A study of a multi-century coral stable isotope record from Rarotonga, southwest subtropical Pacific, for the period 1726-1997
Ren Lei 2002
A Dissertation submitted to the University at Albany, State University of New York in partial fulfillment of the requirements for the degree of Doctor of Philosophy
College of Arts & Sciences, Department of Earth & Atmospheric Sciences
Advisor: B.K. Linsley

This study presents a 271-year (1726-1997) subseasonal oxygen and carbon isotopes (d18O and d13C) records from a coral colony of Porites lobata at Rarotonga (21.5°S, 159.5°W) in the southwest subtropical Pacific. A new method is introduced whereby the effects of sea surface temperature (SST) can be separated from those of seawater d18O composition (d18Osw) on coral d18O by using the coupled coral Sr/Ca and d18O. The reconstructed d18Osw at Rarotonga using this method shows that it contributes significantly to the annual changes of coral d18O for the period 1726-1997. While changes of d18Osw account for ~39% of the total coral d18O variation, changes of SST account for ~61%. The reconstructed d18Osw also shows a positive linear correlation with a satellite-based estimated salinity for the period 1980-1997 (r=0.72). This linear correlation between reconstructed d18Osw and salinity makes it possible to use the reconstructed d18Osw to estimate the past interannual and decadal salinity changes in this region.
Applying a similar method to coral d13C, the effects of kinetic and metabolic activity on coral d13C were also quantitatively separated. The results show that the variation of coral d13C appears to be mainly caused by variation of metabolic activity rather than that of kinetic activity in both tropical and subtropical regions. For the tropical regions, d13C variation in corals is predominantly influenced by changes of metabolic activity (~90%), while for subtropical regions, approximately 70-75% of the total variation of coral d13C is due to the effects of metabolic activity.
The interannual and interdecadal variability in coral d18O at Rarotonga for the period 1726-1997 was also examined. The results suggest that although Rarotonga is located outside of the center of action of ENSO, it is generally sensitive to ENSO variability in this region. In addition, the decadal variability (~12 yr) was further differentiated from the interdecadal-scale variability (~32 yr) for the period 1726-1997 at Rarotonga. Based on the analysis of both tropical and subtropical coral data and comparisons with the Nino3.4 SST index and PDO index, it was hypothesized that the decadal and interdecadal variability might result from separate forcing mechanisms.

Ren L., 2002. A study of a multi-century coral stable isotope record from Rarotonga, southwest subtropical Pacific, for the period 1726-1997.
Unpublished PhD dissertation, State University of New York at Albany. 184pp., +viii
University at Albany Science Library call number:  SCIENCE MIC Film QC 869 Z899 2002 R46
Copies of this PhD dissertation can be ordered from Proquest UMI

        Front matter (title, table of contents, abstract, acknowledgements) - 0.2MB pdf file
        Figure pages in dissertation (colour and greyscale figures, with captions): - 12.7MB pdf file
        Appendices: I - Coral δ18O and δ13C in cores B and C from Rarotonga for the period 1726-1997
                             II - Coral δ18O and δ13C in core 3R from Rarotonga for the period 1926-2000
                                     (Appendices I and II as digital pdf tables) - 0.25MB pdf file

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