Late quaternary paleoproductivity and deep water circulation in the eastern South Atlantic Ocean: Evidence from benthic foraminifera

Two late Quaternary sediment cores from the northern Cape Basin in the eastern South Atlantic Ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition. The locations of the cores were selected such that both of them presently are bathed by North Atlantic Deep Water (NADW) and past changes in deep water circulation should be recorded simultaneously at both locations. However the areas are different in terms of primary production. One core was recovered from the nutrient-depleted Walvis Ridge area. whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to he moderately high. Recent data served as the basis for the interpretation of the late Quaternary faunal fluctuations and the paleoceanographic reconstruction. During the last 450,000 years. NADW flux into the eastern South Atlantic Ocean has been restricted to interglacial periods. with the strongest dominance of a NADW-driven deep water circulation during interglacial stages 1.9 and 11. At the continental mat-gin. high productivity faunas and very low epibenthic delta(13)C values indicate enhanced fluxes of organic matter during glacial periods, This can be attributed to a glacial increase and lateral extension of coastal upwelling. The long term glacial-interglacial paleoproductivity cycles are superimposed by high-frequency variations with a period of about 23.000 yr. Enhanced productivity in surface waters above the Walvis Ridge, far from the coast. is indicated during glacial stages 8. 10 and 12. During these periods. cold. nutrient-rich filaments from the mixing area were probably driven as far as to the southeastern frank of the Walvis Ridge. (C) 1997 Elsevier Science B.V.