POLLEN ANALYSIS OF DEEP-SEA CORE IN THE GULF OF GUINEA - VEGETATION AND CLIMATIC CHANGES DURING THE LAST 225,000 YEARS BP

Pollen analysis of a deep-sea core off the Ivory Coast continental margin (at about 4-degrees-N, 4-degrees-W) shows thirteen pollen zones, correlated with isotopic deltaO-18 stratigraphy of the same sequence over the last 225,000 yr B.P. This study, based on the present regional phytogeographic groups (north of the Gulf of Guinea), determines seven pollen groups considered as the best ecological indicators. These groups, which belong to the Mangrove and Guineo-Congolian, Sudanian, Sahelo-Saharan zones, show an abundant continental flora. Whereas isotopic stages 6, 4 and 2 are considered dry stages and show an increase of the Gramineae, Sahelo-Saharan and Sudanian elements, isotopic stages 7, 5, 3 and 1 are considered humid stages with an increase of the Mangrove and Guinean rain forest. Mangrove pollen percentages provide a record of global humidity and shoreline variations; the rain forest record indicates global humidity. During Stage 5e (warm and humid Interglacial) the Rain Forest expanded maximally (around 124,000 yr B.P.). During the cool intervals 5d and 5b, Podocarpus pollen percentages increased, revealing the occurrence of important paleoclimatic events. The abundance of Podocarpus during interstadials 5d and 5b suggests that there was a broad geographical distribution of this species in western Africa; such former abundance is in contrast to its present-day distribution, reduced to the mountainous areas of Cameroon and Sao Tome Island.