A 340,000 year continental climate record from tropical Africa - news from opal phytoliths from the equatorial Atlantic

Information on the tropical African continental climate and vegetation during the last 340 kyr is derived from a detailed study of opal phytoliths at, the eastern equatorial Atlantic site M16772 (1degrees21'S, 11degrees58'W). Total phytoliths as well as C-3 and C-4 grass phytoliths are compared to the distribution pattern of other continental climate proxies (freshwater and limnobiontic diatoms). Total phytolith accumulation rate is dominated by C4 grasses and their variability confirms the cold stages and interstadials as times of and conditions in the southern Sahara and Sahel regions, and indicates an increase in aridness from Termination II to Termination I. The good agreement between the total phytoliths and freshwater diatom records observed for most of the 340 kyr is interpreted as indicative of atmospheric dust as the main source of both sediment constituents to this core site. Exceptionally higher land rainfall and river input to the eastern equatorial Atlantic are suggested by the excess of freshwater diatoms over total phytoliths and the limnobiontic diatoms observed during ice growth phases of oxygen isotopic interglacial stages 9, 7 and the 5/4 transition. Major alterations in continental aridity and/or wind strength conditions over north Africa, as reflected by the total and and phytolith frequency spectrum, appear clearly determined by global ice volume and the 100 kyr cycle characteristic for high-latitude climate change. Limnobiontic diatoms, which reflect lake desiccation, respond also to the 41 kyr obliquity cycle. Freshwater diatoms, on the other hand, contain significant variance at 23 kyr periodicities, reflecting the precessional forcing of the African monsoons which determine the precipitation level over the south Saharan and Sahelian source regions. Rapid hydrological fluctuations, as depicted by the changes in the relative contribution Of C-3 and C-4 grasses to the total phytoliths, appear to respond to higher than 19 kyr frequencies, which are observable in all but the aridity index spectra. (C) 2003 Elsevier Science B.V. All rights reserved.