Late Quaternary Surface Temperatures and Productivity in the East-Equatorial South Atlantic: Response to Changes in Trade/Monsoon Wind Forcing and Surface Water Advection

摘要: In order to reconstruct Late Quaternary variations of surface oceanography in the east- equatorial South Atlantic, time series sea-surface temperatures (SST) and paleoproductivity were established from cores recovered Guinea Angola Basins, at Walvis Ridge. These records, based on sedimentary alkenone organic carbon concentrations, reveal that during last 350,000 years circulation productivity changes east-equatorial Atlantic highly sensitive climate forcing 23- 100-kyr periodicities. Covarying SST equator Ridge appear be driven by zonal trade-wind intensity, which forces intensification or reduction coastal upwelling, as well enhanced Benguela cold water advection South. Phase relationships precessional records distinct sites evaluated with respect boreal summer insolation over Africa, movements southern ocean thermal fronts, global ice volume. The 23-kyr phasing implies a sensitivity eastern upwelling West African monsoon intensity position subtropical high pressure cell both phenomena modulate strength southeasterly trades. north 20°S lack significant variance 41-kyr periodicity; lead This may indicate obliquity-driven change, characteristic for northern latitudes, e.g fluctuations continental masses, did not substantially influence tropical Atlantic. At cycle Basin lag those about 3500 years. is explained cross-equatorial transport west-east countercurrent return flow modifying relative mid area under central field trade winds. Sea level-related shifts cells phase change also recorded variability along margin off Southwest Africa. They account delay paleoceanogreaphic signal pelagic