A culture-based calibration of benthic foraminiferal paleotemperature proxies: δ18O and Mg/Ca results

Benthic foraminifera were cultured for five months at four temperatures (4, 7, 14 and 21 degrees C) to establish the temperature dependence of foraminiferal calcite delta O-18 and Mg/Ca. Two Bulimina species (B. aculeata and B. marginata) were most successful in terms of calcification, adding chambers at all four temperatures and reproducing at 7 and 14 degrees C. Foraminiferal delta O-18 values displayed ontogenetic variations, with lower values in younger individuals. The delta O-18 values of adult specimens decreased with increasing temperature in all but the 4 degrees C treatment, exhibiting a relationship consistent with previous delta O-18 paleotemperature calibration studies. Foraminiferal Mg/Ca values, determined by laser ablation inductively coupled plasma mass spectrometry, were broadly consistent with previous Mg/Ca calibration studies, but extremely high values in the 4 degrees C treatment and higher than predicted values at two of the other three temperatures make it challenging to interpret these results.