This study aimed to reconstruct temperatures experienced during the larval period by adult Pacific bluefin tuna Thunnus orientalis using high-resolution otolith stable oxygen isotope (δ18O) analysis. A novel otolith sample preparation protocol for secondary ion mass spectro metry (SIMS) analysis developed in this study reduced the background noise of SIMS measurements, enabling analyses of >10 times higher resolution around the otolith core compared to previous studies using conventional isotope ratio mass spectrometry (IRMS). The values obtained from SIMS were compared to those obtained by microvolume δOotolith analysis using micromilling and conventional continuous-flow IRMS (CF-IRMS). There was a systematic offset (average 0.41‰ with SIMS resulting in lower values) most likely caused by matrix effects on SIMS δOotolith values that can be calibrated using a strong linear relationship between SIMS and CFIRMS measurements (r2 = 0.78, p < 0.001). The core-to-edge δOotolith of 5 Pacific bluefin tuna revealed fine-scale seasonal variations in water temperature agreeing with known migration patterns. In addition, the ambient water temperature experienced during larval stages (about 10− 20 d post hatch) estimated from otolith core δ18O ranged from 26.7 to 30.7°C, overlapping with temperatures associated with the occurrence of larval Pacific bluefin tuna. Combining SIMS and microvolume CF-IRMS δ18O otolith analyses offers a microscale examination of fish ecology that is not possible with conventional IRMS techniques. This novel method is particularly useful for understanding the early life history of fish that may be affected by climate change and reconstructing a well-resolved migration history for fish species that have small otoliths and/or narrow growth increments.

中文翻译：

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使用 SIMS 和微体积 CF-IRMS 耳石氧同位素分析重建太平洋蓝鳍金枪鱼 Thunnus orientalis 幼虫的温度

本研究旨在使用高分辨率耳石稳定氧同位素 (δ18O) 分析重建太平洋蓝鳍金枪鱼 Thunnus orientalis 在幼虫时期经历的温度。本研究中开发的用于二次离子质谱 (SIMS) 分析的新型耳石样品制备方案降低了 SIMS 测量的背景噪声，与之前使用传统同位素比质谱法的研究相比，耳石核心周围的分析分辨率提高了 10 倍以上(IRMS)。将从 SIMS 获得的值与使用微铣削和传统连续流 IRMS (CF-IRMS) 的微体积 δOotolith 分析所得值进行比较。存在系统偏移（平均为 0. 41‰，SIMS 导致较低的值）最有可能是由基质效应对 SIMS δOtolith 值造成的，可以使用 SIMS 和 CFIRMS 测量值之间的强线性关系进行校准（r2 = 0.78，p < 0.001）。5 条太平洋蓝鳍金枪鱼的核心到边缘 δOotolith 揭示了水温的细微季节性变化，与已知的迁移模式一致。此外，根据耳石核心 δ18O 估计的幼体阶段（孵化后约 10-20 天）的环境水温范围为 26.7 至 30.7°C，与幼体太平洋蓝鳍金枪鱼的出现相关的温度重叠。结合 SIMS 和微体积 CF-IRMS δ18O 耳石分析，可以对鱼类生态进行微尺度检查，这是传统 IRMS 技术无法实现的。