Accuracy of Otolith Oxygen Isotope Records Analyzed by SIMS as an Index of Temperature Exposure of Wild Icelandic Cod (Gadus morhua)

Global warming is increasing ocean temperatures, forcing marine organisms to respond a suite of changing environmental conditions. The stable oxygen isotopic composition otoliths often used as an index temperature exposure, but the accuracy resulting reconstructions in wild, free-swimming Atlantic cod ( Gadus morhua ) has never been groundtruthed. Based on temperatures from data storage tags (DST) and corresponding salinity values, isotope (δ 18 O) value was predicted for each month tagging compared with δ O otolith values measured situ secondary ion mass spectrometry (SIMS). Paired-sample Wilcoxon tests were applied compare values. difference between mean maximum not significant, suggesting good correspondence SIMS-measured DST-predicted ot olith However, minimum significantly different (all samples: p < 0.01, coastal frontal cod: 0.05), overestimation temperatures. Our results confirm that are well-suited proxies ambient reconstructions. A possible matrix effect absence reliable aragonite standard SIMS measurements appeared cause small divergence which affected estimation absolute temperature. relative changes accurately estimated by SIMS-analyzed