Paleohydrology of Lake Victoria, East Africa, inferred from¹⁸O/¹⁶O ratios in sediment cellulose

δ¹⁸O values of aquatic cellulose preserved in a 7.6 m sediment core from near the center of Lake Victoria, East Africa, record a 13000 yr hydrological history of the basin. Relative to the pres- ent value (+3.4‰),highly elevated lake-water δ¹⁸O values of +8‰±2‰ from 13200 to 7250 ¹⁴C yr B.P. indicate closed-basin conditions and precipitation:evaporation ratios much smaller than at present. An abrupt drop in the lake-water δ¹⁸O to 0 ‰ ± 1‰marks the rapid transition to an open basin between 7250 and 7150 ¹⁴14C yr B.P. From 7140 to 5400 ¹⁴C yr B.P. increasing lake-water δ¹⁸O values from 0‰ ± 1‰ to +5‰ are proposed to reflect outlet downcutting and a likely de- crease in relative humidity. These data have unexpectedly shifted our view of the timing of changes in the Lake Victoria water balance and imply a period of at least 10000 years (17000 to 7000 ¹⁴C yr B.P.) when the Lake Victoria basin did not contribute waters to the main Nile River.