REDUCING UNCERTAINTIES IN DELTA-C-13 ANALYSIS OF TREE-RINGS - POOLING, MILLING, AND CELLULOSE EXTRACTION

Recent developments of on-line methods have provided another boost to the determination of stable isotope ratios in organic material. Along with a significant increase in sample throughput, the sample sizes dec rease, both of which are necessary conditions to acquire long time ser ies from limited wood amounts. In view of this new technique we recons idered the most important factors influencing the measured isotopic si gnature which are (1) pooling, (2) homogeneity, and (3) cellulose extr action. In most cases, pooling (i.e., mixing wood of the same year fro m different trees) can be made in a simple way by mixing the whole woo d available because mass-weighted and unweighted isotope measurements were the same within the error. More attention must be paid in homogen izing the sample. Theoretical considerations underpinned by experiment al results suggest a fineness of 0.15 mm (115 mesh) if cellulose is ex tracted and 0.1 mm (165 mesh) for direct wood analysis. Many of previo us studies did not achieve this fineness. We find that wood is as good a climate proxy as cellulose. This is shown by comparing correlations of wood and corresponding cellulose isotope values with meteorologica l data, which are identical within the uncertainty.