Molecular isotopic heterogeneity of fossil organic matter: implications for δ13Cbiomass and δ13Cpalaeoatmosphere proxies
Poole, I., van Bergen, P.F., Kool, J., Schouten, S. and Cantrill, D.J. (2004) Organic Geochemistry 35 (11-12) pp. 1261-1274
[doi:10.1016/j.orggeochem.2004.05.014]
Abstract
The degree of isotopic variation in fossil organic matter renders bulk δ13C signatures strongly influenced by molecular isotopic heterogeneity. For example, in fossil wood the relative abundance of less depleted 13C moieties, i.e. preserved 13C enriched polysaccharides versus the relatively 13C depleted lignin moieties, can be seen to significantly bias δ13Cfossil wood values. Moreover the variation in δ13C values of specific compounds within fossil material are themselves highly variable and reflect the heterogeneity in isotopic values of different carbon atoms within individual compounds. For studies using δ13C values of fossil plant material as proxies (e.g., for δ13Cpalaeoatmosphere, δ13Cbiomass) it is recommended that the biases introduced through molecular heterogeneity, preservation type and taxonomic status of the fossil material are determined initially. Biases inherent in the bulk signature can then be reduced, rendering this value more robust. Alternatively, compound specific stable carbon isotope measurements of individual moieties preserved through geological time might prove to be an alternative proxy for monitoring changes in the bulk δ13C value of the plant and might reveal atmospherically induced trends.
Notes: This article is selected by the Virtual Journal of Geobiology (Volume 3, Issue 12, December 2004). It has also topped the TOP25 of Hottest articles within the journal Organic Geochemistry.
Do stable carbonisotopes of brown coal woods record changes in Miocene palaeoecology?
Poole, I., Dolezych M., Kool, J., van der Burgh, J. and van Bergen, P.F. (2005) Palaeogeography, Palaeoecology, Palaeoclimatology
[doi:10.1016/j.palaeo.2005.11.013]
Abstract
Stable carbon isotope ratios of fossil wood from the Miocene brown coal deposits in former East Germany are compared with palaeobotanical and sedimentological data to test the use of stable isotopes in determining palaeoenvironment. Significant differences in the chemical composition of samples from different horizons were observed. Those specimens preserved under the most (bio)degrading conditions yielded stable carbon isotope values least representative of original wood specimens. Overall, the chemical preservation of the wood was seen to affect the stable isotope signal but deconvolving the preservational bias using a molecular approach enabled estimations of δ13Cbiomass and δ13Cpalaeoatmosphere that were then used to interpret more fully the palaeoenvironment.