HR: 16:45h
AN: B14B-04 INVITED     [Abstracts]
TI: Preliminary Observations on sea Water Utilization During Calcification in Scleractinian Corals.
AU: Braun, A
EM: alonbr@pob.huji.ac.il
AF: The Institute of Earth Sciences, the Hebrew university, Givat-Ram, Jerusalem, 91904 Israel
AU: * Erez, J
EM: erez@vms.huji.ac.il
AF: The Institute of Earth Sciences, the Hebrew university, Givat-Ram, Jerusalem, 91904 Israel
AB: Coral skeletons contain unique archive of paleo-environmental information on temperature, salinity pH, and other parameters hidden in their skeletal isotopic and trace element composition. This information is important for testing and calibrating global circulation models which predict the response of the atmosphere-ocean system to global changes such as atmospheric CO$_{2}$ increase and global warming. However, the physiological process of biomineralization in corals cause many deviations from expected thermodynamic behavior, so called "vital effects" In order to better utilize the paleo-environmental information hidden in coral skeletons it is essential to understand these processes. We have shown previously that the source of ions for calcification in the unicellular foraminifera is seawater vacuoles that transfer the ions to the site of calcification. In this study we test the possibility that seawater is the solution from which calcification proceeds also for corals. We used confocal microscopy to investigate the calcification process and the involvement of seawater in the scleractinian corals {\it Pocillopora damicornis} and {\it Stylophora pistillata} from the Red Sea. The corals are maintained in the laboratory as free microcolonies that are completely covered by tissue or as small tips which precipitate their CaCO$_{3}$ skeleton horizontally on glass slides and thus allow direct microscopic observations. We used the fluorescent probes Calcein and FITC-Dextran to trace seawater dynamics, and precipitation of CaCO$_{3}$. Natural fluorescence of the coral and its symbionts was used to trace the coral tissue physical movement. Our observations show that the corals precipitate their aragonite skeleton by sequestering seawater into the calcification space between the skeleton and the calicoblastic layer. Pulse chase experiments with membrane impermeable Calcein showed fluorescent skeleton labeling in both types of colonies, suggesting that the calicoblastic space is permeable to sea water, and crystals growth proceeds from these (probably modified) seawater. The exchange of seawater between the calcification space and the environment may be mediated by frequent tissue pulses that pump the seawater in and out. At present we investigate the pH in the calcification space trying to confirm previous microelectrode studies that reported very high (9.3) values. The implications for paleoceanographic studies are far reaching. For trace elements a Rayleigh distillation model may be applied as we suggested previously for foraminifera. For carbon isotopes there must be an important seawater component in addition to the metabolic CO$_{2}$ input, while for oxygen isotopes there may be a significant CO$_{3}^{-2}$ ion effect.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting