INTRA-VARIABILITY OF CARBON-ISOTOPE RATIOS IN MODERN GINKGO AND EQUISETUM: IMPLICATIONS FOR ANCIENT ISOTOPIC INVESTIGATIONS

Carbon-isotope investigations of fossil plant organic matter has received increasing attention over the past decade, due to its usefulness and applicability to providing a greater understanding of the terrestrial response to climatic change. Our understanding of the effect that modern environmental variables have on plant carbon-isotope ratios, and how we can interpret isotopic variability in growth rings is extensive, but very little is known about isotopic intra-variability in modern plant leaves. Two modern Ginkgo biloba leaves were analyzed intensively for their bulk carbon-isotope ratio to ascertain if any isotopic variability existed within these leaves. Carbon-isotope ratios in a naturally dried leaf sampled under a ginkgo tree in the grounds of McMaster University produced a range of values from –29.36‰ to –25.67‰ (3.69‰, n = 264). The other leaf was picked directly from a gingko tree growing in the greenhouse at McMaster University, dried in the lab and produced values from –27.83‰ to –25.48‰ (2.35‰, n = 122). The isotopic variability shown within these two specimens is significant, especially in the sample dried under natural environmental conditions beneath the ginkgo tree. Preliminary analyses on modern horse-tail (Equisetum) from Dundas displays equal variation from –29.23‰ to –26.38‰ (2.85‰, n = 59). Distinct patterns of isotopic variation are recorded in both Ginkgo biloba and Equisetum, hence depending on where an isotopic analysis is made on fossil material (i.e., fragments of cuticle), such isotopic results may be influenced by this internal variability. Investigations of ancient plant cuticle and leaf fragments should consider this isotopic variability, as such variation can skew or bias or lend itself to misinterpretation concerning ancient environments and climates.