Late Quaternary dune accumulation along the western margin of South Africa: distinguishing forcing mechanisms through the analysis of migratory dune forms

Abstract

The west coast of South Africa is situated at a critical location between temperate and subtropical oceanic and atmospheric circulation systems, and palaeoenvironmental proxies from this region have the potential to elucidate issues concerning variations within these systems over glacial–interglacical cycles. While semi-arid climates have hindered the preservations of organic proxies, a variety of aeolian bedforms have been analysed in an effort to improve our understanding of environmental change in the region. Optically stimulated luminescence measurements of 51 samples from 15 reticulate dune sites along the west coast have enabled the identification of phases of aeolian activity, as well as periods of relative geomorphic stability. Combined with data derived from previous studies of the region's sediment accumulating deposits and other palaeoenvironmental proxies, periods of increased windiness are identified at 16–24, 30–33, 43–49 and 63–73 ka From approximately 17–12 ka, decreasing transport capacity resulted in the stabilisation of the west coast's dune fields. During the Holocene Altithermal (∼ 4–8 ka), despite reduced wind strength, increased aridity resulting from higher temperatures and a reduced influence of moisture bearing westerly systems appears to have trigged widespread remobilisation of the region's dune fields. The combination of ages from a variety of dune forms with different development mechanisms, and comparisons with a range of proxy data sources, have allowed for an enhanced interpretation of the region's aeolian archives, moving beyond simple correlations between dune activity and “aridity.”