The oxygen and carbon isotopic records in Holocene freshwater mollusc shells from the faiyum paleolakes, egypt: Their paloenvironmental and paleoclimatic implications

Stable oxygen and carbon isotopes of freshwater mollusc shells from a sequence of dated palaeolake deposits in the Faiyum Depression, Egypt, provide an outline record of lake development during the Holocene. It is argued that the carbonate O18 record provides a proxy for climate change and that the isotope changes are driven by variations in monsoon precipitation in Nile headwaters and in local evaporation processes. Shells from sediments dated to ca. 10,000 to 7700 cal BP had low values for oxygen and carbon isotopes indicating higher precipitation in the local area and intensified monsoonal activity, leading to higher Nile flood discharge and flooding of the entire Faiyum Depression. This was followed by a transitional period characterized by marked variability but with precipitation on average less than before. From ca. 6000 to 4300 cal BP, precipitation was decreased until a dramatic reduction in Nile flood discharge occurred late in the fifth millennium BP. This reduction signalled the onset of arid conditions in the Faiyum, partly as a consequence of changes in Nile headwaters that was concomitant with declining lake levels in East Africa. Lake level decline in the Faiyum was further aggravated after 2700 BP as the Nile inflow further weaken and regulation increased.