Specimens of the benthic foraminifer Ammonia beccarii were cultured in the laboratory in order to determine the relation between temperature and Mg/Ca and oxygen isotope values in their tests. Asexual reproduction in this species provides a large number of juveniles that were allowed to grow into maturity at temperatures ranging from 10 to 27 °C and at salinities ranging from 18 to 33 PSU. The Mg/Ca in a calcite increase exponentially and δ18O decreases linearly with the temperature. Salinity has no significant impact on either Mg/Ca or δ18O. We show how the combination of these two parameters can be used to reconstruct seawater δ18O and temperature in shallow marine habitats.