Carbon isotopic ratios (Δ13C) of C27-C33 n-alkanes and C37 alkenes were measured in the surface sediments from Australian sector of Southern Ocean (47.6¿--65.5 ¿S). The Δ13C of C31 n-alkane derived from higher plant wax shows little change along the latitude (-28.7¿0.6?), whereas Δ13C of C37 alkenes derived from haptophyte algae decreases from -24.6¿0.7? at 47.6 ¿S to -32.1¿1.2? at 63.9 ¿S. Relatively heavy Δ13C values of C31 n-alkane suggest significant contribution of C4 plant waxes or conifer resin whose Δ13C of n-alkanes are significantly heavier than those of C3 plants. The Δ13C of total organic carbon exhibits a latitudinal pattern similar to that of C37 alkenes, suggesting that organic carbon in the sediments is primarily of marine origin. ¿ 2000 American Geophysical Union