We have subdivided single tree rings into between 24 and 35 contiguous samples and measured the Δ13C value for each. These high-resolution measurements show a previously unobserved spring depletion as part of a pattern of enrichment-depletion-enrichment-depletion through a single growing season as opposed to the depletion-enrichment-depletion cycle previously thought to exist. The earlywood/latewood transition does not coincide with identifiable isotopic boundaries and therefore is not a suitable demarcation point for sampling as part of palaeoclimatic study. Latewood and post spring depletion values of Δ13C were separately correlated with geophysical parameters. Post spring depletion wood yielded better correlations and is therefore more suitable for palaeoclimatic study. ¿ American Geophysical Union 1994