This thesis develops and integrates marine ( dinoflagellate cysts) and terrestrial proxy (pollen, spores, and charred grass cuticles) data from the Sanaga and Ogooue fans in west-central Africa in order to assess the timing of the establishment of the monsoon system in relation to the migration of the Intertropical Convergence Zone (ITCZ) over the last 30,000 years. Relationships between abrupt arid-humid climatic transitions in tropical Africa and oceanic conditions such as changes in sea-surface temperatures have been examined to illustrate atmosphere-ocean-land interactions in the tropical Atlantic African sector.
In this study, terrestrial proxies (pollen, spores, and charred grass cuticles) indicate changes in African vegetation from prevailing dry and arid conditions over central Africa during the Last Glacial Maxinum (LGM) to the humid conditions characteristic of the Holocene. In addition, Rhizophora pollen records show a linkage between sea-level rise and the effects of the morphology of the continental shelf since the LGM.
In parallel, the marine proxy ( dinoflagellate cysts) data reveal significant changes in the oceanographical context. The record of heterotrophic dinoflagellate cysts (particularly Brigantedinium spp.) show high marine productivity during the last glacial period, when the west equatorial African continent experienced maximum aridity and the eastern equatorial Atlantic generally lower SSTs. In the deglaciation and early Holocene, the replacement of the upwelling-related species (Brigantedinium spp., P americanum, T applanatum, Echinidinium species and Q. concretum) by non-upwelling-related species (e.g. 0. centrocarpum, Operculodinium sp.2, S. mirabilis and S. ramosus), indicates reduced marine productivity and upwelling intensity in the eastern equatorial Atlantic. The low salinity indicator species Operculodinium sp.2 record, along with published proxy records from the Congo fan, indicate the northward extension of increased precipitation across the African continent during the last deglaciation suggesting that hydrological changes in major African drainage basins were closely controlled by northward migration of the ITCZ.