Late Quaternary climate changes in central Africa as inferred from terrigenous input to the Niger fan

Time series of terrigenous source elements (Al, K, Ti, Zr) from core GeoB49 01-8 recovered from the deep-sea fan of the Niger River record variations i n riverine sediment discharge over the past 245,000 yr. Although the flux r ates of all the elements depend on physical erosion, which is mainly contro lled by the extent of vegetation coverage in central Africa, element/Al rat ios reflect conditions for chemical weathering in the river basin. Maximum sediment input to the ocean occurs during cold and and periods, when precip itation intensity and associated freshwater runoff are reduced. High carbon ate contents during the same periods indicate that the sediment supply has a positive effect on river-induced marine productivity In general, variatio ns in the terrestrial signals contain a strong precessional component in tu ne with changes in low-latitude solar radiation. However, the terrestrial s ignal lags the insolation signal by several thousand years. K/Al, Ti/Al, an d Zr/Al records reveal that African monsoonal precipitation depends on high -latitude forcing. We attribute the shift between insolation cycle and rive r discharge to the frequently reported nonlinear response of African climat e to primary orbital configurations, which may be caused by a complex inter action of the secondary control parameters, such as surface albedo and/or t hermohaline circulation. (C) 2001 University of Washington.