ISOTOPIC COMPOSITION AND PROBABLE ORIGIN OF INDIVIDUAL FATTY-ACIDS INMODERN SEDIMENTS FROM RUOERGAI MARSH AND NANSHA SEA, CHINA

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 mea n delta(13)C values of individual fatty acids are -33.9 parts per thou sand for Ruoergai Marsh and -29.3 parts per thousand for Nansha Sea, i ndicating different biological sources. The isotopic compositions of f atty acids of various chain lengths differ significantly, indicating t hat they have separate origins. The delta(13)C values of long-chain sa turated acids (greater than or equal to C-20:0) from the two environme nts 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 sampl es and from higher-land plants for Ruoergai Marsh sample. The C-16:1 a nd 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 C-13-depleted source. Isotopic composition s of C-14:0 and C-15:0 acids in the two kinds of environments imply ba cterial sources. (C) 1997 Elsevier Science Ltd. All rights reserved.