Changes in the concentration of atmospheric carbon dioxide ( pCO2) affect global climate. Accurate determination of paleo-pCO2 can therefore provide information on the response of climate to changing pCO2. Such pCO2 proxies have been developed from a variety of terrestrial (e.g., plant stomata, paleosol carbonate, and liverworts) and marine (e.g., alkenones and boron) substrates. However, these proxies show a wide range of values and uncertainty throughout the Cenozoic and especially for the early Paleogene (53-63 mya). Here, I demonstrate the use of the carbon isotope composition of n-alkanes extracted from C3 plant waxes as an accurate recorder of changes in atmospheric chemistry. My results show that the uncertainty and range of pCO2 estimates determined using this new proxy are similar to other proxies. Because n-alkanes are abundant, chemically resistant, and not subject to degradation, this proxy represents an excellent opportunity to reconstruct pCO 2 across the last 400 Myr of Earth history. By examining across 4 different chain lengths (n-27, n-29, n- 31, and n-33), I find that only n-29 and n-31 show clear changes in carbon isotope discrimination in response to changes pCO2, whereas chain-lengths n-27 and n-31 did not show any significant response. Using chain lengths n-29 and n-31, I calculate early Paleogene pCO2 = 566 ± 190 and 469 ± 165 ppmv (median ± 1σ), respectively. These results demonstrate that n-alkanes can serve as a potential pCO2 proxy across geologic timescales.
|Commitee:||Borrok, David, Doyle, Thomas, Duex, Timothy|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 57/01M(E), Masters Abstracts International|
|Subjects:||Geology, Environmental Geology, Geochemistry|
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