δ18O and δ13C Analysis in Tree Rings of Pterocarpus angolensis Growing in Zimbabwe

Abstract:

Instrumental weather records in southern Africa are largely limited to the last 100 years and documentary weather-related data are rare prior to the 1800s, hindering our understanding of the natural and/or anthropogenic factors that influence climate variability over this region. Measuring stable isotopes ratios (commonly ¹³C/¹²C and ¹⁸O/¹⁶O) in tree rings can provide a good proxy for extending climate data beyond the instrumental record. The objective of this study is to characterize historical variations in the climatology underlying extreme climatic events in Zimbabwe using instrumental climate records (precipitation and temperature) and a multi-proxy approach (ring width, δ¹⁸O, and δ¹³C) for dendroclimatic proxy reconstructions. A 90-year (1900-1990) δ¹⁸O and δ¹³C tree ring record using four Pterocarpus angolensis samples is being developed and compared to tree ring width, monthly, seasonal, and annual precipitation totals, meteoric water δ¹⁸O values, and mean monthly and seasonal temperature. Preliminary results indicate significant correlations between the average δ¹⁸O record and the previous year December precipitation totals (r=0.41, p<0.0001), current year January precipitation totals (r=0.45, p<0.0001), and combined total precipitation for the previous year November and December and current year January (r=0.57, p<0.0001).  Furthermore, we find that the δ¹⁸O values are strongly influenced by maximum temperature during the previous year December (r=0.39, p=0.0001) and current year January (r=0.40, p=0.0001), and average maximum temperature during the months of the previous year December and current year January and February (r=0.47, p<0.001). We thus present one of the first studies to integrate a multi-proxy approach to investigate historical climate variability in southern Africa using ring widths, and tree ring δ¹⁸O and δ¹³C values of trees growing in Zimbabwe.