Downloaded By: [Bergami, C.] At: 10:12 24 June 2008 Chemistry and Ecology Vol. 24, No. S1, June 2008, 39–46 Mg/Ca ratios in the planktonic foraminifer Neogloboquadrina pachyderma (sinistral) from plankton tows in the Ross Sea and the Pacific sector of the Southern Ocean (Antarctica): comparison of different methodological approaches C. Bergami a,b *, L. Capotondi a , M. Sprovieri c , M. Tiepolo d , L. Langone a , F. Giglio a and M. Ravaioli a a ISMAR CNR Marine Geology Section, Bologna, Italy; b Department of Earth and Geoenvironmental Sciences, University of Bologna, Bologna, Italy; c IAMC CNR, Napoli, Italy; d IGG CNR Pavia Section, Pavia, Italy (Received 19 July 2007; accepted 12 December 2007 ) Mg/Ca ratios in living specimens of the planktonic foraminifer Neogloboquadrina pachyderma (sin.) have been investigated using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP- MS) and ultracleaning procedures on ‘bulk’ foraminifera followed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Atomic Emission Spectrophotometry (ICP-AES) analysis. Plankton tows were taken in the upper 250 m of the water column at different sites in the Ross Sea and at the Polar Front of the Pacific Ocean during 6 austral summers. We found high values of Mg/Ca ratios in N. pachyderma (s.) not previously reported in the literature. Our data suggest that at least two factors influence the results: (1) the presence of some protoplasm in the test of living specimens, which seems to control the actual Mg concentration and (2) the morphotype of the analysed specimens in term of test thickness. Keywords: Mg/Ca ratios; Neogloboquadrina pachyderma (sin.); laser ablation ICP-MS; ICP-MS/ICP- AES; Antarctica 1. Introduction Sea surface temperature (SST) is one of the most important parameters for palaeoclimate stud- ies. The δ 18 O ratios of planktonic foraminifera had long been used as a proxy for past SST (see overview in [1]). In particular, stable isotopes and metals concentration in tests of non- spinose planktonic foraminifera Neogloboquadrina dutertrei and Neogloboquadrina pachyderma are widely used to reconstruct past oceanic temperature in high latitude waters (e.g. [2]). δ 18 O changes in planktonic foraminifera are controlled by SST, salinity and seawater δ 18 O composi- tion, and the latter is predominantly associated with changes of the global ice volume. Therefore, *Corresponding author. Email: caterina.bergami@ismar.cnr.it ISSN 0275-7540 print/ISSN 1029-0370 online © 2008 Taylor & Francis DOI: 10.1080/02757540801963303 http://www.informaworld.com