African environmental and climatic changes and the general atmospheric circulation in late pleistocene and holocene

Abstract

The paper describes the environmental and climatic changes which took place in Africa from the late Pleistocene through the Holocene and the general atmospheric circulation patterns which likely correspond to them. Three major periods are considered: (1) a period of aridity and dune building c. 20,000-12,000 B.P. in which the Sahara advanced considerably southward; (2) a moist, lacustrine period c. 10,000-8,000 B.P.; and (3) a second moist, lacustrine period toward c. 6,500-4,500 B.P. in which the entire Sahara desert contracted considerably. The prevailing atmospheric circulation patterns are theorized on the basis of corresponding changes of surface boundary conditions-primarily changing thermal character-and known dynamic behavior of the atmosphere.

Nutrient regime and upwelling in the northern Benguela since the middle Holocene in a global context - a multi-proxy approach

“…This is predominantly due to the fact that the Antarctic continent is much colder than the Arctic Ocean. Owing to the steeper temperature gradient, atmospheric circulation is more vigorous in the southern hemisphere (Nicholson & Flohn 1980). When the high northern latitudes cool (as a result of decreased NADW-production for instance), the thermal contrast between both hemispheres is minimised.…”

“…When the high northern latitudes cool (as a result of decreased NADW-production for instance), the thermal contrast between both hemispheres is minimised. This results in an equatorward displacement of the ITCZ (Nicholson & Flohn 1980), which further increases the southern hemisphere's temperature gradient (Tyson 1999) leading to an acceleration of the South Atlantic anticyclone in tandem with a strengthening of the eastern trade wind system (Rçhlemann et al 1999;Berger & Wefer 2002). Enhanced zonal circulation brings about upwelling-related cooling in eastern boundary current regions (e.g.…”

“…The resultant shift in the seasonal cycle of solar irradiance causes the thermal equator to strengthen (Tyson 1999;Lorenz et al 2006) and the high northern latitudes to cool (Kim & Schneider 2004). As a consequence, the ITCZ moves southward (Nicholson & Flohn 1980;Tyson 1999) and the trade wind system intensifies. Sediments from the upper continental slope off Walvis Bay (Summerhayes et al 1995) as well as different sites on the South African continent testify to the southward movement of the ITCZ over the last millennia (Tyson 1999;Scott & Woodborne 2007 and references therein).…”

Genesis and geometry of tilted blocks in the Theban Hills, near Luxor (Upper Egypt)

“…We interpreted the Valley of Colors Formation as a breccia that formed on the slopes of the Theban cliffs (see above). Said (1981Said ( , 1990 The youngest pluvials (< ~260 Ka) in Egypt are now well dated (Nicholson and Flohn, 1980;Brookes, 1993;Wendorf et al, 1993;Szabo et al, 1995;Crombie et al, 1997;Sultan et al, 1997;Churcher et al, 1999;Hamdan, 2000;Hoelzman et al, 2000;Nicoll, 2001;Smith et al, 2004;Kliendienst et al, 2006;Kieniewicz and Smith, 2007), but uncertainty remains as to the age of the older pluvials.…”

Historical and human dimensions of climate variability and water resource constraint in the Senegal River Valley

“…Extensive paleoclimatic research on Africa has documented broad cyclical shifts between wet and dry periods, with each cycle lasting several thousand years (see Nicholson & Flohn 1980, Street-Perrott & Harrison 1985, Cockroft et al 1987, Nicholson 1989. These broader temporal scales, however, are too coarse to detect variability on a shorter time horizon of years or decades.…”