Mid Pleistocene foraminiferal mass extinction coupled with phytoplankton evolution

Understanding the interaction between climate and biotic evolution is crucial for deciphering
the sensitivity of life. An enigmatic mass extinction occurred in the deep oceans during the
Mid Pleistocene, with a loss of over 100 species (20%) of sea floor calcareous foraminifera.
An evolutionarily conservative group, benthic foraminifera often comprise 450% of eukaryote
biomass on the deep-ocean floor. Here we test extinction hypotheses (temperature,
corrosiveness and productivity) in the Tasman Sea, using geochemistry and micropalaeontology,
and find evidence from several globally distributed sites that the extinction
was caused by a change in phytoplankton food source. Coccolithophore evolution may have
enhanced the seasonal ‘bloom’ nature of primary productivity and fundamentally shifted it
towards a more intra-annually variable state at B0.8 Ma. Our results highlight intra-annual
variability as a potential new consideration for Mid Pleistocene global biogeochemical climate
models, and imply that deep-sea biota may be sensitive to future changes in productivity.