Abrupt return of the summer monsoon 15,000 years ago: new supporting evidence from the lower White Nile valley and Lake Albert

Martin Williams, Michael Talbot, Paul Aharon, Yassin Abdl Salaam, Frances Williams, Knut Inge Brendeland

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Abstract

The Last Glacial period ended with an abrupt return to warmer and wetter conditions at a number of sites in intertropical Africa, Asia, Australia and South America ∼15,000 years (15 ka) ago. Similar abrupt warming is also evident at this time in high latitudes and in air trapped in Greenland ice. We here report new supporting evidence of this event from a climatically sensitive region in Africa: the White Nile valley of the central Sudan and Lake Albert in the Uganda headwaters. During the Last Glacial Maximum the White Nile valley was even more arid than it is today, with desert dunes active as far south as latitude 12°S. The sudden overflow of Lake Victoria in the Ugandan headwaters of the White Nile ∼14.5 ka, confirmed here by Sr-isotope statigraphy, caused extensive flooding in the lower White Nile valley and severe flooding in Egypt. The volume of fresh water flowing into the eastern Mediterranean at this time ultimately resulted in accumulation of highly organic sediments (Sapropel 1) on the floor of the Mediterranean Sea. Flooding in the central Sudan attained an elevation of 382 m along a north-south distance of ∼400 km. The recessional shoreline of the 382 m White Nile is indicated by concentrations of now buried freshwater gastropod shells and beach sands dated, respectively, by calibrated AMS radiocarbon and OSL to ∼15-16 ka. This mega-flood event marks the abrupt return of the summer monsoon and may reflect a globally synchronous event.

Original languageEnglish (US)
Pages (from-to)2651-2665
Number of pages15
JournalQuaternary Science Reviews
Volume25
Issue number19-20
DOIs
StatePublished - Oct 2006

Bibliographical note

Funding Information:
We thank Mark Bateman and Simon Armitage for their careful reviews. This paper is offered in honour of Emeritus Professor John R. Prescott, who was born on an island on the Nile 81 years ago and who has striven with unremitting energy, diligence and acumen to improve our ability to date the geologically recent past. We thank the Australian Research Council for financial support. MW is grateful to the villagers of the central Sudan for their unvarying courtesy, generosity and hospitality. MRT thanks the Norwegian Research Council (NFR) for support. This contribution is also in memory of Don Adamson and Desmond Clark: inspiring and knowledgeable field companions in the valley of the Nile. Aut Nilus aut nihil.

Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.

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