X-ray micro-CT scanning of planktic foraminiferal tests

Evaluation of foraminiferal test dissolution in deep-sea sediments facilitates reconstruction of seawater chemistry. Here we observed test dissolution processes of the planktic foraminifera Globigerinoides sacculifer, Globigerinoides ruber, and Neogloboquadrina dutertrei from mid-latitudes of the western North Pacific, and tested the ability of a new dissolution index using data from X-ray micro-computed tomography scanning. Although the dissolution process of foraminiferal tests differed slightly among species, dissolution of all species was equally assessed by the calcite density distribution (%Low-CT-number calcite volume) calculated from the CT number histogram. Furthermore, the correlation between the %Low-CT-number calcite volume of tests and the deep seawater calcite saturation state suggests that XMCT scanning is an appropriate tool for evaluating the intensity of foraminiferal test dissolution in the mid-latitudes of the North Pacific. The %Low-CT-number calcite volume of foraminiferal tests can be an invaluable proxy for the quantitative reconstruction of the deep seawater carbonate ion concentrations during glacial-interglacial periods.