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Simulating the transient evolution and abrupt change of Northern Africa atmosphere–ocean–terrestrial ecosystem in the Holocene

Liu, Z. and Wang, Y. and Gallimore, R. and Gasse, F. and Johnson, T. and deMenocal, P. and Adkins, J. and Notaro, M. and Prentice, I. C. and Kutzbach, J. and Jacob, R. and Behling, P. and Wang, L. and Ong, E. (2007) Simulating the transient evolution and abrupt change of Northern Africa atmosphere–ocean–terrestrial ecosystem in the Holocene. Quaternary Science Reviews, 26 (13-14). pp. 1818-1837. ISSN 0277-3791. https://resolver.caltech.edu/CaltechAUTHORS:20120828-081630088

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Abstract

We present the first synchronously coupled transient simulation of the evolution of the northern Africa climate-ecosystem for the last 6500 years in a global general circulation ocean–atmosphere–terrestrial ecosystem model. The model simulated the major abrupt vegetation collapse in the southern Sahara at about 5 ka, consistent with the proxy records. Local precipitation, however, shows a much more gradual decline with time, implying a lack of strong positive vegetation feedback on annual rainfall during the collapse. The vegetation change in northern Africa is driven by local precipitation decline and strong precipitation variability. In contrast, the change of precipitation is dominated by internal climate variability and a gradual monsoonal climate response to orbital forcing. In addition, some minor vegetation changes are also simulated in different regions across northern Africa The model also simulated a gradual annual mean surface cooling in the subtropical North Atlantic towards the latest Holocene, as well as a reduced seasonal cycle of SST. The SST response is caused largely by the insolation forcing, while the annual mean cooling is also reinforced by the increased coastal upwelling near the east boundary. The increased upwelling results from a southward retreat of the North Africa monsoon system, and, in turn, an increased northeasterly trade wind. The simulated changes of SST and upwelling are also largely consistent with marine proxy records, albeit with a weaker magnitude in the model. The mismatch between the collapse of vegetation and gradual transition of rainfall suggests that the vegetation collapse is not caused by a strong positive vegetation feedback. Instead, it is suggested that the Mid-Holocene collapse of North African vegetation is caused mainly by a nonlinear response of the vegetation to a precipitation threshold in the presence of strong climate variability. The implication to the modeling and observations is also discussed.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.quascirev.2007.03.002 DOIArticle
http://www.sciencedirect.com/science/article/pii/S0277379107000674PublisherArticle
ORCID:
AuthorORCID
Liu, Z.0000-0002-6313-823X
Adkins, J.0000-0002-3174-5190
Wang, L.0000-0002-9803-166X
Additional Information:© 2007 Elsevier Ltd. Received 30 July 2006; received in revised form 22 February 2007; accepted 1 March 2007. The authors would like to thank Drs. M. Claussen, P. Hoelzmann and an anonymous reviewer for helpful comments. This work is supported by ESH/NSF. The computation is performed at NCAR CSL.
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Funding AgencyGrant Number
NSFUNSPECIFIED
Issue or Number:13-14
Record Number:CaltechAUTHORS:20120828-081630088
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20120828-081630088
Official Citation:Z. Liu, Y. Wang, R. Gallimore, F. Gasse, T. Johnson, P. deMenocal, J. Adkins, M. Notaro, I.C. Prentice, J. Kutzbach, R. Jacob, P. Behling, L. Wang, E. Ong, Simulating the transient evolution and abrupt change of Northern Africa atmosphere–ocean–terrestrial ecosystem in the Holocene, Quaternary Science Reviews, Volume 26, Issues 13–14, July 2007, Pages 1818-1837, ISSN 0277-3791, 10.1016/j.quascirev.2007.03.002. (http://www.sciencedirect.com/science/article/pii/S0277379107000674)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33591
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:28 Aug 2012 15:41
Last Modified:09 Mar 2020 13:19

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