Report

Late Miocene Atmospheric CO2 Concentrations and the Expansion of C4 Grasses

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Science  06 Aug 1999:
Vol. 285, Issue 5429, pp. 876-879
DOI: 10.1126/science.285.5429.876

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Abstract

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).

  • * Present address: Earth Science Department, University of California, Santa Cruz, CA 95064, USA.

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