Late Holocene dune mobilizations in the northwestern Negev dunefield, Israel: A response to combined anthropogenic activity and short-term intensified windiness

The study of the effects of past climates on ancient cultures is usually based on geologic records pertaining to rainfall and temperature fluctuations and shifts. This study proposes a paradigm of anthropogenic activity and windiness fluctuations to explain aeolian sedimentation and dune mobilization in the northwestern (NW) Negev Desert dunefield (Israel). The proposed paradigm contributes a different approach to estimating the effect of climate changes on the unprecedented agricultural and urban settlement expansion during the late Roman to Early Islamic period in the northern and central Negev Desert. This study builds upon the late Holocene cluster of luminescence ages, coupled with analysis of archaeological finds and historical texts. Whereas the NW Negev dunefield was generally stable during the Holocene, intermittent dune mobilization during the late Holocene, at similar to 1.8 ka and mostly 1.4-1.1 ka (similar to 600-900 CE), are linked to periods of human occupation. The idea that the last glacial dune encroachments alone that formed the NW Negev dunefield is connected to cold-event windy climates that may have intensified East Mediterranean cyclonic winter storms, cannot explain the late Holocene dune mobilizations. A conceptual model indicates a connection between late Holocene dune mobilization, widespread anthropogenic occupation and activity, and windiness. Historic grazing and uprooting shrubs for fuel in the past by nomads and sedentary populations led to decimation of dune stabilizers, biogenic soil crusts and vegetation, causing dune erodibility and low-grade activity. Short-term events of amplified wind power in conjunction with periods of augmented anthropogenic activity that triggered major events of dune mobilization (elongation) and accretion have been preserved in the dune chronostratigraphy. Because they were short-lived, the dune mobilization events, corresponding windiness, and probable dustiness which were examined affected the northern Negev landscape differentially. However, they cannot be shown to have affected the environment sufficiently to influence the decline of the late Byzantine and Early Islam agricultural establishment. This study demonstrates the sensitivity of dunes in arid and semi-arid regions to a combination of local and short-term fluctuations in windiness at times of widespread grazing (anthropogenic activity). The results indicate that in similar future scenarios, sand mobilization may be similarly retriggered to varying degrees. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.