Graduate Thesis Or Dissertation
 

Modern and past climate variability in the eastern Pacific warm pool

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  • Westward transport of water vapor across the Panama Isthmus helps to maintain the salinity contrast between the Atlantic and Pacific Oceans, important in thermohaline circulation and global climate. Relatively low sea-surface salinities and a strong, shallow pycnocline in the eastern Pacific warm pool (EPWP) region near Central America reflect high net precipitation. This dissertation includes a detailed analysis of the modern EPWP moisture budget, the development and application of a new technique for measuring Mg/Ca in fossil foraminifera, a commonly used paleotemperature proxy, and high resolution multi-proxy reconstructions of temperature, salinity, and pycnocline changes in the EPWP during key Pleistocene and Pliocene intervals. A combination of meteorological data and oxygen isotope measurements of seawater and rainwater reveal primary moisture sources for the EPWP region. In addition to a northeasterly cross-isthmus component that is more dominant during boreal winter, southwesterly transport of local Pacific moisture prevails during boreal summer. Sensitivity tests indicate that the EPWP is most sensitive to changes in the average isotopic composition of rainfall, which is primarily controlled by the relative contributions of these moisture sources. This analysis of the modern moisture budget provides important constraints on the interpretation of paleoceanographic reconstructions from the EPWP. Mg/Ca paleothermometry has played a pivotal role in developing temperature and salinity reconstructions in the EPWP. The commonly used batch method for Mg/Ca measurement is plagued by problems of dissolution and calcite phases that contaminate the environmental signal recorded in primary calcite. Here, the application of an alternative method involving flow-through technology to the measurement of foraminiferal Mg/Ca has provided the opportunity to monitor heterogeneity of Mg in foraminiferal calcite, and thus to isolate the Mg/Ca ratio of primary calcite. This new Mg/Ca technology combined with stable isotope ('O) measurements of fossil foraminifera has yielded high resolution temperature and salinity reconstructions from sites in the EPWP for the late Pleistocene (0-30 ka), as well as key intervals spanning the mid-Pleistocene transition and the tectonic closure of the Panama Isthmus. These paleorecords provide compelling evidence of a climatic linkage between the tropics and the high latitudes involving vapor transport and deep ocean circulation.
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