Planktonic foraminiferal assemblages in surface sediments from the southwest African continental margin

Abstract

The relative abundance and distribution of planktonic foraminifera species on the southwest African continental margin have been determined from 152 surface sediment samples. Of the 23 recorded taxa, only 8 make a significant contribution to the foraminiferal assemblages. Individual species proportions are closely related to the surface water hydrography of the Benguela System and the associated upwelling phenomena. Three foraminiferal assemblages can be distinguished by correlation analysis on the abundances of the major taxa. Species composition of these assemblages range from polar taxa in the upwelling area (left-coiling Neogloboquadrina pachyderma and Globigerina quinqueloba) to transitional taxa in the offshore oligotrophic environment ( Globorotalia inflata and Globorotalia truncatulinoides). Globigerina bulloides and right-coiling Neogloboquadrina pachyderma are preferentially distributed in the highly productive intermediate zone of the Benguela System, where upwelled and oligotrophic offshore waters mix. Variability of the hydrological processes (upwelling intensity, strength of the frontal features) may be inferred from frequency variations of individual species, and diversity patterns.