Climatic changes along the northwestern African continental margin over the last 30 kyrs

Two sediment cores were investigated to study the regional climatic variability of the NW African upwelling over the-late Quaternary. Biomarker data and Sea Surface Temperatures (SSTs) predicted from alkenones at 25 degrees N and 21 degrees N-exhibited distinct features. The amplitude of the last deglaciation was estimated to 4.5 degrees C at 25 degrees N and 2-2.5 degrees C at 21 degrees N. At 25 degrees N, terrestrial and marine glacial inputs were higher than Holocene ones as a result of a strengthening of the trade winds:and intensification of oceanic production. In contrast, at 21 degrees N, warmer SSTs and lower organic carbon and alkenone productions during the last glacial suggest a regression of the upwelling and therefore a change of wind regime. Low glacial n-alkanols are consistent with the migration of the vegetation belt during the maximum of African aridity, while their decrease towards the core-top may be indicative of anthropogenic disturbances.