This award will fund the purchase of a scanning micro X-Ray Fluorescence (Micro-XRF) spectrometer for dendrochemical and other research. The research it enables is significant because it permits scientists to reconstruct multiple aspects of past environments and environmental change over time. Many species of trees add a visibly distinct ring of wood each year. The width of the annual ring may vary substantially from year to year, and these patterns of variation may be sufficiently distinctive to allow wood from a given site to be dated by comparison to a master chronology for the region. Dendrochronology was first developed at the University of Arizona in the 1930's. Once dated, the rings may be used to reconstruct variation in the factors controlling ring width. These include annual rainfall, annual temperature (at high altitude), the frequency of forest fires, and in which region the tree grew. A relatively new science is dendrochemistry - the study of variation in chemical composition from ring to ring within a tree. This award will allow researchers at the University of Arizona to undertake novel dendrochemical research on the enormous archive of cores from modern and ancient wood in the University of Arizona's Laboratory of Tree Ring Research (LTRR). The instrument will also be a valuable tool for LTRR'S outreach work with visiting high school science classes. The instrument will be installed in LTRR. A priority will be the search for evidence in dated tree rings of former volcanic eruptions and major forest fires, both of which result in spikes of certain chemical elements that are then taken up by growing trees. Since volcanic eruptions often spread ash (microtephra) over a very large area, they offer a potentially valuable means of correlating archaeological and paleoenvironmental sequences across a large region. Dendrochemical analysis by micro-XRF potentially offers a quick and efficient means of detecting and dating these past eruptions. An estimated 30-40,000 wood samples in LTRR cannot currently be assigned a cutting date because the outer ring is indistinct. Pilot research has however shown distinctive chemical changes at the heartwood/sapwood junction in several species, and also in the penultimate ring. Micro-XRF will be used to scan currently undated cores to look for these signals, from which cutting dates can be derived. This research can potentially make available many more dated samples for archaeological and paleoenvironmental interpretation.