Ocean-surface and wind dynamics in the Atlantic Ocean off Northwest Africaduring the last 140 000 years

A combined micropaleontological analysis of core CAMEL-1, from the oligotro phic Sierra Leone Rise area, has allowed reconstruction of the paleoclimati c and paleoceanographic history of the region for the last 140 kyr. The rat io (N) between the Reticulofenestrids (coccolithophore indicators of relati vely high nutrient contents) versus Florisphaera profunda (a Lower Photic Z one coccolithophore) allowed us to monitor changes in the nutricline depth. These results were compared with those obtained for marine diatom and plan ktic foraminifera assemblages. Thus, a shallow nutricline/thermocline (and high productivity) during stages 6, 5d, 5b, 4 and 2 is proposed. This situa tion can be correlated with maximum input of biosiliceous wind-transported particles (fresh-water diatoms and phytoliths) in sea sediments. The shallo w nutricline is correlated with an intensification in Atlantic divergence a nd/or a North Equatorial Current intensification, when the NE trades were e nhanced for glacial and stadials (cold) periods. A clear precessional compo nent is observed in the surface water dynamics during the last climatic cyc le, minima in the N ratio coinciding with minimum insolation during winter in the Boreal hemisphere. During MIS 5, 4 and 2 dry conditions were dominan t on the northern African continent, corresponding to a more intense NE tra de wind circulation. The increased phytolith concentrations during MIS 6 ar e consistent with a more intense seasonality on the African continent. Cold planktic foraminifera assemblages show an eccentricity component linked to northern Ice-sheet dynamics. This situation is enhanced in isotope stages 6 and 3, due to an intensification in the North Equatorial Current. The ecc entricity component is also observed both in the N ratio (coccolithophore-r elated) and in the total planktic foraminifera. (C) 2000 Elsevier Science B .V. AM rights reserved.