Relative effect of taphonomy on calcification temperature estimates from fossil planktonic foraminifera

This paper explores the effects of preservation and taphonomy on the ultrastructure of recent and fossil (Quaternary and Neogene) Globigerinoides using scanning electron microscopy and thin section petrography. We show preservation states from: pristine (plankton tow) specimens that are “glassy”, have a microcrystalline test structure, and bear sharply defined interpore ridges with delicate spines; through core top and fossil specimens that have gametogenic calcite veneers of euhedral or lumpy deposits covering the interpore ridges and spine bases; to fossil material with extensive dissolution of the test wall and diagenetic calcite formed during shallow burial (less than 300 m below the sea floor). The latter produce a “grainy” texture to the test. Although we cannot unravel the precise effects of ecology and taphonomy on calcification temperature at every site, we show that for well-preserved fossil material with gametogenic calcite, temperature estimates are typically 2-3 °C cooler than modern sea surface, and are similar to those recorded using the δ¹⁸O of core top material from tropical latitudes. In contrast, at tropical sites with poor fossil preservation, estimates of calcification temperature are significantly cooler, sometimes by more than 10 °C than expected from present observations.