Stable isotopes in opal in the Southern Ocean

Measurements of delta 13C, delta 15N, and C/N on diatom-bound organic matter were made over the Holocene and Last Glacial Maximum (LGM) from 3 piston cores in the Southern Ocean, one from each of the three sectors. The site in the Scotia Sea differed considerably from the other two sites by having markedly lower delta 13C, more variable delta 15N and C/N ratios, and a sedimentary diatom assemblage that was never dominated by Fragilariopsis kerguelensis. Although environmental parameters certainly have a strong impact on the isotope ratios, delta 13C is also correlated to the proportion of F. kerguelensis in the 3 cores investigate here (r**2 = 0.8). Extreme values of delta 13C, delta 15N, and C/N at the Last Glacial Maximum were also related to the abundance of winter stages of Eucampia antarctica. These results suggest that diatom specific isotope records should be interpreted in conjunction with information on the species composition of the samples.