Atmospheric paleo-CO2 estimates based on Taxodium distichum (Cupressaceae) fossils from the Miocene and Pliocene of Eastern North America

Neogene atmospheric paleo-CO2 estimates based on fossils of the extant cupressaceous conifer species Taxodium distichum from the Brandywine Formation of Maryland and the Citronelle Formation of southern Alabama are presented. These are important as the first such estimates from eastern North American paleofloras, and provide new evidence from a time for which the role of CO2 in climate change is controversial. Comparisons of the stomatal density (SD) of the fossil leaf cuticles to a calibration curve constructed from modern leaves of the same species collected over the last century of anthropogenic CO2 increase produces Miocene and Pliocene atmospheric paleo-CO2 mean estimates of 360 and 351 ppmv, respectively. Although the temporal resolution of the fossil sites is low, these results are in agreement with multiple independent proxies that indicate near modern CO2 levels during this interval, and demonstrate the utility of T. distichum leaves as instruments for stomatal frequency analysis.