A multi-proxy (δ44/40Ca, Sr/Ca, and Δ47) study of fish otoliths for determination of seawater temperature

Abstract

Fish otoliths are valuable archives for paleotemperature studies. In this study, we have measured δ44/40Ca, Sr/Ca, Mg/Ca, and Ba/Ca ratios in six fish otolith samples of four different species from water with different annual average temperatures ranging from 2 °C to 25 °C. We demonstrate that the δ44/40Ca values of fish otoliths can be used as a temperature proxy. The temperature sensitivity of δ44/40Ca in fish otoliths is 0.036‰/°C which suggests that with the current analytical uncertainty of ±0.08‰ for δ44/40Ca measurements, we can resolve temperature changes of ±2 °C. The Sr/Ca ratio of fish otoliths also shows a negative correlation with water temperature. In addition, both δ44/40Ca values and Sr/Ca of fish otoliths display linear correlations with published δ18O and Δ47 measured in the same otolith powder samples. This study further demonstrates that simultaneous measurements of δ44/40Ca, Sr/Ca, and Δ47 in fish otoliths can be used for robust paleotemperature reconstruction. Using a multi-regression approach, a multi proxy calibration equation is proposed (T (K) = 5.43 × Sr/Ca – 16.8 × δ44/40Ca – 484.6 × Δ47 + 580.9) by combining the δ44/40Ca, Sr/Ca, and Δ47 values in the fish otolith samples, which results in a low uncertainty of temperature estimation of ±0.9 °C. However, the temperature sensitivity of Mg/Ca and Ba/Ca ratios in fish otoliths is not statistically significant and hence, not a reliable proxy for paleotemperature reconstruction.