The Saharan-Sahelian boundary during the Brunhes chron

Atmospheric circulation patterns over NW Africa are recognized in isopoll maps of offshore bottom sediments. Assuming that the atmospheric circulation model of the last glacial-interglacial transition, based on snapshots of three time-slices, holds for the entire Brunhes chron, the 0-7 My-long pollen record of ODP Site 658 has been interpreted. Fluctuating percentages and influx rates of pollen of Chenopodiaceae-Amaranthaceae, Poaceae, Cyperaceae, and savanna elements record a repeatedly shifting Saharan-Sahelian boundary between c. 14° and 23°N during the Brunhes chron. Most of the humid interglacials occured before 280 ka, and extreme glacial conditions are only found during the last 480 ka. Assumptions and possible conclusions are argued. A coherency between the pollen signal of Poaceae and that of Cyperaceae is demonstrated by cross-correlation and a distinct 42 ka periodicity suggests forcing by obliquity.