Résumé
Pollen analysis of a 12.8-m-long core (R96-I) from the southern basin of Lake Rukwa (Tanzania, 8 degrees S, 33 degrees E, 793 m a.s.l.) provides new information on the vegetation history of central eastern Africa and on lake level fluctuations in response to climate changes during the last 23,000 cal yr BP. Between 23,000 and 20,000 cal yr BP (the Last Glacial Maximum), the occurrence of open and poorly diversified local woodland and bushland around the lake, and the significant presence of modern regional afromontane forest components close to Lake Rukwa, indicate cooler and probably drier climatic conditions than today. The deglacial period, between 16,500 and 12,300 cal yr BP, characterised by a retreat of montane elements at higher altitudes on the plateau, under warmer conditions, synchronous with a progressive expansion of local more wooded formations, appears to be climatically transitional, but the permanence of swampy environments near the core site indicates that the lake remained low. From 12,100 cal yr BP, the maximum development and diversity of local woodland and bushland implies an increase in rainfall that persisted until 5500 cal yr BP. More humid conditions are confirmed by the lowest representation of aquatics registered in our pollen sequence, indicating that, during this period, Lake Rukwa was high. After 5500 cal yr BP, a deterioration of the regional and local arboreal cover, the large extension of grasses and of swampy environments near the core site, indicate the progressive establishment of drier conditions in the basin. The aridification trend intensified ca. 3500 cal yr BP toward modern conditions. These palaeobotanical reconstructions in the Lake Rukwa basin for the last 23,000 cal yr BP supplement those previously proposed in central eastern Africa between 4 degrees and 13 degrees S from more incomplete or less well age-constrained pollen sequences. Abstract Copyright (2005) Elsevier, B.V.