HR: 0830h
AN: PP11A-0196    [PDF]
TI: Reproducibility of Geochemical and Climate Signatures in {\it Montastrea annularis}
AU: * Smith, J M
EM: jsmith@marine.usf.edu
AF: University of South Florida, College of Marine Science, 140 Seventh Ave South, St. Petersburg, FL 33701 United States
AU: Quinn, T M
EM: quinn@marine.usf.edu
AF: University of South Florida, College of Marine Science, 140 Seventh Ave South, St. Petersburg, FL 33701 United States
AU: Halley, R B
EM: rhalley@usgs.gov
AF: US Geological Survey, 600 4th Street South, St. Petersburg, FL 33701 United States
AB: Geochemical variations in modern and fossil coral skeletons (Sr/Ca, Mg/Ca, $\delta^{18}$O, $\delta^{13}$C) are increasingly being used to reconstruct climate variability in tropical ocean-atmosphere system on interannual to centennial timescales. Coral-based climate studies are usually carried out using a single coral core from a reef, or a collection of cores covering different time intervals from the same reef site. Cross checking or replication - the generation of multiple climate time series from a single locality - is not a standard operating procedure in coral paleoclimatology because of the expense of generating additional geochemical time series. Quantitative assessment of intra-reef geochemical variability in multiple coral cores from the same reef is needed to verify the fidelity of climate reconstructions based on geochemical variations from a single coral. We perform such an assessment using the geochemical signals derived from two {\it Montastrea annularis} corals (LK1 and LK23) recovered in 2002 from Looe Key reef, Florida USA (24.5$\deg$ N, 81.4$\deg$ W). Looe Key is located in the central portion of the Florida Keys and has an hourly {\it in situ} seawater temperature record extending back to 1990. We extended this {\it in situ} SST record further back in time by splicing in HadISST 1.1 data extracted from the appropriate 1$\deg$ by 1$\deg$ grid point. Paired geochemical measurements of Sr/Ca, $\delta^{18}$O and $\delta^{13}$C were made by sampling coral LK1 and LK23 along their respective major growth axes. Geochemical variations versus depth were converted to monthly resolved time series extending from 2002-1966. The two $\sim$37 year coral time series replicate well in terms of both phasing and mean perspective: ($\delta^{18}$O LK1, -3.90$\pm$0.28 $\permil$, 1$\sigma$; LK23, -3.93$\pm$0.31 $\permil$, 1$\sigma$), $\delta^{13}$C (LK1, -0.80$\pm$0.68 $\permil$, 1$\sigma$; LK23, -0.72$\pm$0.59 $\permil$, 1$\sigma$) and Sr/Ca (LK1, 9.208$\pm$0.080 mmol/mol, 1$\sigma$; LK23, 9.226$\pm$0.082 mmol/mol, 1$\sigma$). Coral Sr/Ca-SST estimates of mean SST over the period 2002-1966 for LK1 (27.25$\pm$2.00$\deg$C) and LK23 (26.71$\pm$1.80$\deg$C) agree to within 0.3$\deg$C of observed mean SST in the instrumental record (26.94$\pm$2.12$\deg$C). Coral $\delta^{18}$O-SST estimates of mean SST (cf, LK1, 26.83$\pm$1.33; LK23, 27.05$\pm$1.79) also match well the mean SST of the instrumental record. Stacking or averaging the LK1 and LK23 records to create composite Sr/Ca-SST and $\delta^{18}$O-SST records improves the estimate of the proxy-based mean SST relative to the instrumental record. Month-to-month comparisons between predicted and observed SST indicate that the maximum misfit for coral $\delta^{18}$O-SST of $\sim$1$\deg$C occurs in March-April and Aug-Oct; whereas for coral Sr/Ca-SST the maximum misfit of $\sim$0.5$\deg $C peaks in September. In summary, Sr/Ca and $\delta^{18}$O records from two {\it M. annularis} coral heads from Looe Key, Florida replicate quite well, which provides confidence that accurate records of climate variability in the tropical Atlantic can be reconstructed from this scleractinian coral.
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
DE: 4870 Stable isotopes
DE: 4875 Trace elements
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting