PALEOHYDROLOGY AND PALEOCLIMATOLOGY OFF NORTHWEST AFRICA DURING THE LAST GLACIAL INTERGLACIAL TRANSITION AND THE HOLOCENE - PALYNOLOGICAL EVIDENCES

Pollen and dinoflagellate cyst analyses of a deep-sea core located off Morocco provide a continuous record of paleoclimatic and paleohydrological change off Northwestern Africa since the last glacial episode. The stratigraphy is given by isotopic analysis (deltaO-18) of planktonic foraminifera, which shows a two-step deglaciation. Xeric conditions on the adjacent land, marked by the increase of steppe taxa (Artemisia, Chenopodiaceae/Amaranthaceae, Ephedra), and the development of the montane taxon, Cedrus atlantica are observed before Termination IA and during the Younger Dryas. These intervals are also marked by a high abundance of Pinus pollen grains, which indicates a strengthening of the northeastern (NE) trade winds. Variations of the surface water temperatures are shown by the fluctuations of dinoflagellate cyst assemblages which reflect a cooling of the surface waters during Termination IA and the Younger Dryas episode. Intensification of the upwelling system off Morocco resulting from enhanced trade winds occurred during these two key-periods. Quercus forests, which are an important part of the present-day vegetation of the Maghreb region, developed around 8500 yr B.P. Dinoflagellate cyst assemblages suggest that present-day oceanic conditions were established during this period.