(Table 2) Mg/Ca and Sr/Ca composition of planktonic foraminifera from ODP Hole 143-865B

To understand the climate dynamics of hypothesized past greenhouse intervals, it is essential to constrain tropical sea-surface temperatures (SST), yet existing proxy records give conflicting results. Here we present the first Mg/Ca-based study of pre-Quaternary SST and investigate early Paleogene (late Paleocene through late middle Eocene; 58.6-39.8 Ma) tropical temperatures, using planktonic foraminifera belonging to the genus Morozovella from Ocean Drilling Program Site 865 on Allison Guyot (western central equatorial Pacific Ocean). Calcification temperatures similar to or warmer than modern tropical SST are calculated using a range of assumptions regarding diagenesis, temperature calibration, and seawater Mg/Ca. Long-term warming is observed into the early Eocene (54.8-49.0 Ma), with peak SST between 51 and 48 Ma and rapid cooling of 4°C beginning at 48 Ma. These findings are inconsistent with the d18O-based SST previously estimated for this site.

Benthic foraminifera extinctions in the Cenozoic record

In the late Pliocene-middle Pleistocene a group of 95 species of elongate, cylindrical, deep-sea (lower bathyal-abyssal) benthic foraminifera became extinct. This Extinction Group (Ext. Gp), belonging to three families (all the Stilostomellidae and Pleurostomellidae, some of the Nodosariidae), was a major component (20-70%) of deep-sea foraminiferal assemblages in the middle Cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid-Pleistocene Climatic Transition (MPT). So what caused these declines and extinction? In this study 127 Ext. Gp species are identified from eight Cenozoic bathyal and abyssal sequences in the North Atlantic and equatorial Pacific Oceans. Most species are long-ranging with 80% originating in the Eocene or earlier. The greatest abundance and diversity of the Ext. Gp was in the warm oceanic conditions of the middle Eocene-early Oligocene. The group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid Eocene-Oligocene cooling event. Declines in the relative abundance and flux of the Ext. Gp, together with enhanced species loss, occurred during middle-late Miocene cooling, particularly at abyssal sites. The overall number of Ext. Gp species present began declining earlier at mid abyssal depths (in middle Miocene) than at upper abyssal (in late Pliocene-early Pleistocene) and then lower bathyal depths (in MPT). By far the most significant Ext. Gp declines in abundance and species loss occurred during the more severe glacial stages of the late Pliocene-middle Pleistocene. Clearly, the decline and extinction of this group of deep-sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water. We infer that the apertural modifications may be related to the method of food collection or processing, and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source, that was more directly impacted than the foraminifera by the cooling temperatures.