The Mid-Brunhes Event in the Southwestern Atlantic Ocean: Coccolithophore assemblages during the MIS 11-9

Abstract

The paleoceanographic dynamics in the Southwestern Atlantic Ocean is still poorly understood, with most studies describing the last 25 ky. In the present study, the coccolithophore assemblages from a sediment core from the Brazilian continental margin (20º01’S) were analysed during the interval between 423-305 ky (Marine Isotopic Stages-MIS-11 to 9), including the important Mid-Brunhes Event (MBE). The coccolithophore assemblage is typically tropical: Gephyrocapsa spp. and Florisphaera profunda dominate the assemblage. The productivity (measured by the N ratio) was high throughout the entire studied interval, pointing to a shallow nutricline, induced by the northeast winds of the South Atlantic Subtropical High or by upwelling development. The coccolith numbers was low during almost all the studied interval, since this group is adapted to oligotrophic environments. However, between 420-410 ky, both coccolith numbers and N ratio were high, which may indicate the lack of silicate in the surface waters (reducing the diatom competitiveness). Globally, the MBE is marked by a high production of carbonate and the dominance of Gephyrocapsa caribbeanica in the coccolithophore assemblages. In this work, this dominance was recognized between 420-328 ky (MIS 11-9). Besides the high production of carbonate, the MBE is also globally marked by a great dissolution (Mid-Brunhes Dissolution Interval), but no significant carbonate dissolution was found in this work.