We examined blooms of the coccolithophorid E. huxleyi, observed in SeaWiFS imagery, with a new algorithm for the retrieval of detached coccolith concentration. The algorithm uses only SeaWiFS bands in the red and near infrared (NIR) to minimize the influence of the absorption by chlorophyll and dissolved organic material. We used published experimental determinations of the calcite specific backscattering and its spectral dependence, and assumed that the absorption coefficient of the medium was that of pure water, to estimate the marine contribution to the SeaWiFS radiance. The aerosol (and Rayleigh-aerosol interaction) contribution to the radiance was modeled as an exponential function of wavelength. These allow derivation of the coccolith concentration on a pixel-by-pixel basis from SeaWiFS imagery. Application to a July 30, 1999 SeaWiFS image of a bloom south of Plymouth, UK indicates that the SeaWiFS estimates are in good agreement with surface measurements of coccolith concentration. ¿ 2001 American Geophysical Union