HR: 0830h
AN: PP11A-0198    [PDF]
TI: Pre-treatment Effects on Coral Skeletal $\delta^{13}$C and $\delta^{18}$O
AU: * Grottoli, A G
EM: grottoli@sas.upenn.edu
AF: University of Pennsylvania, 240 South 33rd Deptartment of Earth and Environmental Science, Philadelphia, PA 19104-6316 United States
AU: Gibb, O
EM: gibb@sas.upenn.edu
AF: University of Pennsylvania, 240 South 33rd Deptartment of Earth and Environmental Science, Philadelphia, PA 19104-6316 United States
AU: Wellington, G M
EM: wellington@uh.edu
AF: University of Houston, 3400 Calhoun Rd. Department of Biology and Biochemistry, Houston, TX 77240 United States
AB: Pre-treatment protocols for coral skeletal stable carbon ($\delta^{13}$C) and oxygen ($\delta^{18}$O) isotope analyses include no treatment, bleach (NaOH), hydrogen peroxide (H$_{2}$O$_{2}$), or vacuum roasting prior to analysis. Such pre-treatments are used to remove organic material prior to isotopic analyses. Researchers that do not pre-treat samples argue that such treatments result in non-linear shifts in coral skeletal $\delta^{13}$C and $\delta^{18}$O thus increasing the analytical error in the $\delta^{13}$C and $\delta^{18}$O values. Vacuum roasting does cause isotopic shifts and is no longer practiced. However, both no pre-treatment and pre-treatment (with either NaOH or H$_{2}$O$_{2}$) coral $\delta^{13}$C and $\delta^{18}$O values continue to be published in the literature. In all previous studies of the effects of NaOH and H$_{2}$O$_{2}$ pre-treatments on coral $\delta^{13}$C and $\delta^{18}$O, the samples sizes were typically small and the exact time interval being sampled and compared was not specifically controlled. Here, we evaluated the effects of NaOH and H$_{2}$O$_{2}$ pre-treatments on coral skeletal $\delta^{13}$C and $\delta^{18}$O in {\it Pavona clavus} and {\it Pavona gigantea} from Panama, and {\it Porites compressa} from Hawaii. In Panama, at least five coral fragments from five different colonies of each species were stained on November 1978 and April 1979 then collected in November 1979. In Hawaii, at least five coral fragments from five different colonies at 1.7 and 7 m depths were stained on 1 September and 21 November 1996 then collected 2 March 1997. For each fragment, a bulk skeletal sample was extracted representing the entire growth interval between the two stain lines yielding at least 24 mg of material. Sampling between the stain lines ensured that all of the fragments from a given site and species were sampled over the same time interval and avoided any potential contamination from the tissue layer. Eight milligram subsamples from each fragment were subjected to 24 hours of the following treatments: NaOH, H$_{2}$O$_{2}$, Milli-Q filtered water (control), or no pre-treatment (control). Each subsample was then rinsed with distilled water ten times and dried at 60$^{o}$C for 48 hours prior to isotopic analysis. In all cases, NaOH pre-treatment resulted in a statistically significant decrease in coral skeletal $\delta^{13}$C compared to the controls. The decreases in $\delta^{13}$C in {\it P. clavus} and {\it P. gigantea} were twice as large as in {\it P. compressa}. These results did not change with depth in {\it P. compressa}. Thus NaOH pre-treatment makes coral skeletal $\delta^{13}$C values less reliable and compromises any comparisons among species. In all cases H$_{2}$O$_{2}$ pre-treatment resulted in decrease in $\delta^{13}$C compared to the controls, though this decrease was not statistically significant. Caution should be taken to avoid pre-treating corals with H$_{2}$O$_{2}$ in order to minimize any additional variability in the $\delta^{13}$C values of coral samples. In all cases, NaOH and H$_{2}$O$_{2}$ pre-treatments did not have any significant effect on coral skeletal $\delta^{18}$O values relative to the controls and does not compromise the interpretation of $\delta^{18}$O values from pre-treated coral samples.
DE: 1040 Isotopic composition/chemistry
DE: 4267 Paleoceanography
DE: 4294 Instruments and techniques
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting