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Relating Dimethyl Sulphide and Methanethiol Fluxes to Surface Biota in the South‐West Pacific Using Shipboard Air‐Sea Interface Tanks
No full textInternational audienceAbstract Dimethyl sulphide (DMS) and methanethiol (MeSH) emissions from South Pacific surface seawater were determined in deck board Air‐Sea Interface Tanks during the Sea2Cloud voyage in March 2020. The measured fluxes from water to headspace (F) varied with water mass type, with lowest fluxes observed with Subtropical and Subantarctic waters and highest fluxes from Frontal waters. Measured DMS fluxes were consistent with fluxes calculated using a two‐layer model and seawater DMS concentrations. The MeSH:DMS flux ratio was 11%–18% across the three water mass types, confirming that MeSH may represent a significant unaccounted contribution to the atmospheric sulfur budget, with potentially important implications for marine aerosol formation and growth in models. Combining data from the ASITs and ambient surface seawater identified significant Spearman rank correlations for both dissolved DMS and MeSH with nanophytoplankton cell abundance ( p value < 0.012), suggesting an important role for this phytoplankton size class in determining regional DMS and MeSH emissions. Applying a nanophytoplankton‐based parameterization to estimate DMS w provided good agreement with a recent DMS climatology. Consequently, the observed relationship between DMS w , MeSH w and nanophytoplankton cell abundances may be applicable for modeling atmospheric fluxes
The case for a low dark matter density in dynamical dark energy model from local probes
No full textInternational audienceIn this work we investigate, through a Bayesian study, the ability of a local low matter density , in discrepancy with the value usually inferred from the CMB angular power spectrum, to accommodate observations from local probes without being in tension with the local values of the Hubble constant or the matter fluctuation parameters. For that, we combine multiple local probes, with the criteria that they either can constrain the matter density parameter independently from the CMB constraints, or can help in doing so after making their relevant observations more model independent by relaxing their relevant calibration parameters. We assume however, either a dynamical dark energy model, or the standard CDM model, when computing the corresponding theoretical observables. We also add, in almost all of our Monte Carlo runs, the latest Baryonic acoustic oscillations (BAO) measurements from the DESI year one release to our core group. We found that, within CDM model, for different combinations of our probes, we can accommodate a low matter density along with the and values usually obtained from local probes, providing we promote the sound drag component in BAO calculations to a free parameter, and that even if we combine with the Pantheon+ Supernova sample. Assuming CDM, we also found that relaxing allow us to accommodate , and within their local values, with still however a preference for values far from CDM. However, when including Pantheon+ Supernova sample, we found that the latter preference for high matter density pushes to much smaller values, mitigating by then a low matter density solution to the two common tensions. We conclude that a low matter density value, helps in preserving the concordance within CDM model. (abridged
Dataset of microscale atmospheric flow and pollutant concentration large-eddy simulations for varying mesoscale meteorological forcing in an idealized urban environment
No full textInternational audienceBy 2050, two-thirds of the world's population will live in urban areas under climate change, exacerbating the environmental and public health risks associated with poor air quality and urban heat island effects. Assessing these risks requires the development of microscale meteorological models that quickly and accurately predict wind velocity and pollutant concentration with high resolution, as the heterogeneity of urban environments leads to complex wind patterns and strong pollutant concentration gradients. Computational Fluid Dynamics (CFD) has emerged as a powerful tool to address this challenge by providing obstacle-resolved flow and dispersion predictions. However, CFD models are very expensive and require intensive computing resources, which can hinder their systematic use in practical engineering applications. They are also subject to significant uncertainties, particularly those arising from the mesoscale meteorological forcing and the internal variability of the atmospheric boundary layer, some of which are aleatory and thereby irreducible. Given these issues, the construction of CFD datasets that account for uncertainty would be an interesting avenue of research for microscale atmospheric science.In this context, we present the PPMLES (Perturbed-Parameter ensemble of MUST Large-Eddy Simulations) dataset, which consists of 200 large-eddy simulations (LES) characterizing the complex interactions between the turbulent airflow, the tracer dispersion, and an idealized urban environment. These simulations reproduce the canonical MUST dispersion field campaign while perturbing the model's mesoscale meteorological forcing parameters. PPMLES includes time series at human height within the built environment to track wind velocity and pollutant release and dispersion over time. PPMLES also includes complete 3-D fields of first- and second-order temporal statistics of the wind velocity and pollutant concentration, with a sub-metric resolution. The uncertainty of the fields induced by the internal variability of the atmospheric boundary layer is also provided. The computation of PPMLES required significant resources, consuming 6 million CPU core hours, equivalent to the emission of approximately 10 tCO2eq of greenhouse gases. This significant computational effort and associated carbon footprint motivates the sharing of the data generated.The added value of the PPMLES dataset is twofold. First, the perturbed-parameter ensemble of LES enables to quantify and understand the effects of the mesoscale meteorological forcing and the internal variability of the atmospheric boundary layer, which has been identified as a major challenge in predicting atmospheric flow and pollutant dispersion in urban environments. Secondly, PPMLES reference data can be used to benchmark models of different levels of complexity, and to extract key information about the physical processes involved to inform more operational modeling approaches, for example through learning surrogate models
The LOFAR Two-metre Sky Survey: Deep Fields Data Release 2. I. The ELAIS-N1 field
No full textInternational audienceWe present the final 6'' resolution data release of the ELAIS-N1 field from the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey Deep Fields project (LoTSS Deep). The 144MHz images are the most sensitive achieved to date at this frequency and were created from 290 TB of data obtained from 505 hrs on-source observations taken over 7.5 years. The data were processed following the strategies developed for previous LoTSS and LoTSS Deep data releases. The resulting images span 24.53 square degrees and, using a refined source detection approach, we identified 154,952 radio sources formed from 182,184 Gaussian components within this area. The maps reach a noise level of 10.7 Jy/beam at 6'' resolution where approximately half of the noise is due to source confusion. In about 7.4% of the image our limited dynamic range around bright sources results in a further > 5% increase in the noise. The images have a flux density scale accuracy of about 9% and the standard deviation of offsets between our source positions and those from Pan-STARRS is 0.2'' in RA and Dec for high significance detections. We searched individual epoch images for variable sources, identifying 39 objects with considerable variation. We also searched for circularly polarised sources achieving three detections of previously known emitters (two stars and one pulsar) whilst constraining the typical polarisation fraction plus leakage to be less than 0.045%
From proto-neutron star dynamo to low-field magnetars
No full textInternational audienceLow-field magnetars have dipolar magnetic fields that are 10-100 times weaker than the threshold, G, used to define classical magnetars, yet they produce similar X-ray bursts and outbursts. Using the first direct numerical simulations of magneto-thermal evolution starting from a dynamo-generated magnetic field, we show that the low-field magnetars can be produced as a result of a Tayler--Spruit dynamo inside the proto-neutron star. We find that these simulations naturally explain key characteristics of low-field magnetars: (1) weak ( G) dipolar magnetic fields, (2) strong small-scale fields, and (3) magnetically induced crustal failures producing X-ray bursts. These findings suggest two distinct formation channels for classical and low-field magnetars, potentially linked to different dynamo mechanisms
Dynamics of low and high density microplastics in the world's largest choked coastal lagoon under contrasting meteoceanographic conditions
No full textInternational audienceThe contamination by plastic waste in aquatic environments has become a global issue, scientifically reported since 1970. The size and durability of microplastics (MPs, 1 μm > 5 mm) have made these debris widely distributed in aquatic environments. Despite various ongoing initiatives, there is a need to fill gaps in understanding how MPs are transported from their release sources to their final destinations. Therefore, understanding the distribution and dynamics of MPs in coastal areas, such as lagoons and estuaries, which are considered continental sources of MPs to the oceans, is essential to help fill these gaps and propose alternatives for managing what is the environmental problem of the century. In this context, this study aimed to assess the transport patterns of MPs in Patos Lagoon, the largest choked coastal lagoon in the world, considering contrasting meteoceanographic conditions in the system dynamics, such as wind and discharge. Using the hydrodynamic model TELEMAC-3D and the model for plastics particles TrackMPD, simulations were performed using a type of MP polymer (Polypropylene - PP). The simulations of MP transport considered advection, dispersion and the contribution of biofilm in increasing particle density (representing high-density microplastics). The results indicated a gradient of MPs retention from north to south, with higher concentrations of MPs occurring in the northern part of the system. The central region of the lagoon showed a greater tendency for MP export towards the southern region than retention. Meanwhile, the estuary region of Patos Lagoon exhibited a tendency for export of low-density MPs free of biofilm and retention of higher-density MPs, subject to the action of the Plastisphere. Additionally, based on the results obtained from density occurrence maps, it was possible to suggest potential accumulation areas of MPs throughout the lagoon system, reinforcing that the system can act as a sink in specific regions
Chroniques insulaires dans le Pacifique Sud : 2000 ans de dynamiques familiales, biologiques et culturelles
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On the origin and distribution of internal erosion signatures in the floodplain protected by river dikes
No full textThe subsoils of river dikes are often composed of highly permeable and low-density river sediments. Thus, erosion signatures (leaks, sand boils, sinkholes) can appear in the protected floodplain during floods, highlighting the development of hydromorphodynamic phenomena below the surface, which may harm the safety of the dike system. A multi-scale methodology is deployed to understand and analyze the influence of floodplain architecture in terms of geological formations on the appearance of local erosion signatures. Particular attention is paid to the morphology of paleovalleys and paleochannels, in order to image the subsurface in terms of substrate types and interfaces using geophysical methods. This information makes it possible to propose internal erosion scenarios. Application to a study area in South of France (the Agly dike system) leads to new results. The classical backward erosion piping scheme is not relevant to explain the observed sand boils, as they are mainly caused by suffusion-type internal erosion process. Suffusion and contact erosion appear to be the origin of sinkholes. The distribution of these signatures appears to be directly related to the shape and dimensions of the paleovalley and paleochannels, as well as to the presence of a low-permeability topsoil
Potential and costs required for methane removal to compete with BECCS as a mitigation option
No full textInternational audienceMethane is the second most important anthropogenic greenhouse gas (GHG) causing warming after carbon dioxide, and the emission reductions potentials are known to be limited due to the difficulty of abating agricultural methane. We explore in this study the emerging option of atmospheric methane removal (MR) that could complement carbon dioxide removal (CDR) in mitigation pathways. MR is technologically very challenging and potentially very expensive, so the main question is at which cost per ton of methane removed is MR more cost effective than CDR. To address this question, we use an intertemporal optimization climate-GHG-energy model to evaluate the MR cost and removal potential thresholds that would allow us to meet a given climate target with the same or a lower abatement cost and allowing for equal or higher gross CO 2 emissions than if CDR through bioenergy with carbon capture and storage were an option. We also compare the effects of MR and CDR on the cost-effective mitigation pathways achieving four different climate targets. Using the ACC2-GET integrated carbon cycle, atmospheric chemistry, climate and energy system model, we consider a generic MR technology characterized by a given unit cost and a maximal removal potential. We show that to totally replace bioenergy based CDR with MR, the MR potential should reach at least 180-290 MtCH 4 per year, i.e. between 50% and 90% of current anthropogenic methane emissions, with maximum unit cost between 11 000 and 69 000 $/tCH 4 , depending on the climate target. Finally, we found that replacing CDR by MR reshapes the intergenerational distribution of climate mitigation efforts by delaying further the mitigation burden.</div
Active biomonitoring of river pollution using an ex-situ exposure system with two model species
No full textInternational audienceIn the context of increasing pollution pressure on aquatic ecosystems, it is essential to improve our knowledge of habitat quality and its suitability for organisms. It is particularly relevant to better integrate early life stages of fish into pollution biomonitoring programs, as they are reliable indicators of ecosystem integrity and because of their high sensitivity to pollutants. To avoid the influence of environmental parameters on their development, a lab-on-field approach, called the ex-situ exposure method, was developed. Aquatic organisms were exposed to a continuous flux of water under semi-controlled temperature, oxygen, and photoperiod conditions to avoid the influence of these confounding factors when interpreting the results. To investigate the potential role of water contamination, this active biomonitoring method was applied to the Garonne River (Southwest France), where migratory fish populations have declined. Two model species from different taxa were used: embryos of the Japanese medaka (Oryzias latipes) and adults of the crustacean Gammarus fossarum. The results showed a significant impact of water quality on embryo mortality and early hatching in two separate experiments on Japanese medaka. In addition, an induction of feeding rate was observed in exposed gammarids, but no impact on their embryo survival, suggesting differences in sensitivity between the two species selected. Chemical and biological analyses did not identify trace metals, pesticides, or microorganisms as potential sources of toxicity in medaka embryos or G. fossarum. These results raise concerns about the quality of the water in the Garonne River and its toxicity to aquatic organisms