North-West African Hydrologic Changes in the Holocene: A Combined Isotopic Data and Model Approach - Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC) - page 103

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

ß

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

δ

re ected in marine surface sediments. D changes in plant waxes covering the last

δ

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 δ D and pre-

cipitation. 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.

δ

Keywords North-West africa Hydrology Compound-specific deuterium

analysis 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 '