Integrated survey of elemental stoichiometry (C, N, P) from the western to eastern Mediterranean Sea

This paper provides an extensive vertical and lon- gitudinal description of the biogeochemistry along an East- West transect of 3000 km across the Mediterranean Sea dur- ing summer 2008 (BOUM cruise). During this period of strong stratification, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were examined to produce a detailed spa- tial and vertically extended description of the elemental stoi- chiometry of the Mediterranean Sea. Surface waters were de- pleted in nutrients and the thickness of this depleted layer in- creased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, with the phospha- cline deepening to a greater extent than that for correspond- ing nitracline and thermocline depths. We used the minimum oxygen concentration through the water column in combina- tion with 2 fixed concentrations of dissolved oxygen to dis- tinguish an intermediate layer (Mineralization Layer; ML) from surface (Biogenic Layer; BL), and deep layers (DL). Whilst each layer was represented by different water masses, this approach allowed us to propose a schematic box-plot representation of the biogeochemical functioning of the two Mediterranean basins. Despite the increasing oligotrophic