Eastern Sahara Research Articles

Mapping the mega paleodrainage basin using shuttle radar topography mission in Eastern Sahara and its impact on the new development projects in Southern Egypt

In the current study, the shuttle radar topography mission (SRTM) data, with ∼90 m horizontal resolution, were used to delineate the paleodrainage system and their mega basin extent in the East Sahara area. One mega-drainage basin has been detected, covering an area of 256 000 km2. It is classified into two sub mega basins. The Uweinate sub mega basin, which is composed of four main tributaries, collected water from a vast catchment region and drained eastward from the north, west, and southwest, starting at highland areas. The first subwatershed basin is in the northern plateau, south of the Abu-Balas area, with a total catchment area of 25 045 km2. The second subwatershed is in the Gilf Kebir plateau and has a total catchment area of 38 257 km2. The third subwatershed drains from the Uweinate highlands and has a catchment area of 46 154 km2. The fourth subwatershed, which is known in literature as Wadi Mokhtafi in its upper reach and Wadi Arid in its lower reach, drains the northwestern highlands of Sudan and has a total catchment area of 28 653 km2. The Tushka sub mega basin includes one watershed that drains from the northeast highlands of Sudan and has a total catchment area of 63 019 km2. The Uweinate and Tushka sub mega basins are joined together to the North of the Tushka depression, which drains northward toward the Kharga depression. This study indicates that the Eastern Sahara Mega Basin is a closed hydrological system independent of the other drainage systems, such as the Nile hydrosystem and the Qena Valley system. The present research illustrates the capability of the SRTM data in mapping the paleochannel networks, as well as estimate the catchment area and direction of the water flow. Finally, the study reveals that the four areas could be potentially used for different reclamation activities due to the ground water accumulations possibilities.

Y-chromosomal evidence of the cultural diffusion of agriculture in southeast Europe

The debate concerning the mechanisms underlying the prehistoric spread of farming to Southeast Europe is framed around the opposing roles of population movement and cultural diffusion. To investigate the possible involvement of local people during the transition of agriculture in the Balkans, we analysed patterns of Y-chromosome diversity in 1206 subjects from 17 population samples, mainly from Southeast Europe. Evidence from three Y-chromosome lineages, I-M423, E-V13 and J-M241, make it possible to distinguish between Holocene Mesolithic forager and subsequent Neolithic range expansions from the eastern Sahara and the Near East, respectively. In particular, whereas the Balkan microsatellite variation associated to J-M241 correlates with the Neolithic period, those related to E-V13 and I-M423 Balkan Y chromosomes are consistent with a late Mesolithic time frame. In addition, the low frequency and variance associated to I-M423 and E-V13 in Anatolia and the Middle East, support an European Mesolithic origin of these two clades. Thus, these Balkan Mesolithic foragers with their own autochthonous genetic signatures, were destined to become the earliest to adopt farming, when it was subsequently introduced by a cadre of migrating farmers from the Near East. These initial local converted farmers became the principal agents spreading this economy using maritime leapfrog colonization strategies in the Adriatic and transmitting the Neolithic cultural package to other adjacent Mesolithic populations. The ensuing range expansions of E-V13 and I-M423 parallel in space and time the diffusion of Neolithic Impressed Ware, thereby supporting a case of cultural diffusion using genetic evidence.

Non‐impact origin of the crater‐like structures in the Gilf Kebir area (Egypt): Implications for the geology of eastern Sahara

Abstract— Several small crater‐like structures occur in Gilf Kebir region (SW Egypt). It has been previously suggested that they could be the result of meteoritic impacts. Here we outline the results of our geological and geophysical survey in the area. The proposed impact origin for these structures is not supported by our observations and analyses, and we suggest an alternative interpretation. The crater‐like structures in Gilf Kebir area are likely related to endogenic processes typical of hydrothermal vent complexes in volcanic areas which may reflect the emplacement of subvolcanic intrusives.

Modeling mineral dust emissions from the Sahara desert using new surface properties and soil database

The present study investigates the mineral dust emissions and the occurrence of dust emission events over the Sahara desert from 1996 to 2001. Mineral dust emissions are simulated over a region extending from 16°N to 38°N and from 19°W to 40°E with a ° × ° spatial resolution. The input parameters required by the dust emission model are surface features data (aerodynamic roughness length, dry soil size distribution and texture for erodible soils), and meteorological surface data (mainly surface wind velocity and soil moisture). A map of the aerodynamic roughness lengths is established based on a composition of protrusion coefficients derived from the POLDER‐1 surface products. Soil dry size distribution and texture are derived from measurements performed on soil samples from desert areas, and from a soil map derived from a geomorphologic analysis of desert landscapes. Surface re‐analyzed meteorological databases (ERA‐40) of the European Centre for Medium range Weather Forecasts (ECMWF) are used. The influence of soil moisture on simulated dust emissions is quantified. The main Saharan dust sources identified during the 6‐year simulated period are in agreement with the previous studies based on in situ or satellite observations. The relevance of the simulated large dust sources and point sources (“hot spots”) is tested using aerosol indexes derived from satellite observations (TOMS Absorbing Aerosol Index and Infrared Dust Difference Index Meteosat). The Saharan dust emissions simulated from 1996 to 2001 range from 585 to 759 Tg a−1. The simulations show marked seasonal cycles with a maximum in summer for the western Sahara and in spring for the eastern Sahara. The interannual variability of dust emissions is pronounced in the eastern part of the Sahara while the emissions from the western Sahara are more regular over the studied period. The soil moisture does not noticeably affect the Saharan dust emissions, their seasonal cycle or their interannual variability, but it can partly control and limit the dust emissions in some parts of the northern desert margin, where the precipitation rates are higher. Our simulations also tend to confirm that the Sahara is the major terrestrial source of mineral dust.

The use of new elevation data (SRTM/ASTER) for the detection and morphometric quantification of Pleistocene megadunes (draa) in the eastern Sahara and the southern Namib

New freely available digital elevation data derived from the Shuttle Radar Topography Mission (SRTM-3) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) allow, for the first time, the use of area-wide high-resolution elevation models. They are useful for various investigations, especially in regions that are devoid of detailed topographic maps. In this contribution, the geomorphological, sedimentological, geochronological, and archaeological results of the Cologne Collaborative Research Centre ACACIA are presented, showing that the southern Great Sand Sea of Egypt (eastern Sahara) is composed of a complex dune pattern of Pleistocene megadunes (draa) and Holocene dunes. A conceptual model is presented suggesting draa, formed by a strong unimodal trade wind regime that acted, most probably, as helical roll-vortices. The draa differ conspicuously in their dimensions and in their evolution from the smaller longitudinal dunes, which arise from the recent bimodal wind regime. First results of comparative investigations in the southern Namib Erg (Namibia) yielded similar conditions and a synchronous landscape development. Based on these results, the second part of the paper evaluates the elevation data for both regions with respect to their availability for the determination of draa and dunes and the morphometric quantification of the draa. Due to their different resolution (SRTM-3: 90 m, ASTER: 30 m) and their different sensor technology (SRTM-3: radar, ASTER: stereo data), both models have assets and drawbacks but can complement each other. With the calculation of geomorphometric parameters (elevation, slope), the ASTER digital elevation model allows the location of the draa of the Great Sand Sea of Egypt, the quantification of their spatial distribution, size, volume, and consequently the Holocene dune movement. In conclusion, the resolution of the ASTER elevation model is applicable for quantitative analyses of well-defined morphological elements with altitudinal variations > 40–50 m. The volume estimation presented provides a tool for a realistic assessment of the sand mass balance of sand seas. This is not possible with the SRTM-3 model and generally impossible with both models if the altitudinal variation is < 20–30 m (e.g. the draa in the southern Namib Erg). As most of the world's ergs contain draa and dunes of respectable heights, the demonstrated methodology could be useful for further investigations concerning dune movement, desertification and climate change.

Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years

Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.

DEM‐optical‐radar data integration for palaeohydrological mapping in the northern Darfur, Sudan: implication for groundwater exploration

North‐western Sudan, as a part of the eastern Sahara, is among the driest places on earth. However, the region underwent drastic climatic changes through the alternation of dry and wet conditions in the past. During humid phases, when the rain was plentiful over a prolonged time period, the surface was veined by rivers and dotted by large lakes. The new Shuttle Radar Topography Mission data (SRTM ∼90 m) revealed a large endorheic drainage basin, which is centred by a large terminal palaeolake, in the northern Darfur State. The use of GIS methods allowed the delineation of the drainage basin and its associated palaeorivers. The SRTM data along with the Landsat (ETM+) and Radarsat‐1 images corroborate the presence of segments of palaeoshorelines associated with the palaeolake highstands. These constitute a convincing argument of the long‐term existence of a possible pre‐Holocene large water body in the region in the past. The remains of the highest palaeoshoreline have a constant altitude of 573±3 m asl. At its maximum extent, the mega Lake occupied an area of about 30 750 km2 (the same size as the Great Bear Lake, Canada's largest lake), which would have contained approximately 2530 km3 of water. This, ancestral lake, which we named the Northern Darfur Megalake (ND Megalake), represents indisputable evidence of the past pluvial conditions in the eastern Sahara. The discovered palaeoshorelines will have significant consequences for improving our knowledge of continental climate change and regional palaeohydorology, and should be taken into consideration in studies of past human habitation in the region. Much of the water carried by the Northern Darfur palaeorivers and the ND Megalake would have percolated into the underlying rocks feeding the Nubian Sandston aquifer. These findings show that the used approach of space‐data integration can help significantly in the groundwater exploration efforts in the Darfur region, where freshwater access is essential for refugee survival, and can be successfully adopted in other parts of Sudan and arid lands in general.

Holocene climatic change and human settlement between the central Sahara and the Nile Valley: Archaeological and geomorphological results

AbstractSupraregional investigations of the Holocene occupational history of the eastern Sahara west of the Nile combined with the study of climatic, environmental, and geomorphological archives were carried out in contrasting desert regions from the Mediterranean coast strip to Wadi Howar in Sudan. The research areas are located far away from groundwater influence and are therefore capable of indicating environmental changes. Climatic development in accordance with nearly 500 14C dates from archaeological sites indicates a Holocene optimum lasting from approximately 9500 B.P. till the beginning of the drying trend that set in about 6300 B.P. (9000–5300 cal. B.C.). Although the faunal and floral remains are arid types, they indicate slightly wetter conditions than today. Surface water was the key factor that influenced the adaptation strategies of the mobile hunter‐gatherers (and in some parts, the pastoralists) in the desert regions. Large episodic camp sites agglomerated at favorable drainage systems and water pools, and settlement patterns strongly correlate with the paleohydrological factors examined with remote sensing cartography, geomorphological work, and the analysis of digital elevation models. © 2007 Wiley Periodicals, Inc.

Fouille de la butte de FA 10 (Banc d'Arguin) et son apport à la connaissance de la culture épipaléolithique de Foum Arguin, nord-ouest du Sahara

The epipaleolithic culture of Foum Arguin stretched from the Oued Draa, in southern Morocco, to the Banc d’Arguin and from the Atlantic shore to the lowlands of northwestern Sahara in Mauritania. Its chronology is vague, located between the eighth and the seventh millenniums BP. It preceded a little the Neolithic, which followed it after 5500 BP on almost all the numerous habitats of this region. Thanks to several sites of the Banc d’Arguin, less plundered than most others, we have been able to define the lithic industry of this culture and to compare it with similar groups, notably those located in southern Morocco. This industry, very varied, is unique and very distinct from other known traditions of that time — for instance the Iberomaurusian and the Caspian. Thus the place of the populations of Foum Arguin in the Saharian cultures of the early Holocene is an essential topic. In particular it is necessary to investigate the possible similarities with central and eastern Sahara, where epipaleolithic or preneolithic cultures are known — yet badly understood and dated as shown by the confusion surrounding the notion of “Ounan point”.

An addendum to ‘Songbird migration across the Sahara: the non-stop hypothesis rejected!’

In our article on songbird migration across the western Sahara ([Schmaljohann et al . 2007][1]), we refrained from citing [Biebach et al .'s (2000)][2] radar study on songbird migration across the eastern Sahara. Our intention was not to enter into details and problems of quantifying bird migration

Radar topography data reveal drainage relics in the eastern Sahara

The Shuttle Radar Topographic Mission (SRTM) elevation data reveal segments of inactive drainage channel systems in the eastern Sahara. Four sites are investigated and their drainage networks are delineated and compared with processed Synthetic Aperture Radar (SAR) and Enhanced Thematic Mapper Plus (ETM+) images. These include parts of the drainage lines that lead to the Kufra Oasis in Libya; the eastern Gilf Kebir drainage system that straddles the border region between Egypt and Sudan; the lower reach of Wadi Howar, the extinct western Nile tributary in Sudan; and a reversed flow channel of Wadi Kubbaniya northwest of Aswan in Egypt. These features are delineated using SRTM data and a Geographic Information System (GIS) hydrologic routine. The results show that the SRTM signals penetrate the desert‐sandy surfaces and map ancient drainage systems in the same way as SAR. The study also demonstrates that SRTM data can be used to confirm or modify pathways of channel courses mapped from radar images alone. Because of this capability, it is also recommended that SRTM data be used in place of GTOPO30 elevation data in hydrologic modelling of sand‐covered deserts.

The application of radar topographic data to mapping of a mega-paleodrainage in the Eastern Sahara

The recently available Shuttle Radar Topography Mission (SRTM) data, with ∼90 m horizontal resolution, are used to delineate the entire Tushka mega-watershed. It is calculated that the watershed covers an area of 150 000 km 2 and composed of four subwatersheds. This study indicates that the Tushka basin is a closed hydrological system independent of the Nile hydro-system, the Qena Valley system, and the Chad basin as well. More importantly, the study demonstrates that this basin drains northeasterly toward the westernmost of the recently flooded lakes in the Tushka depression, west of Lake Nasser. The hydrological activities within the basin resulted in the formation of the largest paleo-lake deposit in Egypt at Bir-Tarfawi. The vast sand sheets that cover the Tushka basin accentuate the theory of El-Baz [1982. Genesis of the Great Sand Sea, Western Desert of Egypt. International Association of Sediment, 11th International Conference, Hamilton, Ontario, Canada, p. 68], which relates sand accumulations within basins in today's deserts to previous fluvial activities. The present study illustrates the capability of the SRTM in penetrating desert sand surfaces and mapping the ancient drainage networks, which remarkably correlate with subsurface channels detected in Radarsat-1 images.

Radar data contributes to groundwater exploration in the eastern Sahara

Radar data contributes to groundwater exploration in the eastern Sahara

Quantitative reconstructions of annual rainfall in Africa 6000 years ago: Model‐data comparison

This paper provides the first set of quantitative reconstructions of annual precipitation for mid‐Holocene Africa, based on pollen data. The estimates of precipitation are based on 85 pollen sites 14C dated at 6000 ± 500 years B.P and distributed over the whole of Africa. To improve the reliability of the pollen‐based climate reconstruction, two methods are used: the “modern analogues technique” (MAT) and the “plant functional types” (PFT) methods. We then conduct a model‐data comparison for five distinct regions, allowing an evaluation of model outputs (the Sahara‐Sahel, the eastern Sahara, western equatorial Africa, East Africa, and Madagascar). The pollen‐inferred reconstructions are compared with 21 mid‐Holocene simulations yielded by Atmospheric General Circulation Models (AGCMs), and coupled ocean‐atmosphere‐vegetation models (OAVGCMs). The large‐scale feature of the hydrological changes is shown to be well captured by most of the models. Data show that during the mid‐Holocene, the Sahara was considerably wetter than today (+200 to +700 mm/yr). The results reinforce the conclusion that the AGCMs significantly underestimate this precipitation increase in the Sahara whereas the OAVGCM simulations are in accordance with the data. Our results show that vegetation and ocean feedbacks do not have a strong impact in the intertropical zone and that models fail to properly reproduce the climatic conditions in East Africa and Madagascar. The model‐data comparison also suggests that the lengthening of the dry season during boreal winter in the west equatorial region is a robust feature although the pollen‐based reconstruction shows no change or only slight drying there.

The Nubian Aquifer in Southwest Egypt

Synthetic Aperture Radar (SAR) images, and topographic and groundwater data are used to understand heterogeneities of the Nubian Aquifer between 20–24.5°N and 25–32°E in southwest Egypt. New fluvial and structural interpretations emphasize that the desert landscape was produced by fluvial action, including newly mapped alluvial fans. In central locations, braided channels are spatially aligned with a NE structural trend, suggesting preferential water flow paths that are consistent with the local direction of groundwater flow. The alluvial fans and structurally enclosed channels coincide with gentle slopes and optimal recharge conditions (1–5%) derived from the new Shuttle Radar Topographic Mission (SRTM) slope map, indicating that these areas have high groundwater potential. The SAR interpretations are correlated with anomalies observed in groundwater data from 383 wells. Results suggest a relationship between the spatial organization of fluvial and structural features and the occurrence of low-salinity groundwater. Low-salinity water exists adjacent to the alluvial fans and in SW reaches of the structurally enclosed channels. Wells in the vicinity of structures contain low-salinity water, emphasizing that knowledge of structural features is essential to understand groundwater flow paths. The new approach is cost effective and noninvasive and can be applied throughout the eastern Sahara to assist in resource management decisions and support the much needed agricultural expansion.

Luminescence dating and archaeology of Holocene fluvio-lacustrine sediments of Abu Tartur, Eastern Sahara

Endorheic basins, filled by a rhythmic stratification of fluvio-lacustrine sediments, are useful archives for studying the interaction of palaeoenvironment and prehistoric development. Archaeological evidence indicates an occupational maximum during the Early to Mid-Holocene humid phase that can be linked to geochronological dates. A wadi has cut these sediments and a wadi profile of about 6 m was sampled for luminescence dating. Palaeodose estimates are based on single aliquot measurements of the sand-sized quartz fraction using the regenerative dose technique. The comparison of equivalent dose results from different aliquot sizes (<100 and >1000 grains) provides interesting insights into heterogeneous degrees of bleaching. Problems arising from substantial variations in environmental dose rates of such heterogeneous sediments are discussed. The luminescence ages indicate two major phases of deposition, both of Holocene age. The lower 2 m of sediments were deposited about 9400 years ago. The sedimentation of the upper 2 m started about 7200 and terminated around 6300 years ago. Radiocarbon ages of charcoals contained in the upper part of the section disagree with that OSL dating. This discrepancy is explained by re-deposition of the charcoal fragments.

Saharan dust intrusions in the Mediterranean area: Three years of Raman lidar measurements

A multiyear climatological study of Saharan dust intrusions in the central Mediterranean in terms of aerosol optical parameters vertical profiles is carried out for the first time. Observations are performed at Istituto di Metodologie per l'Analisi Ambientale (IMAA) Raman/elastic lidar station located in Tito Scalo, Potenza (40°36′N, 15°44′E), from May 2000 to April 2003, in the framework of European Aerosol Research Lidar Network (EARLINET). Desert dust aerosols are observed between 1.8 and 9 km in 112 days. Mean values within the desert dust layer of 76 Mm−1, 1.0 Mm−1 sr−1 and 0.54 Mm−1 sr−1 are observed for aerosol extinction at 355 nm and aerosol backscatter at 355 and 532 nm. Desert dust layer optical depth at 355 nm ranges between 0.001 and 0.68, with a mean of 0.13. The source origin is the central Sahara in about 65% of the cases, the western Sahara in about 31%, and only in four cases the eastern Sahara. The most extended database of Saharan dust lidar ratio data was collected: Values range between 6 and 126 sr following a 3‐modal Gaussian distribution centered at 22, 37 and 57 sr. A mean value of 37 sr is found around the center of the Saharan dust layer. At its extremes, where dust particles are mixed to PBL and free troposphere background aerosols, a mean value of 57 sr is found. Finally, low lidar ratio values of about 22 sr are observed when large amount of dust is transported at low altitudes over the Mediterranean Sea.

Climate-Controlled Holocene Occupation in the Sahara: Motor of Africa's Evolution

Radiocarbon data from 150 archaeological excavations in the now hyper-arid Eastern Sahara of Egypt, Sudan, Libya, and Chad reveal close links between climatic variations and prehistoric occupation during the past 12,000 years. Synoptic multiple-indicator views for major time slices demonstrate the transition from initial settlement after the sudden onset of humid conditions at 8500 B.C.E. to the exodus resulting from gradual desiccation since 5300 B.C.E. Southward shifting of the desert margin helped trigger the emergence of pharaonic civilization along the Nile, influenced the spread of pastoralism throughout the continent, and affects sub-Saharan Africa to the present day.

Revisiting the Age of the Sahara Desert

In their Brevia “The age of the Sahara Desert” (10 Feb., p. 821), M. Schuster et al. state that the oldest terrestrial records for desert conditions in the Sahara are only 86 thousand years old (ka). This is not correct. For example, U/Th dating from the Eastern Sahara gives dates of >300 ka ([1

Use of radar data to delineate palaeodrainage leading to the Kufra Oasis in the eastern Sahara

Radar-revealed palaeodrainage systems are analyzed using Radarsat-1 data covering the Kufra Oasis and parts of southeastern Libya and northern Chad. The analysis shows that two mega fluvial systems exist to the south of the Kufra Oasis. Along the western one, a mappable polygonal fluvial unit covers 13,628 km 2 in area, with the entire watershed extending north beyond the borders of the present 347,160 km 2 study area. The eastern system covers 4321 km 2 in area and is morphologically similar to the Amazon’s Rio Negro, although the African channel is four times wider. The enormity of these features provides some explanation as to why continuous extraction of groundwater in the oasis and nearby circular irrigation farms is possible. Clearly, these mega fluvial systems formed at some time in the past when rain was plentiful over a protracted time period.