Graduation Year

2003

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Terrence M. Quinn, Ph.D.

Committee Member

Benjamin P. Flower, Ph.D.

Committee Member

David J. Hollander, Ph.D.

Keywords

corals, paleoclimate, reproducibility, oxygen isotopes, Sr/Ca ratios, New Caledonia

Abstract

Coral-based climate studies commonly use elemental ratios and stable isotopes of coral skeletons to address seawater temperature and hydrologic balance issues in the tropical surface oceans. Replication, or cross-checking, a standard technique used to assess the fidelity of proxy records in paleoclimatology has not been widely applied in coral-based climate studies, primarily because of the time and cost associated with generating multiple records from a single reef site. Modern and paleoclimate reconstructions based on a single proxy-coral record from a site may contain errors if individual corals from the same reef record different geochemical signals. In this study we perform a replication test using elemental ratios and stable isotopes in three Porites corals from New Caledonia.

The reef complex offshore Amédée Island, New Caledonia is an ideal site to perform a coral replication test because instrumental sea surface temperatures (SST) and sea surface salinity measurements (SSS) have been made there for over 25 years. In this study, we compare sub-monthly resolved, geochemical variations (Sr/Ca, δ18O and δ13C) in three Porites lutea coral heads, located ~500 m apart, with the instrumental SST and SSS records over the interval 1992-1967. The monthly coral Sr/Ca and δ18O time series are well correlated to each other (r=0.86, p<.0001) and to the monthly instrumental SST record (r= -0.86, p<.0001, coral Sr/Ca to SST; r= -0.77, p<.0001, coral δ18O to SST). The three, sub-monthly resolved, 30-year coral Sr/Ca-SST time series have mean SST values that agree within 0.2o C with the instrumental mean SST value. A similar comparison for the coral δ18O-SST records indicate a maximum difference between predicted and observed mean SST of 0.5˚C. Analysis of the monthly climatological means also indicates that Sr/Ca-SST records closely match the instrumental SST record ±0.4˚C; a similar comparison using the δ18O-SST record yields an average offset of ±0.6˚C between observed and predicted monthly SST. Stacking the three records to form composite Sr/Ca-SST and δ18O-SST records does not appreciably improve the goodness of fit between the proxy and instrumental SST records; hence a coral-based proxy climate record from a single coral accurately reflects the observed record of climate variability at this locality. These results support the concept that high fidelity climate records can be generated using a single coral core.

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