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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