Deep drilling throughout the Benguela upwelling system during Ocean Drilling Program (ODP) Leg 175 provided a terrific opportunity for chemists, sedimentologists, and paleoceanographers to study processes related to the deposition, decomposition, and preservation of organic matter; precipitation and dissolution of carbonate phases such as calcite and dolomite; and diagenetic processes involving clay mineral authigenesis. By careful selection of drill sites located in various basins along the southwest African margin (Fig. 1), we were able to sample a variety of depositional regimes characterized by contrasts in terrigenous supply, organic matter content, export production, and sedimentation rate. Variations in these components directly influence the distribution of many important chemical species dissolved in the interstitial waters of the sedimentary sequence at a given site. Because interstitial waters record diagenetic chemical reactions that are often unobservable in the bulk sediment, it is critical to identify the sources and sinks of these dissolved species.
We have several goals with this paper: (1) to provide a preliminary synthesis of results from the analytical program undertaken on the JOIDES Resolution during Leg 175, (2) to identify first-order similarities and differences between the depositional and chemical regimes along the southwest African margin, and (3) to highlight where ongoing and future shore-based geochemical studies are most likely to yield productive insights into the sedimentological and paleoceanographic processes operating in the Benguela Current system throughout the Neogene. In the spirit of a preliminary synthesis, we hope to raise more questions here than we answer.