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Carbon isotope alteration during the thermal maturation of non‐flowering plant species representative of those found within the geological record
Author(s) -
Smith Andrew C.,
Kendrick Christopher P.,
MossHayes Vicky L.,
Vane Christopher H.,
Leng Melanie J.
Publication year - 2016
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7755
Subject(s) - chemistry , decomposition , isotopes of carbon , lignin , botany , stable isotope ratio , carbon fibers , δ13c , mineralogy , environmental chemistry , biology , total organic carbon , physics , materials science , organic chemistry , quantum mechanics , composite number , composite material
Rationale The carbon isotope (δ 13 C value) composition of fossil plant material is routinely used as a proxy of past climate and environment change. However, palaeoclimate interpretation requires assumptions about the stability of δ 13 C values in plant material during its decomposition and incorporation into sediments. Previous work on modern angiosperm species shows δ 13 C changes of several per mille during simulated decomposition experiments. However, no such tests have been undertaken on non‐flowering plants, which are found extensively within the geological record. These plants have distinctly different cellulose‐to‐lignin ratios from those of their angiosperm counterparts, potentially creating hitherto unknown variations in the original to fossil δ 13 C signatures. Methods To test the extent of δ 13 C change during decomposition we have subjected a number of plants, representing more basal, non‐flowering plant lineages (cycads, ferns, horsetails and dawn redwood), to artificial decay using a hydrothermal maturation technique at two temperatures over periods of up to 273 hours. Subsamples were extracted every 12–16 hours and analysed for their δ 13 C and %C values using a Carlo Erba 1500 elemental analyser, and VG TripleTrap and Optima mass spectrometers. Results The %C values increased for all samples through the maturation process at both temperatures with the largest increases observed within the first 24 hours. Decreases in δ 13 C values were observed for all plants at 300°C and for two of the species at the lower temperature (200°C). The maximum shift in the δ 13 C value related to experimental decomposition was −0.90‰ (horsetail), indicating a preferential loss of 13 C during thermal maturation. Conclusions The reduction in the δ 13 C value potentially suggests a preferential loss of isotopically heavier cellulose in relation to the isotopically lighter lignin component during maturation. The isotopic offset observed here (<0.9‰) means that palaeoclimatic interpretation of δ 13 C values from non‐flowering plant material within the geological record remains robust, but only where interpretations are based on variations in δ 13 C values greater than 1‰. Copyright © 2016 John Wiley & Sons, Ltd.