CONCLUSIONS

The lipid biomarker content in selected sediments from several sites along the southwestern African margin reflects different marine environments. The majority of the extracted lipids in all samples is of marine origin, with varying contributions of terrigenous lipids. It should be noted that the limited sample number restricts detailed paleoceanographic interpretations and that this study is solely intended to be an inventory. Conclusions are summarized as follows:

1. In general, two main areas can be distinguished, separated by the ABF. Elevated concentrations of terrigenous lipids and lipids from eustigmatophyte algae were only observed north of the ABF, whereas lipids from archaea and zooplankton are only present in significantly elevated amounts south of it.
2. The sediments below the Congo River freshwater plume received a large contribution of lipids from terrestrial higher plants and mangroves. The contribution of terrigenous lipids is suggested to decrease with increasing distance from the river mouth. At the shallower site, marine lipids were mainly derived from haptophyte algae, diatoms, dinoflagellates, and eustigmatophyte algae. Lipids of these algae were less abundant in samples from the deeper site, whereas the contribution from pelagic archaea and zooplankton were slightly higher. The changes in lipid composition with distance from the river mouth suggest variation of plankton communities with reduction of river influence.
3. The investigated sediments on the Angola margin received a small amount of terrigenous lipids. A highly productive plankton community of haptophyte algae, diatoms, dinoflagellates, and unidentified, keto-ol-producing microalgae probably caused the elevated sedimentary organic carbon contents. Supply of nutrients from the nearby Angola Dome may sustain high productivity.
4. Walvis Basin sediments received an upwelling signal transported by the Benguela Current. Major contributors of marine lipids were haptophyte algae and pelagic archaea. Diatom lipids were detectable in low concentrations as sulfurized compounds.
5. Persistent coastal upwelling off Lüderitz Bay is well reflected in the sedimentary lipids. The investigated samples contain the highest lipid contributions of pelagic archaea, haptophyte algae, dinoflagellates, diatoms, and zooplankton. Anoxic sedimentary conditions were most probably caused by a large supply of labile organic matter.
6. In the southern Cape Basin, sediments probably received plankton material from seasonal upwelling, indicated by their content of sterols and sterol ethers. Their marine lipid content is comparable to the lipids of the sediments in the Walvis Basin. The nearby Orange River did not cause elevated concentrations of terrigenous lipids in the investigated samples.