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High-resolution mapping of the carbonate system in mangrove porewaters
No full textInternational audienceMangrove ecosystems sequester blue carbon at exceptionally high rates, primarily within sediments. However, the extent and variability of carbon stocks and fluxes remain insufficiently addressed. Organic matter degradation governs dissolved inorganic carbon (DIC) production, while the proton balance of diagenetic reactions determines the proportions of CO₂, HCO₃⁻, and CO₃²⁻, influencing CO₂ flux and long-term carbon sequestration. Alkalinity, mainly controlled by HCO₃⁻, buffers pH fluctuations. Conventional techniques lack the spatial resolution to capture fine-scale geochemical gradients, where biologically driven perturbations and redox stratification create strong variability. This study introduces two-dimensional Diffusive Equilibrium in Thin-films (2D-DET) gels for high-resolution mapping of pH and alkalinity in mangrove porewaters. By combining in situ equilibration with colorimetric analysis, this approach provides sub-millimeter-scale insights into carbonate system dynamics. We applied this method to contrasting mangrove ecosystems along the Brazilian coast: Marapanim (MAR, Pará), a macrotidal coastal plain influenced by seasonal Amazonian rainfall, and Mamanguá (MAM, Rio de Janeiro), a sheltered bay with narrow shorelines and moderate tidal dynamics. Our results reveal substantial microscale and regional heterogeneity in pH and alkalinity. In MAM, sediments exhibit an acidic zone (pH ~5.5–6.0) transitioning to neutral conditions (pH ~7.5–8.0) towards the water column, with bioturbation enhancing mixing. Weaker hydrodynamics contribute to sharp pH gradients
Moment-Matching Array Processing Technique for diffuse source estimation
No full textDirection of Arrival (DOA) estimation is a fundamental problem in signal processing. Diffuse sources, whose power density cannot be represented with a single angular coordinate, are usually characterized based on prior assumptions, which associate the source angular density with a specific set of functions. However, these assumptions can lead to significant estimation biases when they are incorrect. This paper introduces the Moment-Matching Estimation Technique (MoMET), a low-complexity method for estimating the mean DOA, spread, and power of a narrow diffuse source without requiring prior knowledge on the source distribution. The unknown source density is characterized by its mean DOA and its first central moments, which are estimated through covariance matching techniques which fit the empirical covariance of the measurements to that modeled from the moments. The MoMET parameterization is robust to incorrect model assumptions, and numerically efficient. The asymptotic bias and covariance of the new estimator are derived and its performance is demonstrated through simulations
Vergisson IV (Vergisson, Saône-et-Loire). Un nouveau potentiel pour la connaissance du Paléolithique moyen en Mâconnais
No full textNational audienceVergisson IV constitue l’un des cinq sites ayant livré des vestiges rapportés au Paléolithique moyen sur le flanc sud de la « roche de Vergisson ». Fouillé par J. Combier sur quelques m² de 1957 à 1962, il a livré un riche assemblage faunique et lithique, resté quasiment inédit. À la suite d’une relecture critique de l’archéostratigraphie, fondée sur l’étude techno-typologique de l’assemblage lithique confrontée à la documentation de fouille, dans le cadre d’une thèse, l’intérêt du site de Vergisson pour la connaissance de l’occupation de la Bourgogne méridionale au Paléolithique moyen a été remis en exergue. Sur cette base, deux opérations de terrain ont été menées, en 2021 et 2023. La première a consisté à reculer partiellement une coupe de la tranchée de fouille Combier afin de réviser la stratigraphie et d’effectuer des prélèvements pour datation par la méthode OSL. Lors de la seconde intervention, cinq sondages ont été implantés en contre-haut et contrebas de la fouille Combier afin d’évaluer l’extension du piège karstique ayant préservé les dépôts archéologiques et d’estimer le développement de ces derniers. Les résultats de ces deux opérations conduisent à une image significativement renouvelée de ce site et en esquissent le potentiel pour la connaissance du Paléolithique moyen et de Néandertal en Mâconnai
Arctic sea-ice loss drives a strong regional atmospheric response over the North Pacific and North Atlantic on decadal scales
No full textInternational audienc
Bedrock Offset Across the Wasatch Fault in Salt Lake City, Utah, from Teleseismic Converted Phases and Its Geologic Implications
No full textInternational audienceIn 2018, 32 three-component geophones were deployed in a linear array with ∼90 m average station spacing across the active East Bench fault (EBF) in Salt Lake City, Utah. This west-dipping normal fault is a relatively young section of the Wasatch fault zone which cuts through the northeastern Salt Lake basin (SLB), west of and mostly parallel to the older Foothill fault section at the base of the Wasatch Range. Here, we investigate the variation of bedrock depth across the fault by examining the first peak of teleseismic receiver functions (RFs) along the linear array. The arrival time of this initial phase at stations in the SLB is particularly sensitive to the depth of a velocity discontinuity, referred to as R2, between semi-consolidated sediment and bedrock, which is consolidated sedimentary rock in most of the SLB. We observe that the first peak times are very similar on either side of the EBF but shift abruptly by ∼0.7 s across the fault. Based on two recent 1D velocity models, one for each side of the fault, this time shift indicates a vertical R2 offset of 810 ± 290 m across the EBF. This offset likely reflects the accumulated slip on the fault since the fault’s activation. Combining this offset with a current slip rate of 1.2 ± 0.2 mm/yr, based on paleoseismic studies of the Wasatch fault, and a range of models for how this slip rate may have changed over time, our best estimate for the age of the EBF is 0.7–1.4 Ma. From the R2 offset and the distance between stations over which it is observed, we calculate that the EBF has a minimum average dip of 81° ± 3° in the top 1100 m
Studies of noctilucent clouds from the stratosphere during the 2024 TRANSAT balloon flight
No full textA transatlantic scientific balloon flight (TRANSAT) was conducted between 22 and 26 June 2024. The TRANSAT balloon, operated by the French Space Agency (CNES), floated in the stratosphere at approximately 40 km altitude between Esrange (Sweden) and Baffin Island (Canada) for about 3.8 days. The scientific payload comprised nine instruments, including two from the Swedish Institute of Space Physics: an optical imager for noctilucent cloud (NLC) studies and an infrasound instrument for atmospheric infrasound wave investigations. The NLC imager consisted of three identical visible-range optical cameras, one of which operated successfully throughout the entire flight, capturing thousands of NLC images. The TRANSAT balloon campaign was supported by ground-based lidar measurements and spaceborne observations from the Swedish MATS satellite. Here, we describe the technical characteristics of the balloon experiment and present early results. Nearly continuous observations of NLC were obtained during the entire flight. A localized warm region in the mesopause was identified as the cause of temporary NLC disappearance, while complex NLC structures exhibiting different motions were found to probably result from horizontal wind rotation with altitude within the mesopause region
Tracing the evolving actor network: a social network analysis of the 2018 Mayotte crisis in the press
No full textInternational audienceAbstract. The media, especially the press, play a crucial role in shaping public understanding during risk and crisis management, acting as intermediaries between various actors and the public. However, their framing of sources can introduce biases into these representations. Limited analysis exists regarding how press coverage portrays relationships between crisis and risk management actors. Using social network analysis, this study maps quotation networks in press coverage of a seismo-volcanic crisis in Mayotte, a French overseas department. This approach allows for an overview of the relationships between actors, highlights unique aspects related to the context and media portrayal, reveals underlying representations and levels of trust among interviewed actors, and visualises the network's dynamics over time. Analysis revealed variations in narrative approaches among newspapers, with some focusing on specific aspects. The results show that national authorities received more attention than local elected representatives and that scientific figures dominated reported speech, while the population's perspective remained relatively passive despite its centrality to the quotation network. Prominent individuals held significant positions, emphasising the importance of personal connections in communication and revealing a potential distrust of political and scientific institutions. This finding underscores the need for greater proximity between information sources and the affected community
Confirming the Magnetic Field Detection at the Surface of χ Cyg
No full textInternational audienceWe present spectropolarimetric observations of χ Cygni obtained with Neo-Narval at Télescope Bernard Lyot in 2025. We obtained observations across three epochs (2025 July, August, and October) near maximum light to search for magnetic field signatures at the stellar photosphere. We detected a clear circular polarization signal in the 2025 August observations (pulsation phases 0.99–0.01). We measure a mean longitudinal magnetic field of B = 3.4 ± 0.6 G. No detections were obtained for the 2025 July and October epochs. The pulsation-phase dependence suggests that field detection is tied to specific shock conditions near maximum light
Improving gamma spectrometry for radionuclide analysis of extraterrestrial samples
No full textInternational audienceRadon (Rn-222) and its radioactive progenies serve as important tracers for the study of geophysical processes within the Earth's lithosphere. On other planetary bodies, such as the Moon, radon is a powerful tool for studying the origin and transport of volatiles along the surface and lunar outgassing. The DORN instrument onboard the Chinese lunar lander Chang’E 6 performed the first measurements of radon and polonium isotopes on the lunar surface in June 2024. To support these results, a new experimental setup was prepared at the Laboratoire National Henri Becquerel (LNE/LNHB-MA) to perform gamma spectrometry measurements on a high-purity germanium detector. The instrument and geometry were optimized for high sensitivity and low mass efficiency to obtain bulk activity concentrations of U-238, Ra-226, Th-232, U-235 and K-40 from a lunar regolith sample. A special treatment was applied to study the unsupported fraction of Pb-210 due to radon emanation.Finally, an optimized geometry of a container capable of holding 1 g of regolith sample was designed and fabricated, minimizing sample auto-attenuation and prioritizing efficiency in the low energy detection range. The total measurement time was over 3 million seconds. The expected specific activities for the gamma emitting radionuclides U-238, Ra-226, Th-232, U-235 and K-40 are 34.4, 21.2, 15, 0.87 and 169 Bq.kg-1, respectively