The late Pleistocene and Holocene stratigraphy and paleolimnology of Lakes Kivu and Tanganyika

Abstract Evidence from diatoms, chemistry, and sedimentology shows that Lakes Kivu and Tanganyika experienced late Pleistocene low stands, −86 to −300 m for Kivu and −250 to −350 m for Tanganyika. Both lakes had higher (2–10 fold) sedimentation rates prior to 11,500 yr B.P. About 9900 yr B.P., upwelling became important in southern Lake Tanganyika, which had been deepening for at least several millenia. By 9400 yr B.P., Kivu had become deep and dilute, with overflow via the Ruzizi River to Lake Tanganyika. Southern Lake Tanganyika became more stably stratified about 5200 yr B.P. Volcanism and hydrothermal activity in Kivu began about 5000 yr B.P., and the salinity reached 3 ppt and the lake became strongly stratified. The Ruzizi River outflow was interrupted from 3500 yr B.P. until recently. The sedimentary record implies that sudden hydrothermal activity and sublacustrine volcanism in Kivu has probably been the cause of its impoverished fauna. These results show that high lake levels in the Eastern Rift of Africa from 10,000 to 7000 yr B.P. were paralleled in the Western Rift. Given the great volumes of these lakes, climate has not caused great variations in salinity; the diatom floras, however, have been remarkably sensitive to changes in stratification and nutrient supply. Volcanism has been a major force in the limnological and biological evolution of Lake Kivu, while both Kivu and Tanganyika have responded to changes in precipitation and wind stress.