Pollen and hydrological evidence for the interpretation of past climates in tropical west Africa during the holocene

International audiencePaleohydrological and palynological data from the three major ecoclimatic zones in modem tropical west Africa -- the Guineo- Sudanian, Sahelian and Saharan -- have been summarized to provide a 12,000 year history of paleoclimatic variation. On the basis of 54 limnological sites and 16 pollen sequences, past rainfall patterns can be distinguished with a 500 year resolution. Paleohydrological data indicate several periods with higher rainfall than present. Those at 9.5 ka-7 ka BP and 4 ka-2.5 ka BP occurred in both the Sahelian and Saharan zones. Two abrupt changes in the vegetation are evident in the palynological data, and these confirm the importance of hydrological fluctuations. At 9 ka BP, the vegetation suddenly responded to an abundant increase in rainfall. At 2 ka BP, the vegetation changed quickly to its modern distribution in response to generally drier conditions. Although evidence exists for a temperature increase at 9 ka BP and increased seasonality in precipitation at 7.5 ka BP, the details regarding these events must be refined