Africa deserts

Fig. 7-6 Satellite observations of global reflectivity for January 1967-1970. White indicates areas of persistent cloudiness and relatively high precipitation, except for northern Africa where desert surface regions are highly reflective. (From US Air Force and US Department of Commerce (1971). "Global Atlas of Relative Cloud Cover," 1967-1970, Washington.)...

Although Australia has a smaller desert area than either Africa or Asia, among the continents it has the highest proportion of arid and semi-arid zones. In fact, aside from some humid and semi-humid areas on the eastern, northern and south-western fringes of the continent, the core of the continent is arid or semi-arid. 

On a desert surface with little or no protection from vegetation, the effects of wind action may be important. Because of variations in atmospheric pressure, winds are often very strong, especially during the day. Some of these winds occur at more or less fixed periods in the year and get special names harmattan (south of the Sahara), sirocco (North Africa and the Western Mediterranean), chamsin (the Middle East), etc. 

The proportion of areas with different precipitation rates varies from continent to continent. For instance, different arid ecosystems, from Dry Savanna to Extra-Dry Desert, are predominant in India and Australia. To a lesser degree these ecosystems occur in Central and South America. In an equatorial belt of Africa, the distribution of areas with different precipitation is shown in Table 1. 

Cold periods in the north meant drought to Saharan Africa and India. About 5,000 years ago a sudden drying spell changed the Sahara from a green region spotted with lakes to a hot sandy desert. 

One outstanding example of the role of pesticides in technical assistance is in the control of the desert locust in the Near East, South Asia, and Africa. Since April 1951, when the United States Government received a request to assist the Government of Iran in one of its worst locust invasions in 80 years, a locust-control... 

Most of the aeolian input of trace metals is in particulate form as weathered rocks and soil. The deposition patterns on the sea surface tend to follow those of the major winds bands, with deserts being the primary source regions (Figure 11.4a). As shown in Figure 11.4b, this results in high deposition to the surfece waters immediately downwind of the arid regions of Africa, the Arabian Peninsula, Central Asia, Australia, and... 

As shown in Figure 14.8, kaolinite concentrations are highest in tropical and equatorial latitudes, particiflarly off the western coasts of North Africa and Australia (>40%) and the northeastern coasts of Australia and South America (30%). The first two are the result of aeolian transport by the Trade Winds from the Saharan and Australian deserts, respectively. The other two are the result of river input from the eastern Australian continent and the Amazon River. 

The morama bean is an underutilized leguminous oilseed native to the Kalahari Desert and neighboring sandy regions of Botswana, Namibia, and South Africa (Limpopo, North-West, Gauteng, and Northern Cape provinces), and forms part of the diet of the indigenous population in these countries. It is also known as gemsbok bean. 

About the same time that meteorites were found in Antarctica, an important collection of meteorites was being put together in Roosevelt County, New Mexico. Over a period from 1966 to 1972, several meteorite hunters collected 140 meteorite specimens representing about 100 separate fall events. This collection demonstrated another way for nature to concentrate meteorites. The meteorites in Roosevelt County were found in blowout areas where up to a meter of soil had been blown away by wind, leaving meteorites in plain view on the hardpan surface. Based on this experience, systematic and successful searches of desert areas in Western Australia have been carried out. Subsequently, the deserts of North Africa have turned out to be especially prolific sources of meteorites. The shifting desert sands expose meteorites that have accumulated over thousands of years. The meteorites are collected by nomads and sold to western collectors. Although most desert meteorites are weathered to some degree, new and rare meteorite classes have been discovered. 

The Apollo astronauts returned 382 kg of lunar sample to Earth, and this collection was supplemented by 326 g of soil samples collected by the Soviet Luna landers. The first lunar meteorite was found in 1982 in Antarctica. Since that time, over 120 lunar meteorites representing about 60 different fall events have been collected. The total mass of these meteorites is -48 kg. About one-third of these meteorites were recovered in Antarctica by American and Japanese teams, and most of the rest were recovered in the deserts of North Africa and Oman. The lunar meteorites have significantly expanded the areas of the Moon from which we have samples. 

Thousands of meteorites have also been recovered from the deserts of North Africa. Terrestrial ages of these meteorites extend out to 50 000 years and again the number of meteorites shows a rough exponential decrease with age. The mean residence time inferred for these meteorites is 12 000 years. 

King Ptolemaeus discovered salt also in the vicinity of Pelusium when he encamped there, a circumstance which induced other persons to seek and discover it in the scorched tracts that lie between Egypt and Arabia, beneath the sands. In the same manner, too, it has been found in the thirsting deserts of Africa as far as the oracle of Ilam-mon. 48... 

The Tsodilo Hills World Heritage Site is located in northwestern Botswana, in the Kalahari Desert, about 40 km from the Okavango River and is surrounded by relict linear sand dunes. This is one of the most interesting archaeological localities in southern Africa, in part because hills in the region are rare, the nearest to Tsodilo being about 200 km away. Evidence of human activity at the... 

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). 

As for the possible use of chemical weapons during operations in North Africa, climatic conditions accentuated one of the principal limitations of offensive chemical warfare, namely its dependence on the weather. No doubt, weapons intended for desert conditions could have been developed, but there was no great pressure to do so. The British, however, did maintain chemical warfare depots in Egypt, but the threat of enemy retaliation in kind against the United Kingdom provided an overriding sanction against their use. 

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

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