δ 13 C Variations in C 3 Plants Over the Past 50,000 Years

Abstract

We examined three sets of data to determine if there are consistent changes in δ 13 C of C 3 plants through time, under the hypothesis that environmental changes from glacial to postglacial may have caused such isotopic changes over the last 50 ka. The records of δ 13 C change in all types of plant data from Radiocarbon and from the University of Arizona Radiocarbon Laboratory archives both reveal significant decline of 0.8–1.0‰ in δ 13 C from pre- to post-10 ka BP averages. The δ 13 C of wood data alone from Radiocarbon shows a larger significant decline of 3.0‰, and twigs, leaves and Juniperus categories from the Arizona data individually show declines of 0.4–1.44‰. Peat and charcoal from both data sets show no significant mean δ 13 C differences. A highly constrained set of wood samples from the Great Lakes region spanning the last 12 ka show isotopic changes of ca. 3‰, but most of that variation apparently does not reflect global environmental changes.