STRONTIUM ISOTOPES IN BIOAPATITES

One application of Sr isotopes makes use of the change in seawater Sr isotope composition through time for age determinations (e.g., DePaolo and Ingram 1985). The 

Terrestrial Sr/ Sr is commonly elevated compared to marine Sr/ Sr, because of radiogenic Sr from old continental crust, and it is possible to use this Sr/ Sr difference as a measure of fish origin (Schmitz et al. 1991, 1997). Ocean water has a Sr concentration that is -100 times higher than fresh water, so even a small marine component would overwhelm any freshwater isotope composition. However, freshwater fish consistently show higher Sr/ Sr compared to marine fish, permitting a freshwater vs. brackish/marine distinction (Schmitz et al. 1991, 1997). Similarly, fish living in different drainages exhibit isotopic differences correlated with bedrock Sr/ Sr (Kennedy et al. 1997). 

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