Diatom-rich nannofossil oozes from DSDP Sites 362 and 532 on the Walvis Ridge continental terrace contain light-dark cycles which are related to fluctuations in upwelling intensity over these sites from Middle Miocene to Holocene times. The dark intervals in the alternations result from dissolution of carbonates and addition of clastic components. Oxidation of marine-derived organic matter is important to dissolution of carbonates in these sediments. Concentrations of organic matter in the dark sections are enhanced by larger contributions of both marine and land-derived material than in light sections. The dark sections appear to correlate with periods of greater Antarctic ice volumes, suggesting that regional upwelling was intensified and that transport of organic matter from Africa by winds and possibly rivers was increased during these times.