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The standing stock of planktonic foraminifers collected at 16 stations by multinet plankton tow has been examined in five discrete depth intervals (0–25 m, 25–50 m, 50–100 m, 100–150 m, and 150–300 m). The assemblages document the status of populations in the surface and subsurface waters of the Southeast Atlantic during February/March 1988. Standing crops document hydrographic conditions in the coastal and geostrophic branch of the Benguela Current, the Angola Current, the Tropical Cyclonic Gyre, and the South Equatorial Current. Standing stocks are highest when primary production is intermediate. Very high primary production reduces foraminiferal crops significantly. Eleven species occur abundantly (average >10% of the total standing stock). A few species (G. glutinata, G. quinqueloba/G. clarkei) are abundant at each station whereas the occurrence of other species (G. ruber, G. sacculifer, G. scitula, G. menardii, G. crassaformis, N. incompta, N. dutertrei) is spatially restricted. G. ruber, G. rubescens, and G. glutinata are abundant in high-salinity surface water. Also, G. ruber is abundant within the Equatorial Undercurrent water, when this water is brought to the surface. High concentrations of N. incompta and G. bulloides are observed in the Angola Benguela Front when nutrient concentration is moderately elevated in surface and subsurface water (upper part of the thermocline). G. crassaformis becomes abundant in the subsurface water of the Angola Benguela Front. This species is restricted to lower oxygenated subsurface water and traces incursions of water transported by the Angola Current. G. menardii is considered as an indicator for the Equatorial Undercurrent below the mixed layer, whereas G. scitula most probably points to an admixture of water transported by the northward flowing Benguela Current. High abundances of G. quinqueloba/G. clarkei in the surface and subsurface waters reflect favorable nutrient conditions, like those present in the geostrophic Benguela Current and in the equatorial divergence zone. G. falconensis, N. dutertrei, and G. siphonifera appear to trace the Southern Equatorial Current. |
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