CALCAREOUS NANNOPLANKTON POPULATION DYNAMICS AND EVOLUTION AT THE MIDDLE EOCENE CLIMATIC OPTIMUM IN THE NORTH ATLANTIC (IODP SITE U1408)

The Middle Eocene Climatic Optimum (MECO), 40 Ma, was a transient warming event amidst the long term cooling trend of the Paleogene greenhouse to icehouse transition. The MECO was a global event sustained over 500-800 thousand years (kyr) with peak warming in less than 100 kyr, recorded by a negative shift in the oxygen isotope record, representing 4-6^oC warming in the surface and deep waters, synchronous with temporary shoaling of the calcite compensation depth (CCD) linked to increased pCO₂. The MECO is commonly associated with the early Paleogene hyperthermals yet is differentiated by the lack of a synchronous carbon isotope excursion and it exhibits a prolonged onset relative to other hyperthermal events.

Here we present calcareous nannoplankton data from IODP Site U1408, a stratigraphically expanded MECO section recently recovered from the North Atlantic Ocean. This interval yields exceptionally well-preserved calcareous nannoplankton allowing us to precisely determine the timing of key bioevents, originations and extinctions, highlight diversity patterns and identify significant taxic shifts, used to interpret the calcareous nannoplankton response to this rapid warming. Calcareous nannoplankton are very responsive to changes in paleoenvironmental parameters, particularly temperature and nutrients, and the study of the calcareous nannofossil assemblage across the MECO will provide insight into the paleoceanographic conditions in the North Atlantic at this time.