Evolutionary Response of Planktic Foraminifera to a Pronounced Global Warming Event 40 Myr ago

A transient interval of pronounced and abrupt global warming ca. 40 Myr ago associated with major perturbations to the carbon cycle interrupts the long-term Eocene cooling trend. This interval has typically proven difficult to investigate because a near-global hiatus truncates many existing deep-sea records approximately 40.5 Myr ago, making complete recovery of planktic foraminiferal biozone E12 (P13 in previous biozonation scheme), to which this event is restricted, extremely difficult. One exception is Ocean Drilling Program (ODP) Site 1051 (Blake Nose, western North Atlantic), the most expanded and continuous sedimentary record from this interval, which also benefits from good preservation of calcareous microfossils. Here we present new high-resolution faunal records (from 40.6 Myr ago to 39 Myr ago) of all the major groups of planktic foraminifera that document the biotic response of plankton to this rapid climatic warming event. The geologically brief duration of biozone E12, to which this event is restricted, is defined by the total range of an unusual and distinctive species of planktic foraminifera - Orbulinoides beckmanni. We test the hypothesis that the origination, subsequent evolutionary development and eventual extinction of this short-lived, biozone marker species was intimately linked to environmental changes associated with this warming event.