Increase in African dust flux at the onset of commercial agriculture in the Sahel region.
The Sahara Desert is the largest source of mineral dust in the world. Emissions of African dust increased sharply in the early 1970s (ref. 2), a change that has been attributed mainly to drought in the Sahara/Sahel region caused by changes in the global distribution of sea surface temperature. The human contribution to land degradation and dust mobilization in this region remains poorly understood, owing to the paucity of data that would allow the identification of long-term trends in desertification. Direct measurements of airborne African dust concentrations only became available in the mid-1960s from a station on Barbados and subsequently from satellite imagery since the late 1970s: they do not cover the onset of commercial agriculture in the Sahel region approximately 170 years ago. Here we construct a 3,200-year record of dust deposition off northwest Africa by investigating the chemistry and grain-size distribution of terrigenous sediments deposited at a marine site located directly under the West African dust plume. With the help of our dust record and a proxy record for West African precipitation we find that, on the century scale, dust deposition is related to precipitation in tropical West Africa until the seventeenth century. At the beginning of the nineteenth century, a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region. Our findings suggest that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for about 200 years.
Mulitza
Stefan
S
MARUM-Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, D-28359 Bremen, Germany. smulitza@uni-bremen.de
Heslop
David
D
Pittauerova
Daniela
D
Fischer
Helmut W
HW
Meyer
Inka
I
Stuut
Jan-Berend
JB
Zabel
Matthias
M
Mollenhauer
Gesine
G
Collins
James A
JA
Kuhnert
Henning
H
Schulz
Michael
M
D000354:Africa, Western; D000383:Agriculture / Q000266:history*; D010367:Arachis / Q000254:growth & development; D001272:Atmosphere / Q000737:chemistry; D001460:Barbados; D003889:Desert Climate; D004391:Dust / Q000032:analysis*; D005618:Fresh Water / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry; D003368:Gossypium / Q000254:growth & development; D049670:History, 17th Century; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D049690:History, Ancient; D010316:Particle Size; D011891:Rain; D012623:Seawater; D014329:Tropical Climate; D014919:Wind
D004391:Dust