Application of Clumped Isotope Thermometry to Benthic Foraminifera

Obtaining absolute temperatures of the ocean in deep time is complicated by the lack of constraints on seawater chemistry. Seawater salinity, carbonate ion concentration, delta O-18, and elemental abundance changes may obscure widely applied paleoproxies. In addition, with foraminifera-based proxies applied over long time scales or through major transitions, taxonomic turnover can impair the robustness of a record. While requiring larger sample sizes than most other proxies, the clumped isotope method is independent of seawater chemistry. Here we test if small benthic foraminifera precipitate their carbonate in equilibrium with respect to the clumped isotope thermometer and if there are any species-specific vital effects. We find that benthic foraminifera fall on the same calibration line as the majority of carbonate minerals including inorganic calcite. In addition, we find no offsets that can be attributed to a species-specific for any of the samples. This finding implies that a necessary amount of sample material can be obtained by aggregating over multiple taxa of benthic foraminifera and allows for the application of this proxy over major climatic transitions that coincide with seawater chemistry changes and foraminifera extinctions.