Cruises LEFE CYBER

The functioning and productivity of oligotrophic systems, and the balance between production and mineralization in these oceanic 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 global ocean organic carbon export. It is important to thoroughly understand the biogeochemical functioning of these vast ecosystems in order to characterize their evolution in the context of climate alteration.

This project aims to give a zonal description of the biogeochemical functioning and biological diversity of the South West (SW) Pacific toward a gradient of macro- and micro-nutrients availability, and produce a detailed study of the biological production and its subsequent fate in 3 contrasting sites, with a specific emphasis on the production sustained by nitrogen fixation.

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 with the diversity/function of nitrogen-fixing organisms in the planktonic community. Comparing different sites, along a zonal 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 (C) 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 C.

We shall describe the functioning of each distinct ecosystem under physical conditions described with new approaches combining satellite localization and drifters for lagrangian strategy, and finally, using experimental and modelling approaches, examine the biogeochemical role of diazotrophs in each system.