Abstract
The termination of the African Humid Period in northeastern Africa during the early Holocene was marked by the southward migration of the rain belt and the disappearance of the Green Sahara. This interval of drastic environmental changes was also marked by the initiation of food production by North African hunter-gatherer populations and thus provides critical information on human-environment relationships. However, existing records of regional climatic and environmental changes exhibit large differences in timing and modes of the wet/dry transition at the end of the African Humid Period. Here we present independent records of changes in river runoff, vegetation and erosion in the Nile River watershed during the Holocene obtained from a unique sedimentary sequence on the Nile River fan using organic and inorganic proxy data. This high-resolution reconstruction allows to examine the phase relationship between the changes of these three parameters and provides a detailed picture of the environmental conditions during the Paleolithic/Neolithic transition. The data show that river runoff decreased gradually during the wet/arid transition at the end of the AHP whereas rapid shifts of vegetation and erosion occurred earlier between 8.7 and ∼6 ka BP. These asynchronous changes are compared to other regional records and provide new insights into the threshold responses of the environment to climatic changes. Our record demonstrates that the degradation of the environment in northeastern Africa was more abrupt and occurred earlier than previously thought and may have accelerated the process of domestication in order to secure sustainable food resources for the Neolithic African populations.
Highlights
The Sahara Desert is presently one of the most arid regions on Earth, and experienced some of the most drastic environmental changes of the past 10,000 years
The d18O of the surface seawater (d18OSW) values obtained for Late Holocene sediments are similar to the presentday eastern Mediterranean seawater d18O [33] (S1c Fig.) and the values for the Holocene fall in a similar range and follow a trend similar to those previously obtained in the Levantine Basin (,2 to 21%) [29]
These various effects cannot be deciphered but they all have the same effect on the d18OSW: a decrease in d18OSW can be interpreted as a decrease in salinity, and/or as an increase in d18O of the freshwater end-member
Summary
The Sahara Desert is presently one of the most arid regions on Earth, and experienced some of the most drastic environmental changes of the past 10,000 years. Due to decreasing summer insolation in the intertropical zone (i.e., between 20 ̊S and 20 ̊N), the rain belt and the vegetation receded to the South and forced the human populations to leave the Sahara at ,6.5 ka BP [2, 3]. It was during this period of large environmental changes that major societal reorganizations occurred, such as the implementation of pastoralism and agriculture into human lives, as well as the development of collective rituals and religious beliefs [3, 4]. The role of the major local environmental changes and their influence on these different models of food production has not yet been clearly determined
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