Desert Sahara

Most deserts and (semi-) arid regions occur between 10° and 35° latitude (e g. Sahara desert, Kalahari desert), in the interior parts of continents (e g. Australia, Gobi desert) and in rain shadow areas in fold belts (e.g. Peru, Nepal). Large parts of the arctic tundra receive less than 250 mm precipitation per annum and qualify as arid regions too (FAO, 2001). 

The area of actual erg and dune formation is delimited by the 150 mm/yr isohyet. This precipitation boundary appears to have shifted strongly in the recent past. Between 20,000 and 13,000 yr BP, the southern limit of active dune formation in the Sahara desert was 800 km south of its present position and most of the now sparely vegetated Sahelian zone was an area of active dune formation at that time. These dunes, mostly of the longitudinal type, are now fixed by vegetation, but their aeolian parentage is still obvious from their well-sorted material. A similar story can be told for the Kalahari sands. Overgrazing in recent times has reactivated aeolian transport in many regions with sands. 

To look at the vast Sahara desert is challenging from the point of view of biochemical research. What do all these never-born proteins (NBP) look like Are they only trivial variations of the proteins we already know, or - since there is such an immensity of them out there - would it be possible that some of them possess unknown structure and properties Have they not been produced simply and solely because of lack of time and bad luck - or due to the concomitance of some unknown and more subtle reasons (Of course we have many still unknown proteins on our Earth, but clearly the question of the never-born proteins has a quite different flavor, as they were never selected). 

Figure 14.35, for example, shows the real (n) and imaginary (k) parts of the index of refraction (17 = n — ki) of three samples of dust collected in the Barbados, but thought to be transported from the Sahara Desert (Volz, 1973), from Afghanistan (Sokolik et al., 1993), and from Whitehill, Texas, in the southwestern United States (Patterson, 1981), respectively (Sokolik et al., 1998). Regions of absorption in the infrared due to some common dust components are also shown the asymmetric C-O stretch of carbonate in calcite near 7 gm seen in the Texas dust, the asymmetric Si-O-Si... 

Dust Sahara Desert, Mali -17 mg kg 1 Holmes and Miller (2002)... 

Some very fine-grained atmospheric dust is capable of crossing oceans and accumulating on different continents. Dust samples from the Sahara Desert of North Africa (Mali) are known to contain at least 17 mg kg-1 of arsenic and may be responsible for contaminating cisterns as far west as the Caribbean and eastern USA ((Holmes and Miller, 2002 Shinn, 2001) Table 3.17). Dust in one cistern from St. John, US Virgin Islands, contained about 38 mg kg-1 of arsenic ((Holmes and Miller, 2002) Table 3.17). Arsenic from Sahara Desert dust may also accumulate in soils, sediments, water, and plants in Florida and surrounding areas (Holmes and Miller, 2002). 

Genetic control of D. melanogaster female components In 1989, Jallon and Pechine found a new type of quantitative hydrocarbon polymorphism specific to D. melanogaster females that affects the positions of double bonds in dienes. Although the double bonds remained at the same relative positions - separated by 2 carbons - they were more frequently located on carbons 5,9 in African flies and on carbons 7,11 in non-African flies. A study of 85 strains from around the world found the African type throughout the whole continent south of the Sahara Desert and in the West Indies and a small number of the Pacific islands. For example, the typical Tai females (Ivory Coast) has 30-40 percent 5,9-heptacosadiene (5,9-HD) and 2-6 percent 7,11-HD. Elsewhere... 

Africa south of the Atlas Mountains and Sahara Desert, Madagascar, and southern Arabia... 

Dinter, K., Paarmann, W., Peschke, K. and Arndt, E. (2002). Ecological, behavioural and chemical adaptations to ant predation in species of Thermophilum and Graphipterus (Coleoptera Carabidae) in the Sahara Desert. J. Arid Envir., 50, 267-286. 

Gehring, W.J., and R. Wehner (1995). Heat shock protein synthesis and thermotolerance in Cataglyphis, an ant from the Sahara desert. Proc. Natl. Acad. Sci. USA 92 2992-2998. 

Seven O, Dindar B, Aydemir S, Metin D, Ozinel MA, Icli S. Solar photocatalytic disinfection of a group bacteria and fungi aqueous suspensions withTi02, ZnO and Sahara desert dust. J Photochem Photobiol A Chem 2004 165 103-7. 

The dust showers which at various times have fallen in Italy and Sicily frequently contain grains of metallic iron. Similar grains are found in the sands of the Sahara desert, and it is not improbable that the dust showers referred to are terrestrial phenomena, the sand being transported from the desert by cyclones.1 In numerous other places small grains of iron have been found, and a terrestrial origin is ascribed to the metal in all of these cases. 

Many parts of the world experience monsoons to some extent. Probably the most famous are the Asian monsoons, which include the distinctly different monsoons that affect India, north China, and Japan, and south China and southeast Asia. Monsoons also affect portions of central Africa, where their rain is critical to supporting life in the area south of the Sahara Desert. Lesser monsoon circulations affect parts of the southwestern United States. These summer rainy periods bring much needed rain to the dry plateaus of Arizona and New Mexico. 

Santorini, G. 1992. The oldest representations of hallucinogenic mushrooms in the world (Sahara desert. 9000-7000 B.P.). Integration The Journal for Mind-Moving Plants and Kultur 2-3 69-78. 

Northern Algeria is one example. Today, the region is in stark contrast to its water-rich past. Once filled with rivers and lined with riparian woodlands, the Tassili plateau has now been engulfed by the expanding Sahara Desert. 

Just as primitive man learned quickly to determine which natural substances around him were beneficial and which were harmful, these are among the subjects he sought to depict in early art. There has been some speculation that rock paintings in the Sahara Desert dating back as many as 7000-9000 years ago are representations of hallucinogenic mushrooms, perhaps Psilocybe and Amanita. Some of these scenes show such mushrooms arrayed around dancers in ecstatic states. 

Some air pollutants are transported far beyond their points of release. For example, otherwise pristine areas have received acid precipitation originating from industrial smokestack emissions hundreds of miles away. Dust from the Sahara Desert in Africa has been detected in South America, and radioactive debris from the Chernobyl nuclear reactor meltdown has been deposited in countries throughout Europe. 

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