The Influence of Pleistocene Megadroughts on Lowland Vegetation in East Africa

Abstract

Resolving past continental climate variability is important for understanding Earth’s climate system, testing climate models and projections of anthropogenic climate change. Here I present a tropical lowland vegetation reconstruction for Eastern Equatorial Africa, for the period 170 to 60 ka covering the African megadrought interval. Based on the stable carbon isotopic composition of terrestrial n-alkane leaf-wax biomarkers preserved in Lake Chala, the proportion of C3 trees and shrubs relative to that of C4 grasses, remained stable at ~55% and ~45%, despite periods of prolonged and severe aridity that is recorded in the seismic stratigraphic record of the lake sediment. High atmospheric CO2 concentrations during the Late Pleistocene, enabled C3 trees and shrubs to outcompete C4 grasses despite substantial moisture balance variation. This study shows that tropical African vegetation is heavily influenced by climatic moisture balance change on short timescales, though on longer timescales appears to follow the main long-term trend in atmospheric CO2.