The Last Global Extinction In the Deep Sea

About twenty percent (19 genera, 95 species) of cosmopolitan, deep-sea (500-4000 m), benthic foraminiferal species became extinct during the late Pliocene-Middle Pleistocene (3-0.12 Ma), with the peak of extinctions (76 species) occurring during the mid-Pleistocene Climate Transition (MPT, 1.2-0.55 Ma). One whole family (Stilostomellidae, 30 species) was wiped out and a second (Pleurostomellidae, 29 species) was decimated with just one species possibly surviving through to the present.

Our studies at 21 deep sea core sites world-wide show widespread pulsed declines in abundance and diversity of the extinction group species during more extreme glacials, with partial interglacial recoveries. These declines started in late Pliocene in southern-sourced deep-water masses (AABW, CPDW) and extending into intermediate waters (AAIW, NADW) in the MPT, with the youngest declines in sites furthest downstream from high-latitude intermediate waters source areas. We infer that the unusual apertures that were targeted by this extinction period were adaptations for a specific food, and that it was probably the demise of this that resulted in the foraminiferal extinctions.

Maybe increased cold and oxygenation of the southern-sourced deep-water masses impacted on this deep-water microbial food source during major late Pliocene and Early Pleistocene glacials when Antarctic ice was substantially expanded. The food source in intermediate water was not impacted until major glacials in the MPT when there was significant expansion of polar sea ice in both hemispheres and major changes in the source areas, temperature and oxygenation of global intermediate waters.