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AGU: Geophysical Research Letters

 

Index Terms

  • Atmospheric Composition and Structure: Aerosols and particles
  • Global Change: Land/atmosphere interactions
  • Global Change: Climate dynamics

Abstract

Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad

R. Washington

Climate Research Lab, Center for the Environment, Oxford University, Oxford, UK

M. C. Todd

Department of Geography, University College London, 26 Bedford Way, London, UK

G. Lizcano

Climate Research Lab, Center for the Environment, Oxford University, Oxford, UK

I. Tegen

Institute for Tropospheric Research, Leipzig, Germany

C. Flamant

IPSL/Service d'Aéronomie, Université Pierre et Marie Curie, Paris, France

I. Koren

Department of Environmental Sciences, Weizmann Institute, Rehovot, Israel

P. Ginoux

National Oceanic and Atmospheric Administration, Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA

S. Engelstaedter

Climate Research Lab, Center for the Environment, Oxford University, Oxford, UK

C. S. Bristow

School of Earth Sciences, Birkbeck College, University of London, London, UK

C. S. Zender

Department of Earth System Science, University of California, Irvine, California, USA

A. S. Goudie

Climate Research Lab, Center for the Environment, Oxford University, Oxford, UK

A. Warren

Department of Geography, University College London, 26 Bedford Way, London, UK

J. M. Prospero

University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida, USA

The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions.

Received 25 January 2006; accepted 30 March 2006; published 4 May 2006.

Citation: Washington, R., et al. (2006), Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad, Geophys. Res. Lett., 33, L09401, doi:10.1029/2006GL025827.

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