Mid Pleistocene foraminiferal mass extinction coupled with phytoplankton evolution

Abstract

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 >50% 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 ∼0.8 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.

Pliocene‐Pleistocene evolution of sea surface and intermediate water temperatures from the southwest Pacific

“…IWT from uncorrected Mg/Ca U.peregrina shows subtle long‐term trends: gradual cooling from a Pliocene average of ~5.2°C begins ~3.1 Ma, a relatively abrupt and pronounced cooling develops from 2.7 Ma (to 0.9°C), and a small (~1°C) warming occurs from 2.0 to 1.3 Ma. After 1.3 Ma, there is an increase in interglacial maxima and a progressive decline in glacial maxima [ Kender et al ., ], superimposed upon a monotonic cooling of ~2°C toward the present day. From 0.8 Ma, interglacial maxima cool to align with modern AAIW temperatures of ~4°C [ Elmore et al ., ], reducing the orbital‐scale variability to c.4°C.…”

“…After 1.0 Ma, large‐amplitude glacial‐interglacial SST variations develop. SST minima are broadly associated with alkenone and chlorin concentration maxima, consistent with previous suggestions of an increased influence of subantarctic waters and equatorward displacements of the STF in the Tasman Sea during glacial stages [ Hayward et al ., ; Kender et al ., ; Nürnberg and Groeneveld , ]. Although the U K 37 ′ index is calibrated to mean annual SST [ Müller et al ., ], seasonality in coccolithophore production has been considered as a potential influence over reconstructed absolute SSTs, especially where multiproxy analyses have been performed [ Sikes et al ., ].…”

“…From 1.1 Ma, the amplitude of glacial‐interglacial SST variability at DSDP Site 593 increased [ Kender et al ., ], and a long‐term cooling trend develops between 0.9 and 0.6 Ma. Increased SST variability is also recorded at ODP Site 1090 in the south Atlantic but without any long‐term trend [ Martinez‐Garcia et al ., ].…”

“…[], extended to 1.1 Ma by Kender et al . []. The shipboard magnetostratigraphic and biostratigraphic datums [ Shipboard Scientific Party , ] were re‐assigned to the GTS2012 time scale [ Gradstein et al ., ], although they include large depth uncertainties due to low‐resolution discrete sampling and/or difficulties identifying the presence/absence of indicator species at this site [ Shipboard Scientific Party , ].…”

“…New Planulina wuellerstorfi δ 18 O minima and maxima [ Elmore et al ., ]; Kender et al . [], and this study] were visually aligned with key isotope stages in the LR04 benthic δ 18 O stack [ Lisiecki and Raymo , ]. Linear sedimentation rates were assumed between all tie points.…”