Atlantic Forcing of Persistent Drought in West Africa
T. M. Shanahan,1,2*
J. T. Overpeck,1,3
K. J. Anchukaitis,4
J. W. Beck,5
J. E. Cole,1
D. L. Dettman,1
J. A. Peck,6
C. A. Scholz,7
J. W. King8
Although persistent drought in West Africa is well documented
from the instrumental record and has been primarily attributed
to changing Atlantic sea surface temperatures, little is known
about the length, severity, and origin of drought before the
20th century. We combined geomorphic, isotopic, and geochemical
evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct
natural variability in the African monsoon over the past three
millennia. We find that intervals of severe drought lasting
for periods ranging from decades to centuries are characteristic
of the monsoon and are linked to natural variations in Atlantic
temperatures. Thus the severe drought of recent decades is not
anomalous in the context of the past three millennia, indicating
that the monsoon is capable of longer and more severe future
droughts.
2 Jackson School of Geosciences, University of Texas–Austin, Austin, TX 78705, USA.
3 Institute for the Environment and Society and Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA.
4 Lamont Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.
5 Department of Physics, University of Arizona, Tucson, AZ 85719, USA.
6 Department of Geology, University of Akron, Akron, OH 44325, USA.
7 Department of Earth Sciences, Syracuse University, Syracuse, NY 13244, USA.
8 Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA.
* To whom correspondence should be addressed. E-mail: tshanahan{at}jsg.utexas.edu
