Calcareous nannofossils in the S-Atlantic during the Middle to Late Miocene: Coccolithophorid carbonate budgets, fine-fraction stable isotopes and their paleoceanographic implications

Abstract

The Cenozoic is characterized by major changes in the global climate system from 'greenhouse' conditions in the Early Paleogene towards 'ice-house'-regime in the Neogene. The main object of this study was to document and understand the role of coccolithophores as the main carbonate producers in relation to changes in ocean circulation and global climate between 12.5 and 7.5 Ma. For this purpose ODP Site 1085 and 1092 were investigated. The distribution pattern of single coccolithophorid species, the nannoplankton assemblage composition and the preservation of coccoliths from the eastern S-Atlantic provided the basis for paleoceanographic studies. Additionally, the nannoplankton contribution to the bulk carbonate production as well as the stable isotopic composition of the coccolith carbonate were explored. Many paleoceanographic signals are preserved in coccolithophorid assemblages, and thus, reflect spatial and temporal changes in surface-ocean circulation. The potential of nannofossil stable isotopes as indicators of conditions in the shallow mixed-layer was shown by comparing these records with those of co-existing planktic foraminifers.