Evaluation of Mg/Ca thermometry in foraminifera: Comparison of experimental results and measurements in nature

We studied Mg/Ca in high-Mg, shallow-water benthic foraminifera in culture and in samples from natural environments, in order to evaluate the expressi on of latitudinal and seasonal temperature variability in Mg/Ca in their te sts. We cultured Planoglabratella opercularis (d'Orbigny) and Quinqueloculi na yabei Asano under controlled temperature (10 degrees-25 degrees C) and s alinity (30-38) conditions. Both species show a linear correlation between Mg/Ga and temperature, but they differ in temperature sensitivity. Salinity does not significantly influence Mg/Ca. In the samples collected in nature , Mg/Ca and seawater temperatures are positively correlated, but there are more complexities than in the records for cultured specimens due to such fa ctors as seasonal fluctuations in temperature. We conclude that Mg/Ca ratio s in monospecific benthic foraminiferal samples may be used as a reliable t emperature proxy, if the lifetime of the species is taken into account.