Core Ideas: OZCAR is a network of sites studying the critical zone. OZCAR covers various disciplines. OZCAR will help disciplines to work together for a better representation and modeling of the critical zone. The French critical zone initiative, called OZCAR (Observatoires de la Zone Critique–Application et Recherche or Critical Zone Observatories–Application and Research) is a National Research Infrastructure (RI). OZCAR‐RI is a network of instrumented sites, bringing together 21 pre‐existing research observatories monitoring different compartments of the zone situated between “the rock and the sky,” the Earth's skin or critical zone (CZ), over the long term. These observatories are regionally based and have specific initial scientific questions, monitoring strategies, databases, and modeling activities. The diversity of OZCAR‐RI observatories and sites is well representative of the heterogeneity of the CZ and of the scientific communities studying it. Despite this diversity, all OZCAR‐RI sites share a main overarching mandate, which is to monitor, understand, and predict (“earthcast”) the fluxes of water and matter of the Earth's near surface and how they will change in response to the “new climatic regime.” The vision for OZCAR strategic development aims at designing an open infrastructure, building a national CZ community able to share a systemic representation of the CZ, and educating a new generation of scientists more apt to tackle the wicked problem of the Anthropocene. OZCAR articulates around: (i) a set of common scientific questions and cross‐cutting scientific activities using the wealth of OZCAR‐RI observatories, (ii) an ambitious instrumental development program, and (iii) a better interaction between data and models to integrate the different time and spatial scales. Internationally, OZCAR‐RI aims at strengthening the CZ community by providing a model of organization for pre‐existing observatories and by offering CZ instrumented sites. OZCAR is one of two French mirrors of the European Strategy Forum on Research Infrastructure (eLTER‐ESFRI) project.

Stable isotope compositions of present day precipitation in the 70°E–160°W longitude range reveal a strong correlation with moisture source and transport patterns and are not correlated with the amount of precipitation, contrary to existing interpretations. Spatially and temporally variable moisture sources and cyclonic circulation result in more depleted isotope values (δ¹⁸O ∼ −5 to −7‰) in the 100°E–170°E range. Oceanic moisture with minimal continental loss or input results in comparatively enriched δ¹⁸O values (∼−2 to −4‰) in the 70°E–100°E range and east of 170°E. Isotope compositions of dated groundwater archives from the Philippines, Vietnam, Thailand and Bangladesh, reflecting past isotopic composition of precipitation, indicate that this distinction in moisture regimes was preserved during the last glacial period and strongly suggest that there was no significant shift in the summer Inter‐Tropical Convergence Zone (ITCZ) in this region.