Implications of carbon isotope ratios of C 27 ‐C 33 alkanes and C 37 alkenes for the sources of organic matter in the southern ocean surface sediments

Carbon isotopic ratios (δ 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°–65.5°S). The δ 13 C of C 31 n ‐alkane derived from higher plant wax shows little change along the latitude (−28.7±0.6 ‰), whereas δ 13 C of C 37 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 δ 13 C values of C 31 n ‐alkane suggest significant contribution of C4 plant waxes or conifer resin whose δ 13 C of n ‐alkanes are significantly heavier than those of C3 plants. The δ 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.