BIOSYNTHETIC EFFECTS ON THE STABLE CARBON ISOTOPIC COMPOSITIONS OF ALGAL LIPIDS : IMPLICATIONS FOR DECIPHERING THE CARBON ISOTOPIC BIOMARKER RECORD

Abstract Thirteen species of algae covering an extensive range of classes were cultured and stable carbon isotopic compositions of their lipids were analysed in order to assess carbon isotopic fractionation effects during their biosynthesis. The fatty acids were found to have similar stable carbon isotopic compositions to each other in all the algae with the exceptions of the C 28 fatty acid in Scenedesmus communis and the polyunsaturated fatty acids in Ampidinium sp. and Gymnodinium simplex which are 3.5‰ more depleted in 13 C and up to 8‰ more enriched in 13 C, compared to the C 16 fatty acid, respectively. Phytol is consistently enriched in 13 C by 2–5‰ compared with the C 16 fatty acid in all algae. The sterols are, however, enriched in 13 C by 0–8‰ compared to the C 16 fatty acid, possibly due to a different pool of isopentenyl diphosphate in the cytosol. These large ranges in carbon isotopic compositions of compounds biosynthesized by the same eukaryotes can significantly complicate the interpretation of δ 13 C values of sedimentary biomarkers.