Changes in style and intensity of production in the Southeastern Atlantic over the last 70,000yr

Accomplishing reliable paleo-reconstructions of productivity and upwelling conditions in eastern boundary current systems requires the use of cores collected in a basin-wide spatial pattern. Based on diatom assemblage analysis and the concentration and the bulk biogenic components of three gravity cores recovered from the Benguela Upwelling System (BUS) between 19 degree and 25 degree S, I describe rapid paleoceanographic changes that occurred during the last 70ka B.P. in the southeastern Atlantic. The pattern of biogenic production and accumulation differs to varying degrees among the three core sites along the SW African coast. The highest sedimentation and accumulation rates at 25 degree S off Luederitz conform with the present-day, well-known pattern of highest productivity and most intense coastal upwelling. Highest diatom values at 25 degree S during MIS3 points to more intense upwelling due to the combination of strong seaward-extending upwelling filaments, shoaling of the upwelled water, and the influence of silicate-rich waters of Antarctic origin. Productivity decreased along the central BUS throughout MIS2, when the siliceous-calcareous productivity regime shifted toward a system dominated by calcareous producers. Although intensity and strength of winds created adequate conditions for upwelling during MIS2, diatom production decreased. The complete replacement of the upwelling-associated diatom flora by a non-upwelling-related diatom community during MIS1 reflects weakened upwelling, weakened seaward extension of the upwelling filaments, and dominance of warmer surface waters. Combining changes in the composition of the diatom assemblage and variations of the bulk biogenic components allows for reliable reconstruction of paleoproductivity and upwelling changes for the SE Atlantic during the last 70ka B.P.