Physical properties of Ice, or How to make an ice core sandwich. . .

Gas bubbles in a small section of ice core.

Thin sections of glacier ice are incredibly beautiful. I love to gaze into these clear windows filled with little bubbles; some spherical, others oblong, all holding ancient air.  The ice refracts light from its crystal faces into multiple planes of shimmering color. I see them as lovely sculptures, but scientists prepare them to study the physical properties of the ice core. I spent some time in the Arch at the WAIS Camp to learn a bit about this aspect of ice research with John Fegyveresi, who works with Richard Alley of The Pennsylvania State College.

Crystal grains can just be made out in this photo

He is at the WAIS field camp to prepare thin sections from every 20 meters of the ice core. These will be sent back to the National Ice Core Lab, where they will be photographed and measured in a variety of ways. One feature to quantify is the bubble number density. There is a measurable relationship between the density of the gas bubbles and temperature. John is developing a method of counting bubbles in a section as well as describing their shape using digital imaging and software. This information goes into a model with other data to reconstruct past atmospheric temperatures and further understand glacier movement and dynamics.

A section of ice being smoothed on a microtome

Watching him prepare his slides, I couldn’t help but think of myself and other artists in our studios creating lovely objects. He begins by shaving a section of the ice core with a microtome. The first smooth side is frozen to a glass plate with water, which doesn’t take very long in the Arch (kept at -27C degrees). The other side is then smoothed and glued with a special adhesive that works in low temperatures. The goal is to have a perfectly smooth seal of the glass to the ice. The slide is then carefully packed to be shipped with the other cores to the National Ice Core Lab in Denver. There the sections will be cut like an open face sandwich. One side will be used to study the gas bubble structure; the other side will be used to study ice crystal or grain qualities.