Much study has been devoted to land-based records of climatic change in tropical Africa through the last several tens of millenia. Paleoceanographers are also unravelling the climatic history of oceans on all sides of tropical Africa during the late Pleistocene. These studies have shed important light on such factors as the history of monsoonal circulation and the impact of fluctuations in the earth's orbit on tropical climate. In addition, the growing sophistication of climate models has opened up the possibility of integrating the continental and marine records of past climates with numerical simulations. The combination of these diverse lines of research has led, in turn, to substantial improvements in our understanding of the earth's climate system, and our ability to predict climatic changes in the future. The equatorial Atlantic is a dynamic hydrographic environment, with a number of different surface currents interacting in a relatively small area. This results in sharp gradients in sea-surface temperature and primary productivity, both of which affect the diatom assemblages in equatorial sediments making them sensitive monitors to climatic changes. The goal of this study is to determine the interconnections between conditions in the equatorial Atlantic and in tropical Africa and other parts of the tropics, and the influence of higher-latitude climates on the climates of tropical regions. To achieve this, the PIs will reconstruct temporal and spatial variations in surface oceanography as well as changes in the intensity of runoff from equatorial African rivers, as revealed by changes in the diatom assemblage. They will also search for significant periodicities in the data, as an aid to understanding the mechanisms which control climatic change in the tropics. The ultimate purpose is to improve the understanding of tropical climates and our ability to model the response of the climate system to orbital or other forcing mechanisms.
