Variations of Calcium Isotopes in Foraminifers Over the Past 24Ma
Variations of calcium isotope ratios of foraminifer shells can be used for the reconstruction of past seawater temperatures or the recontruction of the evolution of teh Ca isotopic composition of seawater. This thesis presents a new multicollector TIMS technique for the measurement of Ca isotopes and a comparison of the Ca isotopic composition of different standard materials. A systematic study of cultured foraminiferes shows that variations the Ca istopic composition can be temperature dependent or can be independent of temperature. A model explaining the mechanisms of this different temperature dependence of Ca isotope fractionation of foraminifers is developed. Measurements of the Ca isotopic composition of foramninifers fractionating Ca isotopes independent of seawater temperature changes are used to reconstruct the evolution of the Ca isotopic composition of seawater over the past 24 Ma.