Orbital forcing of climate over South Africa: A 200,000-year rainfall record from the pretoria saltpan

Abstract

Late Pleistocene variations in rainfall in subtropical southern African are estimated from sediments preserved in the Pretoria Saltpan, a 200000 year-old closed-basin crater lake on the interior plateau of South Africa. We show that South African summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession. As predicted by orbital precession geometry ( Berger, 1978), this South African record is out of phase with North African palaeomonsoon indices ( Street and Grove, 1979; Rossignol-Strick, 1983; McIntyre et al., 1989) ; the amplitude of the rainfall response to insolation forcing agrees with climate model estimates ( Prell and Kutzbach, 1987). These results document the importance of direct orbital insolation forcing on both subtropical North and South African climate as well as the predicted antiphase sensitivity to precessional insolation forcing.