[B-PT02_1PM1] Biocalcification and the Geochemistry of Proxies

[BPT02-14] コユビミドリイシ初期ポリプ骨格の酸素・炭素同位体比

*西田 梢¹、石川 惠²、井口 亮³、田中 泰章⁴、佐藤 瑞穂¹、井上 麻夕里⁵、中村 崇²、酒井 一彦⁴、鈴木 淳¹ (1.産業技術総合研究所　地質情報研究部門、2.琉球大学大学院理工学研究科、3.国立沖縄工業高等専門学校　生物資源工学科、4.琉球大学熱帯生物圏研究センター、5.東京大学大気海洋研究所)

キーワード：coral, temperature, stable isotopes, polyp, kinetic effect

We investigated temperature and growth-rate dependency of skeletal oxygen and carbon isotopes in primary polyps of Acropora digitifera (Scleractinia: Acroporidae) by culturing them at 20, 23, 27, or 31 ℃. We cultured primary polyps of A. digitifera at Sesoko Station, University of the Ryukyus, Motobu, Okinawa Prefecture, Japan for 10 days. From the results of the polyp weight and polyp area, calcification was most rapid at 27 and 31 ℃. The δ¹⁸O—temperature relationship (–0.18‰ ⁄℃) is consistent with reported ranges for Porites, indicating that juvenile Acropora polyps can be used for paleotemperature reconstruction. We found a gap between curves for the experimental polyps and the equilibrium curves for inorganic aragonite of about 3.0‰ for δ¹⁸O and 8.0‰ for δ¹³C, with the primary polyp values being lower than the equilibrium values of inorganic aragonite. The kinetic isotope effect was evident in the polyps cultured at low temperature but disappeared at high temperatures, despite relatively low light levels. The estimated upper calcification flux limit for a kinetic isotope effect (~0.4–0.7 g CaCO₃ /cm²●y) was similar to that of Porites colonies with a linear extension rate of <5 mm⁄y, suggesting that the calcification flux may be used as a measure of kinetic isotope effect dominance in different genera at different growth stages.