Abstract
Interannual variability of African rainfall impacts local and global
communities, but its past behavior and response in future climate
projections are poorly understood. This is primarily due to short
instrumental records and a lack of long high-resolution palaeoclimate
proxy records. Here we present an annually resolved 91,000 year
Early Pleistocene record of hydroclimate from the early homininbearing
Makapansgat Valley, South Africa. Changes in speleothem
annual band thickness are dominated by precession over four consecutive
orbital cycles with strong millennial-scale periodicity. The
frequency of interannual variability (2.0–6.5 yr oscillations) does not
change systematically, yet its amplitude is modulated by the orbital
forcing. These long-term characteristics of interannual variability are
reproduced with transient climate model simulations of water balance
for South Africa from the Late Pleistocene to Recent. Based on
these results, we suggest that the frequency of interannual variations
in southern African rainfall is likely to be stable under anthropogenic
warming, but that the size of year-to-year variations may increase.
We see an orbitally forced increase in the amplitude of interannual
climate variability between 1.8 Ma and 1.7 Ma coincident with the
first evidence for the Acheulean stone tool technology.