Aridity in equatorial Africa during the last 225 000 years: a record of opal phytoliths/freshwater diatoms from the Zaire (Congo) deep- sea fan (northeast Angola Basin)

Abstract

Maps of accumulation rates of freshwater diatoms and opal phytoliths in the surface sediments of the Zaire fan show that both types of microfossils were supplied to the ocean floor by the Zaire River, and that opal phytoliths also have a southern source, probably the region of the Namibian desert. The PhFD ratio, of opal phytoliths to freshwater diatoms, can be regarded as an aridity index for equatorial Africa, and probably for large parts of the central and southern Atlantic. In two cores, the record of the PhFD ratio indicates humidity c225-190ka BP, aridity 190-135ka BP with maxima c170 and 140ka BP and a humid excursion 150ka BP, an increase in humidity 115ka BP, a less humid period 90-30ka BP, more humidity c30-17ka BP with possibly more arid intervals c22.5 and 20ka BP. -from Authors