C01_P08
A 900-Year Isotopic Proxy Rainfall Record from central Botswana
Patrut R1, Woodborne S2, Patrut A1,3, Hall G4, Robertson I5, Winterbach C6, Rakosy L7
1Babes-Bolyai University, , Faculty of Chemistry and Chemical Engineering, Cluj-Napoca, Romania, 2iThemba LABS, Johannesburg, South Africa, 3Babes-Bolyai University, Raluca Ripan Institute for Research in Chemistry, Cluj-Napoca, Romania, 4Mammal Research Institute, University of Pretoria, Pretoria, South Africa, 5Swansea University, Department of Geography, Swansea, UK, 6Tau Consultants (Pty) Ltd, Maun, Botswana, 7Babes-Bolyai University, Faculty of Biology and Geology, , Cluj-Napoca, Romani
High resolution climate archives for southern Africa are essential for designing and validating climate projections. For southern Africa and Botswana in particular, the interannual rainfall variability is associated with sea surface temperatures in the Agulhas Current Core region, which determine the east-west displacement of tropical temperate troughs (TTTs). Stable carbon isotope analysis and radiocarbon dating of the African baobab (Adansonia digitata L.) can provide reliable reconstructions of rainfall variability in its distribution area. We obtained a proxy rainfall record for central Botswana based on the historic Chapman baobab, which collapsed in 2016 during an intense El Niño event. The two investigated samples of the oldest stems of the baobab, which exhibited an open ring-shaped structure composed of 6 stems, provide insight into the precipitation regime over the last millennium, showing centennial and decadal scale variability. The results indicate that the lowest rainfall occurred during the Little Ice Age (1300-1350), while the Warm Medieval Period was marked by relatively stable precipitation. Previous studies suggested positive sea surface temperature (SST) anomalies in the Mozambique Channel led to an eastward movement of the TTTs but our proxy record shows a westward displacement in the past, causing drought in north-eastern South Africa and wetter conditions in the central part of southern Africa. The positive rainfall correlation with SST anomalies and ENSO reversed after 1900, causing a gradual decrease in precipitation and confirming the current aridity trend for Botswana.
The research was funded by the Romanian Ministry of Research CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-201620-2567, No. 145/2021.