Seasonal-Scale to Decadal-Scale Climatic Variability in Southwest Florida During the Middle Pliocene: Inferences from a Coralline Stable-Isotope Record

Authors

Leanne M. Roulier, University of South Florida
Terrence M. Quinn, University of South FloridaFollow

Document Type

Article

Publication Date

6-1-1995

Digital Object Identifier (DOI)

https://doi.org/10.1029/95PA00374

Abstract

We have generated a 49‐year‐long, high‐resolution, stable isotope record from a fossil coral, Solenastrea bournoni, to evaluate regional sea surface conditions during the middle Pliocene (3.0 ± 0.5 Ma) in southwest Florida. Continuous routing of the coral slab at an interval of 0.76 mm produced ∼5 to 6 samples per year. The annual cycle is well defined in δ¹⁸O and δ¹³C records confirming the average yearly growth rate estimated from density banding of 4 to 5 mm/yr. High‐density bands are synchronous with the highest δ¹⁸O and δ¹³C values for 79% and 45% of the annual cycles recorded, respectively. The annual range in δ¹⁸O is 0.70 to 2.27‰ and in δ¹³C it is 0.31 to 2.21‰. Partitioning of the coral δ¹⁸O signal into sea surface temperature (SST) changes and δ¹⁸O_water changes is difficult to estimate in the ancient. However, isotopic mass‐balance calculations, using modern climate data, suggest a partitioning of the δ¹⁸O signal into 8 to 12% salinity and 92 to 88% temperature at the sea surface. If 100% of the δ¹⁸O variation is attributed to temperature, the observed mean annual range in δ¹⁸O (mean = 1.54 ± 0.37‰) corresponds to a seasonal SST range of ∼7.0 ± 1.7°C (0.22‰/1°C), which is a mean of 3.5°C less than that of the present day. Isotope data are consistent with the hypothesis that δ¹³C values covary with the number of sunshine hours. Annually, peak δ¹⁸O values are often observed to precede peak δ¹³C values by one sample (i.e., about 2 months). We infer from the isotope pattern that periods of reduced SST were followed about 2 months later by periods of increased number of sunshine hours. This seasonal pattern is similar to that of southwest Florida today. Cross‐spectral analysis of fossil coral δ¹⁸O and δ¹³C documents coherency peaks, above the 95% confidence interval, at annual and subdecadal frequencies (1.0, 1.6, 2.9 and 5 year). The spectral phase angle between δ¹⁸O and δ¹³C at the annual frequency is −60 ± 10°, at the 95% confidence interval. The temporal equivalent of this angle is approximately 2 months, which confirms visual observations of seasonality from the isotope pattern.

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Terms of use for work posted in Scholar Commons.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Paleoceanography and Paleoclimatology, v. 10, issue 3, p. 429-443

Copyright 1995 by the American Geophysical Union.

Scholar Commons Citation

Roulier, Leanne M. and Quinn, Terrence M., "Seasonal-Scale to Decadal-Scale Climatic Variability in Southwest Florida During the Middle Pliocene: Inferences from a Coralline Stable-Isotope Record" (1995). Marine Science Faculty Publications. 75.
https://digitalcommons.usf.edu/msc_facpub/75