THE ROLE OF POPULATION PATCHINESS AND ENVIRONMENTAL VARIABILITY IN THE BENTHIC FORAMINIFERAL EXTINCTION DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM

The cause and mechanisms for the extinction of 30-50% of all deep-sea benthic foraminifera at the P-E boundary has been an enigma for as long as the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) has been recognized in marine deposits. A large set of causes have been proposed to explain the largest extinction event in benthic foraminiferal history, ranging from ocean acidification, sub- and anoxia of bottom waters, thermal stress, global changes in primary and export productivity, to increased viral activity.

Here we present a new quantitative benthic foraminiferal record across the expanded PETM of North Atlantic DSDP Site 401 (~2000 m paleodepth; ~42°N paleolatitude). Our records show that small r-selective opportunistic or oligotrophic benthic foraminiferal species (e.g. Epistominella exigua, Nuttallides umbonifera) – already abundant in the latest Paleocene - cross the PETM relatively unscathed, while exclusively large K-selective species experience a gradual decline in the latest Paleocene, and ultimately go extinct at the onset of the PETM. Based on the idea that thermally-induced metabolic constraints control benthic foraminiferal population patchiness, we hypothesize that increased pre-PETM environmental variability (i.e. seasonality of export productivity) may have led to critical depensation levels, thus causing the (regional) selective extinction of the typical “Cretaceous” fauna (e.g. S. beccariiformis, P. hillebrandti, B. delicatulus).

Although we acknowledge that population dynamics are complex and a multistressor synergistic cause for the benthic foraminiferal extinction is not excluded, geochemical and faunal (planktic foraminifera, ostracods, radiolarians, calcareous nannofossils and dinocysts) records from Site 401 and modern ecological models support our hypothesis. Similar studies on global faunal PETM records may confirm, refine or refute this mechanism as a driver for the benthic foraminiferal extinction.