CLIMATE-INDEPENDENT PALEOALTIMETRY USING STOMATAL DENSITY IN FOSSIL LEAVES AS A PROXY FOR CO2 PARTIAL PRESSURE

Abstract

Existing methods for determining paleoelevation are primarily limited by (1) large errors (±450 m), (2) a reliance on incorrect assumptions that lapse rates in terrestrial temperature decrease with altitude in a globally predictable manner, and/or (3) are inherently climate dependent. Here I present a novel paleoelevation tool, based on a predictable, globally conserved decrease in CO 2 partial pressure ( p CO 2 ) with altitude, as indicated by increased stomatal frequency of plant leaves. The approach was validated using historical populations of black oak ( Quercus kelloggii ). These analyses demonstrate highly significant inverse relationships between stomatal frequency and p CO 2 ( r 2 > 0.73), independent of ecological or local climatic variability. As such, this is the first paleobotanical method to be globally applicable and independent of long-term Cenozoic climate change. Further, tests on modern leaves of known elevations indicate that species-specific application to the fossil record of Q. kelloggii (= Q. pseudolyrata ) will yield paleoelevation estimates within average errors of ~±300 m, representing a significant improvement in accuracy over the majority of existing methods.