| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990 As a primary feature of ocean circulation and a key component of the global carbon cycle, changes in the thermocline must be accounted for if we are to understand the processes involved in Quaternary climatic fluctuation. Toward this goal, this thesis contains studies of the modern and glacial thermoclines at the Bahama Banks and it presents an novel approach to determine sea level based on the flux of 230Th and 231Pa from thermocline waters to the seafloor. In the first chapter, the hydrography of the modern thermocline in Northwest and Northeast Providence Channels, Bahamas, is investigated using CTD data. Potential temperature- salinity relationships demonstrate that the deep waters and most of the thermocline waters in these channels originates in the Sargasso Sea. Cross channel sections of water properties suggest the following: (1) water from the shallow core of the Deep Western Boundary Current (Fine and Molinari, 1988) may circulate along the channel margins, and (2) where the western end of Northwest Providence Channel opens to the Florida Straits, shallow flow is toward the straits in the southern portion of the channel and away from the straits in the northern portion. In the next two chapters, changes in the temperature and nutrient structures of the thermocline from the last glaciation to the recent Holocene are inferred from isotopic variations of the planktonic foraminifera Globigerinoides ruber (212-250μm) and G. sacculifer (300-350μm) and the benthic foraminifera Planulina wuellerstorfi, P. ariminensis, P. foveolata and Cibicidoides pachyderma (>250μm) in a suite of cores from the margins of Little and Great Bahama Banks. During the last glaciation, δ18O values were from 1.4 to 1.9 per mil greater than during the recent Holocene. Based on the δ18O/sea-level model of Fairbanks (1989), we estimate ...
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