Effect of Cleaning Procedures on the Mg/Ca Ratio of Single-Specimen Planktic Foraminifera

Abstract

Single-specimen analysis of planktic foraminiferal geochemistry has gained increasing popularity for its potential in reconstructing climate variability. However, the comparability between single-specimen and conventional multi-specimen Mg/Ca data remains unclear, which has raised questions concerning the suitability of multi-specimen Mg/Ca-temperature calibrations for single-specimen data. This study developed and evaluated the effects of four single-specimen cleaning procedures on the Mg/Ca ratio of Trilobatus sacculifer. These procedures varied in their inclusion or exclusion of the reductive step and heating for chemical reactions. The most effective single-specimen cleaning procedure (procedure D_single) incorporated the oxidative step while excluding the reductive step and heating. This procedure was subsequently applied to five additional planktic foraminifera species. With procedure D_single, we obtained statistically indistinguishable mean Mg/Ca values for single-specimen and multi-specimen samples of T. sacculifer, Orbulina universa, and Pulleniatina obliquiloculata, regardless of the intensity of the multi-specimen cleaning procedures. For single-specimen samples of Globigerinoides ruber and Neogloboquadrina dutertrei, the mean Mg/Ca values only matched those of the multi-specimen samples when procedures excluded the reductive step and heating. In contrast, single-specimen mean Mg/Ca values of Globorotalia menardii were consistently higher than those obtained through multi-specimen cleaning. The mean Mg/Ca differences between single-specimen and multi-specimen cleaning procedures across species are likely attributable to differences in the microstructure of the calcite tests. In summary, when cleaning procedures involving identical steps and heating conditions were utilized, both single-specimen and multi-specimen analyses yielded comparable mean Mg/Ca values, suggesting that the multi-specimen Mg/Ca calibrations are applicable to single-specimen data.