Strontium isotopic and petrologic evidence for Nile flow failure at the end of the Old Kingdom, Egypt
by
Michael D. Krom
School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK
Coauthors: Jean-Daniel Stanley (Geoarchaeology-Global Change Program, E-206 NMNH, Smithsonian Institution, Washington D.C., 20560. U.S.A.), Robert A. Cliff (School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK), Jamie C. Woodward (School of Geography, University of Leeds, Leeds, LS2 9JT, UK)

Since Predynastic time, Egypt's civilization, has been directly linked to the Nile, its one primary and vital water source. There are few examples where the interaction of climate, hydrological flux and human development is so closely intertwined. Historical records document a long-term decline in rainfall in the Sahel region, and a gradual drying of the Egyptian hinterland from the Predynastic period (ca. 6000 cal yr B.P.) to Old Kingdom time (to ca. 4300 cal yr B.P.). While there is extensive information in support of this major paleoclimatic change from lake basins in the catchment, relatively little data document this drying trend downstream in the river valley itself and the Nile delta. Results from our study of sediment core S-21 collected in the Nile delta show a systematic decrease in the 87Sr/86Sr ratio of the <20 um sediment fraction, from ca. 6100 B.P. to 4200 cal yr B.P. This behaviour was driven by the intensity and length of the rainy season on the Ethiopian Highlands. A decline in rainfall led to a decrease in the vegetative cover and an increase in the erosion rate (Foucault and Stanley, 1989) causing a higher proportion of Blue Nile sediment and a higher total flux of sediment towards the 87Sr/86Sr minimum at 4200 cal yr. BP.

The Old Kingdom collapsed quite suddenly into anarchy at 2160 BC (4160 cal yr B.P.) It has been suggested that this was due, in large part, to catastrophic failure of the annual Nile flood for a period of 30 years. Direct evidence for failure of the Nile flood and low baseflow at that time is provided from two cores collected in the central Nile delta (cores S-86 and S-87) which were recovered within the freshwater region of the Nile delta. A distinctive thin (~5 cm), reddish-brown silt layer containing iron/manganese hydroxide is present in each core and nowhere else within the two mid-Holocene core sections. Sediment which has been allowed to dry out in air will form iron oxides that are resistant to later chemical changes, even once the system becomes flooded again. Visually, these layers resemble modified paleosol horizons characteristic of sediment that has dried out and been sub-aerially exposed for a prolonged period. The age of these two horizons is 4250 cal yr B.P. in core S-86 and 4050 cal yr B.P. in core S-87, based on interpolated radiocarbon ages from these cores. It has been observed that, in addition to Egypt, drought was widespread at ca. 4200 B.P. across much of Africa and Asia, and this abrupt climatic event has been implicated in the collapse of civilisations in Syria, Mesopotamia, Turkey and elsewhere. This widespread event may have been caused by weak monsoons induced by a change in the circulation of the North Atlantic.

Date received: July 19, 2002

Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caji-45.