Hydrological response of an east-Saharan palaeolake (NW Sudan) to early-Holocene climate

Abstract

We present a palaeolimnological record in western Nubia (NW Sudan, eastern Sahara) isolated from large-scale artesian systems and thus reflecting hydrological changes resulting from local rainfall. Past changes in lake water chemistry and water depth are interpreted by combining results from biological indicators (diatoms, ostracodes and charophytes) with geochemical and stable oxygen and carbon isotope data. Palaeolake Gureinat existed from ~10.9 cal. ka BP until at least 7.1 cal. ka BP and is devided into five lake phases. For the first two millennia the lake was shallow and fluctuating salinity conditions prevailed (500 to 3000 μS/cm). After ~8.7 cal. ka BP, the lake level rose, waters became fresh to oligosaline, and the lake had a minimum depth of at least 8 m. Both transgressive and stable lake phases were punctuated by at least three drops in lake level with complete desiccation at around 10.9 and 8.9 cal. ka BP. The third of these regressions may be coeval with the 8.2 ka climatic event. Sediments younger than 7.1 cal. ka BP representing the mid-Holocene fading of the wet phase were removed by deflation. This record shows that lakes in the eastern Sahara registered short-term climatic events, as long as they were isolated from large-scale artesian groundwater systems. Consequently, even in this continental region, early-Holocene climatic fluctuations affected water levels and salinities of hydrologically isolated lake systems.