Vegetation development in West Africa of the biosphere shift during late Miocene to (early) Pliocene

Abstract

Aridification is a major aspect of the climatic trend in Africa during the late Neogene. Main causes of the aridification are changes in the atmospheric circulation as part of the steepening meridional pressure gradient. The trend is affecting biomes largely by shifting, shrinking and expanding vegetation belts. During the Miocene to Pliocene especially the tropical to subtropical savannah grasslands (C4 grasslands) expanded. Triggers of the C4 grassland expansion are not well understood and several mechanisms have been proposed explaining it such as decreasing CO2 levels, aridification, increased seasonality and fire. The thesis focuses on pollen, spores and microscopic charcoal records from a sediment core retrieved at Ocean Drilling Program Site 1081 offshore Namibia. The aim is to investigate the Miocene to Pliocene vegetation change of south-west Africa with emphasis on the expansion of the savannah grassland and the mechanisms behind it. Additionally, dinoflagellate cysts from the same sediments are analysed to study the link between continental and oceanic conditions.