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Lookup NU author(s): Professor Thomas Wagner
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Long-chain, odd-carbon-numbered C 25 to C 35 n-alkanes are characteristic components of epicuticular waxes produced by terrestrial higher plants. They are delivered to aquatic systems via eolian and fluvial transport and are preserved in underlying sediments. The isotopic compositions of these products can serve as records of past vegetation. We have developed a rapid method for stable carbon isotopic analyses of total plant-wax n-alkanes using a novel, moving-wire system coupled to an isotope-ratio mass spectrometer (MW-irMS). The n-alkane fractions are prepared from sediment samples by (1) saponification and extraction with organic solvents, (2) chromatographic separation using silica gel, (3) isolation of straightchain carbon skeletons using a zeolite molecular sieve, and (4) oxidation and removal of unsaturated hydrocarbons with RuO 4. Short-chain n-alkanes of nonvascular plant origin (<C25) are removed by evaporation on the moving wire. Test samples processed using this procedure yielded n-alkane fractions essentially free of interfering components. The δ 13C values obtained by MW-irMS did not differ significantly from weighted averages of individual n-alkane δ 13C values obtained by irmGC-MS. Isotopic variations in compound-class n-alkane fractions from a latitudinal transect of core-top sediments from the Southwest African margin (3°N-28°S) were congruent with those measured by compound-specific isotopic analyses of plant-wax n-alkanes. The amplitude of the variations was smaller, indicating contributions from non-plant-wax hydrocarbons, but the measurements revealed variations in carbon isotopic composition that are consistent with vegetation zones on the adjacent continent.
Author(s): McDuffee KE, Eglinton TI, Sessions AL, Sylva S, Wagner T, Hayes JM
Publication type: Article
Publication status: Published
Journal: G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences
ISSN (print): 1525-2027
Publisher: American Geophysical Union
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