Holocene environmental change along the central Namib Desert escarpment derived from hyrax and owl dung
Fossil pollen and geochemical sequences from a series of hyrax dung deposits from rock shelters along the eastern margin of the central Namib Desert shed light on the Holocene environmental history of Namibia. Grassy pollen assemblages suggest relatively humid conditions during the early Holocene between ca. 9.6 and 7.7 ka. A series of stepwise changes follows, including the prominence of different pioneer plant communities of which changes in ratios between grassy and shrub pollen types suggests moisture oscillations. The development of more C4 plants around ca. 4.5 ka, as indicated by isotope concentrations and persistent grass pollen percentages, point to the development of a different climatic regime than that in the early Holocene, which extended the area of subtropical savanna towards the south at ca. 24°S. This transition can in part be interpreted as a vegetation response to a shift in the rainfall distribution from an early even seasonal distribution to the current late Holocene summer rainfall regime. Climate changes may have been driven by variations in austral summer and winter solar insolation with changes in total solar irradiance (TSI) superimposed upon them. Through its link to Bond events in the North Atlantic, and thus Atlantic Meridional Overturning Circulation (AMOC), TSI may have affected SSTs in the SE Atlantic and SW Indian Ocean, which influence both summer and winter rainfall in southern Africa.