Climate forcing of the Pb isotope record of terrigenous input into the Equatorial Atlantic

Pb isotopic compositions of bulk sediment cores from the Tropical Atlantic are used here to infer variations in the provenance of terrigenous input to the Tropical Atlantic during Pleistocene climate cycles. The 200-ka high precision (2sigma similar to 100 ppm) Pb isotope records of the Ceard Rise (Western Atlantic) and Sierra Leone Rise (Eastern Atlantic) cores show a clear glacial-interglacial cyclicity, reflected by alternating unradiogenic Pb and radiogenic Ph in both cores. The glacial-interglacial Pb isotopic contrast is also observed in Pb-Pb space and can be explained in terms of binary mixing - variations along the mixing lines reflecting changes in the relative proportions of the glacial (unradiogenic) and interglacial (radiogenic) Pb source(s). The Pleistocene Pb isotopic variability of the terrigenous input to the Ceard Rise can be linked to changes in the weathering styles in the Amazon Basin and, as a result, in the Amazon river discharge. These changes are reflected by a greater contribution from the highlands (Andes) Pb source during glacial times, and strengthening of the lowlands (Shield) Pb source during interglacials. On the other hand, Pb isotopic variations in the Sierra Leone Rise core indicate increased Pb inputs from the Saharan dust plume during glacial times, in agreement with the wind patterns over Africa. Furthermore, this result bears some implications on the cause of the enhanced glacial terrigenous fluxes to the Tropical Atlantic, which we infer to be due to increase in winter wind transport rather than glacial hyperaridity. The cyclicity of the Ceara Rise and Sierra Leone Rise Pb isotopic records together with changes in the proportions of mixing sources throughout the last 200 ka monitor changes in the hydrological cycle over South America and the wind systems over Africa, respectively, both of which are linked to the seasonal latitudinal migration of the Intertropical Convergence Zone. The correlation found between Pb isotope cycles and other paleoclimate proxies suggests that Pb isotopes may be responding to variations in Earth's orbital parameters. (C) 2003 Elsevier B.V. All rights reserved.