Evidence of Namibia's Neogene Aridification From Offshore Samples

Miocene-Pliocene Vegetation change in south-western Africa (ODP Site 1081, offshore Namibia)

Authors:

Hoetzel et al

Abstract:

Aridification is an important component of Late Neogene climate change in south-western Africa probably caused by modifications in the atmospheric circulation in relation to the initiation and intensification of the Benguela Upwelling System due to globally steepening of the meridional pressure gradient. Intensification of the meridional pressure gradient influenced the climate intensively which had then an impact on the vegetation. However, vegetation changes of south-western Africa from the Miocene to Pliocene have not yet been reported and only indirectly investigated by sedimentological data. Here, we present a pollen record of marine ODP Site 1081 retrieved 160 km offshore Namibia covering the time between 9 and 2.7 Ma. Using an endmember unmixing model we distinguished three vegetation phases: a relative wet phase, during the Tortonian, showing higher representations of Cyperaceae, a transition phase during the Messinian, when especially grasses expanded, and a dry one covering the Pliocene with a strong representation of desert and semi-desert plants. The three phases indicate ongoing aridification probably caused by intensified meridional pressure gradients. Additionally, aquatic vegetation indicators appear in our pollen record from around 5 Ma on, which we attribute to a relocation of the lower course of the Cunene River to its modern outlet in the Atlantic Ocean. Redirection of the Cunene River toward the Atlantic would have deprived the palaeolake Cunene of an important source of fresh-water ultimately resulting in desiccation of the lake and the formation of the Etosha Pan.