Show simple item record Henry F. en_US C. Richard en_US Paul V. en_US Michael H. en_US Mohammed en_US Sarah J. en_US Eshete en_US 2011-07-01T11:21:36Z 2011-07-01T11:21:36Z 2007-02-01 en_US
dc.identifier en_US
dc.identifier.citation Lamb , H F , Bates , C R , Coombes , P V , Marshall , M H , Umer , M , Davies , S J & Dejen , E 2007 , ' Late Pleistocene desiccation of Lake Tana, source of the Blue Nile ' Quaternary Science Reviews , vol 26 , no. 3-4 , pp. 287-299 . , 10.1016/j.quascirev.2006.11.020 en_US
dc.identifier.other PURE: 168648 en_US
dc.identifier.other dspace: 2160/7120 en_US
dc.description.abstract High-resolution seismic data from Lake Tana, the source of the Blue Nile in northern Ethiopia, reveal a deep sedimentary sequence divided by four strong reflectors. Data from nearshore cores show that the uppermost strong reflector represents a stiff silt unit, interpreted as a desiccation surface. Channel cuts in this surface, bordered by levee-like structures, are apparent in the seismic data from near the lake margin, suggesting fluvial downcutting and over-bank deposition during seasonal flood events. Periphytic diatoms and peat at the base of a core from the deepest part of the lake overlie compacted sediments, indicating that desiccation was followed by development of shallow-water environments and papyrus swamp in the central basin between 16,700 and 15,100 cal BP. As the lake level rose, open-water evaporation from the closed lake caused it to become slightly saline, as indicated by halophytic diatoms. An abrupt return to freshwater conditions occurred at 14,750 cal BP, when the lake overflowed into the Blue Nile. Further reflection surfaces with downcut structures are identifiable in seismic images of the overlying sediments, suggesting at least two lesser lake-level falls, tentatively dated to about 12,000 and 8000 cal BP. Since Lake Victoria, the source of the White Nile, was also dry until 15,000 cal BP, and did not reach overflow until 14,500 cal BP, the entire Nile system must have been reduced to intermittent seasonal flow until about 14,500 cal BP, when baseflow was re-established with almost simultaneous overflow of the headwater lakes of both the White and Blue Nile rivers. Desiccation of the Nile sources coincides with Heinrich event 1, when cessation of northward heat transport from the tropical Atlantic disrupted the Atlantic monsoon, causing drought in north tropical Africa. The strong reflectors at deeper levels in the seismic sequence of Lake Tana may represent earlier desiccation events, possibly contemporaneous with previous Late Pleistocene Heinrich events. en_US
dc.format.extent 13 en_US
dc.relation.ispartof Quaternary Science Reviews en_US
dc.title Late Pleistocene desiccation of Lake Tana, source of the Blue Nile en_US
dc.contributor.pbl Institute of Geography & Earth Sciences en_US
dc.contributor.pbl Quaternary Environmental Change Group en_US

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