CALCAREOUS NANNOPLANKTON RESPONSE AND POPULATION RESTRUCTURING ACROSS THE EOCENE-OLIGOCENE TRANSITION
Here we will document the response of the calcareous nannoplankton to the EOT using the recently drilled section at IODP Site U1411, which has high sedimentation rates and exceptionally well preserved calcareous nannofossils. Semiquantitative data and relative abundance counts highlight diversity change, species bioevents and major shifts in abundance patterns. Determining the precise timing of these events allows us to examine the relationship between plankton evolution and the strongly shifting paleoceanographic conditions in the North Atlantic.
To place these new observations into a wider context we have compiled calcareous nannofossil data from a range of global sites across the EOT that vary in latitude, ocean basin and oceanographic setting. Our results identify significant and coeval population restructuring within this phytoplankton group prior to the early Oligocene climatic shift. These data reveal that elevated rates of extinction and striking reorganization within the dominant reticulofenestrid group was a particular feature of the interval, reflecting the major climatic/oceanographic changes. The evidence suggests that elevated rates of extinction are associated with a reduction of optimal habitat space for many coccolithophores and that global population shifts reflected increases in taxa that favored elevated levels of nutrients or pulsed delivery of nutrients or with more efficient carbon utilisation strategies under declining atmospheric pCO2.