Strontium Isotopes in Water and Rock

Abstract

The Sr isotopic ratio in natural water reflects the contribution made by various minerals as they dissolve in water. Rivers are the major provider of strontium to the oceans and define, to a great extent, the marine 87 Sr/ 86 Sr ratio. Strontium in rivers is mainly derived from two end members: limestone and evaporites as one end member (high Sr and low 87 Sr/ 86 Sr ratio of 0.706–0.709) and silicate rocks as the other end member that are low in Sr and have a higher 87 Sr/ 86 Sr ratio. Processes such as atmospheric deposition, cation exchange, and biological cycling, too, influence the Sr isotope ratio in water. However, unless there have been recent anthropogenic or natural disturbances, annual gains or losses of Sr from cation exchange and biological pool should be minimal.