I-n-Atei palaeolake documents past environmental changes in central Sahara at the time of the “Green Sahara”: Charcoal, carbon isotope and diatom records Christophe Lécuyer a, ⁎ ,1 , Anne-Marie Lézine b , François Fourel a , Françoise Gasse c,2 , Florence Sylvestre c , Christine Pailles c , Christophe Grenier d , Yves Travi e , Abel Barral a a Laboratoire de Géologie de Lyon, LGL-TPE, UMR 5276 CNRS, Université Claude Bernard Lyon 1, France b Sorbonne Universités, UPMC, University Paris 06, CNRS-IRD-MNHN, LOCEAN/IPSL Laboratory, 4 Place Jussieu, 75005 Paris, France c Aix-Marseille Université, CNRS, IRD, UM 34 CEREGE, Technopôle de l'Environnement Arbois-Méditerranée, BP80, 13545 Aix-en-Provence, France d Laboratoire des Sciences du Climat et de l'Environnement, UMR 1572 CNRS, CEA et Université de Versailles, Ormes des merisiers, Bât 701, Gif-sur-Yvette cedex 91191, France e UMR EMMAH Environnement Méditerranéen et Modélisation des Agro-Hydrosystèmes, Université d'Avignon, France abstract article info Article history: Received 22 June 2015 Received in revised form 7 October 2015 Accepted 21 October 2015 Available online 27 October 2015 Keywords: Sahara Holocene Climate Lake Charcoal Carbon isotope During the ‘Green Sahara event’, water bodies developed throughout the Sahara and Sahel, reflecting the enhanced influence of the Atlantic monsoon rainfall. Major lakes then dried out between 6.5 and 3.5 ka. This study investigates land cover change and lacustrine environment during the Holocene at I-n-Atei, Southern Algeria, a desert region lying in the hyperarid core of the Sahara. This site is remarkable by its extent (up to 80 km 2 ) and by the exceptional preservation and thickness of the lacustrine deposits (7.2 m). I-n-Atei was a lake from 11 to 7.4 ka, then it dried out and left place to a swampy environment. Charcoal concentrations show that the surroundings of the lake were vegetated throughout the wet period with two short phases of possible vegetation deterioration associated with a lowering of the lake level at 9.3 and 8.2 ka, coeval with well-known dry events in the tropics. The stable carbon isotope record reflects the penetration of C4 herbaceous populations in replacement of the original C3, typical of the regional vegetation at the time of the maximum lake expansion. The δ 13 C of charcoals increase non-linearly with the 14 C-based ages from -24.5‰ to -13.0‰ (V-PDB). Assuming that these extreme values sample both C3 and C4 plant end-members, mass balance calculations suggest that C3 were replaced by C4 plants according to an exponential decay law with a half-life (t 1/2 ) of 850 ± 110 years. The replacement of C3 byC4 plants occurred in two main steps: a mixed C3–C4 vegetation of “wooded grassland” type was present from 10 ka to 8.4 ka while a C4 exclusive vegetation developed after 8.4 ka. After the end of the lacustrine phase a catastrophic event (flooding?) provoked the lifting of most of the lacustrine deposits and their re-deposition above the lacustrine sequence. © 2015 Elsevier B.V. All rights reserved. 1. Introduction One of the main limitations of palaeoenvironmental reconstructions in arid and semi-arid tropical regions is the desiccation of lacustrine sediments that prevents the preservation of biological remains and favours the removal by wind erosion of exposed sediments during dry periods. As a result, high resolution and continuous records covering the entire Holocene period are extremely rare and the following question remains unresolved: how the environmental change that led to the setting of the “Green Sahara” took place in response to increased rainfall during the African Humid Period (deMenocal et al., 2000a) in central Sahara? Lézine et al. (2011a) showed that the filling of lakes and wetlands north of 10°N started from ca 15 ka onward in central Sahara. This sector benefited from the presence of the Saharan mountains (mainly the Hoggar, Aïr and Tibesti Massifs) which acted as a “water tower” generating primary expansion of permanent water bodies: for example, at Adrar Bous in the Ténéré desert of NE Niger, the first flooding linked to surface runoff and wadi underflows from the nearby mountains was recorded at 15–15.3 ka (Gasse, 2002). Then water bodies widely developed throughout the Sahara and Sahel after 10.5 ka reflecting the enhanced influence of monsoon rains over North Africa and dried out between 6.5 and 3.5 ka according to the latitudes (Lézine et al., 2011a). Regarding the vegetation response to increased rainfall and availability of soil water, recent progress in palaeoenvironmental Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 834–844 ⁎ Corresponding author. Tel.: +33 472448376. E-mail address: clecuyer@univ-lyon1.fr (C. Lécuyer). 1 Also at Institut Universitaire de France. 2 Deceased author. http://dx.doi.org/10.1016/j.palaeo.2015.10.032 0031-0182/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo