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North-West African Hydrologic Changes
in the Holocene: A Combined Isotopic
Data and Model Approach
Enno Schefu
, Martin Werner, Britta Beckmann, Barbara Haese
and Gerrit Lohmann
Abstract To achieve a better understanding of the hydrologic evolution of the
North-West (NW) African monsoon system during the Holocene, in particular during
inferred abrupt climate changes at the end of the African Humid Period (AHP), we
investigated terrigenous plant lipids deposited in marine sediments offshore NW
Africa. Changes in rainfall amount were estimated by compound-speci
c hydrogen
isotope (
D) analyses. The spatial gradient of rainfall isotopic compositions is
ected in marine surface sediments.
D changes in plant waxes covering the last
100 years con
rm the observed decrease in rainfall during the late twentieth century
Sahel drought, and thus can be used for a quantitative calibration of
D and pre-
D changes in sedimentary plant waxes show no abrupt change at the end
of the AHP suggesting a gradual precipitation decline. These results are supported by
Holocene climate simulations using a coupled atmosphere-land surface model, which
includes an explicit modeling of isotopic fractionation within the hydrological cycle.
Keywords North-West africa
Compound-specific deuterium
Climate simulations
Isotope modeling
1 Introduction
A profound scienti
c debate persists on the response of the North-West (NW)
African monsoon system (Fig. 1 c, d) to long-term (orbital) changes at the end of the
African Humid Period [AHP, 14,800
5,500 years before present (BP)]. One
hypothesis favors an abrupt degradation of the vegetation in the once
green Sahara
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