Precise bulk density measurement of planktonic foraminiferal test by X-ray microcomputed tomography

X-ray Microcomputed Tomography (mu CT) is rapidly becoming an important analytical technique for examining the precise morphometry of small objects. The most notable feature of this technique is that it enables nondestructive, highly accurate morphometric measurements at micrometer-order resolution. In the Earth sciences, this makes mu CT extremely useful for clarifying how genetic associations and the surrounding environment affect the morphology of micro-sized organisms. However, the actual analytical methods and the points that must be considered to produce reliable data have rarely been discussed in detail. Here, to address this lack of discussion, we describe in detail our methodology for precise mu CT-based morphometry by using a test of the planktonic foraminifer and marine calcifier Globorotalia inflata. In addition to demonstrating the long-term stability of our mu CT setup and analytical approach, we also propose a new methodology for test bulk density calibration using artificial carbonate phantoms. We expect that mu CT together with our artificial phantom-based methodology will be useful for calculating accurate test bulk densities of micro-sized marine calcifiers.