No abstract

The eastern Sahara Desert is one of the most climatically sensitive areas on Earth, varying from lake-studded savanna woodland to hyper-arid desert over the course of a glacial-interglacial cycle. In presently arid 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 one of the shorelines. Using a profile dating approach with the cosmogenic nuclide 10 Be, we estimate an exposure age of 109 ± 8 ka for this megalake, indicating it formed during the last interglacial period. This age is supported by optically stimulated luminescence dating of Blue Nile palaeochannels 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 lake's existence to seasonal flood pulses as a result of local damming of the White Nile by a more southerly position of the Blue Nile and greatly increased precipitation associated with a super monsoon.

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Geomorphic evidence of former glaciation in the high Drakensberg of southern Africa has proven controversial, with conflicting glacial and non-glacial interpretations suggested for many landforms. This paper presents new geomorphological, sedimentological and micromorphological data, and glacier mass-balance modelling for a site in the Leqooa Valley, eastern Lesotho, preserving what are considered to be moraines of a former niche glacier that existed during the Last Glacial Maximum (LGM). The geomorphology and macro-sedimentology of the deposits display characteristics of both active and passive transport by glacial processes. However, micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes. The application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude (ELA) of 3136 m a.s.l. and palaeoglacier mass balance characteristics comparable with modern analogues, reflecting viable, if marginal glaciation. Radiocarbon dates obtained from organic sediment within the moraines indicate that these are of LGM age. The reconstructed palaeoclimatic conditions during the LGM suggest that snow accumulation in the Drakensberg was significantly higher than considered by other studies, and has substantial relevance for tuning regional climate models for southern Africa during the last glacial cycle.