25th International Meeting on Organic Geochemistry IMOG 2011

P-218
Rainfall variability over NW Africa during the last glacialinterglacial
cycle: a δD record of the last 120 ka
Rony R. Kuechler, Lydie Dupont, Britta Beckmann, Enno Schefuß
MARUM - Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
(corresponding author:kuechler@uni-bremen.de)
Palaeoenvironmental studies of NW African climate
and vegetation changes during the Pleistocene
suggest periodical alternations of humid and arid
conditions [3]. For the last 120 ka, three distinct wet
intervals, i.e., the Holocene African Humid Period, a
period within Marine Isotope Stage (MIS) 3 and the
early MIS 5, were inferred to have experienced much
wetter conditions than the present [1; 2]. It has been
proposed that these humid periods reflect favourable
conditions for mammalian and hominid migrations out
of Africa [1]. Moreover, it has been shown that these
humid events were coupled to maximum summer
insolation in the northern low-latitudes causing strong
monsoonal rainfall with additional influence of highlatitude
climate variability [3]. In particular, the Atlantic
meridional overturning circulation and the associated
heat transport appear to be of main importance for
controlling vegetation distributions [1].
The purpose of this study is to decipher rainfall
variability over NW Africa during the last glacialinterglacial
cycle (last 120 ka). Previous studies [e.g.,
1] infer humidity changes from vegetation type
changes and dust fluxes, but so far, continental
palaeo-hydrologic conditions have not been assessed
directly. Therefore, a molecular isotopic approach will
be applied by using hydrogen, as well as stable
carbon isotope analyses on terrestrial plant waxes.
These compounds will be extracted from deep-sea
sediments, cored off Mauritania at ODP Site 659. This
site is located below the tracks of the African Easterly
Jet and the Northeast Trade Winds to record
environmental shifts of the Sahara/Sahel transition.
The hydrogen isotopic changes of land-derived nalkanes
will be used as a proxy for past rainfall
variability, as applied successfully by Niedermeyer et
al. (2010) for the last 44 ka. Additionally, the δ 13 C
signature of the same compounds will be analysed to
reconstruct variations in vegetation composition
(C3/C4 plants), whereas the accumulation rates of
these compounds will provide information on density
of the vegetation cover and aeolian transport strength.
Furthermore, sea-surface temperatures (SST) will be
estimated by using the U k‘ 37 Index of alkenones to
correlate continental climate with SST. These results
will be compared with palynological data and with
both δ 13 C of benthic foraminifers and dust fluxes
covering this time-interval. The δ 13 C of benthic
foraminifers will be used to assess deep-ocean
circulation changes. In this way, we tend to a better
understanding of the NW African hydrological cycle
during the last glacial-interglacial cycle, its relation to
SST and Atlantic circulation changes, as well as to
identify potential feedbacks between hydrology,
vegetation changes and dust export.
References
[1] Castañeda, I.C., Mulitza, S., Schefuß, E., Lopes
dos Santos, R.A., Sinninghe Damsté, J.S. & Schouten, S.
(2009): Wet phases in the Sahara/Sahel region and human
migration patterns in North Africa.- PNAS 106(48), 20159-
20163.
[2] Niedermeyer, E.M., Schefuß, E., Sessions, A.L.,
Mulitza, S., Mollenhauer, G., Schulz, M. & Wefer, G. (2010):
Orbital- and millenial-scale changes in the hydrologic cycle
and vegetation in the western African Sahel: insights from
individual plant wax δD and δ 13 C.- Quat. Sci. Rev. 29, 2996-
3005.
[3] Tjallingii, R., Claussen, M., Stuut, J.-B.W.,
Fohlmeister, J., Jahn, A., Bickert, T., Lamy, F. & Röhl, U.
(2008): Coherent high- and low-latitude control of the
northwest African hydrological balance. Nat. Geosci. 1, 670-
675.
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