T60 New Voices in Geobiology II

Sunday, 22 October 2017
1:30 PM - 5:30 PM
Room 602/603

FOSSIL ATMOSPHERES: AN ELEVATED CO2 EXPERIMENT UTILIZING OPEN-TOP CHAMBERS TO EVALUATE THE GINKGO PALEO-CO2 BAROMETER

Paper number: T60-2
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

The Earth’s climate during the Mesozoic and early Cenozoic was much warmer than today, and was often punctuated by hyperthermal events. The background warmth and the rapid hyperthermals are often attributed to increased atmospheric carbon dioxide (pCO2), yet paleo-pCO2 proxy estimates for this time interval disagree widely. Given the wide range of pCO2 estimates for the same intervals, it is clear that not all of the proxy estimates can be correct. Over the past decade, many of the marine and terrestrial proxies for pCO2 have been revised by evaluating the underlying assumptions for each proxy. We are evaluating the assumptions that govern the Ginkgo paleo-pCO2 proxy that depends upon stomatal index, a measure of the proportion of epidermal cells on leaves that are stomatal pores. Historical collections of Ginkgo biloba demonstrate that the stomatal index proxy for paleo-pCO2 is strongly correlated with pCO2 over the range of 290-430 ppm. However, despite wide application of the Ginkgo paleo-pCO2 barometer, our understanding of pCO2 in the fossil record has been hindered because the morphological and physiological changes in G. biloba stomata under pCO2 above 400 ppm have been poorly constrained.

To investigate the relationship of Ginkgo to elevated pCO2 conditions, we are conducting an elevated pCO2 experiment we call ‘Fossil Atmospheres’. The experiment is designed to quantify the response of Ginkgo to elevated pCO2 by growing 15 mature Ginkgo biloba trees in open-topped chambers in natural field conditions, under atmospheres with ambient (400), 600, 800, and 1000 ppm of CO2. Each tree is regularly monitored for changes in stomatal index, and rates of photosynthesis and transpiration to constrain parameters used in gas exchange models of paleo-pCO2. We have also engaged citizen scientists to help collect stomatal index measurements on the Zooniverse platform, using the interaction to educate citizens about modern climate change from the less-menacing viewpoint of deep-time climate change events. Our experimental results will be used to infer paleo-pCO2 from stomatal features of Late Cretaceous-Paleogene fossils of the nearly identical species, G. wyomingensis, allowing for paleo-pCO2 estimates from these terrestrial fossils to be compared with records from other paleo-pCO2 proxies.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-308317

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