Abstract:
Carbon isotope analysis of four baobab (Adansonia digitata L.) trees from the Pafuri region
of South Africa yielded a 1000-year proxy rainfall record. The Pafuri record age model was
based on 17 radiocarbon dates, cross correlation of the climate record, and ring structures
that were presumed to be annual for two of the trees. Here we present the analysis of five
additional baobabs from the Mapungubwe region, approximately 200km west of Pafuri. The
Mapungubwe chronology demonstrates that ring structures are not necessarily annually
formed, and accordingly the Pafuri chronology is revised. Changes in intrinsic water-use
efficiency indicate an active response by the trees to elevated atmospheric CO2, but this
has little effect on the environmental signal. The revised Pafuri record, and the new Mapungubwe
record correlate significantly with local rainfall. Both records confirm that the Medieval
Warm Period was substantially wetter than present, and the Little Ice Age was the driest
period in the last 1000 years. Although Mapungubwe is generally drier than Pafuri, both
regions experience elevated rainfall peaking between AD 1570 and AD 1620 after which
dry conditions persist in the Mapungubwe area until about AD 1840. Differences between
the two records correlate with Agulhas Current sea-surface temperature variations suggesting
east/west displacement of the temperate tropical trough system as an underlying mechanism.
The Pafuri and Mapungubwe records are combined to provide a regional climate
proxy record for the northern summer rainfall area of southern Africa.
