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The role of crystal-bubble interactions, outgassing and magma composition in the ascent dynamics of alkaline magmas: Implications for eruptions at Vesuvius
No full textInternational audienceIntermediate to evolved alkaline magmas (phono-tephritic, tephri-phonolitic and phonolitic) exhibit a wide range in eruptive style and have produced some of the most catastrophic eruptions in human history, such as the 79 AD Plinian eruption of Vesuvius (Italy). However, eruptive dynamics are driven by complex, non-linear conduit processes during magma ascent, requiring a holistic approach to investigate their influence on explosivity. This study integrates synchrotron radiation X-ray computed microtomography (SRµCT) with a 1D steady-state conduit model, to investigate how crystal-bubble interactions, pre-eruptive conditions, outgassing, and magma composition affect eruptive style at alkaline volcanic systems, using Vesuvius as a case study.We analyse pyroclasts from the 79 AD Plinian and 1944 lava-fountaining eruptions using SRμCT. Our SRµCT results reveal that heterogeneous bubble nucleation can be promoted further by leucite crystals, contributing to the high bubble number densities (>10⁴ mm⁻³) observed in Plinian products. Despite high bubble connectivity, low throat-pore size ratios (the ratio between the radii of the throat and connected vesicles) and elevated tortuosity restrict gas–melt separation during fast magma ascent, promoting fragmentation. Numerical simulations reveal tephri-phonolitic and phonolitic magmas are prone to fragmentation across diverse conditions, producing highly explosive eruptions. Only relatively high temperatures (>1050 °C) and low bubble number densities (102 to 103 mm-3) can promote lava flow and fountaining activity. Instead, phono-tephritic magmas exhibit highly explosive eruptions at considerably lower temperatures (<950 °C). Temperature controls magma viscosity, influencing the ascent rate and the outgassing efficiency, which, in turn, affects conduit dynamics and the eruptive behaviour.Our findings highlight that for alkaline systems, the parameter space which is conducive to highly explosive eruptions expands as the magma composition evolves and its viscosity increases. These insights enhance our understanding of eruption mechanisms, providing critical insights for assessing volcanic hazard and emergency planning at alkaline volcanic systems
Smoked fish from Gabon: nutritional benefits vs. contaminant risks
No full textInternational audienceSmoked fish is the most common form of fish consumption in many African countries. Smoking is likely to cause changes in nutritional value and in the concentration of certain toxic elements. We assessed these changes in the Bonga shad (Ethmalosa fimbriata, Bowdich 1825). Fatty acids (26), vitamin A, trace elements (14) and polycyclic aromatic hydrocarbons (PAHs, 24) were examined in E. fimbriata at different smoking durations (fresh, 24 h, 48 h and 72 h). Composition of smoked fish revealed high inter-individual variability. Smoking did not affect total fatty acid concentrations, but it led to a 4.5-fold decrease in vitamin A and a decrease in the concentrations of Ca, Mg, Mn, Pb and Sr. Meanwhile, it increased the concentrations of PAHs (by a factor of 42), Cd, Mo and Na. Despite these changes, toxic metals (As, Cd and Pb) and PAHs levels remained within safety limits, except for the B(a)P Toxic Equivalent (TEQ) in 72 h-smoked fish. High inter-individual variability in toxic metals, PAHs and nutrients concentrations is suspected to originate from the heterogeneity of the smoking process, and to natural variation in fish. Overall, our results highlight the safety of artisanal smoked fish for human consumption when processed under certain conditions. To further enhance consumer safety, dietary recommendations would advise ensuring fish skin integrity in order to reduce flesh contamination
Observational strategies for ultrahigh-energy neutrinos: the importance of deep sensitivity for detection and astronomy
No full textInternational audienceDetecting ultrahigh-energy neutrinos can take two complementary approaches with different trade-offs. 1)~Wide and shallow: aim for the largest effective volume, and to be cost-effective, go for wide field-of-view but at the cost of a shallow instantaneous sensitivity -- this is less complex conceptually, and has strong discovery potential for serendipitous events. However, it is unclear if any source can be identified, following detection. And 2)~Deep and narrow: here one uses astrophysical and multi-messenger information to target the most likely sources and populations that could emit neutrinos -- these instruments have deep instantaneous sensitivity albeit a narrow field of view. Such an astrophysically-motivated approach provides higher chances for detection of known/observed source classes, and ensures multi-messenger astronomy. However, it has less potential for serendipitous discoveries. In light of the recent progress in multi-messenger and time-domain astronomy, we assess the power of the deep and narrow instruments, and contrast the strengths and complementarities of the two detection strategies. We update the science goals and associated instrumental performances that envisioned projects can include in their design in order to optimize discovery potential
Hybodont shark remains from Campanian (Upper Cretaceous) continental deposits of southern France
No full textInternational audienceThe hybodont shark (Elasmobranchii, Hybodontiformes) material from the Campanian of two non-marine localities in southern France are described. Some teeth and a dorsal fin spine from the upper Campanian of Velaux are assigned to the genus Meristodonoides (Hybodontidae), whereas a single tooth from the lower Campanian of Villeveyrac is referred to Parvodus (Lonchidiidae), a genus hitherto unknown in the Upper Cretaceous. Among the latest Cretaceous continental ichthyofaunas of the European archipelago, hybodont sharks may have been minor relictual components with spatially restricted distributions, as suggested by their scarcity in the fossil assemblages from France and Romania combined with their apparent absence in other areas (Iberian Peninsula, Hungary)
Gamma rays as leptonic portals to energetic neutrinos: a new Monte Carlo approach
No full textInternational audienceHigh center-of-mass electromagnetic~(EM) interactions could produce decaying heavy leptons and hadrons, leading to neutrino generation. These processes might occur in the most extreme astrophysical scenarios, potentially altering the expected gamma-ray and neutrino fluxes in both the hadronic and the leptonic pictures. For instance, neutrinos could arise from high-redshift EM cascades, triggered by gamma rays beyond scattering background photons, from radio to ultraviolet energy bands. Such energetic gamma rays are predicted in cosmogenic models and in scenarios involving non-standard physics. On astrophysical scales, leptonic production of neutrinos could take place in active galactic nuclei cores, where several-TeV gamma rays interact with the X-ray photons from the hot corona. We explore these scenarios within the CRPropa Monte Carlo code framework, developing dedicated tools to account for leptonic production and decay of heavy leptons and hadrons. In particular, the latter are performed by interfacing with the PYTHIA event generator. With these novel tools, we characterise the spectrum and flavour composition of neutrinos emerging from cosmological EM cascades and from leptonic processes in the core of active galactic nuclei. Finally, we investigate the leptonic production of neutrinos in the context of the IceCube detection of NGC~1068
A cosmologist's take on Little Red Dots
No full textInternational audienceThe James Webb Space Telescope (JWST) has uncovered a population of compact, high-redshift sources, the Little Red Dots (LRDs), which may host supermassive black holes (BHs) significantly heavier than their stellar content compared with local scaling relations. These objects challenge standard models of early galaxy formation and may represent an extreme class of early BH hosts. In this paper, we investigate whether these BHs could have a primordial origin. We first show that the direct formation of these BH masses in the early Universe is excluded by stringent CMB -distortion limits. We then investigate the assembly of massive BHs from lighter, observationally allowed primordial black holes (PBHs) via hierarchical mergers, finding that, although this channel can operate depending on the merger history, it faces challenges in explaining the observations due to the rarity of the required high-redshift dark matter halos. Finally, we estimate gas accretion onto intermediate-mass PBHs, while jointly tracking metallicity evolution, and identify regions of parameter space in which such growth could reproduce the observed properties of LRDs. As a special case, we focus on the strongly lensed source QSO1, whose extremely low metallicity and large mass provide a stringent test of these formation channels
XMM-Newton multi-year campaign on NGC 55 ULX-1: Resolving the wind and its variability with RGS
No full textInternational audienceWinds are an important ingredient in the evolution of X-ray binary (XRB) systems, particularly those at high accretion rates such as ultra-luminous X-ray sources (ULXs), because they may regulate the accretion of matter onto the compact object. We aim at understanding the properties of ULX winds and their link with the source spectral and temporal behavior. We performed high-resolution X-ray spectroscopy of the variable source NGC 55 ULX-1 to resolve emission and absorption lines as observed with XMM-Newton at different epochs. Optically-thin plasma models are used to characterise the wind. We confirmed and thoroughly strengthened previous evidence of outflows in NGC 55 ULX-1. The presence of radiative recombination signatures and the ratios between the fluxes of the emission lines favours photoionisation balance and low-to-moderate densities, which confirm that the lines originate from classical XRB disc winds. An in-depth parameter space exploration shows line emission from a slowly moving, cool, and variable plasma perhaps associated with a thermal wind. Mildly-relativistic Doppler shifts (about -0.15c) associated with the absorption lines confirm, at higher confidence, the presence of powerful, radiatively-driven, winds. The comparison between results obtained at different epochs revealed that the wind responds to the variability of the underlying continuum and these variations may be used to understand the actual accretion regime and the nature of the source
Cluster properties as a function of dynamical state in the DESI Legacy x UNIONS surveys
No full textInternational audienceWe investigate how the dynamical state of galaxy clusters influences their galaxy populations and mass distributions. Using photometrically selected clusters from the DESI Legacy Imaging Survey cross-matched with the UNIONS galaxy shear catalogue, we classify clusters as evolved or evolving based on their rest-frame r-band magnitude gaps and stellar mass ratios between the brightest cluster galaxies (BCGs) and bright satellites. We measure the stellar mass functions, weak-lensing profiles, and radial number density and red-fraction profiles of stacked clusters in both subsamples. Evolved clusters exhibit more concentrated lensing profiles, bimodal stellar mass functions dominated by massive BCGs, and a deficit of intermediate-mass satellites, while evolving clusters show flatter central lensing signals and an excess of massive satellites. Applying the same selection to IllustrisTNG clusters reproduces these trends and links the observed differences to distinct mass accretion histories. These results demonstrate the close link between cluster galaxy populations and the overall dynamical state of their underlying dark matter halo
Deciphering copper and zinc leaching from antifouling paints with different operating modes: flux determination and toxicity evidence
No full textInternational audienceLaboratory experiments were performed using 3 antifouling paints with different operating modes immersed in seawater for 7 days, to estimate copper and zinc fluxes and determine the scale of the related contamination. The toxicity of antifouling paints leachates was also assessed for natural bacterioplanktonic and phytoplanktonic communities. Given the increase in copper and zinc concentrations (4 to 1750-fold enrichment in dissolved Cu and to 7 to 200-fold enrichment in dissolved Zn), a systematic mortality upon phytoplankton was evidenced within 2 days of exposure to leachates produced from 1 hour to 2 days of immersion, whatever the paint. This went oppositely with the environmental risks calculated according to European guidelines, demonstrating an acceptable risk for the environment. Considering that 1 hour of leaching from a 7 cm² painted disk polluted 0.5L of seawater with Cu in our experimental conditions whatever the paint used, we estimated that a painted ship hull of 15 m² can pollute more than 10 m 3 of seawater within the same time. Leachates produced after only 20 minutes even yielded phytoplankton growth inhibition or mortality for insoluble and self-polishing paints, respectively, shortening the time needed for a freshly painted ship hull of 15 m² to pollute 10 m 3 . The bacterioplanktonic community appeared less sensitive than phytoplankton but demonstrated the same hierarchy: the highest toxicity was observed for the insoluble matrix and the lowest toxicity for the soluble one. This study therefore brings added value in terms of biocides flux determination, range of studied paints and concrete toxicity evaluation
Une approche archéologique et géographique du paysage maritime : l'exemple de la baie de Bourgneuf (côte atlantique, Pays de la Loire)
No full textInternational audienceThe Bay of Bourgneuf, an old Bay in Brittany, represents a continuum between land and ocean which is marked by human actions and occupations of this territory from the beginning to nowadays. It also appears as a vast maritime complex combining mooring areas, ports and inland waterways interconnected with former islands that have now disappeared. To understand this complex maritime landscape of the Bay of Bourgneuf, with no break between land and sea, it is necessary to focus on societal and environmental dynamics in the long term. The cross approach between archeology and geography thus allows us to address questions related to the evolution of the coastline, the formation of islands and the different types of human occupation on the coast. This interdisciplinary approach offers a global vision of the transformations, occupations and uses of both coastal areas and the maritime domain. This multidisciplinary study makes it possible to lay the first milestones of a joint work relating to the observation of land/sea interactions on a portion of an oceanic territory in an Atlantic-North context. After a brief introduction, we detail the geo-historical framework of the land under study, the history of research to build a new approach combining maritime archeology and geography, present the documentation and finally the first reflections of this multidisciplinary approach. A diachronic study of this bay, from prehistory to the pre-industrial period, with no break between land and sea, appeared relevant to document both its heritage and a landscape shaped by man and his activity. If studying old maps enables us to trace the evolution of the coastline in detail over the last three hundred years, the technique of sedimentological coring makes it possible to estimate the evolution of the coastal landscape during older periods. It also highlights the major paleo-environmental changes that have occurred over the past millennia. From a series of sedimentological cores, we are therefore trying to detect these marine horizons in the deepest strata of the ground. Once the coring has been carried out, the sedimentological analyzes will permit to finely characterize the origin of all the layers detected in the cores. They highlight the characteristic sea levels likely to testify to the historical evolution of the coastline. These observations are then compared with archaeological data from the Neolithic period to the 1850s, as well as nautical charts and representations of the coast documented since the 16th century. This bay and its surroundings currently form a vast maritime complex combining agricultural and oyster farming areas and protected natural areas. It was in the past a dense navigation area made up of moorings in the open sea, ports and inland waterways thanks to a network of channels and channels interconnected with islands that have now disappeared, because they are attached to the mainland.La baie de Bourgneuf représente un continuum entre la terre et l’océan marqué par la main de l’homme depuis les premières occupations de ce territoire jusqu’à nos jours. Elle apparaît également comme un vaste complexe maritime associant des zones de mouillages, des ports et des voies navigables intérieures interconnectées à d’anciennes îles aujourd’hui disparues. Pour appréhender ce paysage maritime complexe de la baie de Bourgneuf, sans rupture entre la terre et la mer, il est nécessaire de s’intéresser aux dynamiques sociétales et environnementales sur le temps long. L’approche croisée entre archéologie et géographie nous permet d’aborder les questions liées à l’évolution du trait de côte, à la formation des îles et aux formes de l’occupation humaine sur le littoral. Cette interdisciplinarité offre une vision globale des transformations, des occupations et des usages tant des espaces côtiers que du domaine maritime. Cet article permet de poser les premiers jalons d’un travail collectif relatif à l’observation des interactions terre / mer sur une portion d’un territoire océanique en contexte atlantique-nord. Après une brève introduction, nous détaillons le cadre géohistorique du terrain d’étude, l’historique des recherches pour construire une nouvelle approche associant archéologie maritime et géographie, la documentation exploitée et enfin les premières réflexions sur ce travail interdisciplinaire