What Is the Carbon Origin of Early-Wood?

Substantial amounts of annual radiocarbon (C-14) data have recently been produced with the purpose of increasing the time resolution of C-14 records used for constructing the calibration curve and for studying the occurrence of abrupt cosmic-ray events. In this study, we investigate if it is possible to resolve sub-annual scale changes in the atmospheric C-14 content by measuring radiocarbon in early-wood and late-wood fractions from Danish oak. The tree-ring samples span the period 1954-1970 CE, hereby covering the peak of the bomb pulse. A least squares test comparing the atmospheric C-14 content and the new sub-annual C-14 record from Danish tree rings reveals that by measuring early-wood and late-wood fractions, it may be possible to resolve sub-annual variations in past atmospheric C-14 levels.