Abstract : The western tropical Pacific is a complex region where two ecosystems coexist, with very different physical and biological characteristics. In the western part, the fresh warm pool is an oligotrophic ecosystem limited by nitrate. In the eastern part, the cold tongue ecosystem with cold and salty waters, is more productive and limited by iron.
We study the SeaWiFS chlorophyll concentrations as a proxy for the phytoplankton biomass. A statistical analysis (1997-2004) enables us to determine the main space and time scales of chlorophyll variability. We then study successively the seasonal cycle, a bloom linked to the 1997-98 El Niño (interannual variability) and the impact of westerly wind bursts on the intraseasonal scale.
This thesis explores the relatively unknown biological variability in this region, which is at first order controlled by the winds and currents. It also stresses the importance of islands and coastal regions on the chlorophyll distribution and its variability.