Description: The interval spanning from the Early Eocene Climatic Optimum (EECO) to the onset of long-term cooling in the middle Eocene is marked by prominent changes in calcareous nannofossil assemblages and coincides with modification of the North Atlantic deep-ocean circulation. Here we present an integrated calcareous nannoplakton and bulk stable isotope records (δ18O and δ13C) across the early-middle Eocene (~52- 43 Ma) from IODP Site U1410 (northwest Atlantic), where middle Eocene deposits occur as clay-rich drift sediments reflecting the formation of persistent deep currents. Abundance patterns of selected biostratigraphically relevant taxa encompassing Ypresian-Lutetian calcareous nannofossil Zones CNE4-CNE12 served to test the biostratigraphic reliability of the species. In addition, long- and short-term trends documented in geochemical data have been used to determine the temporal relationships between palaeoenvironmental trends and changes in calcareous nannofossil assemblages. After the EECO to the Ypresian-Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm-water and oligotrophic taxa (Zygrhablithus, Discoaster, Sphenolithus, Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. This prominent change occurred during a phase of relatively high δ18O values likely related to the post-EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the study middle Eocene interval, early Lutetian stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a temporary restoration of warmer conditions associated with an increase in abundance of D. sublodoensis. These results confirm previous records of environmental instability but the comparison of our results with different dataset highlights a global enigmatic scenario in term of bio-chemo-magnetostratigraphy.