HR: 0800h
AN: B21B-0874    [Abstracts]
TI: Trace, Minor Elements, and Stable Isotopes in {\it Montastraea faveolata} as an Indicator of Stress
AU: * Holmes, C W
EM: cholmes@usgs.gov
AF: U.S.Geological Survey, 600 Fourth Street South, St. Petersburg, Fl 33701 United States
AU: Buster, N A
EM: nbuster@usgs,gov
AF: U.S.Geological Survey, 600 Fourth Street South, St. Petersburg, Fl 33701 United States
AU: Hudson, J H
EM: harold.hudson@noaa.gov
AF: N.O.A.A.-FKMS, Box 1083, Key Largo, Fl 33037 United States
AB: Coral cores were obtained along the fore reef from Looe Key Reef, Florida Keys, and analyzed for minor and trace elements by laser ablation ICP-MS and stable oxygen and carbon isotopes. Sample locations within the corals were chosen based on the location of annual bands as determined by x-radiographs. The LA-ICP-MS data were obtained along the corallite wall. Boron, magnesium, and phosphorous concentrations can be correlated among the corals analyzed. The highest elemental concentrations and the carbon and oxygen isotopic records in the Looe Key Montastraea faveolata were linked to times of reported bleaching. Boron, a common element in sea water, exists as two species, B(OH)$_{3}$ below a pH of 8.0 and B(OH)$_{4}$$_{-}$ above a pH of 8. Hemming and others (1998) determined that boron varied positively with $^{13}$C, both being coincident with high-density bands. They proposed that photosynthetic activity of zooxanthellae is the driving process, causing the shift in pH. During periods of stress, energy that would be used for normal coral activity (reproduction and growth) is diverted for tissue repair, food gathering, and waste removal. At extreme stress, these activities are reduced. As a result of decreased zooxanthellate activity, the chemistry at the organic-inorganic boundary may change as follows. 1. The pH rises, increasing the boron levels in the carbonate skeleton. 2. Phosphorous, expelled during normal growth activity, is retained, inhibiting the precipitation of "normal" aragonite. 3. The Mg/Ca ratio changes as calcium is being used preferentially. In the Looe Key Reef corals, boron, magnesium, and phosphorous all were elevated during times of reported bleaching. Within the same time intervals, the $\delta$$^{13}$C, which displayed values of between -2 % and -3 % in the "normal" light-density portion of the skeleton, approached a $\delta$$^{13}$C of 0 % in the stressed, high-density portion of the skeleton. Thus, the combination of high magnesium, boron, and phosphorous concentrations, coupled with the stable isotopic records of carbon and oxygen, correlate to stress events, such as bleaching in the Looe Key corals. These relations seem to confirm the model proposed by Hemming and others, and this chemistry may be useful in determining the record of stress events in other corals. Hemming, N.G., Guilderson, T.P. and Fairbanks, R.G., 1998, Seasonal variations in the boron isotopic composition of corals, a productivity signal?, Global Biogeochemical Cycles, v. 12, p.581-586.
DE: 4215 Climate and interannual variability (3309)
DE: 1045 Low-temperature geochemistry
DE: 1065 Trace elements (3670)
DE: 1635 Oceans (4203)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting