Separation of monospeci¢c and restricted coccolith assemblages from sediments using di¡erential settling velocity Heather M. Stoll a; Ã , Patrizia Ziveri b a Department of Geology, University of Oviedo, Arias de Velasco s/n, 33005 Oviedo Asturias, Spain b Faculteit der Aardwetenschappen, Vrije Universiteit, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands Received 28 June 2001; received in revised form 8 October 2001; accepted 11 October 2001 Abstract 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 ( s 70% but in most cases s 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 1.5x in N 18 O and 2.5x in N 13 C, consistent with a range of non- equilibrium effects in culture, and offsets among species are generally constant. While these non-equilibrium effects were originally believed to hamper paleoceanographic studies, new work suggests that these effects can be used to trace different physiological responses of different species. Sr/Ca ratios of separated fractions vary by as much as 75% from the same site, but offsets between species tend to be variable rather than constant, consistent with other studies indicating that coccolith Sr/Ca varies with productivity. The larger coccoliths C. leptoporus and Helicosphaera show a more dynamic range in Sr/Ca variation among different sites. The ability to separate out productivity responses of individual species should greatly expand the use of coccolith Sr/Ca proxies. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: coccoliths; coccolithophores; stable isotopes; Sr/Ca; sample preparation 1. Introduction Analysis of both isotopic and elemental chem- istry of marine carbonates has become a wide- spread tool for paleoceanographic and paleocli- mate studies. The calcium carbonate shells produced by planktic and benthic foraminifera have been the most widely used, because of their abundance in the sediments and the ease with which monospeci¢c samples can be picked. These are used to minimize e¡ects of interspeci¢c vari- ability and occasionally to target particular depth 0377-8398 / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0377-8398(02)00040-3 * Corresponding author. Present address: Geoscience De- partment, Williams College, Williamstown, MA 01267, USA. Fax: +1-413-597-4116. E-mail addresses: hstoll@williams.edu (H.M. Stoll), zivp@geo.vu.nl (P. Ziveri). MARMIC 873 27-8-02 Marine Micropaleontology 46 (2002) 209^221 www.elsevier.com/locate/marmicro