Oases are subject to decreasing resources and changing human activities. Fully aware of their rich heritage, the United Arab Emirates (UAE) have undertaken work to preserve and revitalize these oases. However, there is a clear lack of understanding of the dynamic links between climate change, hydraulic and agricultural management, and socioeconomic activities. To clarify these links, our team conducted a systematic geoarchaeological, geophysical, spatial, and chronological study of the Masafi oasis, UAE. Results indicate the existence of a natural humid area as early as the late Pleistocene (~18 cal ka BP). These conditions persist during the early-mid Holocene with drainage activation and soil development (~12–6.3 ka). During the late Holocene, after the emergence of the “artificial” oasis around ~3250 cal yr BP, cycles of intense management suggesting water availability (~3250–2380 cal yr BP; 550 cal yr BP) alternate with episodes of fluvial detritism (~2380–1870 cal yr BP; >550 cal yr BP) and scattered evidence of farming activities with complex hydroclimatic signatures (~2300–550 cal yr BP). These results, together with regional environmental data, indicate that water and soil resources were available and exploited strategically throughout the Holocene despite adverse climatic conditions, and the oasis of Masafi could have acted as a desert refugium.

Abstract. Lake Mareotis (modern Mariut), located near the Mediterranean coast of Egypt west of the Nile Delta, is bordered by ancient sites dating from the New Kingdom (end of the 2nd millennium BCE) to the Medieval period (8th century CE), the most famous one being Alexandria. In its western part (wadi Mariut), several sites are equipped with harbour structures, but they also have structures contemporaneous with them that are not compatible with the lake level required for the operation of the harbour. Between the 1990s and 2010, several sedimentological studies tried to solve this paradox without completely succeeding. To go further, this study is based on the reassessment of geoarchaeological data and on the analysis of early scholars' accounts (1800–1945), maps (1807–1958) and satellite photographs (Corona). It allows us to reconstruct the extension of the lake(s) at different periods in wadi Mariut. During the 1st millennium BCE, the Mariut lagoon experienced a drawdown in its western part, and several distinct lakes formed, followed by building operations in some emerged areas during the Hellenistic period (332–30 BCE). During the early Roman period (30 BCE–284 CE), the digging of several canals in the 2nd century CE to connect the sites of the wadi Mariut to the eastern part of the Mariut basin reconfigured the lake(s).

International audienceThe Western Desert of Egypt is one of the most arid areas of the world. Because of the extreme scarcity of the rainfall (less than 1 mm of annual mean rainfall in some places) and because of the amount of available sediment, aeolian processes are the major morphogenetic factors. The studies of the palaeoenvironments in this area (Wendorf et Schild, 1980; Sanlaville, 1997; Brookes, 2003; Bubenzer et Riemer, 2007) show that the climate has gradually become hyperarid between 5800 BP and 4500 BP. So, the ascendancy of aeolian processes isn't new. During the Holocene, the aeolian processes and landforms has acted as a resource (moisture of the deposits, arable lands) and as a stress (sanding and silting up, erosion) at the same time. The geomorphological and geoarchaeological survey of the Dush area, located in the South of Kharga basin has highlighted the existence of fine-grained sediment which are neither spring deposits (as described by Bousquet, 1996) nor playa deposits (as described by Embabi, 1972, 1999, 2004). The archaeological data produced since 1976 by the IFAO (Institut Français d'Archéologie Orientale) mission and the sedimentological analyses indicates that the sediment of these deposits had been windblown and trapped by vegetation (fields of the ancient oases). The cultivation of the fields lasted from 2500 BP to 1500 BP, allowing the height of the deposits to reach several meters. The drop of the water table and the uplift of the level of the fields forced the farmers to adapt themselves, up to the abandonment of most of the sites (around 1500 BP). After 1500 BP, the deposits have been eroded by wind, involving the formation of yardangs. The current landscape of the studied hills is the result of the succession of a period characterized by the deposition of windblown sediment linked to the cultivated fields and a period of aeolian erosion linked to the end of agricultural activitiesLe désert libyque est l’une des régions les plus arides du monde. En raison de l’extrême rareté des précipitations (moins de1mm de précipitations annuelles moyennes par endroit) et de la quantité de sédiment mobilisable, les processus éoliens constituent le principal facteur de morphogénèse. Des études paléoenvironnementales (Wendorf et Schild, 1980 ; Sanlaville, 1997; Brookes, 2003 ; Bubenzer et Riemer, 2007) ont montré que l’hyperaridité s’est installée progressivement entre 5800 BP (fin de la dernière pulsation humide) et 4500 BP. La prépondérance des phénomènes éoliens est donc ancienne. Durant l’Holocène, les dynamiques et formations éoliennes ont fonctionné pour les hommes à la fois comme contrainte (ensablement, érosion) et comme ressource (maintien de l’humidité, dépôts cultivables). Les prospections géomorphologiques et géoarchéologiques de la région de Douch, située dans le sud de la dépression de Kharga, ont mis en évidence la présence de dépôts de sédiments fins sur des versants ne correspondant ni aux dépôts de sources artésiennes signalés par Bousquet (1996) ni aux dépôts de playas abonda...

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