Controls on stable isotope and trace metal uptake in Neogloboquadrina pachyderma (sinistral) from an Antarctic sea-ice environment

Abstract

The polar foraminifera Neogloboquadrina pachyderma (sinistral) dominates assemblages from the high latitude Southern Ocean, which is a key region for paleoclimate studies. 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 δ18OCaCO3 and δ13CCaCO3 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, during winter, 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. We suggest an elevated carbonate ion concentration at the ice-water interface resulting from biological utilisation CO2 could influence calcification in foraminifera. We demonstrate that for N. pachyderma (s.) Mg/Ca and Sr/Ca ratios are linear functions of calcification temperature and [CO32-]. N. pachyderma (s.) Mg/Ca ratios exhibit temperature sensitivity similar to previous studies (~ 10 % per °C) and a sensitivity to [CO32-] of ~ 1 % per μmol kg-1). Sr/Ca ratios are less sensitive to environmental parameters, exhibiting < 1% increase per °C and per 10 μmol kg-1. We show how a multi-proxy approach could be used to constrain past high latitude surface water temperature and [CO32-].