The supply of limiting nutrients to the low latitude ocean is controlled by physical processes linked to climate variations, but methods for reconstructing past nutrient concentrations in the surface ocean are few and indirect. This thesis presents the first calibration and downcore application of a new surface ocean phosphate (PO4 SW) proxy derived from coral skeleton P/Ca ratios. Skeletal P/Ca cycles tracked variations in past PO4 SW synchronously with temperature variations associated with seasonal upwelling in a 4-year Gulf of Panamá Pavona gigantea coral. P/Ca records in co-located Gulf of Panamá Pavona gigantea and Porites lobata colonies were strongly correlated to a contemporaneous time-series record of PO4 SW, supporting application of multi-colony calibration equations to down-core records. The P/Ca proxy was applied downcore to reconstruct an 18-year history of central equatorial Pacific PO4 SW. The PO4 SW record decreased during El Niño warm phases, resulting from decreased upwelling. In addition, a large 6-fold decrease in PO4 SW occurred from ~1982-1990, distinct from sea surface temperature changes in the central Equatorial Pacific. The decadal scale nutrient regime shift likely occurred in response to the observed decreases in wind stress and equatorial upwelling with possible linkages to the 1976/77 climate shift and changes in mid-latitude upwelling source water. The reliability of P/Ca was tested in low nutrient environments (Gulf of Eilat, Israel and Florida Keys, USA). Downcore P/Ca variability is low on centennial timescales in the Florida Keys record, implying that other possible influences on P incorporation (i.e. biological vital effects) are minimal and that the P/Ca proxy is not subject to major diagenetic alteration. With further development, the coralline P/Ca proxy could be applied to reconstruct PO4 SW on millennial timescales and be used to place modern tropical and subtropical nutrient distributions and dynamics in a paleoceanographic perspective.Ph.D.Includes abstractVitaIncludes bibliographical referencesby Michèle Gloria LaVign
