Isotopic composition and probable origin of individual fatty acids in modern sediments from Ruoergai Marsh and Nansha Sea, China

Abstract Carbon isotopic analyses of individual fatty acids in modern sediments from Ruoergai Marsh and Nansha Sea, China were undertaken to evaluate the biological sources of individual sedimentary fatty acids. The mean δ 13 C values of individual fatty acids are −33.9‰ for Ruoergai Marsh and −29.3‰ for Nansha Sea, indicating different biological sources. The isotopic compositions of fatty acids of various chain lengths differ significantly, indicating that they have separate origins. The δ 13 C values of long-chain saturated acids (≥C 20:0 ) from the two environments reflect a source from higher-land plants, whereas C 16:0 and C 18:0 acid values indicate an origin is from plankton for Nansha Sea samples and from higher-land plants for Ruoergai Marsh sample. The C 16:1 and C 18:1 monounsaturated acids in Nansha Sea samples probably have a common source as saturated fatty acids with the same carbon number, or are derived in part from a 13 C-depleted source. Isotopic compositions of C 14:0 and C 15:0 acids in the two kinds of environments imply bacterial sources.