Late Miocene Atmospheric CO2 Concentrations and the Expansion of C4 Grasses
Mark Pagani,
*
Katherine H. Freeman,
Michael A. Arthur
The global expansion of C4 grasslands in the late
Miocene has been attributed to a large-scale decrease in atmospheric
carbon dioxide (CO2) concentrations. This triggering
mechanism is controversial, in part because of a lack of direct
evidence for change in the partial pressure of CO2
(pCO2) and because other factors are
also important determinants in controlling plant-type distributions. Alkenone-based pCO2 estimates for the late
Miocene indicate that pCO2 increased from 14 to
9 million years ago and stabilized at preindustrial values by 9 million
years ago. The estimates presented here provide no evidence for major
changes in pCO2 during the late Miocene. Thus,
C4 plant expansion was likely driven by additional factors,
possibly a tectonically related episode of enhanced low-latitude aridity or changes in seasonal precipitation patterns on a global scale
(or both).
Department of Geosciences, The Pennsylvania State University,
University Park, PA 16872, USA.
*
Present address: Earth Science Department, University of
California, Santa Cruz, CA 95064, USA.
To whom correspondence should be addressed.
