A central aim of the drilling strategy of Ocean Drilling Program (ODP) Leg 175 was to obtain records for the reconstruction of productivity along the western African margin between the Congo and the Cape (Wefer, Berger, Richter, et al., 1998). A National Aeronautics and Space Administration (NASA) compilation of satellite-derived pigment distributions (Berger and Wefer, 1996, fig. 4) shows high productivity all along this margin, with a distinct minimum off the shores of the Angola Bight. The annual offshore temperature here is ~23°C, and the latitudinal anomaly is modest (~1°C), reflecting subdued upwelling activity. The nutrient content of subsurface waters, on the other hand, seems normal or on the high side of the range (phosphate and silicate at 100 m depth, compiled by Joseph L. Reid, as contoured in Herzfeld and Berger, 1993; see fig. 27 in Berger et al., 1998). This environment of subdued upwelling, then, embedded within much stronger upwelling activity to the north and south, was the target of Site 1079 (Fig. F1), for which we present a first attempt at reconstructing late Quaternary productivity using benthic foraminifers.
The length of the record is ~230 k.y., as reconstructed from oxygen isotope stratigraphy.
We compare our results with records from the continental margin off Angola (core GeoB1016; 11°46.2´S, 11°40.9´E; water depth = 3411 m), recovered on a cruise of the Meteor (Wefer et al., 1988). Our results are consistent with earlier studies in nearby regions (Schneider et al., 1996, 1997; Wefer et al., 1996) and over much of the low-latitude ocean (Berger et al., 1994), showing stronger upwelling during glacials. However, the transitional position of the area studied, as a minimum between two high-productivity regions, gives rise to more complicated patterns, presumably as a result of alternating expansions of the adjacent upwelling areas. These patterns of productivity are also reflected in changes in abundance and species composition of benthic foraminifers at Site 1079.