Lake Turkana and Its Link to the Nile

Abstract

Lake Turkana is a large, closed-basin lake in the northern Kenyan rift that occasionally overflowed first to the Indian Ocean and then, after about 1.3 million years ago, into the Nile drainage basin. The lake lies in a broad, arid depression surrounded by late Cenozoic fluvial, lacustrine, and volcanic sequences. The climate of the Turkana basin is hot and arid, with extended periods of unusually intense diurnal winds. Seasonal variability in air temperature and rainfall is much subdued compared to the other great lakes of East Africa. Lake temperatures range between 24.5°C and 30°C, the salinity is about 2,500 mg/l, and the entire water column is oxygenated throughout most years. The lake's hydrological budget is dominated by Omo River input and by evaporation. Primary production in the lake is about 700–800 gC/m2y, and is typically limited to the upper 6 m of the turbid water column. Lake level has fluctuated more than 100 m in response to climate change. Analyses of sediment cores from within the modern lake and of lake deposits exposed onshore indicate that Lake Turkana overflowed into the Nile in the early Holocene (11.5–7.8 and 7.4–4.3 kyr), at 102 kyr, and at 195 kyr, with possible links at 123 and 172 kyr as well. Geochemical composition of much older (2.8–0.7 Ma) lacustrine sediments exposed to the east of the lake also suggest periodic overflow to the Nile, but the exact timing of these events are yet to be worked out. Additionally, Lake Turkana very likely was much lower than its present level during the last ice age and at other times of weakened African monsoon, perhaps even completely desiccated.