*3.3. X-ray Micro-Computed Tomography (*µ*CT)*

For X-ray microscopic analysis, in total, 27 specimens were scanned from 3 samples (9 specimens per sample) that correspond to the time interval of the increased mass event (132.2 ka), the penultimate glacial maximum (139.1 ka) prior to the event, and a time interval of increased shell weights that followed (122.5 ka). Each batch of shells was poured into a quartz cylindrical carrier 1 mm in diameter [31]. They were stabilized with diluted tragacanth glue and left to dry prior to scanning. The specimens were subsequently retrieved for the geochemical analyses. The micro-CT (µCT) scanning was carried out with a Zeiss Versa 520 at the X-ray Microscopy laboratory of London Natural History Museum. X-ray source and detector geometry were kept constant throughout the scans. Anode voltage was set at 100 kV, the X-ray tube current was 90 µA, and the exposure time was 2 s at an optical magnification of 4×. By processing approximately 1024 images per sample, a scan resolution voxel size of ~1.2 µm<sup>3</sup> was typically achieved using this set up in order to maximize the number of specimens that could be analysed in a single scan. The images were combined to build a 3D rendering using Avizo software, which was also used for segmentation. The segmentation resulted in the separation of the tomographs into shell area, area occupied by clay infillings (dirt), and internal shell (protoplasm) voids (Figure 2).

**Figure 2.** Example of tomograph segmentation using computed tomography (CT) data visualization software, where (**a**) in yellow, the foraminifera test is solely segmented; (**b**) in red, the area covered by dirt was also segmented; (**c**) dirt and internal (chamber) voids were considered together to calculate the area that was occupied by protoplasm (in blue); and (**d**) protoplasm and shell areas were merged together (in cyan) to calculate the total volume occupied by a foraminifer.

Subject to the degree of segmentation, the X-ray microscopic analysis allows the determination and study of a number of biometric characteristics of the foraminifera shells, such as total shell volume (Figure 2d), thus shell density (volume normalized weight) and calcite (test) volume, and thus test density [32] and calcite (test) surface (Figure 2a). The ratio of calcite volume/calcite surface provides a linear unidimensional quantity in length units and can thus serve as a measure of average test thickness. In this study, in addition to shell density, that is, the ratio of shell volume to shell mass, we use the "specific surface area", that is, the ratio of test volume/test surface, as a measure of average test thickness [32] and the test density, that is, the ratio of test volume to shell mass, as an indication of test porosity. Furthermore, by segmenting the area occupied by clay infillings, we were able to calculate by volume percent the degree of contamination in weight measurements.
