Three-dimensional observations of ice crystal characteristics in polar ice sheets

In ice core studies, mean crystal size is generally measured on a section image of an ice specimen. However, an ice crystal with a complex shape may appear as several cells on a section image; consequently, the mean crystal size may be underestimated by overcounting the crystals on the image. We examined this phenomenon, which we called duplication effect, through three-dimensional observation of crystal shapes, In terms of results, we found that the frequency in which duplicate cells appear on a section image is linear with respect to the frequency of which randomly drawn lines on the image pass a cell more than once. On the basis of this empirical relationship, the error on the mean crystal size caused by the duplication effect can be revised from the section image itself. As to its application, we examined crystal sizes in some Antarctic ice specimens and found that the extent of change of crystal size steadily increased with depth up to 100 m and then fluctuated between 6% and 10% in the deeper parts.