The ocean's role in climatic change through heat transport and control of carbon dioxide is increasingly being recognized. This new awareness, and the urgency that must be accorded the attempt to understand the mechanisms of climatic change, have led to the initiation of large integrated efforts in physical and chemical oceanography. Likewise, the potential of the oceanic record for understanding climatic change has received increased attention in recent years (CLIMAP, 1976; COSOD II, 1987). The Angola/Namibia high-productivity system needs to be studied because of its importance in the global ocean-carbon cycle and to provide for comparison with the Peru and California systems. Only by comparing these systems with each other shall we be able to learn which elements of a system are peculiar, and which have general validity through time and on a global scale. To further these goals, 13 advanced hydraulic piston corer and extended core barrel (APC/XCB) sites were drilled off the southwestern coast of Africa during Leg 175 (Fig. 1) to study the paleoenvironment of the Benguela Current and Angola/Namibia upwelling system, with emphasis on the late Neogene.

Eastern boundary upwelling is strongly involved in modulation of the carbon cycle and, therefore, in control of the partial pressure of carbon dioxide (pCO2) ("biological pumping"; Berger and Keir, 1984; Sundquist and Broecker, 1985; Boyle and Keigwin, 1987; Sarnthein et al., 1988; Berger et al., 1989). It is now generally thought that such pumping is a crucial factor for the explanation of the type of short-term fluctuations in atmospheric CO2 seen in ice cores (Barnola et al., 1987). Along these lines of argument, there is a good correlation between productivity indices in the eastern equatorial Pacific and the ice-core record of pCO2. Likewise, there is good correlation between the ice-core record and estimates of CO2 pressure in surface water.

On a longer time scale, Vincent and Berger (1985) have postulated that depositional pumping by coastal upwelling is responsible for changing the general level of atmospheric pCO2. They propose a climatic preconditioning by upwelling-induced carbon extraction from the ocean-atmosphere system for the beginning of the modern ice-cap dominated world. Their argument is based on the observation that carbon isotopes in deep-sea benthics become 13C enriched just when organic-rich phosphatic sediments begin to accumulate around the Pacific margins. In this view, eastern boundary upwelling, and therefore upwelling off Angola and Namibia, has global implications for the long-term history of the carbon cycle and climate and for the evolution of life and biogeography on land and in the sea.

To be able to predict the effects of changes in productivity on the CO2 content of the atmosphere, the interrelationships among ocean circulation, nutrient transport, and the sedimentation of organic compounds and carbonate must be established for each of the important productivity regions. Until now, there has been no information on Neogene upwelling fluctuations off Angola and Namibia, a region that is probably of considerable importance for the global carbon cycle.

The most important period for understanding the workings of the present system is the time since the Miocene. Within this period, we see the evolution of the present planetary orography, the buildup of ice caps on both poles, the development of modern wind and upwelling regimes, and the stepwise increase in North Atlantic Deep Water (NADW) production, which dominates the style of deep circulation in the ocean. The present system is characterized by a strong 100,000-yr climatic cycle, beginning 700,000 yr ago (Berger et al., 1996). High-amplitude fluctuations associated with buildup and decay of northern ice sheets began around 2.8 m.y. ago (Shackleton et al., 1984; Hodell and Venz, 1992).

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