Effects of temperature on Mg/Ca in neogloboquadrinid shells determined by live culturing

[1] New culturing protocols allowed the development of a Mg/Ca temperature calibration equation for Neogloboquadrina pachyderma (d.). When cultured between 9 degrees C and 19.2 degrees C, Mg/ Ca in N. pachyderma ( d.) shell calcite exhibits a clear dependence on temperature. Shell calcite Mg/ Ca increased exponentially with temperature: Mg/Ca = 0.51(-0.15)(+0.23) * exp((0.10 +/- 0.02* T)). Limited data suggest N. dutertrei exhibit similar elemental temperature relationships to N. pachyderma ( d.). We applied the temperature relationship established by culturing to Mg/Ca in neogloboquadrinid shells collected using plankton tows. Compared to measured SST, the calculated temperatures were within +/- 2 degrees C for Mg/Ca (95% CI). Multiple samples from single tows generally had calculated temperatures that ranged from near-surface values to temperatures consistent with calcification depths down to similar to 70 m. Our work indicates that Mg/ Ca temperature calibration equations for temperate and polar foraminiferal species have a similar exponential constant but a higher pre-exponential constant than those for surface-dwelling tropical species. Therefore accurate paleotemperature reconstructions from temperate and polar species require the use of an equation distinct from those used for tropical species.