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Advancing ocean monitoring and knowledge for societal benefit: the urgency to expand Argo to OneArgo by 2030
No full textInternational audienceThe ocean plays an essential role in regulating Earth’s climate, influencing weather conditions, providing sustenance for large populations, moderating anthropogenic climate change, encompassing massive biodiversity, and sustaining the global economy. Human activities are changing the oceans, stressing ocean health, threatening the critical services the ocean provides to society, with significant consequences for human well-being and safety, and economic prosperity. Effective and sustainable monitoring of the physical, biogeochemical state and ecosystem structure of the ocean, to enable climate adaptation, carbon management and sustainable marine resource management is urgently needed. The Argo program, a cornerstone of the Global Ocean Observing System (GOOS), has revolutionized ocean observation by providing real-time, freely accessible global temperature and salinity data of the upper 2,000m of the ocean (Core Argo) using cost-effective simple robotics. For the past 25 years, Argo data have underpinned many ocean, climate and weather forecasting services, playing a fundamental role in safeguarding goods and lives. Argo data have enabled clearer assessments of ocean warming, sea level change and underlying driving processes, as well as scientific breakthroughs while supporting public awareness and education. Building on Argo’s success, OneArgo aims to greatly expand Argo’s capabilities by 2030, expanding to full-ocean depth, collecting biogeochemical parameters, and observing the rapidly changing polar regions. Providing a synergistic subsurface and global extension to several key space-based Earth Observation missions and GOOS components, OneArgo will enable biogeochemical and ecosystem forecasting and new long-term climate predictions for which the deep ocean is a key component. Driving forward a revolution in our understanding of marine ecosystems and the poorly-measured polar and deep oceans, OneArgo will be instrumental to assess sea level change, ocean carbon fluxes, acidification and deoxygenation. Emerging OneArgo applications include new views of ocean mixing, ocean bathymetry and sediment transport, and ecosystem resilience assessment. Implementing OneArgo requires about $100 million annually, a significant increase compared to present Argo funding. OneArgo is a strategic and cost-effective investment which will provide decision-makers, in both government and industry, with the critical knowledge needed to navigate the present and future environmental challenges, and safeguard both the ocean and human wellbeing for generations to come
JWST reveals a supernova following a gamma-ray burst at z 7.3
No full textInternational audienceThe majority of energetic long-duration gamma-ray bursts (GRBs) are thought to arise from the collapse of massive stars, making them powerful tracers of star formation across cosmic time. Evidence for this origin comes from the presence of supernovae in the aftermath of the GRB event, whose properties in turn link back to those of the collapsing star. In principle, with GRBs we can study the properties of individual stars in the distant universe. Here, we present JWST/NIRCAM observations that detect both the host galaxy and likely supernova in the SVOM GRB 250314A with a spectroscopically measured redshift of z 7.3, deep in the era of reionisation. The data are well described by a combination of faint blue host, similar to many z 7 galaxies, with a supernova of similar luminosity to the proto-type GRB supernova, SN 1998bw. Although larger galaxy contributions cannot be robustly excluded, given the evidence from the blue afterglow colours of low dust extinction, supernovae much brighter than SN 1998bw can be. These observations suggest that, despite disparate physical conditions, the star that created GRB 250314A was similar to GRB progenitors in the local universe
The spin-orbit alignment hypothesis in millisecond pulsars
No full textInternational audienceMillisecond pulsars (MSPs) are spun up during their accretion phase in a binary system. The exchange of angular momentum between the accretion disk and the star tends to align the spin and orbital angular momenta on a very short time scale compared to the accretion stage. In this work, we study a subset of -ray MSPs in binaries for which the orbital inclination has been accurately constrained thanks to the Shapiro delay measurements. Our goal is to constrain the observer viewing angle and to check whether it agrees with the orbital inclination , thus . We use a Bayesian inference technique to fit the MSP -ray light-curves based on the third -ray pulsar catalogue (3PC). The emission model relies on the striped wind model deduced from force-free neutron star magnetosphere simulations. We found good agreement between those two angles ( and ) for a significant fraction of our sample, between 1/2 and 2/3, confirming the spin-orbit alignment scenario during the accretion stage. However about one third of our sample deviates significantly from this alignment. The reasons are manifold: either the -ray fit is not reliable or some precession and external torque avoid an almost perfect alignment
Dermacentor ticks and their human pathogens in various ecosystems of eastern France
No full textInternational audienceDermacentor is Europe's second most important tick genus. It comprises two species: Dermacentor reticulatus, which has a more northerly range, and Dermacentor marginatus, which is typically found in Mediterranean regions. In France, especially in the east, the presence of Dermacentor remains understudied. Leveraging projects on Ixodes ricinus, we identified high-risk ecosystems for Dermacentor ticks. Both species were present, but D. reticulatus was dominant (96.3 %), always coexisting with Ixodes, at densities reaching 30.3 questing adults/ 100 m 2 in Bas-Rhin. This species was found to thrive in wet meadows, alluvial forests, and lakes, where wild boars (Sus scrofa) are common. Among domestic animals, dogs and horses were the preferred hosts. Regarding human pathogens, we focused on the circulation of rickettsiae responsible for tick-borne lymphadenopathy. Acarological risk varied by region, with Rickettsia raoultii being the most prevalent bacterial species in all the departments, whereas Rickettsia slovaca was rarer and present only in 2 Bas-Rhin nature reserves. At the peak of tick activity, up to 18.7 % of Dermacentor adult ticks carried R. raoultii. In the studied region, D. reticulatus is the only known vector of these potentially pathogenic microorganisms.</div
A continuous 500‐year sediment record of inundation by local and distant tsunamis in South‐Central Chile (40.1°S)
No full textInternational audienceAbstract Chile's west coast is frequently struck by megathrust earthquakes and tsunamis, as illustrated by the CE 2010 Maule ( M w 8.8) and CE 1960 Valdivia ( M w 9.5) events. Despite numerous palaeoseismic and palaeotsunami studies, uncertainties remain regarding the rupture extent and tsunamigenic potential of M w 8–9 earthquakes. This study examines the sedimentary record of Laguna Gemela West, a coastal lake at 5–6 m a.s.l. and of 17.5 m depth. It is separated from the Pacific by a 400 m long channel bordered by northward‐propagating dunes and controlled by Pleistocene sandstones forming a knickpoint in the channel profile. Multiple sedimentary proxies (e.g. grain‐size, X‐CT, XRF scanning) identified five distinct sand‐enriched layers, interpreted as tsunami deposits. Age‐depth modelling (based on 137Cs and 14C) allowed linking these deposits to the CE 2010, 1960, 1837, 1737 and 1575 megathrust earthquakes. While historical records confirm significant tsunamis in CE 2010, 1960, 1837 and 1575, no reports exist for a CE 1737 tsunami. However, a potential tsunami deposit and evidence for subsidence were found at the nearby Chaihuín site, albeit with large dating uncertainty (CE 1600–1820). The more precise age for a sand layer at Laguna Gemela West (CE 1672–1746) supports the occurrence of a local tsunami in CE 1737. Additionally, deposits linked to the CE 1837 and 2010 events suggest tsunamis can impact sites >100 km adjacent to megathrust ruptures. A second pulse in the uppermost sand layer may reflect the CE 2011 Japan tsunami, which reached a similar height (~1.6 m a.s.l.) in the nearest tide gauge as the CE 2010 tsunami. Unlike coastal plain sites, which often require coseismic subsidence for deposit preservation, coastal lakes can capture a more complete tsunami history. This study highlights their complementary role in palaeotsunami research, providing insights in local, regional and transoceanic tsunami events
STUDY OF THE LITHOSPHERIC STRUCTURE BENEATH NORTHEAST BRAZIL WITH P-WAVE MULTIPLE FREQUENCY SEISMIC TOMOGRAPHY
No full textInternational audienceWe used the multiple-frequency seismic tomography method to image the upper mantle beneath Northeast Brazil by processing P-wave broadband seismograms in six frequency passbands. The data comprised 87,896 relative traveltime residuals for P and PKIKP phases, simultaneously inverted to obtain 3D models of P-velocity anomalies. We conducted resolution tests using checkerboard patterns with horizontal dimensions of 312 x 312 km and 390 x 390 km. For the 312 x 312 km structures, we observed good horizontal recovery beneath the areas of the Borborema province and northern São Francisco craton at the depths of 136 and 226 km, with the areas of the São Luís craton and Parnaíba basin also presenting recovery, albeit with reduced amplitudes. For the 390 x 390 km structures we observed good horizontal and amplitude recovery throughout the entire study area. Our model was unable to recover the sharp vertical transitions between the anomalies. We present the preferred model for Parnaíba basin and Borborema province. The model shows a fragmented basement for the Parnaíba basin, with two strong high-velocity anomalies consistent with the Parnaíba and Granja blocks, and another slight high-velocity anomaly north of the basin, consistent with the São Luís craton. To the west of the basin, the Parnaíba block appears separate from another high-velocity anomaly associated with the Amazonian craton. A strong high-velocity anomaly south of the Borborema province is interpreted as the northern portion of the São Francisco craton. The São Francisco craton anomaly presents strong high-velocity anomalies, interpreted as a thickening of certain portions of the craton, separated by a weaker positive anomaly, interpreted as the Paramirim Aulacogen. The Borborema province is characterized by a low-velocity anomaly. The central and northeastern portions of this anomaly presented even lower velocities, which was interpreted as lateral flow in the asthenosphere, originating from the passage of a plume to the north of the province. A low-velocity anomaly located west of the Borborema province strikes roughly NE-SW and separates the São Francisco craton from the Parnaíba block and the Amazonian craton. It is interpreted as the Transbrasiliano Lineament. To test the capability of our data to resolve the limits of largescale structures, we created four synthetic models simulating the presence of different cratonic nuclei. The models show good horizontal recovery, with the fourth model, based on our findings, presenting the best correlation between the real and recovered models. Seismicity in the study region is mainly correlated to low-velocity anomalies.</div
Benchmarking the TRISHNA L3 all weather daily evapotranspiration algorithms over contrasted land use and climates.
No full textInternational audienc
Revisiting tidal rectification by bottom topography
No full textInternational audienceTidal rectification plays a key role in controlling mean transport in coastal areas and coast-basin materialexchange. To calculate mean flows, conventional approaches require high-resolution basin-scale numericalsimulations which demands substantial computational resources. This study revisits tidal rectification governedby topographic variation and bottom friction, and proposes a new analytical solution.The first step is to derive solutions in the simplest possible configuration. We thus revisit solutions inone-dimensional (1D) configurations, using a Lagrangian approach from which Eulerian results are derived.Exact solutions are provided for the frictionless case and new approximate solutions are developed for a morerealistic quadratic bottom friction.We then analyze the influence of viscosity on solutions from numerical models. We find that the latter hasmoderate influence when quadratic bottom friction is considered. However, when the steady rectified currentextends over regions deeper than a critical depth, viscosity can lead to spurious effects and alter the accuracyof the numerical results. We show the critical depth can be expressed as a function of friction coefficient, tidalflux and topography variation length-scale.We finally extend the analytical solutions derived for the 1D case to the two-dimensional (2D) case. The 2Dsolutions are compared to results from an ocean general circulation model solving the full barotropic equationsin an academic configuration with a complex topography and a quadratic bottom friction. Comparison betweenanalytical solutions and numerical simulations shows good agreement for both the magnitude and direction ofthe steady rectified tidal current. Sensitivity tests to bottom friction and tide amplitude show that the steadyrectified current is parallel to the isobaths and independent of the magnitude of the bottom friction coefficientat first order
