Controls on stable isotope and trace metal uptake in Neogloboquadrina pachyderma (sinistral) from an Antarctic sea-ice environment
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 CO2. 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 δ 13CCaCO3 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 CO2 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 [CO3 2−]. N. pachyderma (s.) Mg/Ca ratios exhibit temperature sensitivity
similar to previous studies (~10–20%/°C) and a sensitivity to [CO32−] 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 [CO32−] 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 [CO3 2−].
Authors: Hendry, K.R., Rickaby, R.E.M., Meredith, M.P. ORCID record for M.P. Meredith, Elderfield, H.
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