Articles | Volume 12, issue 2
https://doi.org/10.5194/cp-12-439-2016
https://doi.org/10.5194/cp-12-439-2016
Research article
 | 
25 Feb 2016
Research article |  | 25 Feb 2016

Fossil plant stomata indicate decreasing atmospheric CO2 prior to the Eocene–Oligocene boundary

Margret Steinthorsdottir, Amanda S. Porter, Aidan Holohan, Lutz Kunzmann, Margaret Collinson, and Jennifer C. McElwain

Abstract. A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO2, we show that pCO2 decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO2 in parts of the Oligocene was similar to latest Eocene values. These results suggest that a decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene–Oligocene transition and that when a certain threshold of pCO2 change was crossed, the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.

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Short summary
Our manuscript "Fossil plant stomata indicate decreasing atmospheric CO2 prior to the Eocene–Oligocene boundary" reports that ~ 40 % decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene–Oliogocene climate transition. The results endorse the theory that pCO2 drawdown was the main forcer of the Eocene–Oligocene climate change, and a "tipping point" was reached in the latest Eocene, triggering the plunge of the Earth System into icehouse conditions.