Joint project of Aberystwyth University, University of St Andrews, Scotland and the University of Addis Ababa, Ethiopia.
Lake Tana, in the highlands of northern Ethiopia, is the source of the Blue Nile, one of the world's great rivers. Surprisingly, very little is known about the age and history of this lake. Our new geophysical and core data show nearly 100m of accumulated sediments in the basin, interrupted by seismic reflectors that we interpret as desiccation layers. The data show that the lake dried out at 16,000 years ago, and almost certainly at apparently regular intervals during the later stages of the last Ice Age. We hypothesize that the lake dried because of intense droughts lasting one or two hundred years, caused by disruption of Africa's monsoon climate when iceberg-laden meltwater from North America flooded the North Atlantic - the Heinrich events. In this NERC-funded PalaeoTana Project, running from 2006 to 2008, we aim to test these hypotheses by obtaining a well-dated climate record from a long sediment core.
In January 2007, we successfully obtained a 96m core from the northern basin of Lake Tana, 5 km from the shore, in 10m water depth. We used a Longyear diesel-powered wireline drilling system, with a triple tube core barrel. The drill was operated from a 15-ton purpose-built platform, constructed at the nearby port of Gorgora by Addis Geosystems Ltd. Pictures of the drilling operation can be seen here.
The core will be scanned at high resolution using X-ray fluorescence, X-ray and colour imagery, geophysical and magnetic core-scanning technology. The resulting datasets will identify past desiccation events, which will be investigated in detail and interpreted by comparison to sediments of the known desiccation event at 16,000 years ago. Dating the sediments by appropriate methods including luminescence, tephrochronology, and Argon-Argon dating will allow precise estimates of the timing and duration of the droughts.
A long core record of past climate and environment from this part of Africa will have major significance for understanding both regional environmental change, because of the influence of the Nile on NE Africa and the eastern Mediterranean, and global climate. It will contribute to understanding how future changes in ocean temperature and circulation will affect global climate, especially in the heavily populated monsoon regions of Africa and Asia. It may also have significance for understanding the later stages of human evolution in and dispersal out of Africa.
Dr Sarah Davies
Dr Mike Marshall
Dr Harry Toland
Non IGES Collaborators
Dr Richard Bates
Dr Tony Prave
Dr Dei Huws
Dr Mohammed Umer