Thursday, April 12, 2012

Climate at the end of the Pleistocene in Africa

Excerpted from "Africa's Climate in the Holocene" by A. T. Grove from The Archaeology of Africa edited by Thurston Shaw, Paul Sinclair, Bassey Andah and Alex Okpoko (Link)

"The low level of moraines on the high mountains of east Africa and Ethiopia indicate that snowlines were about 1000 m lower than at present in the last glaciation somewhere between about 30,000 and 14,000 years ago.  Temperatures were about 5 degrees C lower than they are now, assuming the precipitation was much the same at the present day, or as much as 9 degrees C lower, taking into account the fact that precipitation between about 18,000 and 14,000 BP seems to have been less than now.  The cooling has been confirmed by analysis of pollen from cores taken from mountain lakes which show that the altitudinal vegetation zones were also lowered by something like 1000 m (Maley, Caballe and Sita 1990).  The whole of Africa was significantly cooler than now.  Periglacial features in South Africa and Lesotho dating from the last glaciation suggest that temperature may have been as much as 14 degrees C lower (Lewis 1988) though a cooling of 5 degrees C is more usually accepted.  With the steeper latitudinal temperature gradients, winds were probably stronger than at present, and climatic conditions at both the southern and northern extremities of continent must have resembled those of Patagonia at the present day.  Northern Africa would have been subject to icy blasts in winter from notherwesterly winds sweeping across the sea-ice, which extended across the Atlantic as far south as Portugal."

   "Between the tropics, towards the end of the Pleistocene, the climate was generally much more arid than now.  Saharan dunes extended some 500 km south of their present limits, ponding back the Senegal, Upper Niger, Logone-Shari, and the Nile north of Khartoum.  Closed basins where lake sediments remained from earlier wetter conditions were deflated.  The entire upper Nile basin was an area of inland drainage with most of the floor of Lake Victoria dry as recently as 13,000 years ago.  However, the northern Kalahari some 18,000 to 15,000 years ago was occupied by great lakes flooding 40,000 square kilometers of the Makgadikgadi basin and extending from an enlarged Lake Ngami northeast to the Zambezi above the Victoira Falls (Shaw, Cooke & Thomas 1988)."

   "The glaciers on the east African mountains retreated about 15-14,000 BP (Hamilton 1982) and after an interval of a millennium or two lake levels began to rise in Tibesti, the Sahel, the White Nile valley south of Khartoum, southern Ethiopia and east Africa."

References:

Hamilton, A.  1973.  Environmental History of East Africa:  a study of the Quaternary.  London:  Academic Press.

Lewis, C. A. 1988.  Periglacial features in southern Africa:  a review, 1987.  Palaeoecology of Africa 19, 357-70.

Maley, J., G. Caballe & P. Sita 1990.  Etude d'un peuplement résiduel à basse altitude de Podocarpus latifolius sur le flanc congolais du massif du Chaillu:  implications paléoclimatiques et biogéographiques:  étude de la pluie pollinique actuelle.  In Paysages quaternaires de l'Afrique Centrale Atlantique, Lanfranchi, R. & D. Schwartz (eds.), 336-49.  Paris:  ORSTOM (Institut Français de Recherche Scientifique pour le Développement en Coorpération).

Shaw, P. A., H. J. Cooke & D. S. G. Thomas 1988.  Recent advances in the study of quaternary landforms in Botswana.  Palaeoecology of Africa 19, 15-26.

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