Separation of monospecific and restricted coccolith assemblages from sediments using differential settling velocity.

Techniques are described to allow concentration of individual coccolith species from sediment samples, for geochemical analysis. Simple repeated decanting and density-stratified settling columns permit separation of sediment fractions whose carbonate is highly dominated (> 70% but in most cases > 90%) by coccoliths from a single species. In each of six different core top sediments from different oceanographic settings, we were able to separate two or more fractions dominated by different species, although the species which can be effectively separated is highly dependent on the species makeup of the original sample. Isolates were obtained of Calcidiscus leptoporus, Helicosphaera carterae, Gephyrocapsa oceanica, Emiliania huxleyi, and Florisphaera profunda. The deep photic zone dweller F. profunda was isolated from all but one site, even where its initial abundance is very low. Separated fractions show a wide range of stable isotope ratios, up to 1.5 ‰ in δ