Technical note: A refinement of coccolith separation methods: measuring the sinking characteristics of coccoliths

Abstract

Quantification sinking velocities of individual coccoliths will contribute to optimizing laboratory methods for separating coccoliths of different sizes and species for geochemical analysis. The repeated settling–decanting method was the earliest method proposed to separate coccoliths from sediments and is still widely used. However, in the absence of estimates of settling velocity for nonspherical coccoliths, previous implementations have depended mainly on time-consuming empirical method development by trial and error. In this study, the sinking velocities of coccoliths belonging to different species were carefully measured in a series of settling experiments for the first time. Settling velocities of modern coccoliths range from 0.154 to 10.67 cm h−1. We found that a quadratic relationship between coccolith length and sinking velocity fits well, and coccolith sinking velocity can be estimated by measuring the coccolith length and using the length–velocity factor, kv. We found a negligible difference in sinking velocities measured in different vessels. However, an appropriate choice of vessel must be made to avoid hindered settling in coccolith separations. The experimental data and theoretical calculations presented here support and improve the repeated settling–decanting method.