地球科学と気候変動ジャーナル

抽象的な

A Review on Late Quaternary Environmental Change in the Namibia, South-Western Africa

Bing Qi Zhu

This paper focuses on the review of geomorphology and late Quaternary environmental change in the Namibia, south-western Africa. The relationship between geomorphology and climate in Namibia reveals the degree and extent to which its landscapes are determined by changing environmental conditions. Case studies of late Quaternary environmental changes in the northern, western and central Namibia are presented. Geomorphological analysis showed that the modern-scale landscape of the south and central Namibia is controlled primarily by tectonics and also by the lithology, base level and climate. At present there is debate on the behavior of Quaternary hydroclimate in the Namibia in response to precessional (19–23 kyr cycle) insolation variations and the effect of glacial versus interglacial boundary conditions. Clues from marine records regarding these debates were obtained. lower leaf-wax δD and higher δ13C (more C4 grasses) recorded in marine sediments over the last 140 ka indicates wetter summer conditions and increased seasonality during the Late Quaternary, particularly during Southern Hemisphere insolation maxima relative to minima and during the last glacial period relative to the Holocene and the last interglacial period. In the central and south-western Namibia, CNB dating suggests that the Namib Sand Sea has a residence time of at least 1 million years. Depositional ages of luminescence dating for dune sediments yields three broad areas of the sand sea, including MIS 5, later in the Pleistocene around the Last Glacial Maximum and the Holocene. The high coincidence of the luminescence ages of the linear dune complexes in the Kalahari over a distance of about 150 km suggests that dune activation in the south-western Kalahari was not the result of local effects but due to sub continental climatic changes. The major dates for dune forms in Kalahari at present are of Holocene age. In the northern Namibia, landscape degradation and desertification are developed during the Holocene. Humification of soils in this region suggests open savanna environments in the past and does not accord with the shrub lands and thornbush savanna at present. Landscape degradation seems to have started in pre-colonial times most likely as a consequence of cattle farming. These examples from different regions of the Namibia offers pointers as to how geomorphological evidence of Quaternary change can be used to assist in the better management of contemporary and future environmental conditions.