Articles | Volume 13, issue 16
Research article
29 Aug 2016
Research article |  | 29 Aug 2016

Dinocyst assemblage constraints on oceanographic and atmospheric processes in the eastern equatorial Atlantic over the last 44 kyr

William Hardy, Aurélie Penaud, Fabienne Marret, Germain Bayon, Tania Marsset, and Laurence Droz

Abstract. A new 44 kyr long record of dinoflagellate (phytoplanktonic organisms) cysts (dinocysts) is presented from a marine sediment core collected on the Congolese margin with the aim of reconstructing past hydrological changes in the equatorial eastern Atlantic Ocean since Marine Isotopic Stage (MIS) 3. Our high-resolution dinocyst record indicates that significant temperature and moisture variations occurred across the glacial period, the last deglaciation and the Holocene. The use of specific dinocyst taxa, indicative of fluvial, upwelling and Benguela Current past environments for instance, provides insights into the main forcing mechanisms controlling palaeohydrological changes on orbital timescales. In particular, we are able, for the last 44 kyr, to correlate fluvial-sensitive taxa to monsoonal mechanisms related to precession minima–obliquity maxima combinations. While upwelling mechanisms appear as the main drivers for dinoflagellate productivity during MIS 2, dissolved nutrient-enriched Congo River inputs to the ocean also played a significant role in promoting dinoflagellate productivity between approximately 15.5 and 5 ka BP. Finally, this high-resolution dinocyst study permits us to precisely investigate the suborbital timing of the last glacial–interglacial termination, including an atypical warm and wet oceanic LGM signature, northern high-latitude abrupt climate change impacts in the equatorial eastern Atlantic, as well as a two-step decrease in moisture conditions during the Holocene at around 7–6 and 4–3.5 ka BP.

Short summary
Our approach is based on a multi-proxy study from a core collected off the Congo River and discusses surface oceanic conditions (upwelling cells, river-induced upwelling), land–sea interactions and terrestrial erosion and in particular enables us to spatially constrain the migration of atmospheric systems. This paper thus presents new data highlighting, with the highest resolution ever reached in this region, the great correlation between phytoplanktonic organisms and monsoonal mechanisms.
Final-revised paper