Assessing the Ethmodiscus ooze problem: new perspective from a study of an eastern equatorial Atlantic core

Several are the hypotheses proposed to explain the occurrence of Ethmodiscus oozes in tropical sediments representative of some glacial periods. In this paper, a review of those hypotheses within a paleoclimatic perspective is presented. Flux records of Ethmodiscus fragments found in site M16772 (1°21′ S, 11°58′ W) during the last 190 ka are compared to the other marine and freshwater diatom accumulation rates (AR) and diatom assemblages composition. Ethmodiscus is present all along the core, but Ethmodiscus-rich levels are found at 185–170 and 150–140 ka (stages 6.6 and 6.4), and at 70–60 ka (stage 4.2), levels where a concomitant increase in the flux of the other marine diatoms, and in the contribution to the assemblage of diatom species related to equatorial and coastal upwelling, and river plume waters is also observed. Climatic conditions favouring simultaneous occurrence of strong equatorial upwelling, coincident with increased advection of waters from coastal upwelling areas and important river run-off are proposed as the explanation for these Ethmodiscus-rich levels.