Late Quaternary palynology in marine sediments: A synthesis of the understanding of pollen distribution patterns in the NW African setting

• Published in: Quaternary international 2006-05, Vol.148 (1), p.29-44
• Main Authors: Hooghiemstra, Henry, Lézine, Anne-Marie, Leroy, Suzanne A.G., Dupont, Lydie, Marret, Fabienne
• Format: Article
• Language: English
• Subjects: Earth Sciences; Sciences of the Universe
• ISSN: 1040-6182; 1873-4553
• DOI: 10.1016/j.quaint.2005.11.005

After a review of the first steps in marine palynology, we show that the understanding of the northwest African setting is crucial to evaluate the potential of marine palynological studies elsewhere. We studied distribution patterns of pollen grains in recent marine sediments off NW Africa and were able to clearly relate patterns to modern pollen source areas (vegetation belts) and operating transport systems (wind belts and ocean currents). In particular patterns of Quercus, Artemisia, Chenopodiaceae–Amaranthaceae, Ephedra, Gramineae, and wet forest trees are very indicative of the position of the vegetation belts on the adjacent continent. Aeolian pollen transport is carried out by the northeast trade winds and the African Easterly Jet (AEJ). In the rain forest belt transport of pollen and fern spores also occurs by rivers. A detailed comparison between recent pollen rain samples from terrestrial and marine sites between 21 and 12°N showed that the latitudinal range of vegetation belts is clearly reflected in the pollen samples of both environments. A migration of the southern border of the Sahara is reflected by the changing ratio between Chenopodiaceae–Amaranthaceae pollen from the desert and Gramineae pollen from the savannah belt. Distribution patterns of pollen for 9000 and 18,000 14C yr BP (last glacial maximum) time-slices, based on pollen records from eleven marine cores between Portugal and the Gulf of Guinea show significant latitudinal migrations of vegetation belts, but a stable position of the main wind trajectories. The AEJ had a stable position around 21°N. The belt with trade winds had a stable position from Morocco southwards. Changing vigour of the trade winds is clearly reflected by the patterns of isopollen contours and by changes in pollen influx records.