Comparison of stable-carbon isotope composition in the growth rings of Isorberlinia doka, Daniella oliveri, and Tamarindus indica and West African climate

Inter-ring variations in stable-carbon isotope composition of cellulose in Daniella oliveri, Isoberlinia doka, and Tamarindus indica stumps were analyzed for nine trees in the Soudan-Sahel zone of West Africa. This pioneer isotopic study is a contribution to on-going efforts to evaluate the feasibility of extracting proxy climatic records from tree-rings in this area. Our aim is to investigate trends in individual floating δ¹³C time series to assess if patterns in variability within and between rings are consistent with those in other climatically sensitive tree-ring δ¹³C series. Samples were collected primarily from tree stumps but kill dates were unknown. Tree age was estimated from stump condition and shoot regrowth. This approach, combined with low sample replication, hindered the establishment of absolute dates. Nevertheless, δ¹³C and discrimination (Δ¹³C), absolute values and variability in the time series are similar to those often seen in tree-rings. Average δ¹³C values for individual series range from −25.90‰ to −23.72‰ and average Δ¹³C values from 16.56‰ to 18.99‰. It is well known that seasonal rainfall is inversely related to the δ¹³C in growth-season-dry environments and positively covaries with Δ. We investigate the possibility of using this relationship to temporally anchor the time series and to identify missing and false rings in wood segments with indistinct growth. The variability in these time series is consistent with expected patterns and shows promise for facilitating the development of stable carbon isotope tree-ring chronologies for West Africa.