Niedermeyer, Eva M. and Schefuß, Enno and Sessions, Alex L. and Mulitza, Stefan and Mollenhauer, Gesine and Schulz, Michael and Wefer, Gerold (2010) Orbital- and millennial-scale changes in the hydrologic cycle and vegetation in the western African Sahel: insights from individual plant wax δD and δ^(13)C. Quaternary Science Reviews, 29 (23-24). pp. 2996-3005. ISSN 0277-3791 http://resolver.caltech.edu/CaltechAUTHORS:20101209-121741039
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To reconstruct variability of the West African monsoon and associated vegetation changes on precessional and millennial time scales, we analyzed a marine sediment core from the continental slope off Senegal spanning the past 44,000 years (44 ka). We used the stable hydrogen isotopic composition (δD) of individual terrestrial plant wax n-alkanes as a proxy for past rainfall variability. The abundance and stable carbon isotopic composition (δ^(13)C) of the same compounds were analyzed to assess changes in vegetation composition (C_(3)/C_(4) plants) and density. The δD record reveals two wet periods that coincide with local maximum summer insolation from 38 to 28 ka and 15 to 4 ka and that are separated by a less wet period during minimum summer insolation. Our data indicate that rainfall intensity during the rainy season throughout both wet humid periods was similar, whereas the length of the rainy season was presumably shorter during the last glacial than during the Holocene. Additional dry intervals are identified that coincide with North Atlantic Heinrich stadials and the Younger Dryas interval, indicating that the West African monsoon over tropical northwest Africa is linked to both insolation forcing and high-latitude climate variability. The δ^(13)C record indicates that vegetation of the western Sahel was consistently dominated by C_4 plants during the past 44 ka, whereas C_(3)-type vegetation increased during the Holocene. Moreover, we observe a gradual ending of the Holocene humid period together with unchanging ratio of C_3 to C_4 plants, indicating that an abrupt aridification due to vegetation feedbacks is not a general characteristic of this time interval.
|Additional Information:||© 2010 Elsevier Ltd. Received 11 September 2009; revised 24 June 2010; accepted 25 June 2010. Available online 5 August 2010. This work was funded by the German Science Foundation (DFG) through the Research Center/Excellence Cluster “The Ocean in the Earth System” at MARUM e Center for Marine Environmental Sciences, University of Bremen and by the U.S. National Science Foundation grant EAR-0645502 to ALS. ES is funded through DFG grant Sche 903/8. EMN acknowledges additional support by GLOMAR e Bremen International Graduate School for Marine Sciences. We thank the captain and crew of RV Meteor cruise M65/1 during which core GeoB9508-5 was collected. The German academic exchange service (DAAD) is acknowledged for funding a research stay at Caltech. We are grateful to Lydie Dupont for thorough comments on the manuscript and thank Jan-Berend Stuut (MARUM) for providing information on the provenance of aeolian dust at the study site. We thank an anonymous reviewer for comments that helped to improve the manuscript. Martin Erbs (Bundesforschungsinsitut Braunschweig) is acknowledged for helpful discussions on the ecology of plants.|
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|Deposited By:||Jason Perez|
|Deposited On:||10 Dec 2010 18:37|
|Last Modified:||26 Dec 2012 12:44|
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