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

first_imgThe polar foraminifera Neogloboquadrina pachyderma (sinistral) dominates assemblages from the highlatitude Southern Ocean, which plays a key role in determining past climate due to the tight linkage betweenAntarctic temperature and atmospheric CO2. Here, we use N. pachyderma (s.) harvested from sediment trapsoff the West Antarctic Peninsula to construct a seasonal time series for the calibration of calcite proxies in ahigh latitude seasonal sea-ice environment where temperature is decoupled from other environmentalparameters. We have used a combination of δ18OCaCO3 and δ 13CCaCO3 to decipher the calcificationtemperature and salinity, which reflect that N. pachyderma (s.) live in surface waters throughout the year, andat the ice–water interface in austral winter. Further, our results demonstrate that the uptake of trace metalsinto N. pachyderma (s.) calcite is influenced by secondary environmental conditions in addition totemperature during periods of sea-ice cover. We propose an elevated carbonate ion concentration at the ice–water interface resulting from biological utilisation of CO2 could influence calcification in foraminifera. Ourcalculations suggest that for N. pachyderma (s.) Mg/Ca, Sr/Ca ratios and Li/Ca ratios are linear functionsof calcification temperature and [CO3 2−]. N. pachyderma (s.) Mg/Ca ratios exhibit temperature sensitivitysimilar to previous studies (~10–20%/°C) and a sensitivity to [CO32−] of ~1%/μmol kg−1. Sr/Ca ratios are lesssensitive to environmental parameters, exhibiting ~5% increase/°C and ~0.5%/10 μmol kg−1. The relationshipbetween Li/Ca ratios and both temperature and [CO32−] is less significant with ~10% increase in Li/Ca ratio/°Cand 10 μmol kg−1.We show how a multi-proxy approach could be used to constrain past high latitude surfacewater temperature and [CO3 2−].last_img

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