A White Nile megalake during the last interglacial period
2014
The eastern Sahara Desert of Africa is one of the most climatically sensitive areas on
Earth, varying from lake-studded savannah woodland to hyperarid desert over the course
of a glacial-interglacial cycle. In currently semiarid Sudan, there is widespread evidence
that a very large freshwater lake once filled the White Nile River valley. Here we present the
first quantitative estimate for the dimensions of the lake and a direct age for the emplacement
of its shoreline. Using a profile dating approach with the cosmogenic nuclide 10 Be, we
estimate an exposure age of 109 ± 8 ka for this megalake, indicating that it probably formed
during the last interglacial period. This age is supported by optically stimulated luminescence
dating of Blue Nile paleochannels associated with the lake. Using a high-resolution
digital elevation model, we estimate that the lake was more than 45,000 km 2 in area, making
it comparable to the largest freshwater lakes on Earth today. We attribute the lake9s
existence to seasonal flood pulses as a result of local damming of the White Nile by a more
southern position of the Blue Nile and greatly increased precipitation associated with an
enhanced monsoon.
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