-Mid
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