UNVEILING VICTORIA’S SECRETS

Africa’s Lake Victoria, the continent’s largest lake, provides a critical sedimentary archive to test models of tropical climate change. Seismic, sedimentological, palynological, geochemical, archaeological, paleontological, and biogeographic data reveal a complex cyclical history of lake expansion and desiccation. Past changes in lake size impacted regional water budgets (e.g., episodic connections to the Nile), cichlid evolution, and major dispersal corridors for a range of taxa such as early populations of Homo sapiens.

Its unique equatorial position makes Lake Victoria an excellent target to study interhemispheric climate variability. Lake level changes after the last glacial maximum (LGM) appear to respond in part to high latitude process and tropical air mass shifts but the limited record hampers assessing the impact of precession and long-term patterns. Three major desiccation surfaces revealed in seismic surveys by the IDEAL project in 1995/96 divide a 40-60 m-thick sedimentary sequence spanning ~400,000 years of equatorial climate history. Tephra deposits are present in these post-LGM sediments with >17 well-characterized pre-LGM tephras found in near-shore terrestrial deposits, dating to ~100-36 ka, and which are likely present in lacustrine sediments. Piston cores have penetrated only the youngest of the basin-wide desiccation surfaces. While the lake desiccated many times, these depositional hiatuses are a critical part of the Lake Victoria record as (a) their timing allows us to test the geographic extent of the megadrought pattern recorded farther to the south, (b) they represent key periods of ecological change that can be linked with contemporaneous terrestrial deposits, and (c) we have already developed a robust method to use paleosols as environmental proxies in the Lake Victoria region and those now buried beneath the lake can rapidly be integrated into this dataset. As the Lake Victoria Basin supplies subsistence and economic resources to ~30 million people, paleoenvironmental data are particularly important in forecasting future changes to the region.