BOUM aims to produce a detailed study of biological production and its fate in several distinct locations, representing different systems, of the Mediterranean Sea. These distinct systems represent, at a regional scale, the main oceanographic features of contrasting environments found in the oligotrophic ocean. We will determine whether organic matter production, remineralization and export ... processes are longitudinally different and if so, study how these differences are related to the structure of the planktonic community. We will focus on several questions of current interest concerning the coupling/uncoupling between carbon and nutrient (N,P,Si,Fe) delivery and removal processes which are controlling planktonic community structures and function and, ultimately, the ability of the ocean to sequester carbon. We shall describe the functioning of each distinct ecosystem under physical conditions as stationary as possible, and finally, from experimental and modelling approaches, examine the responses of the systems to perturbations, i.e. pulsed nutrient addition. The BOUM project federates French teams and is largely open to foreign collaborations. It is based on one cruise on the R/V l'Atalante or the Pourquoi Pas.