Project summary

The functioning and productivity of oligotrophic systems, and the balance between production and mineralization in these areas, is still the subject of much debate. Once thought to be biological deserts, recent research has shown that these systems could largely contribute to the total oceanic organic carbon export. It is important to thoroughly understand these vast ecosystems in order to characterise them and predict any modifications that could occur due to environmental changes. This project aims to give a longitudinal description of the biogeochemistry and biological diversity of the Mediterranean Sea and produce a detailed study of the biological production and its subsequent fate in 3 sites. These distinct ecosystems represent, on a regional scale, the main oceanographic features found in contrasting environments in the oligotrophic ocean as a whole. We will determine whether organic matter production, re-mineralization and export processes are different at these sites, and if so, determine how these differences are related to the structure of the planktonic community. Comparing different sites, along a longitudinal gradient of differing nutrient availability, should provide us with a new insight for identifying and understanding the fundamental interactions between marine biogeochemistry and ecosystems. We will focus on several current issues of interest regarding the coupling/uncoupling between carbon and nutrient (N,P,Si,Fe) delivery and removal processes in the surface layer. These processes control the planktonic community structure and function and ultimately, the ability of the ocean to biologically sequester carbon. We shall describe the functioning of each distinct ecosystem under physical conditions as stationary as possible, and finally, using experimental and modelling approaches, examine the response of each system to perturbations, i.e. pulsed nutrient additions.