The 14 C record in bristlecone pine wood of the past 8000 years based on the dendrochronology of the late C. W. Ferguson

Abstract

When, in 1950, Willard Libby and his coworkers obtained their first radiocarbon ( 14 C) dates, C. W. Ferguson at the University of Arizona Tree Ring Laboratory was working on establishing a continuous tree ring series for the newly discovered bristlecone pine Pinus aristata . Before his untimely death in 1986, he had extended the series nearly 8000 years into the past. From the Ferguson series I obtained for 14 C determinations wood samples grown at various times. Also, two other laboratories obtained such samples. For B.C. times in particular, our measured 14 C-values that deviated consistently from those calculated from tree rings, and the deviations increased with age. This general trend was observed by other laboratories, but the presence of deviations from these trends, of the so-called ‘wiggles’, was questioned by other workers. To me these wiggles indicated the existence of a most interesting geophysical parameter valid for the whole terrestrial atmosphere. Fourier spectra obtained at my request by Kruse in 1972, and by Neftel, demonstrated the consistency of the results, and supported my contention that the secular variations of 14 C in atmospheric CO 2 are related to variations of solar activity.