VEGETATION ZONES IN NW AFRICA DURING THE BRUNHES CHRON RECONSTRUCTED FROM MARINE PALYNOLOGICAL DATA

Six East Atlantic sites between 9-degrees and 35-degrees-N allow the reconstruction of the latitudinal position and extension of the NW African vegetation zones. During the last 0.7 Ma, the response of the vegetation to alternating glacial (dry) and interglacial (humid) climatic conditions has been recorded. The vegetation response to a climatic amelioration starts with the northward expansion of the tropical rain forest, followed by the northward shift of the Saharan-Sahelian boundary, and ends with the southward shift of the Saharan-Mediterranean transitional steppes and the expansion of the Mediterranean oak forests. Most sensitive is the reaction of the Saharan-Sahelian boundary to climatic change. Large shifts of the Saharan-Sahelian boundary seem to occur faster than small ones. Annual precipitation estimates for the latitude of Dakar (15-degrees-N) range from 100 to 1000 mm. At 24-degrees-N, yearly precipitation probably ranged from 0 to 150 mm. Smallest extent of the Guinean tropical rain forest probably occurred during the arid conditions of Isotope Stages 2 and 6 reducing the carbon fixation of these forests to a minimum. Large extent of the Guinean tropical rain forest occurred during most of the odd isotope stages (more humid interglacials).