In 2021, the Nobel Committee for Physics reminded that, in a context of global warming, the modern understanding of the variability of the Earth’s climate is based on the existence of clear separations of processes in terms of space and time scales, whose prediction requires interdisciplinary efforts. Fluid mechanics can therefore be an important contributor to the understanding of these fundamental questions, by providing answers about the interaction between large and small-scale structures in the atmosphere, and how their coupled interaction produces significant velocity and temperature fluctuations. In addition to this geostrophic turbulence, almost two-dimensional, that dominates large scales, gravity waves dominate smaller scale dynamics at mid-latitudes, and three-dimensional turbulent fields act at small scales and contribute strongly to vertical mixing and dissipation. The current project is devoted to the understanding, prediction and modeling of large-scale/waves/micro-turbulence interaction phenomena which are characteristic of the atmosphere and of its variability. It relies on: (a) theoretical developments of transport equations of statistical moments of order up to 4, thus giving access to energy fluxes and extreme events in velocity-temperature fields; (b) high resolution direct numerical simulations providing detailed data of different interactions, in idealized conditions; (c) the atmospheric model WRF for predictions with realistic conditions but with a parameterization of small scales. One important outcome of the project will be a model for accurate prediction of atmospheric variability phenomena, and the numerical database it will produce.

Assessing the consequences of chemical contamination on the structure and funtioning of aquatic ecosystems under urban pressure is a challenging task. Indeed, the link between a biological response, for instance measured at the scale of an organism exposed and collected in the field, and chemical contamination remains difficult to establish. In particular, numerous confounding factors and adaptation processes are likely to modify the biological responses registered. Adaptation to a toxic pressure is characterized by physiological acclimatation and/or genetic modifications which lead to an increase of tolerance or resistance of the exposed organism. At the scale of the community, adaptation is also often related to the disappearance of sensitive species. Understanding and evaluating the impacts of the chemical pressure exerted on living organisms in urban areas thus requires the investigation of the biological processes of adaptation at low concentrations of contaminant which are typical to urban areas. The SequAdapt project aims at exploring both the mechanisms and the consequences of adaptation at the scale of the organism (using gammarids as a biological model) and of the community (using river biofilms). The study will focus on metals (in particular Cu, Cd, Ni, Pb et Zn), which are non-biodegradable pollutants and are dispersed from several sources in the Seine basin (wastewater, erosion processes, atmospheric fallouts, etc.). The study is divided in two parts: - part 1 focuses on investigating the mechanisms of adaptation. At the scale of the organism, we aim at investigating the variability of bioaccumulation toxico-kinetics by pre-exposed or control gammarids. At the scale of the community, we aim at investigating the link between community tolerance acquisition using a PICT (Pollution-Induced Community Tolerance ) approach and the expression of metal-resistance genes using RT-qPCR - part 2 focuses on the ecological cost of adaptation. At the scale of the organism, enzymatic and proteomic approaches will be undertaken to evaluate modifications of functional responses of gammarids that are adapted to metals. As far as biofilms are concerned, community tolerance acquisition evaluated on heterotrophic communities, will be interpreted in relation to measurements of bacterial genetic diversity by microbiome profiling using 16S-rDNA sequencing and to community-level physiological profiles based on the respiration of different substrates in microplaques.

Antimony (Sb) is one of the most enriched elements in urban environments but also the least studied. Given its potential toxicity, it is therefore very important to identify the impact of Sb on the environmental compartments accumulating this emerging contamination. Despite the fact that significant enrichments were registered in urban environment samples, important scientific issues remain totally unexplored, such as the relative contributions of the different sources of Sb contamination, and Sb biogeochemical behavior within and between urban sedimentary reservoirs. In this context, providing information about Sb speciation and transfer pathways is of prime importance in order to control the environmental dissemination of this emerging contaminant in the critical zone. The pluri-disciplinary ANTIMONY project will provide innovative knowledge on the sources and chemical forms of Sb in an urban continuum, from sources to receiving environmental compartments and this up to a long-time range. It proposes a progressive strategy made necessary by the complexity of the processes involved and by the lack of knowledge about the sources and the fate of Sb in urban areas. ANTIMONY is built in such a way as to explore the mechanisms governing Sb behavior at the molecular scale in controlled batch experiments, and to progressively increase the time and space scales of the experiments up to the study of long-term trends and impacts of Sb contamination on urban areas. Task 1 will examine the mechanisms of Sb mobilization in controlled conditions (T1 batch experiments). The number of potential processes (sorption/desorption of Sb species, biotic and abiotic redox transformations) require laboratory experiments in which processes are singled out for study: Sb(V) reduction to Sb(III) by pure bacterial strains or reductants produced by microbial activity (Fe(II), sulfides), ligand exchange from oxygen to sulfur, and oxidative stibnite dissolution. This comprehensive approach will generate novel "fundamental" information concerning the isotope fractionation and mineralogical changes accompanying the environmental and microbial processes that Sb is involved in. Task 2 is dedicated to retention ponds located along roads, which stand as model systems to study Sb transfers from car traffic areas to the aquatic environment. The partition of Sb in these environments, the Sb isotope ratio and the mineralogy of the bearing phases will be documented. Mesocosm experiments with sediments representative of urban reservoirs will be designed to gain insights into the processes affecting Sb mobility and to elucidate the role of bacteria in Sb transfer between water and sediment compartments. We will also use ?123Sb measurements as a probe to monitor the mechanisms involved at the molecular scale (oxidation, reduction, ligand exchange), allowing us to draw hypotheses on the changes in Sb geochemistry observed in the environment. We will take opportunity of this task to carry out isolation of pure or simplified bacterial consortia involved in Sb reduction. Task 3 will explore the behavior of Sb in the ‘road to the pond’ continuum during a rain event to reveal the fast changes in Sb behavior during heavy rain events which are suspected to transport a large part of the road to pond Sb fluxes. The analysis of other than road Sb source samples (e.g. paints, plastics, lead artefacts) will document the isotopic and spectroscopic signature of these sources. In Task 4, sediment archives will be collected in the Seine River Basin to document the influence of source changes vs. post-depositional processes on the Sb contamination trajectory during the last century in relation with diagenesis and source changes. During its course, ANTIMONY will provide sediment and DNA banking material for future studies devoted to Sb biogeochemical cycles and to other emerging contaminants, related to road traffic or not.

Perennially frozen slopes occur in many mountain ranges of the world, and temperature changes in these environments have notable impacts on the state of permafrost, leading to increased slope instability and hazard from mass movements. In areas of discontinuous permafrost, these slopes can be hard to identify with certainty. This project investigates “molards” – cones of loose debris that result from thawing of blocks of ice-rich sediments mobilised by landslides in permafrost terrains. Molards are an understudied landform and have recently been shown to be an indicator of recent and ongoing permafrost degradation. In addition, they have spatial and geomorphic characteristics that reveal the dynamics of large mass movements. The PERMOLARDS project aims to build on these exciting new results and use molards as a geomorphological tool to understand climate change and natural hazard. We will use a multidisciplinary combination of field investigation, dating, laboratory and numerical simulations, modelling and remote sensing analysis to understand molard formation, evolution, morphology, longevity, and their environmental settings. We will explore three unique case studies in Greenland, Canada and Iceland, where we have identified with certainty molards that formed under climatic conditions from the Holocene to the present in a variety of geographic settings. We will constrain the morphological degradation of molards in space and time by using a morphological approach and novel luminescence dating techniques. We will define the range of material properties and ice configurations under which molards can form through field investigations and through simulation via analogue models in a laboratory cold room. Based on these results ancient molards can then be used to infer ground-ice contents. We will establish the baseline criteria to distinguish molards from other mounds in landslide deposits using remote sensing and field data that can be used by other researchers. We will use 3D numerical models to assess the potential role of thaw fluids in molard-hosting landslides in modifying the flow behaviour and its impact on hazard. We will monitor and model the state of permafrost at the field site in Greenland to ascertain the state of permafrost degradation represented by molards in new and recent landsides. Finally, we will establish the use of molards as a geomorphological tool to track permafrost degradation in time and in different geological and geographical settings around the globe. By developing these actions, the project provides insights into permafrost degradation in space and time, and the hazard posed by landslides in cold environments.