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(a)
(b)
-130
Bamako
-140
δ D
-50
-40
-30
-20
-10
0 0
δ
D P [‰ VSMOW]
(c)
(d)
January
July
Rain amount [mm month -1 ]
GeoB 9501-4
ITCZ
Wind direction
GeoB 7920-2
10
20
50
100
150
200
250
Fig. 1 a Satellite image with position of surface sediments and respective compound-speci c
D
δ
composition of n-C 31 alkanes (image: NASA Earth Observations), b
D composition of
precipitation as simulated by ECHAM5-wiso T63 simulation (nudged mode, simulated period
1959
δ
1982), c Average NW African climate in January; black arrows display major wind
directions, green line denotes position of the Intertropical Convergence Zone (ITCZ), red dot marks
the position of GeoB9501-4, green dot marks the position of GeoB7920-2, d same as c in July
-
by a strong bio-geophysical climate-vegetation feedback. The slow decline in
orbital-paced North African summer insolation during the Holocene might have led
to a sudden, i.e., within centuries, deserti
cation of the Sahara in the mid-Holocene
(e.g., Claussen 2009 ). This hypothesis is supported by a rapid increase of dust
export at around 5,500 years BP detected offshore NW Africa (deMenocal et al.
2000 ). A contrasting hypothesis suggests a continuous southward retreat of mon-
soonal rainfall due to insolation decline causing gradual environmental deteriora-
tion (e.g., Kr
pelin et al. 2008 ).
To provide more insights into the paleo-hydrologic evolution of NW Africa over
the Holocene and unravel past climate and vegetation changes, we conducted a
combined data-modeling study.
ö
D compositions of terrigenous plant lipids, pro-
viding direct insights into continental hydrologic changes (Sachse et al. 2012 ), were
δ
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