Description: Planktic foraminifera data from three cores of the Angola-Zaire margin are used to reconstruct palaeopositions of the Angola-Benguela Front (ABF) between the warm Angola Current and cold Benguela Current for the last 180,000 years. Strong northward shifts occurred in stages 4 and 3.3-3.1, but not in stages 6 and 2. The Benguela Current did not penetrate into the Gulf of Guinea. The southernmost positions, not far from the present one, were occupied in stages 5.5 and 1, but also in stage 6.3. The record of the shifts contains significant variance in the 23 ky**-1 orbital frequency band and there are indications for a strong 100-ky**-1 frequency component. There is also much variance at 15 ky1, the sum frequency of the 23-ky**-l and the absent 41-ky**-1 cycles. This cyclicity is a real feature in the records. The Benguela Current system performs a combination of two types of precessional (23 ky**-1) movements: shifts of the ABF to the south and north precede swings between more zonal and more meridional directions respectively of the Benguela Oceanic Current by 6.6 ky. The extreme positions of the ABF may be described by the 100-ky**-1 eccentricity component which is also documented in cores from Walvis Ridge and Cape Basin. Both the 23-ky and 100-ky shifts of the ABF are in phase with the meridional movements of the Subtropical Convergence zone (STC) in the southern Indian Ocean, and with advection variations in the equatorial Atlantic. The movements of the STC are probably driven by meridional displacements of the belt of westerly winds over the southern hemisphere. These caused displacements of the circumpolar fronts, the SE trades and the Benguela Current system, and made the cool advection at the equator fluctuate. The northernmost positions of the ABF coincide with strong sea-surface temperature minima in the Arabian Sea and the equatorial Pacific Ocean. These minima are probably the result of increased advection of relatively cool surface water from the south which is also caused by the northward eccentricity-driven movement of the westerlies and the associated oceanic polar fronts.

Description: Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations for taraxerol and Rhizophora pollen down-core show that increased taraxerol and Rhizophora pollen abundances occur during transgressions and periods with a humid climate. These environmental changes modify the coastal erosion and sedimentation patterns, enhancing the extent of the mangrove ecosystem and/or the transport of mangrove organic matter offshore. Analyses of mid-Pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity. This demonstrates the complex environmental response of the interaction between precession-related humidity cycles and obliquity-related sea-level changes on mangrove input.

Description: We present a high-resolution reconstruction of tropical palaeoenvironmental changes for the last deglacial transition (18 to 9 cal. kyr BP) based on integrated oceanic and terrestrial proxies from a Congo fan core. Pollen, grass cuticle, Pediastrum and dinoflagellate cyst fluxes, sedimentation rates and planktonic foraminiferal d18O ratios, uK37 sea-surface temperature and alkane/alkenone ratio data highlight a series of abrupt changes in Congo River palaeodischarge. A major discharge pulse is registered at around 13.0 cal. kyr BP which we attribute to latitudinal migration of the Intertropical Convergence Zone (ITCZ) during deglaciation. The data indicate abrupt and short-lived changes in the equatorial precipitation regime within a system of monsoonal dynamics forced by precessional cycles. The phases of enhanced Congo discharge stimulated river-induced upwelling and enhanced productivity in the adjacent ocean.

Description: Lipid compositions of sediments recovered during Ocean Drilling Program Leg 175 in the eastern South Atlantic reflect a variety of oceanographic and climatological environments. Most of the identified lipids can be ascribed to marine sources, notably haptophytes, eustigmatophytes, dinoflagellates, archaea, and diatoms. Elevated concentrations of cholesterol suggest zooplankton herbivory, characteristic for sites influenced by upwelling. At these sites, sulfurized highly branched isoprenoids from diatoms are also present in high amounts. Sterols, sterol ethers, hopanoids, and midchain hydroxy fatty acids could also be detected. Terrigenous lipids are n-alkanes, fatty acids, n-alcohols, and triterpenoid compounds like taraxerol and -amyrine. n-Alkanes, fatty acids, and n-alcohols are derived from leaf waxes of higher land plants and transported to the sea by airborne dust or fresh water. Triterpenoid compounds are most probably derived from mangroves and transported solely by rivers. Lipid compositions below the Congo low-salinity plume are strongly influenced by terrigenous material from the Congo River. Elevated organic carbon contents and predominantly marine lipid distributions at the Angola margin may indicate a highly productive plankton population, probably sustained by the Angola Dome. Sedimentary lipids in the Walvis Basin contain an upwelling signal, likely transported by the Benguela Current. Sedimentary lipids off Lüderitz Bay and in the southern Cape Basin are dominated by plankton lipids in high to intermediate amounts, reflecting persistent and seasonal upwelling, respectively.

Description: The composite depth scale for Holes 1077A and 1077B (Shipboard Scientific Party, 1998) contains imperfections between 115 and 155 meters composite depth (mcd). The spliced magnetic susceptibility record shows discrepancies when compared to the record of Site 1075 at 120-125 and 140-150 mcd (Ocean Drilling Program [ODP] Site 1077 scale) around marine isotope Stages 22 and 34, respectively. In addition, the offsets applied to transform the standard meters below seafloor (mbsf) depths into composite depths cause overlaps between cores of the same hole at the transitions between Cores 175-1077A-12H and 13H, 175-1077B-12H and 13H, and 175-1077B-13H and 14H. These overlaps are supported neither by visual investigation of the lithology in the core photographs (see 'Site 1077 Core Descriptions and Photographs' in Wefer, Berger, Richter, et al., 1998, doi:10.2973/odp.proc.ir.175.1998) nor by the pollen and dinoflagellate content. For these reasons, we have reassessed the Site 1077 composite depth scale.