LIVING PLANKTONIC-FORAMINIFERA IN THE EASTERN SOUTH ATLANTIC DURING SPRING - INDICATORS OF WATER MASSES, UPWELLING AND THE CONGO (ZAIRE) RIVER PLUME

Planktonic foraminifera were collected from pumped surface-water sampl es and net tows over the upper 150 m of the water column in the easter n South Atlantic Ocean during October and November 1989. Of the 24 rec orded species, 12 occur abundantly and form 6 foraminiferal assemblage s. The assemblages correlate with the physico-chemical properties of t he 6 major surface-water masses. The correlation of species with low s alinity is due to properties co-variant with salinity. At several loca tions, high concentrations of planktonic foraminifera were observed ca used by frontal mixing or reproduction. The G. sacculifer-G. ruber whi te assemblage marks the South Equatorial Current in the surface waters , a minor contribution of G. menardii and N. dutertrei to this assembl age reflects the subsurface Equatorial Under Current. The N. dutertrei -G. siphonifera assemblage reflects the South Equatorial Counter Curre nt and Equatorial Under Current. The N. pachyderma-G. bulloides assemb lage reflects the coastal upwelling over the shelf and the filaments o f mixed oceanic and upwelled water in the coastal branch of the Bengue la Current (BC). The Angola-Benguela Front, at the interface of the wa rm currents and the BC, is reflected by the G. inflata-G. bulloides as semblage. An unusual coincidence of G. sacculifer-G. bulloides in one assemblage results from the interaction of the subtropical gyre and th e oceanic branch of the BC. The G. ruber pink-hi dutertrei assemblage is attributed to the warm low-saline plume in front of the Congo (Zair e) River. (C) 1998 Elsevier Science B.V. All rights reserved.