SAHARAN WIND REGIMES TRACED BY THE SR-ND ISOTOPIC COMPOSITION OF SUBTROPICAL ATLANTIC SEDIMENTS - LAST GLACIAL MAXIMUM VS TODAY

New Nd-Sr isotopic data on the < 30 mu m lithic particles of surface a nd Last Glacial Maximum sediments recovered along the African margin b etween the Equator and the Gibraltar Strait are presented in combinati on with grain-size measurements. This < 30 mu m size fraction allows u s to eliminate any hemipelagic contribution that could occur in the co arser fractions. In the eolian fraction, both Sr and Nd isotopic trace rs reveal the same major northwestern origin (Mauritania, Mall, southe rn Algeria and Morocco). The Archaean formations of the western Sahara n shield could be the source of the very unradiogenic ratios observed here. The more southern regions (Senegal, Guinea) act only as secondar y sources. A similar pattern is observed for the LGM. Lithic particles are mostly transported by both Trade and Saharan Air Layer (SAL) wind s, along an approximate NE-SW axis; this main feature matches the 'sou thern plume', characterizing the dust transport observed during winter . No significant latitudinal shift of the belt winds is observed betwe en the LGM and today. At the LGM, however, dust fluxes were 2-4 times higher than today, leading to a more 'Archaean-type' imprint in the de posits. We do not observe any clear relationship between the latitudin al variability of the upwelling systems identified in this region at t he LGM and the location of the major wind systems. Both enhanced aridi ty on the continent and increased wind speed probably occurred togethe r over western tropical Africa during the Last Glacial period. (C) 199 8 Elsevier Science Ltd. All rights reserved.