Early Holocene greening of the Sahara requires Mediterranean winter rainfall

[en] The greening of the Sahara, associated with the African Humid Period (AHP) between ca. 14,500 and 5,000 y ago, is arguably the largest climate-induced environmental change in the Holocene; it is usually explained by the strengthening and northward expansion of the African monsoon in response to orbital forcing. However, the strengthened monsoon in Early to Middle Holocene climate model simulations cannot sustain vegetation in the Sahara or account for the increased humidity in the Mediterranean region. Here, we present an 18,500-y pollen and leaf-wax δD record from Lake Tislit (32° N) in Morocco, which provides quantitative reconstruction of winter and summer precipitation in northern Africa. The record from Lake Tislit shows that the northern Sahara and the Mediterranean region were wetter in the AHP because of increased winter precipitation and were not influenced by the monsoon. The increased seasonal contrast of insolation led to an intensification and southward shift of the Mediterranean winter precipitation system in addition to the intensified summer monsoon. Therefore, a winter rainfall zone must have met and possibly overlapped the monsoonal zone in the Sahara. Using a mechanistic vegetation model in Early Holocene conditions, we show that this seasonal distribution of rainfall is more efficient than the increased monsoon alone in generating a green Sahara vegetation cover, in agreement with observed vegetation. This conceptual framework should be taken into consideration in Earth system paleoclimate simulations used to explore the mechanisms of African climatic and environmental sensitivity. © 2021 National Academy of Sciences. All rights reserved.

Disciplines :

Earth sciences & physical geography

Author, co-author :

Cheddadi, R.; Institut des Sciences de l'Évolution de Montpellier, CNRS, Institut de Recherche pour le Développement, University of Montpellier, Montpellier, 34000, France

Carré, M.; Institut Pierre-Simon Laplace-Laboratoire d'Océanographie et du Climat, Expérimentations et approches numériques, CNRS, Institut de Recherche pour le Développement, Muséum National d'Histoire naturelle, Sorbonne Université, Pierre and Marie Curie University, Paris, 75006, France, Centro de Investigaciòn Para el Desarrollo Integral y Sostenible, Laboratorios de Investigación y Desarrollo, Facultad de Ciencias y Filosofia, Universidad Peruana Cayetano Heredia, Lima, 15102, Peru

Nourelbait, M.; LGMSS, URAC45, University Chouaib Doukkali, El Jadida, 24000, Morocco

François, Louis ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Modélisation du climat et des cycles biogéochimiques

Rhoujjati, A.; Laboratoire Géoressources, URAC42, Université Cadi Ayyad, Marrakech, 40000, Morocco

Manay, R.; Centro de Investigaciòn Para el Desarrollo Integral y Sostenible, Laboratorios de Investigación y Desarrollo, Facultad de Ciencias y Filosofia, Universidad Peruana Cayetano Heredia, Lima, 15102, Peru

Ochoa, D.; Centro de Investigaciòn Para el Desarrollo Integral y Sostenible, Laboratorios de Investigación y Desarrollo, Facultad de Ciencias y Filosofia, Universidad Peruana Cayetano Heredia, Lima, 15102, Peru

Schefuß, E.; MARUM - Center for Marine Environmental Sciences, University of Bremen, Bremen, 28359, Germany

Language :

English

Title :

Early Holocene greening of the Sahara requires Mediterranean winter rainfall

Publication date :

2021

Journal title :

Proceedings of the National Academy of Sciences of the United States of America

ISSN :

0027-8424

eISSN :

1091-6490

Publisher :

National Academy of Sciences

Volume :

118

Issue :

Peer reviewed :

Peer Reviewed verified by ORBi

Funders :

ANR - Agence Nationale de la Recherche
F.R.S.-FNRS - Fonds de la Recherche Scientifique

Funding text :

This work contributes to the Vulnerability of Populations under Extreme Scenarios (VULPES) project, funded by Belmont Forum (Project ID: ANR-15-MASC-0003), and to the Agence Nationale pour la Racherche-Joint Programming Initiatives Climate—Belmont Forum Paleo- Constraints on Monsoon Evolution and Dynamics project (Grant ANR-15- JCLI-0003-01). L.F. was supported in Belgium by the Fonds de la Recherche Scientifique (Grant PDR-WISD-05). R.C. thanks Anne-Marie Lézine for providing pollen laboratory facilities with which to treat samples of the Tislit core. E.S. and leaf-wax analyses were supported by Centre for Marine Environmental Sciences. We thank Ralph Kreutz for laboratory support. M.N.’s postdoc was funded by the VULPES project. We are very grateful to Tadeusz Namiotko, who helped us with ostracod identification. A. Benkaddour took part in the field trip to collect the Tislit core. We thank the Laboratoire de Mesure du Carbone-14 staff, ARTEMIS national facility, and Unité Mixte de Service 2572 CNRS-Commissarait à l’Energie Atomique-Institut de Recherche pour le Développement-Institut de Radioprotection et de Sûreté Nucléaire-MCC for the Accelerator Mass Spectroscopy dating. We are grateful to the three anonymous reviewers who provided very constructive comments to improve our manuscript.

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since 23 June 2021

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