HR: 1340h
AN: PP23B-1424    [Abstracts]
TI: Geochemical Signatures in Corals from Looe Key, Florida since 1870 A.D.
AU: * Smith, J M
EM: jsmith@marine.usf.edu
AF: University of South Florida, College of Marine Science 140 Seventh Avenue 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 Avenue South, St. Petersburg, FL 33701 United States
AU: Halley, R B
EM: rhalley@usgs.gov
AF: US Geological Survey, 600 Fourth 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. Sub-annually resolved, centennial-length records of climate from the Atlantic that overlap with and extend beyond the instrumental record are sparse, yet required to assess interannual climate variations over decades to centuries. We address this data gap by presenting a %\sim$132 year time series of monthly geochemical variations in {\it Montastraea annularis} (complex) corals from Looe Key reef, Florida USA (24.5$\deg$ N, 81.4$\deg$ W). We first reconstructed estimates of hydrographic and temperature variability at Looe Key using temperature calibrations developed over the decade in which we have thermistor data. Calibration-verification exercises over this interval indicate differences in mean values of 0.6$\deg$C Sr/Ca-SST and 0.2$\deg$C $\delta$$^{18}$O-SST. Next we extended the calibration-verification intervals by comparing the coral geochemical variations with a SST record extracted from the HadISST 1.1 database using the appropriate 1$\deg$ by 1$\deg$ grid point for Looe Key. These longer-term verification exercises show a better agreement in estimation of the mean in $\delta$$^{18}$O-SST (0.15$\deg$C) than Sr/Ca-SST (0.47$\deg$C). Comparisons of monthly Sr/Ca and $\delta$$^{18}$O anomalies with monthly temperature anomalies over the entire record reveal weak relationships (r = -0.13, -0.10, respectively); however, there is a strong coupling between Sr/Ca and $\delta$$^{18}$O anomalies (r = 0.51) that shares spectral power in the decadal band. The relationship between decadally smoothed geochemical values and the AMO is also weak (r = -0.13, 0.09; for Sr/Ca and $\delta$$^{18}$O) despite a strong correlation between the AMO and SST from the Looe Key region (r = 0.72). The low correlation between SSTA/AMO and the coral proxies (Sr/Ca and $\delta$$^{18}$O), despite the good fit between the coral proxies themselves, could be the result of 1) difficulties in sampling the variable skeletal architecture of {\it Montastaea} or 2) it could indicate decoupling of the local thermal and hydrographic conditions from the larger-scale surface ocean conditions, which would suggest that a regional climate signal is being masked by local environmental variability at Looe Key. We are performing additional tests to better define the source of misfit between coral proxies and instrumental data at Looe Key.
DE: 4825 Geochemistry
DE: 4870 Stable isotopes
DE: 4875 Trace elements
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting