A New Insight of the Sahara Formation and Paleoclimate Evidence

Abstract:

Six thousand years ago, the Sahara was lush and green. About 5700 years ago, the Green Sahara suddenly started to wither. The wilting began in the standalone Great Chotts Basin, which is in the rain shadow of the Atlas Mountain range. When the water cycle stability in this basin was broken, the Great Chott Lakes dried quickly and the strong rain shadow effect became fully active, triggering desert formation. The desert expanded east and south, like a spreading wildfire powered by the westerlies and trade winds.

The sudden drying of the Green Sahara occurred with a net output of a huge amount of water vapor – rivers became empty, megalakes vaporized, surface water dried up, the groundwater table sank, air humidity dropped, and vegetation withered. All these contributed to the water losses from the northwest Sahara around 5650 BP. This large amount of net water output in a very short time must have been felt in the downwind surrounding areas as additional rainfalls and instabilities. Some time-series paleoclimate records are selected from publications to show the likely signals reflecting the water vapor spillover corresponding to the drying start of the Sahara.

The destabilization led to desertification and aridification in North Africa, West Asia, and the Mediterranean which have continued synchronously until this day. This process spans and affects most of human history as we know it, including the prosperity and desolation of Mesopotamia, the rise and fall of Egypt, and the civilization shifts from east to west across the Mediterranean and the Atlantic. This presentation shows the step-by-step spread of the Sahara desert and its impact on West Asian and the Mediterranean regions, with corroborating archaeological records and paleoclimate data.