RAPID PALAEOCEANOGRAPHIC CHANGES IN THE BENGUELA UPWELLING SYSTEM FORTHE LAST 160,000 YEARS AS INDICATED BY ABUNDANCES OF PLANKTONIC-FORAMINIFERA

Two sediment cores retrieved from the continental slope in the Benguel a Upwelling System, GeoB 1706 (19 degrees 33.7'S 11 degrees 10.5'E) an d GeoB 1711 (23 degrees 18.9'S, 12'22.6'E), reveal striking variations in planktonic foraminiferal abundances during the last 160.000 years. These fluctuations are investigated to assess changes in the intensit y and position of the upwelling centres off Namibia. Four species make up over 95% of the variation within the core, and enable the record t o be divided into episodes characterized by particular planktonic fora miniferal assemblages. The fossil assemblages have meaningful ecologic al significance when compared to those of the modern day and the relat ionship to their environment. The cold-water planktonic foraminifer, N eogloboquadrina pachyderma sinistral [N. pachyderma (s)], dominates th e modern-day, coastal upwelling centres, and Neogloboquadrina pachyder ma dextral and Globigerina bulloides characterize the fringes of the u pwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the subtropical waters. In the fossil record, episo des of high N. pachyderma (s) abundances are interpreted as evidence o f increased upwelling intensity, and the associated increase in nutrie nts. The N. pachyderma (s) record suggests temporal shifts in the inte nsity of upwelling, and corresponding trophic domains, that do not fol low the typical glacial-interglacial pattern. Periods of high N. pachy derma (s) abundance describe rapid, discrete events dominating isotope stages 3 and 2. The timing of these events correlates to the temporal shifts of the Angola-Benguela Front (Jansen et al., 1997) situated to the north of the Walvis Ridge. Absence of high abundances of N. pachy derma (s) from the continental slope of the southern Cape Basin indica tes that Southern Ocean water advection has not exerted a major influe nce on the Benguela Current System. The coincidence of increased upwel ling intensity with the movement of the Angola-Benguela Front can be i nterpreted mainly by changes in strength and zonality of the trade win d system. (C) Elsevier Science B.V.