87Sr/86Sr Ratios Measure the Sources and Flow of Strontium in Terrestrial Ecosystems

Abstract

The measurable variations in the isotopic composition of strontium in ecosystems, unlike those of the lighter elements discussed in this volume, are entirely caused by the mixing of strontium derived from different geologic regimes of differing isotopic composition and are not due to fractionation by biological processes. The values and variation of strontium isotope ratios within an ecosystem can therefore yield information about the sources of strontium to and the patterns of strontium flow within the ecosystem. The lack of measurable isotopic fractionation of strontium means that information about processes is not obtainable directly, but must be inferred from mixing calculations. The lack of measurable isotopic fractionation also means that there must be variations in isotopic composition between various sources of strontium to an ecosystem in order for there to be any internal variation in isotopic composition.