## 4 Paleolakes and Groundwater
### Hypothetical Paleolake between Kharga and Toshka
In addition to the explored localities, the later phase of the Early Neolithic is attested at numerous unexplored basins and represents the most common Holocene occupation in the depression [29]. In the Middle Holocene (after 8200 BP), settlements are rare during the Middle Neolithic (\(\sim\)7100-6600 bp) and include only two more substantial and other smaller occupations left behind by highly mobile mixed pastoralists in three basins (nos. 7, 11, 12), but the evidence is difficult to evaluate due to severe aeolian erosion after this humid phase. Subsequently, there is a clear reduction in settlement between the Late (\(\sim\)6500-5800 bp) and Final (\(\sim\)5700-4500 bp) Neolithic between Kiseiba and Toshka from west to east, towards the Nile, with only three basins of five reoccupied during the latter phase. The characteristic of the remains (mostly short-lived camps) in these three basins (nos. 2, 11, 12) suggests a rather mobile lifestyle, with the locations serving as fixed points in otherwise mobile landscapes and as places of ceremonies (Nabta Playa) and burials (Ramlah Playa) for otherwise dispersed communities [29; 55]. All three are located at different elevations (see Table 1), and it is possible that the presence of a conspicuous mountain (_gebel_ in Arabic) in each of these areas (Bargat El-Shab, Gebel Nabta, Gebel Ramlah, respectively) might have been decisive for the selection of these areas for occupation in addition to the presence of subsurface water. For the first time during the Final Neolithic, small artefact concentrations attest to ephemeral occupation also in the vicinity of the modern wells (_bir_ in Arabic) at Bir Tarfawi and Bir Sahara and near Bir Safsaf situated further to the west (see Figure 19 for the locations of these wells). Second, there was a medium-term variation in the levels of the lake(s), with expansion of the lake(s) during the humid interphases (each lasting between \(\sim\)350 and 1200 years) and their contraction (or even desiccation) during the arid phases of 100 to 150 years that punctuate the regional chronost stratigraphic sequence [29]. Furthermore, the presence of remains of occupation from the same phase both near the edges of the playas and close to the centers of the playas and on the playa silts, where they could be placed only after (partial) contraction of the lake(s), suggests short-term fluctuations within individual humid phases, related both to differences between wet and dry parts of each year as well as inter-annual variation in the amount of rainfall [27; 29]. Although the Early and Middle Holocene was a period of a substantial climatic amelioration (as compared with the late Upper Pleistocene and most of the Late Holocene), it was still comparatively dry, with annual precipitation equating to 100-200 mm even during the climatic optimum [29]. Rains constituted the main source of water for the playa lakes which occupied the low-lying deflational basins that dot the surface of the Kiseiba-Toshka depression and which drained comparatively large areas in some cases (e.g., Nabta Playa, ca. 1500 km\({}^{2}\)). In this connection, the absence of Early and Middle Holocene sediments and any substantial occupations at Bir Sahara and Bir Tarfawi, two deflational basins with evidence of robust occupation during the Lower and Middle Paleolithic [27], could be of interest. Nevertheless, despite the comparative closeness of the Toshka-Kiseiba depression to the Nile, no direct evidence for high Nile floods contributing water to the local Holocene lake(s) has been brought to light so far--the remains of fish and Nile bivalves are extremely rare in this area and most likely constitute imports rather than evidence for overflow of the Nile [27; 29]. Interestingly, the influx of water from the Nile through the Toshka spillway was recently suggested as one of the sources of water for a large Holocene lake reconstructed in the northern part of our research area--in the Kharga Oasis.