Controls on stable isotope and trace metal uptake in Neogloboquadrina pachyderma (sinistral) from an Antarctic sea-ice environment Katharine R. Hendry a, ⁎, Rosalind E.M. Rickaby a , Michael P. Meredith b , Henry Elderfield c a Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, UK b British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK c Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK abstract article info Article history: Received 17 March 2008 Received in revised form 18 November 2008 Accepted 20 November 2008 Available online xxxx Editor: P. DeMenocal Keywords: N. pachyderma isotopes trace metals sea-ice carbonate ion The polar foraminifera Neogloboquadrina pachyderma (sinistral) dominates assemblages from the high latitude Southern Ocean, which plays a key role in determining past climate due to the tight linkage between Antarctic temperature and atmospheric CO 2 . Here, we use N. pachyderma (s.) harvested from sediment traps off the West Antarctic Peninsula to construct a seasonal time series for the calibration of calcite proxies in a high latitude seasonal sea-ice environment where temperature is decoupled from other environmental parameters. We have used a combination of δ 18 O CaCO3 and δ 13 C CaCO3 to decipher the calcification temperature and salinity, which reflect that N. pachyderma (s.) live in surface waters throughout the year, and at the ice–water interface in austral winter. Further, our results demonstrate that the uptake of trace metals into N. pachyderma (s.) calcite is influenced by secondary environmental conditions in addition to temperature during periods of sea-ice cover. We propose an elevated carbonate ion concentration at the ice– water interface resulting from biological utilisation of CO 2 could influence calcification in foraminifera. Our calculations suggest that for N. pachyderma (s.) Mg/Ca, Sr/Ca ratios and Li/Ca ratios are linear functions of calcification temperature and [CO 3 2- ]. N. pachyderma (s.) Mg/Ca ratios exhibit temperature sensitivity similar to previous studies (~10–20%/°C) and a sensitivity to [CO 3 2- ] of ~1%/μmol kg - 1 . Sr/Ca ratios are less sensitive to environmental parameters, exhibiting ~5% increase/°C and ~0.5%/10 μmol kg - 1 . The relationship between Li/Ca ratios and both temperature and [CO 3 2- ] is less significant with ~10% increase in Li/Ca ratio/°C and 10 μmol kg - 1 . We show how a multi-proxy approach could be used to constrain past high latitude surface water temperature and [CO 3 2- ]. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Atmospheric gases trapped in bubbles within ice cores show the partial pressure of carbon dioxide (pCO 2 ) was 80 ppm V lower during the Last Glacial Maximum (LGM) compared with modern values (Petit, 1999; Siegenthaler et al., 2005). Of the many hypotheses proposed to account for this CO 2 shift, a significant focus has been placed on past changes in productivity, chemistry and circulation in the Southern Ocean (Anderson et al., 2002; Sigman and Boyle, 2000). Accordingly, there is a clear motivation to obtain reliable information about these processes in the past Southern Ocean. The stable isotopic and trace metal composition of planktonic foraminiferal calcite provide impor- tant geochemical tools for reconstructing past changes in sea surface conditions. In particular, Neogloboquadrina pachyderma (sinistral) is a species of interest as it dominates modern planktonic assemblages in the high latitudes and Southern Ocean sediments. However, inference of past calcification conditions from N. pachyderma (s.) chemistry can be ambiguous, in part because the species can live in a variety of habitats, including sea-ice. Open water N. pachyderma (s.) are generally considered pycnocline dwellers, but can calcify below the mixed layer, occupying a wide range of depths shallower than 200 m (Kohfeld et al., 1996). In sea-ice conditions, N. pachyderma (s.) are associated in high but patchy cell concentrations with the bottom community of sea-ice diatoms, which grows in the more porous layers at the ice–water interface (Lipps and Krebs, 1974). In the autumn, the adults conduct gametogenesis, such that juveniles appear in the upper part of the water column and become incorporated into the forming frazil ice (Spindler and Dieckmann, 1986). There is an increasing appreciation that multiple factors control stable isotope and trace metal chemistry of foraminifera. In particular, the role of carbonate ion concentration, [CO 3 2- ], and salinity on the uptake of trace metals (Mg, Sr and Li) into planktonic foraminiferal calcite is not fully understood (Ferguson et al., 2008; Lea et al., 1999; Marriott et al., 2004; Mortyn et al., 2005; Russell et al., 2004). Further, Southern Ocean waters are undersaturated with respect to calcite such that foraminifera have a low preservation potential in slowly Earth and Planetary Science Letters xxx (2009) xxx–xxx ⁎ Corresponding author. E-mail address: kathh@earth.ox.ac.uk (K.R. Hendry). EPSL-09588; No of Pages 11 0012-821X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2008.11.026 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl ARTICLE IN PRESS Please cite this article as: Hendry, K.R., et al., Controls on stable isotope and trace metal uptake in Neogloboquadrina pachyderma (sinistral) from an Antarctic sea-ice environment, Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl.2008.11.026