Exploring the dissolution effect on the intrashell Mg/Ca variability of the planktic foraminifer Globigerinoides ruber

Abstract The Mg/Ca ratio of the planktic foraminifer Globigerinoides ruber is widely used for reconstructing past sea surface temperatures. The shell Mg/Ca ratio is also lowered by dissolution, which results in lower sea surface temperature estimates in partially dissolved shells. Here we use an electron microprobe image mapping technique to map the intrashell variability of the Mg/Ca ratio in G. ruber (white) sensu stricto shells to explore changes in the intrashell Mg/Ca ratio associated with dissolution. We examine shells from shallow and deep cores (Ceara Rise, western tropical Atlantic) from the Holocene and Last Glacial Maximum that represent a preservational gradient. Image map results show that the Mg/Ca ratio is highly variable both within a single shell and among samples obtained from the same sediment interval. Our results show that intrashell Mg/Ca variability is retained in samples that have undergone dissolution. Quantitative analysis of the data from Mg/Ca mapping suggests that preferential loss of high‐Mg/Ca calcite alone cannot account for the difference in intrashell Mg/Ca variability of shells from shallow and deep cores in both time periods. Rather, the data imply that, in G. ruber analyzed in this study, there is a loss of high Mg/Ca ratios accompanied by a more uniform lowering of Mg/Ca over the range of intershell Mg/Ca variability of shells subjected to dissolution at the 1 µm resolution of the microprobe analysis in this study.