Implications of carbon isotope ratios of C27-C33 alkanes and C37 alkenes for the sources of organic matter in the Southern Ocean surface sediments

Carbon isotopic ratios (delta(13)C) of C-27-C-33 n-alkanes and C-37 alkenes were measured in the surface sediments from Australian sector of Southern Ocean (47.6 degrees-65.5 degrees S). The delta(13)C of C-31 n-alkane derived from higher plant wax shows little change along the latitude (-28.7 +/- 0.6 parts per thousand), whereas delta(13)C of C-37 alkenes derived from haptophyte algae decreases from -24.6 +/- 0.7 parts per thousand at 47.6 degrees S to -32.1 +/- 1.2 parts per thousand at 63.9 degrees S. Relatively heavy delta(13)C values of C-31 n-alkane suggest significant contribution of C4 plant waxes or conifer resin whose delta(13)C of n-alkanes are significantly heavier than those of C3 plants. The delta(13)C of total organic carbon exhibits a latitudinal pattern similar to that of C-37 alkenes, suggesting that organic carbon in the sediments is primarily of marine origin.