Calculation of coccolith volume and it use in calibration of carbonate flux estimates

Estimates of coccolith volume help in determining total coccolith carbonate fluxes and the relative contributions of various coccolith species. It is argued here that the best approach to deriving such coccolith volumes is to calculate shape factors, ks, for each species separately based on reconstruction of cross profiles and to determine mean sizes from measurement of size variation in the sample of interest. Then volume=ksl3. Values of ks are given for the most important extant coccolith species based on reconstruction of cross-sections, followed by calculation of a volume of rotation using an iterative routine implemented in an image analysis package. Substantial errors, ca. 50%, are inevitable in such calculations, but the resultant data are nonetheless of value. Coccolith assemblages from North Atlantic (47°N 20°W) JGOFS 1989 sediment trap samples are analysed as a test case; calculated coccolith PIC fluxes constitute 30–80% of the chemically determined total PIC fluxes.