Carbon-13 in tree-ring cellulose as an indicator of past climates

Abstract

Following Urey's suggestion1 that the 13C abundance (usually expressed as a relative ratio: 13C/12C or δ13C) fixed in plant carbon may be temperature dependent, several authors have investigated the relationship between δ13C and climate. These workers searched for a coefficient relating δ13C variations to temperature variations2–7. The results, obtained on field collected samples, failed to yield agreement about the extent of a climatic effect or even its existence. Growth chamber experiments, performed on different plant species in controlled conditions to eliminate environmental factors other than temperature, showed no clear relationship between δ13C and temperature8,9. These various contradictory results suggest that factors other than temperature contribute to determining δ13C in plants. We now present evidence that the variations of the relative abundance of stable isotopes of carbon in tree rings indicate past climate changes. Thus carbon isotope composition appears to be a proxy indicator that may help to extend the meteorological data base into pre-instrument times.