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

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 duri ng their biosynthesis. The fatty acids were found to have similar stab le carbon isotopic compositions to each other in all the algae with th e exceptions of the C-28 fatty acid in Scenedesmus communis and the po lyunsaturated fatty acids in Ampidinium sp. and Gymnodinium simplex wh ich are 3.5% more depleted in C-13 and up to 8 parts per thousand more enriched in C-13, compared to the C-16 fatty acid, respectively. Phyt ol is consistently enriched in C-13 by 2-5 parts per thousand compared with the C-16 fatty acid in all algae. The sterols are, however, enri ched in C-13 by 0-8 parts per thousand compared to the C-16 fatty acid , possibly due to a different pool of isopentenyl diphosphate in the c ytosol. These large ranges in carbon isotopic compositions of compound s biosynthesized by the same eukaryotes can significantly complicate t he interpretation of delta(13)C values of sedimentary biomarkers. Copy right (C) 1998 Elsevier Science Ltd.