HR: 0800h
AN: B21B-0875    [Abstracts]
TI: Intercolony variability of skeletal oxygen and carbon isotope ratios of cultured corals: temperature-controlled experiments
AU: * Suzuki, A
EM: a.suzuki@aist.go.jp
AF: Geological Survey of Japan, AIST, AIST Tsukuba Central No.7, Tsukuba, 305-8567 Japan
AU: Hibino, K
EM: kobino@nifty.com
AF: Kansai Environmental Engineering Center Co., Ltd., 413-10 Tsui, Inami, 649-1535 Japan
AU: Iwase, A
EM: k038552@eve.u-ryukyu.ac.jp
AF: Graduate School of Engineering and Science, The University of Ryukyus, Sesoko, Motobu, 905-0227 Japan
AU: Kawahata, H
EM: h.kawahata@aist.go.jp
AF: Geological Survey of Japan, AIST, AIST Tsukuba Central No.7, Tsukuba, 305-8567 Japan
AB: The skeletal oxygen isotope ratio of {\it Porites} corals, together with the carbon isotope ratio, is the most frequently used proxy of past seawater temperature and composition for tropical and subtropical oceans. However, field calibration of the proxy signals is often difficult owing to the covariation of temperature and salinity, which control the oxygen isotope composition of the water, under natural conditions. We conducted tank experiments in which we grew {\it Porites} spp. colonies in thermostated seawater at five temperature settings between 21 \deg C and 29 \deg C under moderate light intensity of 250 \mu mol m$^{2}$ s$^{-1}$ with a 12:12 light:dark photoperiod. A skeletal isotope microprofiling technique applied along the major growth axis of each colony revealed that the oxygen isotope ratios of newly deposited skeleton in most colonies remained almost constant during tank incubation, thus providing an ideal situation for precise calibration of proxy signals. However, the oxygen isotope ratios displayed a surprisingly large intracolony variability (1 \permil at each temperature setting although the mean slope (0.14 \permil \deg C $^{-1}$) obtained for the temperatureskeletal oxygen isotope ratio relationship was close to previous results. The variations in the oxygen isotope ratios were appaently caused by kinetic isotope effects related to variations in the skeletal growth rate rather than to intraspecies variability or genetic differences among species. Although no significant correlation was found between skeletal carbon isotope ratios and temperature, carbon isotope ratios also correlated with linear growth rates, suggesting a kinetic isotope control at low growth rates.
DE: 3670 Minor and trace element composition
DE: 4267 Paleoceanography
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting