A culture-based calibration of benthic foraminiferal paleotemperature proxies: δ ¹⁸O and Mg/Ca results

Benthic foraminifera were cultured for five months at four temperatures (4, 7, 14 and 21 °C) to establish the temperature dependence of foraminiferal calcite δ ¹⁸O 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 °C. Foraminiferal δ ¹⁸O values displayed ontogenetic variations, with lower values in younger individuals. The δ ¹⁸O values of adult specimens decreased with increasing temperature in all but the 4 °C treatment, exhibiting a relationship consistent with previous δ ¹⁸O 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 °C treatment and higher than predicted values at two of the other three temperatures make it challenging to interpret these results.