Varying Isotope Response of Freshwater Molluscs to Environmental Change: Equatorial Africa

Stable oxygen and carbon isotope ratios from modern African freshwater molluscs and water samples were examined to ascertain the reliability of such information as a proxy in the study of paleoclimates and paleoenvironments. In this study, the isotope ratios of the freshwater molluscan shell samples were determined from both the apertures and at interval of accretionary growth of individual shells collected at monthly intervals, from four sites. These ratios were examined to ascertain the extent to which they correlate with temperature, rainfall, water isotope ratios and other ambient conditions. The samples studied were collected from a tributary of the River Pra at Krobo, in the Western Region, River Densu at Achimo ta, in the Greater-Accra Region and a stream in Sunyani, Brong-Ahafo Region, all in southern Ghana approximately 700 km south of the Sahel, and from the Winam Gulf of Lake Victoria at Kisumu, Kenya. Molluscan shells and water isotope ratios responded to heavy rainfall, as well as variations in temperature and evaporative effects. Oxygen isotope ratio values can be used to estimate seasonality, and in turn, the life span of the molluscs. For application of this method to fossil molluscan shells for elucidation of paleoclimates, however, additional geological and geographical data are desirable