Identification and quantification of major lipid biomarkers in deep-sea sediments have been features of many Ocean Drilling Program (ODP) and Deep Sea Drilling Project (DSDP) studies. Compilation of this data has allowed molecular stratigraphic studies to elucidate the origin of sedimentary organic matter and the influence of water-column and postdepositional diagenesis and to determine various proxy signals of paleoenvironmental parameters (e.g., Brassell et al., 1981, 1986a; ten Haven et al., 1990, 1992; Farrimond et al., 1990; Poynter et al., 1989; Repeta et al., 1992).
Coastal upwelling systems provide environments well suited to biomarker analysis owing to elevated photic zone primary productivity, causing high sedimentation rates of organic matter-rich material. Preservation of the organic matter may be enhanced by rapid incorporation into the sedimentary matrix, limiting the length of time labile lipids are exposed to oxygen (Hartnett et al., 1998; Müller and Suess, 1979). Upwelling regimes of the Atlantic and Pacific Oceans and the Arabian Sea have been studied for their biomarker distributions in previous ODP and DSDP Legs (see ten Haven et al., 1992, for a review). The Benguela Current system (BCS) represents the eastern boundary of the South Atlantic gyre and is analogous to the eastern boundary currents off California, Peru, and northwest Africa. Cold, nutrient-rich South Atlantic Central Water is upwelled in the BCS off Namibia owing to the southeasterly trade wind-driven Ekman transport (Dowsett and Willard, 1996; Shannon, 1985). The BCS was previously studied for organic molecular parameters during DSDP Legs 40 and 75. These and other studies of the BCS have tended to concentrate on sediments deposited on Walvis Ridge and in Walvis Bay (e.g., Boon and de Leeuw, 1979). The Walvis sediments are displaced northward from the intense upwelling cells that occur off Lüderitz, where filaments of cold, nutrient-rich waters from the coastal upwelling area extend well off shore and mix with low-productivity oceanic water, forming a zone of year-round high phytoplankton productivity (Lutjeharms and Stockton, 1987). Site 1084 is located within the zone of year-round high phytoplankton productivity (25°31´S, 13°2´E, North Cape Basin), and the high organic carbon contents and high sedimentation rates have led to suboxic conditions (Wefer, Berger, Richter, et al., 1998).
Micropaleontological, geochemical, and molecular reconstructions of the late Neogene history of the BCS indicate that the intensity of upwelling has fluctuated in accordance with the oscillations of the global climate system (Hinrichs et al., 1999; Kirst et al., 1999; Summerhayes et al., 1995) with an underlying trend toward intensification since the mid-Pliocene (Berger et al., 1998; Diester-Haass et al., 1992; Hay and Brock, 1992; Lange et al., 1999; Marlow et al., 2000; Meyers, 1992).
In this study we have analyzed two samples from upper and lower cores of Hole 1084A for lipid biomarkers. The biomarker data allow a preliminary assessment of how the intensification of upwelling and depth/time-dependent diagenetic transformations may have influenced the input and preservation of the major lipid biomarkers present in the sediments. In addition, identifying and quantifying the major biomarkers for Hole 1084A will add to the inventory of data for further molecular stratigraphic studies.