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

Abstract

New culturing protocols allowed the development of a Mg/Ca temperature calibration equation for Neogloboquadrina pachydermia (d.). When cultured between 9°C and 19.2°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*). 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°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 ∼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. Copyright 2005 by the American Geophysical Union.