2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 106-3
Presentation Time: 8:30 AM

A COMPARISON OF MULTIPLE PROXY ESTIMATES OF ATMOSPHERIC CO2 FROM AN EARLY PALEOCENE RAINFOREST


KOWALCZYK, Jennifer B., Department of Earth and Environmental Sciences, Wesleyan University, 265 Church St, Middletown, CT 06459, ROYER, Dana L., Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459 and MILLER, Ian M., Dept. of Earth Sciences, Denver Museum of Nature and Science, Denver, CO 80205, jkowalczyk@wesleyan.edu

Proxy estimates of atmospheric pCO2 are critical for reconstructing Earth’s climate history and for understanding long-term climate sensitivity. Because each proxy method has underlying assumptions and inherent limitations, our confidence in estimated pCO2 will be increased by comparing results from multiple proxies for a given site. The well-studied and unusually diverse early Paleocene (63.8 Ma) Castle Rock fossil site from Colorado’s Denver Basin allows for such a comparison. Using fossil leaf cuticle from multiple Castle Rock taxa (Ginkgo sp., a liverwort, and angiosperms including two Lauraceae morphotypes), I compare pCO2 estimates from three leaf-based proxies: stomatal index, a new proxy based on a gas exchange model of C3 photosynthesis, and the BRYOCARB model for liverworts. Preliminary estimates from Ginkgo give pCO2 values in the range of 470 – 560 ppm, slightly elevated over previous stomatal index and paleosol estimates for the early Paleocene, which are closer to present-day pCO2. Reconstructions of mean annual temperature and precipitation from Castle Rock flora show a climate similar to modern tropical or paratropical rainforests; the existence of this climate in the Denver Basin during the early Paleocene at pCO2 values only moderately elevated over the present-day implies a high climate sensitivity.
Handouts
  • GSA_presentation_Kowalczyk.pdf (8.1 MB)