Increased aridity in southwestern Africa during the last-interglacial warmest periods

Abstract

Abstract. We use pollen analysis of marine sediments from core MD96-2098 to produce a paleoenvironmental record spanning from 190 to 24.7 ka (thousand years before present) from southern Africa. Our interpretations of the pollen record are supported by an analysis of present day pollen spectra for the region. We apply canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) on pollen spectra from terrestrial surface samples to investigate pollen spectra-climate relationships. We identify pollen taxa that are suitable indicators for the different South African biomes, and assess in detail the distribution and potential interpretation of Poaceae pollen signals in marine sediments along the southwestern African coast. The pollen record from MD96-2098 documented major increases of Poaceae pollen percentages, that are interpreted as expansions of semi-arid southwestern African biomes (i.e. the Nama-Karoo and fine-leaved savannas) during Marine Isotope Stage (MIS) 5e, 5c and 5a substages. These expansions coincided with minima in precession and global ice volume. They likely resulted from a combination of reduced Benguela upwelling; expanded subtropical high pressure and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone (ITCZ); and a southern displacement of the westerlies and decreased austral-winter precipitation. During glacial isotopic stages MIS 6, 4 and 3, Fynbos expanded at the expense of semi-arid biomes. Stage and substage transitions were characterised by small but rapid increases in Podocarpus indicating a humidity increase. Increased millennial-scale variability in the vegetation and climate of southern Africa is also suggested for the last 100 ka.