[M-TT38] 地球化学の最前線

[MTT38-P01] Radiocarbon quantifies ontogenetic change in carbon sources of fish otolith

*安東 梢^1,2、横山 祐典^1,2、宮入 陽介¹、西田 梢³、林 正裕⁴ (1.東京大学大気海洋研究所、2.東京大学大学院理学系研究科地球惑星科学専攻、3.筑波大学 生命環境系、4.海洋生物環境研究所)

キーワード：放射性炭素、耳石

Fish otolith microchemistry provides valuable information on fish ecology and biology. However, few studies have considered the carbon sources in otolith, which limits the application of carbon isotopes to ecological and biological studies. Carbon sources of fish otolith are dissolved organic carbon (DIC) in the ambient water and metabolic carbon released from cell respiration, but the proportion of carbon derived from the two sources are still under debate. Studies that have quantified the contribution of metabolic carbon (M) uses δ¹³C, which is subject to biological fractionation. Additionally, uncertainty of end member associated with wild-caught fish further raises question to the accuracy of M estimation. Finally, no study has considered the ontogenetic variability in M, which is crucial when attempting to obtain ecological data from otolith formed at different life stages of fish. In this study, we will examine the ontogenetic change in M of fish using ¹⁴C, a novel proxy that is of higher sensitivity and does not require the correction for biological fractionation. Using a reverse radioisotope labelling established by Nishida et al. (2020), we controlled the Δ¹⁴C of aquaria seawater DIC (Δ¹⁴C_DIC) and food (Δ¹⁴C_diet) of Banggai cardinalfish (pterapogon kauderni). We then measured the Δ¹⁴C_DIC, Δ¹⁴C_diet, and Δ¹⁴C of outer edge and inner core from the otolith using AMS in Atmosphere and Ocean Research Institute, the University of Tokyo. Using the two-component mixing model, we determined M for juvenile and adult fish. M obtained from outer edge of otolith (i.e. otolith calcified after maturation) were which is within the M from previous studies using δ¹³C. We will further discuss whether there is a ontogenetic change in M by comparing M of juvenile and adult.