Palaeoclimates at Lake Turkana, Kenya, from oxygen isotope ratios of gastropod shells

Abstract

Climatic changes in the Plio-Pleistocene of East Africa during the evolutionary development of early man have been identified only in their broadest outlines. A variety of palaeontological^1–3 and geochemical⁴ techniques have already been applied to the study of palaeoclimates in this area, but the use of stable oxygen isotope ratios, so helpful in marine palaeoclimatology, has not been fully exploited^5,6. The frequent occurrence of well-preserved mollusc shells in the sedimentary column at Lake Turkana provides a sensitive oxygen isotope record, varying over a range of 7‰, which can be interpreted in terms of evaporative concentration of the heavier oxygen isotope in waters of the closed lake, alternating with isotopically lighter freshwater when the lake has been open. I report here the results of a study of the ¹⁸O/¹⁶O ratios of three species of gastropods from the sediments of the Koobi Fora region of Lake Turkana, and evaluate how the technique might be applied to the study of the palaeoclimates of other tropical lakes.