Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
Ibaraki College, Hitachinaka, National Institute of Technology, Ibaraki, Japan.
Rapid Commun Mass Spectrom. 2022 Oct 30;36(20):e9366. doi: 10.1002/rcm.9366.
The recent progress in micro-scale isotopic analytical techniques for otoliths has enabled the reconstruction of the experienced water temperature history of fish in every few days resolution using the stable oxygen isotope ratio (δ O) of otoliths. We aimed to improve those techniques and extract the daily δ O records of otoliths formed during the juvenile period.
Growth rings were formed daily in fish otoliths. We precisely distinguished the daily rings in otoliths of Japanese jack mackerel Trachurus japonicus, and milled them along daily growth rings using a high-spatial resolution micromilling system (Geomill326). Then, we determined the stable carbon and oxygen (δ C, δ O) isotopic compositions using a high-precision micro-scale isotopic analytical system (MICAL3c with IsoPrime 100).
We successfully milled each daily ring with width ranging from 14.0 to 62.9 μm (average 27.0 μm) during the high growth period (30-70 days after hatching), and determined the isotopic compositions of otolith aragonite.
Our improved micro-scale analytical method is the first to determine the daily δ O history of fish otoliths. By using our method together with the δ O - water temperature equation, the daily history of experienced water temperature can be elucidated. Our high-resolution milling and analytical technique can also be applied to high-resolution isotope analysis for stalactites, clams, and corals.
最近微尺度同位素分析技术在耳石方面的进展使得我们能够使用耳石稳定氧同位素比值（δ O）以每隔几天的分辨率重建鱼类经历的水温历史。我们旨在改进这些技术并提取幼鱼期形成的耳石的每日δ O 记录。
鱼类耳石每天形成一个生长环。我们精确区分了日本鲐 Trachurus japonicus 耳石中的每日环，并使用高空间分辨率微铣系统（Geomill326）沿每日生长环铣削。然后，我们使用高精度微尺度同位素分析系统（MICAL3c 与 IsoPrime 100）测定稳定的碳和氧同位素组成（δ C，δ O）。
我们在高生长期间（孵化后 30-70 天）成功地铣削了每个宽度在 14.0 到 62.9 μm 之间（平均 27.0 μm）的每日环，并测定了耳石文石的同位素组成。
我们改进的微尺度分析方法首次确定了鱼类耳石的每日δ O 历史。通过使用我们的方法和 δ O-水温方程，可以阐明经历的水温的每日历史。我们的高分辨率铣削和分析技术也可应用于钟乳石、蛤和珊瑚的高分辨率同位素分析。
