[B-PT02_1PM1] Biocalcification and the Geochemistry of Proxies

[BPT02-14] Skeletal isotope compositions of Acropora coral primary polyps experimentally cultured at different temperatures

*Kozue NISHIDA¹, Kei ISHIKAWA², Akira IGUCHI³, Yasuaki TANAKA⁴, Mizuho SATO¹, Mayuri INOUE⁵, Takashi NAKAMURA², Kazuhiko SAKAI⁴, Atsushi SUZUKI¹ (1.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 2.Faculty of Science, University of Ryukyus, 3.Department of Bioresources Engineering, Okinawa National College of Technology, 4.Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, 5.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords: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.