Robotic micromilling of tree-rings: A new tool for obtaining subseasonal environmental isotope records

High-resolution, intra-ring δ18O, δD, and δ13C values of modern tree species (Picea glauca, Larix laricina, and Populus grandidentata) were obtained using a robotic micromill. The micromilling apparatus permits accurate mapping and sampling of growth bands at a resolution of a few μm, producing a fine, homogenous powder that facilitates chemical processing and analyses of very small aliquots of α-cellulose and cellulose nitrate (~ 100 μg). Considerable intra-ring isotope variability observed in tree samples in this study correlates with temperature and precipitation data indicating that intra-ring variability in δ18O, δ13C, and δD has great potential for reconstructing high-resolution variation in meteorological conditions throughout the growing season.