New geochemical and palynological data and a sedimentological reinterpretation of two cores from Lake Albert allow a revision of the paleoclimatic and paleohydrologic history of northwest Uganda over the last 30,000 14C yr BP. Our findings document one and possibly three periods of significantly reduced inflow to the Nile River system from the White Nile. Based on sediment fabric and mineralogy, shifts in percentages of total organic carbon (TOC) and total organic nitrogen (TON), hydrogen index (HI), and δ13C and δ15N, as well as poor preservation of sporopollenin and siliceous microfossils, we recognize two mature paleosols that formed between 18,000 and 12,500 14C yr BP at the surface of exposed lacustrine muds. A thin fossiliferous zone between the two soils documents a brief period of flooding Lake Albert was below the level of the coring site, and thus a closed basin, for several thousand years during the late Pleistocene. Around 12,500 14C yr BP the younger vertisol was flooded by a major rise in lake level. Relatively deep-water conditions were established soon after this transgression, but an apparent change in sedimentation rate sometime between 8,000 and 3,400 14C yr BP may reflect another, briefer period of low water, which resulted in interruption of sedimentation at the coring site. Palynological data document a rapid and abrupt shift to drier conditions around Lake Albert from 11,400 to 9,900 14C yr BP coincident with the cool Younger Dryas event of the Northern Hemisphere. Geochemical evidence suggests that throughout the terminal Pleistocene and early Holocene, and again in the late Holocene, the water column was relatively well-mixed with little tendency to persistent anoxia.
Bibliographical noteFunding Information:
This work is a contributiotno the International Decade for East African Lakes (IDEAL). Financials upportw as providedb y the National ScienceF oundationa nd the NorwegianR esearch Council( NFR). We greatlya ppreciatteh etechni-cal supportp rovidedb y Duan Trinh, and wish also to acknowledgteh e contributiono f all those mentionedin Harvey (1976) who assistedT . Harvey and D.A. Livingstonei n obtainingt he coresu sedf or this study.C onstructivree viewsb y FranqoiseG asseand Rick Foresters ignificantly improveda n earlierv ersiono f them anuscript. The paperi s contributio#n 510f romthe Limnological ResearchC enter,U niversityo f Minnesota.
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- Organic geochemistry
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