Temperature-dependent oxygen isotope fractionation in otoliths of juvenile Chinook salmon (Oncorhynchus tshawytscha)

Abstract

Oxygen thermometry has become a widely used technique for reconstructing thermal history in calcifying organisms but interpretation can be subject to predictive error from vital effects. To better understand these processes in Chinook salmon (Oncorhynchus tshawytscha) we experimentally constructed a temperature-dependent, otolith–water fractionation relationship for oxygen isotopes (δ18O) by rearing post-yolk absorptive juvenile fish at nominal temperatures from 6 to 21 °C. Temperature and otolith precipitation rate had significant effects on the otolith–water δ18O fractionation, but somatic growth rate did not. The slope of the δ18O fractionation equation also differed significantly from that of synthetic aragonite. Our results suggest the expression of kinetic effects on δ18O fractionation in otoliths of Chinook salmon that are increasingly constrained at higher temperatures by other physical and physiological processes involved in mineral formation. Species-specific δ18O fractionation equations have considerable utility to reconstruct temperature history in Pacific salmon, but applications should recognize the potential for inferential uncertainty arising from interacting vital effects.