Date of Award

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

First Advisor

Braddock K. Linsley

Abstract

To gain a more complete history and understanding of the full amplitude of climate variability prior to instrumental records, science must rely on natural proxy archives that are sensitive to fluctuations in key climate parameters. Calcium carbonate skeletons of long-living hermatypic corals in some locations have been shown to be natural archives of surface ocean variability. This study investigated the fidelity and reproducibility of coral derived Sr/Ca time series from Clipperton Atoll, Fiji, and Tonga as accurate proxies of sea surface temperature (SST). The replicated high-resolution Sr/Ca time series record monthly and bimonthly SST changes, though with a greater magnitude of variability than instrumental records. Coupled measurements of coral Sr/Ca and δ18O records were also used to reconstruct δ 18O of seawater from each region, and showed good agreement with in situ sea surface salinity (SSS) measurements. Longer-term, lower-frequency trends in the proxy records appear to reflect the changing position of the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). Coral skeletal growth parameters were then examined for possible effects of ocean acidification. These results showed some coral colonies with increasing calcification while others showed decreasing calcification, suggesting other effects play an important role. The results of the analyses of growth and paleoclimatology proxy reconstructions were also inconclusive, since slight influences were present in some but not all colonies. Finally, inter- and intra-colony comparisons were made using Mg/Ca as the proxy results in the Fiji and Tonga colonies. However, because of alterations and discontinuities in the skeletal material, Mg/Ca lacked coherence at long timescales and should not be considered as a reliable SST proxy.

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