Living planktonic foraminifera in the eastern South Atlantic during spring: Indicators of water masses, upwelling and the Congo (Zaire) River plume

Abstract

Planktonic foraminifera were collected from pumped surface-water samples and net tows over the upper 150 m of the water column in the eastern South Atlantic Ocean during October and November 1989. Of the 24 recorded species, 12 occur abundantly and form 6 foraminiferal assemblages. The assemblages correlate with the physico-chemical properties of the 6 vapor surface-water masses. The correlation of species with low salinity is due to properties co-variant with salinity. At several locations, high concentrations of planktonic foraminifera were observed caused by frontal mixing or reproduction. The G. sacculifer-G. ruber white assemblage marks the South Equatorial Under Current. minor contribution of G. menardii and N. dutertrei to this assemblage reflects the subsurface Equatorial Under Current. The N. dutertrei-G. siphonifera assemblage reflects the South Equatorial Counter Current and Equatorial Under Current. The N. pachyderma-G. bulloides assemblage reflects the coastal upwelling over the shelf and the filaments of mixed oceanic and upwelled water in the coastal of the Benguela Current (BC). The Angola-Benguela Front, at the interface of the warm currents and the BC, is reflected by the G. inflata-G. bulloides assemblage. An unusual coincidence of G. sacculifer-G. bulloides in one assemblage results from the interaction of the subtropical gyre and the oceanic branch of the BC. The G. rubber pink- N. dutertrei assemblage is attributed to the warm low-saline plume in front of the Congo (Zaire) River.