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Single-cell imaging reveals efficient nutrient uptake and growth of microalgae darkening the Greenland Ice Sheet
No full textInternational audienceBlooms of dark pigmented microalgae accelerate glacier and ice sheet melting by reducing the surface albedo. However, the role of nutrient availability in regulating algal growth on the ice remains poorly understood. Here, we investigate glacier ice algae on the Greenland Ice Sheet, providing single-cell measurements of carbon:nitrogen:phosphorus (C:N:P) ratios and assimilation rates of dissolved inorganic carbon (DIC), ammonium and nitrate following nutrient amendments. The single-cell analyses reveal high C:N and C:P atomic ratios in algal biomass as well as intracellular P storage. DIC assimilation rates are not enhanced by ammonium, nitrate, or phosphate addition. Our combined results demonstrate that glacier ice algae can optimise nutrient uptake, facilitating the potential colonization of newly exposed bare ice surfaces without the need for additional nutrient inputs. This adaptive strategy is particularly important given accelerated climate warming and the expansion of melt areas on the Greenland Ice Sheet
Prevalence and dynamics of antimicrobial resistance in pioneer and developing Arctic soils
No full textInternational audienceAntimicrobial resistance (AMR) in soil is an ancient phenomenon with widespread spatial presence in terrestrial ecosystems. However, the natural processes shaping the temporal dissemination of AMR in soils are not well understood. We aimed to determine whether, how, and why AMR varies with soil age in recently deglaciated pioneer and developing Arctic soils using a space-for-time approach. Specifically, we assess how the magnitude and spread of AMR changes with soil development stages, including antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and antibiotic-resistant bacteria (ARB). We showed that ARGs, MGEs, and ARB are present, and exhibit a non-uniform distribution in the developing soils. Their abundance generally increases with soil age but at different rates overall and across different glacier forefields. Our analyses suggest a strong positive relationship between soil age and ARGs and ARB, which we attribute to increased competition between microbes in older soils. We also observed a strong negative relationship between soil age and ARG diversity mediated by soil organic matter -suggesting facilitation due to the alleviation of nutrient limitation. These contrasting results suggest that both competition and facilitation can regulate AMR spread through time in the Arctic, but competition might be the stronger determinant of AMR spread
Holocene trends in Nile Delta fire regimes driven by cropland expansion and reduced precipitation
No full textInternational audienceFire played a pivotal role in promoting early agricultural development in ancient Egyptian societies. In the Nile Delta, since the Predynastic period, fires have predominantly been initiated by human activity. However, the long-term alterations in precipitation patterns and Nile floods might also have significantly influenced the evolution of the human-induced fire regime. Here we investigate 8000 years (10,000 to 2000 BP) of fire activity in the Nile Delta using a composite sequence based on cores taken from the Predynastic sites of Buto, Sais and Kom El-Khilgan. We compared and contrasted the long-term evolution of fire activity with precipitation data, Nile flow dynamics and the emergence/development of agriculture to disentangle the factors that modulated the occurrence and intensification of fires during the Holocene. Until 6100 ± 70 BP, sustained precipitation, in tandem with significant flooding of the Nile, was the foremost factor inhibiting human settlement and the use of fire in the delta. During the period spanning from 6100 ± 70 to 4700 ± 70 BP, weakening Nile discharge and increasing human-induced fire significantly promoted agriculture. Since 4700 ± 70 BP, cropland expansion, driven by declining intensity in Nile flow and reduced precipitation, has contributed substantially to the upward trend in fire activity over the delta. This increase in burned areas likely resulted from the need for sustained agricultural production to cope with rapid population growth in Egypt and the socio-economic changes that occurred during the Dynastic period. The Nile Delta data are consistent with those of the eastern Mediterranean, suggesting that the entire region underwent significant transformation between 5500 and 4500 BP
Denoising radio pulses from air showers using machine-learning methods
No full textInternational audienceThe Giant Radio Array for Neutrino Detection (GRAND) aims to detect radio signals from extensive air showers (EAS) caused by ultra-high-energy (UHE) cosmic particles. Galactic, hardware-like, and anthropogenic noise are expected to contaminate these signals. To address this problem, we propose training a supervised convolutional network known as an encoder-decoder. This network is used to learn a coded representation of the data and remove specific features from it. This denoiser is trained using high-fidelity air shower simulations specifically tailored to replicate the characteristics of signals detected by GRAND. In this contribution, we describe our machine-learning model and report initial results demonstrating the sensitivity enhancement resulting from our denoising algorithm when applied to realistically simulated GRAND signals with varying signal-to-noise ratios.</div
Localisation and host galaxy identification of new Fast Radio Bursts with MeerKAT
No full textInternational audienceAccurately localising fast radio bursts (FRBs) is essential for understanding their birth environments and for their use as cosmological probes. Recent advances in radio interferometry, particularly with MeerKAT, have enabled the localisation of individual bursts with arcsecond precision. In this work, we present the localisation of 15 apparently non-repeating FRBs detected with MeerKAT. Two of the FRBs, discovered in 2022, were localised in 8 second images from the projects which MeerTRAP was commensal to, while eight were localised using the transient buffer pipeline, and another one through SeeKAT, all with arcsecond precision. Four additional FRBs lacked TB triggers and sufficient signal, limiting their localisation only to arcminute precision. For nine of the FRBs in our sample, we identify host galaxies with greater than 90% confidence, while two FRBs have ambiguous associations with two host galaxy candidates. We measured spectroscopic redshifts for six host galaxies, ranging from 0.33 to 0.85, demonstrating MeerKAT's sensitivity to high redshift FRBs. For galaxies with sufficient photometric coverage, we performed spectral energy those of known FRB hosts. This work represents one of the largest uniform samples of well-localised distant FRBs to date, laying the groundwork for using MeerKAT FRBs as cosmological probes and understand how FRB hosts evolve at high redshift
A Simulation Framework for the LiteBIRD Instruments
No full textInternational audienceLiteBIRD, the Lite (Light) satellite for the study of -mode polarization and Inflation from cosmic background Radiation Detection, is a space mission focused on primordial cosmology and fundamental physics. In this paper, we present the LiteBIRD Simulation Framework (LBS), a Python package designed for the implementation of pipelines that model the outputs of the data acquisition process from the three instruments on the LiteBIRD spacecraft: LFT (Low-Frequency Telescope), MFT (Mid-Frequency Telescope), and HFT (High-Frequency Telescope). LBS provides several modules to simulate the scanning strategy of the telescopes, the measurement of realistic polarized radiation coming from the sky (including the Cosmic Microwave Background itself, the Solar and Kinematic dipole, and the diffuse foregrounds emitted by the Galaxy), the generation of instrumental noise and the effect of systematic errors, like pointing wobbling, non-idealities in the Half-Wave Plate, et cetera. Additionally, we present the implementation of a simple but complete pipeline that showcases the main features of LBS. We also discuss how we ensured that LBS lets people develop pipelines whose results are accurate and reproducible. A full end-to-end pipeline has been developed using LBS to characterize the scientific performance of the LiteBIRD experiment. This pipeline and the results of the first simulation run are presented in Puglisi et al. (2025)
Inter-species comparison of life traits related to amnesic shellfish toxin kinetic in five scallop species.
No full textInternational audiencePectinid species (scallops) hold significant economic value, but their filtration activity makes them vulnerable to harmful algal blooms, particularly Pseudo-nitzschia species producing domoic acid (DA). This neurotoxin, responsible for Amnesic Shellfish Poisonings (ASP) in birds and mammals, leads prolonged sales bans when concentrations exceed the regulatory threshold. However, DA retention is species-specific, and the underlying mechanisms remain poorly understood. This study aims to compare pectinid species to assess whether interspecific differences in energetic traits influence DA retention. Using Dynamic Energy Budget (DEB) theory and the AmP multi-species estimation procedure as a common conceptual framework, we compared five pectinid species: two slow depurators (Pecten maximus and Placopecten magellanicus), two fast depurators (Argopecten purpuratus, Mimachlamys varia) and Nodipecten subnodosus, hypothesised fast depurator. We collected and compared life-history traits, focusing on life cycle transitions and reproductive effort, to establish the multi-species DEB parameter estimation. Three key parameters were then examined to explain differences in DA retention: specific assimilation, somatic maintenance costs and energy conductance. Our results, in addition to refine individual parameter estimations for the five species, revealed differences among species in these three parameters. However, only energy conductance consistently increased along the “slow-to-fast’” depuration gradient. Furthermore, we identified a limitation in describing the bivalve life cycle due to inconsistencies between larval and adult growth data. This study lays the groundwork for DA kinetics modelling and highlights the potential of multispecies parameter estimation for species comparisons. The presentation will cover key hypotheses, challenges and insights from this multispecies parameter estimation approach
The Impact of the Transport of Chemicals and Electronic Screening on Helioseismic and Neutrino Observations in Solar Models
No full textInternational audienceThe transport of chemical elements in stellar interiors is one of the greatest sources of uncertainties of solar and stellar modelling. The Sun, with its exquisite spectroscopic, helioseismic and neutrino observations, offers a prime environment to test the prescriptions used for both microscopic and macroscopic transport processes. We study in detail the impact of various formalisms for atomic diffusion on helioseismic constraints in both CLES (Scuflaire et al. 2008a) and Cesam2k20 (Morel and Lebreton 2008; Marques et al. 2013; Deal et al. 2018) models and compare both codes in detail. Moreover, due to the inability of standard models using microscopic diffusion to reproduce light element depletion in the Sun (Li, Be), another efficient process must be included to reproduce these constraints (rotation-induced: Eggenberger et al. 2022, overshooting -or penetrative convection- below the convective envelope: Thévenin et al. 2017, or ad hoc turbulence: Lebreton and Maeder 1987; Richer, Michaud, and Turcotte 2000). However, introducing such an extra mixing leads to issues with the CNO neutrino fluxes (see Buldgen et al. 2023), which seem to be systematically lower than the Borexino observations (Appel et al. 2022). Another key aspect to consider when reconciling models with neutrino fluxes is the impact of electronic screening (Mussack and Däppen 2011)
Genetic evolution of a multi-generational population in the context of interstellar space travels -Part II: Phenotypic effects of gene expression
No full textInternational audienceIn the first paper of this series, we included the effects of population genetics in the agent-based Monte Carlo code HERITAGE under the hypothesis of neutral phenotypic effects. It implied that mutations (genetic changes) had only neutral physical manifestations. We now relax this assumption by including genetic effects of mutation and neo-mutations (from radiations) onto the population's life expectancy, fertility, pregnancy chances and miscarriage rates. When applied to a population aboard a generation ship that travels at sub-light speed towards a distant exoplanet, we demonstrate that natural selection indirectly affects the genetic structure of a population via the contribution of phenotypes, in agreement with past studies in conservation biology. For large starting crews (about 500 individuals), the effect aligns with the neutral hypothesis and the frequency of alleles (for non-sexual chromosomes) is stable over centuries. Results are completely different if the spacecraft shielding, integrated into hull design, fails to efficiently protect the crew from high-energy cosmic rays and showers of secondary particles. We tested different scenarios, in which the level of radiation is either fixed at normal or extreme levels, or changing over time due to, e.g., shield degradation, on-board nuclear incident or the outburst of a supernova situated 50 light-years away.</div