HAL-IRD
Not a member yet
83947 research outputs found
Sort by
Do large earthquakes start with a precursory phase of slow slip?
No full textInternational audienceIn a recent publication, we showed that a stack of all GPS time series recorded before Magnitude ≥ 7.0 earthquakes suggests that large earthquakes start with a precursory phase of accelerating slow slip (Bletery and Nocquet, 2023). While no peer-reviewed comment or publication has formally contradicted this result, informal discussion has emerged on various platforms. We present here the different elements of discussion and address them through a series of tests. In particular, it has been proposed that correcting GPS time series from network common-mode noise makes the signal vanish. We confirm this result, but we show that this common-mode filtering procedure may inadvertently remove an existing tectonic signal. Moreover, the analysis of past records indicate that the likelihood that common-mode noise produces the signal we observe is well below 1 %. Additionally, we find that the signal is maximum at the location of the impending earthquakes, and for a slip direction (rake angle) close to the one of the upcoming events. The collective outcomes of these tests make very unlikely that the signal solely arises from noise. Even though the results of our tests do not irrefutably demonstrate the existence of a precursory phase of slow slip, they do support its existence. We hope that this study will motivate further work by others to provide a definite answer to the question of the tectonic origin of the observed signal and confirm or refute that large earthquakes start with a precursory phase of slow slip
Prenatal Hemoglobin Concentration and Long-Term Child Neurocognitive Development
No full textInternational audienceAnemia in pregnancy, defined by a hemoglobin level (Hb) of less than 110 g/L, contributes to infant mortality and morbidity in sub-Saharan Africa. Maternal Hb changes physiologically and pathologically during pregnancy. However, the impact of these changes on long-term child neurocognitive function is unknown. This study therefore investigates the association between Hb at specific antenatal care visits and prenatal Hb trajectories during pregnancy and long-term child neurocognitive function. We analyzed data from a prospective cohort study that included 6-year-old singleton children born to women enrolled before 29 weeks of gestation into an antimalarial drug clinical trial. Hemoglobin level was analyzed from venous blood collected at least twice during pregnancy and at delivery. We used group-based trajectory modeling to identify distinct prenatal Hb trajectories. In total, 478 children (75.1% of eligible children) had assessment of cognitive and motor functions at 6 years of age. Three distinct Hb trajectories were identified: persistently anemic (Hb <110 g/L throughout the second and third trimesters), anemic to nonanemic (Hb <110 g/L at second trimester with increasing Hb toward the third trimester to Hb ≥110 g/L), and persistently nonanemic (Hb ≥110 g/L throughout the second and third trimesters). Children of women in the persistently anemic and anemic-to-nonanemic groups had significantly lower neurocognitive scores than children of women in the persistently nonanemic group (β = −6.8, 95% CI: −11.7 to −1.8; and β = −6.3, 95% CI: −10.4 to −2.2, respectively). The study shows that maintaining an elevation of Hb at or above 110 g/L from the second to third trimester of pregnancy may be associated with optimal long-term child neurocognitive function
The Kerbernez long-term experiment: A dataset on crop yield and soil organic matter evolution in forage crop rotations and permanent grasslands in a temperate oceanic climate
No full textInternational audienceForage crop rotations including grasslands, common in dairy systems, are known to ensure good productivity and limit the decrease of soil organic matter frequently observed in permanent arable land. A dataset was built to compile data from the Kerbernez long-term experiment, conducted in Brittany(France) from 1978 to 2005. This experiment compared the effect of different forage crop rotations fertilized with ammonium nitrate and/or slurry, with or without grassland, on forage production (quantity, quality) and changes in soil physio-chemical characteristics. These forage crop rotations were based on silage maize and cut monospecific grasslands of Italian ryegrass (Lolium multiflorum L.) or perennial ryegrass (Lolium perenne L.). More precisely, the experiment compared silage maize monocultures, rotations with silage maize and Italian ryegrass established for 6 to 18 months, and rotations with silage maize and perennial ryegrass established for three to more than 10 years. They are representative of the forage crop rotations and permanent grasslands that were at the heart of Brittany's forage revolution in the 1970s. The dataset includes information about the climate and soil conditions, the management of crops and grasslands, the evolution of topsoil organic carbon and nitrogen stocks, the inter-annual variations in crop and grassland dry matter yields and nitrogen contents. The dataset also includes characterisation of soil structural stability, particle-size soil organic matter fractions and potential soil carbon and nitrogen mineralisation at the end of the trial. It consists of fourteen csv files. This dataset can be used for a variety of purposes, namely for assessing the ability of mechanistic models to simulate soil organic matter dynamics and associated fluxes, and to estimate the influence of grassland presence and duration in forage crop rotations on such fluxes
Développement méthodologique de la surveillance des élasmobranches dans le cadre de la DCSMM
No full textLa méthodologie d’évaluation proposée dans le cadre du cycle 3 de la DCSMM aura permis d’évaluer quantitativement le critère D1C2 de 21 espèces de raies et 15 espèces de requins dans une ou plusieurs sous-régions marines (SRM) de France Métropolitaine. Cette évaluation, basée sur l’utilisation de l’indicateur FC1 : « Rétablissement de l’abondance des populations d’espèces sensibles » développé dans le cadre d’OSPAR repose sur la mobilisation des données de présence et d’absence issues des campagnes de chalutage scientifique. Dans le cadre des travaux présentés dans ce rapport, nous avons cherché à mobiliser l’ensemble du jeu de données compilé dans le cadre de la sous-action 1 « Cartographier la présence et la sensibilité des différentes espèces d’élasmobranches réglementées » de l’action 1 et avons appliqué la méthodologie de calcul de l’indicateur FC1 sur ce nouveau jeu de données. Ce dernier est constitué des données de campagnes de chalutage scientifique (DATRAS, MEDITS), d’observation de surface (PELAGIS Megascope) et du suivi de la pêche professionnelle (ObsMer).Les principales conclusions de l’étude ont permis de mettre en évidence plusieurs éléments :3 espèces (Dipturus oxyrinchus en SRM Manche - Mer du Nord (MMN), Gymnura altavela en SRM Golfe de Gascogne (GdG), Leucoraja circularis en SRM MMN) sont présentes dans la liste d’espèces D1PC évaluées au cycle 3, mais sur la base des données compilées dans le cadre de l’action 1 du PdA et de la littérature, ces-dernières ne sont pas présentes dans les eaux françaises. Il sera proposé au prochain cycle de les retirer des espèces à évaluer dans ces SRM ; 10 espèces supplémentaires (Bathytoshia lata, Centroscymnus coelolepis, Chimaera monstrosa, Dasyatis tortonesei, Deania calcea, Etmopterus princeps, Etmopterus spinax, Hexanchus griseus, Pteroplatytrygon violacea, Scymnodon ringens), non présentes dans la liste d’espèces D1PC évaluées au cycle 3, pourraient selon notre méthodologie faire l’objet d’une évaluation quantitative du critère D1C2 au prochain cycle. Ceci est particulièrement important pour les espèces dites « red-flag » (i.e. au statut UICN dégradé et/ou inscrites aux annexes de(s) convention(s) internationale(s)) telles que Bathytoshia lata (statut UICN VU en Méditerranée), Centroscymnus coelolepis (listée OSPAR et statut UICN EN en Europe), Deania calcea (statut UICN EN en Europe), et enfin Hexanchus griseus (annexe I de l’UNCLOS).Parmi les espèces présentes dans la liste d’espèces D1PC évaluées au cycle 3 et qui ont fait l’objet d’une évaluation qualitative, 8 espèces pourraient faire l’objet pour la première fois d’une évaluation quantitative du D1C2 pour une ou plusieurs SRM (Dipturus batis en Mers Celtiques (MC) et GdG, Myliobatis aquila dans la division Golfe du Lion (GdL) de la Méditerranée occidentale (MO), Alopias vulpinus dans la division GdL de la MO, Centrophorus squamosus en MC et GdG, Cetorhinus maximus en MMN et GdG , Isurus oxyrinchus en MC, Lamna nasus en MMN, MC et GdG, Prionace glauca en MMN, MC et GdG) Enfin, la méthode permet, pour 8 raies et 4 requins, de réaliser 21 nouvelles évaluations quantitatives du critère D1C2 à l’échelle de SRM qui n’avaient pas été évaluées jusque-là. Par ailleurs, ces travaux apparaissent comme particulièrement pertinents dans l’objectif d’améliorer le niveau de confiance des évaluations grâce à une meilleure adéquation des échelles spatiales et temporelles. Pour rappel, les zones et périodes d’évaluation à considérer pour la DCSMM et OSPAR sont différentes, et réaliser des évaluations quantitatives à l’échelle des SRM françaises et pour une période d’évaluation adaptée au cycle DCSMM permet un plus fort niveau de confiance. La méthodologie du FC1 a ici été mobilisée en utilisant uniquement les données disponibles dans les SRM de France métropolitaine et non à l’échelle des régions OSPAR comme cela a été réalisée lors de la précédente évaluation du BEE cycle 3. De plus, l’indicateur OSPAR FC1 se base sur des campagnes de chalutage scientifique qui sont globalement peu adaptées à la capture des élasmobranches. En analysant les données à notre disposition qui comprennent, en plus des campagnes scientifiques, les données du suivi de la pêche professionnelle ObsMer, on note un nombre d’occurrences plus important pour un grand nombre d’espèces d’intérêt dans les données du suivi de la pêche professionnelle que dans celles issues des campagnes scientifiques. De plus, l’indicateur OSPAR FC1 se base sur des campagnes scientifiques qui sont généralement déployées lors d’une seule saison. Ceci peut provoquer un autre biais d’interprétation ou un manque de données notamment dans le cas des espèces présentant une saisonnalité dans leurs occurrences. Autre élément à considérer, les périodes utilisées comme « références » ou « à évaluer » lors du calcul de l’indicateur OSPAR FC1 ne sont pas en adéquation avec les cycles DCSMM français. En effet, la période évaluée de 6 années par OSPAR varie entre 2013 et 2020 selon les campagnes alors que l’évaluation du 3e cycle de la DCSMM en France correspond à 2016 - 2021. Il est donc important de réévaluer en sélectionnant les périodes en cohérence avec les cycles DCSMM français afin d’éviter tout biais d’interprétation. En conclusion, les résultats montrent qu’il est possible et intéressant, en particulier dans le cas d’espèces à occurrences rares, d’appliquer l’indicateur FC1 à différents jeux de données. En perspectives , il reste cependant à approfondir la méthodologie à appliquer pour la sélection des données issues du suivis de la pêche professionnelle afin d’avoir une cohérence d’effort (i.e., saison, durée des opérations de pêche) entre les périodes de référence et celle à évaluer
Iterative Helmholtz Surface Wave Tomography Using Generalized Wave Equation Smoothing Splines - Application to Western Europe
No full textInternational audienceOver the last decade, the expansion and densification of broadband seismic networks has led to an increased interest in tomographic approaches based on gradiometry, which relies on the spatial derivatives of the phase and amplitude of surface wavefronts. Nevertheless, the use of amplitude information remains challenging. In this study, we present a novel approach to Helmholtz tomography based on the use of generalized wave equation smoothing splines. The application of these generalized smoothing splines results in the generation of smooth amplitude and phase fields that satisfy the Helmholtz and transport equations, and hence the wave equation. This enables the direct derivation of phase velocity maps using the Helmholtz equation. We apply this new Helmholtz tomography approach to Rayleigh waves recorded by permanent and temporary networks in Western Europe from 2008 to 2022 to obtain phase velocity maps for periods between 25 and 120 s. These maps reveal the detailed structure of the crust and upper mantle in this region. Compared to eikonal tomography, the phase velocity anomalies obtained by Helmholtz tomography are stronger in amplitude and more sharply defined
An Inverse Modelling Approach to Constrain Be Cycling in the Subpolar North Atlantic
No full textInternational audienceBeryllium-7 is a short-lived cosmogenic radionuclide that has been used as a tracer of atmospheric deposition at the sea surface and of physical processes in the upper ocean. These applications generally assume that (i) the fraction of marine 7Be in particulate form is negligible, and/or (ii) the interactions between the particulate and dissolved forms of 7Be in seawater can be neglected. In this study, we test different steady-state models of upper ocean 7Be cycling from measurements of total 7Be and particulate 7Be activities collected at two stations of the GEOVIDE cruise in the subpolar North Atlantic (May-June 2014). The most complete model includes vertical advection, vertical diffusion, gravitational settling, radioactive decay, atmospheric deposition, and the reversible exchange between dissolved 7Be (7Bed) and particulate 7Be (7Bep). This model reproduces the measured 7Be activities at both stations to within their uncertainties (± 1 standard deviation). In the East Greenland-Irminger Current (station 51/60), models that do not consider adsorption and/or desorption can still reproduce the measured activities, while in the southern Labrador Sea (station 69) models that neglect reversible exchange or desorption poorly fit the data. Thus, 7Bed at station 51/60 could have been supplied entirely by surface deposition, whereas 7Bed at station 69 originated at least partly from the release of particulate 7Be into solution. The subsurface 7Bep maxima, present at both stations, seem to require a flux of 7Be between particles and solution at station 69 but not at station 51/60. At both stations, most of the total 7Be deposited at the ocean surface was removed by radioactive decay, with at most 5% removed by sinking of 7Bep, suggesting that reversible exchange can be neglected in applications of total 7Be as a tracer for atmospheric deposition. However, reversible exchange is important to consider in applications of 7Bed as a deposition tracer, with a maximum bias of 40% when reversible exchange is neglected. The steady state assumption does not alter our results regarding the solid-solution exchange of 7Be, but it does result in a significant bias when deriving atmospheric 7Betot deposition fluxes from water column 7Betot inventories. Overall, our findings suggest that reversible exchange could significantly influence the oceanic cycling of 7Be at some locations, and should not be systematically neglected when using 7Bed as an oceanic tracer
Thermochronology of the Western Alps (Pelvoux Massif) Reveals the Longterm Multiphase Tectonic History of the European Paleomargin
No full textInternational audienceThe Variscan and Alpine long‐term thermal evolution of the European paleomargin in the external Western Alps is still unknown, although important for reconstructing the geodynamic evolution of this orogen. Here we combine zircon fission track and apatite fission track and U‐Pb double dating analyses of the Pelvoux massif in the Western Alps. Apatite U‐Pb ages of <310 Ma and >320 Ma define a bimodal age distribution that reflects differential cooling across the East Variscan Shear Zone. QTQt thermal history modeling reveals a two‐stage rifting evolution on the European paleomargin, initiated with the Alpine Tethys rifting episode during the Early Jurassic and reactivated during the Cretaceous Valais rifting event, leading to peak temperatures of ∼350°C at 90 Ma. The subsequent cooling records a pre‐Priabonian phase of exhumation between 80 and 50 Ma that is related to N‐S oriented Pyrenean shortening. It is followed by Alpine collision‐related burial of the Pelvoux massif from below the foreland basin and the Penninic Frontal Thrust at around 30–25 Ma
Pollen-based climatic reconstructions for the interglacial analogues of MIS 1 (MIS 19, 11, and 5) in the southwestern Mediterranean: insights from ODP Site 976
No full textInternational audiencePleistocene interglacials, specifically Marine Isotope Stages (MISs) 19, 11, and 5, have been suggested as analogues of MIS 1 due to similar solar forcing patterns, greenhouse gas concentrations, and sea levels. There has been substantial debate regarding which of these is the most suitable analogue and so far there has been no consensus, although what really emerges from recent work is the high variation in regional climate during these periods. One of the limiting factors in our understanding of these potential analogues is the fact that very few long sequences cover the entire duration of these interglacials at high resolution. In this study, a multi-method approach is used to produce climatic reconstructions for MIS 19, 11, 5, and 1 using pollen data derived from a single long marine core from Ocean Drilling Program (ODP) Site 976. This represents the first study which attempts to use pollen-based climatic reconstructions to compare MIS 1 with its analogues, representing a necessary contribution to the debate with a focus on the relationships between vegetation and climate in the southwestern Mediterranean. Three methods of quantitative climate reconstruction have been adopted: two more widely used methods, the modern analogue technique (MAT) and weighted-average partial least-squares (WAPLS) regression, and a more recent machine learning method known as boosted regression trees (BRTs). The reconstructions show consistent changes in temperature and precipitation during MIS 19, 11, 5, and 1, which correlate well with climatic changes observed in other regional and global proxies and highlight distinct climatic characteristics of each interglacial period in the southwestern Mediterranean. MIS 19 exhibits high variability and colder temperatures compared to subsequent interglacials and MIS 1. Conversely, MIS 11 displays warmer temperatures and greater stability, which makes it a useful analogue to understand prolonged interglacials, crucial when considering the anthropogenic impacts on the duration of warm climate during the Holocene. MIS 5 exhibits overall warmer conditions, and its higher temperature, coupled with fluctuations in solar forcing, makes it a less suitable MIS 1 analogue. Although past interglacials do not offer direct predictions for the Holocene's future, they provide essential insights into Earth's responses to various forcing factors, serving as crucial benchmarks for understanding the Mediterranean's sensitivity to global changes
Regulation of co-translational mRNA decay by PAP and DXO1 in Arabidopsis
No full textInternational audienceBackground: mRNA decay is central in the regulation of mRNA homeostasis in the cell. The recent discovery of a co-translational mRNA decay pathway (also called CTRD) has changed our understanding of the mRNA decay process. This pathway has emerged as an evolutionarily conversed mechanism essential for specific physiological processes in eukaryotes, especially in plants. In Arabidopsis, this pathway is targeted mainly by the exoribonuclease XRN4. However, the details of the molecular regulation of this pathway are still unclear.Results: In this study, we first tested the role of the 3ʹ-phosphoadenosine 5ʹ-phosphate (PAP), an inhibitor of exoribonucleases in the regulation of CTRD. Using 5’Pseq approach, we discovered that FRY1 inactivation impaired XRN4-CTRD activity. Based on this finding, we demonstrated that exogenous PAP treatment stabilizes CTRD mRNA targets. Furthermore, we also tested the implication of the exoribonuclease DXO1 in CTRD regulation. We found that DXO1, another exoribonuclease sensitive to PAP, is also involved in the CTRD pathway, probably by targeting NAD + -capped mRNAs. DXO1 specifically targets mRNAs linked to stress response.Conclusions: Our study provides further insights into the regulation of CTRD in Arabidopsis and demonstrates that other exoribonucleases can be implicated in this pathway
Timing of syn-orogenic extension in the Western Alps revealed by calcite U-Pb and hematite (U-Th)/He dating
No full textInternational audienceUnderstanding fault activity over time provides valuable insights for reconstructing the tectonic history of an orogen, assessing seismological risks and understanding mineralization processes. In the Western Alps, one of the main controversies in existing tectonic models is the understanding of syn-orogenic extension. Seismological evidence shows widespread extensional deformation related to the reactivation of major lithospheric structures, such as the Penninic Frontal Thrust (PFT). However, the onset age and origin of extension are still debated due to the lack of suitable geochronological data. Fault hematite and calcite geochronology as well as clumped isotope data can be used to relate fluid regimes to fault activity. The analysis of calcite brecciae from extensional faults above the PFT shows that two distinct fluid regimes were present. The first regime, occurring before 2 Ma is associated with upwelling of deep fluids and is recorded by fault calcite at a temperature > 110 degrees C. The second fluid regime is characterized by a meteoric signature and temperatures around 36 degrees C, representing crystallization since 2 Ma. This study presents a new model for the Miocene tectonic history of the Western Alps that combines (U-Th)/He and U-Pb geochronology on fault hematite (13.3 +/- 0.8 to < 0.8 Ma) and calcite (5.3 +/- 0.6 Ma). Results demonstrate a progression of extensional fault activity from east to west, from the Middle Miocene (ca. 13 Ma) to the Quaternary. The onset of extension in the inner part of the belt coincides with the development of the fold and thrust belt in the western Alpine foreland. Our new model proposes that extension occurs in the hanging wall of a large top-to-the-west thrust, known as the Alpine Frontal Thrust. This thrust, located to the west of the External Crystalline Massifs gives rise to their uplifting and extension at the rear. (c) 2024 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing)