At about 18,000 ybp (Late Pleistocene, at the height of the last major glacial advance), the Sahara/Sahel boundary lay at about 10°N latitude. Worldwide temperatures were significantly colder then than they are today. The Early Holocene, by contrast, was a time of warmer temperatures worldwide than either the Late Pleistocene or the modern era. The Early Holocene is commonly referred to as the "Early Holocene Climatic Optimum". on the geological record preserved in the Sahara from the Late Pleistocene, Early Holocene, and present, what might you predict for rainfall conditions in the Saharan region if global warming results in long-term worldwide temperature rise? Explain your answer, and provide evidence. Major Floristic Regions Of North Africa With Characteristic Pollen Taxa III – Saharan: desert with very limited pollen flora. Wadis typically contain Tamarix, Cornulaca, Calligonium, Fagonia, Salvadora, Maerua. IV – Sahelian: sparsely wooded desert grassland and thorny shrubland; grades into Saharan type in the and to Sudanian type in the south. Acacias of various species are ubiquitous (these are the thorny trees of the Sahel); also Commiphora, Blepharis, Balanites, and the shrub Tribulus. Rainfall determines which annual and perennial herbaceous plants and shrubs form the ground cover in a particular place. In the wetter parts of the Sahel, Graminae (grasses) and Cyperaceae (plants that grow on and stabilize inactive sand dunes) dominate. In drier (notice that I spelled this correctly this time, and didn’t use “dryer”, as in washer and dryer, like I did last time...) parts, Chenopodiaceae and Amaranthaceae dominate. V – Sudanian: wooded savanna and dry forest. The most common tree taxa are Grewia and Piliostigma. Other species of plants include Celtis integrifolia, Combretaceae, and Lannea. Team #1 Haijad, in the Taoudenni Depression
Taoudenni Depression is a internally-draining basin that currently contains no surface water, seeps, or springs. During the Holocene, however, many lakes and marshes developed in the area. The Taoudenni paleolake that we looked at earlier today is the most well-known of all of these lakes, because it was hypersaline and left behind salt deposits that have been exploited for centuries. The other lakes in the Depression do not have associated salt deposits. Haijad paleolake lies about 20 km southeast of Taoudenni paleolake (see the map at your table and at a slightly higher elevation. Modern rainfall in the Haijad area averages less than 5 mm per year, and vegetation is virtually non-existent. Team #2 Adrar Bous, in the Ténéré Desert Adrar Bous is large area of exposed bedrock located in the drifting sands of the Ténéré Desert about 65 km east of the Aïr Mountains of northern Niger. Locate Adrar Bous on your large map. Agorass N’Essoui paleolake that formed in a small depression on the south side of Adrar Bous. Modern rainfall in the Bous area averages well less than 50 mm per year, and vegetation is virtually Team #3 Selima, in northern Sudan Selima paleolake is on the margins of what is now an uninhabited oasis in northern Sudan near the Egyptian border. Selima paleolake lies just south of the “radar rivers” we talked about in class. Locate Selima on your large map of the Sahara. Before the end of the slave trade in 1898, Selima was a major watering place on the trade route from Darfur, Sudan to Assyut on the Nile. The oasis depression does not contain a modern lake. Selima is located within the Darb el Arba’in Desert (remember the "route of the 40 days" that goes from Assiut, Egypt through El Kharga and Baris Oases and west of the Toshka Depression into the Sudan). The area now averages less than 10 mm of rainfall per year. Team 4 Oyo, in northern Sudan