Site 1084 documents the northward migration of the Benguela Current system from the Miocene to the Quaternary, as well as the shoreward and seaward migrations of the upwelling center. The upwelling area of the Benguela Coastal Current (BCC) is fed from the thermocline by South Atlantic Central Water, which originates at the Subtropical Convergence Zone by mixing and sinking of subtropical and subantarctic surface water (Lutjeharms and Valentine, 1987). Filaments of cold, nutrient-rich waters from the coastal upwelling area extends well offshore (as much as ~600 km offshore; Lutjeharms and Stockton, 1987; also see Fig. 1). Here, it mixes with low-productivity oceanic water and forms a zone of intermediate productivity.
Coastal upwelling within the Benguela Current system varies with the seasonal extremes of summer and winter (Shannon and Nelson, 1996). The seasonal pattern is used to divide the system into a northern Benguela Region (NBR) and a southern Benguela Region (SBR; Dingle, 1995). This is seen in the modern-day planktonic foraminiferal distributions (Giraudeau, 1993; Fig. 2) and has been demonstrated using benthic ostracoda (Dingle, 1995) and satellite imaging (Lutjeharms and Meeuwis, 1987). The boundary between the NBR and SBR (Lüderitz Boundary) is the site of maximum upwelling intensity at 26°–27°S, which has the coldest and the most persistent upwelling.
Upwelling in the area north of the Lüderitz Boundary (at the location of Site 1084) is typified by year-round high productivity and enhanced accumulation of phytoplankton (Brown et al., 1991). Wind speeds are of medium intensity with a wide, oceanic, filamentous, mixing domain (Lutjeharms and Stockton, 1987). Surface sediments are rich in organics with a maximum in the inner-shelf belt of diatomaceous ooze (Bremner, 1983; Rogers and Bremner, 1991). The SBR has a highly seasonal upwelling regime, with its maximum in summer, and a restricted mixing domain (Lutjeharms and Meeuwis, 1987; Giraudeau and Rogers, 1994). Sites 1085 and 1086 are located within the SBR.
Site 1084 is expected to provide a high-resolution record because of high sedimentation rates. Its close vicinity to the Lüderitz upwelling cell should result in well-expressed organic carbon, diatom, and coccolith cycles via cyclic productivity intensity. In addition, this site is closest to the area with elevated primary production and should have the best representation of coastal upwelling signals. Rapid oceanographic changes in the Benguela upwelling system for the last 160,000 yr are indicated by fluctuating abundances of planktonic foraminifers (Little et al., 1997). The coincidence of increased upwelling intensity with the movement of the Angola-Benguela Front has been interpreted mainly by changes in strength and zonality of the trade-wind system. A close tie-in between pelagic and terrigenous sedimentation is expected to be present within the slope record. Previous work in this area has documented anaerobic, in part varved, sedimentation in the upper margin regions (for a summary, see Dingle et al., 1987; Summerhayes et al., 1995). Phosphatic deposits also are abundant (Calvert and Price, 1983).