HR: 10:20h
AN: PP42A-01    [Abstracts]
TI: On The Build-Up Of The Isotopic Signals In Coral Skeleton
AU: * Shemesh, A
EM: Aldo.Shemesh@weizmann.ac.il
AF: Weizmann Institute of Science, Department of Environmental Sciences, Rehovot, 76100, Israel
AU: Mizrachi, I
EM: IdoM@tauex.tau.ac.il
AF: Weizmann Institute of Science, Department of Environmental Sciences, Rehovot, 76100, Israel
AU: Mizrachi, I
EM: IdoM@tauex.tau.ac.il
AF: Tel Aviv University, Department of Zoology, Tel Aviv, 69978, Israel
AU: Rosenfeld, M
EM: micha@ecoocean.com
AF: Weizmann Institute of Science, Department of Environmental Sciences, Rehovot, 76100, Israel
AU: Yam, R
EM: Ciyam@wisemail.weizmann.ac.il
AF: Weizmann Institute of Science, Department of Environmental Sciences, Rehovot, 76100, Israel
AB: The isotopic composition of reef coral's layered skeleton is extensively used to reconstruct past environmental conditions although both isotopes, carbon and oxygen, are out of isotopic equilibrium with respect to inorganic carbonate precipitates. Calibration studies produce the local correlation coefficients that determine the linear association between oxygen isotopic composition and SST. These studies are species-dependent and usually fail to produce the full range of environmental variables expected from considerations of temperature and salinity dependent fractionation. Sampling of coral skeletons for environmental-reconstruction purposes is usually vertical, along the maximal growth axis, which provides the time aspect and is the product of several calcification processes occurring within the tissue layer. To study the interrelations of the calcification processes with the isotopic composition of the skeleton, we follow the built-up of the isotopic signal at monthly resolution by a horizontal sampling of the newly added skeleton. We report the results of two in-situ underwater experiments following the growth of several Porites sp. colonies at 6 and 40-meter depths for 12 and 20 months. We show that the first, newly formed carbonate skeleton does not contain the isotopic seasonal temperature signature that is expected from the annual temperature variation of the ambient water. On the other hand, sampling along the main growth axis of the same corals reveals that the seasonal isotopic signals are well developed in skeleton materials which are older than about one year. Hence, calcification in more than one step and a strong biological control are required in order to explain these results. The weak correlation between carbon and oxygen isotopes of the newly formed skeleton also suggests that it will be inadequate to adopt a single step fractionation model to describe the isotopic compositions of shallow-water symbiont-bearing corals.
DE: 0419 Biomineralization
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 4916 Corals (4220)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting