OZCAR: the French network of Critical Zone Observatories: principlesand scientific objectives

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUInternational audienceThis contribution aims at presenting the principles that underlined the creation of the OZCAR research infras-tructure, gathering various Critical Zone Observatories in France, and the scientific questions that drives theobservation settings.The Critical Zone includes the fine zone between the lower atmosphere at the top of the canopy down to thebedrock-soil interface. This lithosphere-atmosphere boundary is critical for the availability of life-sustainingresources and critical for humanity because this is the zone where we live, where we build our cities, from whichwe extract our food and our water and where we release most of our wastes. This is the fragile zone on which thenatural ecosystem relies because this is where nutrients are being released from the rocks.OZCAR is a distributed research infrastructure gathering instrumented sites and catchments on continentalsurfaces all dedicated to the observation and monitoring of the different compartments of the Critical Zone atthe national scale. All these observatories (more that 40) were all built up on specific questions (acid deposition,flood prediction, urban hydrology. . . ), some of them more than 50 years ago, but they have all in common tobe highly instrumented, permanently funded as infrastructures. They all share the same overarching goal ofunderstanding and predicting the Critical Zone in a changing world. OZCAR gathers instrumented catchments,hydrogeological sites, peatlands, glacier and permafrost regions and a spatial observatory under the commonumbrella of understanding water and biogeochemical cycles and the associated fluxes of energy by using naturalgradients and experimentation. Based on the collaboration with Southern Countries, OZCAR’s sites have a globalcoverage including tropical areas and high mountainous regions in the Andes and the Himalaya.OZCAR benefits from a French investments project called CRITEX (Innovative equipment for the critical zone,https://www.critex.fr/critex-3/observatories/ ) that is centered on the development and deployment of innovativeinstrumentation in the sites.OZCAR was launched in 2016 under the leadership of the French Ministry in charge of Higher Education andResearch, assembling all French Research Institutions involved in environmental studies and with the ambitionof facilitating interdisciplinary research in terrestrial surfaces, stimulating instrumental development and beingvisible at the international level.The paper will presents the main common scientific questions, challenges in terms of instrumentation andexperimentation deployment, in particular in terms of co-location of sites, data base and modelling activities thatthe OZCAR network plan to address in the next years