CONTINUOUS LATE PLEISTOCENE PALEOCLIMATE RECORD FROM THE SW AFRICAN MARGIN

Late Pleistocene sediments recovered from Site 1085, ODP Leg 175 are used to generate a high-resolution record of the geochemical, sedimentological, and clay mineralogical variations in the sediments of the Cape Basin for the last 200 k.y. using the terrigenous component of marine sediments. The location of Site 1085, the SW African continental slope, provides a continuous hemipelagic record. The analyses provide insight into relative differences in 1) weathering (clay mineralogy, elemental geochemical determinations) and 2) precipitation (grain size and sedimentation rates) on the continent that is essential to determining the paleoclimate record for the late Pleistocene. Terrigenous sediments recovered from Site 1085 are either fluvial or eolian, with terrigenous load possibly being controlled by monsoonal circulation and insolation (Christensen, et al., 2002, and Murray et al., 2002).

Our proxy record for continental weathering (% terrigenous, clay mineralogy and bulk elemental geochemistry) is anticipated to vary downcore with southern hemisphere solar insolation. It also provides a means of corroborating the 1085 color reflectance data (highest reflectance indicates highest carbonate values). The sediments are generally comprised of carbonate (benthic and planktonic foraminifera, and calcareous nannofossils) so deviations from high color reflectance indicates a greater percentage of terrigenous or organic carbon. We use a lower color reflectance as a proxy for productivity or increased terrigenous input. Our weight percent sand data increases when color reflectance is high and expect changes in the coarse fraction weight percent to covary with insolation. In the absence of an isotope chronology, which is under construction, the proxy records are compared with SPECMAP (Imbrie et al, 1984) oxygen isotope record in order to determine possible periodicity and the relationship to Northern Hemisphere glaciation and we anticipate productivity will vary with glaciation. Comparison of our data with the Pretoria Saltpan record from NE South Africa (Partridge et al., 1997) will provide further insight into continental climate dynamics.