GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 282-17
Presentation Time: 9:00 AM-6:30 PM


SCHUBERT, Brian A., School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA 70504 and JAHREN, A. Hope, Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, N-0315, Norway

Controlled growth experiments across a wide range of atmospheric carbon dioxide (CO2) levels (up to 4200 ppm) showed that CO2 concentration affects the carbon isotope (δ13C) value of C3 plant tissue. This work produced a unifying hyperbolic relationship between CO2 and net carbon isotope discrimination and reconciled a wide range of field and chamber studies conducted across smaller changes in CO2. The applicability of this relationship as a proxy for CO2 was demonstrated through comparison with CO2 data from ice core records across the Pleistocene-Holocene transition, and provided the framework for quantifying CO2 in deep-time records from C3 plant remains. However, some studies have misapplied this application, while others have confirmed use of the C3 plant proxy. These disparate evaluations have added to the general confusion as to best practices for interpreting δ13C change in recent and deep-time terrestrial settings. Here we dissect each issue and demonstrate the proper application of our work across a wide range of previously published datasets. Quantitative reanalysis bolsters our proposed relationship between CO2 and carbon isotope value, and therefore, the efficacy of the C3 plant proxy. Our integrated evaluation of existing datasets allows us to describe the common flaws encountered when applying the C3 plant proxy, while further demonstrating the value of its correct application across Geologic Time.