Chronological studies of tree-rings from the Amazon Basin using thick target PIXE and proton backscattering analysis

A tree-core sample (Aspidosperma obscurinervium, popular name: "pequia marf im") about 161 years old (cut in 1990), from the Ducke Reserve at the Amazo n Basin, Manaus, Brazil was analyzed by PIXE (Particle Induced X-ray Emissi on) and proton backscattering in 136 different spots along its life. Twenty -two elements plus the density of the wood were measured (C, O, H, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Co, Rb, W and Pb). Average C, O, and H results ( 49.77% +/- 0.15%, 44.29% +/- 0.14% and 5.95% +/- 0.1 2%, respectively) compare well with literature values for the biomass in th e Amazon region. The variability of trace elements alone the tree rings sho wed important features that could be caused by modifications in the environ ment during the life of the tree. The well behaved variability of some trac e elements (like K, P, Mn, Ca, etc.) seems to reflect the physiological res ponse of the tree to external changes in the environment. The concentration of K varied from about 4 up to 2000 ppm in a given period of the life of t he tree. The same period also shows important changes in the bulk compositi on and structure of the rings (e.g. C and density series). Multivariate sta tistical methods (cluster and factor analyses) were used for data interpret ation, helping in the separation of periods of important transformations in the tree. The elemental time series is compared with historical records of regional development and with some global events that could possibly affec t the tree. The period of maximum variation in the elemental concentrations appeals to be related to the Brazilian rubber boom (1859-1912), responsibl e for several transformations in the Amazon region. In particular in the Ma naus legion, large development has occurred in the beginning of the 20th ce ntury, which are reflected in the results of this tree-core analysis. (C) 1 999 Elsevier Science B.V. All rights reserved.