A White Nile megalake during the last interglacial period
Geological Society of America
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 10Be, 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 km2 in area, making it comparable to the largest freshwater lakes on Earth today. We attribute the lake’s 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.
We thank Ted Maxwell and two anonymous reviewers for their constructive suggestions. We thank the Australian Research Council for fi nancial support (grant DP0878058 to M. Williams) and the Geological Research Authority of the Sudan for logistical support. Sayed Nagi Abdalla Mohamed (Field Manager, Danfodia Company for Contracting Roads and Bridges, Jebelein), generously allowed the use of a bulldozer for excavating the trench at site A.
This is the author accepted manuscript. The final version is available from Geological Society of America via http://dx.doi.org/10.1130/G35238.1
Vol. 42, pp. 163 - 166
Data Repository item 2014043